(help) Alignment Table Size??

[Dave Kirk]

Here's why I think the way I do. Say you're out 20 thou. You stick a big bar in there and yank on it pretty hard to get it to move. But say you go too far, say 5 or 10 thou. Why do you barely need to breathe on the thing to go back those 5 thou? I think bending fork blades is a bit different because you are clearly going past the yield strength of the material to get it to deform. I dunno. I can only say what I observe. It was astounding to watch how hard it is to move a titanium tube when aligning a frame, but how easy it was to go back a few thou if they went past the zero point.

You are experiencing the results of a system. If you had just a seat tube stuck to a BB shell and you cold set it it will be pretty damn stable. You move it .010" and it will stay there. When you then hook a top and down tube to the seat tube and try the same thing you get a different result. If you then cold set the seat tube .010" you are not cold setting the top and down tubes - they are just loaded or flexed into that new position. They have not taken a set and when you push back on that seat tube you are then flexing it (not cold setting) and the tension built up in the rest of the system will hold it back a small amount. So you think that it's the 'memory' of the seat tube calling it home but in reality it's the other tubes, in constant torsional tension, that are pushing it back toward where it used to be.

The tubes don't want to go back where they were once cold set. Once you deform it it has a new 'home'. It's the other tubes influence on the system or package that give you this impression.

dave

[zank]

I can dig that. All the more reason to build it straight to begin with.

[Archibald]

I can tell you with 150% confidence, without a shadow of a doubt, that steel does have a memory, and under load/stress it will go back to a home position.

Only when working within its elastic range. Once it's been stressed beyond its yield into its plastic range it will have a new "memory." When you're bending tubes such as fork blades and stays, to keep it bike specific, you get what is commonly referred to as "spring back." That is because once a tube has been stressed into its plastic range, it still wants to return to its original shape but cannot.

[Archibald]

You are experiencing the results of a system. If you had just a seat tube stuck to a BB shell and you cold set it it will be pretty damn stable. You move it .010" and it will stay there. When you then hook a top and down tube to the seat tube and try the same thing you get a different result. If you then cold set the seat tube .010" you are not cold setting the top and down tubes - they are just loaded or flexed into that new position. They have not taken a set and when you push back on that seat tube you are then flexing it (not cold setting) and the tension built up in the rest of the system will hold it back a small amount. So you think that it's the 'memory' of the seat tube calling it home but in reality it's the other tubes, in constant torsional tension, that are pushing it back toward where it used to be.

The tubes don't want to go back where they were once cold set. Once you deform it it has a new 'home'. It's the other tubes influence on the system or package that give you this impression.

dave

Agreed w/ the caveat of my last post.

[Dave Kirk]

Agreed w/ the caveat of my last post.

Cool. Does this mean I can have a shot of the good stuff at the next show?

It's funny. Some treat this like there is some black magic/fairy dust thing going on and of course there is nothing of the sort. The complication comes from the fact that while a bike frame is pretty damn simple in concept that it's a complicated structure once all together and harder to understand what is going on.

dave

[zank]

you callin me a fairy?

[Dave Kirk]

you callin me a fairy?

Are you covered with dust?

dave

[zank]

cologne.

[Curt Goodrich]

You are experiencing the results of a system. If you had just a seat tube stuck to a BB shell and you cold set it it will be pretty damn stable. You move it .010" and it will stay there. When you then hook a top and down tube to the seat tube and try the same thing you get a different result. If you then cold set the seat tube .010" you are not cold setting the top and down tubes - they are just loaded or flexed into that new position. They have not taken a set and when you push back on that seat tube you are then flexing it (not cold setting) and the tension built up in the rest of the system will hold it back a small amount. So you think that it's the 'memory' of the seat tube calling it home but in reality it's the other tubes, in constant torsional tension, that are pushing it back toward where it used to be.

The tubes don't want to go back where they were once cold set. Once you deform it it has a new 'home'. It's the other tubes influence on the system or package that give you this impression.

dave

Bingo! I only used the fork blades and chain stays to illustrate the fact that once bent the tubes stay there unless bent again. But like Dave wrote so well there are other tubes of varying diameters, wall thicknesses and butt profiles that are all connected. When bending the frame into alignment some of the tubes actually bend while others may only flex into place. This builds in tension that's less than ideal. So build them straight in the first place is the goal. I will say that any frame builder that claims to never bend a frame is either posturing or hasn't built enough bikes yet or has very loose tolerances.

[steve garro]

I have to say that I depend on the table ALLOT. while I can stand, one of my legs is 1.75" longer and I cannot wrench on anything accurately. Many of my frames use a 1/.7/1mm x 35mm Supertherm DT. you are not going to cold set that, you will snap your tacks or twist your TT 1st. I have to pull with tacks. almost always towards the non-drive, I tack different {lighter} with my left hand......but like I'm assuming everyone does, the CS's need a few MM of massaging every time one way or the other. I see large diameter tubing as a "fixture" of sorts. a tight fishmouth goes a long way. thanks for the great thread, guys. good stuff! - Garro.

[e-RICHIE]

I will say that any frame builder that claims to never bend a frame is either posturing or hasn't built enough bikes yet or has very loose tolerances.

i guess it all depends on where the boundaries are atmo.

my standard is to allow one (only) alignment check to exceed no more than 1mm error,
OR have all alignment checks cumulatively add up to no more than 1mm error. the stuff
i measure includes the linearity of all tubes in relationship to the table surface, the axis
of the steering lin in relationship to the table surface (as well as to the other pipes), and
the split distance of the rear of the bicycle in relation to the front it. one spec i won't
"allow" this error on is the wheel placement in the seat stays. it must be centered and
beyond scrutiny.

forks are no brainers atmo. blades must have the exact same offset. both offsets should
be in the same plane. and the tips should be equidistant from the steerer center-line.

[cement shoes]

Tony,

I have a 30x36 cast iron table. I bought it from Industrial Surplus (they're in CT) for $250 and had it shipped to Baltimore for $165 (actually Elkridge, MD where there is a freight center). The trucking terminal loaded it onto my pickup (Ford Ranger) via forklift. Myself and a friend unloaded the table and carried it to its resting spot, one of us on each end. It's webbed underneath and the top surface is around 3/4" or 7/8" I think, total thickness is 2". I have Bringheli accessories on it. It's adequate but I'd really like it to be bigger. If I could have any table, I'd like to have a 3x6 cast iron on a base with leveling pads and locking casters so I could move it when needed since my shop is tiny. I'd also like to have that part from Carl Strong's table that slides into the seat tube. I think Ant Bike Mike has something similar. The Bringheli part that does that job is kind of a hassle to set up but does the job. You have a nice advantage that you have a loading dock integrated into your shop and you can probably find something very local to you to cut down on the transport costs. I self-rigged my mill about 200 miles round trip. That was not cheap after truck rental, fuel costs and my time (cheaper than paying a trucking outfit though).

I was at Drew's when he got his new table and can say it's quite nice.

[EricKeller]

I have a 2'x3'x6" table, and I would suggest a 3'x4' if it is easily available. Then again, if I had a lot of room I'd probably have more than one table.

My monthly student loan payment tells me I should remember the technical aspect of this from engineering school, but I honestly can't right now. I do work at a 177 year old cutting tool manufacturer that makes everything out of steel. I can tell you with 150% confidence, without a shadow of a doubt, that steel does have a memory, and under load/stress it will go back to a home position.

I'm going to say there is no engineering school in the world that will teach that to you. There is probably some old Ph.D. that has done a lot of consulting in the sheet metal industry that has looked at the dislocation structure of steel after plastic deformation and understands this pretty well. I've been thinking about cold setting recently, there has to be some material in a cold set piece of steel that still carries some residual stress in the elastic range. And there are slip bands in all ductile metals, so there is some room to move back. But my experience is that cold setting is pretty much permanent.

cranking the tubes around definitely worked better in the old days. The 6' long x 1" diameter steel bar was a fixture in a traditional frame shop. One of the visual memories I have of Trek was the guys with a frame on the alignment table really putting some muscle into straightening a frame. The fixturing there wasn't idiot proof, you could easily fail to get a head tube in straight. This experience left me with a strict aversion to cold setting, but since I've seen some pretty radical cold setting, I'm not afraid to do it.

[PCW]

Maybe I ask what brand of table you use? ::dig dig::

Sure, PM2000, the only table saw to have from what Dad taught me.

POWERMATIC ® - PM2000, 3HP 1PH Table Saw, w/ 30 Accu-Fence System

[Dazza]

To get the material to take a new set, you have to go past yield (and why it's such a bad idea to align frames made from heat treated tubing). Doing that leaves residual stresses in the frame (and a thin wall tube is basically a stress skin structure) and so "going back" is not as hard for that first little bit.

Don is totally correct, this is all total fact.
The thing is the amounts are small, and are noticable with typical equipment we have in our workshops

Example. Cold set the tube 1.00mm using force of 10kgs. Use 2kg back the other way and you will see .10mm movement back. But to get it to go all the way back to where is started may take 9-11kg pending the type of material and hardening taking place due to the cold working etc .
The numbers are just for explaining

[Dazza]

This is getting into technique so it is better in a nother thread
rather than the subject of a 48" x 36" inspection table is the size you need to be manly
stay tuned

Oh, and Donissimo, Dave, Eric and Curt and Richie are correct atmco