Do I need a body mold?

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Peter Wilcox
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Do I need a body mold?

Post by Peter Wilcox »

It seems to me, (never having made an archtop instrument), that an archtop could be free assembled like a flat top - that is, by bending the sides to a pattern, then gluing them to the head and tail blocks, gluing on the lining and then gluing on the top and back as illustrated in Cumpiano/Natelson, and which I've done a number of times. I'd need to make a caul with a rim to accommodate the arch.
Since this is a one-off this would be my preferred method. However, never having made an archtop it is likely I'm not thinking this through and am missing something.

Let me know your thoughts about the feasibility and problems I might run into.
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Freeman Keller
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Re: Do I need a body mold?

Post by Freeman Keller »

I am currently building my first (and probably only) archtop basically following Benedetto's book. I made a body mold for two reasons - to hold the body while I glue everything together and because I use the cut out inner part to make the mold for my side bender.

The other important jig that I made for this is a carving cradle to hold the top while doing all the carving. The cradle can be attached to the side mold kind of like when you use a radius dish to build a normal flat top guitar.

The carving cradle also became a clamping caul for when I glued the top to the sides - it was a nice flat surface to back up the clamps.

Freeman Keller
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Re: Do I need a body mold?

Post by Freeman Keller »

To add a couple of things to my post above, it should be reasonable to build an archtop on a work board. The top and back are frequently parallel (ie the sides are the same height end to end) and the way the recurve works it is flat where the top joins the sides rather than the pesky angle like a "flat top". You don't have the issue of building the neck angle in like on a classical - most archtops have a standard dovetail which gets cut after the box is closed. I guess I don't see any reason not to build on a work board (with the center hollowed out), I'm just used to a body mold.

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Peter Wilcox
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Re: Do I need a body mold?

Post by Peter Wilcox »

Thanks for your input Freeman. I've already "carved" the top and the back clamped over shims on a bench, using power tools (safe-t planer, router, angle grinder and orbital sander) and will make a rimmed caul (as illustrated in Benedetto) to sit on the work board for gluing.
I don't know if it will be better to glue the head and tail blocks to the sides before attaching the top and back, or gluing them to the top (as I've always done) before attaching the sides, since the glue surfaces may not be completely flat after carving.
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Alan Carruth
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Re: Do I need a body mold?

Post by Alan Carruth »

I use 'curtate cycloid' cross arch patterns. I want the low point of he arch right over the inside edge of the liners, so I need to the have the outline settled before I carve the arch. Working in an outside mold establishes the outline from the start. Actually, an inside mold, as for a fiddle, would probably work even better, but I have not tried that on a guitar yet.

Clay Schaeffer
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Re: Do I need a body mold?

Post by Clay Schaeffer »

Fleta used an inside mold for his classical guitars - can't argue with the results!

Alan Carruth
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Re: Do I need a body mold?

Post by Alan Carruth »

The problem with an inside mold on a guitar is holding the waist in. Fleta came in from violin making, and was used to it, but on a violin the 'c' bouts are held in by the corner blocks. You push the ribs in against the mold as you glue them to the blocks. When I made 'peanut' shaped fiddles I used a couple of wood side reinforcements above and below the waist to hold the sides in; corner blocks without the corners. I don't know what Fleta did.

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Beate Ritzert
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Re: Do I need a body mold?

Post by Beate Ritzert »

I don't know if the question is still relevant, but i would like to add that i put together an archtop body without using any mold. In my case the rims had been cut from massive wood (it is an electric thinline, and i wanted to try out that approach although it is a waste of material), so keeping them in correct schape was not an issue at all.

So basically it works - and if You, Peter, already have the experience on flattops -- i do not see a reason why that should not be possible with archtops as well.

A remark regarding the bracing: maybe it is better to mark the positions on the top alone (->handling), then glue the sides with already attached end blocks to the top, and then glue in the braces (and sanity check if their fit is still correct). And then, of course, close the box.

If You have to repair an archtop, You usuallay will have to do that without any body mold, and often even without a caul

best regards


Beate

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Peter Wilcox
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Re: Do I need a body mold?

Post by Peter Wilcox »

Hi Beate - glad to see your still alive and kicking!

It's been going slowly due to lack of energy from aging, but it's getting there. It's worked out OK, but probably would have gone faster and easier if I'd made a mold. I just need to put in an end graft and install a JJB under bridge pickup (have to glue on the piezos while it's open), and then close it up and sand in the recurve.

Here's some pics with the top on, and with the back just lying on it. Next will be binding (just black plastic) and starting the neck.
Attachments
archtop-top-1.jpg
archtop-interior.jpg
archtop-back-1.jpg
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Beate Ritzert
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Re: Do I need a body mold?

Post by Beate Ritzert »

Peter Wilcox wrote:
Sat May 28, 2022 3:59 pm
Hi Beate - glad to see your still alive and kicking!
Unfortunately i still lack energy for even making the neck of my Bass VI or repairing my amps.

Reasons: an old house - isolating and more - still cannot be userd for living and restoring and improving an old velomobile (see attachments if Youre interested - that frame in the room will become a wall and the space behind it will carry my wood resources...)


I like that guitar very much! Especially the soundholes and their relation to the body proportions!

But a question related to physics: at the joint of the edges of the endblock and the top resp bottom the tension will reach pronounced maxima. How large is the danger of cracks spreading from these edges? To what degree ist it useful to round these edges?
Attachments
DSC_4659.JPG
DSC_4819.JPG

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Peter Wilcox
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Re: Do I need a body mold?

Post by Peter Wilcox »

I'm not sure which edges you're referencing. Do you mean round the end blocks here?
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round-edges.jpg
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Beate Ritzert
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Re: Do I need a body mold?

Post by Beate Ritzert »

Yes, i do. Again, that was meant as a question.

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Peter Wilcox
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Re: Do I need a body mold?

Post by Peter Wilcox »

That is an interesting question I can see that having that part of the top (or back) held firmly to the end block along a single grain line, if there were a change in expansion due to humidity or temperature it might cause a crack to form there. By rounding the block (or at least the glue area) it might diffuse that change across multiple lines, spreading out the stress.

But too late for my top. :)
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Darrel Friesen
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Re: Do I need a body mold?

Post by Darrel Friesen »

That archtop is coming along nicely Peter. Nice work.

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Peter Wilcox
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Re: Do I need a body mold?

Post by Peter Wilcox »

Slowly making progress. Body pretty much done, now that I found the courage to route the dovetail mortise without possibly destroying all the prior work. I made a template and screwed it in position over the body being held by clamps screwed to the bench too. Now onto the neck. I'll route the tenon before I put much work into it, in case it becomes a do-over.
dovetaiil-mortise-1.jpg
dovetaiil-mortise-2.jpg
dovetail-mortise-3.jpg
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Peter Wilcox
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Re: Do I need a body mold?

Post by Peter Wilcox »

Finally got all the parts done, put it together and strung it up with some cheap cello strings I had around, prior to spraying. It didn't collapse, and it makes sound.
Attachments
archtop-top-2.jpg
archtop-back-2.jpg
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Eric Crawford
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Re: Do I need a body mold?

Post by Eric Crawford »

That looks really nice.
I can’t tell from the angle of the picture, is the tailpiece bolted to the end block through the top?

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Peter Wilcox
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Re: Do I need a body mold?

Post by Peter Wilcox »

The tailpiece is free floating on a screw into the tailblock. The attachment will be covered with an inlaid Mexican 5 peso coin - I've been using coins lately on headstocks, including Indian head pennies.
tailpiece1.jpg
tailpiece2.jpg
tailpiece3.jpg
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Karl Wicklund
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Re: Do I need a body mold?

Post by Karl Wicklund »

I like the design of this, including the coin. These speaks of an individual taste, but not an attempt to grab attention by being wildly different.
Kaptain Karl

Eric Crawford
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Re: Do I need a body mold?

Post by Eric Crawford »

Very nice.
I may step the coin idea for a screw cover.
I used to collect ancient coins, and have a few of low value that would do the trick nicely.

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