Z axis cutting depth errors

[huntfairchase]

I have a new PRS standard 48x96 with a router motor. When drilling holes or cutting pockets using a 1/2" Bit I get the following errors in Z depth within the same program. The error in Z appears to be incremental. I have tried different bits with the same results.
.125 cuts .020 to deep
.250 cuts .035 to deep
.375 cuts .070 to deep

[jeff]

Have you checked your unit values? You may have to adjust them for accurate movements.. for example, if the z unit value is set at 1000 and when you jog to 2 inches, and it only goes 1 inch, the unit value should be 2000.. these are not the accurate numbers, just an idea... check what the unit values are and what they should be.

Jeff

[dlcw]

If you go to:

C:\Program Files\ShopBot\ShopBot 3\Settings\PRS ShopBots\PRS_standard Tools

you will find a file for your machine that you should run. This will set all your values for your machine.

Don
www.dlwoodworks.com (http://www.dlwoodworks.com)

[michael_schwartz]

If the error is consistent it would be your unit values (VU) as the first two posters suggested. Follow Dons instructions to load the correct settings for your machine.

I encountered this myself with all 3 axis not moving the correct distance, and when jogging the machine would only move roughly 1/2 the correct distance. The culprit was indeed VU settings, which the setup utility did not load when I selected my machine. Manually loading the settings was a quick fix.

You will probably need to load them manually from the file path don posted.



Otherwise the next thing to check would be if your loosing steps. This would be more consistent with a situation where the machine is not cutting correctly, and inconsistently, vs moving a consistent distance but not the correct amount.

Check the cut/jog speeds on your Z axis, and make sure they are within the specifications. Nothing should be binding on a new machine but that could be another cause of step loss and would be something to investigate.

[jerry_stanek]

also check that you are in inches and not mm.

[huntfairchase]

Don & Michael;
This happens with 1/4 or 1/2 bits and when using drilling or pocketing cuts. I use the Z-Zero Plate and have checked the Unit Values and they appear correct. I am running in inches and the cut jog speeds are normal. The Z depths are the same if I cut in X or Y directions. X & Y dimenstions are good. I still get the following results.

.125 Z-depth cuts .020 to deep
.250 cuts .035 to deep
.375 cuts .070 to deep
.500 cuts .120 to deep
.750 cuts .170 to deep

[navigator7]

Just some brainstorming/troubleshooting thoughts that might help?:
Is there a gear train involved in the Z axis?
Are you using a dial indicator for measurements?
Is your collet slipping?
Have you tried measuring the spindle but not the material?
Have you put a dial indicator on the material being drilled to see if it's moving?
Is the table bowed or hogged?

[huntfairchase]

The depth problem is consistant. It cuts the holes listed above at the same depths every time. Always too deep. I'm checking with an electronic caliper and the table and material are dead flat with an indicator.

[navigator7]

Right on!
So that means you are not measuring material that is moving up.
It's not a collet issue.
Hmmmm???

Is the Z axis error consistent along the whole table?

[myxpykalix]

Mike if these errors are the same when you try them more then once then that says to me it might be in your settings rather then some type of bit slippage.

I would take a couple of different pieces of similar scrap and do this. Make a drilling toolpath, make a pocket toolpath, make a profile toolpath and (cut on vectors), on each piece.

Place them on different areas of the table.
Then measure them to see if there is a difference between the pocket and profile toolpath depths because you don't mention a profile toolpath depth issue above.

If all are the same consistent depth errors from different areas of the table, to me, that eliminates bit slippage or table height difference issues.

If all the errors were the same differences i'd say check the setting for the thickness of your Zzero plate. I think it should be .121(?) but i don't think it's that.
What version of control software are you using? Have you upgraded lately?
You might want to revert to a previous version that you knew you had no issues with, but ask someone more knowledgable then me before doing that.

[jerry_stanek]

I had that problem when I upgraded to the 4g and it was my unit vales were off for the Z had to recalculate them using my dial gauge. I set the gauge at zero and moved my z up 1 inch and it moved over an inch. just kept adjusting my unit vales till it was dead on.

[dlcw]

My Z-zero plate is .118" thick. I make sure the zeroing routine goes to the same place on the plate each time for consistency. I have calipered the plate to not be uniform thickness.

As far as dropping back a version - don't do this. Gary Campbell and I have traced many problems directly to going back and forth from one version to another. Tech Support highly recommends against this as well.

Try what Jack indicated about using the same exact cut file on scraps in different places on the table. This will at least eliminate bit movement in undo flex in the machine as the culprit. If all cuts are the same but depth is still off, then there is something wrong in the settings that is causing these problems.

Don

[myxpykalix]

this is why i added the caveat " but ask someone more knowledgable then me before doing that" lol
because as Don points out that Gary traced problems to doing that. I believe it may be due to remnants of an ini file confusing things within the program, but i am not sure.

Bottom line, defer to the experts like them on that part of it.
But Don I would not think that flex would give you the exact same error measurements all the time but would be different?

That is why i go back to thinking it is in the settings somewhere if these differences are the same each time, with each cut.

However what is confusing is that the cutting error depths are not consistent with a unit value error or they would all be the same depth of error per cut but they are not....

It's one of those things that make you scratch your head and go..HMMMMM...

[bill.young]

Mike,

What happens if you make Z moves without doing any cutting? If you zero the z-axis and then give it an MZ,2 command, does it go up exactly 2 inches or something different?

Bill

[dlcw]

Jack,

The ini file and registry both have remnants of versions laying around. Ryan at Shopbot can walk you thru how to clean your machine up.

Mike,

It might be an idea to call Ryan and have him walk you thru a harddrive cleanup and do a reinstall of the control software. At least that would eliminate that part of the equation.

In regards to flexing of the machine, my PRS Alpha 96x60 was flexing more in the middle of the table. There was a definite droop in the rails and whenever the gantry moved over the middle of the table I could see it flexing. I added 2x4 supports under the middle of the X rail and that problem went away. Also, the table is much flatter now.

I would suggest the multiple pieces of material scattered around the table and use an identical cutting file to cut each piece. This will help to eliminate any position dependent depth problems. Computers can do strange things.

Getting back to your original post, I am led to believe it is a settings problems but it doesn't hurt to rule others things out as well. I had the same depth of cut problems on the original Standard Buddy I had in '08 and '09 and found out it was a combination of settings values and hardware problems. Eventually got it ironed out by having Shopbot send a whole new Buddy and shipping back the original.

The important thing is to hang in there. I know it sounds bleak right now and you probably think it will never get resolved. It will, it just takes some time. It took me about 2 months to finally get my PRS Alpha operating correctly and reliably. Between this forum and tech support you will eventually have a smooth operating machine and will look back and winder how you were able to function without a ShopBot before you had it.

Don

[dlcw]

Jack,

One other bit of information learned about the unit values with the Buddy troubleshooting was that the depth of cut differences were actually cumulative not consistent. The deeper you tried to cut the worse the difference was. This had to do with drive motor gear ratios and rack&pinion gear ratios.

Don

[huntfairchase]

Bill,
I performed the MZ,2 move and the tool moved up 2.0 on the button. The tool will Zero off the Zero Plate and return to zero without any problem. However, I just tried to cut a .600 deep slot in a differnt location and ended up with .750. My Zero Plate setting is .121.
~Mike

[huntfairchase]

Don,
I'm tring to keep my chin up, but I have 400 parts to make before a Feb. 18th deadline, so I'm starting to sweat just a litte bit. I sure apprecaite all the input I get from everyone on this forum. This thing is harder to figure out than my wife....

[dlcw]

Mike,

I'd suggest calling tech support today and leave them a message to call you back. Let them know the urgency of getting this problem resolved and they will stay on the phone with you until you get something figured out. They will probably call you today and start working with you.

A really great thing about Shopbot is weekend tech support.

Don

[navigator7]

When troubleshooting equipment some questions we always ask are:
1. What was the last thing you repaired or replaced?
2. What problems have occurred in the past?
3. What was the fix?
I don't have a clue what the solution is. Plus, I realize you just pulled your machine out of the box. However, troubleshooting basics are universal.

Is it possible a batch of pinion gears meant for another application got mixed up?

Or perhaps the rack got mixed up?

Not casting any dispersions, of course but "Stuff Happens".

Counting your rack teeth over say 6" and counting your pinion teeth and measuring the diameter and comparing the findings with other owners of the same machine might produce some interesting results?

Just more brainstorming to add to the mix.

[huntfairchase]

All,

Thanks so much for the support. It sure is nice having guys behind you when you need help!!!

I figured out the problem with the help of Ryan at Shopbot Support. I guess they installed the wrong gear on my Z stepper motor on my machine. One with 25 teeth instead of 22. I changed my unit values and bingo. +/-.003 in Z at all depths!!! Thanks again for all your suggestions and support.

~Mike

[dlcw]

Congratulations Mike!!!!

I knew the guys at ShopBot could help with the problem. I'm glad it was something simple and you didn't have to ship your machine back.

Go have fun and make chips fly!

Don

[navigator7]

Sweet!
Congratulations....Now trust the machine a little.
It will talk to you!
;-)

[myxpykalix]

Like bugs bunny would say...."What a Maroon" lol