View Full Version : Z Depth cutting to deep.

06-27-2006, 08:37 PM
O.k Maybe this issue has already been tackled but I couldn't find the solution here. I finally made the jump from the old DOS to the new windows based Control software...but ...Now I'm getting quite a bit of overtravel when cutting in Z. XY seem o.k. but the final pass in z is cutting into the spoilboard. I checked my unit values and the default loaded with the software seems o.k. I am using the z zero routine when cutting and the default there is being used as well. My default unit values are 733.386 in XY and 916.7324 in Z.
The overtravel is different based on the cutter used and depth set, but on a .75 depth cutout using a 1/2" straight cutter the overtravel was a full 1/4 inch into the table??

Any help appreciated. I have a pre 2001 4x8 PRT. I also hooked up a brand new computer with winxp home( this spurred the decision to try the new win software)


06-27-2006, 10:59 PM
So the only change is SB DOS to SB3, right? Any other changes?

If you zero at the spoilboard surface and then move to zero (0), is it lightly squeezing a piece of paper or is it gouging the spoilboard? I'm wondering if the issue your having is gradual or may have to do with your zeroing routine or something alike?

Have you checked for accurate positioning by moving to a defined value, say 1 inch or two and gauge with a ruler?

What kind of over travel are you having; 0.01", 0.03" or 0.125"?

Based on the last part of your post, I would readily think that the unit aren't correct... still, we need more data...

I don't think it's related to the new PC.

Whenever I upgrade SB3 to a new release, I copy my current shopbot.ini on the desktop and compare to the "new" to find any changes... have you?

06-28-2006, 08:37 AM
O.K. Paco ,
I did test defined values in x and y with a basic tuler and it does seem to be travelling correctly. My actual cutouts are o.k. in x and y. The zero routine seems to be working alright as well when I test. Zero's right to the surface. The problem happens when I actually run the part file and the depth seems to be off by a perccentage. For example .04 depth of cut seems to come out at .10 with a 1/8" cutter. hmmmm
A 3/4" depth of cut came out at a full 1" with a 1/2" cutter. The problem seems repeatable regardless of what software was used to create the post. Tried in Partwizard and V Carve Wizard. This tells me its either something in the SB3 or possibly Zero routine. I copied my old DOS unit values and plugged them in but they were way off in XY so assumed that the defaults in SB3 were the correct parameters for my PRT.
I can try a few other things to narrow the problem down like try without using my zero plate routine.
The only things that are new are the computer and SB3. HMMM?

Thanks for the help

06-28-2006, 08:56 AM
Come to think of it maybe my z unit values are off. When I tested I zero'd to material then meved z upt to a defined value of say 1" then back down twice by 1/2" then 1/2" again and the bit touched the surface, however I didn't measure the 1" rise and the drop downs by 1/2" . these distances are just what I plugged in but didn't measure them when the move was made. so they could be off on their own parameters.

06-28-2006, 09:07 AM

Does the z value on the screen read right according to the desired depth? Does the depth change gradually throught the cut or does it change immediately? Could you be getting some z-axis creep or bit slippage? Can you air cut the file and see what may be happening? You could try reinstalling SB3 and be sure that the control box firmware is updated since this is the first time using the windows version.

06-28-2006, 09:15 AM
Hey Bill,

You snuck in while I was typing. Try a gauge block of a known thickness (1") and zero on a surface, move up 1" and see if your block slips under.

06-28-2006, 09:39 AM
I had the same problem when I UPGRADED software once. I traced it down to the z-zero plate thickness. My plate is .125 the software was using .133 thus I was cutting .008 too deep.

06-28-2006, 09:47 AM
If it zero correctly, then the zeroing routine must be fine.

I would check the unit value of the Z axis. That sound to be the problem.

Do you have problems in both running a file AND with the K mode?

Sometime, the shopbot.ini file get corrupt at upgrades; you might want to cut and paste the current on the desktop and have SB3 create a new one and test it WHEN you'll be sure to have the correct unit value for your Z axis.

06-28-2006, 09:22 PM
Man... this is why Shopbot is the Best Value. 24hours and I get great response from fellow botter's.
We have two winners. Scott's stopblock test confirms that it must be Z unit values diagnosed by Paco.
Zero'd to table surface then moved z to +.75" the actual move was +7/8"
+1" actually moved to 1 3/16".

O.K. any ideas on the correct unit values for my PRT or is there a mathmatical equation that I need to calculate the proper unit values base on these movements.

Thanks for the help guys.


06-28-2006, 09:38 PM
Page 117 of the Users guide. There might be more within other documents...

Have you e-mail SB support, they MIGHT help you if you are VERY friendly...! ;-)

06-29-2006, 12:13 AM

Some time ago, this spreadsheet of unit values was sent to me. Maybe it will be of some help to get you zeroed in.

Unit values
Unit Values.xls (http://www.talkshopbot.com/forum/messages/20164/Unit_Values-13885.xls) (15.4 k)

06-29-2006, 06:17 PM

Perfect, This spreadsheet did the trick. This needs to be accessable on the shopbot webpage if it isn't already. I have changed my computer out several times and had to change my unit values. Would be nice if other botters had a way to access tis info.
It was definitely the z unit value.
Thanks a bunch for all the help guys. I'm back up and running.


06-29-2006, 06:59 PM
4466 (http://www.shopbottools.com/documentation.htm)

07-05-2006, 03:13 PM
Paco, does that document tell you to divide all the unit values by 25.4 if you are set up for millimeters? The spreadsheet above is for the inch guys only, as discovered over here (http://www.talkshopbot.com/forum/show.cgi?tpc=7&post=23462#POST23462).

To get older links inside this forum working again, take the /cgi-bin/discus out of the URL

07-05-2006, 04:54 PM
No it doesn't. Neither the User guide.

07-06-2006, 06:41 AM
I think you enter the (inch) unit values with units set to inches on the VD page, they then convert automatically when you change back to mm in VD.

07-06-2006, 06:55 AM
That was the standard drill for us - if something didn't work as anticipated, change the machine to its mother language. Millimeter users are at a disadvantage.

11-11-2006, 11:02 PM
I have the exact same problem Bill did, but the right Unit Values weren't shared! I don't have excel so can't decode the spreadsheet Scott posted... drat!
Help somebody?

11-11-2006, 11:49 PM
openoffice.org is a free MS Office compatible application. Their spreadsheet program is Calc.


11-11-2006, 11:49 PM
David, here's a table of the Excel file.

Pinion Gear # of teeth1/2 Stepping PR-PRT1/4 Stepping PRT1/8 Stepping PRT-IMS1/2 Stepping PR1/4 Stepping PRT1/8 Stepping PRT-IMS1/8 Stepping PRT-IMS 18127.324254.648509.296254.648509.2961018.592141.4 711 20114.5916229.1832458.3664229.1832458.3664916.7328 127.324 2591.5733183.3466366.6932183.3466366.6932733.38641 01.8592 3076.3944152.7888305.5776152.7888305.5776611.15528 4.8826 3663.662127.324254.648127.324254.648509.29670.7355 Z Axis Unit Values 3.6 Gearbox7.2 GearboxDirect Drive Pinion Gear # of teeth1/2 Stepping PR-PRT1/4 Stepping PRT-IMS1/8 Stepping PRT-IMS1/2 Stepping PR-PRT1/4 Stepping PRT-IMS1/8 Stepping PRT-IMS1/16 Stepping PRT-IMS 18509.2961018.5924074.3681018.5922037.184565.88441 131.7688 20458.3664916.7328366.6932916.73281833.4656509.296 1018.592 25366.6932733.38642933.5456733.38641466.7728407.43 68814.8736 Benchtop X & Y unit values Current tool


11-12-2006, 09:01 PM
Thanks for posting that.
After much number crunching and head scratching and trial and error I had found the right Unit Values, which were 733.3864 - same as the X&Y. Looks like the previous owner never figured it out, since they upgraded it a couple of years ago.
I, too cast my vote to have this chart available as a download at the shopbot site.
Thanks again...

11-13-2006, 11:14 AM

I added your chart to my reference manual. A valuable asset. Thanks for posting it.

It would be nice if we could find info like this on the Shopbot web site.

Bill Thorpe

11-15-2006, 12:09 AM
I can't take the credit for it. I got it from Gary Beckwith a couple of years ago.