Official Luthiers Forum!

Michael

I never knew it to Forget it

Unless of course I have Forgotten that I knew it

Thanks B

An thank you everybody else too, your awesome.

Ok, you all beat me to it. That's what I get for screwing around on the job.

[QUOTE=MichaelP] Phil you have not been out of school long enough I have long since forgot the dates of Newton's publications not to mention those of my contemporary, "Pythagoras" [/QUOTE]

Ah - but I have been out of school long enough to confuse Newton and Euler. It was really Leonhard Euler - or, "Lenny", as we used to call him - (1707-1783) who first described buckling.

Sorry about the confusing wording. I really did meam what most of you concluded: if you double the diameter, the force would go up 16 times. So, you would have to make the larger diameter rod four times as long to bring the force back down to the original level.

Phil

Russell, I recommend that if your deck remains at 24" high, that you make some shorter rods for the top and back application. The longer rods will work, but with that much deflection, it is hard to make them stay in place. I just bought a secong bunch of rods and cut them about 3.5" shorter for the top and back. Worked great.

Ron

_________________
OLD MAN formerly (and formally) known as:

Ron Wisdom

Somewhere in the middle of Arkansas......

Ron,

So, on a 24" deck, you have your bracing rods set at 1" shorter and your top and back rods are 4 1/2" shorter than the base measurement ID?

Mike

Thanks Ron

What I was thinking was if I made the Deck deeper and then had a removable platform in the bottom, when bracing tops and backs, I would have the platform in, when joining the top and back to the rim I could take it out, then I would be able to use rods all of the same length.

The other way I thought would be to make the height of the top of the deck adjustable, but I haven't quite figured a good way of achieving this.

Russell, removable platform for closed boxes, 1-1.5" deflection (it will vary with different braces), keep all the rods at 24". OK?

By the way I occupied Isaac Newton's rooms, at Trinity College, Cambridge, for three years. Unfortunately he didn't leave his genius behind!

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

Thanks Colin

The Rods all arrived this morning what a great firm to deal with, thanks for the great tip.

I am keen on a solution that allows me to have all my rods the same length. So I'll go the platform root.

Now that must have been a great buzz for you, I reckon you can't be doing too bad, if people want you to go all over the world doing work for them.

Hi guys, is there a consensus here on rods heights ? Is 24" the consensus? I was thinking of making rods long enough to start clamping from my bench top and up to the shop ceiling, would you recommend i would not do this or is it ok?TIA

Serge

That's pretty much what I have. Although, I like Russell's idea of a removable platform and only using one size rod.
But, it is not a problem having two rod sizes.

Ron

_________________
OLD MAN formerly (and formally) known as:

Ron Wisdom

Somewhere in the middle of Arkansas......

Thanks Ron, thinkin' of it, it makes a lot of sense too especially for the small shop, less clutter if i have only one size heights rods.

Russel,

I have resolved to use the same solution as you. My deck is 3/4 MDF bottom, 3/8 inch ready rod ("all thread" I guess?) for the columns and 3/4 inch ply for the 'roof'. I have found that I need to support the roof as it defelcts, I have some maple cut that I will screw in a grid to the top side of the roof, that will stiffen it up. For gluing braces I had my deck set at about 23 inches above the radius dish I had placed on the deck and it worked great (I use 3/16 fibreglass rods, 24 inches long). Then I used the deck to attach the top and back and just raised the roof. This is doable but unneccessary and time consuming. So I am going to build a sub-base that will go under the radius dish for gluing braces and will be removed for gluing on the top and back. My guitar has a taper from front to back of about 1 inch, so that is taken into account when setting the deck top height!

Great minds think alike!

Shane

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Canada

Thanks Shane

My old deck has the same problem with the deck deflecting, one of the reasons I want to build a new one and to incorporate the deck for rims and some Rod storage.

I can't claim the deck indea as my own, I have seen it somewhere, can't remember where probably someone on the forum.

What a brilliant idea! storage in the platform, ya got me by the belly there Russ, sure gonna try this for mine and Shane, threaded rods sure is the way to go and maybe 1" thick MDF should do the trick for deflection, maybe? i'll give it a try and let you know!

Thanks ya bunch a brilliant folks!

Serge

Serge, the top of my deck is two layers thick. One MDF (3/4) and one plywood (3/4). I haven't noticed any deflection.

Ron

_________________
OLD MAN formerly (and formally) known as:

Ron Wisdom

Somewhere in the middle of Arkansas......

3/4 mdf will deflect nearly a 1/4" depending on the numbers of gobars and the loading pressure , 3/4 -5 ply will deflect about 1/3 as much, 3/4-10ply even less. but any deflection can lead to a aready set go-bar letting loose while setting another. This can be tragic. I suggest 2 sheets of 3/4 10ply lminated togather for both the top and base and 3/4" allthread posts. I find 1/2" allthread posts do not have quite enough rigidity fo my taste.MichaelP38786.5721643519

Serge

Glad I gave you an idea

Michael Thanks for the advise on the deck, my current one has 3/4" ply but as you say it deflects too much, I will double up on the ply.

Thanks guys, so let's say i take 2 layers of 1" thick MDF glued together for both the bottom and top with 3/4" threaded rods as columns, i should be ok?

Would have thought that would be good Serge.

Russell: I've found a way to have an adjustable go-bar deck, thanks to an
idea from an Internet friend, Mark Frazier. Here's the page on my website
which describes it (I don't know how to post an image in this message!):

http://pweb.jps.net/~msm/htmlpages/ps15.html

It just uses part of those Pony clamps to hold up the upper deck.

Kathy Matsushita

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Kathy Matsushita
San Jose, CA USA
http://theamateurluthier.com
Facebook: https://www.facebook.com/kathy.matsushita

[QUOTE=bbeardb] It's divided by Length, so if the rod is shorter, the forcer is greater.

So in your example, if you half the thickness, you have to make the rod four times shoter in order to keep the same force as it had in the beginning.


At least that's how I'm reading it.


Boring math below if it helps. I'm bored, and it's been a long time since I've had to do any kind of math.


Arbitrary numbers, but let's say the rod is "2" thick and "2" long, force equals 39.44 (9.86*2^4/2^2) - 9.86 is Pi squared -. Now make the rod 4 thick, and keep it 2 long, force now equals 631.04 (9.86*4^4/2^2), 16 times greater!. In order to increase thickness but make force equal, length must increase to 8 (9.864*4^4/8^2 = 39.46 - same as the first, rounding error.)[/QUOTE]

Come on! Now you're just showing off!

You're starting to sound like my dad!

"Son, since you're having problems with long division, I want you to sit down and spend you're Saturday, doing these "easy" problems I have written out for you" 4 hours later....

A luthier was born!!!

Regards, Steve

Kathy

Many Thanks.

Thats an ingenious solution.

Russell

Hey Kathy, glad to see you with us. you need to stop in way more often MichaelP38786.8024305556

[QUOTE=kmatsu] Russell: I've found a way to have an adjustable go-bar deck, thanks to an
idea from an Internet friend, Mark Frazier. Here's the page on my website
which describes it (I don't know how to post an image in this message!):

http://pweb.jps.net/~msm/htmlpages/ps15.html

It just uses part of those Pony clamps to hold up the upper deck.


Kathy Matsushita[/QUOTE]

Kathy, is that you! I was just thinking of sending you an e-mail to invite you to this great forum since you have already helped so many people already and me also by the same way, your contribution here will be more than appreciated!

Hey folks Kathy is here with us, we must have done somethin' good to deserve this.

Just in case, my sincere welcome Kathy!
Serge Poirier38787.0582060185