Over cutting corners problem.

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Tony Mac
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Post by Tony Mac »

Hi Jim,

Measuring the tool geometry off your photo and it looks like the tip diameter
is closer to 1.5 mm than 0.79 mm.

Can you try recalculating a toolpath with a larger diameter and running this on
the machine to see if it makes any difference.

Tony

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BradyWatson
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Post by BradyWatson »

The first question (and the one most overlooked) is: How are you holding down the material? If the parts are not held down tightly to a FLAT spoilboard, then the material will walk up the bit or move X,Y. Carpet tape or a properly setup vacuum fixture usually rules this out.

Second thing...How clean are the vectors? Often times when zoomed out you can't see variations in the vectors OR they are not closed or complete, but appear to be at 1st glance.

-B
High Definition 3D Laser Scanning www.IBILD.com

James E
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Post by James E »

Good idea Tony.
I was going off the manufacturers spec to input the bit profile, it being an R1/64 tip, R being radius, therefore 1/32 diameter=.79375mm, but I seem to remember measuring it when it first came, and thinking 'I must check which bit this is'..- I ordered a few sizes.

braidmeister. The bed is flat. I surface it using a square spiral pattern, - this takes out any z axis input. It's one long path like an LP, but square.
I hold the stuff down with spray adhesive. A light coat on the back of the acrylic cover film, a light coat on the bed. When its gone tacky, I weight the thing down and then put a screw in each corner. I know nothing moves because i have to be careful when I lift the letters, they are stuck so well. - The glue comes off the bed with the job.
Also each letter is identical in its errors, so there are no high and low spots.
The vectors are clean, I emailed them to Tony, and he says the'yre OK

I'll get the tip measured tomorrow.


Thanks a lot guys.

Jim

James E
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Post by James E »

No the bit is bob on.

James E
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Post by James E »

Here's a pic after machining some lamintate with a 30degree vbit, sharp internals selected. There isn't the over cutting of the corners,but theyrre not dead sharp either.A close look shows a tiny bite taken out of the apex of the corner. Machined down to 2.5mm....dunno what else to say.

Jim
Attachments
cnc square 003 S.jpg

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Tony Mac
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Post by Tony Mac »

Hi Jim,

I'm not 100% sure what the picture shows but guess that your have machined around
the outside of the square?

Having Sharp Internal corners selected when cutting around the outside of a rectangle
will not make any difference because all the corner are external.

Engraving around the Inside of the square with Sharp Internal corners should show
whether the tip of the cutter is being lifted precisely into the corners. Can you try
this and see what the results are?

Tony

James E
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Post by James E »

Tony

That is a 20mm square machined on the inside, with sharp corners selected. (gives me an allowance of .67mm for the cutout tool). The paths show the tip rising into the corners, the g code rises, the machine rises, but this is the result.

Jim

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Tony Mac
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Post by Tony Mac »

Hi Jim,

There's something wrong here because there doesn't appear to be any sharp
corners on the inside of the square?

You should see the radius of the cutter at the specified depth in each corner then
the tool should be lifted into each of the corners to form the sharp internal shape.

Do you see this happening?

Tony

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