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Parabola Routing Jig?

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Forum topic by totalrewind posted 03-31-2020 06:38 PM 503 views 1 time favorited 19 replies Add to Favorites Watch
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totalrewind

61 posts in 3003 days


03-31-2020 06:38 PM

Topic tags/keywords: jig question

What I want to do is to be able to make a large wooden parabola for focusing sound.

I picture starting with a glue-up of rings with a router that cuts a path through them to refine the shape.

If you can read my MS Paint scribbling, something like this (cutaway side view):

Now, if I wanted a circle, that would be relatively simple. All I’d need is a central pivot. But my question is, can anybody suggest a mechanism to do a parabolic curve instead? (My gut tells me there ought to be some kind of linkage that could do this)

-- For more projects (not just woodworking) check out my project blog at http://theheadlesssourceman.wordpress.com


19 replies so far

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Walker

344 posts in 1203 days


#1 posted 03-31-2020 06:42 PM

Do you mean a parabola in one plane…or in all dimensions, like a satellite dish? You could do it with an adze and some patience.

-- ~Walker

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totalrewind

61 posts in 3003 days


#2 posted 03-31-2020 06:46 PM



Do you mean a parabola in one plane…or in all dimensions, like a satellite dish? You could do it with an adze and some patience.

- Walker

Like a dish. (Although even if I could figure it out in 2d, I could just put the thing on a lazy suzan and cut&turn, cut&turn, etc.)

-- For more projects (not just woodworking) check out my project blog at http://theheadlesssourceman.wordpress.com

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DaveMills

16 posts in 130 days


#3 posted 03-31-2020 07:00 PM

Here’s a start… https://www.youtube.com/watch?v=lVbfLlSLrZA

Getting to 3D will be interesting :)

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tvrgeek

941 posts in 2380 days


#4 posted 03-31-2020 07:55 PM

Just get a Miro Snow Sled. As we learned in the early Microwave era, they were a really good parabola!

No help on industrustables either I see. Bust I can suggest is making a 2D template and sand to fit.

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Dark_Lightning

4044 posts in 3840 days


#5 posted 03-31-2020 10:07 PM

When I taught physics I made two 8 foot diameter parabolas for one demonstration. The structure was 1/2” plywood cut in the parabolic shape, and then had paper glued to them. That means that the sections of paper between the ribs were flat, not following a circular path. Still had plenty of gain for the purpose of the demonstration. How big do you want to make the reflector? I watched the video, but it was simple enough to lay out points and connect them with a pencil line and cut the ribs out. They were rectangular with 1/2 the parabola cut in each of them.

-- Steven.......Random Orbital Nailer

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Kazooman

1464 posts in 2683 days


#6 posted 03-31-2020 10:41 PM

Gonna make one of those microphones that can hear what the neighbors are saying? Or the opposite focussing a beam of high intensity sound to pulverize anything in its path? Either way I love the concept. I just have no clue how you would do this with a router sled as you suggested. Any router would have a good sized base to its frame. The bit would have to extend a huge distance to do the cutting while keeping the base from rubbing on the surface. Some sort of industrial overhead CNC machine with no need for a support base night work, but probably not a standard router.

I think the “many parabolic ribs with something in-between” like Steven suggested might be an easier approach. Figure out how to do the layout and cut them on the bandsaw.

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Walker

344 posts in 1203 days


#7 posted 03-31-2020 11:09 PM

how large is large? Too big for a lathe?

-- ~Walker

View waho6o9's profile

waho6o9

8879 posts in 3308 days


#8 posted 03-31-2020 11:37 PM

Look Around 7:34

https://www.youtube.com/watch?v=uvUQyAJ0r14

Best of luck

View JackDuren's profile

JackDuren

1133 posts in 1690 days


#9 posted 03-31-2020 11:48 PM

This jig I found on Woodnet many years ago. You move the jig and not the wood. Change the radius you dont change the jig. I believe you can make this to a 12”- 24” radius….

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totalrewind

61 posts in 3003 days


#10 posted 04-01-2020 03:19 AM


Or the opposite focussing a beam of high intensity sound to pulverize anything in its path?

Close, though hopefully not pulverizing anything. :) I was just thinking about doing one of those narrow-beam speakers like they sometimes have in museums, only for a lobby information desk. That way people standing in front of a “welcome” video would be able to hear it, and nothing else… meanwhile everybody else, vice-versa.

After looking into this a little more, now I’m thinking I may be making this too difficult. Why not do the same kind of router jig that people use to hollow out chair seats, only with a (yet-to-be-determined) parabola profile? Do you guys think that might work??

-- For more projects (not just woodworking) check out my project blog at http://theheadlesssourceman.wordpress.com

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therealSteveN

5545 posts in 1305 days


#11 posted 04-01-2020 04:45 AM


Look Around 7:34

https://www.youtube.com/watch?v=uvUQyAJ0r14

Best of luck

- waho6o9

I’m not sure which came first, looks like the same principal.

Seems if you based it on a Lazy Susan, you could swing 360 to make a dish. Arm stays still, and part rotates maybe? I also saw one years ago, where the swing went side to side from a pair of arms. Doing that you could drop the Lazy Susan.

https://www.woodomain.com/online-store/The-JKB-Universal-Routing-table-Ebook-p158404091

-- Think safe, be safe

View Walker's profile

Walker

344 posts in 1203 days


#12 posted 04-01-2020 05:37 AM

I googled parabolic speakers and got some very expensive results, a few cheap “cell phone” amplifying devices that looked like little more then bowls. And a few DIY tutorials on how to make your own, using a bowl. You could try to find a wooden bowl that is more parabolic then spherical. Or make one on a lathe.

Honestly I think 3D printing is better suited for this. I have no idea what the cost is, but there are websites you can send a file and they will 3d print for you.

Of course being woodworkers, we understand the fun and challenge of making it yourself. Even if the cost ends up being higher. I still say a solid piece of hardwood, an adze, and some time is all you need. Not that I’ve ever used an adze myself, but that Woodwright fellow makes it look easy!

-- ~Walker

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Tony1212

428 posts in 2466 days


#13 posted 04-01-2020 01:21 PM

Do you have a lathe and any experience turning bowls? This seems right up a turner’s alley.

If not, I would go with the chair seat jig with parabolic rails.

-- Tony, SW Chicago Suburbs

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Sylvain

1027 posts in 3230 days


#14 posted 04-01-2020 05:44 PM

Maybe doing it in more phases:
1. doing a convex parabola (no need for a long bit)
2. making it abrasive (paint + sand?);
3. make a concave form approximately parabolic;
4. using the convex abrasive parabola to refine the convex one.

Now,
- wood might not be the best sound reflector;
- it doesn’t need to be perfect for this application (it is not an optical telescope) so an approximation with straight (conical in fact) segments is probably good enough.

-- Sylvain, Brussels, Belgium, Europe - The more I learn, the more there is to learn

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gwilki

344 posts in 2205 days


#15 posted 04-05-2020 01:36 PM

If you have access to a CNC router, it would be and easy carve.

Otherwise, take a look at Izzy’s Youtube site. He has another jig to cut parabolas/bowls on a table saw.

-- Grant Wilkinson, Ottawa ON

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