A bloody ripper of an idea

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sebastiaan56
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A bloody ripper of an idea

Post by sebastiaan56 » Fri Feb 01, 2008 4:07 pm

Check out these go bars this bloke made on the mando forum, a ripper of an idea,

http://www.mandolincafe.net/cgi-bin/iko ... =7&t=50743

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Kim
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Post by Kim » Fri Feb 01, 2008 5:11 pm

These are pretty cool to.

http://www.hanalima.com/tooltips_pvcgobar.shtml

The same guy uses spring loaded go bars as well only he has the spring at one end of the go bar so that a dowel sleeve loads directly against the top shelf of the deck rather than having a spring in the middle pushing two rods apart.


Here it is.. http://www.hanalima.com/tooltips_gobar.shtml

Cheers

Kim

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sebastiaan56
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Post by sebastiaan56 » Sat Feb 02, 2008 4:28 am

Cool,

thx Kim, there is always more than one way to do a job.

Bob, my post appears to have gone forth and multiplied, Im sure I only told it once. FYI

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kiwigeo
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Post by kiwigeo » Sat Feb 02, 2008 6:40 am

The PVC spring idea is great but the go bars with the spring wouldnt be so great IMO.

With the latter the clamping presurre is being supplied by the spring. Youre stuck with a limited range of distance you can have been the top and bottom of the deck before the spring bottoms out and you going to start to flex and add additional pressure to that supplied by the spring.

Maybe Im looking at this wrong?

Hesh1956
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Post by Hesh1956 » Sun Feb 03, 2008 12:05 am

We have a guy who made go-bars like this on the OLF too and he likes them.

I would be concerned about being able to get that ideal 8 pounds of clamping force at all times and not being dependent on how much the bar was compressed or spring tension.

Maybe it's just me here but to me the beauty of a go-bar is that it is nothing more then a simple stinkin stick.......

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hilo_kawika
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Post by hilo_kawika » Mon Oct 13, 2008 1:27 pm

As Hesh1956 notes, the amount of pressure applied depends on the amount of spring compression. If you always want the same amount of pressure applied, I suggest that "classical" go-bars are the way to go.

The interesting thing about the "classical" go-bars is several-fold:

First, the amount of pressure applied by the go-bar when its bent depends on the material stiffness, rod cross-section dimensions and length of the rod. So if you know these values and use the correct formula (Euler's formula for column buckling), you can taylor the rod dimensions to whatever applied pressure you wish to use.

Second, when the rod begins to bend (or the column begins to buckle under load) the applied pressure remains the same for a considerable amount of bending. That is, if the rod is bent a little or a great deal the applied pressure is ~ the same.

Try this simple experiment to validate the above statement: You'll need a wooden dowel about 3 feet long and 1/4" in diameter (pardon the non-metric units), a 3" square by 1/2" thick piece of wood and a postal scale that can go to ~10 lbs. Place one end of the dowel vertically on the scale and the other on the underside of the square piece of wood that's protecting your hand. Now slowly press down on the dowel until it bends slightly and look at the postal scale reading. Continue to slowly press on the dowel bending it more and see if the scale reading changes noticeably. It shouldn't!

I have used 1/4" fiberglass rods ~ 3' long for 3-4 years now and really like them. They don't warp and always apply the same pressure.
How to become a millionaire? Start with $2 million and become a luthier...

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Bob Connor
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Post by Bob Connor » Mon Oct 13, 2008 2:29 pm

I think Waddy Thompson has made some similar.

David don't worry about the non-metric stuff. Most of us down here work with both.
Bob, Geelong
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Mainwaring and Connor Guitars

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sebastiaan56
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Post by sebastiaan56 » Mon Oct 13, 2008 4:26 pm

bob wrote:I think Waddy Thompson has made some similar.
One of those ideas that had to come? They both appeared about the same time, I was curious about that as well. Im not claiming any plagiarism happened just curious they both happened.
make mine fifths........

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Taffy Evans
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Post by Taffy Evans » Mon Oct 13, 2008 9:37 pm

I'm on holidays so just checked in.

My go bars are spring loaded, I must have been using them for 12-15 years now. My Go Bar deck has an adjustable top that allows adjustment for spring pressure changes if needed.

I have the regular type of bars also, but use them rarely.
Taff

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