I'm rounding out my tool collection and forging a set of 1/4" to 1" square drifts for finishing holes. I'm planning on using them for joinery and such, or anyplace I need a square hole for farm work. The thinking is to hot punch a hole first and be able to drift it progressively larger into the square size needed.

These are a mix of junk pile steel and purchased W-1 steel. The corners of the junk square stock vary in sharpness, but the new W-1 is very sharp. My questions are:

1) When you make a square drift, how sharp do you want the corners on the body of the drift? Should they be left as purchased or rounded slightly? I could see there being issues with sharp cornered holes tearing out when drifting or in service.

2) Similarly, how much should the corners on the working taper on the drift be rounded? Particularly if starting with a round hole and drifting it square.

Look forward to hearing how some of you guys do it.

I just made a walkway arbor and drifted 27 of the crossing joints. They are 3/8” and I milled the drift from S7, heat treated it and left it sharp on the corners as milled after debur. My punch did fine but there was not much to drift as the pilot was 5/16”.
On a separate note I’ve started making all my punches / drifts from one bar size in S7 and then using a universal holder sleeve/striker out of 4140. The thinking is I save the S7 for the business end of the tool and the end I hit with a hammer is big 1 ½”. I don’t miss hitting it with the hammer as much and it’s larger longer diameter that I can hold better. I drill and ream a hole in the lathe to except the punches/drifts. Then set screw them in place. I use the same striker on all the punches and drifts so I only made one. I think this saves material and keeps me from holding some wennie diameter shortish punch.

Drifts are for opening up slots. Drifts are not for stretching holes to size. Metal is very resistant to stretching. You can stress metal if you try and stretch it. When drifting holes it is best to make the appropriate size slot the use the appropriate sized drift to open it. It does not matter weather you have sharp or rounded corners, you just need the appropriate slot and drift. When you have that, all you need is mild steel for your drift for opening, shaping, and sizing holes. The only exception is drifts for making hammers and top tool since they act like anvils inside the hole so you can forge the cheeks of the hammer or top tool with fullers or hammer.

Is there a way to determin the correct size slit for the hole you are trying to get...such as I want a 1/2 by 1/2" square hole so ill cut a slit 5/8" big? Forgive my ignoranc.

For that answer you need to do some forging...Wot you have to work with,,steel types, and how you hit it al make a difference . if youi are driftin slit holes in one inch stock and you use a mild steel punch thta is taking time to get throuigh, it will heat up and change shape,,and or rivet itself into the hole. If youi can strike it hard enough to gor throuigh in a few strikes it will do just that..as to the size of the slitter you may find you need a differeent size than i do...if th eslitter is a little too long it will leave a divot in each end of where it slit beforfe drifting ,,when you are done..i have not seen chartgs for sizes to match with holes.

OK, what you you guys have stated on corners not mattering much during forming from a slot and the stretching of metal makes good sense. I still will probably add a slight fillet to the corners so as to reduce the stress concentrator at the corner in service for parts subject to fatigue. The engineer in me shies away from sharps for that reason... Makes me think of why there's no square windows in an airplane.

Brian, to make sure I've understood how you slot and drift:
If you don't want to stretch the metal, then you would want to slot cut/punch an opening with the same perimeter as the final desired hole size. So for the 1" square drift I would need an opening with about a 4" perimeter. From what I've seen in your posts it sounds like you use a slitter for this?

Thanks for the advice so far.

Clodbuster you need to check out this thread.

Clodbuster you need to check out this thread.

Ditto. Thanks, MOblacksmith0530!

Checked it out. Thanks for the tips guys.