The stem is easy to press out of an alloy bottom clamp, some heat and a small press. Even a threaded rod up through the centre and a washer on top, then a short tube bigger than the pressed in bit and a washer and nut, Heat the alloy and tighten the nuts and the rod will come out easy.
Café Commando build thread
- Thread starter Jeandr
- Start date
That shaft is easy to remove, you press it thru the bottom a little to expose a circlip, then you press it back twards the shaft and it;s out. I learned this the hard way after lots of heat and I pressed the clip thri the lower tree. Needledd to say I dammaged the hole. I had to shorten the shaft and adjust for bearing size, so I bored the hole and made an adapter/plug to weld in. After turning it on the lathe I pressed it back in, all is good now.
The way you cut it, just put a sleeve on the inside of the shaft, drill some holes in the shaft, and use a few rosette welds on each side of the cut.
The way you cut it, just put a sleeve on the inside of the shaft, drill some holes in the shaft, and use a few rosette welds on each side of the cut.
The bottom yoke is a forged part and it is welded to the stem. Impossible to remove without damage. I just clamped the two pieces in an angle iron and welded ell the exposed joint, then I welded the rest, stayed straight and true. I will try to find a picture of the yokes I was talking about only held with a threaded rod and post it here, I will also ask about what I did in the chassis design list and see what they say about it.
By pressing it out of the bottom part, there is no garantee it will be true and square when pressed back together, the way I did it, at least it is as square and true as it was.
Jean
By pressing it out of the bottom part, there is no garantee it will be true and square when pressed back together, the way I did it, at least it is as square and true as it was.
Jean
lcrken
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I'm with you on this one, Jeandr. There is very little tension load on the stem, and a welded steel one is plenty strong enough. The only significant load on the stem is shear load at the bearings and yokes. There was a lot of discussion of using just upper and lower stub stems on the chassis list a while back, and Tony Foale, among others, pointed out how little need there is for much material in the middle part of the stem.
Ken
Ken
I like the idea of the 21" rims, not from a looks perspective, which, as far as I'm concerned, is ALWAYS secondary to performance, and I think you will be surprised at how sharp the steering will be. What width rims did you fit? I'm looking forward to this one as well.
lcrken said:
While searching for backup to what I did I found one post from a drag racer who had made his own triple trees all from aluminum, both upper and lower tables and the stem. While a dragster runs on glass smooth tracks, most of them have severily raked front ends to get lots of trail and high speed stability so they have more stress on the bearings, the neck and even the fork tubes yet a complete aluminum triple tree was OK and the racer totally confident in his design.
When I look at how bicycles are made, I am more worried about the front end coming apart than what I did, how often do you hear of a stem breaking on a bicycle? My onw bicycle has a fork made out of carbon fiber, a plastic part :!: totally safe and sound with more stress on the bottom than my weld will ever see.
"What me worry" Alfred E. Newman
Jean
grandpaul
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My machinist simply chucks the japanese bottom yoke/stem assmblies into his lathe from the threaded end, turns down the appropriate bearing surface sections, then fabricates a new threaded section where required and chops off the excess stem length.
Voila.
Voila.
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If you are fitting forks from another bike, its sometimes possible to press out the original steering stem, and fit this into the new yokes, which can either be bored or sleeved to suit. This method allows use of the original bearings, seals and adjuster nuts etc, and of course the stem is the right length to fit the headstock perfectly.
I couldn't find the picture of the triple trees held with a threaded rod, but here is a drawing of the forks from a Greeves. Look at the size of the bolts tying the top yoke to the fork legsand the long thin bolt tying the top and bottom yokes together.
Jean
Jean
Fullauto said:
Yes, I have over reacted to a poor engineering job, I just found it stunning that someone would cut and weld when it could so easily be done properly, as grandpaul suggested,I would have no problem with a properly designed alloy stem, although would prefer steel stem shrunk into alloy yoke.
Whers it going to go if it breaks , nowhere, but take a look at your 850 and tell me where the stems going if it breaks
Would also be illegal to put on the road here, welded steering components...
lcrken
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No offense intended, but some of you guys clearly didn't read what Jean said.
First of all, forget about simply pressing the shaft out. Jean explained that the bottom yoke is steel, not aluminum, and the shaft is welded to it at the bottom. Yes, you could bore the weld out and then press the shaft out, but he also explained that his lathe doesn't have enough swing to chuck the shaft up and turn it with the yoke attached.
Same comment about all the suggestions on shortening and cutting new threads. Can't do it if it won't fit in the lathe.
I don't think it's right to call it "poor engineering". It appears to be a sensible way for Jean to do it without taking it to someone else for machine work. And it seems clear there is really no safety issue with the technique.
I really don't see what all the concern is over welding on "steering parts". Traditional British clip-ons were welded together, and I don't recall any concern over it. Plenty of people have fabricated fork yokes from welded sheet steel, again with no concerns. Some wheels (Performance Machine) are welded together. It used to be common to cut Honda Hawk wheels apart and weld them back together with more width. I've seen older steel fork sliders fabricated with welding. There's nothing wrong with a proper welding job.
Doesn't seem fair to insult Jean over his solution, just because you wouldn't do it that way.
Ken
First of all, forget about simply pressing the shaft out. Jean explained that the bottom yoke is steel, not aluminum, and the shaft is welded to it at the bottom. Yes, you could bore the weld out and then press the shaft out, but he also explained that his lathe doesn't have enough swing to chuck the shaft up and turn it with the yoke attached.
Same comment about all the suggestions on shortening and cutting new threads. Can't do it if it won't fit in the lathe.
I don't think it's right to call it "poor engineering". It appears to be a sensible way for Jean to do it without taking it to someone else for machine work. And it seems clear there is really no safety issue with the technique.
I really don't see what all the concern is over welding on "steering parts". Traditional British clip-ons were welded together, and I don't recall any concern over it. Plenty of people have fabricated fork yokes from welded sheet steel, again with no concerns. Some wheels (Performance Machine) are welded together. It used to be common to cut Honda Hawk wheels apart and weld them back together with more width. I've seen older steel fork sliders fabricated with welding. There's nothing wrong with a proper welding job.
Doesn't seem fair to insult Jean over his solution, just because you wouldn't do it that way.
Ken
Jeandr said:
Jean,
So far I love the project and will be following it closely. I am thoroughly impressed by the talent on this forum! i am also enjoying the debate on the engineering of your stem. I won't comment on that but, In looking through your opening photos for the second time I suddenly had to laugh.
Are you the cyclist?
Gary
T95 said:
My daughter has a blog and she was very pleased when she had her first "haters" I am sure Hobot loves it too. Keep watching and look at my other crazy ideas when I put up new pictures. You know the best way to end an argument is to agree with everything.
Jean