After measuring the pipe length to give the range of adjustment you want with the aluminum insert installed (it has a lip that adds fractionally to the over all length) pull the insert out, wrap the pipe in tape where you are going to cut it from the side you are going to keep.(helps minimize any potential fraying and much easier to see than pencil) Use the edge of the tape as your cutting line and use a fibre cut off wheel on your dremel tool to do the cutting. At least thats what I do.

I would try to avoid any kind of clamping/crushing action of a hand saw even though the pipe seems substanial and solid. Pull the dremel against it's rotation when cutting so it doesn't want to travel around the tube. Hold firmly, no limp wrists here. I usually set the pipe down on my benchtop and hold down with my left hand, and hold the dremel in my right, parallel on the bechtop and align the area to cut. I kinda roll the pipe a 1/4  turrn at a time as I cut. I find this more managable than doing it "in the air". All mine are done this way. Clean up the edges with sandpaper (220 should do). Slip in your insert and your good to go.

Randy may have another method, but I thought I'd share what I do. Actually, I think it was probably Randy that told me to use the Dremel in the first place.

EricV

I would try to avoid any kind of clamping/crushing action of a hand saw even though the pipe seems substanial and solid.

Another good way to support the pipe while cutting is to slip it over a wood dowel.  Use the largest size dowel that will just fit inside of pipe.  If necessary get the next size larger and sand it down till it just slips inside pipe.  Clamp the dowel in vise, put pipe over the dowel and cut thru pipe and dowel together.  Cutting thru the dowel helps control the cut.  I use a 32 tooth hacksaw blade, which I think is the finest tooth available.

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after you have cut it have you ever had the wood dowel drop inside the pipe?then what,lol.


Never had that happen, but I've only cut 3 pipes.   
To prevent that from happening cut only half way, take pipe off and finish the cut on the dowel only.  Then slip pipe back on to cut other half of pipe.   Or you could make half cut, slide pipe over about 1/4" and rotate pipe 180° to cut the other half of pipe.  Either way you never cut all the way thru the dowel while its inside the pipe.

Thank you Allen