Only 2 angles to worry about, the point and chip clearance, they vary slightly with the material you are cutting (drilling is cutting) with a twist drill. How to on a bench grinder: start with a big (3/8 or bigger) so you can see what you're doing. On the fine wheel (dressed flat) hold your bit so the 50% of the point your are going to grind lines up parallel to the face of the wheel (I'm assuming that the bit is still beveled) now as you slowly roll the bit into the wheel face give it a little movement into the twist "shoulder" to create 2 to 3 degrees of chip clearance. Remember that the leading edge of twist is the cutting edge and the whole thing is pretty easy to understand. I've taught some pretty backwards guys to put a pair of sharp cutting edges on some badly burned bits.
In High School metal shop the FIRST project was to make a drill sharpening guide...
the SECOND project was to learn how to use and hand sharpen drill bits...
40 years later that skill is STILL valuable... (and I still have the guide)
Best story was when I was in the service, (USCG 1973) working A2N (Aids to Navigation), stuck on 'Mile Rock' in the outer SF bay when the 1'st class BM rips the web of a 1/2 bit and the Chief BM figures were screwed for the day. Funky old E3 me says 'aww no prob'... as I clamp the fricken die grinder we have in a vise and hand sharpen the thing better than when we got there... took about a minute (had to take quite a bit off to get it centered)... Jaws drop... I shrug and hand it back...Uh needless to say THEY bought the beer that day and ever after I was the guy they wanted on the team...
--.- Dave (403-029 one more number I'll remember for the rest of my life)
"Way back when", when I did my apprenticeship one of the first things that an apprentice was taught (just after how to sweep the floor) was how to sharpen drill bits. I don't believe in my years in machine shops I ever saw a drill sharpening machine or a machinist that didn't hand sharpen his own drills.
================== If you do this you will wind up with a large number of taps and drills that you will never use.
As an alternative think about the threads you use for the projects you work on and purchase only these taps and drills.
I suggest using screw machine length drills as the jobber length drills will require you to run the drill head up and down to change between the spotting drill, the tap drill, the body drill, and the tap thus losing position.
Basically you will need a spotting drill [not center drill] to start & locate the hole. Again get one about the same length as your taps and screw machine length drills for the sizes you use. One of these should cover a range of tap sizes.
A tap drill for 75% depth of thread [in many cases this will not be a fractional size, but a number or letter drill]
A body drill both for providing clearance for the screw in the mating part and to drill a slight counter bore so act as a guide or lead in, and to make sure any burr that you kick up when tapping or when you pull the thread when tightening is below the surface.
I find that while the cobalt drills are harder and would last longer in a production environment, they are also more brittle and prone to chip/break in the home shop environment. They also cost more and are harder to sharpen. Black oxide and bright finish HSS should be adequate. If you use the spotting drill the drills with the 135 degree split point are the ones to get. These provide less end thrust [force required to drill] and also have less tendency to walk.
Several taps for each thread.
I suggest a taper gun tap for through holes as these are the easiest to start and the chips clear the tap very well. Be sure to brush the chips off the tap that extends through the part before you back the tap out as these may jam or damage the thread. [buy two, their cheap]
For blind holes I suggest starting with a taper tap as this is easiest to start, and then switching to a plug or bottoming tap depending how close to the bottom of the hole you need the threads. FWIW- I find that drywall screws make good tools to extract the chips.
Another trick for blind holes is to use a stick type tap lube and fill the hole. Then as the tap goes into the hole, the tap lube squirts back out and takes the chips with it as well as providing lubrication. In a pinch bar soap or lard/crisco will also work.
If you have a thick part, try not to tap more than about 1-1/2 to
2 diameters deep. That is a 1/4 tap should not go over 3/8 to a
1/2 inch deep. The threads that the tap generate and the tap threads are not a perfect match and excessively long engagement is likely to jam or break the tap. This is where the body drill comes in. Simply body drill the hole deep enough so that you only tap 1-1/2 to 2 diameters. You can drill from either side but maximum assembly strength will be obtained with the longest length screw and the maximum stretch. This is particularly important for the smaller sizes [#10 and down]
I find that the 20 round plastic ammo boxes that re loaders use make good containers to keep the taps and drills together but protected. Most HF stores have these in a verity of sizes, or sporting goods store that sells reloading supplies should have these in stock.
A black sharpie pin is also handy for marking the required depths on the taps and drills.
Many tapping/drilling problems in the home shop can be traced to a worn out drill chuck. If your chuck is not in good shape, you can get a good china import for c.20$US with the mounting shank from wholesale tool, enco, HF and a bunch more. Note that for tapping a key operated chuck is better then the albrecht style.
Some good liquid tap lube and possibly stick for blind holes is also a requirement. (WD40 spray won't cut it and will make a mess.)
Good luck and let the group know how you make out. If you have questions or problems locating this stuff, post to the ng.
Unka' George [George McDuffee]
------------------------------ Watch out w'en you'er gittin all you want. Fattenin' hogs ain't in luck.
Joel Chandler Harris (1848-1908), U.S. journalist. Uncle Remus: His Songs and His Sayings, "Plantation Proverbs" (1880).
It is a quick way to get a reasonable (if not pretty) point on the larger drills.
For the smaller ones -- 1/4" down through #70 -- I have an interesting drill sharpener once made by DuMore, but now abandoned. It makes a much prettier point -- though what I really want is something which can do a good job of splitting points. The older Drill Doctor sort of works for larger drills, but not for the smaller ones which I more often want to have split points.
Yes -- I *should* mount my 8" bench grinder on a proper post and teach myself to hand grind the larger bits -- following Teenut's wonderful article on the subject. I still miss him.
I do my split points by hand too, but only on larger drills. I don't try to sharpen drills much smaller than 1/8, they just go into the trash. is there a Drill Doctor that does a good job on small drills?
Split points are relatively easy to accomplish. Take any old twist drill, and grind the "back flats" on the trailing side of the flutes first, using a split point drill as a visual reference. Then the point is ground normally, which creates the cutting "teeth" of the split point style twist drill.
Here is a method of utilizing the arc sweeping type sharpening fixture
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The bottom of this page shows a holder for small drills
getting all flutes to meet truly in the center is the tricky part, I would think.
Hmm ... the DuMore drill grinder can be thought of as a arc sweeping type turned on its side. The drill bit is held in a 3-jaw chuck, and the tip protrudes through a collet to give sufficient support even with #70 drill bits. A magnifier and mirror are used for aligning the flutes properly. It produces a beautiful tip.
Neat. Is that a ball bearing assembly adjacent to the drill bit being sharpened?
Don, it doesn't appear to be a ball bearing assembly on that drill holder. The head of the center bolt has a washer located beside it which makes it look wider in the lower left image.
Locating (and grinding with respect to) the thinnest portion of the center web is an important aspect of grinding or resharpening drills. Without split points, it's usually desireable to have the chisel edge formed at the web to be as narrow as possible, since the chisel will be displacing (not cutting) the workpiece material.
The force required to displace material (particularly in metal) is greater with conventional drill points. With split points, the drill starts cutting material as soon as it touches the surface of the workpiece. Additionally, split points are less likely to skate away from the point of contact.
I've seen some new drills ground with split points, where the cutting faces were ground as two flat facets, rather than being gradually relieved in an arc. I don't know the reason for that type of grind, but they cut with what seems like significantly less effort.
Google for 4 facet drill grind, and 6 facet drill grind.
Dead easy to grind the angles, set and forget the tooling (or at least set up and index quickly from one angle to the other) on pretty basic grinding equipment.
O.K. I was thinking that it was like a jeweler's screwdriver sharpening fixture which I had in the past -- a pair of bearings which rolled on the stone while holding the screwdriver in one of two positions to remove from one or the other side of the tip.
Understood.
That is why I *prefer* split points. You don't need to preach their benefits to *me*. :-)
I've even managed to drill a 1/16" hole through a 1/4" shaft mounted in an awkward position using a hand-held electric drill motor with no problems using a split point bit.
Those are the split points which I am familiar with. I've got examples from 1/2" down to something like #50 (I think -- without going down to look at the number size index's contents. :-)
I think that form gives greater chip relief for the chips made by the near-center area of the split point.
Yep Don, I didn't expect that I was telling you something that you didn't know.
I found quite a bit of interesting technical info by searching for "twist drill geometry" (with quotes). This site covers grinding for production use, and includes the Winslow-Helical point (S-shaped chisel edge/web line), which has been brought up here in RCM in the past.
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This site shows several sharpening fixtures, including one that has a fixture that sits on ball bearing "wheels"
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The main hurdle (time consuming) in building precision grinding/sharpening fixtures (particularly for small drills), would be the number of small collets usually required for holding various sizes of drills.
Although he needs only four collets for the range of his version.
I was also interested in the mention of the problem of the direction of the grinding scratches in the General drill sharpener attachment -- and on thinking about it, the Dumore drill grinder puts the scratches in the proper direction.
In case you are interested in what the DuMore looked like, I put up a web page when I was restoring it to proper function.
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or
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I lucked into an almost complete set of collets later on, and (still) have not photographed them for the web site.
Thanks Don, for the link to your grinder restoration page. That's an interesting machine, and the chuck/bushings (collets) combination looks like a good system.
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