Mitering/Coping tubes

It’s been a pretty big learning curve trying to decide on shop equipment to build frames. I’ve spend hours upon hours using Google to learn all i can from the plethora blogs and message boards covering all aspects of framebuilding.   I’m almost happy that I didn’t goto UBI for my first class since I think I’ve had to learn a lot of it the hard way – trial and error.

Just starting  out, I didn’t want to spend the thousands of dollars on a Bridgeport milling machine especially since we’re moving out west soon and those things weigh almost as much as they cost!  Although not the highest end shop tool, Grizzly Industrial has some pretty nice priced mills – from the mini-drill/mill i got for under $500 to big mills that go for 10 times that.  I got the smallest and cheapest one they have and it still weighs 100 lbs.  It’s got a rotating dove-tail column which helps me with coping tubes to the correct angle.  I use a digital protractor to get the angle set on the column just right.  Most people have a rotary table attached to their mill but the largest rotary table that would fit on this mill is a 4″ which won’t do the job since you have to attach a heavy vise to it that can hold the wood or plastic blocks that hold the tube you’re mitering.  I never knew how many variations on the vise there are…it’s insane.  You can spend $1K on just a nice vise!

Here’s a picture of the mini-mill.  The sliding table goes left/right and back/forward and is about 4″ wide x 16″ long.  I put a self-centering vise on the bench ($119 from Grizzly) that has 1.5″ deep jaws – just enough to tightly hold the oak blocks holding the tube.  I like the self-centering vise because i don’t have to re-center the tube to the hole-saw every time I change tube diameters.  It definitely isn’t the stiffest laterally but I did my best to get parts that would help.  For one, I bought Paragon Machine Work’s 3/4″ hole-saw arbors which are totally sweet.  I fit the arbor into an end mill that takes the place of the drill shank and collet that come stock.  This mill uses the old style Morse #3 (MT3) tapered collets which i have found out is a bummer.  The newer R8 collets are much easier to come by in any size and supposedly hold the arbors better.  I haven’t found any problems with my end mill holding the Paragon arbor though.  I’ve found that the flex isn’t coming from the end mill/arbor or even the regular hole saws i’m currently using, but from the mini-mill’s column.   And this is the crux…the bigger the better in terms of mills because bigger means stiffer (ok…no pun intended…!). The small mill shudders a bit when under stress but by tightening the column locking mechanism it helps a lot and also helps with micro-adjusting the downward motion of the hole saw as it miters the tube.  If I had more money, I still wouldn’t have gotten a Bridgeport (yet) but a larger pretty reasonably priced Grizzly like the G0619.  I’m using cheap hole saws for the time being while i practice TIG welding on 1.5mm 4130 steel tubing.  It copes (mitering is actually not the correct way of describing this process i’ve heard!) the tubes pretty perfectly so I have to do very little finish work with the half-round file.  Another tidbit of information is that you want to use hole-saws with a constant pitch instead of what is at most hardware stores – variable pitch.  This just means (i think) that the teeth are all in-line with each other and don’t go in/out of the circular plane of the saw.  Constant pitch saws are meant for cutting sheet metal which is more consistent with bicycle tubing and will allow for a smoother cut.  The only constant pitch hole-saws I could find had to be special ordered and are from Starrett.

The walls of the garage are all foundation cement.  Not easy to hang tools on so I had to overkill it and make this lil tool holder out of angle-iron.   It holds just the few tools that i frequent over in this area of the shop.  The wrench on the left is hanging from a nail i welded onto the angle-iron and it is what loosens the column to adjust the miter angle.  Nothing too cool, but this 30 minute dealio makes life easier and cleaner by not to have tools lying around on the workbench!

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