.75" pvc letters

[shimpj@bellsouth.net]

pvc letters are being cut from 3/4" sheet.
The letters are face down, so i can do a drill
hole run for studs that are to hold the letters to a wall.
The problem is that on the all upper case letters the A's P's and letters with "insides corners" (using a 1/4" down sprial bit for pcv and hard plastics) have a pvc welded clump on the face side corner where the bit went in. I can see that heat my be an issue. I just don't know to run more or less than the 14K rpm? Is the bit creating excessive heat going down in that inside corner as opposed to the inside not in the corner?? Should i use a lead-in option??
thanks - Roy Shimp

[rgbrown@itexas.net]

Roy,

Your problem may be couple of things. By using the spiral down bit, the plastic is fed toward the bottom and, guess what, it has no place to go. The second thing will be bit heat - there is no air to cool the bit in the hole. NO, the PVC doesn't help cool the bit.

I think there may be several parts to a solution. Your lead-in might be one. Bit cooling almost always helps on cutting plastic. An up-spiral bit will pull the material out of the hole. Two passes with the second pass as a 'clean-up' would give the material a place to go.

Also, the "Stud holes" could be drilled, the parts rough cut, I would recommend an up-spiral bit for these two operations, the parts would be flipped and bolted down to the table with the stud holes and the parts finished. This method would be more work.

I have used a "Kool-Mist" (I think) brand device that uses air and mists coolant (water) on plastics. It helped a lot.


Ron Brown rgbrown@itexas.net (mailto:rgbrown@itexas.net)

[joecrumley]

Roy,

The information from Ron is correct about the problem with the down sprial bit.

I finished up a job two days ago cut fron 1/2" PVC. The letters we 20" in height. After several tests, with a 1/4" bit, I optioned for a 1/2" bit with a single pass. The cutting speed was .65 I or .75 as I remember. The bit was a strait bit with carbide cutters.

The cut out shavings stay in the well of the cut even though we had a big vacuum on. Pretty smooth cut.

Joe

[joecrumley]

Roy,

I forgot to mention the cooling solutions.

You may wont to look at the www.arizonavortes.com/as an alternative to a mister.

A Vortex Tube is small cooling tube that attaches by a magnet to the Z axis. Plug it in to your air supply and direct the nozel to the bit. The temp out put is down to freezing and you get away from the mister problems. No moving parts, no electricity, just cold air.

Cost is about $250.

I don't think you need a cooling device or mister on PVC. This material chips very nicely. To prove this, take a piece of plex and a piece of PVC and use a propane tourch to heat both.

Joe

[garyb]

Roy,
Although I don't cut PVC I have experienced similiar circumstance of burning to an inside corner on one side only.
Result was from the "Z" axis slightly out of square to the "X,Y" and my "Move Z" setting was too slow.
Burning usually is caused by dull cutters and or the cutter moving too slow, hence the build up of heat.
You will also probably find that spriral up bits will work alot better for you

[Roy Shimp]

Ron-Joe-Gary
thanks a million
Roy Shimp