PRSalpha BT48 buddy vs PRSalpha 48

[aviationmachinist]

Hi everyone, we have been looking into purchasing a shop bot for some time now. We are a business that plans on machining mainly aluminum and copper plate. Thickness's ranging from .020 to possibly up to a half inch. Most of our work will be machining .125 or less. We have been looking into the buddy because we can use the power stick which we may use in the future. This is opposed to a fix table (PRSalpha 48) that limits our options. Our debate here is what is going to get the job done for us with the highest accuracy. The Buddy or the PRSalpha 48? We want to mainly stress that accuracy is a high priority and which ever table can best deliver that accuracy will be our favored choice. We want to use the 5HP single phase columbo spindle to machine our parts. Please let us know what will best fit out needs, the power stick is absolutely expendable if accuracy is compromised.

Thank you!

[erik_f]

What kind of accuracy do you need? I would say the x and y of both machines should function with the same accuracy, but the z using the powerstick would require greater care. A lot of it depends on how good of a machinist you are.

[aviationmachinist]

Do you own one or both of these machines or is this your opinion? Take the operator out of the equation 100%, I'm purely comparing machine to machine. Which one would be better for strictly metal or are they truly equal in accuracy and speed?

[aviationmachinist]

elaborate more please on "the Z axis would require better care", I don't want to invest thousands and have to baby a machine, while i could of went with a different model and less headache if you know what i mean! Thanks Erik Get back to me!

[jporter]

I have a BT 32 with the original aluminum moving table and a Power Stick. I use the Power Stick for cutting out wood furniture pieces and it performs well. However, I do not believe the Power Stick would be as accurate as a solid table for high accuracy machining. A new Buddy only comes with a Power Stick, so I would look to a solid table machine for what you are talking about. Just my humble opinion....joe

[gerryv]

J: My first thoughts are that if you're looking to hold 0.0005 or better all day like a HAAS mill, then you're best to buy a HAAS.

That said, the Buddy is built with the same superstructure components as the bigger machines so logic suggests that the most most rigid of all the Shopbots will be the BT32, whether standard or a Alpha because of it's shorter spans.

Beyond that, I believe it's been suggested on this forum that a spindle has better bearings in it than a router. Being that the application you're describing is what amounts to very large envelope milling machine.

I'd want to find a spindle that's proven to work well at lower RPMs because of the broad range of mills/cutters and related knowledge base available to machinists. You'll need to think about how to get around flooding (chuckle) but then aluminum moves heat away a lot better than steel so that's in your favour.

Again, from the good advise I've read here, not all spindles are what they're cracked up to be in the sub 3000 rpm range. Ceramic bearings, if available, are designed for high speed applications but are more precise at all speeds so again, the tolerances you want to hold are what's most important in choosing a Shopbot or a large CNC mill.

I've looked into this topic as well, but I'm certainly no expert; I've simply amused myself with a few metal lathes and a bit of basic milling.

It was with this kind of flexibility in mind that I bought my BT-32 Standard Buddy. My plan remains to upgrade it to a spindle, and have a "good" machine shop add an extra set of V-groove rollers on the Y and Z axes and have them mount two more tracks (4 in all) to the X axis for the moving aluminum table to run on. Obviously, much care will be needed in the alignment, hence the need for a "good" shop.

I would then surface my aluminum table with a fly cutter in both the X and Y axes.

My very limited knowledge and experience suggests to me that assuming the job is done right this is as far as I could hope to go in turning my Buddy into a large format milling machine that could handle the non-ferrous, soft metals, plastics and woods.

In this case please consider that my two cents on this are perhaps only worth just that so you'd best get solid advise from some of the other fellows who actually know. In that case, I'll not be at all offended if they tell me not to quit my day job because I'll be learning too :-)

What's holding me up at the moment (besides an unheated garage) is that I'm giving serious thought to moving up to a BT-48 and having a 48" X 48" foamed aluminum or honeycomb table made up (with a 1/4" +/- solid alum. skin laminated on top and machined flat. This would keep the weight down enough, hopefully, that the stock steppers would have the torque needed to prevent problems when cutting shapes.

At this point, I will caution you that my wife is shouting in the background, "Don't listen, I'm working on having him committed"! She's hoping some of the guys that know will fire away! Me too actually :-)

[erik_f]

On the new version of the Buddy, as Joseph said, only comes with the powerstick. Yes I have a BT48 standard with the old style aluminum table. I used to own a 4x8 old PRT. As you move farther and farther out from the center of the Powerstick you are moving father out from the most stable portion of the table, thus getting into more and more chance of z variation. On my buddy the whole table is supported by v rollers. I would say for your application the fixed table would be most accurate. I would call shopbot however since the shopbot is more designed as a wood cutting machine as far as I know. The reason I ask what kind of accuracy you will need is because +/-0.005 is average for the shopbot...I usually see somewhere between that and +/- 0.008". So I'm sure you can do better with care of set up...as with any cnc.

[aviationmachinist]

I think i will go with one of the alpha's with a fixed table. Ill post over in there section and see what they say. I'm thinkin a 48x48 because then i wont have to shear the width of my aluminum sheets (because they come 48" wide) just the length.

[harryball]

With the 48" table and an additional stand or table to hold up the cut off, you could cut your 4x8 sheets of aluminum in half using the bot. Wiht some registration trickery, you could cut 4x8 sheets on the bot if you had to do so.

Just some thoughs.

/RB

[aviationmachinist]

i like that idea R ball, i never thought of that.

[navigator7]

Has anything changed with ShopBuddys since February?

I'm with Gerald above who suggested the 32 should be the most accurate machine of all due to the short gantry span.

What am I missing? A dial Indicator or two should be a good indicator if the power stick is hogged or sagged.
The Y axis should be easily checked as well.

I can't imagine a little tweaking is not necessary every time the machine is moved or smacked by Murphy. ...if you are into real accuracy.
I ran a 50 Hp Lodge and Shipley WW2 lathe.
That sucker was built stout!. Did we have to tweak it after picking it up with a forklift? Heck yes!

The other thing I'm missing is... the cutting is done beneath the gantry. IMHO.....a warped or curved board not withstanding....if the material is flat at the cutter head isn't that all that matters?

I'm interested in the full boat PRSalpha 96 x 48 but the ability to pick up and move to remote sites has unusual appeal....and then somebody says you can use a vacuum on a Buddy?

Is this a custom plenum?

[mikeacg]

I have a 48" Alpha Buddy and I can tell you from experience that the 12' Powerstick is not as accurate as I had hoped. If I cut a 32" x 12' sign of 1" Komotex with fairly large letters (say 12-18" high) it looks pretty good though if you look close you can see that there is a bit of variation along the "y" axis. I tried to cut a 32 x 72" sign that had a bunch of 1/2" high letters (donor's names) and the machine failed miserably. The extra weight of the board made the Powerstick sluggish and with the double-cutting method that our software uses, the second pass was never in the same place as the first. I ended up redesigning the sign in sections to fit the 2' x 4' table and everything was fine again. Using registration pins, I can push the size but the extra weight of the substrate must be considered. If I was doing signs on a regular basis I would want a fixed table so the bot only has to move weight of the gantry, not the table and substrate.
Don't get me wrong! I love my Buddy and it does everything I ask but I know its limitations and I don't ask it to do anything outside its abilities.
Mike

[cartar]

I am a new user so I have no experience. I have the 48AlphaBT because of space problems. When I need the Powerstick can I not beef up the support to prevent some of Michael's problems?

[mikeacg]

My problems are not related to support. I have both infeed and outfeed conveyers so the piece slides smoothly in both directions. I built the conveyors with plenty of wheels and they are absolutely flat. My 'problems' are related to relatively small items like bunches of 1/2" type. The machine is fine for everything else. I'm not sure what a piece of 32" x 12' - 1" thick Komotex weighs but it is more than I can lift (I get it in 8 ft. sections from the sign shop). The weight of the board is definitely what is causing the problem. It is better when I slow it down but still not optimum. I was just trying to be sure that everyone understood the limitations of the machine.
Mike

[erik_f]

A dual X motor system would help with long runs of powerstick. To Chuck...I have seen people fix trailer jacks to each leg for the bigger machines.

[mikeacg]

I like that idea Erik! I guess the second motor could face the existing motor and run in reverse, keeping the two gears closer together so as not to run out of the 12" extra on each end of the PowerStick. I would love to be the beta-testing site for that concept! (Hint hint)
Mike

[navigator7]

Thanks Eric! Great thought.
I was considering Hilman rollers.
I'm following you guys on the Dual Motor system but would a gear reducer accomplish the same goal?

Does a gear reducer confuse toolpathing?

[erik_f]

A gear reducer would be easy enough to account for in the control software, but you will lose speed (if that is a concern to you. Michael, I was thinking along the same lines...for the GEN I BT's I don't think it would be to hard to outfit a second X motor for power. Like you said you might lose a little x travel...but you could make the set up with a release so you only engage it when it is needed.

[mikeacg]

Exactly, Erik! And with a 12' stick, I think you could afford a few inches! Not sure how to wire it to run backwards but I'm sure someone out there can help us with that problem!
Speed is always a problem! I hate tying up the machine for long periods!
Mike

[erik_f]

Not sure how to wire it either but I'm pretty sure you can just change it in the control software.

[Gary Campbell]

Erik, Michael...
All the full size machines use 2 X motors and one of them is always running the opposite direction of the first.
Gary

[erik_f]

good point Gary

[mikeacg]

Cool! So maybe we could get ShopBot to offer us a retrofit for our Buddys to make them work better? Hint hint!

Mike

[Gary Campbell]

Michael...
IF I were to buy a Buddy to "play" with, I would add a system similar to the JessEm Mast R SLide (2 of them) and have a very rigid platform with 48" range of motion. That would put a total of 60 roller bearings under the table. This should increase both the load capacity and the level of accuracy. Add a 3/8" solid Aluminum table base for a super setup. Those parts and a longer rack should be under $2k. Very nice prototype machine.
Gary

[mikeacg]

Gary,

I like the concept! But, if I had more room, I'd have gotten a full-size machine to start with. That wasn't in the cards when I ordered this machine. I accept the limitations of my Buddy and will look to buy a bigger unit when I get my new shop in a year or two. The Buddy is pretty amazing and will pay for itself in no time. It does all the things I need for my businesses (the large signs were an after-thought to make extra cash and help out a friend). I think I was asking too much to expect it to do 1/2" letters on that big a piece. Even with an extra motor it might be a tough task! I'm working on a flat-surface table right now (Humidity is an issue here so it will be a plastic or aluminum eggcrate type construction) but I am slammed until Spring so it will have to wait. I may trim my stick to 8' to help with the weight issues (especially now that I better understand how to index stock with pins) and see how that works. I do so little oversized stuff that I don't see that as a limitation...

Mike