Cutting Sonotube

[Stuart Polansky]

Several projects are on the board which will require Sonotube. Trying to cut it square and neat can be a challenge. Tried building a jig for the table saw. It works pretty well, but needs to be tweaked a bit. After that, excellence is expected. Not much money for parts and just a few hours if anyone needs to build it.

Enhancements needed are:

1) Corner to corner cable bracing for the slider section to keep it square. It can easily be squared in use, but would be nice to keep it stable.

2) Replacement rollers; the PVC is too flexible. Rigid conduit will work well here, but cutting wood bushings may also be an improvement. Keep the rollers concentric. Not absolutely necessary, but nice nevertheless.

3) A better method of holding the backstop square to the rollers. When the rollers are tightened into place, the backstop bows. It's not terrible, 1/8" top to bottom using a 12" tube, but undesirable and must be allowed for when cutting the tube to length. It can also affect the first cut if the rough end is not pretty decent. The 12" tubes already cut turned out nicely however. [Looking for suggestions here. Thought about gusseted metal braces on the corners, but they will interfere with cutting 24" tubes.]

4) Support of the cutting board when the tube to be cut is long (over 36") and the cutting jig is cantilevered well off of the table saw.

Next up is cutting one more 12" tube, then a pair of 18" tubes, followed by a pair of 24" tubes. The larger tubes will need bigger backstops. One of the rollers will have to move over a couple of inches for the 24" tube to sit close enough to the blade.

Still, the concept worked very well and should result in decent finished products.

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Last edited by Stuart Polansky on February 8th, 2016, 12:13 pm, edited 1 time in total.

[Stuart Polansky]

More pics

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[tomp]

Stuart:

Great solution. I did something similar when building my mid bass arrays. Instead of amking a special fixture as you did I sort of cobbled togehter an array using the rollers off of my table sau run out supports. Yours is definitely better. In my case the problem is I needed a lot of small slices so keeping the tube stable was critical. Here are a few photos.

Tom

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13Sonotube slice.jpg (27.22 KiB) Viewed 28357 times

12Cutting sonotube.jpg (52.32 KiB) Viewed 28357 times

11Sonotube setup.jpg (51 KiB) Viewed 28357 times

[Stuart Polansky]

Love that table saw, Tom! Can you put in a word with Santa for a dedicated wood working space, big saw and vacuum system for me, please? I promise to be nicer!

Thanks for the kind words. Sharing here makes all of our projects turn out better!

Stuart

[tomp]

Stuart:

I heard a rumor from Santa that he will be bring all that stuff to you right after he brings my set

Tom

[Guy]

Stamped shelving brackets might replace gussets to square the stop, and they take less functional space. You may be able to shim the rollers or cut adjusting slots so they don't pull the jig out of square when tightened down - if fact, they could hold it square.

You can get another piece of plywood (or whatever sheet stock,) cut slots in it so it goes over the rollers, and then screw it to your existing stop to increase coverage for larger diameters of tube. You may not even have to cut slots - just screw it in place above the rollers where the tube will contact.

To square the table, you can use cable as you said or add a piece of angle on a diagonal to hold it square. Angle doesn't stretch much in this case.

To support larger tubes, could you make the bottom MDF board longer (it doesn't slide on the saw table, right?) and support the overhanging parts with legs or roller stands.

Just ideas. Maybe they will inspire you!

[Stuart Polansky]

Thanks for the ideas Guy!!!

Yes, the platform is designed to slide (not easily), for cutting length adjustment. Could make it longer, but my longest planned cut so far is about 31", so no sweat. Storing a longer one will be a challenge.

My plan was to use a sawhorse bracket and cut legs to the needed height. Deck screws through the platform into it in use.

Good idea about notching/slotting the ~ 27" x 25" square piece for cutting the 24" tube.

Stamped shelving brackets may be the key. Just plugged them into a CAD drawing and they do clear.

The 2" x 6" can probably go away for $3- or so. That will also remove a couple of # on the "droopy" end.

As to squaring the angle jig, the cable seems simple and it's on the shelf, so we'll give it a whirl. If not acceptable, then a pair of flat aluminum ~1" wide bars should do fine (in a cross pattern).

Attacking this next weekend!

Stuart

[Guy]

As to squaring the angle jig, the cable seems simple and it's on the shelf, so we'll give it a whirl.

On-The-Shelf wins it for me!

[tomp]

With the setup I had I used the rip fence to adjust the size of the slice. Nothing else needed to move. It is a little bit of a chore to set the original roller set ups and end support, but it was OK for a one time use. I haven't had a need for it since then but If it was a regular thing I would make a better jig like Stuart did. Here is two photos of how the rings were used as dams for pouring cement into the space between the dams and the frame holding the six 10" drivers and what it looked like after the pour.

Tom

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28Frame with cement.jpg (44.73 KiB) Viewed 28331 times

26Preparing to pour cement.jpg (50.99 KiB) Viewed 28331 times