I need some help...

[Curtis O. Seebeck]

Hey guys, I need some help!

As some may recall, I am new to CNC and I have a CRP 4848 CNC router with a Hitachi M12v and Super PID. I have a Kent's dust shoe hooked up to a Harbor Freight dust collector blower. It goes out the wall of my building so there are no bags and about as efficient as possible with the shortest hose possible transitioning to rigid pipe. I am very familiar with how to properly set up a DC system since I have a complete system with a ClearVue for the rest of my shop.

Currently, I am cutting mostly 3/4" and 1/2" grey PVC (type 1, the hard stuff). I am using a 1/4" 2 flute upcut Vortex spiral bit. I have been cutting at 10,000 RPM and 200 ipm with a depth of cut per pass of .20" or so. Basically, I cut 6 roughly 9x9" squares out of a 20x30" piece using vacuum hold down. I cut down to within .02" to leave a skin for the vacuum.

The problem I am having is that after the first pass, on subsequent passes, the chips are not being extracted from the cut. They are NOT welding back but they pack in and the vacuum can not get them out. Then, on the next pass, I am cutting through them in addition to the new depth of cut. Maybe this is normal but it seems to be to be affecting the cut quality. On the outer edge cuts where it is open and there is no kerf packing, I am getting a reasonably nice cut quality. What can I do differently? Do you have any suggestions?

[John McClanahan]

Have you tried raising your dust shoe slightly to increase the draft?

John

[Richard Coers]

Is that vortex bit made for plastics? Most plastic cutting bits are not spiral and they have a lot less cutter angle. Switch to an Onsrud single O flute (ground for cutting plastic), and/or add a compressed air line right near the cutter. Won't take a lot of psi to remove the chips. Since you are leaving an onion skin to hold the parts, you could be a little more agressive with the cutting and leave it a few thousandths oversize, then a full depth finish pass for cleanup. That final cut will have smaller chips and no packing in the kerf. Are you doing a lead in and lead out for the cuts? Also makes a better finish when you do that. And yes, I am that Richard Coers that organized the Midwest Penturners Gathering.

[Tony Joyce]

add a compressed air line right near the cutter. Won't take a lot of psi to remove the chips. Since you are leaving an onion skin to hold the parts, you could be a little more agressive with the cutting and leave it a few thousandths oversize, then a full depth finish pass for cleanup. That final cut will have smaller chips and no packing in the kerf. Are you doing a lead in and lead out for the cuts? Also makes a better finish when you do that.

What he said works for me also.

Tony Joyce

[Curtis O. Seebeck]

Hey Rich,

I figured you were the same guy!

I took a closer look at the Vortex bit I have been using and it is a model 4233 two flute low helix upcut finisher. From Vortex webste regarding this bit: "Our double edge low helix spiral bits are recommended for cutting hard plastics, such as acrylic and phenolics." That said, I have already ordered a couple of Onsrud 56-082 v flute straight cutters. These are the ones listed as best for hard plastics on Onsrud's website. Just waiting for them to get here. I have thought about doing a clean up pass but wanted to try to avoid it since my parts are nested quite tight for material usage. Even with a clean up pass, I would still have the same problem since the kerf would be packed from the previous cut unless I cleaned it out or used the air line. I am not doing a lead in and lead out but am ramping in. I don't have the room for a lead in and lead out. With 3/4" PVC costing $.07 per square inch, I am trying to conserve all I can! I had to raise my prices with the change to PVC lids but I have a backlog that I have to fill at the old price that are getting the new lids! I will try some air and see what happens.

Thanks for your help and suggestions!

Is that vortex bit made for plastics? Most plastic cutting bits are not spiral and they have a lot less cutter angle. Switch to an Onsrud single O flute (ground for cutting plastic), and/or add a compressed air line right near the cutter. Won't take a lot of psi to remove the chips. Since you are leaving an onion skin to hold the parts, you could be a little more agressive with the cutting and leave it a few thousandths oversize, then a full depth finish pass for cleanup. That final cut will have smaller chips and no packing in the kerf. Are you doing a lead in and lead out for the cuts? Also makes a better finish when you do that. And yes, I am that Richard Coers that organized the Midwest Penturners Gathering.

[Curtis O. Seebeck]

John,

Thanks for that suggestion! Such an obvious thing that I did not think of! My dust shoe is currently quite low to the pint the the brush is compressing and coming in contact with the bit. Never even thought to raise it! So many things to think of with CNC!

[james mcgrew]

there is still enough heat to cause it not to want to let go,, test lowering rpms and/or increasing fpm until the material is removing chips !!

[Jerome Stanek]

I get this also when I cut 25 mm Sintra running at 10,000 and 300 ipm. I just cut 3 sheets of 25mm sintra today .25 0 flute

[Curtis O. Seebeck]

there is still enough heat to cause it not to want to let go,, test lowering rpms and/or increasing fpm until the material is removing chips !!

I will give this a try. I have done the bit touch test immediately after cutting and it is cool to the touch so I figured I was close to the correct settings. Also, it seems when I try to slow down the RPM's I get a poorer quality cut and am afraid to cut faster! Maybe it is just my imagination! After all, I am very new to this!

[Mike Heidrick]

Is PVC considered a hard plastic?

Try cutting .125 passes, half the width of the bit.

Get the single O flute bit.

[Richard Coers]

Thanks for the backup on my recommendation Mike. They work for me.