Acrylic Edge Quality

[toe_jam]

Okay I'm running into a problem with acrylic edge's. It's okay with other plastics but really sucking with acrylic...I Think. Is this as good as it gets with edges on Acrylic. I have a acrylic Belin Tools bit, 3 actually and tried all 2 of the 3 in case it was the bit. I'm doing this at 15k RPM's at 2.5 inch/sec as they specified. I was exporting dxf files from flexi, but now just did these in part Wizard incase exporting and importing was adding more points. This looks like a sproket to me, I would really have to sand the #%$ out of this to flame polish. All the rollers and bearings seem to be seating right. I have even updated the control software to the latest December update. Any Ideas?

http://www.thesignindustry.com/miscs...etteredge1.JPG

http://www.thesignindustry.com/miscs...etteredge2.JPG

http://www.thesignindustry.com/miscs...etteredge3.JPG

http://www.thesignindustry.com/miscs...etteredge4.JPG

Oh and I am using Cast Acyrlic

[paco]

http://www.thesignindustry.com/viewtopic.php?p=171#171

[Brady Watson]

Erik,
You will notice an immediate increase in edge quality if you use a 1/2" bit instead of a 1/4". The 1/2" is more rigid...you also might try using a 3/8" so that you don't eat up as much material.

While this would reduce the # of 'gear' marks on the outer edge, you still will show signs of bit stepdown as seen in your pics. I would recommend offseting (using Allowance) the toolpath so that you leave maybe .02 on the piece. Stepdown and leave a .03 skin on the bottom. Then run a single profile pass to the desired size at full depth to give a nice clean edge.

-Brady

[ron brown]

I'll agree with Brady on a finish pass of .020-.030 high speed on the feed and more rigid bit. Be sure and look at your "waste". If it has a better finish, you are cutting the wrong direction.

Ron

[elcruisr]

Erik,
like the other guys said, bigger is better. I try never to cut acrylic with anything smaller than 3/8" . I've had my best success with climb cutting and onion skin/finish pass tactics described by Brady. The new Onsrud "superflute" plastics tools seem to be giving me the best edge quality so far.

YMMV
Eric

[paco]

Do you think that Erik could have done better than what he got guys (take a look at his pics)? I believe he has got a quite good cut on thoses letters.

[Brady Watson]

Paco,
Yes. For one, he could eliminate the water line marks by doing a finshing pass as directed...and the higher rigidity of a larger bit would reduce flex and give a less jagged edge.

What might be a great cut to some is a horrible cut to others ~ meaning that if you were going to flame polish or buff the edge, the number of grit steps or time post finishing can be dramatically reduced by doing a finishing pass with a larger bit. Again, it depends on the application and customer's needs.

-Brady

[paco]

I agree with all that Brady. I'm somewhat suprised that you believe that the cut could be better... though I'm open to the best! I tend to use small bit (1/8-1/4" and even 1/16") since I often have to deal with details which you "loose" with bigger tool; let say a 4" "W", cut with a 3/8" CED tool bit it would look quite "undetailed"... unless it match the font... But I was to cut circles or squares, I would look for a bigger tool for sure.

[simon]

Erik
It might just be the material that is flexing, and not the machinery. This will be generally worse as the cut gets further away from the clamps.

[paco]

Good point Simon!
Hold down is important on plastic; especialy on thin stock...