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Go-bar Clamping Strength
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=15327		 Page 1 of 1
Author:  Wes McMillian [ Fri Jan 11, 2008 3:52 am ]
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What do you consider a "proper" clamping strength for go-bars? Anybody checked with a set of scales. etc? I know many of you use the typical formula of a (24"?) deck with fiberglass rods, how do those test out?

Reason I ask is, I am setting up to brace my first one since moving and setting up shop again. Rather than building the "typical" deck height, I'm looking at bracing off the ceiling, so my go-bars are gonna be pretty long, in the 5' range. I'm ripping them out of some old unindentified hardwood stock and testing by feel, and they seem to be coming out about 1/2" thick. Realizing that clamping strength will be a function of material, length, thickness, etc, I thought a ballpark would help me know if I'm getting close at all.

Ballpark is plenty close. No need to set up a deflection testing rig, vibration analysis or calculating MOE, please!
Author:  Bruce Dickey [ Fri Jan 11, 2008 4:16 am ]
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Wes, a half an inch?

Those are some mighty gobars sir.

Everything's bigger in Texas I suppose.

We have folks from Iroquois Falls to Adelaide doing it all sorts of ways, with kite parts, driveway markers, hardwood dowels (me), spring loaded PVC. So I expect yours will work just fine.

Here is the test, if you get squeeze out it's working.

Test 2, if your braces fall off as you continue to build, reconsider test one, you got it too tight!   

Others will be along to give their magic formulas of testing in a bit. Be patient, or.... go look in the archives...   
Author:  Wes McMillian [ Fri Jan 11, 2008 4:27 am ]
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[QUOTE=Bruce Dickey] Everything's bigger in Texas I suppose. [/QUOTE]

You got it! I figger with enough clamping pressure I won't even need glue, just fuse the material together!

I know 1/2" would be WAY too much on a typical length go-bar, but these are so long, I thought the extra girth would be needed. To ME they feel approximately what my old go-bars did on a shorter deck. But, then again, they were ripped from old stock too so, who knows, they may not be the best base line. That's why I figured clamping pressure may be a better indicator.
Author:  Michael Dale Payne [ Fri Jan 11, 2008 4:28 am ]
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Between 8 and 11 lbs of loading force per rod is ideal. Check the arcives and you will find colum calulations. You will be supprised How little the amount of bow makes
Author:  Michael Dale Payne [ Fri Jan 11, 2008 4:30 am ]
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Should have read

You will be surprised how little difference the amount of bow makes on the column loading force.
Author:  burbank [ Fri Jan 11, 2008 4:31 am ]
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wow. 5 ft seems really unwieldy. Can you put a sort of upside down table on the ceiling, say 2 or 3 ft tall, and use shorter bars?

like this?



One edge is anchored to the wall, the other has 2 x 4s going to the ceiling joists (he diagonal on the right is just for the shelf on the right, not connected to the deck).
Author:  burbank [ Fri Jan 11, 2008 4:35 am ]
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[QUOTE=MichaelP] Between 8 and 11 lbs of loading force per rod is ideal. Check the arcives and you will find colum calulations. You will be supprised How little the amount of bow makes [/QUOTE]

I got in that range with 3/16" x 24" fiberglass bars. And it's true, you get pretty constant force over a wide range of deflection.
Author:  Michael Dale Payne [ Fri Jan 11, 2008 4:42 am ]
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Once a column is loaded it is loaded. All additional force goes into deforming the column creating a loded spring not downward monent.
Author:  Wes McMillian [ Fri Jan 11, 2008 5:32 am ]
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Thanks for the education, guys. Interstingly (at least to me) I got ~10# with 3/8" or slightly less, even at a final length of 4'9". And, in keeping with the cube rule, the width of the rod made little difference.

This is somewhat a temporary measure at this point, and I am actually bracing on top of my table saw. I intend to put in something more permanent along the lines of what you've got, Pat. Been thinking about some free hanging cabinets over my 8' island workbench that will allow me to use the whole thing as a go-bar deck. At any rate, I'll have it pretty tall. At over 6', I like plenty of room to work without bumping my head.

I noticed I've got a little give in the OSB in my ceiling. Where one go-bar tested at 14-17#, five of them tested to 50#. Another reason to build a more permanent structure.

Forgot to mention, I'm using HHG for most everything soundbox related. If my understanding is right, which it rarely is, I may be able to get by with less clamping force, anyway. Right?

Back to the shop! Thanks again!
Author:  Hesh [ Fri Jan 11, 2008 5:43 am ]
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[QUOTE=burbank] [QUOTE=MichaelP] Between 8 and 11 lbs of loading force per rod is ideal. Check the arcives and you will find colum calulations. You will be supprised How little the amount of bow makes [/QUOTE]



I got in that range with 3/16" x 24" fiberglass bars. And it's true, you get pretty constant force over a wide range of deflection. [/QUOTE]

I measured the Stew-Mac and LMI go-bars before and posted pics, which I can't find at the moment.....

But what I recall is that the LMI metal go-bars, my favorite, are around 8 pounds and do best with around 1" or less of deflection.  Beyond 1 1/2" deflection and the clamping force went down......

The Stew-Mac fiberglass bars had something like 17 pounds of pressure with 1 1/2" deflection but I am not sure if I am remembering this correctly.
Author:  JohnAbercrombie [ Fri Jan 11, 2008 5:56 am ]
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Wes-
Moving to a shelf (well-braced) and 36" or so bars will probably be more convenient than messing with 5' gobars.
I have my ambient air filter unit and some other junk on top of my shelf, which has a solid 2x4 frame.

That said, 1/2" is not unreasonable at all for a longer bar, depending on the wood species you are using. You can always use 'em for kindling if you change your setup, or run them through the thicknesser to get more flex.

For the calculations, download rodbuckle.xls from
Left Brain Lutherie site...a bit of messing with numbers will tell you what you need to know (if anything) about the theory.

Cheers

John
Author:  Hesh [ Fri Jan 11, 2008 6:06 am ]
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Here is the thread where we evaluated go-bars.

http://www.luthiersforum.com/forum/forum_posts.asp?TID=12720 &KW=go%2Dbars#forumTop
Author:  Michael Dale Payne [ Fri Jan 11, 2008 6:07 am ]
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Wes my nex trip to Ft Worth I may have to stop by and see ya.
Author:  Wes McMillian [ Fri Jan 11, 2008 7:06 am ]
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Thanks for the link Hesh. That Guests guy did a pretty cool test on go-bars too!

Todd, I did test these at 3/8" and with my "mystery wood" go-bars I got 10# or so, on average.

I'm still making up my mind how I want to do the permanent fix - whether using my island workbench or build a separate go-bar bench along a wall. Either way, when I do I'll use an overhead shelf or cabinet. Can't have too much storage space in a small shop. John, that's sounds like a perfect location for an ambient air cleaner. I like that.

Michael, stop by any time! I'm literally jsut over a half mile from I-20. Hopefully I'll be off work when you come through. Danged ol' power plant schedule. I worked over 800 hours O/T last year! Not planning to this year, though...
Author:  Rick Hubka [ Fri Jan 11, 2008 7:16 am ]
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The Hubka Gear Driven Go-Bar Deck.
If I had known how much work and $ this would have been for the small benefit I get out of it I would never have done this.
I need to start thinking as a guitar builder and not a ex homebuilt airplane builder.  I'll say one thing...  It allows for easy pressure adjustment.  Here's a picture for your amusement.
Author:  Michael Dale Payne [ Fri Jan 11, 2008 8:01 am ]
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Out of curiosity how do you lock it to maintain load tension? Seems to me if there is no lock on the gear and chain it could freewheel to lose. never mind, I am guessing there are nuts both sides of the risible deck. That would likely keep enough friction on the threaded bars to avoid freewheeling
Author:  burbank [ Fri Jan 11, 2008 8:11 am ]
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Seems to me a thread pitch anywhere near 20 tpi (20 turns to move it an inch) would do it.
Author:  Rick Hubka [ Fri Jan 11, 2008 8:18 am ]
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There is no freewheeling due to my sloppy building.  It actually takes about 5 pounds pressure just to move the adjusting arm on top.  At first I was upset about this.  It was a lucky mistake
Author:  grumpy [ Fri Jan 11, 2008 8:25 am ]
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My bars are 3/4" wide by 1/4" thick(all measurements approximate) and just under 30" long. I have shorter ones for closing bodies. They put out around 12lbs each.

Instead of altering the go bar deck height, just keep a handful of 24x24" slabs of MDF beside the deck. Stack them up as needed... Setup the deck use at least one slab(for example, if you plan on using 24" bars, make the deck 24-3/4"), and then you can go either way.
Author:  Rod True [ Fri Jan 11, 2008 10:14 am ]
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I have a built in go bar deck I've shown many times before but will do again.



The nice thing with this design is that I don't need to store a separate go-bar deck somewhere and actually, I use the bench space for many other things (you can see my vice set there). This is a very inexpensive go-bar deck, it's all just scrape 2x4 and plywood for both the lower deck as well as for the loft above and it holds many other purposes other than just a go-bar deck. I highly recommend this style

I've taken many que's over the years from Mario, maybe it's my turn to name a guitar after him, but I don't want to call a guitar grumpy, it might not sound very good    (this is a joke of course)

I like Mario, use 3/4"x1/4" hardwood scrap. Actually, I have some fir pieces which don't excerpt as much pressure as the maple pieces I use in the picture there. The hardwood I have came from flooring scraps when my neighbour was putting down new maple flooring. I've not measured the force these bars put down, but they certainly do the job just fine.

Also like Mario, although I didn't get the idea from him but someone else I think, I stack MDF dishes to adjust the height of the deck.
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