Limit Switch /Zero Problem

[kelly]

I am running a BT32 Standard with a PC router, 3/8 bit - I am milling 1 1/4" fir for the upper half of the "boiler" of a set of Ride On Trains (5 Inch Arch, 2 1/2" thick sliced in Partworks 3D)
The problem:
I have been starting by using the C3 command to zero the x and y axis. I run the file and it runs without issue. After finishing the part, I set my new part (I have a jig set up to put the part back in the same place each time as I need to make 12 of the parts) and rerun the part file but on the second run, about 5 cuts in, the Y limit switch is triggered and the system halts. The good news is the limit switches are working, the bad news is that it appears to be losing it's Y location.
If I run the C3 command before I cut each part, the file runs without a problem.
I am using the slice command when creating the part but other than that it's a straight forward file. I have only had my machine for a few weeks and this is one of the few challenges I have hit.
Any suggestions are appreciated.

K.Z.

[Gary Campbell]

Kelly...
Some of the prox switches seem more sensitive to the distance to the pickup than others. Double check that the target bolts are tight and the correct distance (gap) to the switch for better consistancy. Mike Richards gives some good ideas in this post: http://www.talkshopbot.com/forum/messages/312/31117.html
Hope it helps, Gary

[kelly]

Thanks Gary, I have checked the bolts are they are tight and they are currently in place where they were set at the factory. I have not ground the bolts flat but I will put that on my list to see if I can increase the accuracy.
I plan to recreate the cut file and see if it happens again. I suspect it's a software issue or maybe something I am doing between parts, as I have cut several other parts without problem.
I will post an update after I get through some parts today.
Be well,
K.Z.

[Gary Campbell]

Kelly...
Check the gap betweeen the target bolts and the prox switch. The PRS assembly manual calls for .080" gap. Check this gap and possibly adjust til you get satifactory results.
Gary

[kelly]

Quick update, I have been cutting parts most of the day and the problem does not seem to be related to my Prox switches. (It happens if I manually set Zero or use the Prox switches.)
I re-saved the file and the Y appears to be moving between 1/32 and 1/6th of an inch with each part run. (Less than before, from what I can tell and it seems to always move to the right as I face the machine)
It doesnt appear that the X is losing location. I plan to set up some cuts on flat stock with some guage lines to check and see if it is specific to these files or if it happens with others as well.
I am running 3.5.9 with the latest firmware but I see there is a newer version. I will download that just to be sure it wasnt a bug in the system.
Has anyone had a similar problem on the BT32?

Thanks
K.Z.

[beacon14]

Sounds like a loose pinion.

[sawdust535]

Just a stab in the dark, (because I'm not too clear on the location of your jig to the x,y axis)but when you attach a new part to your jig without using C3 again, you may need to start your nect cut using a 2D Offset. (You mentioned the problem doesn't happen when you do a C3).

[kelly]

Hi George, the jig is setup to place each part at the same place in the X and Y axis. (Each block of Fir is the same thickness, width and length) At the end of the cut, the system homes the X and Y and puts the Z at 1". The issue appears to be related to the Y moving off the home position but I am still not sure when. If I re-zero the X and Y, (C3 on my BT32) the part is cut correctly but if I run the file without re-zeroing, the Y is off by 1/32 to a 1/16 of an inch. (It appears to be accumulative)

Hi David, I will do a search on a loose pinion and check it out this weekend when I get back into the shop.
Thanks for the feedback.
K.Z.

[sawdust535]

When you say "accumulative", it sounds like David may be on the right track. Have you tried performing a [ZT] after the [C3] command? This will zero the Table Base Coordinates.

[dana_swift]

Kelly try using much lower feed rates and see if the problem goes away. The "standard" stepper motors can lose a step from time to time, which gets worse with speed. Each time you do a C3 you remove the accumulated errors, so it works well for a while.

If that turns out to be the problem, upgrading to an alpha may be worth considering- they have a method to detect when that has happened and correct themselves. That allows much higher feed rates without losing their position accuracy.

D

[kelly]

Thanks for the feedback guys, I have checked the pinions and they are tight.
I will try changing the feed rate this evening and see if that is part of the problem. I have been cutting the "rough" cuts in the Y axis and then following with the finishing cuts in the X axis. (Shorter runs and slower feed rate)
I am not sure but I think the rough cut feed rate was at 6. I knew this was high but I have been experimenting with how to reduce cut time without losing accuracy/quality. I have been pleased with both but this may be a result of the high speed.
I will let you know what I discover.

K.Z.

[kelly]

Quick update on my problem - It appears to be directly related to the feed rates I have been running on the Partworks 3D cut files. I have been running some of the parts as fast a 6 IPS (PW3D) but my Partworks (2D) files were running 1.7 IPS. Slowing the feed rate fixed the problem.
I have a question for the group, is there any damage caused by running the parts this fast. I have been getting good results for what I need and its an easy re-zero after each part but I don't want to damage the motors.

Thanks
K.Z.

[richards]

When you run a stepper motor too fast, all that happens is that it looses steps. With a stepper motor, as long as the voltage from the power supply is matched to the motor, almost nothing can damage the motor.