Strange ridges

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Ms Wolffie
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Strange ridges

Post by Ms Wolffie »

tool Info.PNG
terrible cut.jpg
Finish Witch.PNG
Tool setting WITCH.PNG
I am having a problem with a clipart file that I am trying to cut.
First finishing path is with a 3 mm Ballnose bit, 5% stepover, showing some bad ridges.
Second Finishing path is with a 1.5 mm Tapering Ballnose bit, 5% stepover.
Although the ridges in the second cut are much smaller, they are still there.
Rich Auto B18E handheld.
1325 CNC, 3 axes, Helical rack and pinion on X and Y, ballscrew on Z.
7 kw spindle, vacuum table plus double sided tape.
What am I doing wrong, please?
Cheers
Wolffie

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Pete Cyr
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Re: Strange ridges

Post by Pete Cyr »

Very odd. Not sure what the issue may be. How did the preview look.

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Ms Wolffie
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Re: Strange ridges

Post by Ms Wolffie »

perfect, actually too perfect.
Cheers
Wolffie

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Pete Cyr
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Re: Strange ridges

Post by Pete Cyr »

In circumstances such as this when Aspire displays a good simulation the issue is usuall the post processor, a machine mechanical/electrical issue or a material setup issue.
You have been doing this for quite a while so I lean toward a machine or post processor issue.

If you have carved other models without issue I would discount the post processor. That leaves a machine issue.

I would look for factors that create static electicity/poor grounding.
If you use a dust collection - is it well grounded - that could cause what you have.

Can you carve another clipart model without issue (size it to be similar to the one that failed and in aprox the same location on the machine)

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BalloonEngineer
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Re: Strange ridges

Post by BalloonEngineer »

What is the steps/inch or steps/mm set to? 5% if 1.5mm is a pretty small amount, does the machine have the mechanical resolution to move by that amount?

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TReischl
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Re: Strange ridges

Post by TReischl »

Hmmm, lately there seems to be more posts that have someone stating that a post will cause issues like this or something similar.

Posts don't work that way. I know, I wrote posts for CAM software for about 25 years.

Generally speaking the CAM software prepares a generic machine file of one sort or another. Those files do not contain instructions like "pocket" or "finish cut", etc. All they have in them are generic terms for raising the head, lowering the head, turn coolant on, set feed rate, etc. In addition they have all the numerical information as to where the cutter is to move. The post does NOT calculate pockets, that is done by the software and placed in the file.

The post processor is exactly what it says, a POST processor. It massages the generic file into g code for a specific machine.

Posts can obviously cause problems, lots of them. But they do not calculate machine motion in regards to cutting moves. Some posts, like the one Ger21 created for his ScreenSet 2010 will create motion like raising the head to a safe position after the program is finished via a macro call.

I suppose someone could write a post that performed all sorts of arithmetic operations for some odd reason and cause the part to rotate or be moved. But this is not generally done since it is much easier and faster to do that sort of thing in the CAD software itself.

Hope that helps folks out. It is all pretty simple if you have been doing it your entire career. CAD designs information. Information is stored in a file that contains the data about every line, arc and circle. CAM reads that file, reorganizes to suit the NC programmer and allows him/her to tweak what will happen and when it will happen. That program writes a file with those instructions (no, the CAD data is not in that file), just machine motion initiated by the NC programmer. The post reads the new file and converts it for a specific machine.
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Savannahdan
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Re: Strange ridges

Post by Savannahdan »

I notice that it appears you have a different cnc than the one listed in your profile. Hate asking this but did you change the postprocessor for it?

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adze_cnc
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Re: Strange ridges

Post by adze_cnc »

This looks like a case where:

- a screen-shot of the Aspire preview cut would be useful
- size of area being cut (looks not much more than 100x100mm)

"Strange ridges"? I couldn't see anything in the photo that I might call strange. Looks like standard artefacts one sees when use a ball-end bit to cut a 3D model.

Steven

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Re: Strange ridges

Post by DLWOODWORKS »

This looks like it might be a problem in the machine mechanics. Something loose, a ridge of metal developed on something? The pass in the lower left looks ok. If you follow a line from the lower right to the upper part of the carving, it looks like something specific to that combination of X,Y coordinates.

I'd look on my machine for a piece of wood lodged into something, a metal bur that developed, something loosened up, etc. I'm pretty sure the PP would not create this.

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mtylerfl
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Re: Strange ridges

Post by mtylerfl »

Hi Wolfe,

Since no one else has mentioned or posed the question, I will...

Why are you running two Finish Passes rather than first running a standard Roughing Pass (with material allowance), then a Final (single) Finish Pass?

I’m wondering if the strange ridges are a result of deviation from the norm. Could you do a test carve with a Rough then a Finish and report back?
Michael Tyler

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