Jig to perfectly split sonotube on tablesaw?

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I'm going to be working on a project where we will be splitting many sonotubes ranging in diameter from 8" to 16" and in length from 12' to 16'. We need to rip them into perfect (as much as possible) half-rounds.
I'm thinking that there must be a jig I can build for my tablesaw that will allow the tubes to be fed through the blade that will make a very straight cut. A V notch would keep the tube centered on the blade, but I can't think of a way to make sure the cut doesn't wander radially from one end to the other. The half rounds are going to be placed on walls and need to be super flat and straight.
One idea was to snap a chalk line along the length of one side of the tube. Then, on the jig, have an arm that extends over the top of the tube that has an indicator on it showing the blade position. As the tube is fed through the blade, keep the chalk line on that indicator. Then flip the tube over, tape the cut just made so the tube doesn't fall apart as the second cut is made. Run the tube through again, this time using the first cut as the guide line on the indicator.
Here's a picture of that idea:
http://www.proudviews.com/TubeRipper.jpg
Would this work or is there a better way to do this?
-- TRW _______________________________________ t i m . w i t o r t _______________________________________
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can you find a large band saw?
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charlie seemed to utter in

Not *that* large! The only band saws I know that can cut 16" material are huge industrial machines.
-- TRW _______________________________________ t i m . w i t o r t _______________________________________
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"Tim Witort" wrote:

<snip>
You don't want to go down the table saw road.
Might consider the following:
Build a dedicated jig for each tube size that will clamp the tube in position and guide a circular saw to make the first cut.
After first cut rotate 180 degrees and locate in final position with a 2nd jig to insure accurate 2nd cut.
Moving the cutting blade rather than moving the tube will make the job a whole lot easier, IMHO.
Lew
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What you want to do is build a v-shaped jig like you mentioned, and directly behind the blade you'll build in a "splitter". This is straight piece of wood the thickness of your saw blade that will serve to keep the kerf you just cut from closing up, and will also prevent the sonotube from rotating once you've started your cut. The only issue is to be careful you make the second cut 180 degrees around from the first. Good luck!
JP
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Jay Pique seemed to utter in

Yeah, I thought about having a 4' long splitter going out the back of the saw - maybe 1/8" aluminum L bar. That would alow the kerf to ride on the splitter like a fence. Thanks for the idea, Jay.
-- TRW _______________________________________ t i m . w i t o r t _______________________________________
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Lew Hodgett seemed to utter in

Thanks for the idea, I'll have to think about that one.
-- TRW _______________________________________ t i m . w i t o r t _______________________________________
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On Thu, 05 Jun 2008 16:18:45 -0500, tim snipped-for-privacy@hotmail.com (Tim Witort) wrote:

Tim:
I'd fix the tubes up onto a section of extension ladder that was resting on as many sawhorses as you would need to maintain a level line.
Then I'd cut two square pieces of ply to the dimensions of the diameter of the largest Sonotube (so that it could be recut to the smaller diameter when needed). I'd make a mark at the centerline of the top edge and use this to lay out a chalk line on the Sonotube.
Then I'd hotmelt a piece of ply to the base of your circular saw and hot melt a couple of blocks to that, so that the saw would bear on three points - the cut line and the two blocks.
Then I'd cut to within a sixteenth of the inside face of the tube, flip it over and do the same trick 180 degrees away.
I'd then cut through the remaining sixteenth with a utility knife and clean up the edge with a sander.
Just my take on it, you understand.
Then Regards,
Tom
Thos.J.Watson - Cabinetmaker tjwatson1ATcomcastDOTnet www.home.comcast.net/~tjwatson1
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The jig in your picture looks a lot like a radial arm saw except that instead of a pointer indicating the location of the blade down below, you'd have the actual blade that you could see up above. There will always be people who freak out at the thought of ripping with a RAS, but the idea is so crazy it just might work.
Lee
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To e-mail, replace "bucketofspam" with "dleegordon"

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Lee Gordon seemed to utter in

Yeah, I see the resemblance. If I had a RAS, I might consider that one. My only saw options are tablesaw, skill saw, jig saw, and recip saw. Seemed the tablesaw was my best option for getting a clean, straight cut.
-- TRW _______________________________________ t i m . w i t o r t _______________________________________
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Tim,
Build a 3-sided box that will hold the sonotube (only need 1/2 the diameter on the box top and bottom). Make the box a bit longer than the sonotube and install a stop inside on both ends. Clamp the sonotube to the box on the center of the full-length side so the clamps clear the fence .
Slide the box (full length side against the table saw fence) and cut one side at a time. This will give you a smooth edge, repeatable cuts, and a safe means to handle the sonotube.
After cutting lengthwise, remove from the box and repeat.
You will have to flip the box and tube to make the second cut, but with two people, you should not have any issues.
To allow easier tracking, you might glue a guide strip on both of the short sides that sets in the miter slot on the table saw ... thus eliminating the fence (and the potential interference with the clamps), and ensuring you always track the entire cut.
Hope this helps.
Regards,
Rick
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Rick M seemed to utter in

Good idea, Rick. I think I'm starting to get a good design in mind now...
-- TRW _______________________________________ t i m . w i t o r t _______________________________________
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<< If I had a RAS, I might consider that one. My only saw options are tablesaw, skill saw, jig saw, and recip saw. Seemed the tablesaw was my best option for getting a clean, straight cut.>>
Depending on how long the tubes are, here's one more option. Build a rectangular frame with wedges running along the bottom of the long sides, so you can clamp the fixture to the sonotube and run a router with a straight cutting bit from one end to the other. That would give you a clean cut and allow you to see what you were doing.
Lee
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use your bandsaw it will be less dangerous and give you a smo tther cut

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jim seemed to utter in

I don't have access to a bandsaw with a 16" cutting height. Heck, I don't even have access to a bandsaw with an 8" cutting height! The big commercial bandsaws can do 16", but that's not an option on this project.
-- TRW _______________________________________ t i m . w i t o r t _______________________________________
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On Jun 5, 5:18pm, tim snipped-for-privacy@hotmail.com (Tim Witort) wrote:

How many of those cuts do you have to make? I have thought of a jig, but the quantities will have make it all worth it.
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Robatoy seemed to utter in (Tim Witort) wrote:

Roughly 100 Sonotubes will need to be split for this project.
-- TRW _______________________________________ t i m . w i t o r t _______________________________________
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On Fri, 06 Jun 2008 18:31:12 -0500, tim snipped-for-privacy@hotmail.com (Tim Witort) wrote:

For 100 tubes, a jig is definitely worth it.
What about a foam insert? It could be solid or a series of disks. -- or -- A "case" that would guide a circular or jig saw along the top, or a table saw along the bottom? You could tape the first cut together to do the second.
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On Jun 6, 7:31pm, tim snipped-for-privacy@hotmail.com (Tim Witort) wrote:

I'm curious - what are you making?
JP
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Jay Pique seemed to utter in (Tim Witort) wrote:

We're doing an acoustic renovation on an auditorium. The half-tubes need to be placed on the walls at specific locations to tune the acoustics of the room.
-- TRW _______________________________________ t i m . w i t o r t _______________________________________
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