Mid Bass Horn Design 80-800 Hz

[jnorv]

This what you need, http://www.deltaportercable.com/Products/ProductDetail.aspx?ProduciID=11108. A tilt base laminate trimmer. You can do it from the bottom using a standard ball bearing follower.

And then one of these to mount it on to keep it square. http://cgi.ebay.com/Drafting-Machine...QQcmdZViewItem

Jim

<font color="#FFFFFF"><font size="1">[ December 12, 2007 06:05 PM: Message edited by: Jim Norvell ]</font></font>

<font color="#FFFFFF" size="1">[ December 12, 2007 06:15 PM: Message edited by: Jim Norvell ]</font>

[bfish]

I've got a cheaper B/D laminate trimmer...you want it?

That P/C unit looks better, mine's little more than a bulky, clumsy Dremel tool. It walks nicely through formica, but anything heavier chokes it. The base is so small, precision relies more on your freehand skill than anything else. The next time I use it, I expect it to do like all the other cheap B/D stuff I've had, and start throwing little bits of plastic and carbon out the vent slots right before you smell the smoke...

[jnorv]

The bottom shape is the same as the top shape. It is just shifted towards the front by the thickness of the plywood multiplied by the Sine of the angle (about 15 degrees if I interpret your drawing right).

Another method. A friend of mine has a drill press with a table that can be rotated from perpendicular to the drill axis. You could rotate the table to the required angle and then use a 2 to 3 inch drum sander chucked up to cut away the excess material. You would have to do this free hand.

Jim N

<font color="#FFFFFF" size="1">[ December 13, 2007 11:08 AM: Message edited by: Jim Norvell ]</font>

[Steve Mac]

Originally posted by Jim Norvell:
The bottom shape is the same as the top shape. It is just shifted towards the front by the thickness of the plywood multiplied by the Sine of the angle (about 15 degrees if I interpret your drawing right).....

Jim N

<font size="2" face="Verdana, Helvetica, sans-serif">The angle is 20.4 degrees...
And this is a great idea!
The reason why is that I can immediately trace the pattern without measuring a dam thing. Just simply align two on top of each other lining up on the angle the wedge meets the rear chamber:
Aligning 2 wedges pieces

That is clever as I took a pencil and just traced it out:
Aligning Tracing

But this also means something else. I can use a router bit like I have now and slice off an 1/8" and be darn close.

Then, and this is cute as h.ell, simply figure out how far to shift the piece again to get another 1/8" and slice...then repeat 4 more times. Time consuming, but pretty accurate. If I figured the distance for each slice I could make 5 or 6 of them and pull one out, shift, rout, pull another out, rout...I can see this working well. And the hand sanding afterwards would be pretty easy. I haven't considered the other idea you had yet...but I'm liking the possibilities of the first.

<font color="#FFFFFF" size="1">[ December 13, 2007 11:51 AM: Message edited by: Steve Mac ]</font>

[Steve Mac]

Originally posted by bfish:
I've got a cheaper B/D laminate trimmer...you want it?

<font size="2" face="Verdana, Helvetica, sans-serif">That's a kind gesture. But no thanks. I set up the whole job tonight, clamps and straight lines and all to take a shot and right at the moment of truth I said...umm...I'm gonna firetruck this up, I just know it. So, I punted.

[Steve Mac]

Originally posted by Jim Norvell:
This what you need, http://www.deltaportercable.com/Products/ProductDetail.aspx?ProduciID=11108. A tilt base laminate trimmer. You can do it from the bottom using a standard ball bearing follower.

And then one of these to mount it on to keep it square. http://cgi.ebay.com/Drafting-Machine...QQcmdZViewItem

Jim

<font size="2" face="Verdana, Helvetica, sans-serif">Yeah, a friend of mine down in Texas autocad'ed( I know that ain't a word ) up this picture which is exactly what you are describing:
Router with arm

With the wood base on the router I have, the router bit is just barely NOT long enough to expose the ball bearing to keep me from the edge. The router link with adjustable base would expose it and it is a possibility. You obviously understand the problem completely!

I decided not to use my brother's cnc cad router table back in NY, which is a mammoth machine and could cut this out easily in multiple passes. Oh well. A new friend here in Indy where I now live built his own cnc router this summer, which works...and he was able to cut a template...unfortunately he hadn't squared the table so I just went old school and got this far. Old school really isn't all it's cracked up to be.

Since last week my friend said the table is now square. Perhaps, and this is a possibility I could calculate and send him an autocad file of the shape for the bottom of the plywood out of 1/4" whatever, clamp it to the 3/4" wedge piece, turn it sideways, clamp it and just grab a jig saw or sawzall and free hand carefully. This is not as precise, but it's safer than the router...and much cheaper if he can cut the shape...correctly.

[bfish]

Originally posted by Steve Mac:
...Ya gotta appreciate how simple this is.

<font size="2" face="Verdana, Helvetica, sans-serif">Then how come you're still jackin' with it?

[Steve Mac]

OK, I ordered a bit that's still top mounted but smaller than the one I have which will simplify things. So I'm going to have to wait a few days. This is the bit I need: Router bit - top mount ball bearing
That'll give me a bit more time to get the jig perfect anyway. I'm pretty sure I may find use with this setup when I tackle filling in the sides of the wedges so...halftime. Where's the cheerleaders?

[Steve Mac]

Here's the jig...
The first pic shows two pieces lined up together in the jig:
Two wedge angle pieces lined up together.

The second pic shows the two pieces lined up with the spacers pulled out of the jig.:
Two wedge angle pieces lined up to cut the dimension of the bottom side of the piece.

The third pic shows the two pieces with one of the two spacers pulled out which would find the edge right in the middle:
Two wedge angle pieces set to cut middle dimension

I'll have to make one more spacer half the thickness of the two spacers shown to work the cuts. If I want to double the cuts, yet another spacer half the thickness of the thinner one just mentioned.

A little more work to set up, but very safe and pretty cool.

The only weirdness is that I can decide whether I want to fill the edge or sand the edge.
This is illustrated here:
Sand or Fill ???

<font color="#FFFFFF" size="1">[ December 13, 2007 09:01 PM: Message edited by: Steve Mac ]</font>

[jnorv]

Got a link to your new router bit?

Jim