hi,
I was wondering if anyone had a link to what size drills to use with metric taps.
what I mean is, if for example I have an M10 bolt and I want to tap a hole for it in some mild steel, obviously I cant use a 10mm drill or there will be no steel left for the tap to cut a thread into.
on the other extreme, the largest drill bit I have that will fit into a hole threaded for an M10 bolt is 8.5mm. (Drill bit set has .5mm increments)
I have searched google and only got imperial data. surely there is a metric chart out there somewhere? the action of tapping probably reduces the diameter of the hole a bit, so I am thinking if I drilled it at 8.5 it would be too small so is it 9mm or 9.5mm?
If I go too small I risk placing too much pressure on the tap as it is in use and risk breaking it or if I go too large there wont be enough metal in the hole to tap properly and it will strip too easily.
Does anyone have access to a chart for metric threads? greatly appreciated if someone can help me.
Doug