flat drills

I need to drill a couple of holes bigger than my biggest blacksmiths drill. Was thinking of making a flat drill from an old file and harden and temper. I've heard of this but never done it or seen it used. Is it just a matter of grinding the cutting angles on and some clearance behind ? I imagine it will take a fair bit of power to drill steel so might have to make different sizes. Any advice welcome.

Hello Gordon,

I suggest you run out and purchase the next issue of "Model Engineers' Workshop, wherein Henry Hicks describes his method for making spade drills.

Neil

Thanks for that Neil, it's a 70 mile round trip so think I'll wait for the post, that's only a mile walk.

Gordon - Drill your hole with the biggest bit you have then open it up with the desired sized "D" bit you have made from a piece of silver steel - hardened and tempered.

Rik

When I was a lad a lot of the old boys had various fingers missing, I suspect as a direct result of what you are proposing to do. Spade drills are dangerous things, especially if not completely concentric and should only be used in a industrial machine tool. Files are carbon steel and therefore prone to shattering if not used for their intended purpose of being pushed backward and forward. The "D" bit approach would be, in my opinion, the preferred option.

Henry's technique uses a silver steel blank.

Surely any problem with using files as a source of raw material would be due to their not being properly annealed before hardening and tempering? Carbon steel properly heat treated can be less brittle than HSS.

Neil

After posting this I did think that it might be easier to make a hefty boring bar, at least it will be useful later. Old files ,heat treated are not easily broken, I made three tyre levers as an apprentice and still use them, made several wood tools also. I thought D bits were for reaming holes not for moving metal? Am thinking of 2" holes in steel and cast iron, only about 3" deep.

You don't need a 'hefty' boring bar for 3" deep. A large boring bar is only needed for deep holes. I have just done a job boring out from 25mm to 40mm x 5" deep with a 10mm dia boring bar.

The point I was trying to make regarding the unsuitability of files to make spade drills, has nothing to do with annealing the file before attempting the manufacture. The file, with its thin and wide section is completely wrong for this application, because as soon as the drill started to bite into metal the torque would snap it like a carrot.

Back in the day spade drills were forged from round carbon steel bar, so giving them the molecular structure needed to withstand the torque pressures and providing a round shank with which to hold it in the drill.

The photo's are from an old workshop text book I have in my collection, which also goes to underline my point about missing digets.

I would forget about drilling 2 inch holes with a flat drill, a two inch twist drill has a no 4 morse taper,so you would need a big drillng machine to hold the flat drill ,flat or twist it will need the same power to drive in cast iron,in steel the flat may need more as there is no rake angle on a flat drill, thats why the Victorians cored or punched holes as it was easier than using flat drills.. Bore the job in the lathe or mill or if you only have drilling machine make a boring tool and bore it out using small cuts.

OK, have decided against making a flat drill. I was thinking of a flat drill rather than a spade drill, and holding the flat in the toolpost at center hight. Thinking a bit more ,this will be no more than a double sided boring bar, was not intending to actually drill the hole from scratch.

Gordon,

Are the holes deep or through plate, if plate or sheet use a tank cutter. and finish by boring to size.

Martin P

One design of boring bar is a flat double ended blade through a slot in a bar, which saves a great deal of material.

Neil

This is a flat bit used for railways track maintenance, this one is 25 mm (maybe 1", it's HSS, and I use them to make lathe tools. Ian S C Great what you can do with an angle grinder.