Official Luthiers Forum!

Hello all. Here's another series of questions...

I bent the sides on my OM yesterday (using a bending iron) and left them in the mould with spreaders overnight. There is some spring-back so I think the waist needs a little more work. I would like to know a few things.

The first is how tolerable should I be with spring-back? I.E if I have then out of the mould how much should I allow them to go out of shape before thinking about getting the bending iron back out? I have bent sides before but they were walnut which was soft like butter whereas these sides are padauk and a little more tough (so maybe more spring-back is expected?).

Once I am happy with the above I then move onto my next question. Woody_B gave me a tip a while ago about how to accurately cut the excess off the sides ready for joining in the mould , however, is there an easy way to locate exactly where the neck and tail block goes? Obviously I need to make sure the neck block is perfectly glued & square. Again while on the topic, I have seen a lot of people who pre-cut the mortise and a lot who wait until the box is closed. I think with my tools I would be best to do it beforehand. What is a good way to do this and how deep/wide should the mortise be?

lastly (until I think of something else), I was given a neck blank by someone who used to sell guitar quality wood before he started getting too many orders on regular lumber to keep up with the luthier side of things. It is Alaskan yellow cedar and I know it is good quality, however would this work on a steel string? From what I have read and pictures I have seen, it has been used on classical guitars before. I know Spanish cedar is used on necks, but this looks completely different.

Thank you .

Peter-
If the sides conform pretty closely to the mold when I have the waist spreader in place, I'm happy. I don't 'crank in' a lot of pressure with the spreader- I like to be able to easily make the side conform to the mold with hand pressure at the waist. It's 'lumps and bumps' that would send me back to the bending iron. Some (say 10mm or less) springback at the waist doesn't worry me much. The linings stiffen things up a bit anyway.
Other builders like to have the side 'perfectly' bent, but I'd rather have a bit of springback rather than chance scorching or hardening the side with too much time on the iron.


IF you are going to use M&T and cut the mortise in the block before gluing into the body, you do need to get it positioned accurately. So some careful measuring and marking is in order; you could even consider using CA to fasten a few small positioning blocks to the inside of the sides- chisel them off later.

However, I wouldn't use that method.
I use bolt-on non-M&T style.
When I built a few M&T bolt-on guitars, I routed the mortise after gluing the box together.


Cheers
John

Thanks for the reply John.

How do you route the mortise after gluing up the box? I have a few sets of neck bolts lying around so I was planing on using those rather than using a set neck. My main concern is how to ensure accuracy when doing the job.

Any other advice is greatly appreciated.

Peter-
You just have to make up a jig to guide the router cuts. If you search around you should be able to find some pictures. If you plan carefully you can often find some spots to fasten the jig in place with screws rather than depending 100% on clamps.
Bill Moll's jig is a nice example:(you have to sign in at MIMF to get the library links to work..)
http://www.mimf.com/library/body_mortise.htm
I'd really recommend just using a butt-joint with bolts - much easier and plenty solid enough.
Glue the fingerboard down, bolt on the neck.
I set hanger bolts into the heel with epoxy; you can also use threaded inserts in the heel if you are careful.
The holes can be enlarged a bit if necessary for fine adjustment at assembly.



A more complex version with the fingerboard bolted down:
http://liutaiomottola.com/construction/Bolton.htm

Cheers
John

I have never looked into using just a butt-joint bolt on neck however it seems like it may do the job. I assume you just make the neck as per usual (minus the Tenon). I have 3 or 4 sets of neck bolts I got from LMI when I placed an order a while back. I will have a look around for some photos etc.

Thanks again.

Peter-
If you look around, you should be able to find bolt-on hardware in the UK- it's commonly used in the knock-down furniture world.
In North America the 'BigBox' home improvement stores all sell similar hardware.


re- building neck-
Since my drilling jig indexes off the guitar top, I drill (starting) holes in the heel with the same jig before I glue the fingerboard to the neck. Otherwise, pretty standard stuff -neck is completely shaped and finished before bolting/gluing to the body.

Cheers
John

Thanks for the reply again. I'm working for another 6 days before my next day off work where I can get more than 1 or 2 hours of work done.

Be careful with the drilling guide that John shows. The lip that catches on the top of the guitar must have an angle that is over 90 degrees. You have to take into account the fact that the top does not meet the sides a a 90 degree angle. the angle is more like 92 or 93 degrees. You'd think that a two degree difference wouldn't be enough to worry about but I found (the hard way) that it raised the gauge enough that the holes don't align with the neck holes. The extra 3 degrees doesn't cause a problem when doing the neck side. It catches just fine.

I don't use the bed bolts that John shows. I use screw in inserts. Because the inserts, (or the bed bolts) would be screwing into end grain, I drill a 3/4 inch hole all the way though the heel and insert and glue a 3/4 inch hardwood dowel. The inserts then screw into side grain which is much better. The fret board and the heel cap cover the ends of the dowel.

Good point. This will depend on the arching of the guitar top, so pay attention. Make sure that the jig 'lip' is no bigger (wider) than necessary and that you are getting good contact between the inside 'corner' of the jig and the centerline of the guitar body. It hasn't been a problem for me.


Threaded inserts are commonly used and work well.

If I were screwing the bolts into the heel, I'd use a dowel as Mike is suggesting. Threaded inserts are even more problematical and the dowel is even more important as the inserts are, in my hands, quite difficult to insert securely and squarely into a skinny heel without worries about splitting. Getting the hole size 'just right' can be tricky. It's also a bit difficult to 'lock' the insert into place without fouling the threads. I epoxy the bolts into oversize holes, which is a much stronger alternative. That's a technique from the boatbuilding world where hardware bolts (including keel bolts) are often epoxied into oversize holes.
(A very small 'blob' of epoxy putty sets the bolt into place in the hole. Once that is set (10 min), a syringe is used to fill the hole (from the bottom) with WEST epoxy. It will need a bit of 'topping up' as the wood absorbs the epoxy.)

Lots of ways of doing this will work just fine.

Cheers
John

I have actually given up on doing it that way. It is just prone to too many mishaps that make you pull your hair out later. I now glue the block up solid (and the tongue is solid as well) then route the truss rod access and the mortise right before I glue the top on. I find that it is MUCH easier (and faster) to do it this way.

Just my .02 worth.

_________________
Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Regarding the drilling jig angle. I am making this guitar with a completely flat top, so I assume that I will be able to use a 90 degree jig still whereas if I used a radii on the top I would have to account for that?

Are you saying if the top had a radius you would have to cut the mortise on an angle, or your jig couldn't be a 90 degree ledge?

There is a variation of this that works like a charm for cutting mortises. You could make one if you preferred.

http://www.luthiertool.com/edge%20vise.html

_________________
Brock Poling
Columbus, Ohio
http://www.polingguitars.com

If you are talking about the jig for non-tenon bolt on: You should be fine- just don't make the locating 'lip' on the jig.too wide. Adjusting the holes a mm or so with a rat-tail file is not big deal in my book - with the fingerboard glued down and the bolts tight, the neck is not going to move.


Brock-
I think Peter was referring to Mike's comment about my drilling jig (to position holes), but I may be wrong.

Cheers
John