http://popularmechanics.com/home_improvement/workshop/2001/1/Metalworking_Update/print.phtml Mitring
program in Excel for use with Autocad - http://members.austarmetro.com.au/~cesnur/Subject: Cutting large diameter tubing
The usual way is with a hole saw. It will take a drill press, and a good vise. PEI and others make a neat centering gadget to go in a drill chuck. (its a pivoting V). To get the angle, I would just tilt the table.
You can come surprisingly close without the tilt by offset drilling. The tube miter template program (on the web site) will be helpful in positioning. (I modified the one that came as source to print a center mark) I would use a slightly smaller hole saw, and finish up with files/grinder, as the offset method doesn't produce quite the right shape ellipse.
If you don't have a drill press, I would make a wooden guide block (as solid wood will cut less erratically than partial engagement of a metal tube. I would consider this hole a good excuse to spend the $150 or so that a medium size hobby grade machine would cost. (for hole saw work, look for one with slow speeds. 200 rpm or less preferred)
Lots of folks use lathes for mitering. It has it's limitations but works well and offers a very rigid structure. Myself, of all the different methods, I prefer a horizontal mill.
Using end mills for mitering tubing works - the thicker the tube wall, the better. The down side is cost and the fact that even multi-flute end mills can crush a tube in a blink of an eye if your feed rate is not perfect. End mills of proper size for bike tubing are also expensive - sometimes very expensive. If you decided to pursue using end mills, then I suggest you use multi-flute roughing end mills. Roughing mills do not impart the torque loads on the tubing that a standard end mill does and they still make a fine, smooth, miter. The thing to keep in mind is that with thin wall bike tubing, the greater the TPI (tooth per inch), the better cut you're going to get and the less tooth load you have on the cutter (which means a lesser loads on an easily deformed or crushed tube). David Bohm is developing a cutter that sounds very promising and I look forward to using one. If you want a easy/safe way to miter tubes, then use a vertical spindle belt sander with interchangeable mandrels for miter size and flood coolant. I'm in the process of developing a reasonably priced version for resale to hobbyist and pros and the testing is very promising.
From: Tom & Sheila
To: framebuilders@phred.org
Subject: [Frame] quiet mitering
I just discovered something useful. You know how tubes sometimes make that horrendous screeching noise when you're filing and sawing on them? I HATE that noise. I want peace and quiet when I work. And after all, bike are supposed to be peaceful, quiet machines, right? Of course often you can get rid of the noise by clamping the tube closer to where you are working (or wearing ear plugs). But sometimes that is not practical (and ear plugs are a nuisance).
So today I found that you can use a spring clamp (the type they sell in hardware stores that look kind of like giant clothespins) to eliminate much of that noise. Just clamp the thing onto the tube somewhere between where you are working and where the tube is chocked in your vise. With a little experimentation you will be able to find just the right location to deaden the unwanted vibrations. And the clamps that have vinyl coated jaws seem to work better than ones with just bare metal.
From: tubus_nl, import & framebouw
Subject: Mitering small tubes
List-Id: Amateur and professional bicycle frame building <framebuilders.phred.org>
You can get some pretty small holesaws, but not in the welded variety. And allthough you can miter tubes with a hacksaw and a file, it can be a pain with small flexible tubing and shallow angles, as the clamping blocks get in the way. So you increase the unsupported lenght of the tubing and the file starts to chatter. Machining with a holesaw is then the way to go, as you won't need a clear exit as with a file. If you use the time honoured hacksaw and file method, don't make the beginners mistake of cutting out V-nothes with your saw. Turn the tube 90 degrees, and cut off the top and bottom of the fishmouth. You now start with a nice round bottom, instead of a sharp V. With thinwall tubing you can do most of your filing with a large flat file. Machining thinwall tubing with a 2 or 4 fluted mill is risky. The unsupported leading jaw of your fishmouth stands a fair chance of getting caught in the flutes of the cutter. Bad for the tube, the mill and your nerves. A holesaw with a smooth cylinder will support the tube.
-- Marten Gerritsen
From: Dave Bohm - Dave Bohm Bohemian
BicyclesSubject: hole saws
Date: Thu, 31 Aug 2000
List-Id: Amateur and professional bicycle frame building <framebuilders.phred.org>
If you need to make a cut deeper than the maximum depth of you hole saw, go through about half way, snip off the waste piece with some dikes and proceed. everything should be fine.
Concerning hole saws. Good miters can be made using standard higher quality hole saws like Morse or Starret. It really depends on the level of quality you are looking for and the welding/brazing processes you are using. The ground high speed steel hole saws have many advantages and make absolute perfect miters without tube chatter, catching tubes etc. If treated well they will also outlast (with resharpening) dozens of standard holesaws and give you better results throughout. An example of this is tight tube miters for TIG welding. Ever wonder how some people seem to be able to get super tiny tig welds? Its mainly tight tube miters. Also tight tube miters help alignment tremendously.
One reason for many builders not having good results with ground hole saws is a lack of education as to there use and the incorrect tooling and featuring to use them. To get good results with any machine tool you must have as much rigidity as possible (the main reason harbor freight tool don't work). If you are using a small drill press, handfeeding, or have a drill press vise or jig-a-notcher thingy the good hole saws won't work for you.
One small off the subject rant. I know that many framebuilders don't have enough money to just go out and buy all sorts of expensive stuff. It's kind of fun to know you made something or figured out a way to do something just as good for cheaper than normal. But....In general I have been disappointed in my cheap tools over the long run. Either they don't last or they do a poor job. A quality tool prevents lost down time in trying to repair it or replace it and is a joy to work with compared to the harbor freight specials.