How to machine a metal slot/hole

The shape is correctly described as obround (at least in UK engineering terms; oh you can spell aluminium, so you're not in the USA ;-) You really want to keep the hole that shape, if you make a rectangular slot you'll create stress-raisers in the corners which could lead to cracking and failure of the pulley. I would use a small diameter cutter and mount the pulley centrally on a rotary table in order to generate the 2 arcs at the end of the slot. Martin

It's "aluminum" here in Canada, too, eh! So you're outnumbered 2-1 :p

CVC

Aluminium here in Australia. 2-2 :-)

-- Jeff R.

A shaping operation, using a shaper or a lathe, could do it. The challenge then would be getting the cutting tool the right shape. Ordinarily, I'd make the hole first, mount it to a shaft, then turn the pulley groove - easier to keep concentricity.

Jordan

Maybe I'm sloppy, but I'd just drill for a setscrew to bite on one or both flats. If it needed more strength, a cross-dowel with a flat ground on it (in a wedge fashion) would do it, in the fashion of the old bicycle cottered cranksets.

That pully is pretty thin for its diameter, and aluminum is a soft material, so what's going to keep it tight and square on the motor shaft? I didn't see a setscrew hole, and even if there were one I don't think you'd get a good square running pulley that way. Are there some kind of collars on either side of it queezed up against it to keep it in line?

If there are, and you only need two pulleys, I'd vote for milling a slot in the pulley and filing the ends to clear the shaft by trial and error.

Jeff

GRRRRR...

LOL :)

CVC

TOP POSTING CORRECTED.....

I would agree with the idea of making a broach. It would be a relatively simple lathe/mill project. The hole is small, the pulley is thin and you're only doing a couple pieces. So, you could make the broach out of mild steel and not have to heat treat it (it won't stay sharp long, but it doesn't have to...). Then, drill a 6.00 hole, take a 6.00 end mill and elongate the hole 2.00 each way. That way, all your broach has to do is clean out the corners.

Of course, I assume the dimensions are in mm. If they are centimeters, inches, furlongs or some other goofy thing, life gets a little more interesting...

Jerry

Beside the other answers, a simple solution: Bore the hole with 10mm. Turn some round to 10mm OD. Slit it in half and mill the halves down to 6mm. Now you can put the "half-moons" in the pulley's hole. It only takes a little imagination (I'll leave that part to you), to find out how to fix the half-moons to the pulley.

Nick

I suppose you know: This means war!

Let the war between the ium and um factions begin!

BTW: Is it Illudium Q38 or Illudum Q38? I'm not sure, which may explain the absence of the KABOOM.

Best Regards, Marvin

Hi all,

@Martin Whybrow - thanks for your suggestion, i see how that would work. Unfortunately, I'm doing my milling on the lathe and don't have a rotary table. I'll try and mill a rectangular hole but with rounded corners to ease the stress.

@Jeff Wisnia - yes I agree it is very thin - while machining them I've made them thicker (80mm). There's an abuttment at the start of the motor shaft to hold the pulley square and the end of the shaft is threaded so I can place a nut on the end to hold it in place.

@ snipped-for-privacy@gmail.com - I see, seems quite a simple solution - I reckon I could do that.

@Rich D & Jerry Foster - thanks for your suggestions regarding the broach. Addmitedly it's the first time I've heard of the thing, so I'll do a bit of finding out on that.

Thanks for your replies!

--Amr

Careful setup on a rotary table.

Zero the RT center,under the spindle center.

Drill a hole smaller than the distance between the flats.

Do your calculations. You need to calculate the offsets from the center point for the arcs, as well as the degrees of rotation you require to cut them, and the length of the flats.

You will end up cutting an arc, then the flat, or the flat then the arc, using the offsets from center position, as well as table travel to run the straight lines, and the movement of the RT to run the arc cut path.

This would be non trivial unless you can rely on your handwheel movements to be accurate, or you arrange a reliable method of measuring table movement, such as dial indicators or a DRO on the table.

That's how I would do it, anyway.

Cheers Trevor Jones

This would be a real easy job for an EDM.

Take a round piece of graphite, mill or grind the flats on it until it looks like your motor shaft, then burn it in the pully.

Thanks for your reply. Very interesting method, but unfortunately I don't have the capabilities to do it.

--Amr

Dave Ly> > How would others have gone about this?

Drill or bore round hole to fit round part (10MM) of shaft (perhaps drill undersize and ream to size).

Drill & tap for a pair of setscrews/grub screws. Perpendicular to the flats. Largest convenient diameter. Place brass or aluminum shim under point of screws, or get fancy screws with built-in soft point. Loctite the whole mess.

OR

Drill & ream for pins or taper pins (inward face parallel to and touching the flats) (only pulley gets drilled/reamed).

OR

Ignore flats, drill & ream for taper pin through the non-flatted section of the shaft (both shaft and pulley get drilled/reamed).

Barring some massive power input, should work, over with quickly, on to the next thing.

I recently finished a sentence with an "eh" tossed in. My wife was astounded that I spoke "Canadian", and without an accent! :-)

Harold

Yeah, but you guys have kangaroos and live upside down. . Not sure you count. :-)

Harold

Hahahahaha, welcome to a better world, eh!?

Priceless,

CVC