cutting pvc pipe

[jim shula]

I'm making some flyrod holders for my boat. Basicly I'm cutting a 1" swath out of 2" pvc with a larger cutout for the reel seat. I'm leaving a few inches of the pvc uncut on the ends, and the total part is about 74" long.

I have a pretty good system to hold the pipe down, and if I put a screw thru the bottom of the pipe and into the table, it seems to resist the tendency for the pipe to roll as the bit passes by.

Using a 1/4 down spiral end mill, the trial piece came out pretty ragged along the cut line...a lot of chatter marks etc...that would take a while to smooth out. Is there a better bit to use when making this cut? 1/4" carbide router bit maybe?

Thanks

Jim

[knight_toolworks]

solid carbide is always best. but it sounds like vibration is more the issue. some two part clamps would work well just two 1/2 circles with lips that you can screw down to the table. also offset the toolpath bout .02 and make a cleanup pass so it is really light and not moving the material. a 1/8" bit would not move the material as much either.

[jim shula]

Thanks Steve. I hadn't thought about a second pass to slightly widen the slot.

[chiloquinruss]

Jim, how about sliding a small piece of wood dowel in the end of the pipe and fastening it down. That might elimnate the vibration and also keep the top from rolling from the pressure of the bit. Russ

[jim shula]

Russ, since the part I'm cutting is 74" long and pipe comes in 10' lengths, I have extra pipe on the table. I put a 3" screw down thru the top and bottom of the pipe just beyond the ends of the part. This stabilizes it pretty well from wanting to roll while the bit is going thru it. I also have continuous 2x4's screwed tighly along each edge, with 1x stock with a 45 degree beveled edge screwed to the top of the 2x4 extending over and holding down the pipe to the cut line.

[dlcw]

I think this I would do on my tablesaw with the blade that came with the saw. Just move the fence over a little at a time until you get the width slot you want. You could also double up a couple of blades to reduce the number of passes you have to make.

I suspect you could get it done by the time you figure out how to setup the Shopbot to do the work.

Just my opinion.....:D

[Gary Campbell]

Jim...
PVC pipe is easy to cut, hard to hold. An O flute is best, but others work well also. If you have excessive chatter, parts is not held well enough, period.

You will also have to fight the fact that the better you hold it down, the harder the pipe is squeezed together when you cut thru it. This will also add to the chatter, in fact may be the cause of it. There is also a built in tension that makes the pipe want to either spring apart or together as you cut it.

You dont say how long the slots are, but can you set it up so that the slot has solid on either end of it? I think you need a better strategy more than you may need a better bit.

[myxpykalix]

I kind of had the same issue when i was cutting hollow spirals in wood and where it was cutting thu would chatter and pull up and want to jerk it apart.

I solved my problem two ways. I used a straight flute bit because the spiral bits wanted to pull up on the thin wall.

Then i filled the hollow spiral with a tight dowel in the center to give the underside of the wood or in your case the pvc pipe support to keep it from chattering around.
Depending on where your hole is you are cutting i would think you could have a sacrificial dowel the same ID as the pvc pipe to fit in snugly and that would solve your problem.
Here are some pics that might illustrate what i mean. If you look at the sides of the spirals you'll notice they are very smooth.

[jim shula]

The slots are 1" wide by 66" long so there is uncut pipe on each end of the slot. I'm just putting the pipe in the jig wild, and cutting to final length on the chop saw after the machining is done.

The 1" slot widens out to a 1.5" slot for the last 3.5". This is where the reel sits allowing the rod to be put in horizontally while the reel sits vertical. To accomplish the scooped out area for the reel, I have to make the depth of cut 1.25". That means 2 passes at 5/8" each, and I noticed on the prototype that the second cut takes just a little more off than the first, and now I'm getting a good smooth cut.

Will post final results later.