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44henry
04-26-2007, 05:53 PM
We are experiencing some problems with our new ShopBot. When using the zero plate everything appears OK, however, the distance that shows up on the Z readout does not follow the distance that we measure from the workpiece to the cutter. Moving the z axis up manually gives readings that are considerably different than what we measure. My students have made a few programs using the Partwizzard. Everything looked ok in the simulation run, but when it started to cut half the time it would be above the surface of the part and the other half it would plunge much deeper than was specified. Is there a calibration that must be performed on this system for the Z axis before we attempt any further cuts? Should the head be trammed again before going any further, visual inspection doesn't suggest that the head is out of alignment, but something is definitely wrong. Any help would be appreciated.

Regards,

Alex Johnson
University of North Dakota

Brady Watson
04-26-2007, 07:27 PM
Alex,
It sounds to me like your unit values are wrong. What model do you have, a PRT, PRTAlpha, a PRS Standard or PRS Alpha?

-B

44henry
04-26-2007, 10:13 PM
Brady, it is just the standard PRT96. I have just started working with it this week. We have tried a number of things, tonight I tried cutting the demo shopbot logo, but after setting the z axis with the z plate it never more than scratched the surface during the cutting operation. I think if I can get the Z axis to behave the machine would be great, I just am not sure what I've been doing wrong. Any information you could provide on the units would be very helpful.

Regards,

Alex Johnson

Brady Watson
04-26-2007, 10:31 PM
Alex,
If you are running the Windows version of the software (SB3) your unit values for a PRT with 3.6:1 motors (most likely) and 25 tooth pinions on the X & Y axes, and 20 tooth pinion on the Z, should be the following:

X Unit value: 733.386
Y Unit Value: 733.386
Z Unit Value: 916.732

You can check & change these values by entering the VU command in SB3. Just type in the numbers for each axis in the yellow fill-in sheet & give it a test.

If this is not correct, help me help you by answering the following:

1) Are you running the ShopBot in the DOS (v2.39_m) software or Windows vSB3? If SB3, what version?

2) Count the pinions on the X or Y axis. How many teeth? (a Sharpie marker helps to mark your starting tooth for counting)

3) What is the model number of the motors on the machine? (Just read #s off of the X and Z motor label) This will help to identify the motor and if it has gear reduction or not...some came with 1:1 drive.

4) How old is the PRT? Some early models used IMS 1/8 stepping drivers, while the majority of them used Allegro 1/4 stepping drivers. A 4G version (within last 6 months) uses 1/10 stepping drivers.

-B

44henry
04-26-2007, 10:42 PM
Brady,
Thankyou for the help, I'll get this information posted here tomorrow morning. Thanks again.

Alex Johnson

44henry
04-27-2007, 10:53 AM
Brady,

I tried inputting the unit values you gave me this morning and ran the ShopBot logo program one more time after zeroing the bit on the surface of the workpiece. Again, the Z axis indicated on the computer it was starting at 1" when in fact it was only about half that. The program ran, without touching the surface, and when it was done it said the Z axis was at .25" which it looked like it was. Maybe I'm just not understanding the setup on the machine, I don't know. The information you requested is as follows.

We are running the program from windows and it is SB3.4.30 as labeled on the disk.

The Y axis pinion has 348 teeth on it.

The motors on the X and Y axis both have the same numbers which are A6497-9412KTG and they are 2 phase 0.5"/Step they also each have SB296-2TH3.6 written on them. The brand appears to be VEXTA

The ShopBot is very new, we received it in January and finally got it setup a few weeks ago.

Thanks again for your help.

Regards,

Alex Johnson

Brady Watson
04-27-2007, 11:25 AM
Alex,
OK...let's see if we can get you sorted out. See points below:

1) A pinion is a round gear, the long flat gear is the rack. You probably have 25 teeth on your pinion gear. It is also called a spur gear.

2) If you are running V3.4.30 and you bought this in January, your PRT is most likely the 4th generation PRT, commonly referred to as a "4G". This uses Gecko microstepping drives, and your unit values *should* be as follows:

X and Y = 1833.465
Z = 2291.831*

*The Z's unit values will be 2X this number if the motor label says 2 phase 0.25° step.

See if the values above work for you. If not, give ShopBot a call. They'll know exactly what you have and how to get you going again.

-B

44henry
04-27-2007, 12:35 PM
Brady, thanks for the help. I plugged the unit values in and that corrected the z axis problem. Unfortunately I seem to be having problems now associated with the XY axis. I created a simple vector drawing with the letters TD centered in a circle, everything ran fine in the preview mode, but when I cut the object the letters were off center in the circle and the spacing between the letters was way off. Any ideas what could be causing this problem, possibly another unit value issue with the xy axis? At least the depths of cut were correct this time.

Regards,

Alex Johnson

Brady Watson
04-27-2007, 12:59 PM
Call ShopBot. There may be a chance that your pinions are a non-standard (25T) size. Be sure to count them before you call. (The round gear...not the long rack)

-B

44henry
04-27-2007, 08:48 PM
Brady,
I called ShopBot this morning and with their suggestions along with the information you so kindly provided, I managed to get things in operation and even cut a few signs. Thanks for all the help.

Regards,

Alex Johnson