Ken Sterling (Ken Sterling) wrote in message
...
Gang,
Quick question.... possible situation ... need to tap a hole in, say
1/2" plate, through to the other side, but needs to be "perfectly
aligned" and say the plate is mounted on a piece of machinery that
can't be moved to another location and the tapping has to be done by
hand. Possible solution - is it possible, (or has anyone ever done
this), by grinding a "pilot" on the front end of that tap and then
relieving the cutting edges again to look almost like factory just
behind the end of the pilot? Is this a viable concept?

I agree with Ecnerwal. Your idea of a piloted tap is overly complicated
(esspecially for a one-off situation) and a hole is easily tapped by hand
squarly using a machinist's square or tapping block.

We drill and tap hundreds of holes at work by hand (big dies in funny
places). I've been doing it for a while so I just eye-ball it and can nail a
hole quite accuratly using that method. This takes practice and I think you
have to have a certain eye for it.

You didn't say if you needed to drill the hole (or does it already exist?)
The drilling is far more difficult than the tapping. You have to go slowly
and check the angle of the drill consistantly as you go. Because you're
drilling through steel, you'll likely be pushing pretty hard which
frequently makes for a crooked hole. Be aware of this and check squareness
consistantly.

As for tapping by hand (or using the drill), just make sure to check your
squareness consistantly as you normally would. Easy.

HTH.

Regards,

Robin