Baffled by flatted-shank spot weld drills

[Bill PhinnParticipant @billphinn90025]

I recently bought two sets of spot weld drills from two different sellers on Amazon (example pictured).

I’m baffled by the single long flat on the shanks. A three jaw chuck won’t hold them concentrically if you insert them so that one of the jaws tightens down on to the flat; the only way to get them to run concentrically is if you carefully insert the shank into the chuck so that two of the chuck jaws grip on the rounded part of the shank right on the boundary of where the flat begins.

So what is the function of the flat? Is there some sort of dedicated hand-held side-lock drill out there specifically designed for these sorts of spot weld drills?

I should add that in the ad. all of the many images show only a smooth round shank, though a 360 degree view is nowhere shown.

[DC31kParticipant @dc31k]

The drill bits themselves are three different diameters.

The shank (with flat) is a common size.

That immediately suggests they are not designed to be held in a gripping device with variable diameter capability.

Recall that in auto body work, air-powered tools are very common.

Perhaps search for the machine that is designed to turn them and enlightenment will follow.

[Bill PhinnParticipant @billphinn90025]

Thanks for shedding light on the “mystery” drill that I felt must have been out there. Presumably, the back stop attachment angles out of the way when there is no access to the rear of the weld.

The remaining mystery is why the adverts, in addition to picturing straight-shank drills, explicitly state:

“Fits Straight Into a Standard Power Drill Chuck: Each bit features a 46 mm overall length and a straight shank compatible with most corded and cordless drills, so you can get to work with the tools already in your garage or workshop bay.”

[Robert Atkinson 2Participant @robertatkinson2]

Either:

They are making an incorrect statement or

They sent the wrong items.

In either case you should ask for a refund as the goods are not as described.

Robert.

[Clive FosterParticipant @clivefoster55965]

The “mag drill” commonly used for things like structural steel work to make holes in situ use drill bits with flats held by  setscrew. Common type, rotabroach et al, have two flats at 90° but single flat version like your picture will work in the holder.

Typically drills up to 50 mm have a 19 mm (3/4″) nominal Weldon flat shank, larger ones use 32 mm.

Adapters can be found to hold rotabroach bits in standard chuck. £25 ish I think. But making one isn’t rocket science. Bore needs to be accurate size and concentricity between shank to be held in a normal chuck and the weldon holder needs to be very good.

Clive

[Bill Phinn]

On Bill Phinn Said:

Presumably, the back stop attachment angles out of the way when there is no access to the rear of the weld.

Find the brand name/best quality item from which the Amazon ones have been copied and peruse the instruction manual.

I am wondering if the device works as an air-powered G clamp so the weld still gets removed if you are too posh to push.

[Bill PhinnParticipant @billphinn90025]

Thanks a lot for the further replies.

Robert, in line with your advice, I did a 3 minute Amazon chat. The agent refunded the full cost of both sets of drills without even inquiring what the problem was. I don’t need to send them back. £18.48 better off now and no traipsing to the post office.

Clive, I have quite a few Rotabroach (and other brand) cutters with the 3/4” double Weldon shanks. The present drills are all 8mm shank, so won’t fit a mag drill holder. I do have an adapter with a B16 taper on one end and 3/4” double Weldon shank on the other that allows me to use a standard drill chuck stuck in the end of the dedicated mag drill holder.

DC, I’ll look into that. Doubt whether I’ll ever justify buying one but it would be useful to know how the back-stop thingy works/doesn’t work.

[Clive Foster]

On Clive Foster Said:

making one isn’t rocket science. Bore needs to be accurate size and concentricity between shank to be held in a normal chuck and the weldon holder needs to be very good.

Clive

I forgot I made a Forstner bit extension many years ago for 8mm shanks. That will do for now for hand drill work.

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