H-5 Mandola tops and backs.  Click on image to see Mandola Gallery.
Exact cnc carving on F-5 scroll does nearly all the work.  Click on the image above to see Mandolin Gallery.
Why Use an Inside Body Mold?

I started using an inside body mold right around the turn of the century (suddenly I feel old!).  Anyone that has used a typical outside body mold knows the painful, frustrating process of trying to squeeze (expand??!!) all the curvy parts that make a mandolin rim into the mold.  No matter how hard you try, there are one or more blocks and side pieces aren't exactly where they should be.


The inside body mold is a wonderfully simple, elegant solution that has been standard practice used in violin building for centuries.  It ensures that the blocks are exactly where they should be, and if the blocks are where they should be the sides will be also!  It also makes bending sides and assembly much easier.


How To Use an Inside Body Mold (with some side bending tips)


Here's a picture of an inside mold.  That's all there is to it.  Anywhere a block will end up, there is a cutout on the mold.  The large holes are used to clamp the sides against the inside blocks when gluing.  The small holes are for lining up the inside template.

First, the surface of the blocks that will contact the mold are cut to shape.  Place the mold on top of the wood you will be using and scribe a line where the block will touch.

Using a bandsaw or coping saw, cut the block right up to the line.  You can clean up the edge you cut with sandpaper wrapped around a large dowel if you want, but this will never be seen, so it's not necessary.
On a flat surface, place the inside mold on top of one or more shims and raise the mold off the surface about 3/8" (exact height is not important) and lightly tack glue the block in place.  At this point the rest of the block is left over-sized.
Tack glue the tail block and the front point in place at this time also.  The rear point block is not glued in place until after the long side piece is bent and attached to the neck and tail block.
With these three blocks in place you are ready for the inside template.  First, the 3/16" locating pins are inserted in the holes on the mold.  These are just plain old 3/16 wire you can get at any hardware store.
The "Inside Body Mold Template" is placed on the pins, and used to mark the blocks.  The template takes into account the thickness of the side material, so the blocks are marked the the body shape, minus side material.  When you cut the blocks on your bandsaw they will be perfectly sized to accept your bent sides.
Back to the band saw
Clean up the blocks and you are ready to start bending.
Here are a few side bending straps.
I find the more figure a piece of maple has the less water I use to bend it.  Soaking a piece of highly figured wood makes break much easier, so just dip it quick, then re-wet if needed.  Use the long bending strap to make the initial scroll bend.
Looks good, needs to be a little tighter at the end, do that with the short strap on the tightest part of your bending iron.
Scroll is done, now on to the waist.
Here's where that bending strap with the slot cut in it comes in handy.
Once the waist is done the rest is a walk in the park.  Bend the side all the way around past where the lower point will be.
Use the scroll caul to clamp the side in place and let it dry overnight.  Any cauls you will need are on the plans.  They are very simple to make from a piece of scrap 2" x 4".  Once the side has completely dried you can "dry bend" any spots that need a bit of re-bending, then we'll glue the side to the blocks.
As usual, the side un-bent a bit overnight, so after a quick dry bend it's ready to go.  You can either wax the mold or put wax paper on the mold where glue might squeeze out.
The side is glued to the scroll first.  Yellow glue is the easiest but if you are looking for historical accuracy good old hide glue is the ticket.  Contrary to anything you've heard, neither glue "sounds" better than the other.  If you are worried that yellow glue will make your mandolin sound bad the solution is tighter joints, not a "better sounding" glue.
Once the scroll is done use a couple spring clamps to hold the side in place and glue it to the tail block.  As this picture shows, the front treble side was bent and glued at this time also.
Finally, tack glue the end to the mold at the last spring clamp.  This needs to be past the rear point.  The extra will be removed after the rear point block is attached to the rim.
Cut a block for the rear point slightly oversize.  Place the template back on the mold and determine where the block will contact the side.
Shape the side of the block so it matches the side.  Use the template to draw the rear edge only on the block.
Cut the rear edge only leaving the front oversize.
Bend the rear maple piece, and glue it to the block.
Trim the maple to mate with the side and glue it to the side.
Place the template back on the mold and draw the front edge of the rear point.
Cut the block right up to the line on your bandsaw and clean it up.  Cut right through the rib and remove the piece that was tack glued to the mold.  Use a caul to hold the rear point in place.
Clean up the front side piece to match the front block.
I prefer to bend the front point bend first on this side piece.  Then, after getting the front bend to fit well, holding the rib against the mold, roll the rib around to the back point and determine where the rear bend starts.  Make a small pencil line on the rib and bend the rear point.  Once both front and rear point fit well, make the large radius bend in between the two.
To glue the sides you will need the front and two rear cauls and a bit of wax paper.
The next is to flatten the top side of the rim set.  You can build the rim set with the top of the bottom side facing your workbench.  I prefer the top down so all the blocks and side pieces are even.  It makes flattening the top easier.

Tape a piece of 120 grit sandpaper to a flat surface and push the rim across the paper until fresh wood is exposed on the sides and blocks.  If you were careful making the sides you should not need more than a few strokes.

Use a 1/4" or 1/2" chisel and small hammer to remove the blocks from the mold.  Start gently working from both sides if the blocks are stubborn.  Increase force until the blocks break free.  Resist the urge to pry them off.  A good sharp blow with the hammer will pop them off.  In most cases a small piece of wood will break off.  That is totally normal and each block has a bit of extra wood to take that into account.
Using the plans, draw a line on the blocks to mark the extra wood that needs to be removed.  Remember the curved line on the neck block.
And that it, you're done!  Here's a couple pictures of the blocks after they have been shaped.
If you have any questions feel free to email!