Machined dimension different from design dimension

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Machined dimension different from design dimension

Postby ChetR » Mon Apr 16, 2018 8:59 pm

The design dimension for a sundial is 10" diameter.
However when it is machined, the diameter is 9.75"
I created the file with V Carve v9 and then output it to a NWA Shark II CNC machine.
I'd upload the crv file, but it is too large to attach....
(the file is over 3 MiB)
[Yes, I can re-design the drawing to 10.25" diameter, but I'd still like to know why there is a discrepancy....]
Thoughts?

AND when the same program is output to a Mach 3 CNC machine,
the object area is no longer centered on the work piece????
Suggestions?

Chet
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Re: Machined dimension different from design dimension

Postby adze_cnc » Mon Apr 16, 2018 9:17 pm

Different cut size versus design size is usually one of the following:

1. you think you are cutting with a certain diameter tool but the diameter specified in the database is wrong
2. you think you're cutting outside (inside) the line and you aren't
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Re: Machined dimension different from design dimension

Postby ChetR » Mon Apr 16, 2018 10:06 pm

Dear adz_cnc,
Thank you for your suggestions.
But I found the answer to the discrepancy.
When I imported the bmp and re-sized it to 10", I neglected to factor in the invisible border size that accompanied the bitmap.
It was that unseen border that was 10".
I'll have to remember to factor that in.
When the bmp file is selected it reveals a normally unseen frame slightly larger than the drawing....

Still hope to resolve the toolpath to Mach 3 issue......
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Re: Machined dimension different from design dimension

Postby martin54 » Mon Apr 16, 2018 10:08 pm

First thing to do is to check the toolpath preview, have a look to see if firstly it is machined where you expect it to be in the material block & secondly check the size to see if it is 10" or 9.75"

If it is in the right position on the material & is 10" in diameter then the problem lies else where, if it is 9.75" in diameter then check you have toolpather it correctly :lol: :lol:
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Re: Machined dimension different from design dimension

Postby martin54 » Mon Apr 16, 2018 10:13 pm

Just read your reply but had already posted lol, did you resize the BMP & then use the auto trace tool to convert to vectors ? If you did then you might want to rethink your work flow, as bitmaps increase in size they decrease in resolution which can cause you extra problems when using the trace bitmap tool. You are normally better tracing the bitmap at its imported size & then scaling the vectors to the required size :lol: :lol:
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Re: Machined dimension different from design dimension

Postby adze_cnc » Mon Apr 16, 2018 11:57 pm

Well, you didn't mention a BMP file. That explains why the file is greater than 3 megs in size.

Steven
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