Segmented fork, take 2

After bending my first segmented fork when seeing how it’d hold up, I got right to making #2 since I don’t have a fork for the RivBomb frame to ride yet. I swear, what takes most people 4 hours takes me 4 days. Of course, I tend only to get a few hours a day to work on bike stuff but it’s mostly because I’m just plain slow!

I remember reading an article on Paul (Paul’s components) and the interviewer asked why he didn’t get into making bike frames.  Paul said that he tried it out, but said something like, “you have to get your process so dialed that I just didn’t have the patience for it.” My paraphrase but that was the general idea.  Now that I’m trying it for myself, I can see what he means.  I’m not sure machining bike parts would be any less process-intensive, but maybe it’s more automatic once the computer models are created and let run on the mill (?)..I have no idea.  Anyways, it was a glimpse into what I was getting myself into.  I love it, but there are times when I just chuckle at how inefficient I am.  For example, it took me maybe 10 minutes to miter the two crown pieces for this segmented fork in the mill, but then almost 45 minutes to finish the filing since the fork legs’ offset is a few degrees off vertical.  I know it’ll get better the more forks I build, but man!

I tried a new process for this fork, and I am going to continue with it from now on since it worked much better.  Instead of brazing last, I welded the dropouts to the 1″ legs first, then silver-brazed (Harris 50N) the sleeves to the main legs.  Then I tacked it up in the fixture and welded the crown pieces to the steerer and legs.  I was hesitant to silver braze first because I heard from another guy that when welding the silver can heat up enough to splatter or undo itself…but this luckily didn’t happen for me.

Because of advice I got from mtbr frame forum members, I recycled the last sleeves (seen above) because they were too thin-walled for this purpose.  The tubes I made the sleeves out of were 1.125″ x 0.035″ wall thickness when I should’ve used 1.125″ OD x o.o58″  tubes…but I didn’t have any lying around.  For those that glaze-over when seeing these numbers, a thinner walled tube will have more space between the sleeve and the fork leg.  It’s possible to braze them together but it’s just not a good idea.  Too much room to fill with silver which is very costly, and it probably isn’t as strong or straight as a tight fitting sleeve. The silver or brass needs to fill in the difference in diameter between the outer diameter (OD) of the leg and the inner diameter (ID) of the sleeve.  Because the gap was still rather large, I used the Harris 50N silver which is better for larger gaps (bought through Henry James).  There are other silvers to use, but this is what i had.  I weighed the roll before and after and the sleeves used about 0.2 ounces each.  I definitely could’ve used less, but that’s user error.  That means, at current prices (50N is a little cheaper than 56%), doing the fork this way cost me $14 in silver…ouch.

Last fork, I used brass to braze on the sleeves and overheated the tubes.  I also didn’t get much penetration down the sleeves so I was pretty worried about riding the fork. Silver is MUCH easier to get in tight spaces (for me).  I feel really confident that most of the sleeve is brazed to the leg now, versus the other fork where I maybe had a 1/2″ on the top and bottom.

Once I brazed the sleeves on, soaked the flux off for an hour in hot water, and did some minor cleanup with emery cloth and small files, I cleaned all the tubes (AGAIN) and fixtured it up. [The one thing ‘they’ don’t tell you is how much you have to clean the tubes inside and out.  The more you clean, the better with TIG.  Some day I’ll post a blog just on cleaning tubes, once I perfect my method…but I spend WAY more time cleaning than i thought I would.]

I tacked the fork up, welded the steerer to the crown first, then the legs to the crown pieces.  I found the magic number of amps for these thickness tubes for me – 56amps for the steerer to crown pieces, 52 amps for the legs to crown pieces.  My welds turned out the best yet.  No pulser or pulsing with the foot pedal, I just laid it down and dabbed the filler rod as I went. I didn’t do a second pass on the entire fork, just on a couple spots that needed a bigger bead or a cosmetic touchup.  My starts/stops are still not where I want them to be! I left the welds un-cleaned so you could see the color pattern that the heat creates on the tubes.  It gives some indication on how hot you’re getting the tubes too by what colors appear and how far from the weld they show up.  If any real builders are out there reading…i’d love comments on how i’m doing…!

Still a little shaky on the hands – i still get nervous – but I’m really psyched on these welds for the most part.  I know that by moving a little bit faster I’d be less shaky (seen by the wandering of the bead in some places).

I kept the fork in the Anvil fixture the entire time, trying to position it as best I could to get good sight on the weld.  It’s definitely not as easy to get to some spots, but probably a good habit to get into.

Now, I just have to braze the top caps on the legs, braze the crown race on there, weld on the disc mount, then clean and paint…and THEN it’ll be ready to ride on the RivBomb.

2 Responses

  1. Where oh where can I get a segmented crown fork, as beautiful as this, in raw, for a size large peace 9er? Cheers!
    Joe

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: