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Author Topic: problem with getting detail  (Read 2521 times)

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problem with getting detail
« on: August 29, 2008, 10:51:42 AM »
I'm having real problems with my CNC setup right now. Not sure where the problem lies, or how to determine what it is.

I'm using mach3, have a sherline 4 axis mill, and the IMService's servo system (converted for use with Mach).

The attached simulation image is what the program should be cutting, as seen in Rhino3d with RhinoCam. The other image is what I am getting when I cut the wax.

All the detail in the feathers and such is gone. It's pretty flat. I cut 1 piece, looked great but decided I needed to reduce the stepover to reduce the size of the steps, and try changing cutting direction from across the X axis to along it.  I reprogramed the part and cut it. Next run was good, but I didn't go quite deep enough and it wasn't cleaning up the workpiece. Dropped my Z .02" and restarted. Ever since, I have not been able to get any detail.

I've rebooted the PC, reduced the velocity and acceleration on the Z axis by about 1/2, went back to a XML file that worked flawlessly (a copy is attached, the accel/velocity changes not included though), tried reprogramming again, reduced my feed to 3 IPM  (first piece was cut at 8 IPM), and nothing has changed the problem. I'm still getting almost no detail.

What's really wierd is that if you look at the simulation image and the wax, it looks like the step up from the flat cylinder to the wing is ok, but it cuts off almost all the feathers. The step up to the wing doesn't look to be as much as it should be, but it's consistently making that step and not making the step over the feathers.

I have cut quite a few 4 axis things before, without a problem. This is my first wax cutting job.

Any suggestions? I'm desperate to get this part out. Been playing with this for a week and am at my wits end.

Thanks

Offline Sam

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Re: problem with getting detail
« Reply #1 on: August 29, 2008, 12:15:06 PM »
That's a pretty small part. What size and type of cutter are you using?
"CONFIDENCE: it's the feeling you experience before you fully understand the situation."
Re: problem with getting detail
« Reply #2 on: August 29, 2008, 12:20:33 PM »
I'm using a 15deg profile cutter with a .004" tip.
Re: problem with getting detail
« Reply #3 on: August 29, 2008, 01:34:51 PM »
Think I figured out the problem. For some reason, I all of a sudden have huge backlash on the Z axis, like about .025 or so.

I'll never get another Sherline again. Can't say they are bad machines for the money, I've just had problem after problem with them. I buy a 3rd party add-on and the problem goes away.

Anyway, ordered a precision leadscrew Z axis from A2Z, hope to get it tomorrow and I can finish this stuff up this weekend.

Offline Sam

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Re: problem with getting detail
« Reply #4 on: August 29, 2008, 03:10:56 PM »
Glad you got it sorted. Be sure and post a pic of the end result. Once you post a work in progress, it's against the rules to not show the finished part.
"CONFIDENCE: it's the feeling you experience before you fully understand the situation."