#1 in progress: cedar/mahogany medium jumbo scratch build

Take us through building your guitar step by step. Post pictures and tell us what you're doing.
Post Reply
nkwak
Posts: 729
Joined: Sat Nov 13, 2010 9:55 pm
Location: Pittsburgh PA suburbs

Re: #1 in progress: cedar/mahogany medium jumbo scratch buil

Post by nkwak »

Installment 8: finishing the rims

By this point I'd detected a problem with the bracing on my top that I'll come back to in the next installment. I was told that it would be best to get the rims done first. The rationale I'm told is that once I finish the bracing on my plates it's best to get them glued to the sides quickly lest they distort like potato chips. So moving right along by July I'd set out to do just that:

Fun with clothes pins; another fun part for me:

Image

I stopped to admire the progress I'd finally seemed to be making:

Image

Then on to "driving the bus" as John Hall puts it. My set up isn't as exact as his (note the bit drilled directly into the table) but the process was similar, albeit I had to really dig in and make a lot of dust. The top rim has a 28' radius, the back rim a 20' radius. I also decided to add walnut side slats for insurance against key cracks:

Image

The aftermath:

Image

At this point my sides were just about ready to accept the plates.
~ Neil
nkwak
Posts: 729
Joined: Sat Nov 13, 2010 9:55 pm
Location: Pittsburgh PA suburbs

Re: #1 in progress: cedar/mahogany medium jumbo scratch buil

Post by nkwak »

Installment 9: back to the soundboard bracing:

As I'd alluded to earlier, there was a mistake with the top that wasn't apparent until I performed my first tap test. There was a slight buzz that meant that my braces weren't fully glued to the top. That meant that they had to come off. Another major setback.

Maybe it was for the best. One thing I must say though is that I've found the online lutherie community to be among the most generous and supportive - even for the likes of me who are riddled with adult-onset ADD with a little OCD sprinkled in. My friend and I actually met through a mutual friend who is a luthier in central Ohio. He happily chiseled off my braces and confirmed what I'd done wrong. It took him 15 minutes to erase 3 months of my work! He dug into his pile for a pre-lapjointed pair and a new UTB to replace them though which was awful nice I must say.

These new braces were different than mine though. He looked at my plans and noted that the angle of the X brace was a bit tight to accommodate where the bridge was to go. The X that he gave me has a wider angle (which I'm told had several benefits) so I basically had to throw out my template and rebrace the top with the safety of a pre-rendered set of outlines. I like to think I was up to the challenge though, so I got to work:

Image

I decided to save them for last and followed Natelson and Cumpiano's order for installing the braces:

First were the finger braces and upper transverse brace which have no radius on the underside

Image

Then on to the X brace which has a 28' radius:

Image

Inletting the other braces into the X:

Image

Finishing up with the lower face braces and osage orange bridge plate which don't have a radius, leaving the X alone to provide the arch for the top:

Image

Then taking my work home to finish up in my own go-bar deck:

Image

The final pre-scalloped bracing:

Image

Next time on to the back plate...
~ Neil
nkwak
Posts: 729
Joined: Sat Nov 13, 2010 9:55 pm
Location: Pittsburgh PA suburbs

Re: #1 in progress: cedar/mahogany medium jumbo scratch buil

Post by nkwak »

Installment 10: the back plate bracing

I must say that I think I'm really starting to make process and working a little more efficiently. I'm still learning though but I think it's starting to pay off and I'm thinking a couple steps ahead now.

This past month I braced up my back plate. It all started when I finally cut out the outline in my friend's band saw. Then I marked where the braces were to go with my template and notched the center seam reinforcing strip:

Image

My braces were pre-cut just the day before and all I had to do was radius their glue surfaces to a 20' radius using a radius dish/sanding disk. You all remember that debate elsewhere in this forum!

Image

Then on to the glue-up:

Image

Moving forward, things have gone much more quickly than with my top bracing. That's because I haven't paid as much attention to voicing. I'm more interested in structural integrity, though I am please with how the profiles came out:

Image

Image

Image
~ Neil
nkwak
Posts: 729
Joined: Sat Nov 13, 2010 9:55 pm
Location: Pittsburgh PA suburbs

Re: #1 in progress: cedar/mahogany medium jumbo scratch buil

Post by nkwak »

It's been about 4 weeks since I braced the top and about 2 since I braced the back and scalloped each. After that I had the hardest time notching the kerfing but I think it's ready to go. The back more so than the top so I'm going to glue up the back as soon as I can.

There are a couple of issues I'm willing to move past if they're not crucial. Firstly, it took me a long time to find the right position for the back plate and several times while cutting the kerfing I had to adjust it, leaving gaps. Will it be an issue if I don't fill them in with scrap? The kerfing is also a little high around the waist, though; it stands proud of the sides about 1/32"-1/16" in places. Will that be an issue?

FWIW when I was "finished" with the slots I set the sides on the back plate and applied a little pressure since the back is losing its radius. I turned out the lights, then used a flashlight to find any leaks." The only ones were around my braces:

Image

Once I was satisfied with the placement of the centerline I held everything fast with a pair of bungie cords and flipped the mold:

Image

Then I went and marked where to trim the center strip. I had to take everything apart and the lack of a radius on the back made the trim less precise than I would have liked but I'll live with it for now. Once I got everything back in place I went and traced the outline along the kerfing. That's so I know where to put the bead of glue when it's time to quick hymning and hawing about it:

Image

All is still not quite ready yet though. Firstly, I don't have access to the 20' radius dish I used to brace the back, but I don't think that's going to be an issue. My plan is to lay the mold face down with the back up so that I can apply the go bars using some scrap soft wood as cauls:

Image

Another factor is the RH in my basement; it's all over the place. Recent rainstorms have spiked the RH to the upper 40% range. I'd rather it were in the upper 30's. It seems the closer to the floor the higher the RH. Having a couple of desk lamps nearby seems to help - at least in the immediate area. Hopefully it's good enough:

Image
~ Neil
nkwak
Posts: 729
Joined: Sat Nov 13, 2010 9:55 pm
Location: Pittsburgh PA suburbs

Re: #1 in progress: cedar/mahogany medium jumbo scratch buil

Post by nkwak »

That's good to know about the kerfing and my little "extra" spaces. When you brought up the subject of the binding it all made sense. I only hope that my binding covers up all my mistakes!

I don't know why, but the idea of gluing the plates while it's raining outside concerns me; I don't have a dehumidifier in my basement. I'm wondering how long it will take the Titebond to set up and how I'm going to wipe up any squeeze-out if I can't get to it. The top is also ready to go on as well (the kerfing on both times are notched) so I'm contemplating on gluing that first instead. If there's too much squeeze out when I put the back on then maybe I'll try and get my 4 year-old to reach inside to clean it up. It'll be payback for all those times he had me on my knees under the kitchen table cleaning up his scraps!
~ Neil
kencierp

Re: #1 in progress: cedar/mahogany medium jumbo scratch buil

Post by kencierp »

Yes -- gluing bracing to the top and/or back and gluing the top or back to the rim in an environment without humidity control on a rainy day should be a concern. those parts and assemblies need to be their driest (smallest) during those processes. Its when the parts that are glued together start to shrink (dry out) that causes the cracks and failed glue joints.
naccoachbob
Posts: 477
Joined: Thu Dec 03, 2009 9:25 am
Location: Nacogdoches, Tx

Re: #1 in progress: cedar/mahogany medium jumbo scratch buil

Post by naccoachbob »

Neil, I think I saw where you talked about the cure time for Titebond. I think if you use glue the back and sides together with it and leave it overnight, you'll be fine. If it makes you nervous, use 24 hours. You're patiently taking your time on this build (I wish I had that patience), and 24 hours will definitely be enough.
As to the humidity of a wet day, I bow to Ken.
Keep at it.
Bob
nkwak
Posts: 729
Joined: Sat Nov 13, 2010 9:55 pm
Location: Pittsburgh PA suburbs

Re: #1 in progress: cedar/mahogany medium jumbo scratch buil

Post by nkwak »

Image

OK, I took the whole thing over to my friend's place where a dehumidifier keeps the RH at a stable 40% and I put the back on. It was getting late though so I'm a little worried that I may have rushed things, particularly with the centerline. Oh well. What's done is done. I could live with things being off 1/16" if that's what happens. I still can't wait to get back over there though and inspect the results though. After I pull the back & sides out of the mold I plan to get that neck block extension planed to the correct angle and then close the box.

On the bright side, I pulled my rosewood binding strips out of the bin and they'll cover up the bracing inlets on the sides just fine. I still have to get through the whole routing trial though. At any rate I feel like I'm really starting to make progress at long last.

Also, while it was all clamped up in the gobar deck I gave the back many a thump and it hit me that it's really starting to sound like a guitar. Sure, the back is .12" thick but I've still got a bit of sanding to do which should whittle down the thickness a tad. The top's got a nice ring to it as well and I can't wait to hear how it sounds once it's glued up to the sides as well.

BTW, I bought some 1/4" x 5" x 24" riftsawn maple and walnut at the local Rockler. I already have a 3/4" x 6" x 24" board of Honduran mahogany that's been sitting for a year now so I figure after the holidays I should be able to start working on the neck.

Like I said, it looks like it's about to really start coming together. Seeing the thing take shape in three dimensions has really put some wind in my sails and I'm hoping I can keep the momentum going!
~ Neil
nkwak
Posts: 729
Joined: Sat Nov 13, 2010 9:55 pm
Location: Pittsburgh PA suburbs

Re: #1 in progress: cedar/mahogany medium jumbo scratch buil

Post by nkwak »

It's close to being a box. Right now I'd call it a bowl or a basket or something. That just means I could take it out of the mold without worrying about the waist flexing and setting it down on the router table to trim off the excess. Flip it over and it makes a nice conga noise too! :D

Image

Image

Image

Image

Yes, there was a little tearout that was the result of a crack that had formed when I did a dry fit with the go-bar deck, but that's going to be routed out for the binding/purfling anyway so no big deal. All in all, not bad since I didn't use a flush cut bit on the router.

Image

Next up is to flatten the extension on the neck block so that it's flat (so that there's no hump at the 14th fret) and at 1.5° so that the neck angle is right when the time comes. I've yet to sign the underside of my soundboard but I have a little more sanding to do in order to get rid of all the flat surfaces.
~ Neil
David L
Posts: 1319
Joined: Thu Jan 06, 2011 8:04 pm
Location: Slidell, La

Re: #1 in progress: cedar/mahogany medium jumbo scratch buil

Post by David L »

Hey Neil, this is Kit Guitars Forum not kit drums forum, we be building guitars all up in here! BTW, how does it sound as a bongo? (LOL) Moving right along, keep going.

David L
Post Reply