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Rough Transitions
« on: June 05, 2009, 01:53:11 PM »
Anybody have or know how to fix this issue?

I made a 4" square and rounded the corners with a 1" arc radius.  If I run this part kerfed to the outside, it moves CCW and it is perfectly smooth all the way around.  However, if I run the same part kerfed to the inside, it moves CW and every transition from a line to an arc makes a noticable jolt that shows up on anything being cut.

Since the CCW paths work perfectly, I can't see how this is a simple setting change.  Any ideas?

Offline jimpinder

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Re: Rough Transitions
« Reply #1 on: June 07, 2009, 04:09:32 AM »
What I take it you mean is that, if the cutter is cutting on the outside of the piece, it is fine. Cutting on the inside, it digs in.

When you are cutting the outside of the piece, the cutter is rotating clockwise and moving anticlockwise. When it comes to the rounded corner, the natural movement of the cutter is AWAY from the workpiece, i.e. there is no pressure on it to DIG IN. Also (if you have backlash on the machine), there is no pressure on the tool to pull it into the work. It depends on the drive on the motors to move it round the profile of the job

When you are cutting an inside profile, as the cutter comes to the corner, more of the cutter comes into contact with the work, and it pulls in.If you have any backlash on the machine, the available movement will allow the cutter to move towards the workpiece, as the pressure on the cutter changes, with the change in direction. Say you have cut up one side then the backlash has been taken up in a downwards direction.You run along the top (no backlash on that) then you start down the other side, the pressure on the backlash changes to upwards and allows the cutter to move into the work. The same applies on the left and right sides (but with the other axis)

I can only suggest you check your machine for backlash, and if there is any try and get rid of as much as possible mechanically ( I recently changed my machine from ACME screws to ball screws, with a great decrease in backlash)  ,and then  try to compensate with backlash compensation, which, although tedious, does work.
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Re: Rough Transitions
« Reply #2 on: June 07, 2009, 12:40:23 PM »
The machine is an new zero-backlash ballscrew driven router, so backlash is absolutely not the problem.

Also, I'm cutting "in air".  There is no material being cut at all.  This is just raw motion.  CCW - excellent, CW - bounces froma line to an arc.

Is it possible that this is some sort of setting?

Offline ger21

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Re: Rough Transitions
« Reply #3 on: June 07, 2009, 01:05:08 PM »
Can you post the 2 different g-codes?
Gerry

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Re: Rough Transitions
« Reply #4 on: June 07, 2009, 05:54:14 PM »
LOOK to see if one of the codes turns ON exact stop. Sounds like one set of code is running CV and the other not.

Just a thought, (;-)

Offline jimpinder

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Re: Rough Transitions
« Reply #5 on: June 08, 2009, 03:05:33 AM »
I'm sorry I misunderstood, but your post said that  "it moves CW and every transition from a line to an arc makes a noticable jolt that shows up on anything being cut." Have you tried this with any material in - if so how much of a "jolt" is this. Does the cutter dig n, or come away from the material.

Have you handwritten this program, or is it generated by CAD/CAM.

Is "tool diameter" part of your program, or is it just a straight cut.

Not me driving the engine - I'm better looking.
Re: Rough Transitions
« Reply #6 on: June 09, 2009, 08:52:04 AM »
The programs were generated by SheetCam,  One version is an outside kerf, one is an inside kerf.