Errors in part files: gremlins are adding circles

[greg@germanguitars.com]

I'm cutting some mother-of-pearl today. 0.060" depth material, 1/32" bit, 0.15"/sec xy speed.

The pattern for my toolpath was created in Vector as a single chain of 126 entities, reorganized, with no gaps or misalignment.

When I cut the toolpath, there are two places where the shopbot deviates from the nearly straight line in the file in order to cut a small circle before continuing along the chain.
I've re-generated the NC, re-organized the chain, etc. No dice.
I remember this happening once before, but I can't remember how I fixed it...
Anybody else seen this?
-Greg German

[rgbrown@itexas.net]

Greg,

The best bet on finding the "FIX" is the VECTOR forum board.

I think the discussion is here:

http://www.imsrv.com/discus/messages/12/99.html?1056249384

[greg@germanguitars.com]

Thanks, Ron.

[gerald_d]

Greg, is there a command for this small circle in your .sbp file? In other words,
- The command is visble (Vector problem)
- the command is not visible (ShopBot Problem)

This may be completely un-related, but ShopBot has had a record of glitches with small circles. Make sure that you have the latest de-bugged SB programs installed.

[frank]

Greg,

When you are in the "insert NC object" window select "Options" and then "Coordinates." In the pop up window make sure that "Decimal digits" is set to "6". You can then click on "Special," "Options," "Defaults," and "Save to custom" in the main window to save the settings.

[sheldon@dingwalllguitars.com]

I've had problems with smallcircles getting missed. They were in the NC file generated by Vector. I'll check the Decimal Digit setting.

[gerald_d]

Vector says (http://www.imsrv.com/discus/messages/12/1882.html?1061002234) you should have 4 decimal digits.

I am too scared to look at how many decimal digits we are using!

[imserv@imsrv.com]

Unplanned circles are caused by arcs smaller than the number of decimals in the CNC program.

In the CG command ( Circle, G-code format), an arc is defined from a beginning position, an ending point, and the incremental distance to the center of the arc.

In order to cut a circle, the ending point is set to the same value as the beginning position.

Shopbot has recommended in the past (often), that Shopbotters use 6 decimals to minimize the chances of inadvertently creating CNC code that has circles or loops that are unplanned.

There are several other things that can be done to eliminate unwanted circles.

1) Back plot your CNC code in Vector to check for loops. (Available in Vector 9.3 and later)

2) Use the free G-code loop-delete program that is posted on our user forum. (Vector 9.3 and later can convert , SBP code to G-code)

3) Vector 9.4 added an automatic filter in the code generator that filters out duplicated arcs when using too few decimals

4) Change-Break-Interpolate to replace arcs in a chain with an accurate linear approximation.

Fred Smith - IMService

[jkforney]

Greg
Also a way to avoid any circles is to Change-break-interpolate. This changes the arcs to line segments.

John Forney

[jkforney]

I see Fred posted during the time I read and replied.

John Forney

[gerald_d]

We work in millimeters and our Vector is set to 3 decimal places only. No small circle problems so far. Increasing the number of decimals will increase the size of the .sbp files.

My logic tells me that a blanket 6 decimal recommendation is an overkill for metric users?