Starting out on J45

[Richardl]

Hi. Recently bought the excellent book (s) which I have been enjoying and have been busy making jigs and molds. I'm having a go at the J45. As a beginner, I have a couple of questions that i hope someone can answer (that probably show that I don't know what I'm doing)!

The first thing I noticed is how light the bracing is compared with other plans and the (only) other guitar I have made, all of which are 10 mm wide.... So presumably the instructions to make 20x10 mm brace blanks in 7-3 is a bit of an overkill in this case as they are planed to 6.3 mm.

I guess my (perhaps dumb) question is with this lighter bracing, is there more chance of failure of the body or is there more than enough meat in there for strength? I guess there must be as its a model that has been around for a while - just interested why the bracing is relatively thin.

Is there any advantage to notching the finger braces into the X-braces to avoid any liklihood of the finger braces coming adrift, or is Titebond so good that it is completely unnecessary?

As far as i can tell, the plan shows the bridge plate touching the bracing (and glued to the bracing?). Other plans I have seen have the bridge plate beveled at the edges with a 1 mm or so gap between the plate and the X-braces. Have I understaood this incorectly or doesn't it matter in terms of strength or acoustics?

Thanks
Richard

[Trevor Gore]

It's very easy to over-build a J45. The originals were made with less-than-best wood and retailed for $45 (i.e. cheap) compared to say the J200 which was originally $200. So if you choose good materials it's easy to end up with everything too stiff.

Having just re-read Section 7.1, I can see that it is not the clearest bit of writing! The dimensions given (20 x 10mm) are essentially back brace dimensions and the procedure described is primarily the back brace making procedure. You need to modify the dimensions to the X-braced plan you're using. The plan from the book can use brace blanks starting at ~15 x 7mm so you can finish at ~1/2" high at the X and a width of 1/4" (~13mm x 6.3mm), Section 11.2.2. The better your jigs and shop practices, the closer you can start to the finished brace dimensions, but the same procedure as for making back braces can be used, whilst leaving the un-gabled bit for the X as described in Section 7.1. These are the dimensions we use to get the resonant frequencies in the right target zone without risking undue distortion. Most published plans (usually taken from factory made guitars) are way over-braced when good materials and assembly practices are used.

There is no need to notch finger braces or face braces into the X braces. If you make good joints with fresh surfaces and glue with Titebond, the wood will fail long before the glue (at normal temperatures).

The bridge plate is beveled or rounded on the exposed top and bottom edges (Section 11.2.2.2) and is glued down first and then acts to locate the X-braces accurately when they are glued down. The X-braces are tightly butted up to the bridge plate edges, to which they are glued.

If you follow the procedures and plans, you should be pretty right. A good many people have been pleased with the results. However, if you do find anything else that requires clarification, just ask here.

[Richardl]

Many thanks Trevor. That is very helpful. I'm sure other things will crop up so its great that you are willing to offer advice here.

I was a bit uncertain whether i should fork out for the books but i'm very glad I did and have learned a heap. Actually, I'm a trumpet player not a guitarist and am in the proces of upgrading my Bb instrument. It's fascinating that the sound of a collection of pipes that, in most respects look the same, can sound so different. A hand-built Trumpet by a craftsperson at the top of their game can yeild a far better instrument than many of the well known mass-producers...or so I'm told. Guess I'll find out when I order one! In that case, the differences in build are very subtle (e.g. where the braces are positioned to get the right rsonane from the metal). Dont know if the topic has had the same scientific treeatment so it may be mostly trial and error.

Cheers
Richard

[Richardl]

Just noticed the upper transverse brace in 7.3.5 says 10x20mm. I'm assuming that the plan is right and its 13 x 16mm, so maybe 15x20 stock. Or do I laminate 2 bits of 10x20?

Does the number of growth rings or growth ring density have any impact on the build? It varies a lot between 2 or 23 upto 10+.

actually, I think I have answered my own Q, the brace is discussed in 11.2.2.2

Cheers
Richard

[Richardl]

Softwood species where the growth rings have a gradual transition from earlywood to latewood (e.g. the spruces and the firs). In these species growth of the denser latewood part of the growth ring is relatively constant irrespective of climate, whereas the earlywood part varies from year to year. This means that that a wider ring has more of the less dense earlywood and so density might decrease with increasing growth rate. The relationship is not consistent, however, as the density of a given ring width is affected by the genetic makeup and growing conditions of a tree, and can also be influenced by its stage of development. Therefore, particularly for timber of mixed origins, ring width alone is not an accurate predictor of wood density.

So I guess that might also be true of wood strength as density and strength are related (http://woodlot.novascotia.ca/content/le ... rties-wood).

[kiwigeo]

Actually, I'm a trumpet player not a guitarist....

Sell the trumpet and use the money to buy a drum sander

[Trevor Gore]

I think I have answered my own Q, the brace is discussed in 11.2.2.2

Yep. Chapter 7 is more about the techniques for making braces. Chapter 11 and the plans give specific sizes for the different types of guitar.

(http://woodlot.novascotia.ca/content/le ... rties-wood).

I hate it when people write about "strength". A far too ambiguous term. One thing to keep in mind is that there is a wide range of densities and stiffnesses within a species. So, for example, to say that Sitka is stronger than Engelmann is pretty meaningless, whereas to say that Sitka has, on average, a greater Young's modulus than Engelmann has more meaning. However, because the properties of Sitka and Engelmann overlap so much, if particular material properties are important to you, you need to measure the properties of the piece in your hand.

[Richardl]

I guess I was just wondering whether the number of growth rings per cm had any influence on the likely failure of a brace and how I should choose the bit to use for the most critical braces as the number of growth rings can vary considerably. It seems maybe there isnt a clear relationship. Bought the trumpet. Plays well ! A decent drum sander would be nice though.

Cheers
Richard

[Richardl]

Hi - I've recently completed the soundboard, braced carefully at 45% RH (or a little below). It has been sitting at about 55% RH in the house for a day or two and has developed quite a convex curve (from the outside as shown in the book). I'm assuming that the rest of the glue-up will also need to be done at the same RH - i.e. the back bracing and the assembly - back to sides and soundboard to sides. I'm hoping when re-dried, the sounboard will come back to it's oringinal shape!

My question is, is there sufficient cross-grain distance in the sides, to necessitate bracing these at reduced RH as well?

I usually do woodwork in the garage at home so working at 45% RH requires moving into a room in the house and dehumidifying for a few days, so I'm interested to know the steps where RH control is essential.

Must say, last time, I only worried about RH with the soundboard but I guess a back (and possibly sides) can split just as easily. Is that true?

Thanks

Richard

[Trevor Gore]

I do all assembly at 45% RH.

The sides can be problematic because they tend to be heat and damp tortured and then ignored. They are often assembled at unknown RH and, mostly, people seem to get away with it. I tend to bend the sides early in the process and give them a week to normalise at 45% before I cut to length and glue in the end blocks, then linings and side stiffeners. The more you move away from "standard" woods (EIR, mahogany, blackwood) toward the less used local woods, the more I'd want to assemble everything at 45% RH, not just the top and back.

[Richardl]

Hi Trevor
Thanks for your reply, that helps -I'll just have to take over a room in the house for a bit! I'm somewhat out of sequence in this build unfortunately as I still haven't sorted out a bending iron. I'll do it differently next time. The back and front will have to just sit around for a bit until the sides are ready. In this case, I'm using mahogany. I'm surprised how stiff it is compared with Blackwood.
Thanks
Richard

[Richardl]

Hi again. I recently finally got a Carbatec mortise kit to do the neck mortise. It came with a 1/2 and 1/4 inch mortise bit (I'd asked for 3/8). How critical is that square hole - is a 1/2 inch hole too big? I suspect it'll be easier to find 3/8 brass bar (have yet to look) but just wondered how critical the size is. If it sounds too big I'll try to swap bits.

Cheers
Richard

[kiwigeo]

Hi Richard,

A 1/2" mortising bit is probably cutting it a bit fine, especially if your heel gets smaller than the one on the drawings in Trevor's books. You should be able to source a 10mm/3/8" bit for that Carbatec mortise kit. Is it the full mortising machine or the kit you attach to a drill press?
I'm pretty sure I got my mortising bits from Lee Valley. It's also a good idea to get a couple of cone sharpeners to keep the chisels sharp.....even a slightly dull chisel edge makes the job of drilling the mortise bar hole a pain.

3/8" brass bar....both Mitre 10 and Bunnings seem to stock the stuff here in Australia.

Hi again. I recently finally got a Carbatec mortise kit to do the neck mortise. It came with a 1/2 and 1/4 inch mortise bit (I'd asked for 3/8). How critical is that square hole - is a 1/2 inch hole too big? I suspect it'll be easier to find 3/8 brass bar (have yet to look) but just wondered how critical the size is. If it sounds too big I'll try to swap bits.

Cheers
Richard

[Trevor Gore]

Definitely need 3/8" or 10mm, preferably 10mm for the mortise chisel. Often, 3/8" is sold as 10mm, so be sure you know what you're getting. 1/2" is too big and 1/4" is too small! The bar size is typically 3/8" for brass (which needs filing to fit in the 3/8" hole, hence a preference for 10mm) or 10mm should you decide to use Aluminium (which works fine, but is easier to cross-thread and strip).

[Richardl]

OK, thanks. I dont think metric are available. Can always make a 3/8 brass bar marginally smaller.


Cheers
Richard

[Richardl]

Hi again

well, I have invested in the 3/8 Carbatec mortise chisel to add to the Carbatec set. I've just installed it on my rather undersized but faithful old Ryobi drill press that has seen much action over the years. I can't get it to do much more than make a small dimple in some soft pine. So, I'm wondering if you really need
1...considerable downward force that would ruin my drill press (even heaving quite a bit really doesn't have an effect ) or
2... whether I'm doing something completely wrong or
3...that the chisel isn't sharpened but for this sort of thing, you'd expect them to work out of the box to some extent (if not perfectly).

Any thoughts other than drilling the hole and using the mortise chisel with a mallet!?

Thanks

Richard

[Trevor Gore]

I bought a drill press attachment style mortiser from Carbatec many years ago. It and the 3/8" chisel it came with haven't ever given me any trouble. I haven't even had to sharpen the chisel, though its getting ready for it now! I use it on a 16mm chuck, 16 speed drill press. Reasonably heavy duty, but far from industrial.

I know that other people (on this and other woodworking forums) consider the attachments style mortisers to be junk, but that has certainly not been my experience. If I was a joiner cutting mortise joints day in/day out, my opinion might change, but for one hole per guitar I don't have any complaints.

The other day I even managed to source a real 10mm mortise chisel. That extra 0.5mm will make life soooo much easier...

[Richardl]

Hi Trevor

OK, thanks, I'll have another look at it...at least I don't need a heavy-duty drill press. The drill bit makes a small hole and the 4 points of the chisel make dents and that is it. The drill press is a bench mounted one and not even bolted down so I can't exert a huge amount of force, but as mentioned, I'm afraid I'll wreck it. I have a second 1/2 inch chisel so I'll try that too. Yes, the casting and general quality of the mortise kit and chisels is junk, but if the principle works then I should get some sort of square hole, so obviously something is not right with the gear or my operation of it. You tube may hold some answers?

Cheers
Richard

[Bruce McC]

Hi Richard

Have you seen this video on setting up a mortising attachment?
Thought it could be helpful for you.

https://www.youtube.com/watch?v=hxyWfze3qzQ

[Steve.Toscano]

Worse case - drill a 3/8 round hole and hand chisel in corners to make it square.
Not ideal, and takes some extra time, but will get the job done. I did this for years before getting a morticer.

[Richardl]

Thanks for the replies. Yes, just found the video. I wish mine worked like that. I have sharpened as best I can and honed the outside of the chisel to a mirror. Its set up correctly and I have got it to work after a fashion (cut a small square hole in pine) but it will break my drill press if I heave on it more. I think that is the problem. Quite a bit of downward force is needed. So, I'm trying to find someone with an extra heavy-duty drill press that will withstand it. The kit came with 2 mortise chisels - I tried the 1/2 inch. I couldn't get that to work either.

The only other alternative I can think of is to drill the hole and use the outside of the chisel as, well, a chisel. I tried that, bashing it with a mallet and it worked, after a fashion! More or less made a square hole in pine. Doing that on my neck doesn't really appeal though.

Cheers
Richard

[Richardl]

and..yes, the hand chiselling route may have been the quicker option. I have a mortise chisel that would have done. In fact, I imagine only the one face needs to be flat so could have ground the brass bar to a D shape to fit.

[kiwigeo]

Thanks for the replies. Yes, just found the video. I wish mine worked like that. I have sharpened as best I can and honed the outside of the chisel to a mirror. Its set up correctly and I have got it to work after a fashion (cut a small square hole in pine) but it will break my drill press if I heave on it more. I think that is the problem. Quite a bit of downward force is needed. So, I'm trying to find someone with an extra heavy-duty drill press that will withstand it. The kit came with 2 mortise chisels - I tried the 1/2 inch. I couldn't get that to work either.

The only other alternative I can think of is to drill the hole and use the outside of the chisel as, well, a chisel. I tried that, bashing it with a mallet and it worked, after a fashion! More or less made a square hole in pine. Doing that on my neck doesn't really appeal though.

Cheers
Richard

Hi Richard,

If you're having trouble getting the mortise bit through the wood then there are three things things to check/consider:
1) make sure the drill bit/chisel clearance is set so the chisel is only having to square off hole already drilled by the bit...ie the bit should be protruding out of the chisel by about the thickness of a coin. https://www.woodmagazine.com/woodworkin ... g/mortiser
2) Make sure the cutting edge of the chisel is sharp. There really is no other way to sharpen these chisels than with a special cone shaped diamond sharpener that works the inside face of the chisel. I wouldnt worry about getting a polish on the outside of the chisel....a couple of minutes flossing with the cone will make it sharp enough.
3) Even with dedicated Carbatec mortiser a fair bit of pressure is needed on the lever to get the hole cut. Make sure you drill to a depth that allows for the fact the bit is deeper than the chisel.

[Dave M]

I think there is a thing going on here which we toilers in our sheds all tend to suffer from. You really don’t have to own all the machines stroke tools that are needed. There is almost certainly another woodworker near you who actually has a morticing macihine and would happily let you use it for the twenty minutes or so that is all that is needed.

I speak as one who is badly afflicted by this issue. My excuse is that I am in a small village with no other woodworkers that I know of. (and I am an antisocial bugger!) But really for these very short one off tasks we should able to call on our fellow craftsmen. It is not like borrowing a tool for weeks on end.

[Steve.Toscano]

I speak as one who is badly afflicted by this issue. My excuse is that I am in a small village with no other woodworkers that I know of. (and I am an antisocial bugger!)

No excuses!!
I made my first lot of independent builds with nothing more then: a 600 * 1200 bench with vice, 4x chisels, a no3 and no5 plane, a Japanese saw, fret saw, coping saw, set square, 6 clamps, battery drill, jigsaw, aluminum tube and butane torch (for bending), files, sandpaper, scraper, calipers, ruler, and a few scribes.
All in a 2m x 3m space.
I made around 10 good quality guitars like this while slowly adding extra to the kit.