[Bob in St. Louis]

John, your square toilet seats are looking very nice!  Sorry man, I couldn't resist! Don't hurt me. HA HA!

I haven't decided whether to round the corners or leave them square (input is welcome).

I like the corners as a 90` angle. Radiusing them might be too much visually??

Nice rig on the hot wire John, that's pretty slick. I love the dimmer switch add-on too. And the feed table, like a joiner, now that's using you noggin! A+ 

You've got me thinking about this whole foam thing. It's looking pretty interesting.

A fellow on Hawthorne posted a link to some cool stuff to use as an alternative to resin:
http://www.caglue.com/glassing.html
A co-worker of mine has used one of the products for R/C aircraft and says it works very well. He hasn't seen it in years, didn't think they still sold it.
Looks like a neat product, but for the quantities we'd need it might not be cost effective.

Here's a link to a guy that makes and sells various hot wire cutters. A bit expensive, but it gives some good ideas on how to build your own.:
http://www.mossfoam.com/MainPages/hotwire.htm
(Be sure and check out his power source)

Bob

[JohninCR]

I'm going to do up 4 hand cutting tools today while epoxy cures.  I think I sourced some better wire.  The stuff I'm using is for on-demand hot water and is only about 1 ohm/ft, so I really have to crank up the juice to heat it up.  No way a wall wart could work.  Adjustable is absolutely required, because resistance increases with temp.  Too hot and it melts foam a distance from the wire, so I crank it wide open to get it red hot, and turn the dimmer down to just below red hot.  It's so easy to sand that cutting a little large makes sense.  It cuts great with a steady movement, but the inevitable pauses cause some widening of the cut.  It's actually kind of fun.  Most of my time has been setup, so slower than I hoped.  Maybe I'll pick up some more foam and whip out a pair of line array surfboard baffles today.

We'll see how smooth the epoxy turns out.  I don't want a sanding nightmare.  I hope to have some rings done this afternoon, but wifey is trying to steal me for part of my day off.  She never tells me no, so I try to do the same.

[Bob in St. Louis]

John, Check that link I posted. The guys sells just the wire. $1 per foot. (15" actually)

"Sanding nightmare", Yea...I think I'll know exactly what your talking about next weekend.

Good idea keeping the wife happy. You wife has got to be the #1 most tolorant wife in ALL of audiophile land!!! John, you've got a winner there for sure. And attractive too!  aa

I'm suprised you didn't take a shot back at me about the toilet seat comment John.

Bob

[Russell Dawkins]

- from years ago when I took the trouble to make a variety of glue joints with plywood and particle board (cheap mdf).

I made a number of experimental joints edge-to-edge and after allowing a week or so to completely dry, I broke them to see how and where the failure was. This was 35 years ago so I can't remember all the details, but the ultimate conclusion is still clear.

This all started when an edge joint that I had made broke and the fracture line was the glue surface itself, as if the glue hadn't really bonded well with the surface. I thought about what I saw and, knowing that white glue is water based and that the surfaces were very dry, I reasoned that the glue was drying to the hardening point before it had time to penetrate to any significant extent the material being glued.

So then I tried moistening the surfaces with a wet sponge. This indeed proved by far the superior bond. Edge to edge plywood would behave as if there were no discontinuity at the joint. When I forced the issue and broke it by pressure over the edge of the bench, the plywood laminations were pulled apart 1 inch or more into the edge. Since then I have never not moistened surfaces to be bonded with white glue. A white glue joint is surprisingly strong, done this way.

This also relates to adding sawdust to the mix. I would put the sawdust in water to which was added just a drop of detergent to break down surface tension and allow wetting. Drain, then add that to the white glue.

[JohninCR]

Bob,

At least you have multiple grinders to choose from.  Be sure to have some of those flexible disk grinding wheels available.  Even that will be surprisingly slow to cut down ridges.  That's why I was saying that smooth from the getgo is what you're after.

I was holding off on the toilet seat thing until you see the rings.  They'll really look like toilet seats.

Re: Wire-  About the only thing I have the patience to order online is drivers, and that's only because I have lots of surplus.  It's part of the challenge down here, get something you need by finding something similar enough that's used for a totally different purpose.

[JohninCR]

- from years ago when I took the trouble to make a variety of glue joints with plywood and particle board (cheap mdf).

I made a number of experimental joints edge-to-edge and after allowing a week or so to completely dry, I broke them to see how and where the failure was. This was 35 years ago so I can't remember all the details, but the ultimate conclusion is still clear.

This all started when an edge joint that I had made broke and the fracture line was the glue surface itself, as if the glue hadn't really bonded well with the surface. I thought about what I saw and, knowing that white glue is water based and that the surfaces were very dry, I reasoned that the glue was drying to the hardening point before it had time to penetrate to any significant extent the material being glued.

So then I tried moistening the surfaces with a wet sponge. This indeed proved by far the superior bond. Edge to edge plywood would behave as if there were no discontinuity at the joint. When I forced the issue and broke it by pressure over the edge of the bench, the plywood laminations were pulled apart 1 inch or more into the edge. Since then I have never not moistened surfaces to be bonded with white glue. A white glue joint is surprisingly strong, done this way.

This also relates to adding sawdust to the mix. I would put the sawdust in water to which was added just a drop of detergent to break down surface tension and allow wetting. Drain, then add that to the white glue.

Russell,
That's very interesting.  I wonder if it holds true with today's PVA glues.  I've always gone by the instructions, which seem especially important for dense hardwoods.

[Russell Dawkins]

I don't know if PVA glues are water based. Logically, it would seem to apply to any water based glue - after all what exactly is carrying it into the surface of the material to be glued? Just the water content which, of course, is finite.

Further in the same vein, the degree to which the surface needs to be wetted would be a function of the porosity, and that would be where the skills of the cabinetmaker would rise to the surface as a good judgement call!

[Bob in St. Louis]

John, Understood about 'starting off smooth', mine didn't turn out too bad in that regard. Next weekend I'll run a quick "big and nasty" grinder over the surface to knock off the 'drip tits'. Then the face will get one more coat of resin only. The back will get one more coat of cloth and resin. The entire wooden structure will get a medium sanding and one final coat of resin.

I may have missed it? But what type of resin did you decide on? Is it fiberglass resin?

Plenty of grinders in the arsenal from the wrench turning days, from 2" to several inch with various types of abrasive discs/pads/wheels.

Russell, good info about the adhesives. I've often thought about my own little "mythbusting experiment" testing various woodworking adhesives. But as time went on, I've gotten complacent with my choices: Yellow "Titebond II" for hardwoods, and Gorilla Glue for porous and rough surfaces. Beyond that and the occasional squirt of Liquid Nail, That's the extent of my adhesive use for woodworking in the basement workshop.
I like the sawdust mixture idea. I'm thinking about using that for the final coats on the baffles. It's like your very own liquid MDF!  aa

Bob

[JohninCR]

More of a play day than productive.  I put the epoxy resin on a was instantly discouraged by the texture.  Hopefully this sands easier than fiberglass.  If not, then a material covering for sure.  For the backsides, I may include a layer or 2 of newspaper for a smoother texture off the bat.



Here are some mini OB's I'm finishing up for my daughter.  The top driver is an Adire AV3, and the bottom is a generic 4" I found locally.  They're both shielded so they make great TV or computer speakers.  These will get stuffing in the back, since they'll probably near a wall.  Bottom end assistance will come from a computer sub, that will soon be converted to a U-baffle.



Here are the beginnings of some surfboard baffles.  Drawing them took longer than the cutting including roundovers.  The one on the left is straight from cutting, and the right one is after about 10min with a sanding block and 80 grit.  These will definitely get something added to ensure a smooth texture in the initial resin stage.  These are a great candidate for a concrete+plaster casting to avoid the necessity of a magnet mount.  Even easier for someone with the right resources would be an aluminum, bronze or lead casting using the lost styrofoam method.

[Paul W]

John, where did you find the foam sheets?

I have tried "Yellow Glue and MDF to failure" with a sledgehammer...MDF always failed before the joint.  Liquid Nails tends to skin too quickly and may not bond well.  Success with Gorilla Glue was between the two extremes.

[Bob in St. Louis]

John, Darrel Hawthorne's "Duets" have a nice black speaker cover material over the entire structure. Not that that's anything special in and of itself, but the super cool thing, is underneath this material is a thin "foam rubber[?]" underlayment. It doesn't do much for the appearance since it's covered. But it give a real nice tactile feel when you touch the speaker. This foam would be think enough to cover your 'unevenness' and the black material over it would give it the finishing touch.
No, or very little, sanding required.
On the Duets, it's one of those "nice little touches", if you know what I mean.
It gives a level of quality over the typical crappy wood covered in cloth type speaker designs.

Bob

[JohninCR]

Bob,

These are waveguides.  Foam and material may very well be part of tuning (Dr. Geddes fills his entire waveguide with a very lightweight foam).  Keep in mind that these are experimental.  The epoxy is only going on now because the styrofoam is so easily damaged, but I want to learn the best and easiest process.  If foam isn't needed for tuning, then a glossy is the way to go.  The B200 set definitely will need foam, so a slick upholstered look will be part of the functionality.

This avenue is showing enough promise that I'll want to build some oblate spheriod waveguides, and what I learn now will be called upon for the next stage, since there's no way for me to construct them out of wood.

[Bob in St. Louis]

Foam and material may very well be part of tuning ..... If foam isn't needed for tuning, then a glossy is the way to go. 

Good point John.

since there's no way for me to construct them out of wood.

How about a wood lathe, even one of those cheap 'jigs' that'll hold a drill in place. Then you could make wood waveguides. You could get fancy and use a router down the wooden "pole" you just turned on your new lathe for a channel the center baffle would rest into. Basically, you'd be making a big picture frame with sheet stock wood as "the glass", and your lathe turned "poles" would be the frame.
Whatcha think?

Bob

[JohninCR]

I think it sounds difficult since I don't have a lathe.  With roundovers we're talking 20"+ diameter, so I don't know if that's even possible.  Reinforced pottery keeps coming to mind though.  I might even be able to find the right dimensioned bowls and add roundovers.  A couple of years ago someone posted about using some large commercial light fixtures as waveguides, but I think the shape was prolate spheroid instead of an oblate one.  It's definitely one of those cases where finding the right thing intended for another use could save a bunch of work.

[Bob in St. Louis]

I think it sounds difficult since I don't have a lathe.  With roundovers we're talking 20"+ diameter, so I don't know if that's even possible.

I meant to make your 4" diameter foam/PVC "frame" around your center baffle section. Then cut the 45 degree angles. All just like you'd do for a picture frame.
Am I doing a crappy job explaining? 
I'll find a pic of what I'm talking about. (hopefully)


 

I might even be able to find the right dimensioned bowls and add roundovers. ......... It's definitely one of those cases where finding the right thing intended for another use could save a bunch of work.

Now we're back talking about walnut bowls, and Chinese woks...

Bob

[Bob in St. Louis]

Ok, see the size of wood this guys is turning? That's what I'm talking about. Then cut the ends at a 45 degree angle for the corners.

[JohninCR]

No, closer to birdbath size but deeper.  The salad bowl thing wouldn't do much more than create a bunch of diffraction.  Wood is mostly cheap here, but not 4x4's for some reason.  Otherwise I could turn them into round stock without a lathe.  I'm going to need circular stuff (like donuts), not cylindrical.

[markC]

What is that radio active wood? What's with the breathing apparatus?

[Bob in St. Louis]

I understand John, you're wanting the entire baffle ROUND. NOT square with round wave guides, right? No 90, and no 45 degree angles.
You're taling about something like a childs swimming pool float ring, hemroid cushion, or motorcycle tire.
Hey, yea, how about a motorcycle tire filled with expanding foam?

Mark, That's reclaimed wood from Chernobyl.     
Actually, it's an ad for the "ultimate" in dust and hearing protection from Rockler.

Bob

[JohninCR]

I understand John, you're wanting the entire baffle ROUND. NOT square with round wave guides, right? No 90, and no 45 degree angles.
You're taling about something like a childs swimming pool float ring, hemroid cushion, or motorcycle tire.
Hey, yea, how about a motorcycle tire filled with expanding foam?

That would just be the roundover at the mouth.  Think of the Earth cut in half at the equator, and then put a life ring for kids around the equator.  The interior is the oblate waveguide, and the life ring helps prevent diffraction at the mouth which causes reflections back into the WG.