What factors drive the selection of the drill bit angle? I need to restock on bits and I've always just bought jobber TiN bits. Now, I'm doing some research and am wondering about the angle. The jobber bits have always worked just fine for me.
Second related question: are cobalt bits worth the additional cost over TiN for drilling mild steel and occasional tempered steel? I am not dealing with "ordnance"/extremely hard steels - mostly raw stock and various automotive-related parts.
135 degree Angle Point This point is frequently preferred for hard and tough materials such as high alloy steels. Increasing the point angle increases the effective rake angle of the cutting edge (lip) and reduces the length of the lip. The result is a reduction of the driving torque required to drill these materials. The feed pressures are increased. Reducing the lip relief angel strengthens the lip. To produce this point, simply set point angle at 135 degrees and align chuck arrow with 135 degree mark on chuck grip band of relief setting fixture.
90 degree Angle Point Many soft and low-strength materials, such as some cast irons, aluminum, plastic, and wood can be drilled more efficiently with a reduced point angle. Although this change reduces the effective rake angle of the cutting edge (lip) and the length of the lip is increased, the driving torque required to drill these materials usually remains with acceptable limits. The reduced feed pressures and the increased lip relief angle frequently permit higher feed rates. To produce this point, simply set point angle at
George, The Cobalt bits are Much better than HSS in both wear and heat resistance. Often a requirement for stainless steel. Tin bits are simply coated like Titanium bits. In both cases the coating allows the chips to leave the drill bit without creating as much friction and thereby allowing the bit to remain cooler and last longer. Steve
Thank you Robert. I'm going to assume that the 118 degree bits must be a compromise between the two angles you mentioned. I notice the
118 bits seem to be cheaper and will likely move with those. I've only had a couple of occasions where I wished I could cut hardened steels - one was a jammed stop nut that just laughed at all my bits.
George, No. No compronise - 118 deg. bits are, by far the most common. Darex only mentioned 135 deg. because their equipment can sharpen that angle which is a little better for harder material. IMO, you can probably do just as good a job in harder material with 118 deg. bits, if you are extra careful -- and if the bits are quality; which is more important than the point angle. Personally, I never use anything other than 118 deg.even though I have the equipment to grind 135 deg. points.
Aside from what has already been discussed, another factor is "split points". These offer some significant advantages.
1) They take less force to drill through a given material, because you are not having to force the "chisel edge" in the center of the point into the workpiece. (This is more of a problem with larger sizes, but can be a benefit for any size.
2) It is a lot easier to *start* a drill bit where you want it with a split point. Normally, you can use a center punch to produce a guide for the drill bit -- but in some materials (Titanium, and some stainless steels) the work hardening caused by the center punch can make it more difficult to start cutting, as the drill bit is having to deal with a hardened material.
As an example of how much of a help a split pont can be, I had to drill some pins *in place* on my garage door. One end of the pins held the rollers which traveled in the track, and the other end tended to sometimes move too far and drop out of one side of the stamped metal "bearing". With a 1/16" split point, I was able to start the hole, and drill through using a hand-held electric drill, no center punch, and no fixturing. The diameter of the shaft was 5/16" IIRC -- enough of a curve to make starting a normal drill bit more difficult.
Also -- another thing to consider is drill bit length. There are some times when you need a jobber length, and even some times when you need the aircraft drills (6" or 12" long), but for most things, you can use the "screw machine" length, which is shorter than the jobber length, and thus stiffer.
I have several sets of standard HSS drill bits, but my favorite is an index of screw machine length cobalt drills with split points in the number (0-60) size range. Some of these days, I hope to get the same in fractional, letter size, and even metric.
Of course, they are more expensive. This set I got when MSC was offering the set on sale -- in a HUOT index which was modified to hold the shorter bits properly.
O.K. Though remember that a split point is not the same thing as a 135 degree bit -- you can have 118 degree bits in split point format as well.
Be aware that while the Drill Dr. claims to be able to produce split points, it seems to work only on larger drill bits -- while I often want them on smaller bits.
I use the Drill Dr. on larger bits (greater than 1/4"), but I also have a drill bit sharpener for bits from 1/4" down to #70. This one was made by DuMore (the maker of toolpost grinders), but it is no longer made. All in all, it is a really neat design, and works quite well -- once you have all of the collets -- one per bit size. A pity that they were discontinued. (Though it, also, does not produce split points, it does do a much nicer job of sharpening the smaller bits.
When you discover that it is time to replace a given drill bit which you use frequently, I suggest that you order a 10-pack (the normal minimum quantity) from MSC or somewhere else, in cobalt, and with a split point, and you will be amazed how much nicer it is.
Don, I've always wanted to sharpen my old bits because I feel guilty and pitching otherwise good bits. I'm basically a do-it-yourselfer who enjoys metalworking, fixing cars, etc. Thus, I tend to be a fairly basic drill bit user.
I've heard others say the Drill Doctor 750 did fine by them & am going off that - I've never used one. Would you recommend it to a basic user such as myself?
It does fine as long as you don't want split points on smaller drill bits. (And I'm not sure how it does on the tiny bits (e.g. 1/16" or perhaps a #33), but it does fine on larger bits, and I use it for anything above 1/4". (Sometimes the ponts look a little strange, but they work well, which is what matters.
However -- one thing that I have read can be a problem. It will
*not* work (using the fixture which sets the angle of the bit on initial clamping into the collet) if you have a drill bit with an unusual spiral (either high-spiral or lo-spiral), because the fixture is setting things based on a point some distance back from the actual tip. There are ways to fake it, but the proper setting points are nor marked.
For the typical drill bits, it will work fine. It is just those with unusual twists which are a problem. (Also -- if you have any left-hand bits, they also will not work at all. And left-hand drill bits are particularly good for drilling out broken off screws, so I have a few.)
So -- you opted to try both the new material and the new point angle at the same time. You should have a pretty near indestructible set of drill bits, especially for drilling in tough steels, with that combination.
I would have considered it more interesting to try just the new material first. Then the new point angle -- and perhaps not a full fractional set for the first try. But you should get years of service out of that set.
Are you using them in a hand drill, or a drill press, lathe, or other stationary power tool? I would have opted for the standard 118 degree point for hand held electric drills (drill motors) -- or even better split points, simply because the 135 degree takes a bit more force applied by the tool, and is easier to control in something like a drill press than with a hand-held drill motor.
I probably would not have asked this if you had gotten a number size set or a letter size set, but fractional are more often used in the hand-held tools.
I do both handheld and drill press. I didn't mention it, but I bought one of their cheap 135 degree HSS import sets for $14.95 for situations where I'm pretty sure the bit will be at risk due to the angle or situation in general. It was $9.95 for the 118 degree so I spent the extra money. There sure have been times I wishes the bits would enter the work easier.
Yeah, I took the plunge. I've been itching to try the cobalt drills but thought a set would be well over $100. As things dull, I definitely have a dollar incentive now to sharpen them. I looked at a Lisle sharpener for $995 and it sure made the Drill Doctor seem attractive at $125 plus the posts over the past year seemed generally favorable. I do very little drilling under 1/8" but do a fair number of 1/8", 3/16" and 1/4" sheet metal holes for rivets, welding, etc. I have packages of drill bits in those sizes plus step drills and a Roper Whitney Jr. punch. I tell you, I sure like the step drills & punch for sheet metal vs. twist bits.
Don, can you clarify what a split point bit is? At first I thought it was related to the angle and since this thread started I've inferred from some of the posts that it is not.