118° or 135° for larger HSS drills?

[Mud]

I occasionally use S&D HSS drills for simple jobs in manual machines. Needed a 19/32 yesterday in aluminum. I had one but it had a corner knocked off. I suck at hand sharpening, never really tried to get good at it. I generally send them out to a service because it's so cheap and they come back so nice but I only have one of most of these over 1/2" and don't have spares to send out. So I cleaned up the ancient Darex rig and repointed this drill to drill the one hole. I made it 135° and it worked fine opening up a 1/2" hole, was .0015 over nominal. It was already 135 so I must have ground it previously. None of these need to be split point, they will always have pilot holes, either in steel or aluminum.
I also question what angle I should ask for when having them ground. I have HSS drills here up to 2+" that occasionally see use in repair or oneoffs.
What would you specify? Does it make a difference in this application?

 

[MwTech Inc]

well...never thought about this myself either...have s&d with both angles........

 

[Garwood]

I think the quality of the grind and the material is more important than the angle for larger twist drills.

Lower quality drills lose their edges quickly. Better quality cut faster and longer.

I have found it real easy to grind big drills on a belt grinder. When I grind, I just eyeball the angle close to what it was so I'm not grinding 1/4" off the end (takes so much time).

I rarely split the points because I don't like pushing big drills without a pilot. I occasionally have done it and I just use a cutoff wheel on a die grinder.

If there was a drill sharpening service around me I'd send them all out, but there isn't. So I doctor them up as needed.

BTW, .0015 on a twist drill is excellent, but you did have a pilot. No pilot and the point has to be absolute dead nuts to get on size holes.

 

[Mud]

I have found it real easy to grind big drills on a belt grinder. When I grind, I just eyeball the angle close to what it was so I'm not grinding 1/4" off the end (takes so much time).

That's what I do but it takes me fucking forever until I'm satisfied and both sides match.
I have a Black Diamond for 1/2 and under, every time I go to use it I have to relearn it to get the points split right. The Darex is actually easy to use, and it's the very first model attached to a bench grinder, does up to 3/4. Must be 30+ years old.

 

[Mud]

So why are screw machine drills usually 135°? Does that stay on center better than 118°, or is it easier to split, or is it something else? I know 135° breaks through the bottom more suddenly in a hand feed condition, don't recall reading an explanation for the different point angle.

 

[Garwood]

I remember learning this in High School shop class. I wish I could remember what it was that I learned.

 

[mach ramsey mn]

135 degree is a “flatter” point, making a stronger tip.
In a pinch I’ll just wing a tip on a drill on a bench grinder, split it, measure the lands with a scale. 8 out of 10 times it’s good enough. If the process needs something closer that .005/.010 well then it’s time to have a finishing operation. When it’s Saturday and the customer wants his Friday afternoon ordered parts to n the dock Monday morning, ya do what ya have to do to get it done.

 

[Litlerob1]

It IS easier to split 135°. The result of a split pount is a drill that centers itself better. A smaller chisel, as it were. And as Ramsey said, "it's stronger". A 118° point is a general purpose thing-supposedly, but that doesn't lend itself to the stronger theory. General purpose might mean assorted materials though.

I have a lot of experience in hole making and sharpening drills. Albeit not always great, just a lot. I almost always sharpen drills to 135° regardless of size. But the topic got me thinking in relation to size, and I don't know the answer. I DO know, I can't find a 135° drill point gauge like the 118° pocket one I've had since Kansas city was still in Kansas.

But thinking about the subject leads me to believe that 118° on a bigger drill is probably best. It's also got me thinking that 135° may not actually be stronger over-all....

R

 

[Dualkit]

135 cuts with less pressure but more likely to walk, 118 cuts with more pressure but is more likely to stay on center.

 

[Vancbiker]

135 cuts with less pressure but more likely to walk, 118 cuts with more pressure but is more likely to stay on center.

On a 118, there is a bit more chip thinning than a 135 due to the longer cutting lip. Is it the longer cutting lip what causes the cut pressure to be greater?

 

[Herding Cats]

Flatter cutting points are better for more difficult materials and make a more robust cutting edge. I don't exactly know why. You often see high performance carbide drills being 140 degrees or even flatter.

 

[MwTech Inc]

We sharpen our black oxide drills at 118, split and get great results in 304 SS...... been doing this for years.

 

[Dualkit]

On a 118, there is a bit more chip thinning than a 135 due to the longer cutting lip. Is it the longer cutting lip what causes the cut pressure to be greater?

Yes, or so it seems.

 

[Spruewell]

I prefer 135 or greater on drill points. I also split points on drills up to 3” and run with no pilot. Running a pilot on any hole under 1” is a waste of time. If the drill is properly sharpened with a well centered split point, it will cut true and with less chatter than following a pilot. Most people will run pilots that are too big, leading to chatter and reduced tool life. I’ve even heard of people (and I thought it was a joke) running through their whole set of S&D drills by 1/16ths to get a 1” hole.

 

[eKretz]

The longer the cutting edge in contact, the greater the thrust pressure. As I understand it, the 135° point originally came about for deep hole drilling in tougher materials, to prevent the drills from bowing/flexing under feed (thrust) pressure. Cutting edges being closer to in line with the thrust also helps keep the drills cutting straighter.

Longer cutting edges on a drill (smaller included angle) will actually last longer than shorter ones - all else equal, but they do require more pressure to cut. As with most everything else, it's a compromise. Gain in one area, lose in another.

 

[Vancbiker]

Shop I worked at in the 70s ran a few jobs on big W&S turret lathes where we drilled with a 6” spade drill and no pilot. We also did twist rills up to 4” with no pilot on a big radial arm drill. Same part got an 8” counterbore. Trying to clear chips from those tools sometimes became a tug of war and usually the chip won.

 

[Garwood]

If I have flood coolant, a decent drill and a beefy machine with powerfeed no pilot is fine.

The reality is there's a 70% chance the big twist drill I'm going to use is a little beat up and I'm in a hurry so I probably won't grind an 1/8" off the end to fix it. I'm going to use it in my anemic 9" column radial that can't push hard enough, hand crank it in a lathe tailstock or run it in my manual HBM without flood coolant. So I'll drill a 3/8" or so pilot (whatever size nice 1/4"-1/2" split point drill bit I find nearby).

When I run twist drills in a cnc I never use a pilot hole, but I make sure the thing is sharp and I thin or split the point.

 

[eKretz]

On a twist drill it's fine to run a pilot if you have a reason. On spades it's almost always not good. They will usually chatter.

 

[Litlerob1]

135 cuts with less pressure but more likely to walk, 118 cuts with more pressure but is more likely to stay on center.

It may be do to the length of the drills I like to use. But I find exactly the opposite to be true.

It may be due to the split point or the length, generally all Screw Machine or Stub length drills are 135° split point. But it's one of the things I like about that type of drill, rarely spot drill anything. I never fight position. Jynx!!