4 facet drill "sharpening"

I am able to regrind drill points reasonably well by hand on an offhand grinder but having read quite a bit about the four facet method of sharpening I thought I’d give it a go today. (Don’t hold your breath mind!)

This is my little T&C grinder I used to do the job:

Standard angles used for the drill point – 118 degrees included with the recommended 10 degrees for the primary lip edge and 25 degrees for the clearance angle – these angles being recommended by Harold Hall in his book on tool and cutter grinding.

My first attempt on a 3/8” drill left primary lips distinctly out of parallel as seen in the pic.

I experimented a little and found that by inserting a .1” slip between the tip of the indexing finger blade and the indexing ring register I was able to bring the primary lip width back to, approximately, parallel. (I have yet to work out what is going on there!)

So does it work? In short, no – at least on this first attempt. I tested the finished result by chucking the “sharpened” drill in the tailstock and drilling a bit of 1” dia aluminium. The drill wandered on the bar end so I used a centre drill to give it a start then had another go. It drilled reluctantly with the swarf coming away mainly from just one edge which leads me to believe that ER collets are not suitable for this purpose. Oh well, it was worth trying!

So a disappointing first attempt but nil desperandum as they say, I’ll have another go in a day or two.

Rik

Why do you think ER collets are not suitable for this type of operation?

The reason I ask is that I'm currently thinking of making an ER20 holder for my Quorn T&C grinder for this type of job.

Clive

Good article ***here*** by Gadget Builder on 4 facet drill sharpener.

John

Hi Rik

I can assure you the 4 facet method does work but I guess if you only had swarf from 1 flute the flutes are of unequal length.
I usually have to adjust the rotation by a degree or so to get absolutely parallel land between primary and secondary angles, never found the reason.

Emgee

ER collets are definitely suitable for the task. Many Chinese drill grinding machines use ER collets. They usually mount them backwards: small end facing the grinding wheel. I have a Chinese clone of a Deckel tool grinder. It normally uses R8 collets. I put in a collet chuck, R8 x ER32. That lets me hold odd sized tools. It works perfectly for a 4 facet grind. I also have an ER32 collet chuck in the work head for my KO Lee tool & cutter grinder. I have no issues with the ER collets.

Maybe check your collet for runout ?

I've used ER collets for this job and they do work.

I have two suggestions; make sure the cutting edges are horizontal and parallel when mounted and this is much easier with a bearing collet nut which won't move the collet and drill as it's tightened.

HTH

Jon

I have some cheap 'Parkside' drills from Lidl that are ground 4-faceted. I notice their point angle is much more obtuse than the 118-120 deg I was taught for offhand grinding - perhaps 140-150 deg.

I was wondering whether there's a geometric factor that forces this if the grind is to be effective. Which in the case of the cheapies I mentioned, it certainly appears to be.

I use ER20 collets, in a home made holder on my Worden, for four facet grinding. The holder fits in the 31 degree angled base fixture from Hemingway. The only problems come from operator error! (Always always because the cutting edges are unequal in length)

Four facet drills cut very well, better than "normally" sharpened drills.

I have made a little jig to ensure that the cutting lip of the drill is horizontal when clamped in the collet, ready for grinding.

Although four facet drills are reputed not to need centre drilling, I always do.

Howard

Update to my OP. The disappointing results I have recorded here, were, it transpires, caused by the drill itself – it was bent! I only noticed this morning as I attempted to have another go with a different drill.

So, I have ground the point on a fresh victim and this time the visual result was more encouraging:

So does it drill ok THIS time? Sadly no. It was pretty hard going on good quality aluminium rod producing uneven straggly swarf again, mostly from one edge only.

As I found the procedure over fiddly even using an accurate T&C grinder I have decided for the time being to abandon “four faceting” and revert to sharpening on the offhand grinder. Life’s to short to “fiddle” it away.

However, if you are contemplating trying this method of sharpening please do not let my experience put you of as I might well be doing something wrong. After all, Howard seems to be quite pleased with his results.

On the positive side, grinding the second drill gave me a chance to try out my new CBN cup wheel. It knocks spots of the aluminium oxide wheels I have used in the past – very pleased indeed.

Rik

I seem to get away with sharpening 4-facet drills offhand.

Neil

Whatever gets the dirty job done Neil - results is what matters isn't it, wasn't it?

Rik

4-facet grinding off hand - down to what size Neil?

Joe

It's not reputed, it's a fact. When drilling on the Bridgeport/CNC mill I never centre pop or centre drill first. For ordinary accuracy I just drill straight off with the 4-facet drills. If I need to be certain of better accuracy then I start with a carbide spot drill.

There is a caveat, the surface being drilled needs to be flat. The drills doesn't work on round bar without spot drilling first.

Andrew

About 6mm / 1/4", maybe a bit less

I don't pretend to any great accuracy, but if I need to get a drill cutting again in a hurry and can't be bothered to get the drill sharpener out... naturally i wouldn't do my split-point dormers off-hand!

That said I did a 1/2" one and it drilled me a 0.501" hole

Neil

I have never tried hand grinding a four facet drill but back in the 60's and 70's when I was in the Air Force I spent a lot of time doing skin repairs and modifications on aircraft, this involves a lot of precision drilling, even when removing redundant rivets. We all soon acquired the necessary skill to hand grind twist drills, mostly 1/8 or 3/16, if it didn't cut square after sharpening then you soon acquired the wrath of those in charge as it would jeopardise the structural integrity of the task you were working on. Nowadays I have trouble seeing an 1/8 drill let alone be able to sharpen it, the toll of advancing years.

Dave