Enlarge a hole in metal plate

Make about a 3/4" hack saw cut in a 1/4"-5/16" dia. wood dowel rod that is about 5" long. Take two pieces of 200-300 grit sand paper that are about 1.25" X .75" and place them back to back in the dowel cut. Chuck in a drill press or hand drill held in a vice. Fit the sprocket onto the sand paper dowel and while holding the sprocket by hand, turn on the drill. It will self center if you don't force it.

If you held the sprocket in a vice and used a hand drill, you would be more likely to make an off center enlargement.

With only 0.4mm to remove (0.2mm [two sheets of paper] at any one point) you could also just wrap a small piece of sand paper around a 1.4" dowell, hold the dowel horizontal, place the sprocket on the dowell and spin it by hand. This method will not work if the part is hardened as I suspect it may be.

I screw up when typing the measurements. The hub is 45.5 mm and I need to the sprocket is 45.1 m

Sorry. But the biggest issue I have is the large size of the hole. I have thought about a unibit, but have not seen one that large.

Has anyone seen a monster unibit?

Yes I have a drill press

Tapered reamers are usually called bridge reamers or construction reamers when they are machine driven instead of by hand. Most bridge reamers have a straight part at the top that is the ultimate finished size and they taper down from there.

45.5 is about an inch and three quarters [1.791338583 inches]

I couldn't find one at H-F, look around for a fly cutter. Seriously, that is a word.

Dan

Fly cutter:

$40 to someone with a lathe?

For that big of a hole, I would just take it to a machine shop. It will be done right and they shouldn't charge much for that small of a job.

I would offer to do it, but shipping from Redmond, WA to here would cost more than both parts.

Dan

The fly cutter would probably work if you can get it set up right with the sprocket perfectly centered under your drill press. Maybe if you set up the cutter under the piece, adjust the cutter so it's exactly the size of the existing hole, then incrementally adjsut the cutter to shave the hole until you reach the dimension required.

That said, you only get ONE chance to do it right...

There are times when it may be better to take it someplace where they have the tools and experience to do it right the first time.

Ian F noted the best way to use a fly cutter for this type project, the centering won't be that difficult. The real problem is clamping the sprocket tight enough so that it won't move when the blade hits it, a drill press table might be able to move. A mill might be the answer, but that's not something the average GRMer has hanging around the garage.

yeah... most "consumer grade" drill presses don't have tables that secure tightly enough to handle milling a hole that size. At least neither of the ones I have don't...

Yeah - using a fly cutter as a boring bar on a drill press is just asking for trouble.

Fly cutter with a pilot, to keep the hole centered. Or a large counterbore with pilot. Maybe even a 1-3/4" holesaw, followed by one of the previous handwork suggestions to finish.

Still don't have details from OP about the material, the fit needed, etc.

But a lathe is the way to go.

Drum sander in a drill press with course emory paper in it will do the trick. I'd use about an 1 1/2" diameter sander.

The trick is to apply even pressure to the sander as you move the plate around the sander (opposite to the sander rotation).

You're not removing that much.

Lathe would be hard to center. Reamer would taper. Fly cutter with a pilot won't work because there is no center to the hole. Fly cutter with no pilot is asking for trouble- hard to get perfect, easy to get the plate transformed into a high speed rotating digit remover.

Really, the drum sander would do a very nice job.

I'm no machinist, but why don't you use screws to hold the part to a piece of metal or wood. Then you would have a center point for the fly cutter.

Hocrest wrote: I'm no machinist, but why don't you use screws to hold the part to a piece of metal or wood. Then you would have a center point for the fly cutter.

The problem isn't necessarily keeping the part attached to the table, but the table being stable under the cutter during the operation. This is one of the more functional differences between a drill press and a mill. The table of a mill is much more solid.

The drum sander idea could work, but again, you have to be very careful about enlarging the hole evenly around the entire circumference. It really depends on how critical the fit of the part is.

SVreX wrote: ... won't work because there is no center to the hole.

A hole with no center... Trippy. So is that kind of like "There IS no spoon"?

In reply to SVreX: Lathe: Assuming the outside of the pulley is concentric, any 3 jaw chuck will hold it true and centered. If not, a 4 independent jaw chuck allows you to adjust until the existing hole runs true and centered. Reamer: Taper is probably not important, although the OP has still not supplied details about how the pulley is attached to the shaft (HINT HINT). Otherwise, make a series of small cuts with the reamer, alternating sides, until the part just fits. Fly Cutter/Centerbore with pilot: Hocrest has it right; The pulley gets clamped to a supporting flat piece of material (dense wood, aluminum, etc.). The pilot runs in a hole in the material, the trick is to make sure the existing hole in the pulley is centered with the pilot hole. Drum Sander: Depends on steady hands, taking only a little material at a time, while moving the workpiece around a lot, and luck. Lacking any tools or machine shop access, this is the way I'd attempt it.