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Hello,

Would like to get some feedback from the group. Which mold style do you prefer? For D, it could be any variation on the theme such as a clasp on one end and hinge on the other.

Please add E for other and post a pic if possible.

Appreciate any feedback!



Brad


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C or D.

MDF make poor molds
C or D I recommend matching spreaders

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I like D. I have a bunch for various sized guitars and ukuleles. I go to a great guy that just posted before my post that makes them.

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D with spreaders. Here's the one I made for my dreadnought shape. The upper bout spreader in the photo turned out to be unnecessary. I also originally made a lengthwise spreader that goes from the head block to tail block. Never found that I needed that either.

The spreaders in A eliminate the option of leaving them in until after the box is closed. I like having that option. I would not make a mold shaped like B. It would be very heavy. B also doesn't lend itself to clamping things like side braces. You would have to remove the rims from the mold to clamp side braces at most locations on the rims. The outside shape of A would make clamping while leaving the rims in the mold easy.

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Mine are all of the C variety with a spreader from tail to heel to ensure that the blocks remain square during
assembling and closing the box. I wouldn't venture to say that one is better than the other though.

I make mine from two layers of plywood, with spacer blocks (from ply cut offs) in between; I think spacing them out helps keep the sides vertical. Of course, you have to make the mold that way to begin with. I see no advantage in having the mold split apart at the ends. Once the sides have been trimmed to length and glue to the blocks you should only need two spreaders; one at the waist and one along the length, but the upper and lower bout ones help get you there.

I think my forms must be similar to Alan's.

I know now what my next mood is going to look like! Never thought to space them out like that.

I like the screw pressure points further away. You can make a lighter weight mold without the spreaders deforming it.

This one is also tapered so i can leave it in the mold while I put my top and bottom linings on and also gets it out of the way of the dish sanding.

Pat

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Pat

Tapering the mold is a slick idea.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Brad—

Like this:

https://www.luthiersforum.com/forum/vie ... hilit=Mold

D. All the way. I like being able to quickly open and close my molds. My last two have been four layers of 3/4" birch ply, but my first few from Bluescreek have been three layers. I think I prefer the three.

D with spreaders and I secure the neck and tail blocks
I want to hold symmetry and control the neck block until the box is closed.
I use the same basic design and the martin production floor before they went with aluminum molds
a few years ago.
the better you control the body in the mold the better the fit , finish and geometry in the end result

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Following up on my post above: On my molds, I adopted John Hall’s approach of using screws, driven in from the outside of the mold, to secure the blocks to the mold at the center lines. The center lines get covered by either the tail wedge or the neck later, so why not? It avoids the use of a head-to-tail spreader. Great idea.

I favor the connecting bolt through end tab approach, because it is light and strong and the bolt is never in the way, like some connecting systems could be. It is slower to connect and remove, but I don’t mind that.

Option C in three layers of 18mm/ 3/4" birch plywood. 2-1/2" width to resist spreading, with outside shape closely following body shape (all the better to allow clamping) with carriage bolt & 1/4-20 nut closure. I frequently found clamping from end blocks to mold necessary (e.g., neck, tail block glue-up), so any closure at the ends of the mold (as with D) just got in the way.



Being able to clamp to the head block or tail block avoids the need to screw or bolt into the mold, and with the use of the mold as clamping form for those blocks at rim glue-up, the distortion sometimes seen with blocks glued to sides out of the mold is prevented.



Four layers of ply did not allow use of the mold in the radius dish without losing registration between mold and body (a big no-no), while two layers was a bit scant on clamping area and support for acoustic guitar-depth bodies. A 5/8" hole through the neck end of the mold allows safe, secure hanging of a rim using a screw-in ladder hanger (heat the last bend in the hanger to reshape). Worth noting that all spreaders are sized to come out through the sound hole after the body is closed...usually after one end is unscrewed.





Finally, give some thought to storage. Outside molds take up some room once fabricated. The best argument for adjustable molds for the hobby builder is exactly this space argument. We solved the problem with some minor adjustments to the shop.

And yes - I am back at Greenridge for a few weeks, providing a useful set of fingers while Todd (aka, The Boss) recovers from his hand surgery.

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It’s C for me. I prefer plywood, 1-1/2” thick, bolted together. A thicker mold gets in my way during certain operations. There are a thousand ways to skin a capybara...

M

Why would MDF make a bad mold? I don't use molds but I use MDF a lot for other fixtures. I always finish it with a floor varnish in case it gets wet. I like it because it's always dead flat.

MDF is too heavy for us aged type.

One little trick I learned is that when I cut out the outside mold, the inside pieces become the bending jig for my Fox bender. A quick pass on a oscillating sander to make the kerf a bit wider and and bingo, I'm ready to bend.

Any of them except C. C works fine but, it takes significantly more sheet material to make that style. Those extra couple inches on each end can sometimes mean needing to get an extra sheet of ply.

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I use a D-style that is 1" shorter than the final body depth, shaped to match the slope of the back. I have removable feet to help register the sides level for the top against the bench, with the back facing up. Then I take a small Dremel circular saw that has a flat side surface that I use as reference (it sits 1/2" from the blade) to slide along the mold and cut the body to the correct slope. If not for that I would go C... but being able to cut that slope is a big time-saver. Once I make that cut I can go to the radius dish for a quick true-up on the top and bottom before kerfing. Down side is that I make them from Baltic Birch and they are heavy. Got this approach from Somogyi.

I like the Kinkead style.


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The only solid form I have made was the first one. The rest are plywood with the spacer blocks, as Alan describes. Much lighter. I use two spreaders; one longitudinal and one across the waist. The outside profile is a uniform 2" larger than the pattern, which simplifies clamping the sides in place to trim the ends accurately.



I use 1/4" bolts and wing nuts to join the mold halves. They are fully inside the perimeter of the mold.




In action.

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John

Here in Los Angeles (and I imagine at any large dealer), I buy a lightweight MDF, which is significantly less weight than the standard MDF, but seems just as durable to me. I use 1" MDF for my fixtures and things, including side laminating molds. As has been said, it is flat and with a finish, quite long lasting. Also, no voids as in some plywood, from the veneer being pieced together, and it is pretty cheap.