First attempts at bending

[veryredbike]

Ok, I've got a form, and have tried on a few scrap chain stays because they seem pretty similar to fork blades. I'm finding that they kinda... de-ovalize near the bend. Like, the section that's bent is wider and has a more circular cross section than the rest. Otherwise, the blades are smooth.

Is this unsafe? Is this just because I'm maybe not as careful getting the blade rotated 100% straight on practice stuff? Any ideas?

[afwalker]

Are you filling the chain stay with anything? Sand or frozen dish soap water? Saw that in a google group on framebuilding.
Some folks heat the tube first, more experienced builders can chime in here.
cheers
andy walker

[veryredbike]

No, I hadn't seen folks filling for basic fork blades, so I didn't try. Also, would that help with it going round? Seems like that'd mostly help with kinking, and that the tube "rounding" actually increases internal volume.

[e-RICHIE]

Why in the world are you bending chainstays atmo?

[EFHeath]

... tried on a few scrap chain stays because they seem pretty similar to fork blades.

Using what's at hand to get some practice before messing up some expensive new fork blades?

[veryredbike]

Why in the world are you bending chainstays atmo?

Just using them to practice, had a few that I've no use for at the moment and figured that they'd give me insight before I dig into fork blades.

[veryredbike]

Ok, tried packing with salt and got to work on the actual blades (thanks walker, it did help). First set ended up pretty great. Exactly the right rake and a nice smooth bend. There's a tiny bit of a bulge in the bend, but I think I may be being too anal retentive if I worry about that. I can't see it with my eye, but if I really carefully feel along the inner radius of the bend (slightly to the side), I can just barely feel a change along the curve. Too anal retentive? Not too anal retentive enough?

Thanks!
Jim

[e-RICHIE]

Ok, tried packing with salt and got to work on the actual blades (thanks walker, it did help). First set ended up pretty great. Exactly the right rake and a nice smooth bend. There's a tiny bit of a bulge in the bend, but I think I may be being too anal retentive if I worry about that. I can't see it with my eye, but if I really carefully feel along the inner radius of the bend (slightly to the side), I can just barely feel a change along the curve. Too anal retentive? Not too anal retentive enough?

Thanks!
Jim

Fork blades are made to be curved - chainstays are not. That's going to be a
problem for you if you're using the latter to troubleshoot for the former atmo.
And bend these cold, with no sand and no nuthin'.

[afwalker]

Maybe it's a fat bike mountain thing, but I've seen it talked about,
http://farm8.staticflickr.com/7291/8...391ca4b1_b.jpg
This weeks FNL's example.
cheers
andy walker

[afwalker]

Which end of the chainstay are you bending?
Maybe I'm thinking the fat end and you're bending the dropout end for practice?
Show a picture:)
cheers
andy

[veryredbike]

Fork blades are made to be curved - chainstays are not. That's going to be a
problem for you if you're using the latter to troubleshoot for the former atmo.
And bend these cold, with no sand and no nuthin'.

Roger! I moved on to real fork blades today. And ok, I'll cut out the salt... geez, you're just like my doctor ;-) j/k

Which end of the chainstay are you bending?
Maybe I'm thinking the fat end and you're bending the dropout end for practice?
Show a picture:)
cheers
andy

Yep, was on the dropout end before I got going on the blades proper.
These are the first fork blades, one done one in progress. Please ignore messy bench!

Any thoughts on that little bit of bulge? It's not visible with the naked eye unless you angle it just right so that it reflects a bright light just right, then you can see a tiny bit of ripple on the inside of the curve. What level of perfection do you go for on the bend? Is this an "any deviation from perfect and toss it" kind of thing or is there a bit of fudge room?

I'm aiming for "better safe than sorry" since it's my first fork, but I've been known to take that to silly extremes. Say the word and I'll get another pair put in the mail. Er, also... I have one slightly thicker fork blade left (I botched the first one in that pair), is mixing a .9 and a 1.0 going to create uneven stresses or anything if I use that to replace the slightly rippled one?

[veryredbike]

Edit: found that one of the fork blades that I thought I'd raked too far was actually fine... so it looks like I do have two .9 blades to work with, properly bent. Woo!

Still very interested in the answers to the above questions.

[e-RICHIE]

Re the above - here, look at this set from 2004...
bending a fork blade atmo - - a set on Flickr
Notice the pictures near the end, and the pieces of wood I use to show the blade who's boss.
Also, if you rake one more than the other, simply stand the longer one on the bench with the
curve facing down, get a rubber mallet, whack the back of the blade in the bend, and show it
who's boss atmo.

[veryredbike]

Re the above - here, look at this set from 2004...
bending a fork blade atmo - - a set on Flickr
Notice the pictures near the end, and the pieces of wood I use to show the blade who's boss.
Also, if you rake one more than the other, simply stand the longer one on the bench with the
curve facing down, get a rubber mallet, whack the back of the blade in the bend, and show it
who's boss atmo.

Cool! Are you clamping that to align the curve with the ovalized section?

[e-RICHIE]

Cool! Are you clamping that to align the curve with the ovalized section?

Of course atmo. I even further squeeze it even further to give all
the blades a flatter profile when I am done squeezing them further.

[fortyfour]

Maybe it's a fat bike mountain thing, but I've seen it talked about,
http://farm8.staticflickr.com/7291/8...391ca4b1_b.jpg

For the record, the tubes in that picture are chainstays for a 650b mountain bike (made from 4130 seamless aircraft tubing .75" O.D. / .035" wall thickness).

Richard makes a great point that you should be using fork blade samples to practice with - they will bend differently than a stock chainstay. You can bend chainstay's from the stocklist, but greater care and attention to point of tangency needs to be taken into account and most likely why you are getting a flat or slight bulge out of the chainstay samples.

To bend chainstays, from my experience, you need to have the tube fully supported along the circumference of the tube. The follower CANNOT get ahead of OR behind of the bend. Point of tangency must be maintained during the bend. If point of tangency is not maintained, this opens up the possibility of a void which is an unsupported area of the tube. Depending on the degree of the bend, the tube will either buckle, bulge or flatten because of this. Material is moving for you to make the bend. The inside of the tube's bend is compressing, while the outside of the bend is stretching. The larger the diameter of the tube and the thinner the wall thickness, you need to start thinking of supporting the tube both externally and internally. But that's a whole other can of worms.

[Mike Mcdermid]

Re the above - here, look at this set from 2004...
bending a fork blade atmo - - a set on Flickr
Notice the pictures near the end, and the pieces of wood I use to show the blade who's boss.
Also, if you rake one more than the other, simply stand the longer one on the bench with the
curve facing down, get a rubber mallet, whack the back of the blade in the bend, and show it
who's boss atmo.

I dont know why richard but ^^^^^reminds me of orthopaedic surgery

[e-RICHIE]

I dont know why richard but ^^^^^reminds me of orthopaedic surgery

You can't respect the process if you kowtow to the material atmo.
If you're making the frame, you have to own every step along the way.

[veryredbike]

Thanks for the advice all! I got some thicker blades (1.0 without the pre-butting, so it ends up being like 1.8 on the small end) and kept working at it. I may do a bit of (lightly) loaded touring in the future, and I figured that there was no reason not to overbuild it, especially on the first fork. I have enough materials for about three forks, so I'll braze and cut one for practice, braze the second with the heavy blades, and if that goes well braze a third with the light ones for a future bike. If the second doesn't feel like it went together perfectly, I'll just grab another set of heavy blades and try again with the other parts on hand.

Went much much smoother this time. I think some of the rippling was from not being super careful with exactly where the clamp grabbed the blade, leading to the successive adjustments being slightly out of phase.

I was getting the hang of nice smooth bends, but ended up bending too far a couple of times while trying to sweep it right to the right place. E-ritchey's advice about laying it on the bench and smacking the crap out of it with a soft-headed hammer worked like a charm, and was way more fun than I'm entirely comfortable admitting.