MODIKOSO BICYCLE MACHINE AND WELD WORKS
NOTES ON THE BELT-MITER (COPER)
Cutting Out A Tube's Rough Miter Joint Shape, Prior To Abrasive Beltmitering
By James Morikawa
2 February 2008
Mike, This webpage is for you. I hope it clarifies things.
Today, I took some pictures to document how I create a "rough miter-joint shape" on a tube. It's done prior to abrasive grinding the tube on the Beltmiter. Saves "wear and tear" on the abrasive belt.
So, below are my pictures and explanations
That roll of 8 inch wide aluminum sheet is called, "roof flashing". I purchased it from my local Home Depot hardware store. It can be found in the roofing section of most hardware stores. I'll be using a small piece to make a layout template.
I've wrapped the aluminum around the tube. I need to get it as snug as possible, then tape it from unraveling. I want at least 2 layers of aluminum wrapped around the tube. One layer is not rigid enough. The idea is to create a short aluminum sleeve.
I found wrapping the aluminum difficult at first, but it became easy after a few attempts.
I've slid the "wrapped aluminum sleeve" up to the end of the tube. The sleeve has to protrude pass the end of the tube. I then tape the sleeve to the tube to secure it. Using the Beltmiter, I'll be grinding a rough shape of the miter joint on the wrapped-aluminum-sleeve.
The tube holder has been adjusted for an 8 degree miter cut. This will be for the seat-tube/top-tube joint. The aluminum sleeve taped to the end of the tube is ready for mitering. I will not be mitering any part of the Ti-tube itself . . . just the aluminum . . . extension.
I miter the rough shape of the joint on the aluminum sleeve. The aluminum cuts fairly fast, and does has a tendency to distort. This is no problem because all that's needed is a rough shape of the miter joint.
The roughly cut miter shape. This is the actual template.
I've removed the securing tape, and slide the "mitered template" over the tube. I outline the miter shape with a marker pen.
Here, I've the removed the template. You can see the outlined miter shape. The tube's miter shape is ready to be rough-cut with a cutting snip.
I've found the best type of snip to use is the one above. It's called a "notching snip". It looks like Aviation Snips, but the difference is that the cutting blades are shorter. Has more leverage then Aviation Snips. You can use Aviation Snips, but this is far easier to cut with. The tube I'm cutting in these pictures is Titanium, and I have no problems cutting it. It's more difficult with aviation snips. The "Wiess" brand snips are the best for me, I only buy those.
A roughly cut miter joint done with the snip
The tube remounted back onto the beltmiter
Abrasive mitering for a precison fit.
The finished Seat-tube/Top-tube miter joint, after deburring, and fine finish filing as needed.
Of Course this is how I do it. I never say, "It's the best way". It is a workable system for me, and I presently use it.
OK, That's it. Good night.