Tapped, Slitted Hole?

[Splat]

I'd like to make a DTI holder for my QCTP. I've never done a tapped and slit hole like this and I'm down to my last piece of .5" steel so I don't wanna screw this up. I need to make a 3/8" hole for the DTI, a #25 hole for the clamping screw to be tapped 10-24, then slit one side so it'll be a clamping type setup like in the pic. So since the hole for the clamping screw will result slightly apart and should I tap it after slitting or before? Thanks.

View media item 96765

 

[Cavediver]

Shouldn't the top side of that hole be drilled for clearance instead of being tapped? (...or maybe I'm misinterpreting your post?)

 

[RJSakowski]

I would drill through with the tap drill, drill a clearance hole to slightly past center, and tap. I would then slit and chase the threads to remove any burrs from sawing. The clearance hole will be oversized enough to allow for any misalignment from spreading or tightening the gap. However, there is no problem with slitting first either. If previously slit, I would still drill through with the tap drill, followed with the clearance drill so the flutes just break through the top half. Tap and deburr with the clearance drill.

 

[Splat]

Cavediver, I'm not getting you, sorry.

RJ, thanks. Gonna get to this tomorrow, maybe. It's always a "maybe".

 

[Cavediver]

RJ''s post covered what I was trying to say (plus some!).

 

[rgray]

When I've done that I always tap drill, then slit, then clearance drill to the slit(makes it easy to feel when to stop). then tap the threads.
Like RJ's said at the end of his post.