Prism cutting problem

[steve_g]

I am hoping that some of you who cut letters all day can help! I’m experiencing a cutting imperfection when prism cutting. The first photo shows the small ridges that are left after the cut; I’m using a 2” 120° bit from Magnate. They sand out easily… but for what I’m getting for these I don’t need to be spending extra time. Is this par for the course, or do I have a something set wrong? 2nd photo shows what I’m using for the settings.

The third photo is “just for fun”… I had a small amount of Sculpt Nouveau Iron, Copper, and Brass coatings left over. I combined all three and this is the result… an interesting combination of oxides!

Steve

[Gary Campbell]

Steve...
My guess is that your bit is not exactly 120 degrees. Your results look similar to those shown on the Vectric forum. Do a search there and you will find a method to check the angle.

[steve_g]

Gary:
I suspect you’re right… Something I would never have guessed. I always thought that if I bought a 120° bit it would be 120°. I don’t know if I found the thread you were referring to but the method I found was for determining gross differences like 60° vs. 90°, my best guess is that my bit is off just a few minuets. As I see it I have 2 choices:
1.) Redefine the bit a few minuets off and see if it’s better or worse… trial and error
2.) Do a final full depth pass a few thousandths offset inward… takes more time but works with any future 120° bit.
Did I overlook other options?

I’m curious… what have others experienced with other manufactures of bits?

Steve

[Gary Campbell]

Steve...
Many of the lesser cost bits use lesser quality materials and are built using lower accuracy standards. I have a number of Magnate bits and have experienced similar results.

If you do the math and geometry, you can make a test scenario for your 120 degree bit similar to what was done for the 60 - 90 on the Vectric site. may of us have had to tune for off angle bits.