Stop the Hop!!

[K2csq7]

I have had this problem for years and usually eliminate it by adjusting gap settings...

Is there a correct or sure fire way to remove the hopping up the tool wants to do, or do I just play with the settings till its gone?

Thanks!

[Colin Gilchrist]

The 'Gap Size' is the distance between where one 'slice' of the surface(s) ends, and the start of the next slice begins. The two techniques I usually use to reduce any unwanted retract motion are:

 

1. Increase the 'Gap size' distance value (I almost always choose distance instead of % of tool diameter). I usually start with a 1" gap size, and increase if necessary.

 

2. Change the method that Mastercam uses for 'Motion less than gap size' to "follow surfaces", and remove any tangential extension.

[K2csq7]

Thanks Colin, my settings are exactly as you describe (my gap was set to .600) (3/16" ball EM)

I changed the check surfs to some that were a bit less perpendicular to the drive and it got rid of 99% of it.

 

Please feel free to add some input since every situation is unique and may require different approaches.

[rickcact]

The 'Gap Size' is the distance between where one 'slice' of the surface(s) ends, and the start of the next slice begins. The two techniques I usually use to reduce any unwanted retract motion are:

 

1. Increase the 'Gap size' distance value (I almost always choose distance instead of % of tool diameter). I usually start with a 1" gap size, and increase if necessary.

 

2. Change the method that Mastercam uses for 'Motion less than gap size' to "follow surfaces", and remove any tangential extension.

 

 

A 1" gap size? I have been stopping at .100 and accepting what I get.I guess I just never knew better.

[Colin Gilchrist]

The 'Gap size' in a nutshell, tells the system how you want to move between each cut, or how to move between areas where the toolpath detects a gap between the surfaces.

 

I've used a Gap size up to 20-30" on some parts, where I wanted to force the tool to stay down on the surface and feed back to the next start point. This is rare though, and should be used cautiously, as you can get unwanted results. (Be especially careful of gaps between your surfaces when using a large gap size value, as you could cause the tool to plunge somewhere unexpected.)

 

I can see how the check surfaces would be causing that motion. I try not to include vertical check surfaces if possible, or sometimes I'll set the operation to leave .0001 on the check surfaces. I find you will also get less retracts if you use a containment boundary instead of check surfaces (where possible).

[K2csq7]

A 1" gap size? I have been stopping at .100 and accepting what I get.I guess I just never knew better.

 

And I'd bet you don't actually have any gaps bigger than .004 right?

I have mine set to .600 and only 1 drive surface....no gaps.

 

It never made a lot of sense to me, but they are old toolpaths....

 

I want to leave at least a .005 cushion near my check surfs. And I am also using containment...

[Colin Gilchrist]

Don't just think of a "gap" as a physical distance between surfaces. A Gap also exists between each slice of motion. Take the example of a flat ruled surface, 10 inches square. Use a Surface Finish Parallel toolpath. The 'Max stepover' now controls the 'gap distance' between each slice. If your 'Gap size' is larger than the distance between each pass (slice), then you will get retract motion between each pass. If your gap size is larger than that distance, then the tool will stay "down" and use the transition method indicated in the drop down menu: Direct, Broken, Smooth, and Follow Surface.

[Jeremy Herron@DBS Solutions™]

Can you just shift you tool containment by that wall by like .001 (or however much cushion you want) so your tool cannot get to that wall? I generally try to draw my tool containment so my tool cannot get to surfaces I would want to use as "check surfaces" and I do not use check surfaces unless absolutely neccesary for exactly this reason.

[K2csq7]

Don't just think of a "gap" as a physical distance between surfaces. A Gap also exists between each slice of motion. Take the example of a flat ruled surface, 10 inches square. Use a Surface Finish Parallel toolpath. The 'Max stepover' now controls the 'gap distance' between each slice. If your 'Gap size' is larger smaller than the distance between each pass (slice), then you will get retract motion between each pass. If your gap size is larger than that distance, then the tool will stay "down" and use the transition method indicated in the drop down menu: Direct, Broken, Smooth, and Follow Surface.

 

I think you meant to say smaller up there...

My stepover was .012

My gap size was .600

You said you normally start up about 1", are you using stepovers bigger than 1"?

on the part you had a 20-30" gap size set, did you really have gaps or a stepover up near 19"?

 

Can you just shift you tool containment by that wall by like .001 (or however much cushion you want) so your tool cannot get to that wall? I generally try to draw my tool containment so my tool cannot get to surfaces I would want to use as "check surfaces" and I do not use check surfaces unless absolutely neccesary for exactly this reason.

 

I just draw boxes..... that's a good one Jeremy, check surfs always bite me one way or another...

[Jeremy Herron@DBS Solutions™]

Takes longer to draw but you can have a lot better control of the toolpath IMO, You can always use the CreateBoundary c-hook and offset as necessary, but it usually gives up splines which can be a pain sometimes, but it is a quick start.

[huskermcdoogle]

Change your system tolerances. Try that, then up your toolpath tolerance. May give you completely different results.

[Chris Rizzo]

Choose as few (ideally none) check surfaces as possible.

 

I instruct people to just pick drive surfs and see what happens. THEN if needed start adding contain, then check surf. The more it has to avoid, the more erratic motion you will see.

 

Also when experimenting with settings and doing alot of regens, open up the tolerance just so it gen's faster. Then tighten up when your getting good motion.

[K2csq7]

Thanks for the ideas Guys, great tips!

I love the old paths because I get what I expect (Solid results) first shot.

 

edit:

Then tighten up when your getting good motion.

Careful, lots changes when you change the tolerances....

 

Also, the buttons for check retract motion for gouge & check gap motion for gouge in the gap settings may help alleviate the hops.

[shazam/TPP]

great topic with a lot of useful tips

[Chris Rizzo]

Careful, lots changes when you change the tolerances....

 

i hope so