Drill Sharpener

[kiwi2]

Hi,
I splashed out $100 on a drill sharpener as shown in the picture - mainly because I'm hopeless at freehand sharpening.
I thought there might be some interest in how it performed.
On the plus side, it does what it says in that the old drills I sharpened were in fact sharpened and cut both aluminium and steel very well.
On the minus side, the holes were 0.5 - 0.8mm bigger than nominal. I noticed this first on an ancient rusty drill I sharpened. It was obvious the drill was a very sloppy fit in the hole it had drilled.
I then drilled a hole with an 8mm drill which was in a reasonably good condition. It made a hole which was 8.1mm dia. I then sharpened the drill and drilled another hole. It made a hole 8.6mm dia.
It seems that these sharpeners are OK if you are drilling say a clearance hole for a bolt and the final diameter doesn't really matter, but if you are drilling a pilot hole for a tap or a reamer then they are definitely not OK.
I think I'll sharpen a set of my worst drills and use them for rough work and keep a good set for finishing work where the diameter matters.
Hope this is useful information.
Regards,
Alan C.

 

[Cogsy]

Good info - thanks. I've considered something similar once or twice but not if it is going to mess up my drill sizes that much.

 

[abby]

If the holes are being drilled oversize then the cutting edges are of uneven lengths i.e the drill is ground off-centre , is there no way to adjust this on the sharpener ?
Dan

 

[goldstar31]

If the holes are being drilled oversize then the cutting edges are of uneven lengths i.e the drill is ground off-centre , is there no way to adjust this on the sharpener ?
Dan

I sorta agree with Dan but two things arise. The jig is plastic and probably either oversize or wobbly and the risk of a early replacement of the wheel would preclude me from this.

Sadly, I've been pretty well in such matters. It is probably cheaper to get a cheap 6" DE grinder , change the wheels from round bits of paving and buy a cheap metal affair.

Sorry to be a misery but-- but?

Norman

 

[vidio1]

A drill bit will always drill a hole with clearance. It's the very rare exception when it doesn't. It's simply using the correct tool for the job at hand. If you need to hold a tolerance than you should bore, or ream a hole to size.

 

[BaronJ]

Hi Guys,

I pretty much agree with Norman, I've played around with comercial drill grinders, from the cheap ones to quite expensive and not really found anything under £200 that you could call a precision drill grinder.

I would recomend building one. The two/four facet drill grinder on the Gadget Builder web site is to be recomended. I wouldn't want to part with mine.

 

[purpleknif]

Uhhh... drills don't cost all that much !

 

[goldstar31]

Uhhh... drills don't cost all that much !

Quite but if a machine is capable of - as Baron intimates, it will do other things with equal capability.
There isn't a fat lot of difference between a drill and a slot drill nor an end mill for that matter.
Again, the average home grinder is or should be able to 'do' a modest surface grind.

If one follows John's recommendation to visit John Moran's excellent site and reads the construction and use of the home built tool and cutter grinder, it will grind needles for carbs as well as special tools which would probably be nigh impossible or inordinately expensive otherwise.

A few bits of round, a few bits of steel bar , a tatty Chinese grinder or a redundant wood router plus the inevitable purloining of grandma's best felt hat - to exclude the grit:thumbup:----- and there you go, laughin' and scratchin'

Regards John B, I thought that you fliggied the nest:hDe:

Grumpy Norm

 

[Brian Rupnow]

I have a "drill doctor 350x" and it performs very well on drills from 3/16" up to drills 3/8". It too is made of plastic. Does it make the drills give an oversize hole?--I don't know. I never checked. I do know that whenever I have a hole which should be reamed, I don't go one drill size under (0.0156") as recommended. I always drill .030" undersize. If I go 0.0156" undersize, my reamers sometimes are cutting air. I've ruined a few parts doing that. As someone said earlier, drills do not cut "on size" even when brand new. If you drill a hole with a brand new 3/8" drill, a 3/8" piece of tool steel will fall thru the hole you drilled.

 

[kiwi2]

"If the holes are being drilled oversize then the cutting edges are of uneven lengths i.e the drill is ground off-centre , is there no way to adjust this on the sharpener ?"

Hi,
I thought the same myself but the drill looked symmetrical to me (although that may be why I'm crap at hand grinding them).
I ended up mounting the drill in a collet on the lathe, bringing the sharp point of a tool up to the intersection of the land and the drill circumference with the help of a magnifier, then rotating the drill 180 degrees. The tool seemed to have the same relationship to the land/circumference intersection on both sides, suggesting the grinding is symmetrical. I'm not sure where that leaves me.

"I would recomend building one. The two/four facet drill grinder on the Gadget Builder web site is to be recomended. I wouldn't want to part with mine."

I had a look at the Gadget Builder website. It was a bit clever for me to digest straight away, but I shall return to it.
One interesting thing I found on the website was this:

"
Drilling a hole to accurate size is best done by drilling one size under and then removing the small amount of material remaining with the final size drill. Using a drill with SPAs works well for the final pass, cutting to size and leaving an almost reamed finish. When hole finish is important, stop the drill prior to withdrawing it. For really accurate hole size drill a few thou under and ream to finished size (assuming you have the needed reamer).
Drilling to accurate size in one go is possible but tricky. As drilling starts the drill isn't constrained by the lands touching the hole; extra thrust is helpful because it causes the point to stay fully into the cone. A split point helps by providing more cone area and encouraging rapid penetration with modest thrust. If thrust is relaxed the drill often attempts to cut a reuleaux triangle as first one lip and then the other catches, causing the drill to ricochet around in the hole. When this is happening, if you stop and look at the cone in the hole you'll often find 3 or 6 lines radiating out from the center of the (oversize) hole. Once depth is greater than about one diameter things usually settle down but this early rattling around can cause an oversize or bell mouthed hole. Accuracy in sharpening is needed for size accuracy - drill point concentricity and symmetry are necessary, SPA's and point splitting improve results and make drilling technique less critical."


Tomorrow I'll try drilling a pilot holes 1/64" and 1/32" less than the nominal to see if I can get the finished hole to be close to nomimal.
I may have unfairly maligned the grinder.
Regards,
Alan C.

 

[BaronJ]

Regards John B, I thought that you fliggied the nest:hDe:

Grumpy Norm

Hi Norman,

Still kicking, but it gets harder to do the things that I used to do without having to think about it.

 

[BaronJ]

Hi Guys,

Getting a hole on size is not at all easy !

Drills are flexible things and become less so as they get bigger, and become more flexible as they get longer. Ignoring play and runout in the machine, the more acurately a drill is ground the less the drill point will be inclined to wander about. You can easily have a drill with very length acurate cutting edges but are several thou away from the true centre line of the drill. As mentioned this causes the drill to make oversize holes.

As far as four facet grinding is concerned the idea is to make the very tip as small as possible, and extending the cutting edge right to the centre, this reduces the amount of pressure needed to cut and improves the accuracy by reducing the distance that the tip can wander when starting the hole. Because of this a four facet ground drill can often start to cut without the need for a pop mark, though I confess that I always pop centres.

Having said all that, any drill grinder is better than having none.

 

[Hopper]

Can you post pics of the drill tips that drilled the way oversized holes? It would help to be able to see exactly how they look before we draw conclusions about what the problem with the sharpener is.

 

[goldstar31]

The old gurus went on and on and into pages of explaining 'Why' and I've read most of it.
One comment has yet to be mentioned and whilst touching on it, the much admired George Thomas did not elaborate. Probably, GHT expected us to understand Archimedes and the 6th Proposition of Euclid- and so far here- NADA! The Square Root of Bugger All.

Here's my précis for your delectation. We stick a perfect correctly ground and sized drill in a 3 jaw chuck. Now that's a miracle to have such a thing but let me assume. With everything chiming merrily, the end result will be probably a hole - plus 6 thous or worse oversize.
Why? The lathe chuck- unless it is one of those fancy Griptru's or similar will be out by at least 3 thous. Your three jaw was NEVER spot on and with use or misuse, it will cut a radius of say 3 thous and if we have not been paying attention that day at school , it will cut a diameter of 6 thous. Which we all know is why we are discussing rattling bad fits!
The same holds good ( or bad) for a drill chuck which has much the same alarming characteristics. BUT, but, but, if the tailstock is out, it will act as another cutting tool and add to the rattles. It may- it may be bad enough to break a lip on the drill.
This is where someone has rushed out and bought a wobbly drill grinder.

And as my testy old maths teacher would add- QED. Quo Erat Demundstrandum or laughingly 'Quite easily Done.'

That is only part of the Saga. Sorry to take up your time but if you know this already, I'm wasting my time.

Norm

 

[SmithDoor]

Most of the Drill sharpening machines that I have found are for the drilling in wood. For some one that rarely needs the sharpen a drill they work great.
I do all my sharpening by hand on a 6" grinder . It takes about 10 min to teach some to hand grind drill bits.
Note: If you are going to some shop at time they will test on hand sharping
Both ways work (by machine or hand)

Dave

Hi,
I splashed out $100 on a drill sharpener as shown in the picture - mainly because I'm hopeless at freehand sharpening.
I thought there might be some interest in how it performed.
On the plus side, it does what it says in that the old drills I sharpened were in fact sharpened and cut both aluminium and steel very well.
On the minus side, the holes were 0.5 - 0.8mm bigger than nominal. I noticed this first on an ancient rusty drill I sharpened. It was obvious the drill was a very sloppy fit in the hole it had drilled.
I then drilled a hole with an 8mm drill which was in a reasonably good condition. It made a hole which was 8.1mm dia. I then sharpened the drill and drilled another hole. It made a hole 8.6mm dia.
It seems that these sharpeners are OK if you are drilling say a clearance hole for a bolt and the final diameter doesn't really matter, but if you are drilling a pilot hole for a tap or a reamer then they are definitely not OK.
I think I'll sharpen a set of my worst drills and use them for rough work and keep a good set for finishing work where the diameter matters.
Hope this is useful information.
Regards,
Alan C.

 

[kiwi2]

Well I've had an interesting day.
John Moran on his site:
http://www.gadgetbuilder.com/DrillSharp.html
says:
"
Drilling a hole to accurate size is best done by drilling one size under and then removing the small amount of material remaining with the final size drill. Using a drill with SPAs works well for the final pass, cutting to size and leaving an almost reamed finish. When hole finish is important, stop the drill prior to withdrawing it. For really accurate hole size drill a few thou under and ream to finished size (assuming you have the needed reamer).
Drilling to accurate size in one go is possible but tricky. As drilling starts the drill isn't constrained by the lands touching the hole; extra thrust is helpful because it causes the point to stay fully into the cone. A split point helps by providing more cone area and encouraging rapid penetration with modest thrust. If thrust is relaxed the drill often attempts to cut a reuleaux triangle as first one lip and then the other catches, causing the drill to ricochet around in the hole. When this is happening, if you stop and look at the cone in the hole you'll often find 3 or 6 lines radiating out from the center of the (oversize) hole. Once depth is greater than about one diameter things usually settle down but this early rattling around can cause an oversize or bell mouthed hole. Accuracy in sharpening is needed for size accuracy - drill point concentricity and symmetry are necessary, SPA's and point splitting improve results and make drilling technique less critical."
His description of the lips of the drill ricocheting around to produce a bell shaped hole is spot on to what I'm experiencing.
Today, I sharpened a 5/16" (7.9mm) drill and drilled a hole through a 10mm piece of aluminium. The top of the hole had a diameter of 8.7mm which is not acceptable for tapping a thread.
I then sharpened a 1/4", 17/64", 9/32" and 19/64" drills and used them to drill pilot holes for the 5/16" drill.
The diameters at the top of the resulting holes were 8.2mm, 8.1mm, 8.1mm and 8.3mm respectively. Thus it seems that drilling a pilot hole 1/64" smaller than the final hole isn't quite enough while drilling one 1/16" less than the final hole leaves enough meat for the lips of the final drill to start bouncing around again. It seems that the optimum is to drill a pilot hole 2/64" (1/32") less than the desired diameter. The hole thus produced, while still marginally larger (0.2mm = 8thou) than the nominal is acceptable.
I think I will sharpen all my drills and routinely drill pilot holes which are 1/32" undersize for imperial sizes and 1mm undersize for metric drills.
After all this I'm quite glad I got the sharpener which is quick and easy to use.


Regards,
Alan C.

 

[goldstar31]

Just imagine the task of drilling a hole less than an 1/8th in diameter and say 12" long, perfectly parallel ?

I wonder just how many people could attempt and succeed. And yet it was and is the task of bagpipe makers.
Moreover, said he clearing his throat- I've done it.

I've also done tapered holes.

I'm interested in the technique which others might adopt

Norman

 

[Blogwitch]

Getting away a little from the sharpening side.

I have used for many years bullet tipped drills made for Black & Decker. They are a bit limited in their sizes, but when used in conjunction with a spot drill (not centre drill) then they cut a very precise hole.
They are also very good for thin sheet work as there is no snatch at all when they break through, which is usually a problem with normal drills and the cause of oversized holes as they are snatched to one side as they break through.

I do have a Martek drill sharpener from about 20 years ago, driven rather than by an electric drill but an old model marine motor that was too 'dirty' for radio control work.
It does an almost good job, but on smaller sizes it fails rather badly as you have to set it up by locating the cutting faces in a plastic jig, and that was the major downfall.

If you are going to resharpen drills accurately, then the only way is to buy an industrial sharpener with a cam operation, as used in large workshops. All others sold for the model engineering fraternity are hit or miss, and to my way of thinking are a total dead loss.

John

 

[mcostello]

I worked in a screw machine shop, There was a Guy there that could sharpen 1/8" drills and get Them to cut .001 over diameter. That's counting centering up the bit and all. I was only good to about .003 and could not get any better. It's possible and done in production settings everyday. Used a bench grinder also.

 

[BaronJ]

Hand sharpening drills is a good skill to aquire.
I guess that I'm lazy nowadays, I even use a jig to sharpen small drills less than 3 mm.
However I agree that they are very cheap even though half of the new ones are only fit for the scrap bin.