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| Go Bar pressure ? http://luthiersforum.com/forum/viewtopic.php?f=10101&t=36864 |
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| Author: | brazil66 [ Wed Jun 20, 2012 2:35 pm ] |
| Post subject: | Go Bar pressure ? |
I just started using a go bar deck, and like it....after using a vac bag previously. My question relates to the distance set between the two surfaces of the deck..top and bottom plates. I'm using a 24" fibreglas rod 3/16" and have the space set at 23" between the radius dish surface and the top of the deck. So far this seems plenty of pressure. Wondering what the general distance is amongst those here....and what the actual pressure/ force might be at this generally accepted distance. Thank you. Michael |
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| Author: | Barry Daniels [ Wed Jun 20, 2012 3:00 pm ] |
| Post subject: | Re: Go Bar pressure ? |
The interesting thing with go-bars is that the pressure doesn't change with the amount that the bar is flexed. A little bowing or a lot will make no difference in pressure. The only way to get more or less pressure is to change the material or cross sectional area (i.e.; larger diameter) of the bar. |
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| Author: | Bryan Bear [ Wed Jun 20, 2012 3:05 pm ] |
| Post subject: | Re: Go Bar pressure ? |
I don't know what the force for you particular bars would be (randome guess is a bit under 10 lbs. per bar). The force exerted will not increase with more bend/shorter distance. I suppose you could push one down on your bathroom scale to get an idea of the force. Oops, I see Barry beat me to it. The only thing I would add is that thicker bars will increase the pressure but longer bars will decrease the pressure. In asmuchas a taller deck with 48 inch bars will provide less pressure as a shorter deck with 24 inch bars of same thickness. . . |
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| Author: | Joe Beaver [ Wed Jun 20, 2012 3:30 pm ] |
| Post subject: | Re: Go Bar pressure ? |
There are times when I wish I had a go-bar deck. But then when I do the math it doesn’t seem to add up. If the bars exert only ten pounds pressure and you are gluing a ¼ x18” brace, and you want 100 lbs per sq inch clamp pressure, as the titebond boys say, then you would need to use 45 bars per brace. Can that be right? |
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| Author: | brazil66 [ Wed Jun 20, 2012 4:41 pm ] |
| Post subject: | Re: Go Bar pressure ? |
Thanks Todd, for the 101. Definitive. I will save THAT. ...and thanks guys for your info. Michael |
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| Author: | Ken Franklin [ Wed Jun 20, 2012 5:19 pm ] |
| Post subject: | Re: Go Bar pressure ? |
Put a bathroom scale in your go bar deck and load it with ten go bars. Then divide the weight by ten. As you change the amount of deflection you will see where the optimum amount of deflection is and how much pressure you are getting from each go bar. I have different go bars I've collected or made over the years and they vary from 5 to 12 pounds of pressure. |
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| Author: | bluescreek [ Wed Jun 20, 2012 5:38 pm ] |
| Post subject: | Re: Go Bar pressure ? |
What Todd's explanation is saying is the most force applied is just before the bars bend. I find 8 to 10 lbs is a good force for a rod |
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| Author: | brazil66 [ Wed Jun 20, 2012 6:12 pm ] |
| Post subject: | Re: Go Bar pressure ? |
I'll give the scale thing a try...interesting. Thanks Ken....John, always a pleasure. |
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| Author: | SteveSmith [ Thu Jun 21, 2012 6:59 am ] |
| Post subject: | Re: Go Bar pressure ? |
I use 3/16" fiberglass rods from "In the Wind" kite supply. They measure about 7.5 lbs pressure each. |
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| Author: | Clay S. [ Thu Jun 21, 2012 7:12 am ] |
| Post subject: | Re: Go Bar pressure ? |
Joe , Would you really want to put a 450 pound weight on top of your guitar brace? |
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| Author: | Barry Daniels [ Thu Jun 21, 2012 7:35 am ] |
| Post subject: | Re: Go Bar pressure ? |
The pressure specified by Franklin is not relevant to bracing and most other joints in a guitar. If a joint is well prepared and close fitting you can use a "rubbed joint" which is basically zero psi. From a practical point of view, you really only need enough pressure to get the two surfaces in close contact. |
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| Author: | Stuart Gort [ Thu Jun 21, 2012 10:10 am ] |
| Post subject: | Re: Go Bar pressure ? |
bluescreek wrote: What Todd's explanation is saying is the most force applied is just before the bars bend. I find 8 to 10 lbs is a good force for a rod This would be the case with anything being bent and constrained like a Go Bar. The thing to note however is that as the bar approaches a straight configuration...the force gradient will increase dramatically. The net result of this is that it will get increasingly more difficult to control how much pressure is applied as the bars get straighter. I believe the designers would suggest to use the bars at a healthy, practical bending radius and then vary the rod thickness in order to achieve any particular amount of pressure. |
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| Author: | mkellyvrod [ Sat Jun 23, 2012 10:14 am ] |
| Post subject: | Re: Go Bar pressure ? |
Michael, Since you started the thread, can I ask you why you decided to go with the "go bar" over the "vacuum bag". I haven't decided the best way to go. Right now, I'm just clamping braces, but am looking down the roard. I was leaning toward the vacuum bag (since I have an auto AC vacuum pump that sets idle most of the time), but seems like the go bar would be easier in some respects to build and operate. Didn't realize that each go bar exerts 7-10 lbs of pressure; always learning something. Thanks, guys. |
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| Author: | SteveSmith [ Sat Jun 23, 2012 11:43 am ] |
| Post subject: | Re: Go Bar pressure ? |
mkellyvrod wrote: Michael, Right now, I'm just clamping braces, but am looking down the roard. I was leaning toward the vacuum bag (since I have an auto AC vacuum pump that sets idle most of the time), but seems like the go bar would be easier in some respects to build and operate. I have both options and choose to use the GoBar deck because I find it more convenient. There are others who prefer using the vacuum bag. So I guess it's whatever works for you. Attachment: DSCF0628.JPG
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| Author: | brazil66 [ Sat Jun 23, 2012 1:31 pm ] |
| Post subject: | Re: Go Bar pressure ? |
Martin; I still like the vacuum bag...but will use it less...mainly because of glue clean up, and the ease of working closely with the braces as I'm gluing them (in the deck). I can see, make adjustments clean up, and if I choose...glue the whole brace pattern up in one session. And do this at a calm pace. The bag...even if I carefully position the braces in place...tape them to secure that position, I can still get a possible, shift or tilt after the fact. And , I need to move along spritely as I'm whipping this little bit of millwork together. Lastly...I don't enjoy taking the top out of the bag after 10-15 min......cleaning glue, ...then putting it back in. I have a very comfortable degree of control with the Go Bar set up. One other point , is that I want to use hide glue for bracing, as I get more comfortable using that, and at this point gluing with hide glue using the vac bag....seems impossible to me. I now can work on two tops at a time, using the bag and the deck. Im on my 5th guitar , and this is my experience so far. |
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| Author: | mkellyvrod [ Sat Jun 23, 2012 6:54 pm ] |
| Post subject: | Re: Go Bar pressure ? |
Michael, Steve and Brazil66, Thanks for the replies. Looks like I'll be working on a Go-bar deck. Good point about the hide glue and the vacuum set-up - wasn't even thinking hide glue, but I got some awhile back for another unrelated project so maybe I'll be giving it a try, but not right away. |
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