Drill sharpening

[trlvn]

I've bought a fair number of auction box lots while getting into metalworking and have accumulated an eclectic assortment of abused drill bits. I've watched the videos on sharpening by hand on a grinder and felt that I would ruin quite a few drills before I mastered that skill. If ever.

So I bought an inexpensive drill sharpening guide from Lee Valley:

https://www.leevalley.com/en-ca/shop/tools/sharpening/guides/32965-drill-grinding-guide

This jig is intended to sharpen against the side of grinder wheel. Frankly, that scares me. I wanted to use it with my little 1 inch belt sander. The past couple of days, I've been trying it out and I'm pretty pleased. Here's how I mount it to the sander:

Just a 1 inch thick piece of aluminum as a spacer and a chunk of angle to support it. Here's the base in place:

Unfortunately, I have to remove the lower belt guard to get the jig close enough to use; at least for smaller drills. Here is a drill mounted in the holder and ready to sharpen:

Note that this is about the maximum length of drill that the jig can handle (6.5 inches long). I move the base up so that the drill is lightly in contact with the belt before locking it down. I'll swing the drill bit away from the belt before I start up the machine. Note that you can adjust the amount of clearance you're going to get behind the cutting edge by making the drill project further or less from the jig. Further out means a flatter arc and less clearance--but a somewhat stronger edge. This might be useful if drilling really hard material.

After the initial pass the ground face looks like this:

Note that the centre portion hasn't been sharpened yet. The two thumbwheels at the far end of the jig let you move the drill forward in a controlled manner. After getting a good sharp face on the first side, you loosen the clamp on the drill and rotate it 180 degrees. The drill should be projecting the exact same amount as for the first face. So just grind that face and you should be done. I then pull it out and use a drill gauge to ensure the point is really in the centre. If not, I can usually put the drill back into the jig and grind just one side to even things up.

Here are a couple of newly sharpened drills:

The newly sharpened faces are actually shiny--it is hard to get decent photographs of shiny objects!

Craig

 

[trlvn]

I tested with a 1/2 inch drill after sharpening on the jig:

No pilot hole; not even a centre punch but I did use cutting fluid. Chips seemed to be coming out evenly from both sides. The hole is very close to 1/2" in size. Not the greatest finish inside but I think this is just crappy steel. No apparent wear on the drill bit. I'm happy!

Craig

 

[Brent H]

Nice job Craig!!

Next month home I am going looking for a used but good/cheapish sharpener or tool grinder for end mills/drill bits etc. Would be sweet to tie in planer knives and saw blades

 

[CalgaryPT]

Nice work @trlvn. I know experienced guys who swear by your method, but I could never master it to the point that made me happy. I ended up buying a Drill Doctor that does split points and just use that. I know others hate Drill Doctor, but it works for me.

Your bit looks good and the results tell the story. Good for you.

 

[Crankit]

Impressive solution Craig!

I was buying a bunch of tooling from a retired machinist, who mentioned at the shop he worked it was common practice to pitch dull drills and get a new one. He would dig them out of the basket and bring them home to sharpen, he showed me bags upon bags of drills he had resharpened with a Drill Doctor and put into his collection.

Wayne

 

[YYCHM]

I may have to try one of these. My Drill Doctor is kind of hit and miss, some bits sharpen well, others not so much.

 

[trlvn]

The instructions that come with the jig are pretty poor. There is a really detailed write up on drill sharpening on Harold Hall's web site:

http://www.homews.co.uk/page354.html

Be sure to click the links to his sketches and click through all the pages. I didn't follow his procedure exactly but he does explain the theory and process quite well.

I should add that one drill has given me problems: a 3/4 inch with a 3-flat reduced shank which is only 3/8" diameter. It appears to have been ground down quite a bit in the past--the full diameter portion is about 3.75 inches long. A drill is supposed to project from the jig by about one diameter, so only about 3 inches is available to clamp on. It is also the biggest drill that the jig is supposed to be designed for. The trouble is that I can't get it to clamp flat. The shank end points off at an angle when I clamp it and the angle is different depending on which cutting flute I'm trying to grind. This screws up the flute geometry and I wasn't able to get an even grind on the two flutes.

Harold Hall's pages also describe a method for "four facet" drill bit sharpening. I've been experimenting with this for my drills that are too long or too large a diameter for the jig. If anyone is interested, I can try to post some pictures later today or tomorrow.

Craig

 

[trlvn]

4 facet sharpening...

So the idea is to grind a primary and secondary clearance angle on each drill flute. Ideally, these all meet at the very centre of the tip and then the drill will start without walking. I plan to use such bits only after a pilot hole, so I'm not so concerned about a perfect tip. This is what I got on my first attempt:

Not bad but the primary bevel is a little wide--there is very little metal to remove and it got away from me. BTW, you might notice that the secondary bevel doesn't go all the way to the back end of the flute. The previous owner really abused this poor guy. Also, I bobbled while grinding the secondary which makes the primary 'fade out' at the outside edge of the bit. Neither should make any difference to the way it cuts now.

Anyway, going back, this is how I set up the sander. First, I locked the table for the normal 118 degree point angle of the drill. I used the protractor head of the combination square:

The drill then needs clearance angles behind the cutting edge. Harold Hall says 25 degrees for the secondary and 10 for the primary. That seemed a bit high for me and I found elsewhere that a guy was using 20 and 7 degrees which seemed more reasonable to me. To get achieve those angles, I drew lines on the table--again set with the combination square:

Here is the drill ready to grind in the secondary angle:

I did the secondary angle on both flutes and checked with the drill gauge that the point was centred. As above, the primary angle takes very little grinding. I checked again that the flutes were equal length after this.

Craig

 

[PeterT]

That's neat Craig. So the knob on the end is kind of equivalent to feeding the drill into the belt? Do you find the knob position is reliable to match side-1 with side-2 or is it better by eye looking at the point/center?

Its been a while since I've looked at my 'blue belt' supply but I think they finer grit versions too. I might be getting mixed up with my brown belts ones though. the blue ones last longer on metal, that I do know.

 

[trlvn]

That's neat Craig. So the knob on the end is kind of equivalent to feeding the drill into the belt? Do you find the knob position is reliable to match side-1 with side-2 or is it better by eye looking at the point/center?

Its been a while since I've looked at my 'blue belt' supply but I think they finer grit versions too. I might be getting mixed up with my brown belts ones though. the blue ones last longer on metal, that I do know.

Yeah, the two knurled nuts at the shank end of the jig let you advance the drill in small increments. Really, the one nut does the pushing and the other is just a lock nut. When I turn the drill 180 degrees to do the other flute, as long as I get the shank in contact with the pusher, the second flute ends up the right length. Or close enough--drilling isn't really a precision cutting operation.

I can't find a picture of the drill point gauge that I use. A more complicated version from KBC is:

https://www.kbctools.ca/itemdetail/1-804-518

Craig