measuring angles.

If I understood you right, you want to drill a hole, rotate (and maybe move axially) the tube and drill another hole. Right?

If so, depending on how accurate that has to be, here is one solution: Align your Vee with the tube in it. Clamp the Vee to the table. Drill first hole. Put a pin through the hole, rotate the tube and with an angle check for the propper rotation. Drill other hole.

Or a rotary table / dividing head in the mill. If the tube isn't too long.

Nick

On or around Wed, 13 Jun 2007 14:37:00 +0200, Nick Mueller enlightened us thusly:

pretty much. The holes in an ideal world go through the tube at a 10-degree angle, but in practice they get drilled from both sides with an axial offset

- trying to drill at an angle generally doesn't seem to work, the drill always wanders off down the slope. So in practice I know the OD of the tube, work out by trigonometry what the offset is for 10 degrees.

Recently realised I was doing it wrong though, the tube (actually, 2 tubes one welded inside the other) have, together, about a 6mm wall thickness, so to get my 10 degrees by offsetting one hole, it has to be measured from the outside of the tube one side to the inside the other. See ASCII-art below:

\\ __________ \\ |\\ \\ __________| \\ \\ \\ \\ \\ \\ \\ \\ x \\ \\ \\ \\ __________________\\ \\ |\\ __________________| \\

The smaller angled tube fits into 2 half-holes in the large tube and is welded in. The 2 half holes start off as 2 holes and the tube is cut in 2 on the slant. The additional hole needs to be roughly where the x is but it's in different places depending on the geometry of the machine. The angle I'm trying to measure is the one between the 2 sets of holes.

The biggest problem is finding the centre of the tube to measure it. The large tube is about 34mm OD at the end where the holes are and steps down to either 1" or 1.1/8" depending on what it's for at the other end.

Hmmm. thinking about rotary things... might be possible in the lathe:

grip smaller end of tube in chuck. affix angle gauge (I have one for torque setting I could modify) to lathe spindle. placing a sharp pointy thing at centre height in the toolpost, I can then scribe along the tube by moving the saddle. The lathe can be rotated by hand to any desired angle, using the said gauge, and more lines scribed. I could thus scribe all the lines before drilling any holes. Shouldn't be hard to make something to hold the angle gauge in the back end of the spindle, and the centre pointer can be held in place using a 1/2" drive socket handle, in fact, gravity should do that OK since the hub in the middle of the gauge is free to rotate.

See, it's worth asking. I'd not have thought of that if I'd not just read "rotary table".

Ah, so this is a T-joint. A slanted T-joint. Like an italic T. Well, I'd do that in the mill with either a milling bit of the right size, a boring head or a hole saw. If you can tilt the mill's head to the side and it has a quill. It's done that way with all the hand-made bicycle frames or bike frames.

OK, it is offset. Well that's hard to do with a drill. But if you start with an NC-spotting drill (kinda centre drill, but looks more like a drill and is as rigid as a centre drill) it won't wander. When you have to drill the second wall, start with the spotting drill again (not boring from the other side). Or with a milling bit. Start with a small one, so the final one doesn't have to cut in the center, that makes them wander.

Edge finder? From both sides and then half the distance. Maybe I still don't understand your problem completely or I'm assuming tools you don't have yet. :-))

So, even the most stupid answers can be helpful! ;-))

Nick

On or around Thu, 14 Jun 2007 21:51:38 +0200, Nick Mueller enlightened us thusly:

I do use a holesaw on the thin-wall bike tubes. The thicker ones I can drill, they're also smaller holes.

it's not a problem to drill from both sides - the tubes that are fitted across the main tube are welded in so a bit of a taper to fill is no problem. drilling from both sides is simple and easier than arranging to hold the workpiece at 10 degrees, the mill/drill doesn't have a tilt head.

there are ALWAYS tools you don't have yet. I'm not into buying anything too pricey - I'd rather use a bit of ingenuty and invent something.

hehe. I fancy the lathe approach; though I now realise that I lent the angle gauge to a friend, so it'll have to wait a few days. In fact, any form of angle indication on the lathe will do. It's not got to be super-accurate.

So you sometimes can use the change wheels on the spindle. Depends on the model and gears available. Some kind of indicator (AKA bent wire), a line with chalk and you have what you need.

Nick

On or around Fri, 15 Jun 2007 15:49:48 +0200, Nick Mueller enlightened us thusly:

The student doesn't have a spindle like that. However, see other post for the current state of play...