Thread: Big drill grinder with point splitting.

SAM_0592.jpgSAM_0593.jpgSAM_0594.jpgSAM_0595.jpgSAM_0596.jpgSAM_0597.jpgSAM_0598.jpgHello from the Old Goat again.
I did start with this in the Projects file but this thread gets more response. Not after glory, I want your ideas too.
This is built from scrap and a piece of 1.5 X 1.5" angle. The length stop is a piece of 1.5" rnd bar with 2 flats cut with the shaper. A piece of 3" fire pipe with a screw secures it. Using my sub plate it fits the Clarkson well and can change from grinding on to the edge to off the edge by swinging left or right. No clamping is used at the business end as I rotate the drill every 2 thou of feed. Pic 2 has the primary facet at 10 deg. Pic 4 has 25 deg set for secondary facet. Pic 5 has my setup tools, the CNC part is hidden. No 6 shows how to set it up for split pointing and as the Clarkson has no table stops I pass thru when splitting the point as seen in the last pic. My biggest drill is 1 7/8" and just fits under the wheel for splitting.
When I get time I will dimple the stop for the clamp screw and drill it thru for a fine adjust screw stop. 24 TPI. I didn't have a chatter problem but would prefer to use it on a larger grinder. The Clarkson is only 280kg and with the jig cantilevered off to one side it's not too rigid.
The Ruby grain wheel is not as agressive as a 38A unit but the finish is as good as CBN 180 grit. It may burn if not kept dressed. It's the same grain as used in saw gulleting wheels. I have had 2 wheels, of different width, for gulleting annular cutters on the same grinder for 13 years. Not that I do many but maybe 2000 cutters gulleted so far. And little wear.
Lets kick the ball along for a grinding and toolroom sub forum.
BC

Dose it cut?

Hay mate nice post and grinder?what do you think of the result you get??
How does it work for you. do Resharpen drill after a couple of uses? or
wait to there relay had it? Ive never seen a drill above about 14mm sharpened split point.
well done
aaron

Just clarifying terminology, METALWORK GENERAL is a forum, as is METALWORK PROJECTS.
"Big drill grinder with point splitting" is a new thread.

A collective group of forums (technical "fora") are just called forums, in our case METALWORK FORUMS
They don't exist in the the Metalwork forums but over in the "Woodworkers Forums" some of the forums have sub-forums.
Maybe sharpening warrants a sub-forum rather than its own forum?

Am I missing something here to need all of that to sharpen a drill?

Hi Guys,

It depends upon what sort of grind do you want on your drill !

Most drills have a conically ground point. If you want it to self centre, then you need a four facet ground point.
Point thinning reduces drilling pressure by making the web narrower. Accurately sized holes need the cutting edges to be exactly the same length.

It all depends upon what you expect from your drill ! Most people don't have a clue why drills are ground differently.

Originally Posted by BaronJ

Most drills have a conically ground point. If you want it to self centre, then you need a four facet ground point.
... Accurately sized holes need the cutting edges to be exactly the same length.

Hmm. Not sure that I can accept those claims without some further clarification. Randomly ordered thoughts below

• When drilling in metal, I would rarely drill anything to final size without either a centre pop, centre drill or pilot drill (or a combination of any of these). As soon as there is something for the point to work in, it is centred. Worth noting though that if the drill is not square to a surface, it will wander and if the axis of the pop, centre drill mark or pilot drill is not in line with the axis of the drill spindle, it will pull the hole over. These days I watch most carefully when starting to drill as particularly with small diameter drills, they will deflect easily.
• Once upon a time I read that the reason the Prof Chadwick adopted 4 facet grinding on the Quorn (and so introduced ME's to it) was that he could not grind a conical point with the design he had. Given that the vast majority of commercially made drills are supplied with a Conical ground point, and similarly industrial drill sharpening gear grinds conically, I can't see why if 4 facet is superior that it would not be the grind of choice. Particularly when you think about how complex it is to get a 'good' conical grind complete with relief (my drill sharpener has cams in it and requires drills to be accrately set up in a holder for example).
• Cutting edges being the same length are not all there is to an accurate hole. I can see for example that it is important for the grind angles to be the same, as if they are not, the drill lips will tend to deflect more on one side compared to the other. If drilling in a pilot hole, the hole does not know exactly where the point of the drill is so that it is irrelevant what length the lips are provided the angle is correct.
• I have a small selection of stub drills - 135 degree point, short length. Hardly deflect at all compared to normal (jobber length) drills. Deflection of things like drill bits and boring bars is related to their length to some power (from memory, something like L³ or L⁴). Any reduction in length will help reduce drill wander and improve the likelihood of the hole being where you want it.
• A hole that wanders while in the material is due to a number of factors; it is too simplistic to put it down just to the style of grind used. If a drill needs 2 equal lips to cut properly for example, gun drilling with a single lip cutter should be a dismal failure.

Michael

Hello to you all.
Pipeclay. Yes it does cut OK, 1 and 1/32" drill without a pilot into 40mm MS bar. Hand fed, but on a small radial.
Azzrock. It is an easy to make unit and is accurate because the cross feed helps to keep both edges equal. I persue this as well ground drills make 1000's of holes, if used correctly. I have checked my recent stock and all drills over 4mm have a split point due to the wide web. Different to 4 facet.
Bob L. You have lost me with the terminology. I still think tool grinding and toolroom work would be a worthwhile heading.
Snapey. A well ground drill performs better and produces many more holes.
Baron J. Correct. Most people don't have the knowledge. That is why jigs are used. I need them too.
Michael G. Conical ground drills over 4mm are now split point. This is cheaper to make with less flute grinding needed. It becomes a problem when you regrind them. I dissagree when you say the cutting edges do not need equal length. If not equal 1 edge will get there first and deflect the drill.

For interest. The drill was good steel and hard to grind. An old drill with the brand Worko. I have never heard of them.
Regards
BC.

Originally Posted by steamloco1954

Michael G. ... I dissagree when you say the cutting edges do not need equal length. If not equal 1 edge will get there first and deflect the drill.

I had thought I said
"Cutting edges being the same length are not all there is to an accurate hole. ... If drilling in a pilot hole, the hole does not know exactly where the point of the drill is so that it is irrelevant what length the lips are provided the angle is correct."

Michael

hi bc and every body.
sorry mate i confused split point with 4 facet.
id like to make a cool drill sharping rig like you one. bit probably never will.
I only seem to a 50 50 positive result with hand sharping or worse.
aaron

Hi Guys,

Just a point about 4 facet ground drills.

The reason that 4 facet drills self centre without a pop mark, is because the very centre of the web is not a flat like a conically ground drill.

If you examine a 4 facet drill tip you should see that all four edges come to a point and the drill actually starts to cut at that point just before the main cutting edges do. Essentially creating its own pop mark.

Just to answer a point about drills wandering. Its quite possible for the drill point to deflect if the surface that is going to be drilled is rough, I'm thinking cast iron or steel with mill scale on the surface. This deflection is worse for small drills.

As far as "D" bits are concerned, they are basically a single point fly cutter and once the hole diameter is fully formed supported by the back of the bit running in the bore.