Regrinding a 118 degree drill to 135 degrees

[Garage Dog]

Can it be done?

I don't have any 135 degree bits to compare to my 118's so I'm not sure if there is some difference it the bits that would prevent regrinding.
I have a General tool 825 which works fairly well for the 118 and it has a scale to sharpen 135's as well. I have a few drills I can experiment with but would like to get any tips or tricks you guys might use. TIA!

 

[woodchucker]

yep, any drill can be ground to most any point.

 

[GeneT45]

No problem (other than time). Same as resharpening at 118, except more material to remove (the first time) and hence heat is more of a consideration. Consider quenching periodically. If your wheel is very fine, or your bits very large, consider moving to a faster wheel or a course belt to rough in before refining your grind with your tool.

GsT

 

[projectnut]

OK, Question for the Drill Guru's. What caused the industry to settle on the standards of 118* and 135* for drill point angles. Why not 120* and 140* or any other angles within reason? Drills sharpened by hand aren't necessarily 118* or 135*. Generally, they're pretty close, but unless you have years of experience, I'm betting more are slightly off the mark.

My Black Daimond drill grinder can grind drills from 80* to 140* in 1* increments.

 

[Jimsehr]

OK, Question for the Drill Guru's. What caused the industry to settle on the standards of 118* and 135* for drill point angles. Why not 120* and 140* or any other angles within reason? Drills sharpened by hand aren't necessarily 118* or 135*. Generally, they're pretty close, but unless you have years of experience, I'm betting more are slightly off the mark.

My Black Daimond drill grinder can grind drills from 80* to 140* in 1* increments.

Projectnut
I agree why not 120 degrees?
I have ground so many drills that it does not bother me what angle I grind them to. And 60 years ago I learned to split the points grinding by hand.
I also learned to hand grind short drills flat.
When I had my shop I saved up the dull drills and hand sharpened them when I had long cuts on my CNC.

 

[Garage Dog]

Thanks Guys! I'll give it a shot.

 

[RaisedByWolves]

OK, Question for the Drill Guru's. What caused the industry to settle on the standards of 118* and 135* for drill point angles. Why not 120* and 140* or any other angles within reason? Drills sharpened by hand aren't necessarily 118* or 135*. Generally, they're pretty close, but unless you have years of experience, I'm betting more are slightly off the mark.

My Black Daimond drill grinder can grind drills from 80* to 140* in 1* increments.

It has to do with how different tools and their angles work together.

Using a center drill as an example, the point and lead of the center drill are ground to work in a distinct way. Being this is generally the first in a series of tools you will likely use in succession, its angles take precedence, and the angles of each successive tool follow suit.

The machine and material have a bearing on the drill point angle and this can vary widely. Speed, feed, process all can play a part and personal preference also plays a part.

For decades all I had available at work were 118* drills and we used them for everything. Having hired a different supplier a few years back they carried 135* drills and now we have those to chose from also. The specific numbers were likely solidified by a guy wearing a suit, at a drafting table using a slide rule, and inertia likely carries these callouts to this day.

 

[ChazzC]

I generally do not reference PM, but . . .

https://www.practicalmachinist.com/forum/threads/why-118-why-135-drill-angle.152137/

All the info you want (plus possibly more?). One post also notes that 135° bits have thicker webs, but that may be because thinner webs aren't required for that geometry, or just to save $$.

 

[Batmanacw]

I admit that it is only an opinion, but I think 118⁰ cuts a more round hole. I use both interchangeably. When drilling by hand I often grab 135⁰.

Splitting the point on any point angle seems to lower cutting forces. Worth the time to learn.

 

[RJSakowski]

No problem (other than time). Same as resharpening at 118, except more material to remove (the first time) and hence heat is more of a consideration. Consider quenching periodically. If your wheel is very fine, or your bits very large, consider moving to a faster wheel or a course belt to rough in before refining your grind with your tool.

GsT

You really needn't be concerned about quenching while grinding HSS. Even less for M42.

M2 HSS has a tempering temperature of more than 1025ºF, at which point, it will be beginning to glow. The point at which it begins to lose hardness is around 1150º and is definitely glowing.