How to save this pulley.

[FTlatheworks]

Yes, they expand by tightening the screw. If you turn them true or indicate them true in a 4 jaw, they are very accurate. You can also buy them in sets, they come in handy a lot for me.

Did you say I could make one, or do you just mean a tapered piece of stock? I don’t have a mill.

 

[Eddyde]

Did you say I could make one, or do you just mean a tapered piece of stock? I don’t have a mill.

You don't need a mill or taper the mandrel.

You can even make a simple mandrel on the end of a piece of steel or aluminum bar stock by turning it to a tight slip fit to your bore (you can leave a shoulder on it for registration), Affix the part to the mandrel with Cyanoacrylate Adhesive (Super-glue). Machine the part then use heat to remove the part. Use some sort of coolant so you don overheat the part and release it prematurely while turning.

You can make an expanding mandrel like the one in the link, but it isn't necessary for a one off part. Basically, it's a flathead screw through the center in a countersunk hole, when tightened it pushes the segments outward to grip the part. You can cut the slots with a bandsaw or even a hacksaw.

 

[FTlatheworks]

You don't need a mill or taper the mandrel.

You can even make a simple mandrel on the end of a piece of steel or aluminum bar stock by turning it to a tight slip fit to your bore (you can leave a shoulder on it for registration), Affix the part to the mandrel with Cyanoacrylate Adhesive (Super-glue). Machine the part then use heat to remove the part. Use some sort of coolant so you don overheat the part and release it prematurely while turning.

You can make an expanding mandrel like the one in the link, but it isn't necessary for a one off part. Basically, it's a flathead screw through the center in a countersunk hole, when tightened it pushes the segments outward to grip the part. You can cut the slots with a bandsaw or even a hacksaw.

I definitely would use an expanding one. I can’t buy this pulley since it’s custom. The most accurate hole is the one on the outside that I bored with a boring bar. It’s exactly 1.372. What dimensions would you use for the expanding mandrel? what size threaded hole to expand it?