Official Luthiers Forum!

I use wooden dowels too!

[QUOTE=ToddStock] This is an easy test...place a bathroom scale on the bottom of the deck, place a go bar between top of scale and top of deck. Add 1/4" ply under the scale until the reading maxes out...for a 3/16", 24" bar, should be 8 lbs and about 3/4" to 1" or so reduction in length and 1-1/2" deflection.

Remember, for a constant diameter, the longer the bar, the less pressure is exerted before maxing out. Think in terms of how much force it takes to bend dried spaghetti...try it with a 1/2" long piece (poke holes in fingertips before it bends) and then with a full length piece (very little pressure required).[/QUOTE]

Terrific info everyone. Thanks again!!!

I rebuilt the deck using (2) 3/4" thick pieces of plywood for the top (laminated them together) and did the same thing for the bottom. I'm using 3/8" threaded rods that are 36" long, so lots of room to expand the height of the deck.

The 24" rods seem to be deflecting correctly now but when I used a scale to check I'm getting about 7 lbs rather than 8. When a rod is sitting on an average size brace on top of the radius dish the gobar is about 1" taller than the space from the top of the brace to the top of the deck.

Should I lower the top of the deck to increase the preassure until it reaches 8 lbs or leave it as is?

_________________
Ric Hollander
Kings Park, NY
http://www.hollanderguitars.com

If you are interested in seeing how the theory that Todd refers to works, there's a neat little spreadsheet at
http://www.ukuleles.com/spreadsheets/RodBuckle.xls

You can play with some values and see how they affect the pressure.

To add to Todd's (correct) comments, the shorter the bars the more critical the length so you will need more different bars or a bunch of spacers under your work dish. Also, I had a 'shorter' go bar deck and it was more difficult to work 'inside', so I went to the overhead shelf system- 2x4 framing, MDF and lots of junk up there.
Chain link fence tension bars are available in fiberglass from HDepot (in some places only) and they work well in longer lengths- they're about 1/4 by 1/2 inches or so in cross-section . The ends need to be sanded a bit and dipped in epoxy or similar or you will be getting shards and splinters from them- painful. Even with the fiberglass bars on hand, I still use wood sticks for some tasks where less pressure is needed.

Cheers
John

Get away from 1/8" rods and try 3/16" and or 1/4" rods. Also as Todd said check out Euler column theory

I started with wooden dowels. I just found that they were too inconsistent for me. The 3/16" fibreglass rods at 24" are head and shoulders better than the wood dowels that I now have stored away!

Shane

_________________
Canada

Update:

I just glued up the remaining braces using the new (and much improved) gobar deck. Lots of glue squeezeout without any exploding gobars! The 3/16" bars I'm using are giving the right amount of deflection (looks the picture posted by Colin - thanks Colin!

So thats how this thing is supposed to work! What a difference from this morning! The combination of a weak top and over deflection was definately causing the problems I was having. I acutally enjoyed gluing up those braces and did so without any colorful language!

Here's a photo of the updated deck in action.

_________________
Ric Hollander
Kings Park, NY
http://www.hollanderguitars.com

Upper and lower decks on my go bar setup are 20mm chipboard with 45 x 30mm cross braces. Adding cross braces is another alternative to doubling up on the thickness of the deck.

The gobars are 10mm hoop pine dowel. I break about one on every job but can live with it. I've never had problems with the dowels slipping off the work.

A while back I ripped some nice, straight ash on my table saw for gobars. Haven't broken one since I started using them, I love ash for these things!   

_________________
Rian Gitar og Mandolin

Great info! Thanks Todd.

_________________
Ric Hollander
Kings Park, NY
http://www.hollanderguitars.com

Hey Ric,

If your going to Home Depot, check out the fiberglass driveway markers. That's what I'm using for go bars. They are 5/16" and each one gives me about 9 lbs of force at about 25" long. They come 36" long with a rubber tip and pretty colors too. About $2 each.

You can check the force of gobars real quick by standing on some bathroom scales and pushing the gobar into the ceiling with your hand. You can play with the deflection and find a good working zone.

_________________
Horton, MI

Here at our local HD they are white and .1875"(3/16) dia x 48" in length they cost $1.99 with the free reflector as well

Kirt...5/16" (.3125") dia. those are pretty stiff bugers hum?

[QUOTE=Kirt] Hey Ric,

If your going to Home Depot, check out the fiberglass driveway markers. That's what I'm using for go bars. They are 5/16" and each one gives me about 9 lbs of force at about 25" long. They come 36" long with a rubber tip and pretty colors too. About $2 each.

You can check the force of gobars real quick by standing on some bathroom scales and pushing the gobar into the ceiling with your hand. You can play with the deflection and find a good working zone.[/QUOTE]

Hey Kirt,

I've got quite a few of the 3/16" gobars already but I'll have to check the 5/16" ones next time I go to HD. Thanks for the info!

- Ric

_________________
Ric Hollander
Kings Park, NY
http://www.hollanderguitars.com

Ric,

I was wrong about the length on those. They come 48" long and I've shortened mine to 33 1/2". And that gives me about 9 lbs. force. I measured them after I got home Friday. Still 5/16 diam.

_________________
Horton, MI