How to make a tractrix - Router Forums
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post #1 of 66 (permalink) Old 05-12-2011, 06:55 PM Thread Starter
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Default How to make a tractrix

I'm an enthusiast woodworking for many years. I have made furniture, model ships, and now I am making a set of hi-fi loudspeakers. This is my forth pair of loudspeakers, and now I would like to make something "special".

I would like to make a hole in a MDF plank with 40mm deep. The hole has to be a tractrix profile for a tweeter mounting. See the attached file.


I thought of a circle cutting with a milimetric control of radius and deep. The problem is that the for a smaller radius I have a deeper circle cutting. I think a center based circle cutter is'nt the best solution.

Does anyone made something like this, and have a solution?
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post #2 of 66 (permalink) Old 05-12-2011, 07:13 PM
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Hi Pedro

I think if you use a bit like below it will let the horn fit right into place..


Point Cutting Round Over Bits / #8734

MLCS groove forming router bits

http://www.google.com/#sclient=psy&h...8845393480168f

========

Quote:
Originally Posted by pedromdf View Post
I'm an enthusiast woodworking for many years. I have made furniture, model ships, and now I am making a set of hi-fi loudspeakers. This is my forth pair of loudspeakers, and now I would like to make something "special".

I would like to make a hole in a MDF plank with 40mm deep. The hole has to be a tractrix profile for a tweeter mounting. See the attached file.


I thought of a circle cutting with a milimetric control of radius and deep. The problem is that the for a smaller radius I have a deeper circle cutting. I think a center based circle cutter is'nt the best solution.

Does anyone made something like this, and have a solution?



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Last edited by bobj3; 05-13-2011 at 10:30 AM.
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post #3 of 66 (permalink) Old 05-12-2011, 08:21 PM
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Quote:
Originally Posted by pedromdf View Post
I'm an enthusiast woodworking for many years. I have made furniture, model ships, and now I am making a set of hi-fi loudspeakers. This is my forth pair of loudspeakers, and now I would like to make something "special".

I would like to make a hole in a MDF plank with 40mm deep. The hole has to be a tractrix profile for a tweeter mounting. See the attached file.


I thought of a circle cutting with a milimetric control of radius and deep. The problem is that the for a smaller radius I have a deeper circle cutting. I think a center based circle cutter is'nt the best solution.

Does anyone made something like this, and have a solution?
Hi Pedro:

You're going to want to look at the circle cutting jig that Santé has created. The problem is the 76mm depth. I don't know of a router that would do that kind of depth, even with a bit extension.

Santé's jig is independent of the centre of the circle so you can cut it without a circle centre. See it at this url: Association Les copeaux . It's in french but that's pretty straight forward. If you have a problem, contact Sante directly.

If you were to cut progressive holes and then stack the result and sand even, that might work.

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post #4 of 66 (permalink) Old 05-13-2011, 04:17 AM
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Hey Pedro,
The way I'm seeing it, you just need to make the hole through the 40mm deep mdf, and the remaining 36mm of the tweeter is protruding from the hole. So the 40mm depth shouldn't be a problem.
I've attached a reworked version of your image.
I would use a normal circle jig and rout 3-4 concentric circles at varying depths. It looks like you already have the ability to work out what depth to rout at particular diameters.
Start with the shallowest cut on the largest diameter, and work your way in to the deepest cut at the smallest diameter.
In the pic that would mean starting in the blue area, then green, then yellow. You could probably even use a drill and a hole cutter to remove the yellow part.

Then it would be a matter of using a rasp file to even out the 'steps' to the curve that you want. Perhaps even a drum sanding attachment on a hand drill could do that part also.
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post #5 of 66 (permalink) Old 05-13-2011, 12:44 PM Thread Starter
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I don't know why but I can't reply with quote.

Bobj3,

I have made the first loudspeakers with a plastic horn, but this time I want to make the horn directly on the front panel. Thanks anyway.

Alltunbs

I also think that a circle cutting jig without circle center is the best solution for this application. Thanks for the site information.

Gav

Thanks for your idea, this is what ocurred to me. I have thought milimeter by milimiter in diameter and dept, but I think in pratice is not so obvious.

With a circle cutting without center I think its possible, associated to your idea of fewer steps.

Thanks for all.
Pedro
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post #6 of 66 (permalink) Old 05-14-2011, 01:53 AM
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Pedro, the best solution to your problem is to have a machine shop make your cut with a milling machine. Another option is to have a custom built router bit manufactured for this job. That would only be cost effective if you plan on building lots of these. A bit with these dimensions would most likely run around $400.

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post #7 of 66 (permalink) Old 05-14-2011, 07:12 AM
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How about using a thinner material and creating a bigger angled hole in each piece then as you layer them on top of each other it should produces the shape your wanting.

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post #8 of 66 (permalink) Old 05-14-2011, 08:23 AM Thread Starter
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I need to make 5 horns, on the front panels of a home cinema loudspeakers system.

I have imagined something like the attached image. Has anybody a simpler (easier) ideia.
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post #9 of 66 (permalink) Old 05-14-2011, 08:29 AM Thread Starter
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The idea is to use a Dremel machine.

All the ensemble rotates in the 400x400mm fixed square piece.

I think it's not complicated to do and I hope that the precision is good enough for the 5 applications I need.
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post #10 of 66 (permalink) Old 05-14-2011, 09:37 AM
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Quote:
Originally Posted by pedromdf View Post
The idea is to use a Dremel machine.

All the ensemble rotates in the 400x400mm fixed square piece.

I think it's not complicated to do and I hope that the precision is good enough for the 5 applications I need.
Hi Pedro:

Ok, I've been thinking about this and there is another way but it can get complicated. Go here...

http://www.routerforums.com/woodwork...organized.html

Take a look at the article. You're looking for skis, pivot frame and angler and angle router base. Here's what I see in my mind. You can create an oversized circular rail, put guide bearings on the bottom of skis and mount an angle-based router on a skis rails. Infinite sizing completely independent and you're able to carve only what you need to get close to your bell shape and use rasp or sand paper for the rest.

Your Dremel is going to be pretty light for this operation. Even laminate trimmers will be too light. I would suggest something about 2 hp or 1500 watt.

The advantage of the above is that it will allow you to angle your cuts for each layer and allow you to stack them as you need. You can achieve something similar by using a 45 degree bit of an appropriate size and skis on bearings. If you send me a PM, I'll send you some notes on skis that you may find helpful. Also search out Harrysin's article on Skis for beginners. I'm not in favour of threaded ski rods.



Please note that MDF contains formaldehyde which becomes airborne when you're working with it, especially with power tools.

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