Inside Form Removal

[Jim Ayers]

I built an inside mold for a 2 point. For those of you who use an inside mold, what is the best way to remove the blocks from the form after the ribs are in place? I used hide glue and know you use heat, but I don't want my ribs to come loose from the blocks. So far its turning out really nice. I just don't want to screw anything up.

By the way, long time follower, but just a luthier poser (pretender). I love the process but have very little talent unlike most of you.

You can follow this amateur's process on my web page, Ayers Mandolins, or probably more appropriately, Ayers Mandolin, since, even though I tried to build a few mandolins before, they all reached a point where there were just too many mistakes and I stopped...

http://ayersmandolins.webs.com

[sunburst]

The blocks should be glued to an inside form very lightly with hide glue, even to the point of only gluing part of the surface, so the joints can be sheered easily. If you glued them securely, you may have problems getting them loose, and as you've surmised, heat can take your rim apart.
See if you can get them to crack loose from the form first.

[Jim Ayers]

That Worked!!! Thanks!

[MinkBrookRambler]

Once you had separated the blocks from the mold, did you have any difficulty removing the rib set from the mold?

I'm at the very beginning of the process of making a two point mandolin with an inside mold, and I'm not sure how hard it'll be to remove the rib set once the kerfing is all glued in. I haven't glued anything yet.

Here's what I've been thinking about. BTW ribs are 1 7/16" wide and 0.08 inches thick. I've made one mold with two layers of 1/2" thick MDF (for a total thickness of 1"); one layer is cut in half lengthwise (midline and parallel to the strings), and the other is cut in half perpendicular to that (parallel to, and more or less in the same location as, the bridge). I figure once the rib set is complete I could unscrew the two layers from one another, and each layer would come apart in a way that'd be easy to get out of the rib set.

A full inch thick seems like a lot to try to fit kerfing around if my sides are 1 7/16". For this reason I've considered using a one-piece 3/4" MDF pattern I have, but I don't know how hard it would be to get a one-piece mold out of the rib set.

I know violin makers don't typically have problems getting the finished form off an inside mold, but the shape of a mandolin seems different enough that I'm not sure it's a comparable process.

Any other thoughts? Chamfer the edges of the 1" two-piece mold to accommodate the kerfing? Put just one side's kerfing on, then remove the mold, then add the second side of kerfing?

I know many of you have used inside molds, but I haven't seen this specific question addressed.

Thanks for your advice.

[Bill Snyder]

The OP has not logged in since 2010 so don't expect an answer from him.

[David Houchens]

On the inside mold, I have notches cut. I only use a small spot of hide glue in the middle of the block. Then with lite pressure, use a small, slightly tapered wedge in the slot to pop the bond.

[MinkBrookRambler]

I think I can see the notches in the photo you posted. That looks like a great way to get the head block and tail block separated from the mold.

Once those are separated, do you have any difficulty removing the plywood form from inside the rim set? Is the kerfing in when you remove the mold?

[David Houchens]

It will be a snug fit. Also on two points and F model you have to be careful not to put too much pressure with the wedge. There's not a lot of give in the side between the neck block and the upper point/points. My inside form is two pieces thick with alignment pins. I remove the body from the form, separate the halves and replace one back to allow room for my top linings. Once they're installed it holds its shape without any form.

[Rick Lindstrom]

I trick I've heard of is to glue a little paper between the block and form. When you remove the form, the joint separates easily through the center of the paper. Clean up the residue with a scraper or hot water on a rag if you used HHG. IIRC this technique is used by violin makers, maybe.