Fun on the lathe......Waveguides

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Thanks for the compliments. No commissions (yet) That was the first one I have ever made. I will probably start a build thread soon as I almost have all the MDF cut. 2 way bi-amped with automotive based A/D/S 320is woofer and Alpine 6022 tweet. Flame maple front w/ black finish elsewhere. After that will be a 4 channel LM3886 Gainclone project.
 
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Wood lathe is quite old

When doing large items it was usual to use the outside of the lathe, and have a stand on the floor, to support hands and cutting tool

But this can be pretty dangerous stuff if doing it wrong
Even if not doing it by hand but using metal lathe and fixed tools, it can go pretty bad if not secured properly
 
Yes, I made the jig on the lathe also. With the help of a band saw to get the rough circle on the plate.

The lathe is a small metal turning lathe. I hold the piece on with 3 #4 screws that are 3/4" long. It turns true (to within a few thousands of an inch) and is balanced well with no discernible vibration. I had zero issues turning the first one. With one bigger cuts than I am making, and that MDF cuts easily, those 3 screws should be plenty.
 
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I made the flat plate jig myself from 6061 aluminum.

Nice work!
You know you can buy faceplates ready made?

CF4J.jpg
 
OK......here's a few pics of the turning in process.

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Here the MDF has been cut to rough shape and mounted on the jig. The center has been bored to the correct size and the outside has been trued and sized to 4.50". The black marks are from locating the spots where it was hitting the lathe bed and had to be trimmed before it would spin. The 3 small holes close to the outside edge are for the mounting screws to the jig from behind and will be filled later.

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Here it is after the first few cuts. Each diameter cut is .10" smaller in radius than the previous cut. This pattern is followed all the way in.

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Here are a few more cuts. These are a bit deeper than the first cuts and will continue to get progressively deeper as more cuts are made.

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More of the same......Just farther in.

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Here it is with all the cuts done. From here, I just sand down the ridges until I get down to the bottom of the cuts.

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Here we have the rough sanding done. You can still see some ridges. These will disappear as I sand farther down with finer sandpaper. When that is done, I will apply a few coats of sanding sealer and remount the waveguides on the jig and sand with 400 grit. Then it's paint and final sanding.

These are not that hard to do but you do have to pay attention to what you are doing. Screw up one cut and you can bin it and start all over.
 
Progressive curve. But, nothing scientific at all. I drew up full scale and used a French Curve to get the profile I liked. Measured the thickness from the OD inward at .10" intervals. I can do any curve I like. Just plot the thickness from the OD to the ID at set intervals. I'm sure there is a formula for doing this that is frequency dependent but, my algebra and trig really suck. :headbash:
 
Progressive curve.

ah... I did a straight taper. Which I have to think would be far easier.

I'm sure there is a formula for doing this that is frequency dependent but, my algebra and trig really suck. :headbash:

I'd imagine so, but in my attempt it was more about a future proofing for a tweet upgrade. I'm using a rather small neo, and thought I'd fab up a mounting flange which matches in OD the most likely upgrade.
 
John K posted dimensions of the waveguide he used in his TMM waveguide project in a PDF file here...

http://zaphaudio.com/WaveguideTMM-profile.pdf

These should be easy enough to transfer on a lathe.

It's got to be at least a little more scientific than the french curve template method, although there must be a million ways to skin this cat.

One of the (admittedly unorthodox) attractons to waveguides to me is the possibility of once again using grille cloth on a speaker design. I'm a little worn out on the naked speaker look. I''d really like an option to (perm or removeable) dress the speaker in an attractive cloth to blend in a lttle better with the furnishings of my living space. Raw speaker drivers just sometimes scream nerdy techno!!!!! A well designed tweeter waveguide along with a minor smoothed woofer rebate allows a grille (cheap panty hose is the best) to be stretched across them without getting overly concerned with edge diffraction issues and the rest.
 
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I agree that the French curve method leaves alot to be desired. At least it is a progressive curve which should be better than a straight taper. I have that same Zaph WaveGuide Profile pdf. and tried to reconcile the differences between it and the dimensions that I had to work within. Working inside the dimensional limitation that I had, I tried to duplicate the profile the best I could. I also found a formula for waveguides somewhere on here that was wayyy over my head to try to decipher. This is the reason why I didn't post depth dimensions of my cuts as I knew they were not based on any reasoning.

As a matter of fact, these WaveGuides will be used as part of the grillwork on the 2 ways I am building.
 
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