What size hole for sliding fit?

[Wongster]

Hi guys,

Me with my questions again.

I'm helping someone to machine a clamping post for his tennis racket stringing machine.  The stainless steel shaft that the clamp post needs to go on is 11.97mm in diameter.  It must slide on the shaft easily but without noticeable wobbly.  

I made the part and drill through with a 12mm HSS drill.  The part couldn't go on the shaft.

What size should I drill the hole for the part to slide on easily and yet without noticeable wobbly?

Regards,
Wong

[TomG]

It depends on how long the part is. More engagement on the shaft equals less wobble. One thousandth inch of clearance would be reasonable for a 1/2" long part and you'll need to ream or bore the hole to hold the precision. Drills won't make a round hole or one held to that tolerance.

Tom

[Wongster]

Thanks Tom. May I know what size should I drill up to to ream the hole 12mm?

I’m working with 304 stainless supplied to me and the hole is to be drill all the way through (80mm long).

Regards,
Wong

[TomG]

Drill the hole about 1mm under and then ream to size. Make sure the drill isn't drilling the hole oversize before going all the way through (I never trust them).

Tom