Tuba 18 CNC Build

[tomlang]

I'll be building a pair of flanking subs for use listening to music. The compact T18 seemed like a good choice along with the MCM 55-2421 which, if you add the appropriate Promo/Source codes is $25.49 right now. At first, I thought a "double wide" T18 with two MCM's inside would be the ticket but I think I will make two 12 inch wide subs instead, each with a MCM woofer inside.

I've had my Shopbot CNC machine for a few years now and use it all the time for projects like this. The Sketchup model provided along with the plans is invaluable for creating the 2D layouts, which in turn are needed for toolpathing output to the CNC machine. Usually, I have to create the Sketchup model from scratch from all the other plans I have worked with.

While I can cut miters with my machine, it is rather tricky and requires long machining times. However, these plans looked simple enough that I could get by with rabbets and dados and all right angled edges as depicted in the picture. The expanding properties of the PL Premium should have no trouble filling the cavities, based on prior experience. Note that for ease of placement the braces (in red) are also pocketed .1 inch. The numbers correspond to the panel numbers called for in the plans and will be lightly machined on each panel (you can barely make them out in the rendering). Disclaimer: I hate to have to do any measuring, cutting, or marking on any of the pieces after they are cut out.

Preliminary nesting reveals that I can get the pieces for two of these on one sheet of 1/2" thick 4x8 plywood as shown. I intend to cut the end pieces from 3/4 inch plywood. The reason being I'll have extra thickness for the rabbets for the panels to slip into on the inside (.25" deep), not shown yet.

What I have shown however, is a piece with the scroll pattern cut out (.030 oversize) to use as a jig for keeping the panels aligned as they are assembled, not sure how well that will work out, we'll see.

[miked]

This is really cool! Thanks for the detailed explanation of how/why/what. I love detail like that. Putting each piece's number on the panel is a pro touch. Please post as many pics as you can.

Was checking out the MCM 55-2421. Looks like a beastly little driver. Sensitivity is kind of low though; 87db. It needs watts to make it dance, apparently. But with Bill's awesome cab sorcery, they will thump for sure in solid cabs like you're building. The best part will be telling people there's fifty bucks worth of drivers in those cabs...and the wood was $60 and the finish was $25 so yeah, all that bass for about $135. Their heads will explode.

[DJPhatman]

Was checking out the MCM 55-2421. Looks like a beastly little driver. Sensitivity is kind of low though; 87db.

Snag yourself a pair or 2. Stuff them in a TT, AT or T18, and watch 'em, er, I mean, hear 'em dance! They are some inexpensive, bad-ass little drivers.

It needs watts to make it dance, apparently.

You'll be pleasantly surprised how little power they need.

But with Bill's awesome cab sorcery, they will thump for sure in solid cabs like you're building.

Mike, you know better. You have a few of these designs. How loud do your OTops and T48s get, on minimal power? The same goes for the auto and home designs.

This is what happens when you actually design a cabinet correctly, as Bill has done for us, instead of slapping together huge, power-hungry drivers into a box, and feeding it 1kw or more. Not to mention the lack of low end distortion.

[tomlang]

I may cut these prior to the drivers arriving. That said, does anyone know if the MCM 55-2421 has exactly the same mounting hole size and bolt pattern arrangement of the substitute Dayton DCS 205-4? The Dayton has a nice pdf with dimensions but I can't find one for the MCM. Only mention of dimensions of the MCM are Overall frame diameter: 8.25", Required cutout: 7.125" diameter, which DO match up to the Dayton. The Dayton also has 8 bolt holes, however, I need to make sure they line up.

[shawn_g]

I may cut these prior to the drivers arriving. That said, does anyone know if the MCM 55-2421 has exactly the same mounting hole size and bolt pattern arrangement of the substitute Dayton DCS 205-4? The Dayton has a nice pdf with dimensions but I can't find one for the MCM. Only mention of dimensions of the MCM are Overall frame diameter: 8.25", Required cutout: 7.125" diameter, which DO match up to the Dayton. The Dayton also has 8 bolt holes, however, I need to make sure they line up.

Sorry, I don't know the exact answer. But I do know that the user "But It Hertz" tried to do a MCM to Infinity 860W swap and the holes didn't line up. See this thread for details:
http://billfitzmaurice.info/forum/viewt ... 2&start=30

[miked]

Unless you can verify that those two drivers "are the same thing, just different labels" I would hesitate to cut anything without the driver in hand. But, being that you own the CNC machine, you COULD cut it out but NOT ASSEMBLE anything until you verify the thing fits. At the very most, you lose a small piece of BB and some time. Do not assemble anything until verifying though! PL is forever once it cures.