The truth about upgrades and mods!

[searayx350]

I am going to spare you my personal details other than I use to work for a company as a designer that manufactured machines that were in the $90,000 an up range and I am currently writing a book about CNC that includes the ShopBot (I am also reserving the name of the book because I don’t want to appear to be advertising in ShopBot’s forum out of respect to SB and its users).

I actually took on the ShopBot project out of respect for the people at ShopBot and their users. I bought one just to tinker with it and include it in my book but now I find myself using it right beside my other more expensive machines.

Here is the truth; not opinion, not conjecture but pure unadulterated fact.

The ShopBot is an affordable machine; bottom line. Ted and the team from ShopBot have done a great job of blending performance, reliability and affordability and the machines is not inended to compeate or even keep up with an Accu-Router or Komo. If this is what you are expecting you have several tasks ahead of you to achieve industrial level performance.

My Accu-Router can plow through plywood before you even realized you hit start, I can run 3D parts 10 to 15 times faster than with my ShopBot with a 1/8th bit with no fear of breaking it. The machine is so silent that if you weren’t watching you could get hurt. Why the difference you ask? Well, it is a 90,000 + machine with top of the line parts.

ShopBot is in a class of its own. It runs pretty good out of the box but it is designed with affordability and simplicity in mind so if you want a true industrial unit you have some work ahead of you.

In doing research for my book I have spent a lot of time reading trough the forums and fond many offered good advice concerning upgrades but many offered pure opinion!

I will briefly detail some facts to upgrading a ShopBot and you are welcome to do with it what you will. I would also like to note that none of the following is meant to criticize, complain or otherwise be derogatory; is only offered to hopefully help some of you in your effort of seeking high-end performance from your ShopBot. I would like to also make mention that I fully support ShopBot and I like everyone I have had the pleasure of working with from SB.

At the heart of the machine you have the control software. The SB program while functional is not as capable as some of the alternatives. The SB program was designed with simplicity in mind and with simplicity you will always sacrifice capability. This is by design as the people at SB designed a machine that anyone could use. This is not a bad thing, just SB’s approach.

I have seen references in the forums that the control software doesn’t matter and that product X (I don’t need to say the name) is no better than SB. This is simply not the truth. Any time you have full control of acceleration factors, timing, jitter and jerk correction you will have a better system. Period!

Moving on to the control board; I am talking about the standard, 4G and Alpha. The board is designed for the SB software and therefore limited to its design. SB scales things back (as they should) to allow a trouble free, reliable and simple functioning environment. Once again, its limitations are by design.

Serial communication is very slow in comparison to native USB, Ethernet and Parallel. I have a USB breakout that runs native at 75k! The SB system can allow additional axis control but once again is limited. You can buy a true USB 6 Axis breakout board with tons of I/O for about 125.00 and an Ethernet board for about 200.00. This will open you up to tool changers, PLC’s and a host of new options that you have direct control over.

Also, the Alpha is not closed loop as I would define it– it merely notifies the control board that the driver and motor did not sync. There is no communication back to the SB software. With a closed loop system you could essentially coast the X Y and Z and see the results on the DRO in the SB software. In a native closed loop system the software would make “on the fly” positional corrections instead of forcing a reset (one can argue semantics here but I am describing industry standard). You would need to obtain or make an encoder signal splitter, scrap the control board and change the control software to get true closed loop.

Now please don’t think that I am saying that the semi-closed loop of the Alpha isn’t useful; quite the contrary. This feature has saved many parts from being scrap. I would like to also note that true closed loop is overrated. A well tuned machine that is operating within its limits such as the SB does out of the box will yield reliable results.

The next issue is linear motion. (I can only speak about the PRT and PRT Alpha) Any time you place a steel roller on any surface you are going to have rapid wear (this holds true not only for SB but MechMate and other SB clones). Also the fact the gantry and Y car are held down by the motor and spring is an issue for clean cuts at rapid speeds. Routing CAUSES LIFT – even with down shear bits. Motion, jerk and jitter contribute to lift. The slightest lift even sometimes as little as 1/000th will cause chatter, marks and the increased possibility of bit breakage.

You should plan on using some commercial sliders and rails that are designed for multi directional forces. This is probably the single most important upgrade you can do to your ShopBot.

This also leads to the gantry – you can flex this thing easily. If you run the machine as designed then this, as with any of the other issues I describe, does not affect much; but if you want industrial results you will have to perform some surgery or plan on replacing it entirely.

Many swear that a gearbox, mounts, and plates and so on are the end-all upgrade but in actuality you are most likely just getting the spring tension tighter (and wearing out your rails quicker) and therefore avoiding some of the lift. I am not saying that it doesn’t help because it does, but the real performance multiplier is sliders.

Next is the Z. This nifty little device is great but once again not designed for industrial use. It’s subject to the wear I discussed but in addition to the wear issue is the fact it is not stiff enough for industrial use. Plunge a ¼” bit into a scrap piece (clamped of course) and shake the z back and forth. I don’t care how well you assembled your machine you are going to have an oval when you are through.

You would need two men and a small child to move mine. This minuscule movement is responsible for several issues many of you describe including clean cuts in plastic and aluminum .You should plan using ¾” 6061 Aluminum and commercial sliders and fabricate a new Z. This will eliminate the second biggest issue with the ShopBot under industrial use.

I would like to also state that if you have an Alpha you CAN use other control boards. The drivers are well documented and this is a VERY respectable system. The only thing that bums me out about OM is that their motors are not standard NEMA sizes


My book details the complete upgrade of the PRT/PRTAlpha line of CNC machines. Once again I am not going to plug it here (that is at least until ShopBot has reviewed it and given me the OK). Also, I will not give too many details as this would take away from my upcoming book and I would like to sell at least one copy.

All I am saying is that the ShopBot as-is is an excellent machine but many of you want more. I just wanted t throw in my two cents as to hopefully help some of the people with the infamous question as to how to upgrade in the right direction.

I would like to also note that there are many other factors such as learning how to calculate chip load (this will determine feed rates, rpm’s and assist in calculating depth of cut), knowing when to climb cut or use conventional cutting are just a few things one should know about CNC.

When I first got my PRTAlpha I used it stock. Knowing little tricks such as the above plus how to properly setup my tool paths yielded sanding free parts every time. The point to this is that far too many people blame the ShopBot for poor cut quality. Too many times it is just the user lacking the necessary knowledge of how to design part files and calculate the factors to operate within the machines parameters. This holds true for ALL machines…

I would learn how to really use a CNC machine before spending time upgrading.

This is not meant to offend, be argumentative or anything else; just the truth and facts about achieving industrial performance on an otherwise great machine.

Respectfully,

JM

[wcsg]

curious about something.

IS this also you?

Registrant:
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Technical Contact:
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Domain servers in listed order:
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alias: careers@instanthumanresources.com
www.clubfreedom.biz/sylvan2


If so why is it that your address for JS Custom Wood (with no real site) is on a lot of Anti-Scam Sites with warnings and multiple website addresses?

You have been accused of stealing money all over the net, credit card fraud, the list goes on.

Are you selling something again?

Hmmmmmm

[searayx350]

No.
Domains by Proxy are a company/service that when you register a domain through godaddy.com they offer this as a privacy option to help the registrant keep their identity from being posted all over the net. This has cut down on my company receiving spam by a tremendous percentage.
Being that DBP is a ID shield, when someone files a complaint against any of the 1,000,000 or so domains they shield, their info gets associated with the complaint – not mine but DBP’s!
Just so you know, I am working with ShopBot (Ted) on my book. The only reason I didn’t want to blast my information is that I will not plug my book without first asking permission from Ted and I will not ask for that until the book is done and he has reviewed it
At any rate, the post was and is in good faith. I had just finished one of the chapters about ShopBot and posted a web synopsis for the benefit of ShopBotters.
I, being fond of ShopBot, wanted to contribute.
Lastly, I used my real e-mail address in the registration so I am not trying to hide.

My advice is that if you don’t want the advice, don’t use it. As stated “do with it what you will”
I was just trying to be supportive; sorry you failed to see the value in someone who has spent thousands, because I have the resources to do so, so you wouldn’t have to.

Maybe other fellow ShopBot’ers will!


www.jscustomwood.com in not on any listed anti-spam sites to my knowledge and is a VERY real site Only our phone number is different due to us going with another provider. I just haven’t had time to update it (we host our own bandwidth and servers here on site). I own a cabinet shop and an engineering/ machine shop in PLANO, TX if you must know. I cannot speak for domains by proxy.

Lastly, before you associate me with CC scams (as you are confusing the VERY Legitimate service Domains by Proxy offered by godaddy with us) and subject yourself to liable as I am a legitimate business registered with the Texas Secretary of State, I would recommend going to godaddy.com, look up Domains by Proxy and edit your post.

Thank you…

[searayx350]

The only site i could find while googleing mine that said anything about www.jscustomwood.com (http://www.jscustomwood.com) is http://209.85.165.104/search?q=cache:9CPZlTWs5hkJ:www.superpages.com/yellowpages/C-Cabinet%2BInstallation/S-TX/T-Fort%2BWorth/+jscustomwood.com&hl=en&ct=clnk&cd=1&gl=us (http://209.85.165.104/search?q=cache:9CPZlTWs5hkJ:www.superpages.com/yellowpages/C-Cabinet%2BInstallation/S-TX/T-Fort%2BWorth/+jscustomwood.com&hl=en&ct=clnk&cd=1&gl=us)

Once again, I respectfully request that you edit your post.. Oh and by the way – check out www.jscustomwood.com (http://www.jscustomwood.com) in about 10 min….

[wcsg]

lol!

I originally clicked on your name, then your site, and it kept coming up "timed out" until now. I was trying to get more info on who you were as your post made me cusious and doing a "who is" the godaddy address kept coming up followed by "FRAUD!" "Stay AWAY"! haha!

As long as your working with SB, I guess I can trust you


I would edit but it says to much time has gone, the admins can edit in the morning

[searayx350]

Thank you. Also i left you a msg on my site to prove we exist. I will let you read it and then delete it.

Thank you

[searayx350]

Hopefully the Admins delet everything below my original post as to not take away from the value of the original post.

Plus we messed up the whole "anonymous" thing...

[searayx350]

Fellow ShopBotters,
Something that I failed to add is that the last thing I would upgrade if at all is the control board with exception to the PRT original.

I had the recent pleasure of building a machine with the PRT4g and would recommend this to anyone. I am planning to use it on a very special system/package I am working on. Very powerful, very capable and lots of room for tweaking without having to scrap the SB control software.

Also, if you are more familiar with the SB software continuing to use it will not affect you productivity. I use this software everyday and I train the new guys on it because it is easier than teaching them some of the aspects of the more complex alternative.

Jut to reiterate; the sliders, tweaking the gantry and replacing the Z are the most significant upgrades that yielded the most improvement on performance. My modified SB is running like a much more expensive machine with minimal costs because I emphasized on the RIGHT areas to spend money on mods! – Also, weld the frame, add 2 more legs under the C channel in the middle and band the lower with unequal angle. This will help to reduce harmonics and vibration.

The new sliders also allow me to use the custom plywood hold-down I designed for my ShopBot so this is something else to consider.

I only included the board alternatives to unbury the bone that the die-hard tweakers like to chew on.

I also saw in another section someone asking about gantry weight. My new gantry weighs in at 243Lbs with 10hp auto tool change spindle and the OM motors push it around just fine (I have a trick to handling tool changes with the SB I will document and share later in case you were wondering about the ATC spindle).

Last little bit of info I wish to share; I am working on a plug-in that will allow the SB board to be controlled by other software and my last tests were very favorable. With SB’s blessing I will continue development. My goal here is to allow people to experiment without having to change everything.

Thanks again and I hope others find this information to be helpful,

J. Mitchell

[hespj]

What exactly are these "sliders" you recommend?

As for your other comments, I would certainly agree with many of them, both the pros and cons.

John

[rhfurniture]

Very interesting and useful. I like the idea of "heavy is good". One thing I reckon is really good about shopbots is their ability to work ok with dust all over the place, and for 3/4 of what I do, dust extraction is not an option. Sometimes the rails get totally submersed. From what I read, many high accuracy linear slides need as clean an environment as possible.
I would love to read your book when published.

[cjohnson]

JM,
You make some good points about the "industrial" capabilities of the ShopBot. I bought mine just for entertainment and possibly some "commercial" usage later on and it certainly has made me a happy customer. The 4g upgrade was money well spend. Now I can do my hobby faster and more accurate!

The upgrade discussion is always fascinating to me in the search for a better, longer lasting, more productive tool. While I (and my neighbors) never envisioned my ShopBot to work in the “Industrial” arena, any modifications that will improve the tool and provide me enjoyment in making the modifications are well worth it.

Make sure to post pictures and give more info on your mods. I probably won't buy your book, but I certainly will enjoy reading your post here. Good luck on in your endeavors.

Now, back to learning about Laser scanning. My new SB probe is kicking my rear. Wish someone in the know would write a beginners guide to 2d CNC probing….

cj

[elcruisr]

While this may not be a piece of "big iron" you need to look at you parts cutting requirements before getting a machine. Our machine started out as a PRT and is now a PRT Alpha. I compete with big iron guys for parts contracts but pick and choose the type and requirements. In 5 years I have cut and average of 30,000 parts a year with a peak year of 45,000. I have not had a problem with returned parts and have many happy customers. The machine is capable of high volume work as long as you the programmer and operator know what you're doing! The machine has held up well. We have worn out one z axis and rebuilt our spindle once. The bottom line is what machine will fill the need, not dreams, and be PROFITABLE if you want to be in this for a living.

[wcsg]

I'm curious as well as what a "slider" is

[searayx350]

Slider, profile rail -- goes by many names.

http://www.thk.com/eng/products/class/lmguide/cblmguide.html

or look at



http://www.nookindustries.com/profilerail/ProfileRailHome.cfm#SeriesNHEA

[searayx350]

I think Eric synopsizes my point well. The ShopBot out of the box performs quite well if you know what you are doing but it is nice to know that if you want more capability then you don’t have to leave the SB family.

The biggest question is what do you want to do, what do you need and will your needs grow?

I feel that any machine that can be upgraded easily such as the SB is wonderful. Try to upgrade my Accu-Router; unless you fabricate machines professionally such as my machine shop does, it’s not going to happen.

What my research proved is that a ShopBot can be a good entry level machine but can grow as your needs do.

If I under purchase with an expensive machine then I am presented with far more challenges than that of a ShopBot that welcomes upgrades by its very design.

This is what I like most about the SB.

For those asking about the book; it will be out VERY soon. I am excited too! The response and support has been amazing.

I am also going to try to get some vendors to offer a “kit” for the ShopBot community so you can buy the parts at a discounted rate. I will wait and see what Ted thinks about this before I say too much.

I will close by saying that I would put my upgraded SB up against ANY commercial machine. I spent very little to achieve this (that is after spending a truckload on what not to do) and this is a VERY strong aspect of the ShopBot.
I would also like to thank ALL OF YOU who participate in the forums, ShopBot and Ted; you have all helped influence this book.

Your friend,

Josh Mitchell

[bill_l]

Josh,

Can you tell us about your "upgraded" ShopBot and do you have any pictures you can post?

Bill

[searayx350]

Yes I can and yes I do and yes I will.

I will be posting sometime in the next day or so. I can’t reveal too much as stated earlier because I don’t want to spoil the book.

I will however say that I will give enough info here to give you a good start.

Also I failed to mention that I use helical racks by Atlanta Drive Systems (I only mention them directly because they are very nice people) as I feel helical rack offers superior speed to ball screw and an absolute 0 backlash (0 arc min) unit is available. Helical rack rules as far as I am concerned.

I am going to write Ted an e-mail to review some info first – reason for this is that I have some major purchase power with a couple vendors and might be able to get ShopBotters some great deals on the parts I use! That’s a good thing right?

This is Ted’s (and your) house and I don’t want to come in here and appear like I am pushing my vendors or trying to sell you something. This is why I am posting all the details I am regardless of the book. That being said I will get with Ted and make sure he is copacetic and agrees the info will be beneficial to his customers.

Anyway, I am getting everything together for you guys and I hope you have fun with it.

The way I look at it is that if you guys see this is legit and try some of the methods you will support further developments by me which in turn will help you and ShopBot!

I would also like to let you know that the book will give plans, exact details and in-depth information. I can only do so much on a forum ;)

Look for some more posts real soon…

Josh

[dodd]

Well JM, I was wondering when this was going to happen? I have known and witnessed your passion to upgrade the SB, without having to lose its integrity, for a long time ever since you bought the PRT Alpha. Now the cat's out of the bag! I hope we'll all benefit from your dynamic upgrades soon. I like what you did to my PRT using the new frame design and totally stiffening the gantry. I'm really impressed with your upgrade having the PRT running between 12-15 inches per second. I'm looking forward to the next series of rail upgrades. Good Luck with your book and your other machine designs, Thanks. Also, I was impressed with your cnc milling machines and welding. See you soon MJ.

[harold_weber]

JM, your post yesterday mentions "jitter". Can you say any more about this? I'm familiar with servo jitter (too much gain on positional feedback controllers), but since ShopBot does not use servos, don't see how it applies. Then there is jitter as defined in Wikipedia, but this applies to signals approaching 2Gbps, and I don't think we are there yet, are we?

[searayx350]

Anything can have "jitter" including Steppers. What i am referring to is phase jitter. The ShopBot experiences this sometimes at very high speeds.

When mine was stock I often use to cut way beyond its intended design.
For example, I replaced all the M commands with J in a cut file such as my surface program. I would set the jog speed to around 24.
Sometimes the SB would hop for a few inches; this was phase jitter.

------------------------------------------------------------------------------------------------------------------

jit•ter
intr.v., -tered, -ter•ing, -ters.
1.

[richards]

JM,
You've got some interesting information in your posts.

The only suggestion that you made that I disagree with is cutting while in jog mode. (I'm assuming that you're writing about the Alpha with Oriental Motor's Alpha motors and stepper driver.) Light non-critical cuts (such as surfacing a spoil board) would not be a problem; but, since the pulses per revolution are modified when jogging, resolution is cut in half so that a 30,000 pps pulse generator can move the axis at the faster jog speeds. Also, there wouldn't be a lot of torque at those faster speeds. Of course, if you're running linear rails on all axes, you would have much less friction to eat up the torque.

Speaking of linear rails, what size do you recommend? There seems to be very little difference in price between 20mm, 25mm, 30mm and 35mm rails and blocks. I've been thinking about using something in the 30mm range. What do you suggest?

I'm also curious about how you tension the motor to the rack. Maybe I misunderstood and you still use a spring type tensioner (and eliminate the 'bounce' with the linear rails). What worries me, if the motor/spur gear/rack are locked together without the 'give' of a spring, what happens when you have a crash? A spring would allow the motor to push itself away from the rack, but with a hard-mounted assembly, something would have to give. You might be lucky and only lose a $15 spur gear, but, you might not be so lucky and lose a stepper motor. Did I misunderstand your post?

[searayx350]

Mike,
Continued use of the spring is fine but I will mention that I feel if you get everything in a very tight tolerance it will not be necessary.

I can post a video when I have time of us lifting my machine by the gantry with my forklift (no motors attached) after the installation of my new rails. We put a dial indicator on the frame under the gantry – it moved a little under 1/1000th of an inch of vertical lift.

The one thing is that if you chose the right rail, you get your mounting, parallelism and other factors correct then you can avoid using the motor spring as an integral part of the hold mechanics.

The right rail is one that has equal opposition to movement from all directions with the exception of the intended axis of movement.

That being said, if you wanted to, you could consider the spring mechanism to be a mere safety even though I believe it would be rendered unnecessary by proper installation. I personally use a mount that I fabricated from 1/2” aluminum that spans from the original bearing holes (of a stock gantry) and the gantry mount holes are slightly elongated. I achieve tension by simply having my mount designed to allow the motor to be slid up tightly in place.

I run zero backlash helical racks and I will say that due to this I wouldn’t want them to push away as it could damage them. I just make sure that all my limit switches are functioning flawlessly. I put a loop to the stop switch to insure that if the current broke to my relay then it would in essence hit the stop switch electronically. This helps insure that the limit switches are functional without manual testing. (More on this later).

As far as rail sizes are concerned, I use the 25mm on ShopBot machines. This is not too bulky and offers great strength and costs less. The 30mm by some manufacturers are a little on the long side so you end up having to mount them closer together in order to use the full range of motion you would be accustomed to by the roller bearings. Mounting them to close is counterproductive so the 25mm is a good fit.

The key to the sliders is the mounting. Level, parallel and no bends or twists (the ones you can’t see of course). I use a ¼” thick aluminum strip on top of the C channel so I can more accurately compensate the surface. This is overkill and most likely unnecessary but I am an accuracy nut.

I always recommend a self compensating slider to compensate for minor alignment errors.

To answer Ralph about the clean issues, some manufacturers offer an end cap of sorts that works very well. I can load my rail with debris and have no issue or ill effect.

You are absolutely correct about the jogging. I only use this for surfacing with the OM system and ShopBot board.

Thank you for the supportive post and I hope I clearly answered you questions,

Josh

[searayx350]

Here are a few pictures of the Z
I designed and milled. this is before mounting plates and obviously before the spindle is installed for your viewing pleasure.

Pay no attention to the funky gear track looking thing. This is only a support for the helical rack that I wanted to look cool instead of a flat bar and a tab on top to test for clearence!

http://www.jscustomwood.com/ShopBotUpgrades/z.asp

JM

[handh]

I too look forward to your book, sign me up and let me know when you have it for sale.

[Brady Watson]

Josh,
Many of your assessments are clearly based on older model ShopBot CNCs. A large portion of the shortcomings that you list are addressed in the new PRS line of tools. You might want to visit a ShopBot PRS owner to get the latest information so that your book isn't outdated at the time of publishing.

-B

[searayx350]

Here is the Y car. The black things are 1/4" steel... plenty of support - no flex!

http://www.jscustomwood.com/ShopBotUpgrades/Ycar/ycar.asp

[searayx350]

Brady,

ShopBot sent me a ton of info on that wonderful machine. The book will clearly state that the upgrades are intended for a PRT / PRTAlpha.

Please keep in mind that I wouldn’t necessarily call the things I point out as shortcomings – merely issues that are exhibited while pushing the machines to their limits or using them as otherwise intended.

Also, the rule of thumb is that if it has been buit (anything that is, house, car, boat and so on) there will always be room for something to be improved. Aftermarket anything is a huge market in itself.

I may try to obtain a PRS and see what it is I can tweak on it before the release of the book but i would have to do that in the next few weeks and that may be tough to do.

None of this is to point out the flaws; think of it like this. I own a Corvette and my friend owns a Porsche 911. My Corvette cost considerably less than his 911 and does not handle near as well. The Corvette is unquestionably a great car but not intended to perform like a 911.

After I put an upgraded suspension, new breaks and modified transmission I can hang with him at the road race track all day long.

So my point is that there are design elements in all SB’s that are carried over to this point; stamped and shaped steel, steel rollers etc.

I don’t want this to be looked at like I am picking because I am not. I think it’s great that ShopBot sells a machine in the price point they do and if they included everything I talked about it would cost much more.

They bring affordable CNC to the masses and the customer has the freedom due to ShopBot’s design, to upgrade IF THEY NEED TO AT ALL. All I want to do is confirm to people that own SB’s that with a little time and money, they can achieve any result imaginable.

Hey, maybe you guys could convince SB to send me a PRS without motors, controller, and drivers or spindle (since I have all that) so I can tinker with it and try to get it in the book (LOL). I do mean this as a joke.

Thank you for mentioning it though – you fellow ShopBotters have made me feel welcome and I really appreciate that.

Thank you,

Josh

[richards]

Josh,
I'll tell you what I'll do to help your project along. Since I know that writing takes a lot of time, especially technical writing, I am willing to allow Shopbot to send me that PRS without motors, controller, drivers, etc. for experimentation purposes. I'll report my findings to you and you can write about them in your book. As I see it, everybody wins. Shopbot gets a tax write-off, you get a free research assistant, and I get to play with a PRS. Of course, since damage is likely to occur with my thorough experimentation, it wouldn't be fair to expect Shopbot to have to take the machine back at the end of the tests. I just wouldn't feel right about returning something that I had hacked.

On the more serious side, have you performed any measurements showing the force required to move the gantry on a stock Alpha compared to the force required to move the gantry when the Alpha has been retrofitted with linear rails and blocks? The reason that I'm asking is that I'm in the middle of a major project where I'm evaluating some G203 stepper drivers, G100 pulse generator, and various stepper motors. Until this morning at 2:30 (when I locked up my truck after a very quick trip to L.A. to pick up components for the test) and read your post about linear rails and other modifications, I had planned on using a 3:1 belt-driven transmission as part of my testing. The purpose for the 3:1 gearing would be to maintain higher torque - not for resolution, since the components that I'm testing would give me 4X the resolution that I'm currently getting with my Alpha and its 3:1 gearing. That resolution multiplier is totally due to the 2,000 steps per shaft revolution with the new components compared to 500 steps per shaft revolution with my current configuration. So, bottom line, if a Shopbot with retrofitted linear rails and blocks works properly with 600 oz*in steppers, then the belt-driven transmission could be eliminated.

[searayx350]

Mike,

Yes I have but I need to try to find a way to relate my findings without using terms like friction coefficient.

Here is the situation, the steel roller can be a misleading device as when unloaded (without spring tension) can feel much easier to push then the sliders but once again, this is misleading.

If you took a simple gear and shaft (no motor) and mounted it to the SB and tightened the spring as you normally would you would see that there is way more friction that you might expect. This is why I chose to remove the spring mechanism entirely from my configuration even though with sliders it is much less of an issue.

If you also take into account that the roller configuration will allow (and constantly does) the roller to “bite in” to the ground steel rails” this adds to the friction considerably.
A lot of this will be up to your particular need and your opinion but from a purely mathematical and engineering perspective the 600 oz/in should be adequate.

I cut many things with mine in that configuration even with the added weight and found no significant evidence that the system was underpowered.

Sorry to have such a loose answer but this is more complex than it appears on the surface and will depend greatly on your installation, application and so on.

Josh

[richards]

Josh,
There are a lot of things to consider. As far as I'm concerned, cut quality should be at the top of the list, as long as it is affordable. Adding $3,000 of linear rails and blocks would put that modification in the 'must do' list.

Running steppers slowly has me a little worried. If my math is correct, a 4g controlled machine with a 20-tooth, 20-pitch, 20-degree rack and pinion (giving a 1-inch pitch diameter) would require about 636.9426 steps per inch (the reciprocal of pi / 2000). That means that a feed speed of 5-ips is only requiring the stepper to run at 95.5 RPM. Ten ips is still only 191 RPM. Almost 100% of the work that I do falls within those speed perameters. Those operators cutting complex shapes with short moves might be running much slower. That's very good news for a stepper controller, because it means that at 5-ips we would only be using slightly more than 10% of the available pulse train - assuming that the 4g maxes out at about 30,000 pulses per second. BUT, those slow RPMs also mean that the motor might be running in it's 'rough' region. Steppers have harmonic problems at low speeds.

To test that theory, I've been running a Gecko G100/G203 unit driving a PK299-F4.5B motor on my test bench for the last two hours. At 1-ips we're okay, but at 2.5-ips it really runs rough. Three ips is smooth. Speeds faster than 3-ips are progressively smoother. The material and the cutter will determine the feed speed. It would be unfortunate to rule out speeds less than 3-ips because of possible harmonics.

Maybe I'm testing the wrong motor, but the PK299-F4.5B is a motor that matches the AS911 motor that I have on my Alpha. It produces 800 oz*in of torque to about 400 RPM and still produces 600 oz*in at 600 RPM. At about 800 RPM it drops to 400 oz*in. So, with correct ramping, it is a workhorse on a CNC machine. Personally, I like to run a motor in the 300 to 1000 RPM range. That spares me from worrying about harmonics and, if a gear box is added, the gearing replaces the torque that the higher RPMs strip away.

Am I overlooking something obvious?

[bruce_clark]

Mike,

Just one question about your testing. Is the motor loaded or unloaded? Steppers require a load (inertia) to help them reduce jitter or rough running.

Oh, I think your $3K might be a little high. Check out this link for less expensive profile rails:
http://www.kelinginc.net/SlideBlock.html

Bruce

[richards]

Bruce,
I always round up so that I'm not chasing after pennies near the end of a project. The prices at Kelinginc are about the same as the prices at HiWin. The main exception is that I used the price for blocks that have wipers.

You're right about steppers needing a load. That's the way that I test them, although the load that I use is not the same as the load that the motor will work against on a CNC router. (Mine is just a flywheel.)

[searayx350]

Mike

Bruce is right about load but I assume you know that.

The best way to answer without having the benefit of being there or the equipment at hand is that when I design a machine using steppers I try to design a system to accommodate most possible user environments. The emphasis is on MOST.

I have had the occasion to design a machine to do specific tasks at specific speeds but what you have to consider is how flexible do I need the system to be? And you must realize that with any choice is compromise and you have to decide what best fits you.

A gearbox of sorts may be exactly what you need and I would consider it after, and only after real-world testing. I have often found that even though the bench reports something the actual use tests tell the whole story.

Forces exerted against the motor, the mount and several other factors alter the situation greatly.

In your specific case a servo may also be the answer due to the high RPM and generally stable torque curve. As you know, with this you gear down and still can achieve rapid movements, slow movements and smooth operation throughout the spectrum. If you are sticking with the 4g board (doesn’t sound like you are), you can use the step/dir signals from it like any other breakout board.

Once again I would only consider this after real-world tests.

I also wanted to add that variations in amperage/voltage combinations offered very different results for various stepper models/sizes (food for thought). So you can try tweaking this as well.

There is a place you can get a respectable 80v, 850 oz/in servo for very little money. I have several of them and they run great.


Josh

[searayx350]

I also wanted to clarify something;

There is more to load than the defined term. The mount, mounting location, material and so on affect the harmonics.

You can calculate material density, elasticity, and thermal properties of said materials (since there is heat involved) but the math takes longer than it does to bolt a motor and run it in a real- world test.

If you want the formulas I will be willing to divulge but like with anything – if you are unfamiliar with the process the results are meaningless

[richards]

Josh,

I have a G320 servo driver and a very nice ID33004 brushed servo to go with it. That combination, with encoder, cost less than $350, BUT it requires a multi-stage gearbox to get the RPMs down to a usable range and the torque up to a usable range. The motor has a continous torque rating of 225 oz*in and a peak torque rating of 1125 oz*in.

Since I already have 3:1 belt driven transmissions on my alpha steppers, I would use the same thing on other steppers. They're relatively inexpensive to make, triple the torque and move the RPMs up to the 'sweet spot' for the steppers/stepper drivers that I like best.

The linear rail upgrade still has my full attention. Preparing a bed for linear rails is not a trivial matter; in fact, it can cost as much or more for machining/grinding than the rails and blocks cost. But, using extruded aluminum in the structure of the machine would minimize the amount of machining/grinding required.

[searayx350]

Mike,

I built an inexpensive tool to surface long lengths and if you want I can give you the plans (it wouldn’t take me too long to draw it as I originally freehanded the machine).

That being said, the THK SHS series can self align to a certain degree. I have placed them on standard steel C cannel and had pretty favorable results. The biggest issue here is to insure that you have your base level from all applicable points which usually requires some welding and heat shaping.

Another option to save money as the book will detail is to use the ¼” aluminum and a series of shims to level out the aluminum. I unfortunately cannot give all the details of this process as I do wish to sell a few books. This works VERY well as this gets the sub within the specifications of the self adjustment capability.

In my opinion machining should be a LAST resort. You can achieve results within the strictest of tolerances with the aluminum strip quite easily.

JM

[dingwall]

If you have a flat surface to mount your rails to, wouldn't damming the perimeter and flowing a self-leveling epoxy get things pretty close?

[searayx350]

I personally haven’t tried it. I fabricate custom CNC machines at our machine shop side of the business so things have to be 100% reliable.

I know that epoxy technology has improved greatly over the past few years and I have seen people assemble an entire CNC machine using epoxy but my fear would be deterioration over time.

It would be worth a try though.

[dray]

Good post..
I thought almost no one here knew of linear bearings.

I have been building cnc foamcutters for quite a few years using the thk linear bearings and ball screws.

I purchased a pair of 9' + thk's for my PRS but have yet to install them because after setting my prs up properly I have yet to find a problem.

But in time Im sure I will. Before I bought my PRS I went locally to go checkout a Techno which uses ball screws and also linear guides (mounted under table to avoid as much dust as possible)
heh the salesguy was supposed to email me but he never did so I cancelled the check and went with the Shopbot.

For the price you cannot go wrong and that is a huge understatement. If I had seen a PRS at a tradeshow set up properly with no slight of hand and I was able to check cuts with a square I would have easily paid 50k for the bare system.

I origionally had planned on building one but my schedule did not allow for it. The other plus with the shopbot is the HUGE user base and forums.

The best and most sought after products in the world have a large open source ability.




Great post looking fwd to the book

[searayx350]

Danny,

I had the opportunity to review the differences of the PRS before its official release. I knew by looking at it that it was a great machine.

As stated before, I feel that some of the upgrades I discuss are still applicable due to some carry-over concepts.

With any manufacture that cares about their customers such as ShopBot, they continue to make improvements and upgrades and the PRS line is intended to address many of the issues that its predecessor exhibited.

If you would not object, if you e-mail me your phone number I would like to call you today and ask some specifics about the PRS that documentation and pictures do not provide

I am glad you enjoy the PRS and I am confident that you have an excellent machine.

Thank you for your input.

Josh

[workingdog]

Josh,
I have been looking at the idea of adding some linear bearings to my old rack and pinion PR.
I would be more than happy to buy your book if it saved me the concern of entering uncharted water.
I am not afraid of the job, but I can't afford to experiment. I need to know that what I buy for the job will do it right the first time.
So if you have any advice I would like to hear it.
Mike Copeland,

[searayx350]

Mike,

I am here for my fellow ShopBotters!
Expect an e-mail from me in a little while.

Josh

[gskinner]

Josh,

Any idea when your book will be available?

[br928]

After the questioned validity of the original poster, has anyone successfully completed any transactions with JSM and can vouch for his integrity?

[myxpykalix]

He sounds like he knows what he's talking about. Sounds like an engineer to me.

[conceptmachine]

Ted was supposed to review his book maybe Ted can tell us what is going on!

[br928]

I was equally impressed with his knowledge of CNC machines. So much so that I ordered a XY slider upgrade from him and a 3hp spindle the he supposedly took back in trade and was a “killer deal”. You know what they say about a deal that sounds too good to be true! All the contact numbers he gave me have been disconnected and he will not answer his emails. I am posting this to keep any other fellow Shopbotters from losing their hard earned money. I have purchased from other posters on this forum and have always found them to be honest people. Buyer bewares.

[wcsg]

I thought it was strange how Ted never chimed in since the beginning. But if it wasn't true, then why not chime in. I won't trust anyone on the net who hides behind a proxy, it serves no purpose.

That is why I questioned this from the beginning. But why his "Thank you Erick" is still on the front page I have no idea.

Maybe he's away on vacation

[ted]

Hey Guys,

I'm afraid I don't know much more than you. Josh has contacted us. He does have a complimentary 4g board. And he has said he would send a chapter from the book for me to have a look at. I haven't seen it yet, but I am looking forward to it.

The one thing I do know from other contacts is that McGraw-Hill has contracted with Josh to write a book on CNC.

Ted Hall, ShopBot Tools

[Brady Watson]

The book is called: "Applied CNC Machining" by Josh Mitchel

You can get more information like the table of contents etc, via Amazon by following this external link: http://tinyurl.com/2bfw5r

Book Description:

CNC machining is growing in popularity

Applied CNC Machining shows you how to design and build a fully-functional, industry quality CNC (Computer Numerical Control) machine and also details how to upgrade an existing machine to include this type of automation.The author includes hard-to-find comparisons of the tools and software best used for specific approaches and styles.

About the Author
Josh Mitchell is the CEO of J&S Custom, Inc. Prior to this position, he was part of the executive management for a technology firm whose services included software and tool design for industryspecific applications.
_____________________________________

I'm in no way affliated with this guy...just good at researching.


The book sounds to me like it should be titled, "How to copy ShopBot's design from 7 or 8 years ago and upgrade it with modern electronics so you can have a ShopBot from 7 or 8 years ago with modern electronics."

LOL!

-B

[bleeth]

I had several correspondences with Josh and he gave me some excellent advice. The time and thought into his replies was offered gratis. Although I have not tried to contact him for a while now, a sudden "dropping out of sight", based on an opinion from contact to date indicates to me more personal difficulty than malfeasance. I hope he is well.
I would expect that the publishing of his book, much like good manuals for accessories, someone elses' "next video on PW", and someone elses' new cabinet processing software is taking more time than originally estimated.

[br928]

Dave,
If he was holding several thousand dollars of YOUR money, would it still indicate to you more personal difficulty than malfeasance? I am glad you are more concerned about his well being than mine! I only made this post to keep other Shopbotters from making the same stupid mistake that I did. I will gladly post a retraction if this somehow turns out to be a misunderstanding.

[br928]

I finally got a response today. I was promised that some of my material was shipped today and the rest tomorrow. I understand that my post resulted in several cancellations of orders. I feel this is the reason my problem got the attention it deserved. My intention was not to ruin someone’s business but to protect the Shopbot community.

Depending on when I receive the material, I will post again as to the quality of the material received and the willingness to support his upgrades. I will reserve my full retraction until all of the equipment and the installation instructions he promised are in my possession.

He initially told me he would like working with me if I would post my experience on this forum. That’s what I have done. Bad, as it may be. I truly hope this quickly turns into a positive experience and it could if he takes care of business. Stay tuned.

[sara_mitchell]

I would like to introduce myself as Sara Mitchell --- I am the Wife of Josh Mitchell…
First of all, Mr. Stan got a little over zealous with his post and He did not have a foundation for this post – Stan has never had a hard time reaching us with the exception of yesterday. Some people have a tendency to be sketchy – in today’s world I can’t fault him for that even though he was wrong to do this to Josh. Unfortunately we were short handed last week and I was out of the office with my daughter being sick – Stan wanted tracking info – info I handle – I will add that josh tried to hand deliver the order but was unfortunately delayed and that’s all I am going to say about it…
Here is a link to the non-electronic upgrades he purchased.
http://www.jscustomwood.com/stan/stan.asp
The book barley mentions electronics- Josh has spent years designing machines, building them and now the last two tearing into the ShopBot and all those years of experience are rolled into the book!
I am sorry and feel sorry for some of you people as you so cynical. If you don’t want his information then don’t use it – that being said, don’t badmouth him either. All he wants is to be helpful and he does not need people without the facts smearing him. That lacks class to say the least for people to do that!
Yes the book is delayed as there were some added elements and he is working day in and out to make it a great reference for everybody.
I would like to state that the book is not a ShopBot book but has 2 chapters about it – both positive and both helpful with only four pages about electronics of about 70. I like how people read into things like the Amazon link – the book is mainly about design, fabrication and use!
As far as phones are concerned, we have been moving our main service to fiber and there is a hardware delay. Anyone can call Time Warner and can verify this – call or e-mail me and I will give you our reps contact to verify this. We do maintain cell phones as well as alternates and Stan and everyone else has had access – josh may not carry his phone all the time but I do. Feel free to call either of us --- 972-215-9095 is mine, 972-951-8994 is Josh
Eric, How dare you speak about my husband that way – I have watched him spend countless nights designing upgrades for you guys for free, take calls and he gets at least 50 e-mails a day and answers them all.
We do not hide – our address is 1845 Summit Ave #406, Plano, TX 75074. We have over 20,000 sq feet there and full of machines to make machines and parts. We have been around for over 7 years. Try doing your homework Eric. There is no proxy – that is the default option with godaddy and I registered the domain! You have our address, stop on by or Google map it with satellite and see how big a shop we have!
Ted, Josh speaks very highly of you and I thank you for somewhat supporting him here – I know you can’t say more without a longer business relationship.
Anyone who doubts can call me – you have my number.

Sara Mitchell