Loosing X, Y Position

[dpings]

I am fairly new to the shopbot. We purchased one for the school this year and the students are having a blast. I have a hard time getting them to leave for other classes or go home at night. I have the PRS 48x48 with a PC Router. I am running Partworks 3.5 for the drawing software. Once in a while, we have to stop and re-begin the program. For what ever reason. Some files have multiple steps, sometime the kids use the wrong tool...etc. If you stop, and your 0,0 is in the same place, shouldn't the tool cut in the same path as before? I did an Inlay as an example and the first try I had to stop and start over. It was like it was set at a different home location. The last one, It did everything correct until it it cut the octagon out at the end. it shifted it so the flower was not centered any longer. Any suggestions? Here is a pic.

[BTP]

if you are "rough" changing tools, you can nudge it.

[dpings]

I just had a student cutting a 3-d leaf and the power went out. When we regained power, we had to make it go back home. Then we restarted the finish pass and it had shifted itself to a different location. It's almost as if when you tell it to go back to 0,0 it's picking a different zero spot.

[garyc]

Dennis...
Are you using the "C3" file to set your X,Y zero using the prox switches?

You should use this file before each cut file and after each stop to ensure repeatability

[dpings]

I C2 it and then use the zero plate to zero it.

[dpings]

Sorry....to zero the Z axis.

Alex, I don't get what you mean by nudging it? Wouldn't is still set it off from X,Y Zero? The machine says its at a X,Y Zero.

[kubotaman]

I hope I understand you correctly. If for any reason you have to turn off the Shopbot program, you have to re-do the C3 program. Again re-zero the Z axis. Lets just say when stopped the machine it does not know where it is located even though it may never had moved after quitting. Just remember where you made your 0,0 by writing down the co-ordinates. That will make sure you start in the correct place when you start again.

[MogulTx]

What I have learned to do is to use a 1/8 or 1/4" bit and I set a drill point at 0,0. I did not invent this idea. I got it here. Once you have a marked position, if you should lose your zero you can then move the machine back to this point and then re-zero your x and y. It will not be absolutely perfect, but it will be so close that you normally won't have any problem with it.

Now the question is why are you losing your zeros? Bad comm? Bad ground?

Figure out your issues and get it corrected to get the best service out of your Bot!

[wayne_walker]

Dennis,

Post your feed rate, speed of the bit, depth of cut, and type of bit. It could be that you are moving too fast and loosing steps or a dull bit causing the same issue.

I do as MGM suggested on every thing I cut, I mark my 0,0 into the scrap material so that I can find it again. Like he said, it may not be exact but it will put you very very close.

This is the best forum on the net. They will help you find your problem just keep looking and giving them feedback on what it is doing. This is the best educational source when it comes to CNC routers.

Wayne

[dpings]

Thank you all for the suggestions. I will look at some of them. The feed rate varies from student to student. But the problem doesn't seem to change. Most of their projects are being done on MDF. On the 3-D leaf I have them doing, I had them go from a feed rate of 1.7 in/sec to 4 in/sec. We had the same thing happen with both. The picture I posted above is on Oak and walnut and I had the feed rate of 1.7 in/sec.

The Depth is always less then the diameter of the bit. In most cases, we are using a 1/4" dn cut so they do about .125" deep per cut. On .75 thickness of wood, I have them take it in 4 passes with a 1/4" bit. 1/8" bit is about 1/16" per pass.

The speed of the bit is 16000 RPM. We have not changed this at all. IT is PC router so I can switch it on the router itself.

[wayne_walker]

Dennis,

Are you loosing your com? Does the com error screen pop up? Have you check your grounding of the machine?

Have you tried marking your 0,0 spot to see if is returning to the same spot?

I move my X,Y zero all the time depending on what I am cutting. If I have a piece of cut off that may be a weird shape I will adjust to the blank. Example: Using sink cut-outs to make a cutting board.

Since you have a lot of different users, is it possible that one student changed the X,Y zero for his project and then the next student assumed the X,Y zero was at the "shop predetermined" location and did not confirm that he was at X,Y zero for his blank.

I'm just throwing it out, I have done that more than once. I will move the router out of the way to get the blank positioned and clamped or vac'd down. I then move the router where I want the X,Y zero to be and get distracted or have a old age moment and not re-zero. My prior job may have been zeroed only .50" away, so it will go there to start the file. I now have a habit of watching the file start for a minute or so to confirm it starts where I want it to. Moving the X,Y zero all of the time is probably not the best procedure but it seems to work for me.

I cut almost every at 10,000RPM. The majority of what I do is plastic and the higher RPM causes the chips to melt back in the cut unless you can move fast. I cut plastic at 10K and a move speed of 3 IPM and have a air nozzle blowing on the bit. I seems to do the job.

Talking about loosing your zero, here was one of my experiences. I had a problem where I lost the Z zero and after a hour or so I found the problem. A single chip of plastic had landed on top of one of the Z rollers between the roller and the Z mounting plate causing it to loose steps. It would go up but not down. What a pain...

I hope you find your problem.

Wayne

[myxpykalix]

Dennis,
Here is a practice i think you should institute immediately that will help keep the goblins away. Part of your problem is you are letting kids with differing abilities mess with various settings and that starts some of the problems. Here is what i do in setting up a file for cutting.

My personal preference is to have my X,Y 0 in the center of the material but this will work for that or Lower Left corner 0,0

First i mark center on my material

Do a C3 (you are now at the corner of your table)

manually move your bit to the center of the material on the table

(here's the important part)
WRITE THOSE COORDINATES DOWN ON A SHEET OF PAPER
Now Zero X,Y
(this part is optional)
take that sheet of paper and fold it in half horizontally
then take it and fold it in half vertically
then take the opposite 90 degree corners and bring them together to form a pyramid shape
Now take that paper and stick it in your pocket for safe keeping

(back to the important part)
The reason you do that is that if someone messes up some settings or you have a computer problem or comm error or gremlins attack...

You can always find your X,Y Zero point by doing a C3 (going back to 0,0 on the table) then...
carefully reach in your pocket and unfold the paper in the reverse order of folding it previously and do a
MX (the written down coordintes)
MY (the written down coordintes)
And you are now back in business:eek:

Now i was having a little fun with this description but the bottom line is that if you have a problem with the computer or control box and lose your settings this is a sure way to get them back perfectly.
What some guys do is just use an offset to run their files but this is the failsafe way to get back if you lose it all.

What also is happening i think is if the students are hitting the Estop button you lose your settings where if you just hit the spacebar you are pausing the action.
It's not as fast as hitting the Estop but that might be what is also going on.

[shilala]

I have a little different twist on Jack's zero/centering routine.

I made a 6" grid on my spoilboard. It makes it super easy to center any part on the table. That's not completely necessary because I could lay out from the edges of my table, but it's easier on me personally.)
I then run a C3. Then I type in MX24, then MY24, then Z2. Now I'm zeroed (in x and y) in the dead center of my 48" table, and my material is deadly close to dead centered, screwed down, and will never move until it's completely finished, as it should be. (I'm wondering if your kids are removing and replacing their projects?)
If anything happens, all I need to do is repeat C3, MX24, MY24, and Z2 and I'm back at the center.
I always model with the XY axis in the center of my project, as well.

This process always forces my center position and xy orientation to be just as accurate as the C3, and so far as I know, that's as good as it can get.

[dpings]

Thanks everyone. I like the idea of writing the start coordinates down. I also moved my C3 spot so it is no longer the very corner of the table. Part of the issue is I have a 1x4 running up the Y and along the X making a 90d edge for the kids to line their project up on. I think this was messing me up. Now I have it so it always goes to the corner of the project, not the corner of the table.