26
Dec
14

Okay, You Can Thank Me Now

Okay, you can thank me now.

What you are thanking me for is the fact that, rather than inflict upon my Loyal Readership the lengthy essay that I had originally written over the holidays, you are now reading a much-shorter and more photo-heavy replacement on the current state of my latest project. What almost happened here was a long cough-syrup-fueled screed about bicycle fork geometry.

Yup, a thousand or so words on bicycle forks.

I deleted it.

A short explanation: I’ve been down with the flu over Christmas and New Years, and so I haven’t worked much on Number 4.

That’s probably for the best.

In retrospect, it is completely understandable that I wasn’t able to make much progress over the holidays because, having re-read what I had originally put down, I was obviously not in a fit state to be out in the workshop. Frankly, one would have to be on some fairly powerful drugs in order to think that heeding the writer’s call and preserving for posterity my most personal thoughts about bicycle forks was somehow a good idea.

And while my memories regarding this particular winter interlude are somewhat indistinct, I do recall that pathetic, hazy, fatal moment out in the workshop when, deeply despondent, covered in phlegm, and my body wracked by coughing fits, I came to the firm conclusion that “Yes, I may be incoherent to the point where I cannot be safely trusted to attack a bowl of soup using plastic silverware and remain injury-free, let alone be turned loose on steel tubing with powerful cutting tools and a brazing torch. But, My God, if I can no longer work on my bicycle masterpiece then the world must know of the many important insights that I have concerning the gentle interplay between fork offset, head tube angle, and cornering behavior. Quick! To the computer! I must capture these golden thoughts before I tragically succumb to the dreaded grippe and my musings are lost forever!

What made it worse was that, of all the possible subjects that I could have picked to obsess about while pleasantly whacked out of my gourd on prescription strength cold medicine, one could have hoped that bicycle forks were fairly far down the list. Because when it comes to drug-fueled manifestos, holding forth on the nuances of bicycle geometry is hardly gonzo. The good Doctor of Journalism, Hunter S. Thompson, would have been bewildered. And disappointed. And bored. I could have spent my time just as productively (and far more entertainingly) holding forth on gall bladder disease in cattle.

But, no, instead it was bicycle forks.

Anyway, the good news is that the fork for Number 4 is done. And it is a beauty.

2015/01/img_0986.jpg

The fork is built from components from Richard Sachs. Richissimo Crown, Columbus fork legs, and those really nice Richard Sachs fork ends.

2015/01/img_0988.jpg

2015/01/img_0987.jpg

All of it is absolutely top drawer stuff. In terms of specs, I built the fork with a 39mm offset, which should work pretty well with the 74 degree head tube that I am planning on. The brake reach with a 700c wheel is 45mm, so it will work with normal short-reach road calipers. I’m thinking Campy Athena if this turns out as I hope it will.

2015/01/img_0982.jpg

If anyone asks “Why a 39mm offset” the short answer is “Because I tried it on one of my other bikes that had a 74 degree head tube and I really liked it.” It also, interestingly, gives a figure for “trail” that appears to be within the range that Builders With Far More Experience Than I seem to think is just peachy. That is, if there are in fact hard and fast rules about things like “trail” that you should worry about.

That’s not to say that I didn’t try to figure it all out. But after a bit of diving into The Learned Treatise (i.e. the Paterek Manual) and other reading, the best answer that I can come up with is “No, I can’t actually explain why this offset works for me,” if by “explain it” you mean “I understand the basic math and science enough to construct a plausible line of bullshit about why a 39m offset yields the results that it does.” If that’s the standard, I don’t have a clue.

That’s fine for now. Given that I don’t have a lot of frames or forks under my belt, I’ll just go with what I know works for me, and I’ll tweak it as I get more experience. Plus, I’m not sure that I’ve downed enough cough syrup lately to actually feel the need to share my opinion if I had one…

________________________

And in the Shout Out To The Readership Department: Thank you George5 at Tokyocycle.com for the kind words. Hope that I can keep you as a reader. And good luck to DeltaForce on his/her project. Some pictures would be very cool…

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11 Responses to “Okay, You Can Thank Me Now”


  1. 1 Touch0Gray
    January 11, 2015 at 11:16 pm

    At some point in my life, I am driving east, just to meet you. I will request audience in advance.

    signed,
    Touch0Gray

    (soon to be entirely gray and mostly bald)

  2. 3 Anonymous
    January 12, 2015 at 1:16 am

    Greg, It truly is a work of art. I see no tell-tale brazing or heat discolouration. Wish I could do that. On the positive side–for me, anyways–Santa brought me lots of welding safety gear. The kids in the neighbourhood are, of course, deeply disappointed as they prefer to see me set fire to myself. I’ll keep them happy, however, as the likelihood of me igniting some nearby flammable material remains high.

    Would have preferred to read the long version.

    Snow Goose

    • January 13, 2015 at 3:07 pm

      Goose!

      Full disclosure: I did clean the thing up a bit before I took pictures – I’m not THAT talented. Plus silver brazing is much lower temperature. But I will say that the damn thing did turn out nice. The thing that is making me grin is a little trick that I tried when I joined the legs to the crown – each of the “arms” that come off of the steering tube and connect the fork leg socket are hollow. So I took some brazing wire, bent it to fit along the perimeter of where the hollow joins the socket (making sure that the wire rested against the fork leg), and then packed the hollow with flux. When I heated the joint, the brazing wire melted and nicely filled the backside of the socket…which I was worried about doing.

      So Santa brought you some welding safety gear? Excellent. Setting yourself on fire gets a little tiresome after a while. The only appropriate literary allusion that I can offer here are the immortal words of Craig Breedlove, uttered immediately after he crashed his jet-powered land speed record car (the first “Spirit of America”) into a lake at over 500 mph: “For my next trick, I’ll set myself on fire…”

      http://jalopnik.com/181861/land-speed-record-recordrecorded

      http://www.airspacemag.com/history-of-flight/oldies-and-oddities-the-bonneville-jet-wars-46415359/?no-ist=&page=1

  3. 5 Stan Cooper
    January 27, 2015 at 1:33 am

    Terrific job on the fork, Greg! Super clean brazing and cleanup.

    Now, on to the frame!

    • January 27, 2015 at 8:54 pm

      Stan!

      Thank you! The fork really did turn out nice, didn’t it? And it should be very strong – the crown really is a fantastic casting.

      If you read the next installment, the frame is now underway….

      Greg

  4. 7 Jonathan
    March 16, 2016 at 1:39 pm

    Hi there, I’ve commented on your posts before and just stopped back as I remembered that you’d used a Sachs fork kit before and I just got one. Currently working on getting everything to fit together, filed down the male sides of the fork tips enough to fit into my cut blades, and working on flattening out the crown sides of the legs enough to fit into the crown, had to ovalize them more than they were to properly fit into the sockets. Now just working on some socket cleaning then hopefully I can get this thing brazed together fairly quickly.

    I’m intrigued by your dropping of silver into the void to have it melt onto the legs, I may consider trying that. Hoping for the best!

    • March 16, 2016 at 5:16 pm

      Jonathan –

      Hey! Welcome back!

      Bending up some brazing rod to fit into the hollow of the fork crown was pretty easy. It is a good way to make sure that you get full penetration of the silver into the fork pocket. I also used that method for the fork tips (and the plug in drop outs on the chain/seat stays). A couple of coils of brazing rod inside the leg touching the plug, pack in some flux, heat the joint, and it brazes itself.

      I was in the opposite boat with respect to fitting the tips on the fork. I was going for a short (39mm) offset, so I had to trim the curved ends of the fork legs. This made the tips fit a bit loosely. I made some shims to fit inside the legs, brazed them in, and then reamed the opening to fit the tip. So far, so good.

      Let me know how it turns out!

      Greg

      PS: I’m working on building a fixie frame. The fork is done, and I’m now working on the frame. Oversized Columbus Chromor/Tenax. The thing that I am currently puzzling over are the rear dropouts. Bought a pair of beautiful chromoly rear drop outs from Paragon Machineworks. They are made from flat plate, and are very beefy. I need to bend the tabs to roughly match the angles of the chain and seat stays, and I’m torn between just cold setting them or heating them up and bending them in the vise. I’m pretty sure that I will opt for the latter. I’m also thinking of coming up with some sort of jig to get the angle consistent. Maybe a piece of angle iron ground to the correct angle.

      • 9 Jonathan
        March 17, 2016 at 1:58 am

        So I presume you brazed your steerer in first, right? Then you packed the void full of flux and just set the brazing wire at the edge before you pushed the blade into the crown? Any worry that the piece of brazing wire would fall out when the flux liquifies?

        Did you have to squeeze the crown end of the blades to get them to fit into the crown? Mine were’t ovalized enough, so I had to make them flatter/longer in the two axes to fit into the crown. Fun stuff, looking forward to getting it all brazed up.

        Are these the dropouts: http://www.paragonmachineworks.com/cgi-bin/commerce.cgi?preadd=action&key=DR2013 ??

        How far off is your angle? A bunch of the big wigs recently weighed in on this very question over at V Salon: http://www.velocipedesalon.com/forum/f10/rear-dropout-angles-frame-geometry-36740.html

        Keep after it!

      • March 17, 2016 at 3:25 pm

        Taking this in order –

        Yes, the steerer was brazed first. I bent the brazing rod into a rectangular shape with a little tang/tail/kickstand on one corner to help keep it located in the crown when I assembled it for brazing. The void in the crown was angled enough so that it would probably hold the wire in place anyway when you slip in the leg. The little tail that I added was just insurance to keep it in place while I assembled it for brazing. All bets are off as to what it does when it liquefies – as long as it wicked into the socket things were going to work. As for the flux, I didn’t pack it full.

        I did squeeze the crown end of the fork legs to get them to fit. I started gently and sort of snuck up on it. The one thing that I noticed is that the metal has a good “memory” and required a pretty good pinch from the vise to make it hold its new shape. I would squeeze, check, repeat.

        Yes, those are the dropouts. The angle (70 degree) is perfect for what I am doing. What I need to do is tweak the tabs inward- the drops are made from flat plate and don’t have the tweak that some dropouts have (like those from Columbus, etc.).

        Good luck on your project – let me know if/when you have pictures!

        Greg


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