Construction Question for HDBR

[Istari]

HDBR,

I've got a pair of Cornwalls that I bought from Cornwalled that are pretty beat up, actually they look like they had a rough life, probably in a bar.

Short story is that they still sound great but look bad. I'd like to build replacement cabinets, in your learned opinion and years of experience at the factory are the Cornwall boxes that difficult to build? I know that you had jigs for accurate cuts and measurements and clamping devices that held everything together but....

I've looked at the construction of the cabinet, they are birch, black and are butt joints, with 3/4 inch inside supports. If I can find Baltic Birch locally, I've got access to a ShopSmith and will attempt this. Looks like straight cuts, accurate measurements, lots of glue, clamps and staples and taking your time would get a person a cabinet that looks and acts like the original. Have you build any Cornwall cabinets, I know that you built several La Scala pairs with great success.

Any advice??

Thanks!

[jnorv]

I have another question for the Builder. How do you make that 30 degree cut on the front edge of the doghouse on the La Scala's? My table saw only lays of=ver to 45 degrees.

Jim N

[HDBRbuilder]

Hobbit,

Yeah...I have built a few thousand birch decorator Cornwalls...LOL! And yes, they are not rocket science to build...but the key is to have ALL the parts PERFECTLY square. On the butt joints, there was always an ever so slight proudness to the overlapping sides that was puttied-up then belt sanded flush with the top and bottom panels...so keep that in mind when cutting the parts and allow for the overlap needed. Depending on whether the birch examples you have are flush-front models or inset-front models would dictate how I would have to explain the building process, though.

JNORV...

Think about it a minute...ok...do I still need to answer that question? LOL! OK...tablesaw 101 in session: Those cuts are made with the saw blade kicked over just 30 degrees...you have to CAREFULLY run the panels VERTICALLY along the fence to make those cuts...and be SURE that the blade is EXACLTY at 30 degrees, or the "toes" of your doghouse won't go together right...actually...it is best to have the saw blade kicked over to around 29-1/2 degrees...this ensures a good toe fit in assembly. Keep in mind that if your saw is a right-tilting arbor...the fence needs to be to the left of the blade when doing this...vice versa if your tablesaw is a left tilting arbor! Many folks build a jig that snugly slides across the table top using the fence as its guide...kinda like a snug-fitting(but still able to slide easily back and forth)inverted "U" (that wraps over the fence)with a tall panel to clamp the workpiece to in order to keep its tendency to bow in check, while making the cuts. You can find this jig in most table saw jig books and pamphlets...a handy thing to have aorund for this kinda work...alot safer to use too!!

If You are talking about the angles for the wing parts...I built a jig that allowed me to clamp those parts PERPENDICULAR to the "fence" of my miter saw(IOW...aligned parallel WITH the blade, when the blade is set to "0")...in order to cut the 60 degree end of them...with the blade set at 30 degrees...then after cutting them, I just put them to a pre-set stop on the miter saw fence and cut the 30 degree miter on the other end(remember...I ripped my stock to 3" width and oversize in length to begin with)...for the wing parts.

End of Tablesaw 101, Lesson 1.

[jnorv]

Builder, I don't think it is quite that simple. I have tried that cut before and it never turns out what the front edge of my LS's look like. Actually for that to work the saw blade has to just kiss the fence. I have an old Sears table saw with the cast iron table so it is relatively stable. Not nearly as good as the saw I got to use in Richland, wa that had ball bearing table slides. great saw. Manhatten project leftover. Only the Feds could afford that.

Jim N

[HDBRbuilder]

JNORV...if you build the jig for the table saw...the blade barely "kisses" the bottom edge of the jig...if you DON'T build the jig, then you need to install a "sacrificial fence" piece of wood on the right side of the fence instead. I never said it was EASY...I just said that is HOW IT IS DONE!!..LOL! It was also how it was done at the factory...I cut zillions of them!!

[djk]

I've built dozens of LaScala with an old Sears tablesaw.

Tilt the blade to 30*, dry fit some test scraps to get it right.

Screw a scap of plywood onto the fence so it sticks straight up. My fence came with a couple of sloted holes for this very purpose. I use a 12"H X 18"W piece, bigger is fine too. Slide the auxillary fence right up to the blade. The wood goes straight in vertically. You must have a scrap to use as a push stick that is at least 4" longer than the diameter of the blade, this keeps the cut-off piece from falling back into the blade (actually, the next piece acts like a push stick until you get to the last piece). Cut the 3" wide ramps all in one piece, go back and rip down to 3" wide after you have cut the 60* (board fed vertically) and the 30* (board fed horizontally).

I used a brad nailer on the 'V', 8D galvanized casement nails for everything else. Blunt the point of the nails so as not to split the plywood. Use the best plywood you can get, I used 9 ply AA oak.

[Istari]

HDBR,

I'll attempt the recessed front model, that's what I have now. Do you thing the flush front is a sturdier/prettier version?

Any info would be appreciated.

Jim

[HDBRbuilder]

Hobbit,

If you plan to rebuild your Cornwall cabinets, then you have three options:

1. Rebuild them just as the originals are, using birch plywood...BUT...keep in mind that the birch plywood ORIGINALLY used for your Cornwalls is NO LONGER AVAILABLE...so you will have to settle for the birch cabinet-grade plywood with 5 core plys and two outer birch veneers(the original plywood used had 7 core plys with two birch veneers and was specially made up by Georgia-Pacific for Klipsch and was "void-free"). If building these, you can salvage your fronts(motorboards) and/or use them as patterns for routing new ones for your cabinets. I would also recommend adding an AIRY "ladder-type" horizontal brace inside the cabinet, between the sides above the woofer to provide a side-to-side internal brace between the sides...ensuring this brace is glued and solidly affixed in order that it will NOT provide any unwanted resonances from its addition. Now if you decide to rebuild the cabinets in this manner, remember that you will still have the end plys of the sides showing at the top and bottom...as well as end plys showing on the front edges of the cabinets!

2. You can rebuild your cabinets to be flush-front style cabinets...but in doing this, you will have to decrease the front-to-rear dimensions of the parts used before assembly...except for the front panel(motorboard), which will have to be increased in its vertical dimensions. Again, the horizontal interior ladder brace is recommended. In this cabinet design, you will have the edge plys of the sides showing all the way around the perimeter, the front edge of the tops and bottoms will be covered by the speaker front(motorboard), and the top edge plys and bottom edge plys of the speaker front will show. Not only that, but the outside speaker dimensions will be somewhat smaller from front to rear, since this cabinet design does NOT have an inset front(in order for the cabinet to retain the same INTERIOR dimensions)...and in order to use your grille-cloth panels, you will need to add some trim all around the front edge so that the edges of your grille-cloth panels do not show. The main advantage of this flush-front cabinet design is that it is the strongest structural design of the bunch.

3. You can build your new cabinets with mitered corners. This will require the use of corner clamps during construction...with the miters solidly glued-up, then all panels clamped-up...then using a rubber mallet or something akin to it...you have to tap the panels from the inside to align the mitered edges(toes of the miters) before using glued and stapled-in glue blocks to secure these miters from the inside corners of the cabinets. Again, the horiziontal ladder brace is recommended. The advantage to this design is that the only plys that will show are along the front and rear edges of the panels...and these can be easily covered with veneer. The inset front on these will allow you to utilize your same grille-cloth panels, too...and you can utilize the fronts from your old cabinets or use them as patterns for making new fronts.

All of these cabinet types will allow you to re-use your old speaker backs. Aesthetically, the mitered corner versions will give the best appearance, but the flush-front cabinets will give you the strongest structural cabinet. If you decide to go with baltic birch instead of cabinet grade birch...then the speaker cabinets will weigh quite a bit more...but aesthetically they will not be as pleasing to the eye, in most instances, unless you decide to paint them. Even with baltic birch used, I would still recommend installation of the interior horizontal ladder-brace. If you want to go the mitered corner route...you can spend a few extra bucks for a sheet of walnut veneered plywood...or whatever veneer you like best and end up with some real beauties! With a sheet of birch cabinet grade running around 40-50 bucks...and a sheet of walnut veneered plywood running around 100 bucks...I would go for the extra cost of the fine-veneered plywood and have something special...hell...you could even get pecan, cherry, or whatever you like best! To my way of thinking...an additional 100 bucks investment in the plywood used is worth the aesthetic benefits you get out of it!!

[Good2BHome]

HDBR wrote:

"I would also recommend adding an AIRY "ladder-type" horizontal brace inside the cabinet, between the sides above the woofer to provide a side-to-side internal brace between the sides...ensuring this brace is glued and solidly affixed in order that it will NOT provide any unwanted resonances from its addition."

I would like to pursue this idea in a stock pair of Cornwalls. Is this one brace, say a 1" x 1" or several? The term ladder is confusing me (easy to do).

Mike

[HDBRbuilder]

for an example of an "airy ladder-style horizontal brace"...go to 2-channel section...look for the post titled "Going the extra mile--inside the box" by Deang...look at his pic of the inside of the RF-7...you will see two of these kinds of horizontal braces through the cabinet openings in the pic! Easier to show you than to try and explain it!

[mace]

HDBR,

You built my 1977 Walnut Oiled Cornwalls (the ones the mouse ate out the batting in just the same spot on the back boards! ). Would you recommend installing these airy ladder braces? Why or why not?

Just curious,

Mace

[HDBRbuilder]

Mace...the brace is just to eliminate the SOMETIMES...but NOT ALWAYS heard cabinet resonances found in Cornwalls when they are pushed to extremely high volumes...if yours don;t have these resonances...then leave them be. Since Hobbit is intending to build new cabinets, I just recommended this for his...so that it doesn't have to be added later on if he encounters any resonances. Ounce of prevention...ya know?

[Istari]

HDBR,

Congrats on wining the Hersey II's! Good Story too!

I've thought about going the mitered route,I have a set of Forte IIs that are WO and mitered they look great f course. Will more than likely go that route. I've noticed on the cornwalls that they use a 3/4 or 1" strip inside the box for glue strips and that these are stapled in.

Did you use an air stapler to do this in the factory?

Do you think that a rubber mallet will be able to gently pound out the motorboard on the cornwalls? I think its a good idea to reuse the motorboard and back if possible. If I'm careful, I think I can cut the box of the cornwalls out of a single sheet of plywood. Wheredid you get your plywood for your La Scalas?? I've went to a couple of lumber yards here locally and asked for Baltic Birch and they looked at me like I was from another planet...Duh, ain't got none of that,...Don't know where you go and find it either,..What's it used fer again??

I know that you ran a dissertation on wood glues a while back, to make it short, what glue do you use for your builds?

I also took your advice and purchased some of the spray on plastic/rubber coating for dampening the metal horns, was able to get it in black so I got it before asking if you'd tried it before. It seems that it would be a little better looking than gobs of rope putty.

Thanks for all of your help...

BTW where in Ft. Smith do you live... I used to go there frequently when I lived in Little Rock.

The one place I liked best was floating down the Mulberry River, did both the Upper and Lower, camped in the middle of the river at Turner Bend right at the bridge where it formed a small gravel bar. Have you ever floated down the river?

[djk]

"I've went to a couple of lumber yards here locally and asked for Baltic Birch and they looked at me like I was from another planet...Duh, ain't got none of that,...Don't know where you go and find it either,..What's it used fer again??"

Try a local cabinet shop. They usually order it from a large distributor, frequently out-of-state, and have it delivered by a pool truck once a week or so.

In the midwest Paxton is a good distributor.

Also ask for ApplePly. This comes in 4 X 8 sheets, as opposed to Baltic Birch in 5 X 5 sheets. It has the same 18 ply per inch, but with maple faces. A 4 X 8 sheet of 1" 20 ply (18 core + 2 face) hard rock maple cost me about $80 when I bought four sheets. This included two 1/2" sheets of BC (face protection) and delivery fees, $320 total.

http://www.fujimoto-mokkou.co.jp/appleply/appleply.html

The manufacturer:

http://www.statesind.com/

"products are sold to regional distributors who in turn sell them to retail lumberyards and home center stores where they are available to consumers."

They have a zipcode search that turned up 9 distributors near me.

[mace]

HDBRbuilder,

thanks for the reply. I certainly don't think I hear resonances. However, from reading some of these other posts on the 2 channel forum I may just have a tin ear. Folks talking about how CD copies aren't as good as original and about horn phase shifting due to the drivers being at different distances from the motorboard......

I think I'll leave my cornwalls be.

Mace

[HDBRbuilder]

Hobbit,

1. The staples used to secure the 3/4" x 3/4" glue blocks you referred to were duofast 1-1/8th" staples.

2. The glue used to glue up the miters at the factory when I worked there was a powdered brown glue we mixed up with water...and was a urea/formaldehyde glue, the rest of the glue used on everything else in assembly was a white wood glue. You can use tite-bond for the entire thing though...and it is readily available almost everywhere...home depot, etc.

3. You may be able to re-use the original fronts, but don't count on it...if they start to break-up where the original glue lines are...then you will need to just cut some more and use the old ones for routing patterns instead. It is imperative that the plywood used for the fronts is as void-free in its plys as possible! Keep that in mind.

4. You will need to have really good and strong corner clamps to assemble the cabinets if they are gonna be mitered ones. We used cast iron corner clamps secured by chains and a twist-type binder when I built them, but they are virtually impossible to find nowadays...so you may have to settle for strap corner clamps. Be sure to tap the FRONT miters flush with each other when building the cabinets, which means leaving the clamps just a bit loose until the front corners are tapped flush...then tightening up the clamps more in order to tap out and align the miter edges all around the cabinets. Next install the reinforcing inside corner glue blocks...then the long blocks between them(on the front portion)...then the shelf supports, then the shelf itself. It is imperative that all of these blocks are EVEN along the front...IOW inset exactly the same distance...you can use a guide block to ensure this. When stapling in the inner reinforcing corner glue blocks, be sure to glue them up well and make sure that the staples' prongs go into the body of the sides/top/bottom and not into the miter itself, or else the toe of the miter will never be tight!! the last blocks installed are the rear blocks...ensure they are inset equally too from the rear speaker edges...remembering that the speaker back needs a fgood seal there when it is screwed on. Pay attention to the way the plywood glue blocks on the front and rear of your current cabinets were installed and do it the same way...Zbut use SOLID WOOD BLOCKS for the inside mitered corner reinforcing blocks...NOT PLYWOOD!! You will also have to get some latex white caulk and caulk up the corners and wherever there is a gap between the blocks where they meet other blocks in order to get a good seal when the front is installed...same for the rear corners...where the backs are installed. of course this means a relatively close fit of all the blocks to each other...but with just a very small gap between them(about 1/32nd")...so make sure to do it this way!

Yes...I have canoed the Mulberry River many times...it can get real exciting...real fast...if a thunderstorn hits upstream while you are on it too!! LOL!

[KenLehr]

Hobbit:

I continue to use a Shopsmith purchased by my father in the early 50's. I have built several enclosures of the "boxy" style with ease. However, when the requirement is long miters, the Shopsmith, with its tilted table, comes up short. Gravity is the killer. I cut these mitered items on the table saw with an extended table.

For your miter fits, find a friend with a conventional table saw to cut those edges. You get two advantages: gravity is now helping as well as your friend who helps in guiding the cuts.

As for material (plywood), try to locate a small window shop that produces bows and bays. These guys use excellent plywood for the ceiling and floors on these units. All of my disposal fences and mitres come from these stocks.

Good luck

KenLehr