Grinding a step drill

[VicParticipant @vic]

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.

[VicParticipant @vic]

[Ady1Participant @ady1]

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

[peak4Participant @peak4]

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

[VicParticipant @vic]

Posted by Ady1 on 06/02/2023 18:53:20:

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

I want to grind my own step drills:

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

[HuubParticipant @huub]

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.

[noel shelleyParticipant @noelshelley55608]

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

[HopperParticipant @hopper]

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.

[Neil LickfoldParticipant @neillickfold44316]

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.

[bernard towersParticipant @bernardtowers37738]

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

[BazParticipant @baz89810]

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.

[HopperParticipant @hopper]

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.

[Mike PooleParticipant @mikepoole82104]

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

[VicParticipant @vic]

Posted by Hopper on 06/02/2023 23:18:33:

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.

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.

[VicParticipant @vic]

Posted by Mike Poole on 07/02/2023 12:32:29:

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

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

[HopperParticipant @hopper]

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.

[VicParticipant @vic]

Posted by bernard towers on 07/02/2023 09:11:20:

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

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

[VicParticipant @vic]

Posted by Hopper on 07/02/2023 13:18:16:

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.

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.

**LINK**

**LINK**

[JasonBModerator @jasonb]

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

[HopperParticipant @hopper]

Posted by Vic on 07/02/2023 13:27:51:

Posted by Hopper on 07/02/2023 13:18:16:

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.

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.

**LINK**

**LINK**

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.

[VicParticipant @vic]

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.

[DC31kParticipant @dc31k]

Posted by Hopper on 07/02/2023 13:41:56:

…the more usual way to do it would be to drill the small hole then use a counterbore bit to drill the larger hole.

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.

[egaParticipant @ega]

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.

[VicParticipant @vic]

Posted by DC31k on 07/02/2023 14:54:26:

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.

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.

[HopperParticipant @hopper]

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.

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