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Chadmills
May-16-2007, 2:38pm
I'm just starting an "F4." Given the closeness of the head block and upper point block it feels very tempting to make both as one block, linked by a section about 3/16 thick. As an inside mould user this seems like a worthwhile simplification. I would have thought any acoustic effect would be imperceptible, plus or minus. #It would also be quick and easy to make a hole through the connecting piece so that one is left with little more wood than would be in the linings. #Why bother in that case? Just for the accuracy of alignment and fewer pieces to "juggle."
Any thoughts, "give it a whirl," "abomination," "disaster" ?
Tom

sunburst
May-16-2007, 3:17pm
It's hard enough to get the head block to fit the rim really well as it is. Fitting a block into the point and the scroll both at the same time seems like way too much trouble to me.

Also, some 60s (or there abouts) Gibson two point mandolins had both points as part of a huge head block. That's a really big cross-grain glue joint. There was some serious misalignment, binding problems, neck problems with the ones of those I've seen because of wood movenent.

The top and back have to move. They get wider and narrower with changes in relative humidity. Separate blocks let the movement happen without as much stress on the glue joints.

billhay4
May-17-2007, 9:35am
I agree with John on this. It's difficult to get a precise fit of any block, especially the point blocks. And a precise fit is important; it's what holds the rim together after all.
Bill

Chadmills
May-17-2007, 11:17am
I think I'm not making something clear so I'm attaching a sketch with the block I'm talking about coloured in.

I don't see that this will make any difference to the precision of the fit of my ribs to the blocks. #I will apply the short piece of rib to the combined block before I attach it to my inside mould. #(Arguably that small piece of rib could become completely non-structural, virtually a veneer.) Or have I misunderstood the problem you guys foresee?

As to wood movements I can certainly visualise problems with the big block John mentioned, but here it's an extension in long grain of no more than a couple of inches. The rib grain runs alongside this whether there is one block or two. The cross grain aspect is no more than with normal linings.

I'm not "nailing my colours to the mast" on this, just interested, so thanks for the comments above.
Tom

Chadmills
May-17-2007, 11:20am
Here's the sketch

sunburst
May-17-2007, 11:54am
Hope you don't mind my borrowing and modifying your sketch, but here's the problem I'm seeing.

Normally, when you fit the head block to the rim you have to have good contact between the ribs and the block from A to B and from C to D. Not only does that all have to make good contact with the rim, but the rim has to simultaneously make good contact with the form for that whole distance. If you are as picky about the shape of the mandolin as I am, that's a tall order. I use an outside form, and I want my shape to deviate from the form by less then 1/64", especially in the head block area where a line moved can make a big difference in the overall look. Getting the kind of exacting fit that I want all the way from A to B and from C to E just seems like too much trouble to me, especially when I don't see any benefit from doing it that way.

thistle3585
May-17-2007, 11:57am
Correct me if I'm wrong, but didn't older Gibsons, including Loars, often crack between the scroll and the bass F hole as a result of the scroll block being fuller than the one posted above? I believe Phoenix encompasses his head block with his point blocks.

sunburst
May-17-2007, 12:29pm
Yes, a lot of old F5s have a crack in the area between the scroll and the fingerboard extender. It is usually caused by the cross grain glue joint between the top and the head block.

Yes, Rolf incorporates the points of the Phoenix mandolins into the head block. It's all one piece of willow, with no rib material glued to the outside between the points and under the neck heel (he colors that part so the wood doesn't show). I'm not sure what orientation of the grain he uses in that block, but with his epoxy butt joint neck attachment, he could orient it to avoid a cross grain glue joint with the plates, and perhaps he does.

Chadmills
May-17-2007, 5:26pm
Many thanks John, I thoroughly appreciate your input, and see the issue.
I'm intrigued enough to give this a whirl. I've cut out a combined block and it makes a nice sculptural shape (not that this is relevant at all!) I'll see how the fitting of the short piece of rib goes since if I'm not happy at that stage I can revert to convention, cutting it back into two blocks.

I'll aspire to 1/64! At present my target is probably about 1/25, ie 1mm over here in metric-land.
Tom

markishandsome
May-17-2007, 5:44pm
Gosh, I currently consider 1/4" a good day's work. Guess it's back to the shop for me...

Chadmills
May-17-2007, 5:48pm
I did say "my target is" !
Tom

sunburst
May-17-2007, 6:11pm
My methods and measurements are a curious mixture of metric and inches. I'm pretty comfortable working in either one, but on this side of the pond, it's hard to find good metric measuring tools, so for most things, inches it is.
I've found that I've developed my eye to where a very slight deviation from my drawings gives me an instrument that looks different than I planned. I find that moving a line 1/32" (a little under 1mm) or less, can make a very noticeable change in some of my drawings, so I try to work to tolerances well within that.

Chad, if you get the one piece block glued to the rim, let me know how you clamped it! http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif

Steve Hinde
May-17-2007, 8:04pm
The only advantage I see, is the area at D is the weakest part of the rim before the top and back are attached. Sometimes I take the rim out of the mold. When I put it back, this area takes a careful hand. The mass of the head block and the point block don't give. That thin little side can snap, especially in highly figured Maple. Another 1.5 cents. Or sense? Back to the day job, can't afford too much of this.

Chadmills
May-21-2007, 1:38pm
Picture attached of gluing the rib to the combined block. #It just underlines that everything is defined by the block itself since it's not near the mould yet, and that since the block is doing all the structural work, the rib is little more than a veneer, thicknessed accordingly. #The outline of the block has to be cut to allow for that thickness, of course. Low effort "clamping" ! #I put a hole through the linking area as you can see. Not sure it was necessary, but as a matter of principle I wanted to keep the weight reasonably similar to normal blocks and linings.
The corner suffered from a fall. Oh well.
Tom

HoGo
May-22-2007, 6:43am
I've seen at least two Lebeda Fs with that kind of block. With no rib on the outside. Looked OK, but I think it can block some vibrations of top in that area (no problem on oval holed mando).

markishandsome
May-22-2007, 8:02pm
With that big hole cut in there it's really more like integral linings than a one-piece block. If it works for you...