# How to you guy endcaps so perfectly?

Discussion in 'Archived Threads 2001-2004' started by Andrew S, Jan 25, 2003.

1. ### Andrew S Stunt Coordinator

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I eventually want to build a shiva sonosub and I've browsed the various sonosub pages, and still can't figure out how you cut the endcaps so EXACT that it fits just inside the sonotube. Does anyone have any tricks as to how you do this?
Thanks,
Andrew

Edit: Forgive the missing "cut" in the title.

2. ### Dustin B Producer

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3. ### Patrick Sun Moderator Moderator

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Find the true circumference of the sonotube (use a string, wrap it around, measure the string for the circumference, and then determine radius of the sonotube using simple geometry:

radius = circumference/(2*pi) (use pi = 3.14159)

That gives you the outer radius of the sonotube. Measure the thickness of the sonotube, and subtract that from the radius. You might want to add just a smidge, like 1/8" to the final radius.

Once you have the radius, you'll need to use a circle jig that allows you to set the radius for the router cut to the exact length.

It's better to cut the endcap too wide, and then re-route to a slightly smaller diameter, else your endcap will be too small and fall through the hole.

If you're really unsure, first route the endcap using the original radius, and then whittle/route down by reducing the radius by just under the thickness of the sonotube material for a tight fit. Also, you may need to use a rubber mallet to get that tight fit, but don't split the sonotube material with an endcap that's simply too wide.

4. ### Jonathan_D Stunt Coordinator

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Darn, that's why I can't get my circles perfect, I don't have any patients only patience! I guess I need to go to the local doctor's office and get me some.

5. ### Frank Carter Screenwriter

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6. ### Andrew S Stunt Coordinator

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Thanks for the help. I don't even have a router or jigsaw at the moment, so I guess that'll be my next step
Andrew

7. ### Bryan Michael Supporting Actor

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i took the tube of scrap draw a ciecle and cut then take a round over bit to the edge to fot the endcap in the tube

8. ### Allen Ross Supporting Actor

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why don't you guys double up the MDF making a 1.5" piece then route the end cap, that is the same circumference as the sono tube, and then take the thickness of the sono tube off but only going 3/4 deep, so it will be like a lid that will just sit on it, and if you cut it too small, then just seal it up with a few thin layers of silcone around the rim and on the cap, for a nice fit that will sit on the tube

9. ### Patrick Sun Moderator Moderator

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I still prefer to make the inner endcap as tight fitting as possible, so I do the inner endcap and test for fit and then I laminate it to a wider endcap. I've done this with all 3 of my Sunosubs (anyone who's curious, please check my DIY projects page below in my signature).

10. ### ThomasW Cinematographer

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Sonotube tends to be less than a perfect circle before the endcaps are installed.

I use no less than 1.5" thick caps, cut with a Jasper jig. A round-over bit is used to 'ease' the inside edge of the endcap. I install the caps by 'greasing' the edge with siliconized acrylic caulk (slippery when wet, then acts as a glue when it dries).

Then insert the cap in the center of the tube, parallel to the sided walls of tube. Rotate it into position with a dead-blow hammer. Then wipe of the excess caulk.

Nice snug fit