Grinding a step drill

The difficulty with that approach is that the pilot and counterbore are available in only specific combinations of sizes, generally a clearance hole for a nominal fastener diameter and a standard counterbore diameter.

In addition, the length of the small diameter may not suit the OP's particular application.

If you want something other than standard metric sizes, a longer pilot or a tighter counterbore than is usual, there will not be an off-the-shelf solution.

The Granlund counterbore system employs separate pilots which are available in a range of sizes and, if necessary, are easily shop-made; very expensive new but can be had at used prices.

This is what I’ve found. As I work mostly in Aluminium Alloy I started making my own counterbores some years ago from silver steel. They are easily made on a mill and then hardened with a blow torch. I don’t even bother tempering them normally.

If my efforts to grind a drill bit doesn’t work out I may well make a counterbore to fit a suitable size drill bit and see how that works. It will likely need some clearance grooves for swarf clearance though.

Yes it looks like some kind of relief for swarf clearance would be needed if you make your own. The Zoro picture you posted above looks like the small diameter section is tapered back smaller as it meets the larger diameter section, with almost a groove ground around it.

Another way you might be able to remove that much HSS faster in the lathe, other than the use a carbide tool bit and turn it down as in one of the videos you posted, might be to buy a cheap compact bench grinder, the type that has 6" wheels but very narrow, and a smaller motor than the heaver duty models, and mount it on the cross slide then fit it with a smaller and better quality wheel. It would shift metal faster than a router and mounted point, which could be used for finishing off and putting on the taper and swarf clearance groove. It would give more precise control than a pistol drill mounted to the bench grinder. Just be very careful to cover all lathe surfaces to keep the huge amounts of abrasive grit generated out of the slideways, chuck, etc.

Hi,

I think the machine you need to look at is called a Monoset (so perhaps search monoset tool grinding wheels). Using an Aluminium Oxide Cup Wheel and would sometimes be dressed by hand using a Carborundum Stone (or sometimes called a Dressing Stick) and sometimes with a Diamond Dressing Stone.

Personally I would use a drill grinding gauge to help set the heights and angles.

My favourite drill gauge is the shop made version, made from a 500 x 50 x 2 mm thick strip of sheet metal with a small 50x 50 x 90 degree upset to one end in the middle of the upset a centre pin is added and used to locate the centre in the drill tang (away from the cutting edge). The cutting edge of the drill is then swept across the 450 x 50 mm face marking and arc. A comparison is made between the first flute arc and the second flute arc (sorry could not find a picture).

• Personally I would just make a bench grinder work: It will take quite a lot of practice and one of those wonderful Record Power bench grinders with the rough cut and fine cutting wheels. OR...
• As suggested make my own tool from Silver Steel because this is a very effective approach.

Graeme

Edited By Graeme Yorwarth on 08/02/2023 22:38:55

Edited By Graeme Yorwarth on 08/02/2023 22:40:05

This is from Ian Bradley's The Grinding Machine:

Hi Ega,

We used to cut a notch in the vertical member to set the 118 degree angle correctly and confirm the cutting edges were the same length (as the scribed line checks the same height only).

Great picture, needs a modern edit to replace 'engineers marking blue' with 'black marker pen' or perhaps I have this vague memory that some of the old timers used chalk, the history for this tool is probably related to reducing mess:

c 1880: Marking Blue (mainly used for recreation by apprentices)

c 1920: Chalk (used on edge by the cutter grinders and very quick)

c 1980: Black Marker Pen (used by the tool room)

c 2020: Sharpie Pen?

Graeme

I realised I hadn’t posted a picture. The job has been done and the drill bit works fine. This is my second attempt as I overshot the pilot at my first attempt. Luckily I had bought two spare bits - £1.10 each. I made a collar for the bit as a depth stop then drilled a hole in a piece of wood to act as a guide using my bench grinder. It didn’t take too long until I got near the target diameter for the pilot. I’d prefer something more exact but it’s done the job.

Graeme Yorwarth:

Just seen your post. Good point about the angle. I take it that the notch would be in one or both edges of the vertical member, effectively taking the place of the normal angle gauge.