PVA is indeed just a mold release.
first you wax, then you spray a fine mist of PVA onto the mold. the pictures above are showing the gel coat, not the PVA (which is under the gel coat already if I infer correctly).
the PVA is thin stuff and shouldn't print onto the part surface.
a product example:
http://www.tapplastics.com/shop/product.php?pid=67
product instructions:
http://www.tapplastics.com/uploads/products/pdf/pb_tapPVA.pdf
I believe this is the same material but TAP rebrands it. eg the instructions are identical.
http://www.rexco-usa.com/part2.htm
edit: oops, didn't realize there was a whole page of posts explaining it after Dr. Geddes'.
but just another note, if you SPRAY the PVA on, it'll look much better on the finished part.
first you wax, then you spray a fine mist of PVA onto the mold. the pictures above are showing the gel coat, not the PVA (which is under the gel coat already if I infer correctly).
the PVA is thin stuff and shouldn't print onto the part surface.
a product example:
http://www.tapplastics.com/shop/product.php?pid=67
product instructions:
http://www.tapplastics.com/uploads/products/pdf/pb_tapPVA.pdf
I believe this is the same material but TAP rebrands it. eg the instructions are identical.
http://www.rexco-usa.com/part2.htm
edit: oops, didn't realize there was a whole page of posts explaining it after Dr. Geddes'.
but just another note, if you SPRAY the PVA on, it'll look much better on the finished part.
I decided to make a new mold as the first one was too unreliable to use for making more wg´s.
It turned out extremely nice.
I wet-sanded the wg with 400 then 800 sandpaper and applied 5 coats of wax, and one coat of pva.
Then one coat of gelcoat and some layers of fibreglass.
The mold popped right out of the wg.
This is a picture to show the film the pva makes.
It turned out extremely nice.
I wet-sanded the wg with 400 then 800 sandpaper and applied 5 coats of wax, and one coat of pva.
Then one coat of gelcoat and some layers of fibreglass.
The mold popped right out of the wg.
This is a picture to show the film the pva makes.
Attachments
Now I´m finally back to the WG´s, I got a bit sidetracked with my new hobby slotracing 
I´ve changed the first mold to 25mm / 10 degrees throat, to see if it really helped anything modifying the BMS driver.
And guess what, it measures better with the unmodified driver so this is what I´ll use.
The RED curve is the standard BMS driver with 25mm throat, and the BLUE curve is the cut down version having a 16mm throat.
I´ve changed the first mold to 25mm / 10 degrees throat, to see if it really helped anything modifying the BMS driver.
And guess what, it measures better with the unmodified driver so this is what I´ll use.
The RED curve is the standard BMS driver with 25mm throat, and the BLUE curve is the cut down version having a 16mm throat.
Attachments
lathe/tool
Don, that's a very clever tool you made. I'm trying to go down the same path-buy a used lathe, then worry about making that guide if I can. But all the lathes I see are small with the bar limiting the size, i did see an old york that you could reverse so that you were turning on the outside with no size limit. Is that what you are using? Any advise on what brands/models I might look for or how to turn a larger 250hz tractrix would be of interest.
Don, that's a very clever tool you made. I'm trying to go down the same path-buy a used lathe, then worry about making that guide if I can. But all the lathes I see are small with the bar limiting the size, i did see an old york that you could reverse so that you were turning on the outside with no size limit. Is that what you are using? Any advise on what brands/models I might look for or how to turn a larger 250hz tractrix would be of interest.
Most woodworking lathes have an outboard turning option that will allow you you to turn larger pieces.Unfortunately,lathes that are heavy enough to do the job are quite expensive.I was fortunate to run across a deal on a big lathe at a very reasonable price about 20 yrs ago.It will turn 26" dia over the bed,and the limiting factor for the outboard capacity is the floor and ceiling.
I would recommend building your own.You can get a headstock on ebay,and bolt it down on a sturdy bench.A 9" or 10" metal working lathe headstock with a 1 1/2"-8 spindle would work very well,and appear on ebay frequently.Faceplates are available from places like Enco,or ebay.
Brands like South Bend,Atlas,or Logan,are good choices.
Here's a link to a homebuilt lathe if you are a bit more ambitious.
Homemade Lathe on a Budget - Fine Woodworking Article
I would recommend building your own.You can get a headstock on ebay,and bolt it down on a sturdy bench.A 9" or 10" metal working lathe headstock with a 1 1/2"-8 spindle would work very well,and appear on ebay frequently.Faceplates are available from places like Enco,or ebay.
Brands like South Bend,Atlas,or Logan,are good choices.
Here's a link to a homebuilt lathe if you are a bit more ambitious.
Homemade Lathe on a Budget - Fine Woodworking Article
All this talk and nobody has come up with the simplest solution? Get someone else to do it for us.
Dayton audio makes a H12RW 12" round wave guide that is only $13.90. They are a small enough company where if enough of us asked really nice they might possibly make and sell an OS waveguide which would reduce the price to being negligible. I am going to email them tonight when I get home and I think a few others of you should do the same. If we could convince them to build them we could all have OS waveguides for $15 a piece and I think we can all agree we would buy them at an even higher price.
Dayton audio makes a H12RW 12" round wave guide that is only $13.90. They are a small enough company where if enough of us asked really nice they might possibly make and sell an OS waveguide which would reduce the price to being negligible. I am going to email them tonight when I get home and I think a few others of you should do the same. If we could convince them to build them we could all have OS waveguides for $15 a piece and I think we can all agree we would buy them at an even higher price.
Well, this is a DIY forum and your solution is not very "DIY".
Without going into a hundred details, the OS geometry is used around the throat and this geometry is protected by a patent. In the middle of the horn, the geometry is similar to a conical flare (conicals have been around for ages). At the mouth, the geometry need to have some sort of expansion or transition. That transition would need to be detailed (one possibility is a tractrix expansion - there are others and they may or may not be very good -remember these were engineered, tested and not simply thrown together).
Do you think a manufacturer will be willing to take on a project that has portions that are under patent? Rememeber, lawyers are expensive.
Quality control. IOW, how close is close enough. How would you specify the tolerances?
Then there is an issue of "is it fair". Geddes did a lot of work on this design. Whether or not it is "under-the-wire" legally, you have to ask yourself: is it fair? That is a judgement call, not a legal issue. Geddes has been a good sport about helping out and looking the other way on some of this stuff. What do you imagine his reaction would be when a manufacturer (not a DIYer for personal use) starts selling these?
Okay there is the biggest hurddle. Do you really think that $15 will cover the cost of making the first hundred units? Consider all the tooling, design, and start up costs. That eats up a huge number of dollars
I guess you need to think this one through. Or not bother, since I don't think it will ever get off the ground anyway.
I would like to See Dayton do this.
We just found out that QSC will not be selling any more HPR-152i waveguides, which was a very popular DIY choices because of its $12 cost and great measurements (better then anything Dayton has offered up to this point).
Someone posted on PE that Dayton should pick up the QSC horn manufacturing.
There is no Geddes patent on OS waveguides, others are building them and selling them already, see group buy waveguide thread for that info.
http://www.diyaudio.com/forums/group-buys/166312-waveguides-horns-7.html#post2188035, His 12" OS waveguides are $70+shipping for bulk orders. Im hoping Dayton can do it much, much cheaper and shipping CONUS is very cheap.
Also if QSC can sell the HPR-152i waveguide for $12 and Dayton can sell other horns for < $20 there is no reason a OS waveguide mold can not be made and plasic waveguides created.
Who do we talk to at Dayton to get this done?. I have been waiting for a low cost OS 12" and 15" solution for 3 years. I would even order $1000 worth from Dayton to give them atleast a minimum to start and to get it going knowing that I could ship them all out to many other DIYers waiting.
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I believe the only patent on his W/Gs are the foam plugs, but it's still a design that should be credited to him.
I built some....
Building Oblate Spheroid Waveguides Far and away the most difficult project I've done to date. Article By Jeff Poth
I built some....
Building Oblate Spheroid Waveguides Far and away the most difficult project I've done to date. Article By Jeff Poth
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