Make a demagnetizer from an old electric motor.

[mr_modify1]

[desbromilow]

I would be considering lining the inside of the stator with some PVC pipe to prevent any contact with the feild coils.

[mr_modify1]

If you had some pvc the right size it could prevent contact and also stop some demagnetized metal chips from falling inside.

[Toolmaker51]

Cool idea using a motor case and windings! This, sized up somewhat, and a little trolley traversing inside would handle components like punches and dies. One shop had a Magnaflux coil built (modded) that way. Best demag unit ever.
Experience with degaussing parts says it will improve by poking object into and withdrawing slowly from the field is more effective than 'parking' item inside. Same with intentional magnetization.