Need Help with clip art parts file

[mike39]

My friend and I purchased a shopbot about 6 weeks ago. Recently, we ran into a problem when we tried to cut out a part file when using clip art. Our first attempts cutting out individual clip art part files were successful, but yesterday we ran into problems. We were trying to cut out a sign using a saved image part file when out of nowhere it began cutting deeper than the file instructed (i.e. -.25 inches instead of -.01 inches). We have looked at the part file and the saved image file and nothing appears to be wrong.
We would both appreciate any ideas or suggestion that may be causing this cutting issue. THanks for your help!

[windsor@muskoka.com]

I had a problem like that once with my ball screw z axis . ---The ball screw was sticking and the z started skipping steps . i.e. the cuter was at -1.5 but the display gave the position at -.5 . ----I cleaned and adjusted the z carriage and the ball screw and lowered the z speed to .5 and haven't had any problems since . I'm not sure if you can have this problem with the new z axis but it might be worth checking what the display gives as a position when the cutter is all of a sudden lower than it should be ?

[danhamm@abccom.bc.ca]

Mike, I think you should explain your process of
cutting clipart! what programs and file formats
and what you are using to convert to shopbot files.
This will help whoever is familiar with the program you are using to understand your particular problem...

[mike39]

Mike Windsor, thanks for the suggestion, we'll check it out tomorrow.
Dan, we are using clip art found in TurboCad version #6. We start making the image only black and white followed by removing any hidden lines found within the image. Once these step are finished, we save the clip art as a DFX file in TurboCad, run it through the Shopbot file conversion and finally attempt to cut the file using the router with a small dremel bit.
So far this happens very infrequently. WE had thought that it could have be due to our cutting speeds or perhaps the axis' move rates but it happened again using very slow rates. A real head scratcher for us... Thanks again for your help

[jimavey]

I experienced a similar problem. I concluded the z axis was losing steps.

Imagine the "z" loosing a few steps on each jog back up away from the work - on a long part file these would accumulate - and you would end up cutting deeper and deeper as you get into the part file.

But in my case it happened after I had increased the speed settings. I reduced the z axis speeds and the problem went away.

[toys]

James,

If you are loosing steps, your z carriage may be too tight. Or binding in some other way like dust.

[jimavey]

My guess was that the spring that counterbalances the weight of the router could be tighter.

It just was so much easier to just back the speed down a hair. I wish I could remember exactly what speed I was at and what I adjusted down to. It only afffected jogs and only jogs that were pulling the router up out of the work.

I keep z axis jog settings at 2 or less on my files now and there isn't a problem. I think even 2.5 was ok and 3 was too fast.

I do remember I was cutting a file with hundreds of holes (making a fan grill) and a lot of z moves.

I remembered that in the manual it said there is a point where, as you increase speed, you'll lose steps. I figured I'd reached that point and backed off a bit and everything was fine.

[grant@shopbottools.com]

If you have a Colombo spindle or have made some other modifications to your tool that add weight, it is helpful to have two constant force springs on your tool so that the weight is properly counterbalanced. Also on these tools, we have started to equip them with a 7.2:1 reduction gearhead instead of the standard 3.6:1. This lowers the maximum speed of the z to about 1"/sec, but gives up to twice the torque. If you have a Porter Cable router or some other otherwise hand held router, one spring does the job with the standard motor. If you are losing position under these circumstances, then it is sure that you are moving too fast. Stepper motors have a very flat power curve, but it falls off rapidly at the upper end of it's ability. If you go too fast, there isn't enough oomph to make it happen. I rarely run a z axis faster than 1.25"/sec for reliability's sake, although it can be done. There was one carving application where I did set it at 2"/sec, but it was a new and freshly tuned tool. I would not trust that speed in a production situation, day in and day out. I feel like 1.25" is safe on one of our new z axes as a jog or positioning speed. I usually do not cut faster than .7"/sec on the z. It is probably not applicable to this discussion, but it is also a common mistake for operators to execute a straight plunge with a bit that is not "center cutting". That is, it has no fluting under the center of the cutter to remove material, so diagonal plunges, small stepped plunges, or starting off of the material are the only predictable ways to bring these cutters to depth. The one I run across most commonly with this configuration is a .5" straight cutter with two carbide inserts.

[eurocab@bellsouth.net]

Grant,

We have the Colombo spindle and are beginning to have some problems with our Shopbot at higher x/y speeds (2ips). Our Z has never been changed from .5ips. The additonal spring that you are recommending is on which axis? We already have two coil type springs on the z carriage. It was part of the package.

Is there anything we can do to beef up the stepper motors to run at higher speeds?

Thanks

Rick Adams