Profile Cuts

[chuckster]

When using a 1/4" shank, 5 degree tapered bit and cutting an outside profile, the completed product never ends up the same size. In other words, if I am cutting a 40x40 square, it is usually off by a little bit. Any ideas on why this happens?

[david_white]

Did you measure the bit it might not be 1/4 in reality.

Dave

[chuckster]

I thought of that, but no, did not measure the bit. Most of my 1/4" bits are under 1/4"...especially the Whiteside bits. Onsrud seems to be on the mark most of the time. If I am using a 5 degree taper, should I measure 1/4" or the tip of the bit?

[garyb]

It happens because of the taper. You don't say if the 5° is total or half if total and your cutting 3/4" material then the offset would be .0594 for 1/2" material it would be .0813.

You need to figure the offset by the amount of taper over the cut depth.

[jhicks]

I'm sure Gary is correct in his calculations but you dont say if you want the bottom of the cut to be 40x40 or the top?
It will obviously be larger on the bottom than the top surface.
If you know how much undersized it is, offset your art that dimension and redo but that's not the cleanest method.

If you can set up your bit library with the accurate V angle,length, and diameter, you should be able to cut the profile and simply select the V/tapered bit rather than a 1/4" straight bit and it should properly calculate the offset from the vector in the cut file to achieve the dimension at the top surface as it steps down and out.