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JLMCDANIEL
Re: Build your own cabinets
waltdeckhouse wrote:

Thanks for the discussion.Obviously I have a lot to think about. I planned on making the mantle out of a built up box. The $ cost of solid mahogony is too high...so I will use cheaper materials inside. I need to start laminating pieces together this week.

Walt,
If your building a box anyway, you might want to consider a torsion box and a french cleat. The torsion box would cut down on the weight and the cleat would be a lot easier to mount that the whole mantle.
Jack

goldhiller
Re: Build your own cabinets

Walt,

Solid stock or faced-ply wood for the top and bottom of this mantle shelf?

Have you got enough solid stock to make the sides/ends?

If ply is okay with you for top and bottom, you could make it up as a box with sides and a bottom. Place a few braces from front to back inside, but keep them narrow enough to allow your top to insert/drop in. Then drill X number of holes thru the "back" of the unit for anchoring bolts/screws (hex -head tapcons, maybe?) Position the unit and carefully mark thru the bolt/screw holes to the brick. (helper would be mighty nice) Remove unit and drill the holes for bolts/screws. (hammer drill or better yet.....SDS) Hoist it back up and drive the bolts/screws with a socket and rachet. Drop the plywood top in. (Have top edge of mantle sides rabbeted so the top rests on the shoulders of the rabbet)

Yes, this will leave you with a visible seam around the perimeter of the top and the bottom. That can be used as a visual advantage/feature if you make it say 1/8" wide and call it a "reveal". If a "seam/reveal" bothers you or the wifey, then will have to try for a plan b....or c......or d.

Reason for ply would be that it is far less apt to cup when exposed to differing heat and humidity levels. Depending........the bottom of mantles *can* get so hot that you can barely hold your hand on them. Solid stock is apt to cup/twist, particularly if flat sawn stock is used.....and might do so even if quartersawn stock is used. The higher you keep the mantle above the firebox, the better.

Also....with ply you don't have to deal with all the expansion and contraction of solid stock.

waltdeckhouse
Re: Build your own cabinets

Just to update...I have complete wrapping the nearby post with mahogony. I had a rough time getting the pieces to sit flat and tight to each other...with scribing to the wall. In the end, it came out OK and that side of the fireplace looks 300x better.

I have no plans to modify the hearth. We removed the brass fireplace front (with glass panels) and replacing it with a simple chain curtain. All the pieces are black so it looks more appropriate around a fireplace (at least to our tastes). I am waiting to install the curtain until I have filled all the various holes the previous owner left for me to enjoy. There are holes in the mortar and bricks...on both sides of the chimney. When I removed the brass front it became evident the bricks above the firebox are sooty and the mortar near that area has become dry and crumbly. I was planning on chipping it out and repointing...but then it was suggested to let the chimney sweep guy handle it. He was supposed to come yesterday but cancelled at the last minute. (Note: that sort of thing is what motivates me to just do it myself). As I was warned about sweeping the flue I will probably leave that to the expert. I am waiting until all the issues with the flue and chimney are addressed before installing the metal curtain and the mantel.

I will consider the mockup idea. I can probably make it with 2x4 material laying about. that will def. help sorting out the proportion issue.

Just as background...finding hardwood materials in my area is not easy. usually it requires 1/2 a day worth of driving. When I bought the material for the post wrap I picked up extra quater sawn mahogony for the mantel. At the time I did not know how thick DW wanted it...so of course I did not buy enough. To save another lost day of driving I planned on using cherry for the core of the mantel and then wrapping it in resawn pieces of the mahogony. What I am hearing is maybe I should make it out of PW and then wrap that in mahogony?

I will make up a drawing of the cleat I was thinking of mounting with. I am a bit confused on the wording for some of the suggestions on how to mount the mantle.

BTW..what is a "french cleat"? Also...what is a "torsion box"?

JLMCDANIEL
Re: Build your own cabinets

French Cleat

Can be made as simply as taking a 1X and rip sawing it in the middle at 45 degrees.

torsion box- think egg carton. Interlocking dividers with wood glued on the top , front, and edges. Nakes a very stable, solid light weight plateform.
Jack

goldhiller
Re: Build your own cabinets

Walt,

Torsion box.......think hollow-core door for a super-cheapy example. Ever take one apart? Pieces of cardboard on edge, 1" perimeter frame......with 1/4" ply faces.

Your solid wood core of cherry with mahogany laminated to that might work. It'll be heavy......for better or for worse.

My concerns as relates to your original design/notion is that solid stock may/will have greater tendency to cup on you. The bottom surface of the mantle will be exposed to more drying heat than the core or the top as the heat from the firebox rises. This drying will create stresses that *may* tend to cup solid-stock material on that particular type of *stark* "floating" design. What I mean by that is that there is no intermediary slanted piece to shield or deflect the heat/drying effects. Hence the caution to keep the mantle as far above the firebox as possible to minimize these effects. The bottom of a big flat piece of mantle stock will act like a catcher's mitt to that heat....if you catch my drift.

A laminated cherry core with QS mahogany outer layer just might have enough resistance to opposing forces to hold up straight and true. Maybe. It stands a better chance than a single piece of solid stock for some of the same reasons that make plywood more stable than solid stock. (although your layers won't have opposing directions like ply does)

I'll attach an exceedingly simple drawing of what I referred to as a possible approach ....using a torsion box with drop in ply top and bottom. Might suit you (and the wifey), might not.

Gonna be mighty small unless I host and link. If you'd like bigger...say so.

( Huh. Bigger than I thought. )

Attachment: 
canuk
Re: Build your own cabinets

Goldie .... if there were relief cuts on the back .... think hardwood floors ...do you think they would still cup ?

goldhiller
Re: Build your own cabinets
canuk wrote:

Goldie .... if there were relief cuts on the back .... think hardwood floors ...do you think they would still cup ?

Yeah, relief cuts/kerfs would lessen the propensity to cupping, but..........where ya gonna put 'em on a solid stock mantle so that they don't show?

FWIW, I've made and mounted numerous solid stock mantles over the decades for wood burning fireplaces which had "minimal" under-support. (These modern "pretend" NG fireplaces don't require much "special" engineering cause things don't get that hot up at the mantle) The ones that survived in a flat condition the best are those that were 2 1/2"- 3" thick or so, at EMC when they were milled.....and had some manner of supporting "arms" underneath that also served as battons to resist/restrain the forces of cupping over the long haul. Of course, one must use common sense and caution when securing the mantle to these cross-supports so that the wood is free to expand and contract width-wise, so to speak.

One way I've used to do a solid wood "floating" design that still has these supports/battons was to bend up some pieces 2" wide by 1/4" thick flat steel stock to 90 degrees. How many depends upon how long the mantle is, of course. Minimum of two, naturally. The one arm of this bracket is attached/lagged to the fireplace wall before the stone or brick is applied....which hides them. Then the underside of the mantle has pockets routed in it to receive the support arms......and a wood cover plate to hide that portion from the underside. The mortise or pocket for the arms is a stop mortise, meaning it doesn't plow thru all the way to the front edge. The fastener holes thru the steel in the "arm" portion are elongated (or oversized enough) to allow expansion and contraction of the wood mantle. Don't draw the fasteners *too* tight or the wood won't be able to move and a crack will develop in the mantle.

If you ever have to remove the mantle for refinishing or whatever....simply remove the 1/4" or 5/16" thick cover plates, unscrew/unlag it and away ya go.

Again.....super-simple drawing that doesn't cover all the little nuances of any particular installation.

(This same approach works well for folks who want a "rustic" mantle to appear as though it's being supported by small "log arms" projecting from the wall. Just screw short pieces of "log" to the underside of the mantle for the cover-plates and you're done.)

(BTW, you can park your pickup on these things or the whole family can get up there to do an Irish jig. )

goldhiller
Re: Build your own cabinets

I'm sure you get this, but will mention it just in case others might not. The drawing doesn't show it, but those mortise pockets on the underside of the mantle are "step-mortises", so to speak. They have two different depths...or another way to say it is, the mortise for the bracket has shoulders on it...so that the bracket sets deep into the mortise and then the cover plate sits on the shoulders of that mortise. That way the cover-plate is flush to the bottom of the mantle underside.

waltdeckhouse
Re: Build your own cabinets

Wow!! Thanks for all the suggestions. I always seem to throw out the ideas that cause trouble :0)

GH..I like the idea of the metal bracket. I will have to give that one some thought. Seems like it would install much easier than the cleat idea. Of course, lining up the brackets to the relieved area will have it's challenges. I don't have access to a really big brake anymore...so I guess I could just clamp the metal strap in a vise and hammer away at it??

BTW...maybe I should put a taper of some sort on the bottom surface to let the hot air roll off? Nothing huge...just enough so the air does not end up trapped under the mantle.

BTW...totally off topic here...but did anyone notice the mortising jig in the last issue of FWW? It uses a router and is capable of cutting motises on tapered or bent pieces. Do you think it is worth making? I have a Feist (sp?) mortisting machine but I have never been crazy about the results I get out of it. I always end up cleaning things up with a chisel afterwards. Plus it take so much force to get those square chisels (with the drill inside) that it sometimes damages the wood. Just curious how others felt about that jig.

-W

goldhiller
Re: Build your own cabinets

Walt,

Got any local welders in the area? They could weld up the brackets for ya. (make sure they do it very accurately at 90 degess cause you aren't likely gonna tweak them after the fact).

Also, not sure how you'd hide the "other half" unless you remove bricks and plough/dado the backside of them to reinstall.

(Yeah, I know. Basically they're just huge basic shelf brackets. :) )

Not familiar with this FWW router thingie you're referring to.

Sounds like you have a benchtop type mortising machine. ???

I don't have any real problem plunging the chisel and bit in after the first plunge cause then there's somewhere for the material to exhaust. (Rotate your chisel so it's shedding the waste into the existing "open space" created by the first plunge.....and also take slighty less than "full bites".)

If you still have problems....it may be because you don't have the bit leading the chisel quite enough. The cutting edge of the bit must proceed the chisel a little or the plunge/slicing resistance will be high with every stroke and "charring" of the wood will result.

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