Parts array problem - consistency

[Airwurthy@aol.com]

Has anyone had problems with the consistency of cut parts using an array? This is probably a stupid question but I give up. We are using autocad 14 as a frontloader. Drawing one part and then copying the same part a few times to fill up our cutting piece, but there is an error that compounds as we get further away from home. Why is this? Is this something to do with relative vs. absolute distance? Slowing the (move)speed down changes things a little, not necessarily improves, but changes.
We had some seriously frayed cables a few months ago and bought new and the problem seemed to go away but its back again. The problem seems to be related to a closed entity inside another closed entity. Can you get cables too tight? Thanks for any ideas!

[frank]

Hi Skipp,

If this is only a problem when you are doing arrays, then we can rule out incorrect unit values as the cause. Make sure that there isn't any looseness or play in the carriage. Check the post today under proximity switch. If none of this helps we may need to take a look at your file to see what's going on.

[Ted Hall, ShopBot Tools]

Hi Skipp,

There are times when cutting and pasting in CAD can create a problem because of the way the CAD program handles the copies when the dxf file is generated. I don't know whether this is a problem in your case, but you might want to take a look at the .SBP file and make sure that the locations of the copied parts in the array are actually correct.

If not, we might need to look at the generation of the dxf ... or you could consider using the a .SBP program to generate the array. There is a sample in S_array.sbp in your SbParts folder.

Frank's suggestion to send us the file may be the best idea. Then we can rule out the file as the problem and know if we need to look further.

[Airwurthy@aol.com]

emailed the files to Frank, I will try the .SBP array program thing tonight. We have had this problem before with different files, but they all seem to be related to the copy and paste thing.
I also tried moving to a different spot on the table and had similar results. Its not very consistent either, it seems to drift from one cut of a file to another cut of the same file. Thanks for your help.

[Airwurthy@aol.com]

Okay, its gotta be something with the X-axis, I just cut the same array of parts about 30 times and they all came out perfect. I just pivoted the file 90 degrees so they were arrayed along the Y-axis instead. We just changed the x-axis cable about 2 months ago and things were fine for a while. I found one frayed spot already in the new cable. Does this mean it is too tight? Or perhaps a burr on one of the motor spindles or cable drive pulleys? The old worn out cables had several frayed spots, all on the same side of the machine, guess I should start there?

[Skipp Turner]

Hmmmm, we have been cutting on the Y axis for months now and it has started to act up....i.e. cutting the same part yields 2 different sizes. I also noticed the X cable is frayed in 2 spots already. Suppose I should remove both cables and check all pulleys for burrs? Even Y axis pulleys? Anyone else have this happen? Or something like/similar to it?
Thanx

[rgbrown@itexas.net]

Skip,

You are beginning to realize why many of us were happy to build gear-boxes. We rid ourselves of slipping cables and stretched bead-chains. The cute little screen-door rollers went the way of the DO-DO bird.

I highly recommend rebuilding your machine into a gear-drive machine. If you don't have the larger strut on the Y-axis, now is the time to correct that too. If the upgrade to Bishop-Wisecarver wheels on the carriages hasn't been done, that is another upgrade I consider mandatory.

The time and trouble to achieve these changes is worthwhile.

Ron Brown

[bill.young]

Skip,

Occasionally the plastic cover on the cable would detach itself from the wire core, so that for a short section the pulley was moving the cover but not the cable. Sometimes it was hard to find those spots in the cable, but you could sure see them in your parts!

Bill

[Skipp Turner]

The time and trouble to upgrade I have, the $$$ I do not. Thanks for the upgrade info, I would really like to find the problem though. I thought maybe somewhere out there, someone has seen this exact same thing.
Thanks Bill, I'll poke around some more.