Need help with my inconsistant "z" depths

[rossi7]

Using my PRT96 routing a 24"x96" signfoam sign with background relief with raised text. My routing software is Rams. Im getting inconsistant "z" depth cuts (see attached sample).
Ive tried leveling the machine, tighten all hardware. Had router itself overhauled.
Any helpful hints.

matt
3883

[kerrazy]

is it possible that your router bit is slipping?
Ensure your collet is real clean.

Also ensure you have the latest software, for either dos or windows for your control box.
there was a dos version 3.35 I think where the z would lose steps.

and lastly, ensure you z is not racking as it comes up over the surfce of the material. If your bit is to tall and it has to rise really high to clear the material, it will lose steps and cause this to happen.
Dale

[Maxwell (Unregistered Guest)]

Though it does not look like this is the case from that picture ... Somtimes a spindle that is not perpendicular/normal to the surface of the table will leave 'steps' in its passes. However, this problem will be seen on each pass of the tool. That does not look like the problem you have. I have made the error of simply not tightening the collet enough. A tool changing clamp works nicely to really let you put your weight into tightening the collet down. With an upcut spiral it can be very easy for the tool to get pulled out of the collet in some materials. This will happen intermitently as the program runs. (Though I also once saw a tool get pulled out all at once ... not pretty but that one wasn't my fault. ;) ) Good Luck.

[gerald_d]

As unlikely as it may sound, the electrical grounding of all the parts running on bearings is very important. Our early PRT suffered from this problem, and was only cured when we grounded the router housing.

[daveiannone]

Matthew,
Did the "steps" in the material happen after a tool change? If so, it could be that you are not zeroing in the same spot and possibly the material thickness varies slightly ..

Dave

[johnny_s]

what is your z move speed? is it possible that it is too high and the force of the plunge is causing the router to miss steps? are your cuts getting less deep as the program runs? then this might be the case.

[artisan]

I would lean either towards the grounding issue (possible) or towards a software issue (probable). I've used Rams and I've noticed the issues you've illustrated....but I've seen it in Artcam as well. My questions are this....are you grouping large files together as a single toolpath? And....more importantly...are you selecting several functions (vectors) to create toolpaths for at one time?

I've seen the type of inconsistent z depths you've shown whenever I try and save time by asking the software to make too many decisions for me at once. I have better success by creating many simple toolpaths, then grouping similar files (bit types) together. There seems to be a limit somewhere between the toolpath software algorithm that makes the decisions, and the operating software that runs the bot concerning file sizes. It also makes sense that the problem grows exponentially with every vector you select, thus causing possible distortions or errors. This has been my personal experience....especially with 3D files. Try breaking your file into smaller separate toolpaths....clearout, profile, cut etc. and see if this helps....or at least helps you pinpoint the problem....D

[erik_f]

How are you holding your foam down? I have the same problem with MDF from time to time...in the beginning I thought it was the bot, but after more work...I'm pretty sure it was the material...buy this I mean that the MDF would have a bow to it...and as I machined away material the bow would get less or more depending on conditions...so although the material wasn't moving side to side...it was moving up and down and giving me some problems I thought were the Z axis...now I put a level on the MDF and find which side the peak of the bow is on and put the face down on the table...so in this way, when I clamp the edges, I'm pulling the MDF down from the center out...if the bow was up...I think I would get the same problem back...I have noticed some of this even with my new idea on loading sheets of MDF...but it is alot less than before and I imagine it would go away all together if I had a vacuum table...but the machine should be grounded also...but this was my experiance.

Erik F.

[johnny_s]

Okay, I thought I licked my problem before, now I have it again. So, I know its not my z speed, the bit is tight (cause I took the y car out of square tightening it). Here is what is happening.


3884

First movement, second and last, means times the thing goes home for the pocketing. This is really the only place that it is obvious. I tried to group the inside and outside of two paths and clear between them in Artcam. Then no matter how I go about in selecting all 8 areas to pocket, it breaks it up like the way you see.

Another weird thing is that in the first pocket of the first movement, the router clears material about 4 times over and over and in different patterns or directions - then proceedes to next cut.

Here is the fist pocket of
the fist movement, it is fine
- except for all the times it
cuts the same thing over.

3885

This is the final pocket (8) in the string.

3886

Here is the end result.

3887

You see in the final pocket, there is about 3 different depths, all at the same time. The final send from home is cutting the inside out.

By the end of the cuts, my Z was almost a 1/4" lower than when it first started.

When you say grounding the router, does that mean the motor? I have the frame grounded. I don't know about software, I know it is a problem, cause of the grouping thing, but why doesn't anyone fix it? I don't know how to test it either, cause I did try it different ways. I hope I don't have to do it individually, going home 8 times.

Could it be my spring on my Z is getting weak? I have a 3 horse Columbo. I zerod before I started.

Sorry for all the images, but I hope it will help you guys help me.

Thanks.

[johnny_s]

BTW, how do you get such a large image to post? I had a 25k limit at the test page. Matts looks bigger than 25k, unless it is black and white.

[ron brown]

John,

First you will need to determine of it is a bit slipping or the router/spindle. Once that is settled, you may be able to find a solution. Until then, you leave all of us guessing.

To check it, you can measure the length of the router-bit or, figure out a way to tell if the spindle is in the same location when you re-zero the bit.

My last "problem" like that was with a Porter-Cable router. Some kind soul needed a 1/4" collet, borrowed mine and returned a well-worn one. I throw away the insert and save the snap-rings and nut when an insert goes bad. The Insert is about 1/2 the cost of a full collet but is never stocked. I keep at least two spare collets of each size I might need - I never know when another kind soul is going to raid my spares and leave me without the proper collet.

Onsrud recommends spring collets, like the E/R 25 on the Colombo, be changed every 200 hours or so. At $11 to $25 each depending on brand, it is fairly cheap insurance. An hour meter on the spindle would be a good way to keep track of bit and bearing life. I plan on adding one to my Porter-Cable on it's next rebuild - the bearings are starting to growl.

I know my plate thickness and have a one second "pause" before my zero routine executes the "VA" command. If I have a problem like yours I determine WHERE the problem is then look for the root cause.

Ron

[stevem]

John, look for several lines superimposed on top of each other in your drawing. That can cause the repeated movement you see over the same line.

The depth problem may be caused by electrical noise through the unshielded cable used on the Bot. Especially where you have power cable crossing the step and direction cables to the steppers, or static caused by chips going through a dust hose that is not grounded.

[johnny_s]

This is all good stuff. Steve, I checked the file, and no layering of lines. Ron, I am very sure that the bit was tight. Like I said, I took the thing out of square tightening it. I also looked under the collet just to see if it was tightening, and it still had lots of space to close onto the bit, if you know what im saying... collet not tightening on itself. Could be wrong though.

When I get in tomorrow, I will check about the grounding and lines, and measure the heights again. I will have it cut air first, see where it ends up, then try another sheet and measure again.

[ron brown]

One more quick thought John, "Spiral Up" bits exert a consiterable down force on the router. If your springs are on the marginal side, bit force just might be enough to cause a motor to stall.

If the collet is damaged, it won't matter how tight the nut is, the bit will still slip. I have had personal experience with this.

Ron

[gerald_d]

See these threads on this forum as well:
http://www.talkshopbot.com/forum/messages/26/1654.html
http://www.talkshopbot.com/forum/messages/312/1790.html

[chamcook]

John asked early in this thread about the Z speed. I know that if I set the Z speed on my PR machine too high the machine will lose steps and the depth will vary all over the place. What is your speed. Is it always the same? Is this problem repeatable? If the same file doesn't produce exactly the same problem every time then you can rule out problems with your design software and concentrate on problems with the machine and router.

[johnny_s]

Okay, did a lot checking today. Grounding and wires;I moved wires that were crossing over others, jiggled a few ground wires. From some of the links Gerald provided, I decided to hook up an old UPS I had laying around. Don't know if it does any conditioning though.

Checked my collet/bits for tightness, lowered z jog speed (move is already low). I marked my z height at the bit and at the frame. Air cut the same routine with and without vacuum on - z came back unchanged.

Cut 3 pcs of birch ply, no problems - except for the router going over the same paths over and over again. Now I noticed it did it on number 8 cut as well, don't think it did it before.

I don't know what fixed the z problem, but I am also going to add some more grounding to my dust collection. I currently do not have ground running through the dust collection hose that goes over the wire/cable bridge on the bot.

Thanks for all the help guys.

[stevem]

John,

Open your cutting file in the editor or WordPad and manually delete any un required tool path commands, or check for code that causes commands to loop and repeat.

[artisan]

Steve has rightly suggested the next step I think. This can be time consuming, but I believe it will explain your problem once and for all...athough it may not solve it. I believe there is a problem between the toolpaths generated in Artcam (and some other programs) and the way the new operating software interprets them. When I run from the older DOS program, I have not seen these "Z" fluctuations. I have seen them regularly in the new software. It ONLY seems to be happening in the "Clearout" and "Pocketing" sections of the various softwares. Bevel cuts and machining along vectors are trouble free...as Johns pics would also seem to support. I have cut large bitmaps of woodgrain, rocks and basketweaves with no problem at all. This ONLY occurs in the clearout functions. John, does this square with your experiences?

I'm going to step out here and suggest that the mechanical (bit tighness, deflection, steps, springs etc.) and electrical (grounding, noise etc) can be eliminated as the the causes of this particular problem.

I have not had the time to scour my own code except briefly. I have not found the problem yet. I am anxiously looking forward to solving this and anyone's valuable inputs. I suspect a Gremlin is afoot....D

[johnny_s]

i don't know if the code in word pad corresponds with the one in the window that you see when the part is running. I attempted to do that but the window of the control program showed lines of 2000 or more in the first set of numbers. The text file does not show any line of code going this high. I will double check though.

[johnny_s]

Also do you know how to get the software to cut all the cleared areas in one pass, rather than going home 3 times. Is there some kind of limit in artcam?

[artisan]

In the short term, I forgot to mention there is a simple work-around for this problem. Create a "rough out" tool path with all the multiple depth passes first to clear all pockets and "clearout" areas....THEN, create a second finish toolpath that will clear out any missed (steps ?) in ONE pass. This will give you a nice even surface and correct any of the "steps" left out in the multiple passes. The software only seems to get tripped up when making multiple passes....D

[wayne_walker]

I am have a problem with the "Z" on my PR updated to PRT. I am cutting .375 plastic in 3 passes. The 1st pass has a lead in, at a depth of -.125", the 2nd pass at -.250" and the 3rd pass at -.370", leaving a skin to hold the parts in place.

The 1st pass cuts all 32 parts with a uniform cut depth. The 2nd and 3rd pass cuts each part and then goes to the next part. On each part the "Z" depth gets less and less.

The reading says it is correct depth. The part is cut at about -.187" but it reads -.375". I run the bit down to the spoil board and the reading is -.65".

I have Z zeroed the plate several times. Checked the unit values X, Y, & Z are correct for the machine and the A is at default (should this be the same as the unit values?). The gear is tight on the motor.

Any help is appreciated!

Thanks,

Wayne

[gerald_d]

Wayne, you have to change your first name - seriously!


Thread by Wayne Locke - Z Axis Shifts — A LOT (http://www.talkshopbot.com/forum/messages/26/1258.html)

Thread by Wayne Cordrey - Diving Z axis (http://www.talkshopbot.com/forum/messages/26/5828.html)

[pierrewessels@hotmail.com]

Just a thought...
Nobody has mentioned this so far as I can see so here goes...Is it possible that the culprit is your dust collector "sucking" your material up slightly as you remove mass and make it thinner and more flexable? That may explain why it is of varying depths when everything else seems tight. It might also explain why your plywood attempts were more successful. I know I have had this problem with thin MDF sheets with large pocketed areas. This may be exagerated with the use of an up-spiral as well.
Pierre

[gerald_d]

Pierre, a good point, but Wayne's cuts are getting shallower instead of deeper. Wayne, can you check if your bit is moving up the collet as the nearby bearing of your router gets hot? Make marks on the tower slides and see if they line-up for an air-cut versus a real-cut. If they don't line up, you are losing steps, or you are getting electrical interference causing climbing-steps. If the marks still line up, then your bit is slipping.

[wayne_walker]

Gerald & Pierre


Thanks for the input. After checking EVERYTHING several times and giving up for the day. I went out this morning and started the bot up and it cut fine.

I cleaned the collet and set the bit in the collet to the end of the flute to see if it was moving. It was not.

I have my bot at home while I am in the learning curve, so all of my problems show up at night and on the weekends

Thanks Again,

Wayne

[ron brown]

I wonder if the collet itself is worn out. I did have someone "borrow" one of my PC collets one time and replace it with a well-worn one. .

BTW- I usually only replace the insert and snap-ring. I reuse the nut. All the parts are cleaned. Then, the inside taper of the router is cleaned and waxed, the outside taper of the collet is waxed and the threads are cleaned and waxed. Extreem caution is used to avoid getting any wax in an areas where the bit may contact.

According to the bit reps, a collet will last about 200 hours. The inserts are about $10 from a Porter-Cable parts supplier. They are available in several sizes other than 1/4" and 1/2" by special order.

Ron

[wayne_walker]

Ron,

Thanks for the info. I will buy me a couple of collets to have on hand. I am using the collect that came with the machine when I bought it used.

Thanks,

Wayne

[ron brown]

And, let us know the cause if you ever figure it out . We are all curious as to the cure for symptoms as we might be the next ones with said problem.

Having someone else's problem documented is so much easier and cheaper than solving it "blind".

Ron

[workingdog]

Wayne, You said you have an upgraded PR.
Do you have a ballscrew .
There was a post about problems with ballscews and dust.

Mike.

[scott_smith]

Guys, Look at Wayne’s numbers:
“The reading says it is correct depth. The part is cut at about -.187" but it reads -.375". I run the bit down to the spoil board and the reading is -.65".”

Wayne, it looks like you are losing steps on the Z motor for some reason. If I read your post correctly
The display says -.375 but the bit is at -.187. Must be missed steps check your Z move speed, is the bit sharp, is it a plunge bit, Z motor cable good, make sure you are moving the Z into the material not jogging.

I’ve been wrong before but that’s what it looks like from here.
Scott

[wayne_walker]

Mike,

I have the rack and pinion system. The majority of the material I have cut with the machine since I purchased it used, is ABS plastic. The previous owner was cutting mostly wood. The machine was pretty clean.

Scott,

I think you may be correct. Shouldn't the Z-zero taken care of this problem??? OR did I miss something?? I just did not know where to go. I'm still in the very early stages of learning.

Thanks,

Wayne

[gerald_d]

Wayne, maybe I was a bit cryptic when I said "Make marks on the tower slides and see if they line-up for an air-cut versus a real-cut. If they don't line up, you are losing steps, or you are getting electrical interference causing climbing-steps. If the marks still line up, then your bit is slipping."

Basically you have to narrow your problem down to one of three areas:

1. Is something moving/slipping mechanically during the cutting process?
- Bit slipping in the collet
- Router slipping in its bracket
- Material lifting from the table
- Etc.

2. Is the stepper motor losing steps? ie. is it being fed good signals, but because it is overloaded, it doesn't do every step. The overloading can be caused by:
- Using a bit that won't plunge vertically down
- Dirt on ball-screws
- binding rollers on V-slide
- wrong tension in springs
- etc.

3. Is the stepper motor being fed with wrong information? ie. it does what it is told to do, but the control box is sending false info. This false info is caused by electrical interference getting to the control box. There are three directions to check under this category:
- Check emitters: The router is probably the biggest source of emission, especially when the brushes are bad - run the router off a seperate circuit and keep its cable at least an inch away from other cables. The static on a ShopVac hose is a huge emitter. The stepper motor cables can also emit.
- Drain emited signals to ground before they reach the control box. The metal structure of the SB can act as a receiving antenna and it should be grounded electrically. The ShopVac hose needs a ground wire. In some cases even the stepper motor cables need to be shielded and grounded.
- Protect receivers from the emitters: Again the wires of the z-zero plate, the E-stop, etc. can behave as antenna and lead interference to the control board. Keep them away from other cables, and if necessary, shield and ground those wires as well.

[scott_smith]

The Z-zero would fix it until you lose steps again

Another thought:
You could have a Z driver starting to fail. You could try switching the Z and A channel. This would be my last resort after checking everything else.

Gerald, as always, excellent description in the above post. Sorry, I missed the losing steps comment in your post Monday.

Scott

[sw@rwdi.com]

I'd like to add my 2 cents to this... When I first got my shopbot I had the same problem, and Gerald mentioned my problem... Believe it or not, the brushes on my router were causing the problem. I cannot explain why but as soon as I changed the brushes the problem completley went away.

One other culpret that hasn't yet been mentioned, We have a shopbot at work that we use as a plotter. The Z Axis moves down 1 inch then back up one inch. It repeats this move thousands of times per plot. We started hearing a click when the z axis was moving past that one inch up and I could not find it anywhere! What happened is we wore out an area of the z axis then when we moved the zaxis past the 1 inch the bearings would catch and loose steps. I'd suggest taking off the router/springs/stepper motor, And slide the z axis up and down manually to feel for a flat spot on the z axis.

[dingwall]

+1 for brushes.