Drill Bit Sharpening Questions

[devils4ever]

I've been slowly buying replacement drill bits as mine have been wearing out, but it's starting to get expensive especially on the larger sizes. I have 30-40 dull bits that need sharpening right now.

I'm considering the Drill Doctor 750X since it seems to get mostly positive reviews here and elsewhere.

A lot of my drill bits are 118* standard point. I've been buying 135* split point to replace them. So, my question is, can I take my dull 118* standard point drill bits and use the DD to change them to sharp 135* split point bits?

The DD manual states this:
10. Question: Can I change a 135° drill bit into a 118° drill bit?
Answer: While you can change the degree angle of any drill bit, they will perform best when sharpened at the same angle they were manufactured at.

Obviously, I want to do the opposite, but can I do this?

 

[macardoso]

I wouldn't see why not. You will just need to grind away enough of the existing point to form the new angle. I do not believe the flute geometry is different for 135 vs 118, that's usually more of a model or brand kind of thing.

 

[pontiac428]

The flute angle is different, but you can grind the point for the benefits of the angle. Harold Hall explains it well in his sharpening book.

 

[devils4ever]

So, the body of the drill bit is the same for 118* and 135* points? If so, I can't see why I couldn't change the point from 118* to 135*.

 

[pacifica]

I do it all the time, but I use a belt grinder with replaceable belts. Not sure if it would quickly wear the wheel on the drill doctor? Are replacement wheels expensive? looks like about $20 each.

 

[Janderso]

 

[devils4ever]

Yes, there are around $20. Not too bad.

I watched a YT video last night where the presenter claimed the web of split point drill bits are larger than standard point. I measured a few of mine and found this to be not true at least for the Chicago-Latrobe brand I've been buying as replacements.

 

[mikey]

So, the body of the drill bit is the same for 118* and 135* points? If so, I can't see why I couldn't change the point from 118* to 135*.

The drill is the same and you can definitely grind a 135 deg point on a 118 degree drill with a Drill Doctor. You can also split the point.

Just generally speaking, 118 deg drills are best used for most materials in a hobby shop. When drilling stuff that is harder to drill or that can work harden, 135 deg drills are a better choice. I have both and quite honestly, I mostly use the 135 deg drills in stainless. More of the cutting edge is engaged early on and that keeps the drill cutting continuously, which reduces work hardening. Otherwise, and even often when drilling 303, I usually just go with my 118 deg drills.

One of these days, I need to learn to grind 4-facet drills. THAT is worth learning. Until then, a Drill Doctor works fine for me.

 

[savarin]

I'm hopeless sharpening drills and have been trying to persuade myself, so far, in vane, to get a drill doctor for years.
I think I will have to make a round tuit first though.
How easy are they to use?

 

[BGHansen]

I'm hopeless sharpening drills and have been trying to persuade myself, so far, in vane, to get a drill doctor for years.
I think I will have to make a round tuit first though.
How easy are they to use?

Super easy to use. I have a DD400 and a DD750. You stick your bit in an adjustable collet and leave it a little loose. The collet is set in an alignment fixture (angular orientation), while pushing down on a button that pulls back two spring steel fingers. Push the bit in through the collet until it bottoms out on a stop, and release the spring finger button. The fingers set the angular position of the drill bit within the collet. Tighten the collet by turning the base, push the button to release the fingers from the bit and pull the collet/drill bit assembly out of the alignment fixture.

Turn on the DD, insert the collet into the grinding station roughly aligning an "UP" mark. Turn the collet slowly clockwise a full rotation so both faces are ground. Depending on the diameter of the bit and how much needs to be ground, usually 2 - 4 rotations does the job.

The grinding station is a tube that the collet fit into. The station can rock back and forth. There's a cam on the outside of the collet that bears against a post on the base. The cam tilts the collet/bit as it's rotated so you get a relief grind behind the cutting edge.

My DD500 is close to 20 years old and has no adjustments, 118 deg. bits only. The 750X model will grind 118, 135 and a number of angles in between. I think it does split points though I've never done it. There is also a special order collet available for machinists from below the equator who use LH drills.

I've used mine for well over 1000 grinds with no issues though you'll get opinions either way. Lots of plastic in the assembly, but works for me.

Bruce