Building a new OB

Paul W · « **Reply #100 on:** 5 Mar 2007, 11:26 pm »

If you think that's fun, try a whole boat or two

Fiberglass cloth, and especially fiberglass mat, makes a good base for plain old wood glue. Sets up slower than epoxy or polyester, and lower ultimate strength, but plenty strong enough for speakers and a whole lot friendlier to work with. If you want the glue a little thicker, mix in some trusty WP.

DanTheMan · « **Reply #101 on:** 6 Mar 2007, 12:01 am »

S#$T Bob! Sorry to see that happen to such a beautiful start. Don't get too worried though, all that can be cleaned up. It's going to take a lot of work though. Maybe they have some other type of solvent to clean that stuff with?

What's the plan for trimming off the excess?

JohninCR · « **Reply #102 on:** 6 Mar 2007, 01:07 am »

Quote from: Paul W on 5 Mar 2007, 11:26 pm

If you think that's fun, try a whole boat or two

Fiberglass cloth, and especially fiberglass mat, makes a good base for plain old wood glue. Sets up slower than epoxy or polyester, and lower ultimate strength, but plenty strong enough for speakers and a whole lot friendlier to work with. If you want the glue a little thicker, mix in some trusty WP.

Paul,
That's a good one to know. It makes me want to give that a twirl in the near future. What's "WP" ? I've added fine sawdust to make a paste with wood glue. I've also used TP to similar effect, but WP has me

. I'm sure it's just one of those brain cramps I get on occasion.

Bob in St. Louis · « **Reply #103 on:** 6 Mar 2007, 02:02 am »

John - WP is Water Puddy. Paul mentioned it on page 9 (I think). I don't know what it is, but I'll check into it.

Dan - The plan for trimming off the excess is shear brute testosterone manly strenth. = A big assed grinder!

I have multiple grinders for a multitude of jobs. One of them will get the job done. aa
I did get a random oribital sander today at the "Depot".
It's a Ryobi brand, $20 job. I'm sure it's a piece of crap, but hey..It's under warranty for a while.

I'm finished for the weekend. Here's what I'm staring at for the next week:

Bob in St. Louis · « **Reply #104 on:** 6 Mar 2007, 02:11 am »

Come on John, where's your balls? Gimme some pictures!

Bob

JohninCR · « **Reply #105 on:** 6 Mar 2007, 02:16 am »

My weekend starts tomorrow afternoon through Wednesday night, so time for some catching up. Water putty or wood putty? I can just see the look on the hardware store clerk's face when I ask for either one.

Sometimes it amazes me what isn't available down here. eg With moisture an issue during rainy season, but water resistant wood glue is hard to find.....So many things are handmade from wood (all window frames for example), yet woodworking tools seem stoneage and no one has heard of a cabinet scraper.

JohninCR · « **Reply #106 on:** 6 Mar 2007, 02:18 am »

Quote from: Bob in St. Louis on 6 Mar 2007, 02:11 am

Come on John, where's your balls? Gimme some pictures!

Bob

Manana (tomorrow).

Paul W · « **Reply #107 on:** 6 Mar 2007, 03:05 am »

Yes, it is called Water Putty...a powder (normally) mixed with water to make a thick paste/putty which cures very hard. It is similar to Plaster of Paris, but substantially harder/stronger. Several brands are available, usually at stores like Home Depot, Lowes, and on the net if nothing local.

Bob in St. Louis · « **Reply #108 on:** 6 Mar 2007, 01:05 pm »

Paul, I still have not Googled Water puddy yet, but I will today. Do you think WP would handle the vibrations?

John, I love your idea of using sawdust as a filler/thickener. That'd be much easier to deal with than resin. Easier clean up, it could be used inside (no harmful smell during the "wet phase" and could be sanded without much of the worry"). If Gorilla glue wasn't so expensive, that would be fun to try since it expands slightly and could be shaped with a sander.

Bob

Paul W · « **Reply #109 on:** 6 Mar 2007, 01:56 pm »

Here is one brand. Another is Durham's Rock Hard.

http://www.dap.com/product_details.aspx?product_id=325

I wouldn't use Water Putty alone the way you are using the resin but a little mixed in to thicken glue should be fine. It also makes a good casting agent...you can even dry mix it with Plaster of Paris to yield various levels of strength/hardness. My experience with sawdust is that the fibers are too coarse, allowing the glue to drain out of the mix...of course if gravity can be put to use that isn't a problem.

JohninCR · « **Reply #110 on:** 6 Mar 2007, 04:03 pm »

Last night I investigated plasters and casting. I found one very intriguing to test, because it would be so cheap. 3 parts plaster of paris + 2 parts concrete, and it turns out almost the strength of dental plaster. Mass, strength, no toxic fumes with some ability to work it after it hardens, makes it sound like a fun material to get creative with on a small budget.

DanTheMan · « **Reply #111 on:** 6 Mar 2007, 04:19 pm »

John, you must post quickly, that last post was number 666!

JohninCR · « **Reply #112 on:** 6 Mar 2007, 05:24 pm »

Quote from: DanTheMan on 6 Mar 2007, 04:19 pm

John, you must post quickly, that last post was number 666!

Uh oh, plus my name comes up 666 with one of those letters = numbers systems. Don't worry, I'm only taking over the world 1 OB convert at a time.

Wind Chaser · « **Reply #113 on:** 6 Mar 2007, 05:54 pm »

Quote from: DanTheMan on 6 Mar 2007, 04:19 pm

John, you must post quickly, that last post was number 666!

No worries, he's just anti-box.

JohninCR · « **Reply #114 on:** 6 Mar 2007, 11:44 pm »

Bob,

Here's some pics you demanded. First is the hot wire cutting rig. I used a 12volt power supply with a light dimmer switch in front of it to control the temperature. The straight wire unit acts as a table saw, and with a nail through the styrofoam and into the wood, a circle cutter. The other jig is my 2 inch radius roundover cutter. They both work faster than a hot knife through butter. Imperfections are easily sanded away.

Below are some of the results of the hot wire work. I cut 2x4s out of 2" thick styrofoam, and glued them together to make 4x4's for roundover stock. Then I used the roundover cutter to make 4" dia cylinders, which I flush mounted on the dipole waveguides that I already made for FE108's. I'm waiting for the latex glue to dry before doing the other side tomorrow. I haven't decided whether to round the corners or leave them square (input is welcome). Tomorrow I'll paint 2 coats of epoxy onto the roundovers to protect them from damage and from later being eaten by whatever finishing paint I use.

Here's my adaptation of 9and1H's PVC magnet mount idea. A slit sleave of 3" PVC fits right over the magnet and over the piece I cut to make the joint. I plan to fill the pipe and join it to a heavy base using concrete. I'll run piece of hose through the support structure for my speaker wire. I reinforced the PVC glue joint with epoxy and fiberglass just to be sure it never comes apart and enable me to sand the joint nice and smooth for final painting. I plan to mount a small styrofoam core baffle to the driver frame, and the bass augmenter mount will slide into the base for the upper support with foam rubber for isolation of the 2 bases.

doorman · « **Reply #115 on:** 7 Mar 2007, 01:15 am »

Good lookin' drivers, John!

Don

JohninCR · « **Reply #116 on:** 7 Mar 2007, 01:54 am »

Quote from: doorman on 7 Mar 2007, 01:15 am

Good lookin' drivers, John!
Don

I forgot to mention, those 167's are the ones I picked up from Don (Doorman). When I saw the OD of the magnet cover was almost identical to the OD of 3" PVC, I felt compelled to give them a go with a magnet mounted OB.

I tried heating up the PVC to do a stretch fit, but I quickly realized that it would require alot of trial and error to get it right, and still the result might not be pretty. A 2 joint bend probably would have been a better aesthetic match for the circular diffraction rings I'm going to try. I'll save that for the next set and throw a little rebar into the mix so the PVC is just a mold for the concrete.

9anda1f · « **Reply #117 on:** 7 Mar 2007, 02:10 am »

Wow! You guys are really BUSY on this forum (and especially this thread)!! The ideas are flowing like water out of a firehose! Thanks to Bob for posting his very cool new project over at Decware with a link. I like your magnet mounts John...much lower profile to the rear wave using just the pipe. Can't wait to see how these two projects turn out

markC · « **Reply #118 on:** 7 Mar 2007, 02:30 am »

Man oh man John, you are one sick puppy!

Here I think I'm doing things with my filters and tweeters. Life Must be good in C.R. I'm a little jealous - especially since it was -14 F here this morning!

JohninCR · « **Reply #119 on:** 7 Mar 2007, 03:18 am »

Quote from: markC on 7 Mar 2007, 02:30 am

Man oh man John, you are one sick puppy! Here I think I'm doing things with my filters and tweeters. Life Must be good in C.R. I'm a little jealous - especially since it was -14 F here this morning!

It's so bad, my wife didn't even bat an eyelash when Don's drivers arrived last week. Even though I can change anything I want with the active system I use, I'm still trying to see how much I can manipulate things to my advantage with the physical structure. It's a little breezy tonight, so we must be down in the low 60's, and tomorrow I expect another mid 70's high in my garage workspace.

Too bad my helper is on hiatus, or I'd really be able to crank out some different stuff. I've all but decided to do a pair of mini-surfboard looking OB's, since DMason doesn't want to be the first. Using styrofoam as a base material is going to enable me to do a lot of things, especially for addressing diffraction, that I just haven't had time to do in the past. Once I get into measuring, I'll even do a direct comparison of same sized baffles with edge geometry ranging from big roundovers to sharp points.