View Full Version : Drill or Countersink for 30 Included Angle

Ohio Mike
08-14-2011, 11:06 PM
I have project that requires me to fabricate a replacement for a worn shaft. Said shaft is 1" diameter and needs a cross drilled hole at each end for a cotter key. The kicker is there are two places on the shaft where a set screw holds a lever (foot petal actually). The shaft isn't keyed in those locations, the only thing there is the set screw. The screw which is 5/8"-11 has a 30 degree taper cut at the end and a matching hole was then cut in the shaft. If I recall correctly the depth was about 1/2 inch.

So the question is where can I get a center drill or countersink to cut a 30 degree included angle (5/8" or larger).

08-14-2011, 11:13 PM
First off: SURE you don't mean 60-deg. included angle??

If not, I don't expect you to find one. You might try making a simple "d-bit" type drill with the correct angle. Use 0-1 tool steel and harden/quench if you have a torch. Otherwise, no way you could change the screw? Sounds awfully esoteric of an assembly method. Wish I could be of more help.

Ohio Mike
08-14-2011, 11:35 PM
Oh they're 30 degrees alright. At first I thought I can just use my large Cleveland spotting drill I got for free in a box of junk. Then I looked at the hole and immediately said wait that can't be right! So I went and removed a set screw and realized I was screwed. Measured it to be sure 15 on each side, 30 degrees.

08-14-2011, 11:57 PM
Go to http://www.micro100.com/inch/inch_catalog.html and click on Product Index. Scroll down to Runner Cutters and click on that, then click on either MRF or MRT, (both seem to take you to the same page). Scroll down on the new page that opens up (page 171) and you should find 30 degree included angle cutters from Micro 100 Tool Corporation.

P.S. Oops! Those only go to 1/2 inch! I guess you will have to search for 5/8 inch Runner Cutters.

08-15-2011, 12:29 AM
Go to a tool and cutter grinder or grind a single flute 30 degree tool by hand.

08-15-2011, 07:22 AM
Will a tapered end mill do it? You can get them tapered 15 degrees per side, or 30 degrees included angle.

08-15-2011, 08:42 AM
In the first place the angle of the bottom of the hole in the shaft is not really that important. Second, the short screw machine drills have an angle on one side of about 25 deg and will do nicely for what you want to do.

The purpose of the drilled pocket in the shaft is to act like a key to keep the lever from spinning on the shaft. It's not as critical as you think. In fact a regular drill point would do nicely.

08-15-2011, 09:41 AM
+1 to what Carld wrote.

I'd be quite surprised to find out for certain that the spots on the shaft were actually anything tighter than a 60, despite the mating screws measuring 30. I'm thinking that if you are having issues tooling up for it, so did the original manufacturer.

The only thing I'm VERY confused about with what Carld wrote is the part regarding "screw machine drills have an angle on one side of about 25 deg". What? Where? I've never seen standard screw machine length drills have anything but 118 or 135 angles.

Richard Wilson
08-15-2011, 09:50 AM
drill a small parallel hole in the shaft at the required location, then open it up with a 30 degree D bit. Dead easy to make from drill rod (US) or Silver steel (UK)


08-15-2011, 12:41 PM
Could you not just change the set screw to a half dogpoint? Then you drill, (or mill,) a hole of the diameter of the dog. Seems to me that dogpoint setscrews were designed for EXACTLY this application.

08-15-2011, 02:13 PM
Beats me PixMan. I picked up a bit that was near new unground and measured it. I just went to the shop and did an eyeball on it again and here is what I got. I've only used it a few times and it has not been sharpened. The drawing is not to scale.


08-15-2011, 03:54 PM
I would just grind the tip of the set screw down, and use a standard 60 degree countersink, Let it displace some metal when you tighten it down, Should be real secure.

Alternatively, buy a diffrent set screw.

08-15-2011, 04:13 PM
The drill's included angle that you show in your drawing would be 52-deg. Looks like a manufacturer goof on a 60-degree drill to me (assuming new, unsharpened).

08-15-2011, 05:41 PM

The small diagram above shows exactly how the included angle of a drill point should be measured. Take the 154 shown in your sketch, subtract 90, then double the result. That's the included angle.

I'd say you either got a poorly-ground drill of the standard 118 angle or the typical 135 of a thicker-webbed/split-point HSS-Co drill.

BTW, I came up with 128, not 52.

08-15-2011, 06:01 PM
BTW, I came up with 128, not 52.

08-15-2011, 07:05 PM
Sorry, but I strongly disagree. Your adding and subtracting skills are fine. Your method of calculating based upon geometry is flawed.

I really suck at trying to describe it, but the 26 angle shown, multiplied by the two sides, is then subtracted from 180.

Or, look at your figure in the lower left of the diagram. That 64 calculation is spot on. Now consider you have to include both 64 flute edges. Bingo...128 included angle.

Or, correction: You're 100% correct and that is the most absurdly ground drill ever. I'd love to see an actual photo of it because if that 26 angle is real, the diagram is so far out of scale it's ridiculous.

Here's an AutoCad sketch. Which included angle drill point does the drill in question actually have?


08-15-2011, 10:45 PM
Ok, I just went to the shop and used my Brown and Sharpe machinist protractor and I got 135 deg across the end as you said it would be. I measured about ten of them out of the jar of new drills and they are all the same.

I guess I just did a poor job of measuring the first time. Ah well, s--t happens.:o

08-15-2011, 11:35 PM
That was a comedy of errors :D

08-16-2011, 12:48 AM
That was a comedy of errors :D

Nah...I had a strong suspicion I was on the right track all along. :p

BTW, to get this back on track again for OhioMike....

I am now wondering if there was a similar confusion related to the orientation of measuring the angles. Mike, if you relate the angle you measured on those set screws to the AutoCad-generated sketch I made and dimensioned, are the screw tips more like the one on the left of the one on the right? I'm just trying to make things perfectly clear, given the absence of photos.

Ohio Mike
08-16-2011, 10:01 PM
It looks like the one on the right. Visually it just looked like 30 degrees so to measure and be sure I laid it flat on the mill table and laid my magnetic protractor on the angle and it read 15 degrees off horizontal.

I haven't come up with a solution yet. I have a few other things I need to work on anyway.

Ohio Mike
10-08-2011, 10:35 AM
I thought I'd follow up on my post to note the solution I used. I purchased a 5/8" diameter M2 tool steel drill blank and ground a spade bit. Grinding was slow. I cut the taper first and then cut the flat across the blank. Then I ground a relief cut on the back side short of the cutting edge. The project also gave me an excuse to buy a Phase II 5c spin index that Enco had on sale. :)

When it came to making the part I pre-drilled the shaft for the minor diameter and then used the spade to cut the taper. I won't say it was highly accurate but it was nearly as good as the factory taper. So for me it worked excellent and was very affordable too. :cool:

Bob Fisher
10-08-2011, 05:03 PM
Seems an AWFULLY large setscrew for a 1" shaft. Sounds like a treadle pedal on an industrial sewing machine, nothing very critical there. Bob.

Ohio Mike
10-09-2011, 11:32 AM
Tractor brake pedals actually.