Grinding a step drill

I’m wondering if I can grind a step drill on my lathe. I was thinking about buying a 43mm motor mount for my router and using a mounted stone in it. Anyone done this? Two things occurred to me though, where and what type of stone to get and how to dress it if it needs it at some point. It’s not something I need to do very often so I’m looking for an inexpensive solution.

I got a set of them at lidl for about a fiver so they should be about a tenner on the net

Yes, I have used my router as a toolpost grinder;
There photos are just a mock up, as I took them to illustrate a different point to help someone on a Facebook group.





Bill

I want to grind my own step drills:

Edited By Vic on 06/02/2023 19:45:02

I have made a drilling spindle for the tool post using 6009ZZ plain bearings, an ER11 collet holder and a 170W BLDC motor.

I also made a milling spindle using AC7000 contact angle bearings, an ER11 collet holder and a 175 Watt Dremel.

For grinding, I prefer the Dremel milling spindle because it can run high RPM and the spindle is free of play. The spindle has a 3D printed adapter. I also made an adapter for a DC motor from an old cordless drill.

Check the speed of your machine and the max speed of your wheel. I have sent a PM. Noel.

That's a lot of HSS to grind away. And by the time you get down to the smaller diameter, there will be little or no flute left. Step drills have smaller flutes on the small diameter part.

A D bit grinder or a tool and cutter grinder is the easy way to be making step drills, Some drills need web thinning to make them work. It is a challenge to grind the land relief onto the step drill as well, unless you have a finger follower.

I thought that step drills were for sheet metal and the drills you are talking about were piloted drills.

Step drills are for drilling two or more sizes of holes at once, for example a 6mm diameter hole with perhaps a 10mm counterbore. A 10mm drill would be spun down to 6mm for the required length and the counterbore part either flat bottomed ar sharpened to whatever angle is required. Tin drills are used for sheet metal, they are shaped like an upside down W, central pilot and just the outer edges cutting.

But then there are the modern step drills that for sheet metal that start out at about 1/8" and go up in 1/6" increments to 3/4 or 1", alll on one drill. Very handy for sheemetal indeed. All I use these days for thin stuff.

At the price shown for a Dormer step drill I can see why you want to grind your own. As they are so expensive I guess they become economical for production jobs as you avoid the counterbore operation. The drill modified as in the picture was widely used in our tool room for producing a counterbore but of course the hole needs drilling first.
Mike

That is not the case with the few that I have. The flutes are the same size all the way down.

For my use, reducing the tip of a 27/64 drill bit down to 15/64 will leave more than enough flute left to clear the work.

Yes they are expensive, look at the cost of this one! Free delivery though.

Well there you go. They just look smaller because the outer part has been ground away. When you think about it, the flutes still have to go down to the size of the chisel point.

Still seems like an awful lot of HSS to grind away with a mounted point in a router, with an interrupted cut over the flutes. That kind of grinder set up is usually for taking a few thou off for finishing purposes. You might be better off to make up something to hold a pistol drill up square to your six inch bench grinder so the drill rotates the bit and the six inch grinding wheel does the work. I imagine it would go a lot quicker that way.

I’ve always called them Cone bits. They come in both plain and stepped versions.

There are lots of ways to approach the job. I wanted something a little more predictable/accurate though. If necessary I’ll resort to somehow jigging my bench grinder.

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You could rough grind most of the material away free hand on the bench grinder and then set up to finish with your mounted grinder

Looks like he has it all figured out. Simlar idea, hold the bit in pistol drill by hand and run it up against the belt sander. Then you could finish it off in th elathe.

But unless you are drilling many dozens and hundreds of these stepped holes, the more usual way to do it would be to drill the small hole then use a counterbore bit to drill the larger hole. Sets of counterbore bits are available stupid cheap from that large manufacturing country far to the east of you.

Or you can even drill the larger hole with a regular larger drill bit and then finish it off with a drill bit ground to a flat bottom end.

But if you plan to be drilling more than a few dozen such holes, then the step drill would be a definite timesaver.

For this particular application its far more convenient to drill it all in one go. I do make my own counterbores but the counterbored part is too deep in this instance. If step drills were readily available in a range of sizes at a good price I’d just buy them.