Need Advice On Macining A Stem.

[sakurama]

Sometimes, some things are just better off bought instead of built (yes, I actually said that).

Yes, machining is the solution not the goal. I never make parts I can easily buy, like rearsets which are cheap and plentiful.



This took quite a bit of work but it taught me a lot about fits. I held it between a 5c collet and live center and single pointed the two metric threads. Use good inserts specific to aluminum and you can spin as fast as your lathe can go - modern inserts are for CNC capable speeds.

Those of you who've not seen aluminum stems must have quit working on bikes in the 80's. They're ubiquitous on all modern bikes.

The simple solution is generally best.

Gregor

 

[Lood]

Some feedback:

There is no doubt that the stem is definitely aluminum.

So, yesterday afternoon, I decided to make a new stem, that will fit into the 450's triple clamps, but accept the 650's bearings, using a 40mm thick EN8 steel shaft that I have. I started measuring and drawing and then it hit me, I can't make the stem like I was planning to do, or even turn down the original, without also turning down both threaded parts at the top, and make smaller nuts for them. The threaded parts have to be slightly smaller in diameter for the bearings to be able to go over them, without damaging the threads. This means that the complete stem basically has to be turned down substantially, except for the bottom end, which is pressed into the bottom clamp.
Although solid steel would probably be strong enough, the whole thing just becomes too thin for my liking, particularly the bottom part where the OD would differ from 26mm to 31mm.

So, I just went ahead and ordered the conversion bearing kit, which set me back R2560.00 in our money!!!

Anyhow, I learned a lot from this exercise. While measuring the stem, I clearly noticed that all the larger shoulders had a 45 deg angle, plus a radius, while the smaller ones only had the radius.
I'm sure that making a new stem won't be very difficult, but in this case, I'd prefer the bearings. More so, because the original stem is hollow.

Thanks again to all for your expert advice and help, I'm much wiser now, than before.

 

[dave_r_1]

But the original stem for the bike is already that thin...and made of Aluminum...

I see you are ordering the bearings, but what do you think about machining the steel rod you have so it press-fits into the lower 450 triple clamp, then goes through the two bearings [so you install from the bottom, presumably something like how you would install the original 650 triple clamp], and then since the 450's upper triple clamp is expecting a larger diameter shaft, you put a bushing on the shaft to make up the difference, and then threads and a nut or whatever on top?

 

[great white]

Seems 2560 works out to 220 Canadian or 163 USD.

Pricey for a set of bearings, but I'm willing to bet shipping is a big part of that price....

 

[Lood]

Dave: Absolutely possible, but at this stage, I don't feel like reinventing the wheel.

Great White: Almost. The bearings were $120 for both and the shipping was $40. And then I'll have to pay tax when the package lands here.