What is the best way to cut 6" sprial pipe

[Ed Nyegaard]

I am getting ready to redo my dust collection system and have purchase 30' of 24 gage 6" spiral pipe and a bunch of metal fittings from Penn State. What method works the best for cutting the pipe to the correct length? I have tried using a dremel with a cut off blade but it is very slow. Next I attempted the cut using a jig saw with a metal blade. This worked better than the dremel but I am thinking there has to be a better way. Any suggestions?

[Matt Meiser]

Angle grinder with a cutoff disc. It doesn't have to be an expensive one, I have a couple Harbor Freight ones that are good for light work. I'd get better discs though.

[Fred Belknap]

I'm thinking I would use tin snips, it's what I have used on thinner wall stove pipe and it worked pretty good. I really don't know anything about spiral pipe.

[mickey cassiba]

We used a lot of it at the moulding plant...I used a sawzall with an abrasive blade. Made a jig to hold it snugly and the bade just floated through it.

[Jim Finn]

I am a retired sheet metal worker and have installed miles of spiral pipe over the years. It can be cut with just tin snips by an experianced sheet metal worker but I suggest cutting it with a jig saw or sawsall. After cutting with one of these saws you will have a very rough edge that can be trimmed with tin snips easily to give you an acceptable edge to fit into or over a coupling or fitting (ell).

[David Kumm]

I use my sliding miter saw with a metal blade. Cut through the top and rotate the pipe, cut some more, do it again. Dave

[mreza Salav]

finished re-doing my duct work recently and went through this question again; tried dremel (too slow), cut most of it with hack saw (lots of sweating), then tried tin snipes. It works but getting
over those joints (spiral joints I mean) wasn't something I could do, so had to use hack saw again.

[Ole Anderson]

I used an angle grinder with a thin cut off blade to make a starting cut, then a jig saw with a very fine metal cutting blade to finish it off. I had too much trouble keeping a straight line all the way around with the angle grinder. But I was cutting 26 ga snap lock.

[ian maybury]

Another jigsaw fan here, but the choice of blade is quite important in that too coarse a tooth will snag. Bosch do a fine toothed high speed steel (HSS) blade labelled for use on metal around 1mm thick (can't remember the thickness exactly) that's spot on when used with zero wobble (?). It's also very well worth making the equivalent of a saw horse to hold the ducting while you cut - 3 pieces of ply each with a U cutout to fit the duct, and a foot you can fix on the top of a bench or on a heavy plank with a F clamp - it's useful to be able to adjust the spacing depending on the lengths to be cut.

Wrap a length of card around the duct as a guide and use a felt pen to mark the cut line. Use a hacksaw with a good coarse (wide enough) blade to make a slot to get the jigsaw started, then hold the saw on the duct and rotate the duct in the rest into the blade.

It leaves only a very fine burr at the cut edge which a quick wipe of a file knocks off (important so it doesn't cut the foil sealing tape) Watch out for the point that can result when you cut through the seam on spiral ducting - it springs up on one side of the cut and sits ready to spike you. It's best to cut these off with a hacksaw.

The de luxe tool is probably a powered nibbler used in a similar manner, it probably has the advantage of not producing the fine metal sawdust that comes off the jigsaw, and forms the burr on the inside where it's no harm. There's fancy units used by the trade which integrate the saw horse and the cutter.

Beware of the fact that the fit between the ducting and the fittings may be quite sloppy, and so don't necessarily line up perfectly without a bit of help. I built my assemblies on the floor using a ladder as a straight edge to get the sections lined up straight against before riveting. Foil tape with a mastic adhesive is needed or leakage rates may be very high....

ian

[Ed Nyegaard]

Thank you all for all the great suggestions. They just opened a Harbor Freight about 5 miles from the house so it was a good excuse to go and check it out. I ended up buying a very inexpensive 4 1/2" angle grinder and a small reciprocating saw. So in the end I tried many of the solutions that was provided. Here are my experiences with each:

4 1/2" angle grinder - a little scary but gets the job done. Difficult to stay on the line.
Tin Snips - I guess I need some practice with these. Found it hard to cut the 24 gauge
Hack Saw - gets the job done but take a lot of effort.
Reciprocating Saw - made easy work of cutting the pipe but leaves a rough edge. 20 seconds with a file finishes the job. (Metal cutting blade)
Jig Saw - Changed out the bi-metal blade for a fine metal cutting blade and no more wobble. Smoother cut than the reciprocating saw but still needs to be filed.

The process I think I am going to use is to start the cut with angle grinder and finish it up with either the jig saw or the reciprocating saw.

Thanks again for the GREAT suggestions.

[ray hampton]

If you need to cut duct work by hand ,a bolt cutter for the steel wire or vise grips with a wire cutter for the extreme cases, I hope that you can use a grinder, which is the easy method

[Jim Andrew]

I use a hack saw to start the cut, then a metal cutting jigsaw blade. Put the pipe in my vise on the workbench, then rotate it to hold the pipe steady. File cleans up the rough end. The first time I installed the pipe, used caulk, now find the caulk holds the pipe together too well, and just tape it. Used a few hex head screws on top of pipe, and where vertical sections are hanging, otherwise just some good duct tape. I save my short pieces of leftover pipe, as sometimes they come in handy when you get a new machine, and you have to remodel your system.

[james glenn]

I use an old mitre saw with a cut-off wheel for metal on it. I set up damp hanging blankets to form a cover and can then cut inside if I have to. But obviously prefer to do this outside. I do have to roll the pipe to get all the way thru, but it works like a charm and only takes seconds. HF also sells an actual cut-off say for this, and it works ok.

I do use this a few times a month for cutting metal, so having it is beneficial to me. After trying snips, sawzall, and jigsaw with slow results, it then occured to me to use the mitre saw since it was just collecting dust.

[Sean Nagle]

I use my sliding miter saw with a metal blade. Cut through the top and rotate the pipe, cut some more, do it again. Dave

I did the same. Setup the saw out of doors... lots of sparks fly. Cut quickly, the edges can burn. The cut edge only needs a bit of filing to clean up the burrs.