Cutting vent pipe for groundwater system.

[FLUT3Man]

Dear eng-tips community,

This will be my first post here. I've come seeking help. I recently started working for a small environmental company that installs groundwater sampling systems. A very important part of the installation process is a polyethylene pipe that is sent down the borehole and vents air so that the system is able to completely seal the hole. The trouble I am having is in cutting holes, for venting, into this pipe. My boss showed me a method that involves using a box cutter to very carefully slice a curved cut on the edge of the pipe to make small holes. He calls this scalloping. I practiced doing this on Friday and was not successful. Polyethylene is a very hard plastic. It was taking all my strength to get through it. These holes need to be precisely cut so that they make a small hole, but aren't too deep to compromise the strength of the tube. They also need to be very smooth so when the tube is pulled from the hole it does not cut anything on the way out. We also make small holes with a scratch awl, but it helps to have the bigger holes made by the knife.

I could keep practicing the boxcutter technique, but I think that there has to be a better way to do this. We tried using a drill but it makes rough edges around the holes. Our best idea is to find a better tool for cutting these holes. We came up with the idea of using something like a potato peeler that could be dragged across the edge of the pipe to make the cuts. This has the benefit of being safer, too. I don't think that tool exists and fabricating it would be a lot of work. Can anyone think of a tool that might accomplish this? or perhaps a better method for creating these holes? I can probably upload photos if that would help. I greatly appreciate your consideration and any help or thoughts. Thanks for your time.

-Flute Man

 

[Compositepro]

If you want any good suggestions provide some quantitative information (numbers). What size(s) pipe? What size(s) holes? Picture would certainly help.

 

[oldestguy]

Would slots do the same thing? If so, look at a power hack saw for steel.

 

[BridgeSmith]

Perhaps following the drill with a countersink bit or deburring tool. If that doesn't smooth it satisfactorily, I would consider grinding one with a more flared shape, maybe out of a putty knife or something similar, to give you a more rounded edge. Even a utility knife blade with a curve ground into it might work adequately well. If the holes are bigger than about a 1/4", you might find a round-over router bit that would be the right size to smooth the edges.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[chicopee]

Drill the holes with the proper drill size.

 

[GeoEnvGuy]

It's called slotted pipe from a pipe manufacturer to make a screen section in groundwater wells. The slot size is supposed to be fit for the grain size of the surrounding well pack.

 

[FLUT3Man]

Thanks for your responses.

The pipes are usually 1/2" or 3/4", and the holes we are trying to make are about an inch long. They just need to be big enough to vent air quickly but not to deep to make the pipe fragile. A lot of small holes works, but it is not as affective. I'll attach an image that has an ideal looking scallop on a 3/4" tube. Slots might accomplish the same thing, so long as they were wide enough. A power hacksaw might be a good idea to make slots, the only problem being that we often times have to make these holes in the field. Bringing such a large tool often wouldn't be practical for us. Maybe a sawzall with the right sized blade. I brought up countersink bits and deburring tools to my boss but he wasn't into the idea, I forget exactly why. I'll ask him about it and see what he thinks about the round-over router bit. Smoothing the holes is a good idea.

The problems we encountered with drills are that they can push plastic into the tube and that they tend to make ridges on the outside of the tube that could cut our system on the way up. Working our way up from smaller bits might fix this, but it might take to long and not be practical in the field.

If someone sold a slotted pipe that would work for this that would be great. I have looked a little and didn't see anything initially. This needs to be a small flexible tube that can be shipped with our systems, ideally, wrapped on a reel. We need to lower these thing down boreholes by hand to about the water table. Depending on the well, that might be about 500'. Also another important detail is that we only want these holes in about the last five feet of tube.

I appreciate your guys help. I'll try what has been mentioned and let you know how it works.

 

[BridgeSmith]

Look for a point roundover router bit. Mount it at the right depth in a trim router, and it might just do the trick.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[zelgar]

Maybe wrapping the pipe over a curved surface and using an angle grinder.

 

[LittleInch]

PE is a hard material until you warm it up a bit. You may need to get good with a flame gun or bring along a high temperature blanket.
But at about 60 to 70 C it starts to get a bit floppy. Very easy to cut at that point.

I'm a little surprised though that for the last 5ft you don't use pre slotted drain pipe like this

https://www.wavin.com/en-gb/catalog...pes-OsmaDrain/OsmaD-SPipe-BN-BS4660-110-L6-PE

or this

https://www.simona.de/en/company/news/detail/simonar-simodrainr/

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dhengr]

FLUT3Man:
Once we finally see what you are trying to do…, use a high speed steel, ground bur; maybe cylindrical, ball or oval shaped. They are rotary files (burs) used in a hand held rotary motor; a router, drill motor, etc. Google them at McMasters-Carr, or any other specialty hardware outfit. With a battery operated drill motor or router you should be set to go.

Edit: BTW, the box cutter idea sounds like a very dangerous operation. Does your boss still have all his fingers and lower arms/hands, without big scars on them, or I it just that he hasn’t been doing this operation very long, so it hasn’t happened yet? With PE pipe like that, a curved shaped wood carver’s gouge and mallet might work, if you have a means of holding the pipe (a vice or some such) with hands out of the way.

Edit2: Maybe another way would be to use a straight trim router bit about 1.5 or 2” long with a top mounted bearing. The bearing would run on a cutout in the upturned vert. leg of a stl. angle iron. The vert. leg would have a 2” +/- long elliptical shape machined down into it for the bearing to run on. The router base would slide on the vert./outer face of the vert. leg of the angle. The horiz. leg of the angle would clamp up to the underside o.d. of the pipe. You gotta lay this out to determine the exact dimensions and details of the fixture. The biggest problem might be router speed, so you cut nice and clean, without melting the PE. Clean up the edges with mill file or a small deburring tool.

 

[dauwerda]

How about a hot knife?

 

[BridgeSmith]

I like dhengr's idea with the straight trim router bit. If you run it down the side of the pipe and let it dip in slightly, that would get you the basic cutout you want. You may need a jig to control the length and depth of the notch, especially if this is something that will be repeated many times. A strip of emory cloth wrapped around the pipe and pulled back and forth a few times should smooth the edges.

Rod Smith, P.E., The artist formerly known as HotRod10