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Old 08-14-2017, 02:10 PM
KevinF KevinF is offline
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Default How to achieve perfect cut on large PVC pipe

This is one that I've been tossing around a while and I'm struggling a bit.

At work I need to butt connect and seal two pieces of ribbed PVC pipe. I think the diameter is 21". So we need two very good, flat, square, cuts. Luckily a machine shop already took care of one (picture 1). I need to achieve this on the second piece of pipe which is 4m long.

I am thinking of getting a router to make the cut and using a round piece of wood as a guide inside the pipe. Another issue I see is that the base of the router will obviously be flat and might rock as I am trying to spin it around the ID of the pipe. a curved jig could be build for the bottom of the router.

We could take the piece to a machine shop but I am inclined to try this myself..
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Old 08-14-2017, 02:30 PM
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Could you make a guide to follow A rib around the outside that was attached to the router with the router bit set deep enough so the rocking effect would not matter?
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Old 08-14-2017, 06:42 PM
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When I need to cut a tube like that, I grab some of the 18 inch wide aluminum flashing material and wrap it around the tube. That gives me a perfectly round and square(to the tube) guide to cut.

I would imagine sheet metal would work fine, but I have the roll of flashing left over from working on a roofing project.

Edit, how about cutting a plywood circle to bolt(staple?) inside the tube and use it as a guide for the router.
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Old 08-14-2017, 07:02 PM
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If you try the router idea, you might put an oversized bearing on a straight bit so that it leaves a little room for error, and then cut with the router motor on the inside using the rib of the pipe as a guide. You might have to make a wooden shoe for the router that matches the inside radius of the pipe. If you got it cut within 1/16" of the rib, you could use a palm sander to dress it down smooth like the one from the machine shop.
I think it would be easier to make a convex shoe for the router to cut on the inside, than it would be to make it ride smoothly on the outside, and if you use the pipe rib as a guide you don't have any error trying to secure anything to the inside of the pipe.
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Old 08-15-2017, 08:43 AM
Barks Barks is offline
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Ask the pipe manufacturer how to achieve the cut.
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Old 08-15-2017, 09:30 AM
KevinF KevinF is offline
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Quote:
Originally Posted by Matt Shade View Post
If you try the router idea, you might put an oversized bearing on a straight bit so that it leaves a little room for error, and then cut with the router motor on the inside using the rib of the pipe as a guide. You might have to make a wooden shoe for the router that matches the inside radius of the pipe. If you got it cut within 1/16" of the rib, you could use a palm sander to dress it down smooth like the one from the machine shop.
I think it would be easier to make a convex shoe for the router to cut on the inside, than it would be to make it ride smoothly on the outside, and if you use the pipe rib as a guide you don't have any error trying to secure anything to the inside of the pipe.
Shoe! Good word to describe it. That's what I was getting at in my first post. I have the thought about the bearing riding on the rib too. Like you say it would take some hand finishing down to the max rib thickness.

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Originally Posted by Barks View Post
Ask the pipe manufacturer how to achieve the cut.
Beyond their scope, I'm sure. The pipe comes with bells and gaskets that we cut off.
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Old 08-15-2017, 11:31 AM
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Do you put any type of gasket between the two pieces? If you have a little wiggle room this way, I'd be inclined to use a circular saw and follow the rib. If you error big, you could sand down with a belt sander or buffer. Would not be as easy as taking it to a place that has a big enough band saw, but in the hands of a competent person, a circular saw should do it.


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Old 08-15-2017, 12:23 PM
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Not sure what we will use to seal it yet. Probably PVC cement. Maybe try to plastic weld the outside of the joint as well. Low pressure. Won't be any stress on the joint.
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Old 08-15-2017, 02:57 PM
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Kevin,
I would suggest indexing off the outer rib. In fact, I would cut the second half at the rib to look like the first picture and then bolt the two pieces together with a rubberized cork gasket.

As a afterthought, you work in mines there, and they should have one of those hot plate type plastic pipe welding machines you could use for that size, you could join them with it.
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Old 08-16-2017, 04:12 PM
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The do make a type of 'clam shell' connector for connecting two ends of pipe like this.

Trying to make a jig out of wood will be involved to allow a smooth cut using any type of router.

I wonder if one could have the pipe sitting on wedge rollers and turned as if it was sitting between centers on a lathe using a router with a flycutter.
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