unequal radii

[Peteg]

All the corners of this cutout are programmed with the same radius, yet when cut, they clearly aren't. Any ideas as to why this could be happening?


Best

Peter

[Leo]

There are many ways to answer the question. Lots of unknowns here.

It might be:

Machine flex
Accell - decell
cutter diameter
workpiece moving
feed - speed

many other reasons

[WNC_Ed]

Always easier to help if you can post the file.
Looks like a diagonal mirror effect.

[TReischl]

Grab your homemade machine's spindle and give it a pull while you have an indicator touching it. Not dissing your homemade machine, so is mine.

There are so many things as someone already mentioned it is hard to tell, another is how CV is set in the control software.

One thing I can guarantee you is that if you drew those arcs all the same size then you have a machine issue.

Are these the first cuts you have made on your machine?

[TReischl]

Always easier to help if you can post the file.
Looks like a diagonal mirror effect.

Hey Ed,

I have been around for more than 20 minutes and have never heard of the "diagonal mirror effect"? A new one to me, care to enlighten me?

(In NC we do not say hello to each other, we say "Hey" so I am not being rude, LOL)

[highpockets]

It maybe the picture, but it does look like some mirroring and rotation effect going on...

[Peteg]

Humbucker.crv

(163.5 KiB) Downloaded 65 times

Hi

Thanks for the replies.

Work piece didn't move, but I will check the you other suggestions.

I am intrigued by the diagonal mirror effect, please explain.

Cheers

Peter

[TReischl]

That sort of thing can be caused by excessive backlash, curious as to what your method of motion is?

[Rcnewcomb]

The preview is fine and the vectors are symetrical. The stepover on your 12mm bit is large -- I tend to keep it under 50% -- but I didn't see any problem caused by that.

Check your control software for constant velocity setting.
You also may be dealing with machine flex.

Does the shape change if you use Conventional rather than climb?
What about Raster vs. offset?

Each of those will load the machine differently.

[Peteg]

Hi

Thanks for all the replies. I'm going to try a raster cut tomorrow - it's not far off midnight here in England, if I had no neighbours I'd do it tonight

I don't know if this is relevant, but I had this problem before I started using Vcarve; I was trying to learn G code and was programming by hand. I cured it by including a dwell of about .2 seconds before a change in X, Y direction.

Cheers

Peter

[Rcnewcomb]

Peter,
What are you running for a control system? Mach 3/4? UCCNC? LinuxCNC? etc.?

[TReischl]

Hi

Thanks for all the replies. I'm going to try a raster cut tomorrow - it's not far off midnight here in England, if I had no neighbours I'd do it tonight

I don't know if this is relevant, but I had this problem before I started using Vcarve; I was trying to learn G code and was programming by hand. I cured it by including a dwell of about .2 seconds before a change in X, Y direction.

Cheers

Peter

Uh oh, sounds like you have some serious machine flex. I have no clue if a dwell would solve a constant velocity issue????? Never ran into that.

If the machine cannot do that profile cut you should not try to solve the issue by going to a raster cut. The problem needs to be addressed because you cannot run the machine by raster cutting everything, that will drive you bonkers after a while.

[Adrian]

If you can you should slow the rpms way down as well. At those very slow feed rates your chipload is way off for MDF. You're going to be dulling the bit extremely quickly which is only going to exaggerate your issues as the tool will be pushing more than it's cutting.

[Peteg]

Hi

Thanks again for all the replies. I am running Mach 3, and it appears to be an acceleration/deceleration issue with a small amount of flex in the Y axis.

I have made some adjustments in the motor tuning page of Mach 3, and the results are much better. The attached file was a conventional cut with an 11.1 mm clearance and 6.3 mm final pass. The apparent distortion is due to camera angle; everything is within the accuracy I am happy with and can only get better.

Cheers

Peter

I am new to this (as is obvious) and learning all the time.

[sharkcutup]

It is awesome to see that you have the problem solved. Sometimes here on this forum you do not always hear or see about the problem being solved.

Much better looking carving!!!

Sharkcutup