Basic Error! - anyone have a lathe, some 10mm steel stock and a few mins please?

Long story short I've drilled a 10mm hole in some 20mm Alu plate. The hole was to let me be sure that the ball screw shaft I had waiting for a coupler on the other side was in the right spot relative to the stepper motor I was going to secure to the plate. I had planned to use a 40mm holecutter to make the required hole and once positioned correctly mark out and attach a Nema23 stepper on the plate. Problem is the pilot hole for the hole cutter is 6.2mm the hole cutter does a nice tapdance on the plate but cant/wont cut accurately into the 10mm hole, I don't blame the holecutter, I blame me :)

So I believe what I need is a 10mm steel bar somewhere around 100mm long thats been turned down to 6.2mm for around 50mm of its length. Unless there's another way? (I've searched my collection of bolts etc for something that might do the job). Happy to reinburse someone for thier trouble. Thanks. Tony.

I could make that, but I wonder if just clamping a piece of wood (e.g. 18mm plywood) on top of the aluminium plate and drilling through that into the plate would be sufficient to guide the holesaw and let you drill through both?

Jonathan, thanks. I'll try that tomorrow.

Hole saws have a bad habit of starting in the wrong place even if the centre drill is in the right location, Always start slowly just touching the work at first and slowly easing the cutter into the work to allow it to find its centre, Even then the hole can be a mm out.

Regards
John

Best way is with an external hole template firmly clamped to the workpiece exactly as Jonathan has said, then you can cut the hole anywhere, but do go steady to start. G.

Thanks chaps. I followed the advice and got there in the end. :)