There’s some discussions on framebuilding mailing lists and forums at the moment concerned with mitering tubes and what the best set-up is.
A couple of people have asked me how I do mine and if I use a fancy jig or not, so I thought I’d post a quick run down on how I miter my chainstays.
Firstly, I need to know what the actual length of they stay is, measured from axle center to center of bb. This is the actual length and not the horizontal length. My drawing shows the stay length as the horizontal length and the actual length. I double check the actual length by physically measuring it on the jig.
This picture shows what I mean. The number I’m interested in is 455, the other number is what I use to set up the length on my jig using the built in scale.
I normally tack the dropouts before I miter the bottom bracket end. My drawings give me the dimensions I need to cut the stay at the dropout end and once I’ve done that I slot and tack braze the dropout in place. See earlier post for more details on how I do this.
This is a pic of the tacked stay:
This would actually be pretty strong as it is (you can maybe see the nice internal fillet) but I’ll fill the void later ’till it looks something more like this:
Next, I lay the stays out on the alignment table and bolt them to a dummy axle. I then use a normal engineers square and steel rule to measure and mark the length of the stay, in this case 455mm. I also mark the vertical centerline of the stays at this point too.
Once I’ve marked the stays, I take them to the lathe and bolt them one at a time in the milling vice. I again use a square, and a straight edge to make sure the milling vice is at the correct angle to ensure the cutter will miter the tube exactly perpendicular to the dropout (or parallel with the axle if you prefer). You can buy all sorts of fancy jigs for holding stays for cutting in the lathe or a milling machine but I find this works fine. Keep a slow feed rate and even the thinnest tubing is easily cut. I can’t really believe a fancy jig would be much quicker for me to set up but if someone wants to send me one, Ill try it out!
Here’s a pic of the stay in the vice.
You might be able to make out a cross marked on the stay. This is the 455mm length and the centerline. I line this up with my patented centerpointerometer.
The centerpointerometer is just a pointed stick shoved in a hole but in a kinda precise manner. I’ve center drilled and reamed all of my hole-saw arbors to take a 6mm rod with a ground point. This allows me to precisely set up tube lengths for mitering. This is used for all my tube mitering not just for stays.
I don’t change the angle of the milling vice between stays and this makes it really quick to create a nice matched symmetrical pair.
Depending on the tube wall thickness, I’ll either hand feed or use the powerfeed. Here’s an action shot!
The result, one nicely mitered pair of stays. Couple of swipes with some shop cloth and we’re good to go.
That’s all for now.
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