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Equipment Discussions >> ATM, Optics and DIY Forum

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Wes James
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Reged: 04/12/06

Cutting a tube
      #3683280 - 03/15/10 07:54 PM Attachment (177 downloads)

I know this sounds simplistic, but the topic arises not infrequently- what's the best way to cut a tube?
Well, there's quite a few ways- if you have access to a machine shop, no problem... if it's a metal tube- access to a tubing cutter- or a large lathe... sonotube, well, people are sometimes at a loss as to how to cut it.
If you're stuck doing it by hand, all is not lost- you can do a very good job with just a hacksaw. I've cut up to 6" aluminum tubing this way- and 10" Yazoo Paper tubing with 1/4" wall thickness. In all cases, the results were perfect. All it takes is some time- and patience.
I'm currently putting together a 100mm f/13 Carton-lensed refractor, and thought I'd grab my camera and take a few pictures as I worked. Hopefully, this will encourage someone that they can do it themselves.
You need to accurately mark the tube first- this is easily accomplished by wrapping the tube in a piece of paper- you may have to tape 2 sheets end-to-end- and matching up the edges- then taping the paper to itself so you now have a paper sleeve on the tube- and the ends are your marking guide. The paper sleeve should be snug on the tube, and you should have to really work to slide the sleeve along the tubing.
You can then take a Sharpie and run a line around the tube using the edge of the paper to guide the pen.
Then you can slowly and carefully start your cut with a standard framed hacksaw with a fresh blade. Work carefully to start the cut, then- as you get the cut started, slowly roll the tubing a little in one direction or the other- to move the cut along your line. You want to keep the blade in the groove you've started, yet move the blade along your line, extending your groove just a little at a time. In this case, I worked on a tall garbage can with a doubled over work quilt thrown over the top- and then a piece of cardboard. I just keep the saw carefully going, rocking the tube back and forth. When I have a nice groove marked and established over 20-30 degrees of the tube, I'll stop- roll the tube a little- and continue working the groove a little further and further as I rock the tube.
Finally, I've got a cut line established all the way around the tube.
Please note- the cutline is to the right of the hacksaw blade in this picture.


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Wes James
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Reged: 04/12/06

Re: Cutting a tube new [Re: Wes James]
      #3683299 - 03/15/10 08:00 PM Attachment (101 downloads)

As you continue to cut, rolling the tube after half a dozen saw strokes or so- and rolling the tube while cutting, you will find it easier to maintain the sawblade in the groove- as the groove deepens.

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GlenM
Vendor - Lyra Optic


Reged: 05/20/07

Loc: Lancashire England
Re: Cutting a tube new [Re: Wes James]
      #3683300 - 03/15/10 08:00 PM

I cut my tubes with the hacksaw and paper method. I do use an old blade though. I find it doesn't clog as much as a new blade.

I believe a CN member developed this method in the 70's.


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Wes James
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Reged: 04/12/06

Re: Cutting a tube new [Re: GlenM]
      #3683310 - 03/15/10 08:04 PM Attachment (89 downloads)

Finally, you'll find your first breakthrough... but don't keep cutting through the tube, as if you do, you'll find the blade will wander on the far side of the tube- and you will mess up the cut. Simply keep the routine you've now established- rocking the tube slowly while cutting, rolling the tube around as necessary to keep the cut as even as possible. In other words, you want to keep the saw on the top of the tube, not going down into the slot you've broken through.

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Wes James
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Reged: 04/12/06

Re: Cutting a tube new [Re: Wes James]
      #3683316 - 03/15/10 08:05 PM Attachment (85 downloads)

You'll find when you cut through the last little section, that your cut end is really very nice.

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GlenM
Vendor - Lyra Optic


Reged: 05/20/07

Loc: Lancashire England
Re: Cutting a tube new [Re: Wes James]
      #3683320 - 03/15/10 08:07 PM

Sorry for butting in Wes

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Wes James
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Reged: 04/12/06

Re: Cutting a tube new [Re: Wes James]
      #3683322 - 03/15/10 08:08 PM Attachment (85 downloads)

A cleanup with a flat file- evening/truing up the end- and you'll be able to see how true your cut ends up. This took me about 45 minutes to cut- with a few breaks, and about a half hour with a large smoothcut file to true up. As I said, I've also cut through 10" sonotube-type tubing, the same way... with the same hacksaw- working on a kitchen chair, to support the tube/brace it against the back.

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Wes James
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Reged: 04/12/06

Re: Cutting a tube new [Re: Wes James]
      #3683324 - 03/15/10 08:09 PM

It's O.K., Glen! You had no way of knowing I was trying to make a multiple post!!
Wes


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GlenM
Vendor - Lyra Optic


Reged: 05/20/07

Loc: Lancashire England
Re: Cutting a tube new [Re: Wes James]
      #3683330 - 03/15/10 08:12 PM

Thanks Wes,

All you have to do now is POLISH that tube


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Wes James
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Reged: 04/12/06

Re: Cutting a tube new [Re: GlenM]
      #3683346 - 03/15/10 08:21 PM

Quote:

All you have to do now is POLISH that tube




Naaww... powdercoating! Can you imagine how tough it'd be to keep up with the fingerprints???
Wes


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GlenM
Vendor - Lyra Optic


Reged: 05/20/07

Loc: Lancashire England
Re: Cutting a tube new [Re: Wes James]
      #3683392 - 03/15/10 08:41 PM

I cheat and use Nitrile gloves. No fingerprints,good grip on the polished tube and they keep my hands warm

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GlenM
Vendor - Lyra Optic


Reged: 05/20/07

Loc: Lancashire England
Re: Cutting a tube new [Re: GlenM]
      #3683458 - 03/15/10 09:10 PM Attachment (105 downloads)

Me and the Nitrile gloves

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Wes James
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Reged: 04/12/06

Re: Cutting a tube new [Re: GlenM]
      #3683542 - 03/15/10 09:46 PM

You were serious!!! Looks gorgeous, Glen!!! Very elegant!
Wes


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Mayk_It
member


Reged: 10/18/07

Re: Cutting a tube new [Re: Wes James]
      #3683717 - 03/15/10 11:07 PM

Nice job cutting that tube by hand!

My question is more simple...

Where do you get a tube?


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Wes James
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Reged: 04/12/06

Re: Cutting a tube new [Re: Mayk_It]
      #3684047 - 03/16/10 05:18 AM

Thanks! I got mine from Speedy Metals. I've also used Online Metals. There's another supplier on eBay, turbo metals or something like that- you can find if you search aluminum tubing on eBay.
Wes


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arpruss
Vendor: Omega Centauri Software
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Reged: 05/23/08

Loc: Waco, TX
Re: Cutting a tube new [Re: Wes James]
      #3685016 - 03/16/10 03:22 PM

Thanks for the post.

Question: What's the best blade TPI to use for sonotube and is there a way to avoid jagged edges when using this method on a sonotube? I've always been unhappy with how rough the edges are when I cut sonotube.


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GlenM
Vendor - Lyra Optic


Reged: 05/20/07

Loc: Lancashire England
Re: Cutting a tube new [Re: arpruss]
      #3685065 - 03/16/10 03:44 PM

I use a 22 TPI old blade. New blades tend to rip.

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Wes James
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Reged: 04/12/06

Re: Cutting a tube new [Re: GlenM]
      #3685086 - 03/16/10 03:50 PM

You're cutting cardboard, or something close... so you're going to get some roughness/fuzziness when cutting. I seal the raw ends with a 50-50 mix of polyurethane varnish and mineral spirits... it soaks in the endgrain- wipe a coat on with a rag, lightly sand it with something like 220 grip paper after it drys 24 hours ... soak another coat in, lightly sand it after 24 hours. About 3 coats, rubbed in with a rag will give you a nice sealing job. Again, simply work your way around the tube, deepening the cut evenly a little at a time. Don't try to cut through the tube, then move the tube and cut some more until you get through the tube wall, working your way around the tube that way. That will give you ragged results.
Wes

Edited by Wes James (03/16/10 03:53 PM)


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RossSackett
Carpal Tunnel
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Reged: 08/17/07

Loc: Memphis, TN
Re: Cutting a tube new [Re: Wes James]
      #3685147 - 03/16/10 04:12 PM

You want a 1 TPI blade: A utility knife. Use Wes' Paper method, score around lightly with a fresh blade, then deepen. When you cut all the way through, you can varnish the cut or (better) seal it with cyanoacrylate (CA) glue. This way you completely avoid the fuzzies.

Ross


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mattyfatz
Carpal Tunnel
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Reged: 12/27/06

Loc: Boise Idaho
Re: Cutting a tube new [Re: RossSackett]
      #3685250 - 03/16/10 04:54 PM

Wes,
That is a great tip. Thanks for taking the time to make this post.


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