Beveled edge

[jbworden]

I've tried a couple of times to create a chamfered edge with my Shopbot. Both times I end up with it not quite right.

I start out by using a V-bit, once with a 60 and another time with a 90 degree bit. I machine a profile ON the vector using the V-bit to about half my final depth. I then switch to an end mill and machine to the final depth outside the vector. This leaves a lip on the bevel of about 1/32" instead of a smooth transition between the bevel and the straight side. It acts like I'm actually milling the bevel slightly inside the vector.

What am I missing?

[mzettl]

Jim, I've been through all this, and there are several possible causes. First, check the actual diameter of your end mill with a micrometer or dial caliper. It is almost certainly not what you think it is. If it's supposed to be .25, it may actually be .245. This will have the effect of making the cut outside the vector, and the bevel cut appearing to be inside the vector.

Secondly, consider the nature of the material you're cutting, the depth of cut, feed rate, etc. If you're cutting hardwood, like I often do, and try to cut 3/4 inch in a single pass at higher feed rates, you may be getting bit deflection. This will also create a final cut that is not where you expect it to be. In these types of materials, I generally will do a "roughing" pass with an offset of .03 or so, then a finish pass at full depth with zero offset and a lower feed rate. I have found that this technique results in the most accurate result in hardwoods.

Finally, when I'm doing a bevel, I will generally offset the V bit by .03 - .05. If the depth of the bevel is critical, then you can compensate for the offset by increasing the depth of cut by the same amount as the offset in the case of a 45 V. This will compensate for inaccuracies in the cut edge created by the end mill.

I hope this helps.

-Matt

[Gary Campbell]

Jim..
Most V bits dont actually have a "zero" width at the point. Experiment with a toolpath offset to the outside a few thousandths at a time until you get the results you are looking for. Or... find the magic v-bit. (and let me know where)
Gary

[myxpykalix]

Based on the way these guys make their bits and the precision i've watched them cut them with I suggest you contact fred at www.centuriontools.com (http://www.centuriontools.com) I'm not sure you can get much more precise than this.

7869

[zeykr]

I usally use a 90 deg so that I know if I want a 1/4" wide bevel I should cut 1/4" deep and I offset outwards about 1/32" as gary suggests.