What bit?

[chunkstyle]

Hi All,

Thought I'd ask for some advice on cutting PVC again. Thought I'd place my order with Fred @ Centurian for a "O" flute cutter.
Fred mentioned to me that they have a 11 degree engraving cutter that has been giving much less fuzz on color core and should be considered.
Problem is that it will produce a slight bevel which the client will not want.
My question is: Can you get a clean acceptable edge from an O flute cutting PVC without a lot of edge clean up?

My calculations are for a .005" chip load with a single edge cutter running at 18k/ 3" sec.

Would the Centurian 1/8" O flute bit with .75" cut length be a good candidate for cutting .5" PVC?

[andyb]

Tim,
As I'm typing this, I'm cut 3mm Sintra using a Centurian 3/16" Up-spiral Super-O. I normally use their 1/8" straight cut bit but bought the 3/16" up-spiral to try out. I'm cutting 16000 rpm @ 2 ips cutting out in one pass. I noticed the faster I go the edge is not as good (that is in my case.) I use the same scenerio for 6mm. For 1/2" using the 1/8" Super-O, I use David Buchsbaum's method of cutting (your can read about his method in his Shopbot article) the first path using a .02 offset and cutting to a depth of .46 then the finish pass using no offset and cutting all the way through. I get a good clean edge using this method. I use this method for cutting MDF too.

Andy B.

[Brady Watson]

A single spiral-O flute is only good to about 1.5 inches per second or so, before your chipload starts to get too big to get a decent edge. Use either a 2 or 3-flute spiral-O from Onsrud. I believe the 3-flute in 1/4" is a 52-624. Edge quality shows a marked improvement with multi-flute O tools in PVC and Gator.

Plus...more flutes = greater resistance to deflection...and who wouldn't want that? :D

-B

[joe]

Once I discovered the German bit manufacturer "Belin" I left Onsrud. http://www.midwestsign.com/pdf/lit/belinlit.pdf
Give Belin a try. These bits look like a piece of jewelry and are much sharper and last longer.

Onsrud's 52-624 is a double flute not a three flute. I haven't seen any three or four "O" flutes in their catalogue. Perhaps they don't show them online.

Joe

[Brady Watson]

Belin makes excellent tools, but unfortunately, they do not offer multi-fluted O bits that I am aware of. Maybe in metric?

The 52-241 is indeed a 2 flute spiral-O. The 60-200 series is 3-flute and works excellent on plastics, such as expanded PVC. Once you cut with a multi-flute spiral-O, you'll be hesitant to reach for a single flute tool for certain materials.

-B

[dana_swift]

Joe- good to see your post. Last I heard you were retiring.

Dana

[chunkstyle]

Thanks all,

Brady, Thanks for the heads up on the 3-flute. I need it in 1/8" but good to know about the series.
Joe, I found a sighn supplier that is supposed to carry the Belin bits. I'll call em in the morning and see if they have any of these O's in the diameter I need. Turns out I'll be passing by their front door on the way to the plastics house tomorrow.
Andy, thanks for the heads up on David's article. I will be heading there next. Hopefully it will give me a road map to a good cutting result. Gotta get this logotype up on the wall early next week.
Thanks for the advice. It's a big help,
Tim

[joe]

Dana,

I've reduce my regular workload by 70%. I sold off my building and most of the equipment but kept the CNC. At some point everyone reached a point where they need to slow down. That's where I am at this point.

All that said, I'm still working way too much. I'm planning on posting some of the latest work.

Joe

[hh_woodworking]

1/8 3 flute bit here :http://www.precisebits.com/products/carbidebits/ultrabit-soft.asp

[joe]

Good point Edward,

I also use their CM404-100B-SET Carving Bit Set

Joe

[chunkstyle]

Had a little difficulty cutting the 1/2" Sintra today.

I went with a single "O" flute cutter .125 diameter, 5/8 long, 2"/sec. at 15k rpm.
Depth of cut was .18" per pass in .47" material thickness. Three passes total.

From the start the the chips were getting stuck in the kerf. I tried raising the RPM on the fly at the VFD in hopes that the higher RPM's would result in smaller chip load that might help them be evacuated. The end VFD stopped responding at 18k and got stuck at that speed. I made the decision to let it run at the stuck speed as opposed to stopping the file mid stream. The chips weren't re-welding but were just tightly packed in the kerf. The result was the parts having very bad chatter marks.

My guess would be that the bit geometry was insufficient for chip removal. Perhaps the depth of cut needs to be less, as well, for chip removal?
I assume the chatter marks were worsened by the small diameter bit running thru a packed kerf causing it to deflect erratically?

How smooth can the edge cut of pvc be assuming your machine is 'tight' at the start? Am I expecting to much from this small diameter, single "O" flute cutter?

I'll do some more pratice cuts in the scrap tomorrow and see if the shallower depths of cut make an improvement. I'll still aim for a .006 chip load unless someone tells me different. Thought I'd ask here first to help me get up to speed with this plastic stuff.

Yikes, that dust is awful to get rid of!

Thanks for any advice,
Tim

[joe]

Tim,

You are using an Up Spiral, right. Sounds like a down spiral which would give lots of trouble.

This material is so easy to cut I some times use a double fluted strait, on 1/2" stock, making a single pass. This leaves all the filings behind holding the letters tight.

[chunkstyle]

Hi Joe,

I believe the bit was a straight single flute here: http://www.centuriontools.com/router_bits_toolcase/centurion_tools_showcase.html?page=full&cart=1300161841813548&__max=6&--eqskudatarq=18SFO1.752.5RES14&id1=374&id2=714
It appears to be a straight flute.

I went with this particular cutter because it could go past 1/2" depth. I have another "O" flute cutter on it's way from Vortex. Supposed to arrive tomorrow. Maybe it will give me a better cut.

The edge cut chatter was really bad on this run.