UHMWPE Edge forming problems.

Welcome to the forum, @joe.min

As you can see from the informed responses, there are a number of reasons for the chatter.

Most obvious is, keeping pressure against the cutter as you pass through.

What size cutter are you using? Is it bearing guided or against a fence?

If you are just cutting the square end of the work piece, you would need a jig to hold it.

See attached sled from August Home Publishing as a guide.

First of all Thank you all for the welcome and the interest in my problem.
attached is my current setup and the result of the chatter that I was talking about. I don't know if you could see it with the lighting if need I can try to provide a better picture.
so steps that I have tried to eliminate the chatters were
1. run it at high speed and feed very slowly (tried to get all at one time)
2. run it at 12000rpm and feed very slowly (tried to get all at one time)
3. run it at 12000rpm and feed very slowly and divide the cut to 3 times.
4. same as above but higher speed.
5. with the results that I have from above tried to run it multiple times on a high speed and low speed.
6. the reason we went with the full bullnose was when we try half bullnose with the bearing there was less chatter but a lip that we had to either route it down or sand down.

again Thank you all in advance.