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Four string fretless acoustic/electric (chambered)

#81
Ok, thanks! I'll do glue alone. I am not very happy with the shape of that bridge I may make another one out of walnut, now that it's going to be glued down, that becomes a more immediate issue.

One other question - right now the ebony is floating in a slot - I intend to leave it that way - do you guys agree that this is ok?.

I need to write out my next steps from here, I really want to test out the K&K system before I get the front glued up.
 
#82
The ebony floating in the slot is perfectly fine, its no different than an acoustic guitar/bass saddle. You may want to shape it or slot it to where it is angled back towards the bottom of the bass, so that the string break angle is at the very front edge of the saddle.
 
#83
It's 5/16" wide, I am planning on filing the string slots to set the intonation. So let's say the E string needs to be longer, then I would create a crest in the ebony towards the back. If the G string needs to be shorter, then I make the crest in the front of the ebony. I planned on testing where the intonation point is with a small nail or something. All theoretical at this point :-)
 
#85
Jisch said:
It's 5/16" wide, I am planning on filing the string slots to set the intonation. So let's say the E string needs to be longer, then I would create a crest in the ebony towards the back. If the G string needs to be shorter, then I make the crest in the front of the ebony. I planned on testing where the intonation point is with a small nail or something. All theoretical at this point :)
Click to expand...

I gotcha, just like a compensated acoustic saddle, but with much more room to adjust. I would set the front edge of the saddle at the G string at about 1/8" longer than your scale length, with the E string set equal to the sum of the gauge of the E,A, and D strings back from that. That will get you pretty close, and limit the amount of compensation needed to get it intonated properly.
 
#88
mansjasont said:
I think what he is saying is (assuming a 34" scale) set your G string at 34.125" and your E string at 34.425" (.045+.065+.085+.105 = .3)

By the way, this bass is looking so sweet. Can't wait to see/hear the finished product
Click to expand...

Basically, but don't add the gauge of the G string.

To set basic intonation, you set your G string at the scale length, which always has to move back, which is why I added 1/8". For the rest of the strings you set them back about as much as the string gauge. So you would set your D string .065" back from the G, the A .085" back from the D, and the E .105 back from the A. In the case of a single saddle you can only rough out the E and G, which is why you would set it back the combined thickness of the E, A and D string. Which is just about 1/4"
 
#90
Of course, get everything set, and intonated before gluing the bridge down. Once you get it set you can mark its location with a couple 1/16" holes through the bridge to act as indexing pins to keep it in place when you glue it down.
 
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#91
I consulted with a couple of friends who do acoustic instruments, and while neither has done an instrument exactly like this, they did provide some comments on the bracing. I shaped the bracing a bit, taking away material near the edges where the top will be supported and thinned them out overall. The common comment was "it's the height, not the width that provides the strength". One of my friends talked about holding the top with two fingers and thumping it to tune the bracing - I thumped, the sound changed slightly as I removed material, but with exactly one experience in doing this, I have no idea what the final impact of this will be. Everything I've read about bracing says you do the smallest amount to make the top "strong enough", again with limited experience I don't know where that line is. I suspect I'm still far to the "strength" side and far away from the "lightest".

I'm continuing to refine the shape of the braces so they are more uniform, but generally this is what they look like now:
IMAG1792_zps8ddyazpm.jpg


Next I'll need to rework the bridge, including getting the string height and intonation correct. Install the transducers and jack, then put it all together for another dry fit with strings to see what kind of sound I get out of the jack. Assuming all is well it's on to glue the bridge and front on after that. Then I'll have to do a final true up of the front and back and on to finishing.

This work thing really gets in the way though - I won't likely get those steps completed before the weekend.
 
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#93
I'm using transducers so no grounding is necessary - there's no electrical connection between the strings and the ground. Or at least that's the way it works in my head.

I strung up all four strings at lunch, there is no deflection at all, but I had to put a piece of wood on top to keep the bridge from sliding forward. hmmm Bridge plate or no bridge plate. I am thinking I am going to put one in, just so I don't regret it later - there's significant pressure on that piece of wood - thinking that if that's on the top then a bridge plate would be a good idea.
 
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#95
Tonight I strung up the bass and filed slots for the strings, the intonation went fine just by adjusting the peak where the strings breakover. I filed them down to the point where the action looked good, I didn't measure it, but it's about where I think it should be (similar to my other basses).

After I got all four strings set I tried to play it and found that below the 12th fret there is terrible buzz on every string. I checked the bow and it's dead flat. I guess I'll have to "loosen" the truss rod to induce some forward bow. I've put the strings on and off about a dozen times now and two of them are broken. Glad I ordered a new set.

I suppose it's possible I filed the slots too deep, but I think the lack of bow is the big problem.
 
#96
I got the bow of the neck set (I think) by going about 1 turn past tight in the loose direction (wow that's an awkward sentence!). Regardless of whether it's perfect or not, at least I know I can adjust it - I started looking at that thick piece of ebony and that round profile on the neck and thinking "that will never adjust!". Yay for science. I won't know for sure until I get it strung up again - I guess I'll do that one more time to check the K&K system before I glue the top on.

I also realized that when I did my string slotting last night I forgot to put the black dyed wood laminate in between the top and the body, this means my slots are all 1/32" shallower than I thought, so if I did go too deep, I get some of it back.

There are significant forces wanting to push that bridge forward when the strings are at tension - I now realize that's because the strings are coming from a point that is below and forward on the instrument. I put the ferrules there thinking it would give me maximum downward tension and good vibration transfer into the bridge (and therefore into the transducers), that's probably true, but that forward pressure has me concerned. After looking at the bridge and the bracing, I do not believe that a bridge plate is going to do much/anything to help manage that pressure. At this point I think I'm just going to glue the transducers to the underside of the top and forego a bridge plate. The front corners of the bridge will be sitting right on top of the brace, if that can't hold it, then a 1/8" piece of maple isn't going to be able to either. When I make my new bridge I'm going to have it extend forward more than the one I have now - that should give more glue surface and spread out the load a bit. If I ever make another one like this I'll have the strings load from the back end of the instrument instead of through the back.

I need to figure out what to do with the front. After playing it for a few minutes last night, I don't like the sharp edge that is there now (of course I'd relieve the edges a bit in final sanding). Because of the chambering there isn't enough material to do a significant arm relief. I'm thinking of doing a 1/4" round over. I'll have to try it on a test piece to see how it looks, that would expose the black laminate all the way around when you look at it from the front. Sometimes I like how that looks other times I think it looks to manufactured. This instrument has already gone past the "organic" look that I was originally going for - not in a bad way, it has just evolved, so maybe that's not a bad thing.
 
#97
I was going to say the same thing about the bridge plate yesterday and suggest a brace instead. Hard maple, 3/8" wide, 3/4 tall, running in between the X-braces, tapered after it extends past the length of the bridge. If you normally use Tightbond brand glue, don't use it when you glue the bridge down. I had a few acoustic guitar bridges pull up after 6 months or so. I asked a luthier friend of mine what the problem might be and his first question was "what brand glue?" When I told him tightbond he said that was the problem and he had the same thing happen. A couple years ago I told another luthier friend who was building some acoustic flat tops about that problem with tightbond, and he used tightbond anyway. About six months later he called me back to ask what glue to use to repair the bridges that were pulling up on all the guitars he made. Answer is, Elmers Carpenters Wood Glue.
 
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#99
Making a new bridge is giving me fits. I'm on iteration #4 right now, I think this one will be ok once it's shaped, but still I'm not entirely happy, we will see. The router jumps on me, I find a crack in the wood after I'm done or the slot is too long, every one has a different problem. I'll take this next one along and see where I end up, worst case I'll use the ash one I already have.

2015-07-03%2014.25.47_zpsraa9ixyj.jpg


I sanded down the front piece and found a few voids in the joint between the top pieces that need to be filled in.

I also put the jack in - unfortunately the first forstner bit I used had a bigger guide point than the second one, so I had a little drift. I'll be sanding this down to be a smooth transition to the jack. This jack is actually supposed to be used as a strap button, but I don't trust it and I like to use strap locks.

2015-07-03%2015.00.37_zpsfdajpcwy.jpg
 
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