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Go-bar question
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Author:  murrmac [ Sun Dec 09, 2012 1:43 pm ]
Post subject:  Go-bar question
Just out of interest, what length are these fiberglass rods with the rubber tips which I see in so many pics of bracing being glued down in a go-bar deck ?

Not that I am going to buy any (I don't know if they are even available in the UK) but I just wondered what sort of overhead flight space they required.

In the middle of my first build, I am making a quantity of what I would describe as a poor man's version of John Arnold's most ingenious spring powered go-bars ...mine are nothing like so high end ...plastic plumbing pipe , dowel rod and short compression springs will suffice (leastways I hope so ...)

While we are at it, is the correct terminology GOBAR, GO BAR, or GO-BAR ?
Author:  CharlieT [ Sun Dec 09, 2012 2:20 pm ]
Post subject:  Re: Go-bar question
I bought a bunch of 48" x 3/16" solid fiberglass rods from Goodwinds and had them cut them in half for me, so mine are 24". They work great. If you go that route, buy the plastic caps from them and order some extras.
Author:  Fred Tellier [ Sun Dec 09, 2012 2:25 pm ]
Post subject:  Re: Go-bar question
24" works real well for me. You can cut gobars from wood and they also work well, you will need to experiment with sizes to get the pressure needed, the 24" fiberglass bars apply around 8lbs of force.

Fred
Author:  George L [ Sun Dec 09, 2012 2:32 pm ]
Post subject:  Re: Go-bar question
Murray,
I think you are correct using "go-bar" but it shows up in various configurations. From what I've read you want about 1/2" (13mm?) of flex in your rods, so you can make them whatever length corresponds with the distance between your lower and upper decks. Like others, I chose 24" for that distance, but wish I'd made it taller, as I have to duck my head beneath the upper deck to lean in and inspect my work. I think it would be better to have more clearance. As noted above, check with shops that sell kite building supplies about the fiberglass rods and caps.
Author:  murrmac [ Sun Dec 09, 2012 2:33 pm ]
Post subject:  Re: Go-bar question
24" ...?

You do surprise me, I would have thought by looking at the pics of most go-bar decks that the rods were around 36" ...

Like I say, I am making mine out of 15mm plumbing pipe, 12mm dowels and compression springs ...overkill for one guitar, but hopefully they will be reused ... (maybe more than once)
Author:  murrmac [ Sun Dec 09, 2012 2:43 pm ]
Post subject:  Re: Go-bar question
George, (and Charlie and Fred) many thanks for the reply.

I know that many builders have built many guitars using the traditional "flexed" go-bar system, with 100% success, but for some reason it just sticks in my craw.

I just intuitively don't like the concept of bent wooden (or fiberglass) rods exerting the pressure, which is why I am expending a disproportionate amount of time (and money) making go-bars which will exert a straight downward force with no flexing.

The other factor here is that using an adjustable system such as I am making, you can use the same go-bars to glue the braces as to glue the top and back (you just adjust the internal dowel length.) With fixed length go-bars, am I correct in thinking that you can't do this, and that you would need to adjust the height of the ceiling on the go-bar deck ?
Author:  Ed Haney [ Sun Dec 09, 2012 3:08 pm ]
Post subject:  Re: Go-bar question
The most common range of go-bar length appears to be about 24" to 36". I see it as a personal choice based on how you set up your go-bar deck within your specific shop.

My shop is small and I do not leave the deck set up all the time. So I wanted something that was very easy (few parts) and fast (3 or 4 minutes) to set up and take down so that space was preserved. I also wanted something that was not at all restrictive (I'm tall and wanted to be able to sit and/or stand and work around the go-bar deck (the deck can swivel). This meant that 36" long bars worked best for me to allow plenty of room for working within the deck either seated or standing. I bought fiberglass kite stick for the go-bars.
Author:  murrmac [ Sun Dec 09, 2012 4:03 pm ]
Post subject:  Re: Go-bar question
OK, Todd, I got it ... thanks .

Take a line from tip to tip, and as long as that line is at right angles to the interconnected planes, there is no lateral displacement.

Suddenly it seems obvious ...

Except that it still seems to me that you would need two different lengths of go-bars to hold down the braces, compared to holding down the rims of the plates (top and back) ...or else you would need to adjust the ceiling height of the go-bar deck.

Or, is the increased flex of the go-bars when gluing the plates not in fact an issue ?
Author:  Jeff Highland [ Sun Dec 09, 2012 4:15 pm ]
Post subject:  Re: Go-bar question
Yes two different lengths or adjustable top. the height of a body is too much to accommodate with flex of the bar.
Author:  Fred Tellier [ Sun Dec 09, 2012 5:07 pm ]
Post subject:  Re: Go-bar question
Adjustable deck height, Mine is built with 1/2" threaded rods with the top between nuts and large washers, infinitely adjustable up and down as needed, a box platform as Todd suggests is another way.

Fred
Author:  Ron Belanger [ Sun Dec 09, 2012 5:19 pm ]
Post subject:  Re: Go-bar question
I use an adjustable platform and 24 inch fiberglass rods.
Author:  murrmac [ Sun Dec 09, 2012 5:23 pm ]
Post subject:  Re: Go-bar question
Thanks Jeff, and Todd.

Once more, Todd, for the benefit of the slow guy at the back of the class ...you have a gap of 27" between the ceiling of the go-bar deck and the clamping point of whatever you are clamping on the floor, am I right ? (I understand that there will always be a slight variance depending on brace height and plate radius) , but broadly, have I got that right ?

The next question (or two questions) is (or are) .. .if I make the go-bars out of solid wood (I have some ash which would do nicely), then what length would you suggest, and what section would be best IYO ? My gut instinct says 1/2" x 3/8", but I could be way off ...

Doing it this way will save me a shedload of cash...if you are ever over here in Scotland I owe you a dram of Laphroaig ...

Edit: Thanks Fred and Ron as well ...bit of cross posting there ... oops_sign
EDIT: Thank you, Ed, as well ...
Author:  Jeff Highland [ Sun Dec 09, 2012 5:35 pm ]
Post subject:  Re: Go-bar question
More like 4mm thick than 3/8 " but depends on the wood and the length.

Do a trial and shave it down till you get optimum thickness, they should be easy to use, not requiring a lot of force to get in place.
Author:  murrmac [ Sun Dec 09, 2012 5:47 pm ]
Post subject:  Re: Go-bar question
If I place a bathroom weighing scale on the floor of the deck I should be able to measure the force exerted by the bars, am I right ? Or a meringue?

So 8 lbs per bar (as Fred mentioned earlier) is that about right ? It doesn't seem like a lot, but I suppose it all adds up ...
Author:  murrmac [ Sun Dec 09, 2012 8:22 pm ]
Post subject:  Re: Go-bar question
Todd Stock wrote:
No one over that way carry kite supplies?


I see 4mm dia bars ...doesn't seem thick enough intuitively, I would have thought 6 or 8mm would be nearer the mark ...
Author:  Ken Franklin [ Mon Dec 10, 2012 1:58 am ]
Post subject:  Re: Go-bar question
Todd Stock wrote:
Go bars exert a straight downward force despite how deeply they may be flexed...


I have a hard time understanding this concept since the braces can slip some before the glue grabs.
Author:  Mike OMelia [ Mon Dec 10, 2012 10:35 am ]
Post subject:  Re: Go-bar question
murrmac wrote:
If I place a bathroom weighing scale on the floor of the deck I should be able to measure the force exerted by the bars, am I right ? Or a meringue?

So 8 lbs per bar (as Fred mentioned earlier) is that about right ? It doesn't seem like a lot, but I suppose it all adds up ...


Yup. 7-8 lbs. This is for 1/4" rods. Seems to be pretty consistent.
Author:  Mike OMelia [ Mon Dec 10, 2012 10:38 am ]
Post subject:  Re: Go-bar question
Ken Franklin wrote:
Todd Stock wrote:
Go bars exert a straight downward force despite how deeply they may be flexed...


I have a hard time understanding this concept since the braces can slip some before the glue grabs.


Yes, this is hard to understand. The normal force is the force required to buckle the rod. It does not increase if you increase the amount of flex. There is a tangential force component as well, and is proportional to the amount of flex. It's like a spring force. And it increases with flexure. And it is what causes side slip and can be the source of great danger. Never over flex these things. You simply do not need to, nor does any good come from it.

See this: http://en.wikipedia.org/wiki/Buckling
Author:  Bryan Bear [ Mon Dec 10, 2012 12:09 pm ]
Post subject:  Re: Go-bar question
First off this is NOT how you should do it. I recently decided to go with a go-bar set up that uses my ceiling and work bench. I still hadn’t gotten new bars and decided what the optimal length would be for various operations, So I went with what I had handy. I post this to demonstrate that as long as you are careful to put the ends of the bars directly above the point of contact there is no lateral load. You can put in a fair amount of flex and be okay, but it is not the safest thing to do, yes I was wearing safety glasses! Also keep in mind that the height is much greater than 24” in this picture. That makes excessive flex a bit easier because the bars are so long, but remember it also reduces the clamping force generated.

Also of note, the scale may be confusing, this is a mandolin top (about 2/3 the size of an OOO).
Attachment:
gobars.JPG


Edit, let's try this again with it rotated properly.

Second edit: I did not mean to imply that the added flex in a long bar reduces the force, it is the taller gobar deck (requireing long bars) that reduces the force. For a given diameter, the longer the bars, the less force they will produce. . .
Author:  Robert Hosmer [ Mon Dec 10, 2012 12:23 pm ]
Post subject:  Re: Go-bar question
murrmac wrote:
The next question (or two questions) is (or are) .. .if I make the go-bars out of solid wood (I have some ash which would do nicely), then what length would you suggest, and what section would be best IYO ? My gut instinct says 1/2" x 3/8", but I could be way off ...

Doing it this way will save me a shedload of cash...


I have made some out of ash; results were mixed.
Allow me to clarify by stating that they were not for a guitar project, but for clamping inlay into the center of doors and panels (cabinet project).

1/2" x 5/16" with a length of 32".
I did not measure clamping force; simply wanted something to hold the pieces down and provide a little pressure.
So you may have to do some experimenting to determine the proper amount of flex in relation to size to obtain the desired pressure.

For me, a large hindrance to making some out of wood is the fact that wood can be all over the place in regards to providing the desired pressure. It's wood, and, just like selecting and preparing the material for your bracing, the stiffness (and thus the amount of pressure provided by a given cross section) can vary.
I suspect the amount of runout in the wood will have a huge impact on the final results.

So yes, making your own from wood can work, but you're gonna have to experiment to determine the dimensions that will best accomodate your needs, then resign yourself to the inconsistency of using wood.
If you simply do not have the funds for fiberglass rod, it's an option.
If the concern is availability, then places like Goodwinds ship internationally.
Author:  murrmac [ Mon Dec 10, 2012 2:00 pm ]
Post subject:  Re: Go-bar question
Amazing input from everybody on this thread, thanks so much ...I have changed my views through 180 degrees ....

I did a bit of surfing and came up with this company in the UK who are selling 4mm fiberglass rods (which would be the equivalent of the 3/16") for what seems to be to be a staggeringly low price ...I figure I can get a single gobar for like 20 pence, if I buy the 4 metre lengths. Is there a catch? Is it the case that "fiberglass is fiberglass is fiberglass", as I think Gertrude Stein once said, or is there a huge difference in quality between what kite suppliers sell and what window blind suppliers sell?

I have no problem buying internationally from Goodwinds if the product is a quantum leap ahead of what I can get from the company above.

Also, how many gobars would you normally use to close the box? I am thinking one every inch along the rim would be about the mark, is that too many, or too few ? ( I am using fish glue throughout the build btw, for everything).
Author:  Todd Rose [ Tue Dec 11, 2012 6:50 am ]
Post subject:  Re: Go-bar question
I don't mean to start an argument, here, but I wanted to see for myself whether the force exerted by a go-bar increases the more it is flexed. I did a simple test using a scale to measure the force with different amounts of bar flex. The more I flexed the bar (i.e. the greater the deflection), the higher the scale read.

Take it or leave it.
Author:  Robert Hosmer [ Tue Dec 11, 2012 8:39 am ]
Post subject:  Re: Go-bar question
murrmac wrote:
I did a bit of surfing and came up with this company in the UK who are selling 4mm fiberglass rods (which would be the equivalent of the 3/16") for what seems to be to be a staggeringly low price ...I figure I can get a single gobar for like 20 pence, if I buy the 4 metre lengths. Is there a catch? Is it the case that "fiberglass is fiberglass is fiberglass", as I think Gertrude Stein once said, or is there a huge difference in quality between what kite suppliers sell and what window blind suppliers sell?

I have no problem buying internationally from Goodwinds if the product is a quantum leap ahead of what I can get from the company above.

From the previous posts in this thread, it seems that any diameter can be suitable provided it is the correct length. So if we're aiming for approximately 8-10 pounds of pressure, we have already established that 3/16" rod with a length of 24" works well for our application.
The 4mm diameter is slightly smaller than 3/16"; actually closer to 5/32". So will it work? Yes, but with the length of 24", will provide slightly less pressure than actual 3/16".
So what to do? If you use 4mm diameter rod, make it slightly shorter in length. Instead of using 24", try 22" (hopefully someone good with the formulas can verify this).
With your stock coming in lengths of 4 meters, making the rods 24" each can give you 6 rods. But if you cut them to 22", then you can get 7 rods.

Here is how I would approach it: Take your 4 meter length and cut off two rods- one at 24" and one at 22". Determine which length works best for you. If you decide that the shorter length (22") works better, you still have enough stock left to get 7 rods.
Author:  murrmac [ Tue Dec 11, 2012 11:25 am ]
Post subject:  Re: Go-bar question
Thanks again, gentlemen, advice taken regarding the variability of wooden bars.

I have ordered 14 rods @ 4metres and will probably cut them to 22", but will do the experiment which Robert suggested. 22" (or just under) will give plenty of working space, I would have thought.

The cost works out slightly more than I had anticipated, what with tax and carriage, ( plus 200 vinyl caps) but still very reasonable IMO.
Author:  Todd Rose [ Tue Dec 11, 2012 11:41 am ]
Post subject:  Re: Go-bar question
Just FYI, for anyone who finds this to be useful or interesting information... My go-bars are 1/4" D fiberglass, 36" long. With slight deflection, the scale I used (just an ordinary, non-digital kitchen scale) read about 5.5 lbs. At 1" deflection, it's 7.75 lbs. 1 1/2", 8.25 lbs. 2", 8.6 lbs. 2 1/2", 8.8 lbs. 3", 9 lbs. 3 1/2", 9.15 lbs. 4", 9.25 lbs. (These readings are obviously not super-precise, but pretty close.) It keeps going up from there, all the way up past 11 lbs if I really bend the heck out of it, but, as you can see, the pressure went up more than a pound between 1" and 2 1/2", then after that the rate of change slowed down a lot. Beyond 4" of deflection, the pressure only changes about .15 lbs per inch of deflection.

I'd rather get about 9 lbs per bar than 7.75 lbs, so I'm happy having my bars flex about 3" rather than 1". YMMV.

In case you're wondering, I did these measurements really quickly by putting the scale on the floor under my drill press table and lowering the table to increase the flex of the bar.
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