Chatter in PVC edges

[andyb]

I need help. No matter what I do I am getting chatter on the edges of the PVC I cut. I'm using a .125 Super-O. I have tried to slowdown the feed rate. I have tried to speed it up. I have tried changing the RPM but still getting chatter. I;m getting good chip load. I wondering if it is my machine? Maybe something loose but MDF with a .25 compression endmill cuts great.

Andy B.

[myxpykalix]

are you talking about flat pvc or round pipe pvc? if pipe you will need to insert a round dowel the inside diameter to support the thin stock.:eek:

[andyb]

Jack,
I wish I was talking about pipe then I would have and indexer and be a happy man!!! ;) But I'm talking about flat sheets.

Andy B.

[myxpykalix]

well clearly im no expert but it seems to me chatter comes from the type of material and the possible hold down method (along with type of bit) so it is probably a combination of all of those things.

There are others who are more experienced with bit types/cut rates, ect

What type of holddown method are you using? Do you have a picture of what you are trying to cut?
Can you section your cutting toolpaths so that you can clamp something across your project close to the edge you are cutting?

It seems to me with a spiral bit you are either pulling up or pushing down on your material when cutting. Have you tried a straight flute bit?

That combined with a good holddown might help, but as i say its just a guess/suggestion:confused:

post a pic that might help...

[jerry_stanek]

Have you tried reversing you cut.

[andyb]

Jack,
I use a Super-O /125 but with vacuum hold-down.

Jerry,
Yes. Climb cut I get a clean edge but with chatter. Conventional I get a really bad edge.

[jerry_stanek]

When I cut I use conventional and get a better edge on sintra. I use a gerber gold P80368A bit

[ssflyer]

Have you tried a conventional cut, leaving a small skin of material, and go back over at the correct size with a climb cut?

[andyb]

Jerry,
Thanks. I'll look at the bit.

Ron,
That is what I normally do with an offset of .02 or .01 depending on the bit size. I still get a chatter. Sometimes its a lot of chatter and sometimes it just a little. The MDF I cut comes out as smooth as a babys butt.

Andy B.

[meatbal80]

I have a client that we cut up 3/16 sheet grey type 1 PVC. We cut it into large squares but i have found that the bit will cut slightly different at the start of the run then at the end. We tryed many types of bits and cutting methods and this is what i have found.

full depth with a slight ramp
worse cut quality with a "clean up pass"
1.7 IPS @ 13k RPM (PC Router) after bid has warmed up drop to 10K
Onsrud 61-082P
When i find the sweet spot the plastic cuts into small curls and i generally need to speed up if i am getting anything but.
I would try an up cut but the thickness of the plastic and my vac system dont allow

[letterman7]

Not enough information. What thickness pvc? A SuperO is fairly aggressive for pvc - typically I would use a straight single flute for plastic .25" and under and a single up spiral for anything over that, both using a climb cut. Keep your speed to the slower side of things and if it's thin stock make sure it's well secured.

[andyb]

Joel,
Thanks for the info. You gave me some things to try.

Rick,
Any thickness. I'm going to try a single upcut bit and see what I get.

Andy B.

[dengler]

Andy,
I use a Onsrud 5/32" super O down cut for most of my cutting. I can cut letters as small as .375 tall with out chatter or loosing them. 13k on the spindle and a max of 3.0 IPM.

I mainly cut my lettering for retail, so you may find a slower feed gives you the desired edge.

Also, You may have a worn z rail if you are getting chatter. I have an older machine and the new z rail solved most of the chattering issues.