Re - ground Blacksmith drills

[Philip Davies]

I am seeking advice about some drills I have got, which have not been used since they were re - ground, although their shanks show heavy scarring.

The larger on the left seems to be a slot cutter

The smaller looks as though it is for drilling


But if so, what material?
I should like to experiment with these on a variety of materials (and, yes, I do know that material must be secured firmly)
I do not think that I will use the good keyless chuck on my drill, but will use a spare, but do you think I might damage the spindle if I am too rash?
I have bought a compound table and vice so can move very cautiously and will select the lowest speed at first. I shall start with acrylic, then aluminium and then possibly brass or even steel.

What do you think? As ever, very grateful for your advice.

[Toolmaker51]

Those are drills, not capable of slotting. A mill is actually sharpened with relief behind edge, whereas a drill is nearly cylindrical.
The flattened end is to counterbore; flattening bottom of pre-drilled hole of same size.
This is commonly done to get socket head screws flush.

[Philip Davies]

Thank you once again for your information. I was curious about the bigger one, since it seems so similar to this

Which I take to be a small slot drill.
The bigger one certainly has similar reliefs ground behind the edges, square to the axis, and one lip is larger than the other
Would you mind having another look?

[Toolmaker51]

Not at all. That's why we're here. These depict more clearly.
That is an end-mill as termed here (US). "Slot drill" isn't wrong, they'll certainly cut or clean up a slot opened by other means. That also has a grind we'd call center-cutting, which can plunge solid material, which not all milling cutters are capable.
The main warning, be aware those two flutes generate an aggressive cut; best controlled by feed direction. There are conditions to ease or aggravate that work, found a good description here, that I'd have trouble diagramming. Not only your spindle will appreciate the investigation. . .
https://www.harveyperformance.com/in...climb-milling/

Unkle Fuzzy replies below is more accurate to what you have Phllip, those are drill bits with end-mill disguises. Forgot to compare initial pics with the detailed versions. That reduced area behind cutting edge is clearance for contact against binding, the 'ground edges' have no cutter clearance.
https://mastercuttool.com/endmill-design-basics/

[Unkle Fuzzy]

It's a drill with the end ground like an end mill, but a mill would never have a reduced shank. It would snap off in lateral cutting.

I did a similar drill bit in school to round out a spherical powder chamber in a beer-can mortar.

[Philip Davies]

Thanks so much, both! I take the point about aggressive cutting, because really want to avoid dig-in, clearly they were ground for large machines. I could not see the illustrations in the link above, but was able to read through and fortunately have reference material to hand as well as You tube videos I have seen by Joe Piecynzski, which are very good