Building a mold

[thistle3585]

I am building a mold for an octave mandolin. It is a reproduction of a 30's era Regal Octophone. I have a couple questions. It is made from 3/4" plywood. The mold is split in half and I have a corresponding inset to push from the inside out. Also, I made two sets and will space them so that I have about an inch of the sides exposed from the top and bottom. Hope this is clear. My questions are:

1) Mold edge width. I cut two halves out of a narrow piece of plywood, so the width along a short section of the side is about 1" wide. Should I be concerned that the mold will flex there.

2) How much of the sides should protrude from the mold?

3)Should I treat the mold with anything? Maybe spary a coat of lacquer or something similair to seal the wood?

4)What is the best way to join the two halves, left and right not top and bottom? I've seen various types of brackets. What is best?

5) Should I have cut the mold from a single piece instead of having the two halves?

6) Anyone willing to show pictures of their molds? (Not you Mr. Newell, I think you alum molds will put my to shame.) http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif

Thanks for your help.

[arbarnhart]

I am just cutting one for a 2 point. The pattern is on the board as I type. I am using the old Siminoff book, though following a different plan (not making an F). I am going with a one piece 3/4" partly because that is what the book says to do and partly because that is the only way I will feel absolutely sure I have the form all in one plane and properly spaced.

I think an inch on the outside is enough. If your spreaders have the right shape there is nothing to cause a bulge.

If you put lacquer on the form, it will get on your sides and could cause problesm when you stain. You could sand it off, but the side will be sanded pretty thin already.

I am using a scroll saw and keeping the center piece intact also as a shaping aid for bending. I am cutting spreaders separately rather than cutting up my center. I will use my actual block/points (one solid piece - Phoenix style).

Anyway, recapping - a single piece mold of 3/4" is what the old Siminoff book calls for. I also plan to use it for more than one and think it will be sturdier and handy to take to the wood store to shop for backs. I will not put finish on it because it would get on the mando sides.

[Gail Hester]

Here’s a form that I made recently to build my first mandola. I laminated two thicknesses of cabinet grade ¾” Birch plywood. The coupling blocks are ebony and I applied a thin coat of epoxy on the inside of the form as I've experienced problems with excess rim glue if you don’t coat it with something. I don’t use an inside form.

I have a similar form for building F5s but the mandola form has an improvement placement where it comes apart thanks to John “Sunburst” Hamlett which makes the form significantly easier to get apart. Good luck!

[Stephanie Reiser]

Arbarnhart (and everyone else),
Caution using the first Siminoff book:
Apparently the body outline from the first Siminoff book
doesnt quite fit a standard F-model mandolin case. The new book has this corrected.

[arbarnhart]

I am using a different plan - a two point - that is basically just drawings with no instructions. I am using the Siminoff book, some info emailed from Rolfe (because I want to build Phoenix style) and some pages he pointed me toward.

I did find a page on MIMF about mistakes in plans. Siminoff is not alone...

[Mandoborg]

Ever consider an inside mould ?

After building 20+ mandolins with a mold just like the one above, Dave Smith turned me on to the book 'The art of violin making ' and using an inside mould. There are so many ways to do the same job, but i personally found it much easier this way. When i used to fit blocks on the outside mould , it always felt like i was pushing and pulling the rim out of whack every which way and using wedges everywhere to get everything to fit, with the inside mould, rather than pulling the instrument apart, it all seems to close in around the mold and that , personally, felt better as i was doing it.

Inside moulds also take up a lot less room in a tiny shop ! # #http://www.mandolincafe.net/iB_html/non-cgi/emoticons/tounge.gif

Inside moulds are a breeze to make so give it a shot, if it doesn't feel right for you, toss it out, nothing lossed, but something learned.

Jim Combra

[arbarnhart]

One of the reasons I am removing my template intact is the possible use as an inside mold during bending, especially the points. But don't you still need an outside one for assembly?

BTW, I am also cutting a template for all major parts - a wooden set of plans - so I can use a pattern following sander on my drill press.

[arbarnhart]

Got it cut out:
http://home.nc.rr.com/abhobby/images/mando%20form.JPG

[thistle3585]

mandoborg, do you have a photo of an inside mold in use?