some issues with dimensions

[lamesh99]

hi there. i recently managed to finish my first little hobby machine. i am using sketchup for design, meshcam for preparation and kcam for actual work. now, meshcam imports stl in all the correct dimensions and scaling. but when i cut out the model, it seems that it steals a few mm from each cut. for example, i tried cutting router mounts, 100x60x25mm with a 47mm central hole, but the model turned out 97,5x59x25, and the hole was 45,5mm. is there something i am missing here? stepover rate is 1.5mm, router bit diameter is 3mm, i set the toolpath to machine a margin of 3,3mm from the geometry of the model.
any help most appreciated

[robgrz]

If you use only parallel finishing then you can end up with dimensions that are slightly larger than expect (by up to the stepover distance). You can fix this by also using a waterline toolpath, which will accurately cut the profiles the correct size. There is a page outlining this at Using MeshCAM to Cut 2D Objects .

-Robert

[lamesh99]

i didn't try parallel finish, since my machine is only capable of 300mm/min speeds, and i think it would take forever to cut through. for these cuts, i was using only 3d roughing and waterline finish. i changed the file extension from .nc to .gc, because it seems to me the kcam works easier like that. could that have been a problem? also, when i prepare models in meshcam, i ALWAYS have two cutting passes around the entire geometry, one parallel to another, but offset a bit. i'm guessing this is because of the stepover setting, but i would like to use only one pass, because of the before mentioned speeds.
anyway, thanks for the reply!

[lamesh99]

to answer my second issue: it would be okay if i tried reading manuals sometimes obviously, i can do cut-outs, with waterline finish option, without roughing. the page mr. robert linked explains everything. THANKS!

[lamesh99]

to answer my problem way down at the bottom of the page;
i had the steps/mm setup wrong. i roughly calculated the ratio in the beggining, and left it that way. hope this helps!

[DeadTom]

I just read this thread and the first thing that popped into my mind was that your axis ratios are off. I am glad that you have found the answers you needed to succeed.
Tom

[lamesh99]

I just read this thread and the first thing that popped into my mind was that your axis ratios are off. I am glad that you have found the answers you needed to succeed.
Tom

thanks. of course, it would be silly of me to assume that software is a bit off, since there are so many users around, so this was the only logical solution. i just hope this thread helped someone else but me.