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 Post subject: Correct Go Bar Tension
PostPosted: Sat Sep 29, 2018 4:03 pm 
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Walnut
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First name: Jordan
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Hello,

I have the LMI go bar deck and i’m curious how much tension to put on the go bars? I think I had too much because the go bars kept pushing the top up and all the go bars kept falling out. Is there an optimum measurement for this.

Jordan


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PostPosted: Sat Sep 29, 2018 4:34 pm 
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Koa
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Jordan,

The clamping force doesn't increase if you bend them more or less. Get a scale and check it out. Frankly 3/4" MDF isn't anywhere near stiff enough for say 20 go-bars exerting approximately 7 pounds of force each. My go-bars decks use 2 thicknesses of 3/4" plywood, glued, for the top and bottom plates.

Also: here is a link to a less expencive source for your go-bars. https://goodwinds.com/fiberglass/solid-fiberglass.html

Best, M


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These users thanked the author Michaeldc for the post: Pmaj7 (Tue Oct 02, 2018 10:14 am)
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PostPosted: Sat Sep 29, 2018 5:46 pm 
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Brazilian Rosewood
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I use wood dowels for go-bars, which exert 6-8# of force each. My understanding is that once they're bent the force doesn't change all that much: I suppose I should do the experiment. I'm not a big fan of fiberglass bars that put on a lot more force, I'd much rather use more bars and spread the force more evenly. Given the dents a wooden dowel can make when it gets loose I'd hate to see what a really strong fiberglass bar would do. At any rate, my deck is a nice thick bench top. Originally I used a piece of 3/4" ply screwed to the ceiling for the upper part; now it's a box made of ply with a lot of dividers. These stiffen it up and provide for go-bar storage. It will still lift a little bit; I do have bars fall down when they're just at full extension sometimes. On the other hand, when they're too bent you get lots of go-bar explosions. I have several different lengths of bars for that reason.


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PostPosted: Sat Sep 29, 2018 6:20 pm 
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Walnut
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Also: here is a link to a less expencive source for your go-bars. https://goodwinds.com/fiberglass/solid-fiberglass.html

Michael which diameter rods are you using. Thanks Mike Haines


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PostPosted: Sat Sep 29, 2018 6:35 pm 
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Koa
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Mike Haines wrote:
Also: here is a link to a less expencive source for your go-bars. https://goodwinds.com/fiberglass/solid-fiberglass.html

Michael which diameter rods are you using. Thanks Mike Haines



Hi Mike,

I'm using .187"s. They probide between 7-8 pounds of force (my scale isn't very accurate). The Lmii ones I have are a little less powerful which can be handy. As Alan mentioned these things will launch across the room so bowing them less is best as there isn't any difference in clamping force.

M


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PostPosted: Sun Sep 30, 2018 7:28 am 
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Clamping force does vary for practical go-bars, as real materials like unidirectional fiberglass do not behave in the same way as what engineers would call ideal materials (i.e., rods made from materials that behave in a theoretically compliant fashion). At the sort of relatively small 1" -8" deflections over 24" that we see with our rods, there is perhaps 10% - 15% increase as deflections move to the point of becoming dangerously loaded and capable of doing damage if dislodged in an uncontrolled manner.

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PostPosted: Sun Sep 30, 2018 7:59 am 
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The practical answer for the OP: make sure the go bars are at least sprung enough so they don’t fall out when the upper deck flexes (which it will, unless you reinforce it), but not so much that you are at risk of snapping the go bars. Since you have a commercially produced go bar deck that sells itself on the virtue of having an adjustable upper deck, you should be able to hit a sweet spot between those extremes that does the trick. Make sure you are tightening the adjustable parts enough to prevent the upper deck from sliding up the rods. You can’t stop the flexing, but you can, and should, stop any sliding. I think having the go bars flex between 2-6” off of straight is what most folks shoot for. In other words, the apex of the curve in the center of each go bar should be around 2-6” from where it would be if the go bar were not sprung. That’s a very rough estimate, though. If the bars are not falling out, and not snapping, you are doing it right, regardless of flexing variance.


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PostPosted: Sun Sep 30, 2018 10:27 am 
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Koa
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jordangatenby wrote:
Hello,

I have the LMI go bar deck and i’m curious how much tension to put on the go bars? I think I had too much because the go bars kept pushing the top up and all the go bars kept falling out. Is there an optimum measurement for this.

Jordan


It wouldn't take too much effort to stiffen up your Lmii deck so your go-bars didn't drop out due to deflection. A quick stop into Home Depot for a quarter sheet of 3/4" birch ply and some titebond. If your radius dish flexes because your deck flexes you are no longer bracing at whatever your target radius was.

Best, M


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PostPosted: Sun Sep 30, 2018 11:10 am 
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Brazilian Rosewood
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We use spring loaded chinese curtain rods for a smaller go bar deck, used on ukes and small gtrs. They were purchasedoff e bay .Sorry no links


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PostPosted: Sun Sep 30, 2018 1:16 pm 
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Michaeldc wrote:
It wouldn't take too much effort to stiffen up your Lmii deck so your go-bars didn't drop out due to deflection. A quick stop into Home Depot for a quarter sheet of 3/4" birch ply and some titebond. If your radius dish flexes because your deck flexes you are no longer bracing at whatever your target radius was.


Good advice, for sure. It is more important for the lower deck, obviously. The way I deal with the tendency of the lower deck to flex: I don't have a lower deck. My support rods feed right into dog holes in my laminated maple workbench top. The top deck can flex as much as it wants; the lower deck (my bench) always stays flat, so the radius dishes always stay flat (on the bottom) too.

The downside to this approach, of course, is that it takes up space on my workbench. So, it's not a permanent fixture. I set up and tear down my go bar deck as needed. It only takes a few minutes.

I like the idea of those adjustable connectors on the LMI deck, but are they strong enough? This thread makes me wonder.


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PostPosted: Sun Sep 30, 2018 4:24 pm 
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Koa
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doncaparker wrote:
Michaeldc wrote:
It wouldn't take too much effort to stiffen up your Lmii deck so your go-bars didn't drop out due to deflection. A quick stop into Home Depot for a quarter sheet of 3/4" birch ply and some titebond. If your radius dish flexes because your deck flexes you are no longer bracing at whatever your target radius was.


Good advice, for sure. It is more important for the lower deck, obviously. The way I deal with the tendency of the lower deck to flex: I don't have a lower deck. My support rods feed right into dog holes in my laminated maple workbench top. The top deck can flex as much as it wants; the lower deck (my bench) always stays flat, so the radius dishes always stay flat (on the bottom) too.

The downside to this approach, of course, is that it takes up space on my workbench. So, it's not a permanent fixture. I set up and tear down my go bar deck as needed. It only takes a few minutes.

I like the idea of those adjustable connectors on the LMI deck, but are they strong enough? This thread makes me wonder.


It's not uncommon for me to use 50+ go-bars at a time. That's say 350 pounds of force. I'd think the 4 adjustable connectors would handle that no problem. It's the MDF I'd be concerned about.


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PostPosted: Sun Sep 30, 2018 5:41 pm 
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ernie wrote:
We use spring loaded chinese curtain rods for a smaller go bar deck, used on ukes and small gtrs. They were purchasedoff e bay .Sorry no links

I've bought about 50 of these on eBay and since then I've hardly used my fiber glass rods. They are easily adjustable and never explode. I use them for braces and back gluing (and much more) and don't need to change deck height or keep different lengths of bars. Cost me less than $2 each.

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These users thanked the author mqbernardo for the post: Pmaj7 (Tue Oct 02, 2018 10:22 am)
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