Thursday, January 14, 2010

James's Drop bar stem...

James has been patiently awaiting a high rise stem for his Bonty drop bar project so I thought I'd share a few pics of the process from yesterday.

Laying out the dimensions on the table...

The stem will use a removable face plate for a 31.8 clamp diameter, an 1.125 steerer tube and an ovalized/offset stem body for better rigidity and support.

Once the tubing is pulled out of the stock, it's time to cut it up to rough lengths, into the cold saw it goes...

With the rough lengths completed, it's time to turn down to final length, true the edges, debur, and chamfer

Now we'll miter the ovalized center section to fit the handlebar clamp...I'll offset the center of the cut just a bit to allow more material to wrap under the clamp for a bit more support.

Clean them up by sanding off the mill scale, run them through the degreaser tank, and then into the ultrasonic cleaner for final weld prep.   Let's tack them together, shall we?

and weld it all up...

Now to do the steep miter for the steerer section.  A 53 degree miter is required, so I split the difference by setting the stem into the vice with a 30 degree angle plate and tilting the milling head to 23...the cutter is advanced with the quill feed nice and slow so that it doesn't skate across the surface.

Wanna know a little trick to help set this kind of stuff up?  The angle plate the stem is gauged off of is much thinner than the width of the stem body, so it is tough to keep it in place and from falling over while you get the final position dialed.  I use two of those little foam pieces that come in the Thomson Elite stems (to keep the clamp inserts from falling out) on either side of the plate; it snugs everything up and you can still tighten/loosen the vice without changing it's position.  There are a few parallel holders available through MSC and such, but I'm too cheap, I mean innovative ;)

Once everything is mitered and cleaned, it's time to weld it all up... fits the table layout perfectly :)

Next, I tacked on the binders, silvered them in place with 45%, split the binders and plate with the cold saw, and ran it through the media blaster.  Final pics once she's all painted up.




GrumpyOne said...

Yea! The Bontrager is going to be very happy and so will my back. ;-)


Winter Bicycles said...


Rody said...

James, glad you are liking it so far, I think we can do the white/black dart for ya ;)


Normally I'm a Chocolate Milk man, not a Scotch man...oh, that's not what you meant?

Yes, it is a Scotchman cold saw. The cold saw is vital for long production run cuts for bars and such, also is much more accurate and cooler than cutting with an abrasive set up.