Heads up for some bargains.

[ozwood]

Hi All ,

Thought I would share a few Bargains with you all.

Bargain number 1: Kmart has Jakeroo 7.9 mm flexible F/G tent poles 4 per pack 700mm long usually joined together to use on dome tents , but seperatly will make great go bars with the addition of some rubber ends from clarke rubber only $4.00 per pack , that's $1.00 per go bar, they are on Clearance . I got 6 packs , should I grab some more ?

Second bargain: for those with dry rooms and dehumidifiers that have Humidistats that are not really accurate :
http://www.ebay.com.au/itm/320776300824 ... 1438.l2649


Third bargain : Bunnings are changing there supplier of saw blades , so at least at my local bunnings all the Irwin Brand of Blades are reduced , I got a 9 1/4" 60 tooth Weldtech blade for $13 and a 10" Thinkerf 40 tooth weldtech blade for $10.


Cheers,

[Bruce McC]

Thanks for the heads up Paul. I just raided the local KMart store.
Sorry Dom / Graham /Chopper.

[brian64]

Thanks for the heads up, Paul. I headed down to K-Mart Chadstone today and scooped up 6 packs of the F/G poles. I even left a few packs for other ANZLF'ers.

Does anyone have any guidelines for how much to flex them into place? That is, for the 700mm pole, about how much space should there be between the top of the go-bar deck and the point of contact on the item being glued? I haven't used go-bars for a while, and those were hardwood, so not only don't I remember, I'm sure it's not the same.

Thanks in advance,

Brian.

[charangohabsburg]

I even left a few packs for other ANZLF'ers.

Thanks, I'll jump on the next plane to Australia to grab the rest of it!

I am using the "original LMI tentpoles" and I prefer to only bend them a bit more than necessary in order the first bar will not be straight (eg. drop out) when I put in the last one, which of course has to do with the rigidity of the go-bar "roof and floor" (very sturdy in my go-bar setup). In numbers, this means that I bend my 600mm poles (5mm diameter) until their deflection in the centre reaches approximately 30mm. My (adjustable) go-bar deck hight depends on what I put in, I never measured it. If I feel I need more clamping pressure I just add more go-bars.

If you ever get close to break them you went too far! Bending these sticks that much is not necessary at all, it doesn't give you more clamping pressure (but maybe an adrenaline rush).

[68matts]

Thanks for that Paul.
I got 5 packs from my local store, don't know if that will be enough but I guess I'll find out once I set up somewhere to use them.
Cheers

[lauburu]

Now that some time has elapsed since the first post, has anyone had a chance to use the 7.9mm go bars in a build? I had a look at them in K Mart and they felt a bit too rigid. I'm by no means an expert in this area but my research suggests that a diameter of about 5mm is the norm for fibreglass go-bars. Awaiting your opinions to take advantage of the Boxing Day sales.

[Kim]

Now that some time has elapsed since the first post, has anyone had a chance to use the 7.9mm go bars in a build? I had a look at them in K Mart and they felt a bit too rigid. I'm by no means an expert in this area but my research suggests that a diameter of about 5mm is the norm for fibreglass go-bars. Awaiting your opinions to take advantage of the Boxing Day sales.

Its not 'only' diameter, applied pressure is relative to length as well. I have not used 8mm rods but at only 700mm long I suspect you are correct to feel that over that length, 8mm would apply too much pressure with a risk of bruising softwoods like spruce, or being prone to shooting off the work piece at a velocity with potential to cause loss of limb or perhaps even life!!! .....

OK, well that last bit about limb and life is probably stretching it just a little but if someone happened to standing behind you at the time with a revved out chainsaw when you got hit in the face by a flying gobar and stumbled back....it could happen then..If on the other hand you were to hang up a sign each time before you went to use the deck saying "Please Turn Off Chainsaws Before Entering This Shed" then it should be a bit safer I suppose but I reckon the first bit about bruising the spruce and the other bit about being hit in the face are worth taking more seriously.

My gobars are 1/4" or 6>mm. At 940mm they apply over 2kg...can't be more detailed as my only working scale these days tops out at 2kg, but I seem to recall when I first built the deck that just a tad under 10lb was the measurement taken. Anyhow whatever it is a 6.3mm x 940mm gobar applies plenty enough pressure and I think bars 20% thicker x 20% shorter would at the very least prove to be a real handful...

By the way, it is easy to assume that greater deflection of the gobar = more applied pressure....This is not so, applied pressure remains the same regardless of deflection. Consistency of applied pressure is the advantage that standard gobars have over spring loaded bars which increase applied pressure as their springs becomes more compressed.

Cheers

Kim

[Bruce McC]

Lauburu

Yes they are a bit stiff, but I have never used a go bar system before so I have nothing to compare with.
I bought 6 packs x 4 x 7.9 mm poles and fitted 6mm rubber caps from Clarke Rubber to one end of each pole.
I used them recently to glue the bracings on to a sound board and had no problems. I set the height of the
go bar deck to suit the tallest braces ( cross braces) then used wooden shims on poles holding down thinner
braces (finger braces) otherwise they would have been too short. I hope you can follow my ramblings.

Happy New Year.

[kiwigeo]

I adjust height of my deck using a false floor on the deck. The false floor can be set to different heights by sticking different size MDF "chocks" in between the false floor and the actual floor of the deck.

[simso]

Mine is the same as martins, My bars fit straight between the top and bottom loose, I add false floors to achieve my desired tension and flex

[Kim]

Mine is the same as martins, My bars fit straight between the top and bottom loose, I add false floors to achieve my desired tension and flex

My set up is much the same as well, its just my "false floor" is generally the 50mm radius dish or the body mold on top of that dish...I use the very same 940mm x 6.3mm rods either way, but adding that much more height does not increase clamping pressure any, it just increases the likelihood that the bars will slip off the work surface because of increased deflection and the angle that places on the end of the rods.

As I understand the applied pressure of the gobar remains much the same from initial defection to an eventually 'decrease' just prior to catastrophic failure as load is transferred from the ends into the apex of the curve in the flexed member....There is some engineering formula on column loading which explains this but you can prove the same for yourself with a bathroom scale...or perhaps Jeff Highland would be kind enough to jump in and offer some education??...Bottom line for Laubara's question is the greater the diameter of the gobar, the longer it needs to be to avoid applying too much pressure.

Cheers

Kim

[jeffhigh]

It's the Euler formula which gives the maximum load a slender column can carry before (or after) buckling.
Generally for a go bar setup we prefer to have bars which are flexible enough so that we are using them in buckling mode so that the force exerted is the same despite some variation in thickness of the object clamped
If you buckle the rod too far rupture will occur
From wickepedia
"In 1757, mathematician Leonhard Euler derived a formula that gives the maximum axial load that a long, slender, ideal column can carry without buckling. An ideal column is one that is perfectly straight, homogeneous, and free from initial stress. The maximum load, sometimes called the critical load, causes the column to be in a state of unstable equilibrium; that is, the introduction of the slightest lateral force will cause the column to fail by buckling. The formula derived by Euler for columns with no consideration for lateral forces is given below. However, if lateral forces are taken into consideration the value of critical load remains approximately the same.

F=pi^2*E* I/(K*L)^2

where
F = maximum or critical force (vertical load on column), E = modulus of elasticity, I = area moment of inertia, L = unsupported length of column, K = column effective length factor, whose value depends on the conditions of end support of the column, as follows. For both ends pinned (hinged, free to rotate), K = 1.0. For both ends fixed, K = 0.50. For one end fixed and the other end pinned, K = 0.699.... For one end fixed and the other end free to move laterally, K = 2.0. KL is the effective length of the column.

[Kim]

Thanks Jeff...must admit that despite your fine effort nothing much changed for me from the very first time I seen that formula and understood little enough to find my right brain had me out in the shed with kitchen scales... The strange thing is that once proven that way, what is happening before your eyes becomes so logical that its difficult to understand how one could ever have see it any other way...sort of a round earth moment I guess..

That said what happens when one draws a long bow can be misleading to ones logic. Pull the bow back further and the arrow will fly further providing clear proof that more stored energy was released into the arrow with a greater deflection of the bow (column)...Well yes there was indeed 'more' energy released, but that energy had been no more 'intense' than the energy stored in the same bow with a lesser deflection. Rather what made the arrow fly further was stored energy at the same intensity being applied to the arrow for longer duration. So with a greatly deflected gobar, that energy only come into play when you are releasing the glued components from the deck because you then must contend with that energy for a longer period each time you remove a gobar...so not more pressure, just a greater duration of the same pressure as you release the go bar.

Please forgive my use of the word 'intensity' if it is incorrect??, but I am hoping most will understand the rational in my analogy anyhow.

Cheers

Kim

[jeffhigh]

That formula is mostly used by engineers to ensure that their column does not buckle.
Here for a go bar setup we WANT the bar to buckle so we make sure that the value is fairly low by making the bar long and thin.
I just use timber slats and thin them till they feel right to me- no calcs

[lauburu]

Many thanks to all learned contributors. WAY more information than I expected but seeming to confirm my suspicions. Also thanks to Kim for the valuable tips about avoiding chainsaw accidents. I've decided to remove the chainsaw from my workshop altogether even though it means it will now take me a bit longer to scallop my braces and inlay my rosettes.

[Bruce McC]

Oh I forgot to mention, I had to reinforce the top plate of my Go Bar Deck because it
was deflecting with the pressure of the rods. ( The base was a radiused dish.)
Thats how stiff the rods are with minimal deflection. Maybe they weren't such a bargain.

[vandenboom]

Oh I forgot to mention, I had to reinforce the top plate of my Go Bar Deck because it
was deflecting with the pressure of the rods. ( The base was a radiused dish.)
Thats how stiff the rods are with minimal deflection. Maybe they weren't such a bargain.

I'd agree, they are a bit on the heavy side. I got my wife to buy me 6 packs as I was interstate until last weekend. However, by joining two together and using a longer length, you get more flex and a bit more opportunity to control the pressure. I know that doubles the cost, but for me it will make them more usable. Frank

[Bruce McC]

.......I knew those joiners would come in handy someday!!!!!

[charangohabsburg]

[...] to find my right brain had me out in the shed with kitchen scales... [...]

Kim, there is no big difference between you and Euler. It only seems that Euler could not afford a kitchen scale, so he had to derive that formula.

[Kim]

Too kind Markus, thank you mate.

[brian64]

I'd agree, they are a bit on the heavy side. I got my wife to buy me 6 packs as I was interstate until last weekend. However, by joining two together and using a longer length, you get more flex and a bit more opportunity to control the pressure. I know that doubles the cost, but for me it will make them more usable. Frank

I was using the floor as the bottom plate of the deck, and the underside of the bench as the top plate.... until the bench started lifting up when I added the 9th or 10th pole!

Frank, did you use the joiners that came with the poles to join them together? Did the joined poles act as one long pole to all intents and purposes, or are there challenges to look out for when using the joined poles?

Thanks in Advance.

[charangohabsburg]

Too kind Markus, thank you mate.

Dear Kim, I just wanted to let you know that I prefer a kitchen scale over a wikipedia quote... Seriously, I think that the kitchen scale approach is a much better understandable explanation of how go-bars really work or, that the kitchen scale part of Euler's formula is all what luthiers need to know. This is why Euler doesn't matter to luthiers that much as kitchen scales do.

I was using the floor as the bottom plate of the deck, and the underside of the bench as the top plate.... until the bench started lifting up when I added the 9th or 10th pole!

[kiwigeo]

[...] to find my right brain had me out in the shed with kitchen scales... [...]

Kim, there is no big difference between you and Euler. It only seems that Euler could not afford a kitchen scale, so he had to derive that formula.

I dunno....having seen a picture of Kim it's a pretty safe bet that Euler was alot better looking.

[vandenboom]

Frank, did you use the joiners that came with the poles to join them together? Did the joined poles act as one long pole to all intents and purposes, or are there challenges to look out for when using the joined poles?
Thanks in Advance.

Brian, I haven't looked at this closely yet so can only comment on what I think I will do with them.
The gobars I have used until now are 6mm diam and around 1 metre in length. I gather this is probably a bit longer than what many others use. I am used to the pressure they apply and find they work for me. I think the greater length offers a bit more latitude for height variation eg. 15-20mm difference I have between upper and lower bouts body width.
I wouldn't be able to use the shorter/thicker K-Mart poles in this way. But when I very quickly tried flexing two poles joined together with one of the supplied joiners, I was more comfortable with it. What I still need to try is cutting a pole in half (i.e. make 2 go bars out of 3 poles to create something with similar length to my existing go bars) to see if I like the flex that offers. I reckon it will. A bit of duct tape on the joiner will work fine. If they apply a bit more pressure than my other bars, perhaps I will use them on the heavier braces eg. transverse. Frank

[Kim]

If one were to make a "V" jig for their thickness sander to establish a facet in the over sized rod maybe they could be taken down to say 5.5 or 5mm square, or hexagon, or pentagon easily enough to make the bunnies rod work OK...I'm thinking 5 or 5.5mm should be about right for 700mm long but you would obviously need to test the water yourself. If anyone bothers to try this, watch the dust (mask-up) and reseal the rods with epoxy when they're resized to prevent splintering....could be worth a try.

Cheers

Kim