Drill Sharpening

What you will get here is what you will get ... this is usenet after all

- but:

1) I don't sharpen drills less than 7mm or so diameter at all, buy new ones.

From 7 to 13 mm, consider carefully - eg if you use a lot of 8.5 mm drills, then buy a pack of ten 8% cobalt ones and see how long they last.

2) sharpen bigger drills by hand, so they have two flat surfaces - these will meet at a line where the web is.

The important part is the edge of the flats on the outside edge of the drill - it should be almost at right angles to the drill, but with the cutting edge end only just a little higher. This is the part that actually cuts, and the back relief of the cutting edge. Drills do not usually need much back relief, so it should be fairly straight, only a little angle.

I always drill a pilot hole at least the thickness of the web when using a larger drill. That way I don't have to worry so much about getting the edges the same length along the drill, or about how the web will "cut" (it is is basically a chisel being forced down into the work, not a cutting edge).

In fact I don't really try at all hard to get the edges exactly the same length, so one edge will cut more than the other. This doesn't really matter much if the drilling machine is rigid, after all people use single edge drills like D drills a lot anyway. It can make the holes a little oversize sometimes if the machine is sloppy.

3) for really big drills, you can sharpen them as above then grind the trailing edges of the flats off. Again, drill a pilot hole at least the thickness of the web.

There are several zillion ways to sharpen a drill, some coming complete with eleventy-seven points of wisdom, and some of which do actually work better than the rest - but if you aren't drilling industrial quantities of holes, then these guidelines are enough to drill pretty good holes.

-- Peter Fairbrother

Can you get the Darex Drill Doctor? They are fussy and don't get the rake angle right every time, but once you learn the magic sleight of hand they do a pretty decent job.

jsw

I had a Drill Doctor for a while & concluded that hand-grinding was no worse than the results it gave me. Went back on Ebay.

Regards, Tony

When they came out several of us on rec.crafts.metalworking bought them, and were soon loudly complaining. Curt Anderson of Darex told us to sight down the drill bit in the chuck and loosen the nut a little to make the jaw leaves visibly radial, not skewed spiral. That mostly solved our problems.

As a cross-check after grinding, compare the angle between the point ridge and the cutting edges to that of a factory-fresh bit, and make sure there is at least some back rake. I spin the bit against scrap wood with my fingers to see if it bites in.

Here the angle is about 135 degrees, or north-east when the cutting edges are horizontal.

jsw

I have a second-hand Drill Doctor. It might not be perfect, but it's much better than what I can do, until I finish the Quorn :-)

Mark Rand RTFM

I have an old "Toolmaker" surface grinder like this,

a rotatable wheel head similar to the Quorn's so it can use cup and dish wheels at an angle. It has a swivel table for grinding between dead centers but nothing like the Quorn's air-bearing holder.

How much of that complex adjustability is really necessary to sharpen common tooling such as reamers, end mills and taps, and what could be simplified on a home-made version scaled to 5C collets? The grinder already has X rack feed and a Y leadscrew.

jsw

The old fashioned way works best (for me).

An eye glass type magnifier and a fine grinding wheel 0f the correct grade for the drill and frequent examination of the business end.

I bought a DD in the UK, what is now the old design IIRC, and I thought it was originally quite crap but then spending a bit of time learning its quirks I can now do quite a reasonable grind with it and find it quite useful to touch up drills between about 5mm and 13mm. I have smaller drills but they're cheap and near the bottom end of the DD range. I have larger drills but they can take quite a while to grind with the DD, it is rated to 19mm, so tend to try and not blunt them. My neighbour has a common garden drill sharpener jig with a similar range but we have never done a back to back comparison, and probably won't as have better things to do at the moment.

"David Billington" wrote

There doesn't seem to be any harm in grinding the large ones as close as I can by hand and only finishing on the DD. They don't spin fast enough in use to be bothered by a slight imbalance.

I grind away the back sides of the flutes by hand as though I was going to split the point, but stop short. Then the DD grinds only a relatively narrow land, like the cutting edge geometry of an end mill.

jsw

ditto, an old timer showed me how to hand sharpen drills at around age

17 and still use the same, rotate gently, technique, though the smaller sizes were always tricky. Keep in practice by going through the whole drill box from time to time.

If eyes aren't so good anymore, like here, an optivisor works wonders...

Regards,

Chris

--Well yes, but speaking of the Quorn has anyone come up with a widget to make the Quorn toolholder move like the one in a Darex?

Harig makes very nice ones:

So far I've either been outbid or they were too specialized to be worth the cost.

The 5C Spindex comes close but mine isn't rigid or precise enough. Its spindle shows promise, if ground or lapped and fitted to a more versatile base block.

I haven't checked this one's claims

examined this might stop by if he ever gets an SB Heavy 10 taper attachment.

The Darex DD cam ramps appear to be a constant-angled helix of approximately four turns per inch, which could be cut on a lathe. I only eyeballed the ramp against a strip of paper wound around the collet body.

jsw

I bought one of these some years ago (for less that the price of this one):

Useful, proper piece of kit. If you want you can chuck away the stand and bench mount it - in the domestic world the dust extraction isn't critical

Charles

I too have a Dormer 108 and find it great for most drills, however before that I used the 4 facet method on a Clarkson T&C grinder to sharpen all my drills, this method could be used on a surface grinder. If you need an attachment for a conventional toolroom grinder, there was a design recently in MEW that should work well.

Peter

Many thanks to all who contributed. Certainly some topics to follow up.