Part is not to design dimensions.

[Mike Bordner]

I am trying to cut out a zero clearance throat plate for my table saw. I sketched a profile with the minor side being 3.780 inches, and the major dimension of 13.379 inches. The 2d profile path was outside right with ramps. The finished part dimensions are 3.709 x 13.281, differences of .071" & .098", the form is correct, radii are tangent to the sides. Vcarve pro 9.508. What would cause the actual part to be so far off?

[jfederer]

What would cause the actual part to be so far off?

I notice that you didn't add tabs to restrain the part. Is it possible that the part shifted during the cut? From what I can see of your settings, they look otherwise fine. I suggest trying to run it again, this time with at least 2 tabs on each long side. Make the tabs .020" or so to give stability, you will sand them off once the job is done. Ignore all that if you are using a vacuum table!

[Adrian]

Can be lots of things. The bit might not be the dimensions you think it is, the bit could be flexing, the machine could be flexing, the machine might not be calibrated correctly.

A common issue is that people select a tool with 0.25" in the title but the diameter of the tool is not actually 0.25".

If everything checks out setup wise try reversing the correct direction (conventional to climb) as that will change the forces on the cutter. If the dimensions change again then you're dealing with movement in the machine.

[GEdward]

Yes that is a lot. And as Adrian points out it could be lots of things or combination of things. There is one other common issue often overlooked and that is is the tool dialed in. Even if a .250 end mill actually measures .250 it will cut a larger swath dependent on the amount of run out it has.