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Double Bass introduction and questions

#21
Hi Arnold, are you saying that with sitka, you end up with a more consistent thickness, because of the difference between cross and with-grain thickness? Or Do you graduate thinner than with other spruces, because of this stiffness along the grain? My instinct is telling me that I can go thinner on this top. Matthews comment of thinner areas at the recurve is also something I've head of being done. Is this as common as I think it is?

I really appreciate all the advice and observations given, thank you. I've been following you're progress Ctregan, looking good, and thanks for the compliment. The design is my own, I didn't follow any plans specifically, Except to try and keep the dimensions of a biggish 3/4 in mind. And I tried to make it Maggini-ish. ( stole the f-holes from a maggini viola ).

Here's some arch pictures Matthew, what do you think?
 
#23
Hi Darren. I'm in the same spot as you right now. I'm graduating my first sitka top today in fact. In Chuck Traeger's book, "The Setup And Repair Of The Double Bass", he's got a whole section on his theory of bass bar placement, which if you want I could have my wife type out (she types like the wind) and pm it to you. But to start, he says, "I try to place my bars as far from the center of the bass as possible within the F hole position". Another point is, "The further a bar is from the center, the more E string volume will it produce. Don't go too far of the E string will be too loud and the G string will sound nasal." Who knows what's too far though! He basically measures the widest parts of the upper and lower bout then measures either 1/7th, 1/8th, or 19th of these widths from the center line, whichever doesn't intersect with the upper eye, and uses that fraction. For the length, he draws a line where the bass bar will be and measures from rib to rib and uses 3/4 of this measurement for the bar.

As far as graduations, I'm following Peter Chandler's plans and going to 4.5mm at the edges of the upper and lower bout, 6mm at the edge of the C, and doing a vertical center from neck block to tail block of 8mm with the area under the bridge and sound post at 9mm. Going to 6mm inside the 4.5mm areas of the upper and lowere bouts. And 7mm around the F holes. I'm thinking that because it's sitka, I might go to 7mm at the edges next to the neck block and tail block too, which might be good given the long grain stiffness Arnold mentioned. I'm completely and totally shooting in the dark here, and I'm not particularly happy about that. Hope this made some kind of sense and hope it helps. Your bass design is beautiful. Love the F holes.
 
#24
Thanks for the info Don, you're bass is looking beautiful, as well. It is sometimes frustrating to be shooting in the dark, I agree. This reminds me of when I first started making fiddles and violas, it took me eight years to start figuring things out, and I still feel clueless most days! Now on this bass I feel back at square one.
I do enjoy the fact that basses have far less rules than the smaller instruments, I just wish I had the experience and knowledge to be able to take that fact and run with it.

Oh, and I wouldn't feel right to accept you're kind offer of sending me some excerpts of Mr. traegers book, I feel like I should buy my own copy, instead.And I think I will.
Do you have a close up pic of that purfling on you're back? It looks really nice.
 
#26
Sounds good Darren. Even though I'm not sure how well accepted his theories are, I find Traeger's book interesting and will probably put in my bass bar using his "thing", which for my bass would be 1/8th of the upper and lower bout widths from the center.

While looking around on here for graduation info, I ran across a post where there was talk from Arnold about leaving the area under the bass bar a little thicker to make a smoother transition from the "thick" bass bar to the thinner surrounding areas. I'm might do a bit of that. I dunno.

Thanks for the kind words about the button purfling. I'll take a close up pic in a few minutes. I did "borrow" the idea from this guy: [Invalid or Expired Link Removed]. Scroll down to the bottom left of the page to see his version.
 
#27
I'm glad the clamping idea was helpful. I've seen that on guitar making websites. I'm thinking that for clamping a bass bar I may just use 1/8" dowels or cut some willow strips since the fiberglass was unbelievably powerful. Just 4 of the fiberglass bars made two layer of 3/4" MDF glued and screwed together for the top support bow like scary crazy. I had to add two 2x4 braces on top to make it behave.
 

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#28
Darren Molnar said:
Hi Arnold, are you saying that with sitka, you end up with a more consistent thickness, because of the difference between cross and with-grain thickness?
Click to expand...
Precisely. Where I might have 3mm difference from thick to thin on an Engelmann top, I might only have 2mm on a sitka top. But I'm also paying attention to the tap and rub sounds, and flexing the top and pushing on it. A lot of this work is, as you know from violinmaking, tactile and intuitive rather than scientific.
 
#29
Don that purfling looks fantastic. What's that back wood again? Slab cut by its looks, will look great under varnish.

I think a "go-bar" deck big enough for a bass is a bit overkill for the occasional bassbar or brace. Nice to have, but you need the space! I clamped my bass bar and braces with some big F clamps and a few lead-shot bags.
 
#30
Thanks Matthew. The back wood is slab cut curly maple. You can't really see the figure in that pic, but it does look great on my test varnish strips.

I was going to use weights and clamps on the back braces but could tell that I just wasn't getting good solid contact all over. So I chalk fitted the braces and took a couple hours to rig that thing on top of my portable bench. It took less time than making long throated clamps, which was my original plan, and I think worked fantastic at applying intense, even pressure. I especially wanted to do that because I remember an old post where someone was trying out a Chandler bass and a back brace fell off inside the instrument. I definitely don't want that to happen! The contraption comes apart and leans against the wall pretty easily. I'm leaving it up until I install my bass bar this weekend. I'm also planning on building a steel string guitar when I'm finished with the bass, so it should come in handy for that as well.

Also, thanks again Matthew for pointing out my over/under error on the purfling knot! Much better this way.
 
#32
Wow. A plaster-mold. That would definitely keep the top from distorting under pressure. I'll have to think about that. How long did it take to do it?

I was going to use an off-cut of my sitka top for the bass bar, but now I've decided to use some really old englemann from a tonewood dealer in Denver to filter what I imagine might be some stiff sitka harshness. Does this sound reasonable, or am I doing this for nothing? That pushes me back a few days before he can cut it, so I'll be doing more varnish tests. Too many things to think about at 2:30am.:hmm:
 
#33
Hi Don. The plaster mold took less than an hour. But it was done with no desire to make it perfect. I was only concerned with getting the plaster under the bar area and a little more for the plate to sit in it comfortably. So I took the top off of a plywood box that was the right size for the plate to sit on, but not in. Then I took some styrofoam insulation to fill up the box until it almost touched the arching.( this lets you use less plaster, the foam is filler, basically ) Put about 3 kg of plaster in a bucket, then water. As soon as it was mixed well enough I poured it in the box, put a garbage bag over top of that, and then took the top and pressed it in and wiggled it around until there was no tension in the top. Let it sit there for about twenty minutes, then remove top. (plaster heats up a lot as it dries, you do not want to leave you're top in there.) the plaster took over night to set, and it still feels clamy today, but when I glued the bar in, the garbage bag was used as a barier between the top and the plaster once more. I think it took me longer to write this explanation, really. So that was the super crude, but very effective way to do it. I'm thinking that if one had a place to store molds, it would be worthwhile to make a good job of it all, then you have the original arching counter-form for the repairs years down the road!
 
#35
Hi Don, I'm still lurkin around, my bass project was side lined for a while. ( I'll try shorten the whole sad tale. )

The bass was a commision from a local family, for their teen-age boy, who was a very serious student. He had aspirations to pursue a music degree after graduation.

Unbeknownsed to me, not long after I started the work, the kid started getting into the wrong crowds, and family problems started. He ran away, called me to tell me he didn't want he bass any more, and asked for his deposit back. His family called shortly afterwards, saying the same things. So it looked like I was going to be stuck with months of wasted time, a half finished bass,and a couple grand worth of materials spent. Yuk

This was a huge blow to me, my margins are as slim as it gets and it looked like I'd have to put the business on hold for a while, to recover. I'd basically put everything aside to do this one project ( big mistake )

So thats where it sat for a while, I concentrated on the smaller instruments, started showing them around again, built and finished a violin in the mean time, started a viola and a cello, took on some repairs again, etc.

In the mean time the kids teacher got involved, he's a great guy with an awesome moral center. He explained that pulling out of a deal like this was not cool, trying to weasel the deposit back was super-not cool, and they should follow through with the project.

the family listened, and as of a couple weeks ago, the project is back on, they will buy it, and hold on to it in case the kid comes to his senses again. Or sell it later. The kid has now moved to the west coast last time any one heard.

so I've just stated working on it again. I'll post some pictures this week sometimes. Where I'm at is, the top is done, ribs are attached to it, scroll is carved, and the back is being rough carved presently. Fun winter :rollno:
 
#36
Now there's a teacher to deal with! You ought to share this over on MN, where that thread about kickbacks is going. It is nice to hear about a teacher that sets a standard for ethics, even when it is doing himself no good, personally.

Post some pictures of the bass when you get around to it.

Chet
 

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