Sharpening large drill bits?

[slow-poke]

I use a Drill Doctor for small bits. For larger bits I need to hone my drill sharpening skills. I only have one grinder at the moment and the wheel has a very coarse grit. Seems like I should start with a smaller grit wheel. I actually have an older but good white much finer grit wheel so I think that is probably a good wheel to try? Comments?

I just watched a sharpening video at it seemed like the grinder was turning at a much slower speed, total guess but looked like < 1000 RPM vs. my 3600RPM, since I need to get or make a grinder for this white wheel is there an ideal RPM for sharpening?

What about fixtures to maintain the correct angle, unnecessary or a good idea?

I definitely need some pointers. Thanks in advance.

 

[Tom Kitta]

How big do you go?

Speed is determined by the diameter of the wheel for optimal SFM. So 3600 rpm is great for 6" and 1800 rpm is a bit slow for 10" - 1800 rpm is SLOW for 8"

For drill bit sharpening you need soft wheel - i.e. it needs to fall apart easily to expose sharp pieces.

I frequently sharpen by hand larger drill bits on a belt grinder.

Up to about 3/4 or so I use 6" grinder. Touchup up to 3" is on belt. I have no experience above that size.

I also have home build device to sharpen drill bits on a TC&G.

 

[slow-poke]

How big do you go?

Largest bit is ~1". I use annular cutters above that. So mostly S&D 9/16 to 1"

Anyone using a fixture to keep on track angle wise?

 

[terry_g]

I have a gauge to make sure the angle is correct and it is important that both cutting edges are the same length.
I find big drill bits are easier to sharpen than small ones.
I have a 8" grinder with a white medium wheel for sharpening high speed steel and a 6" grinder with a fine white wheel for finishing the grind. Both run at 3450 rpm.
I use a stone and a diamond file on smaller bits.

 

[MrWhoopee]

The size range you are talking about is perfect for hand grinding. Not too big, not too small. Get a drill point gage for checking angle and width of cutting edges. It's a skill definitely worth learning. It teaches you the basics of cutting edge and drill point geometry in a way you will never learn with specialized grinders and jigs. I've recently been thinning the web of #27 drills free-hand on the corner of a grinding wheel with surprisingly good results.

 

[KenjiMcfee]

The size range you are talking about is perfect for hand grinding. Not too big, not too small. Get a drill point gage for checking angle and width of cutting edges. It's a skill definitely worth learning. It teaches you the basics of cutting edge and drill point geometry in a way you will never learn with specialized grinders and jigs. I've recently been thinning the web of #27 drills free-hand on the corner of a grinding wheel with surprisingly good results.

View attachment 63190

great advice. I'm gonna go buy a drill gauge.

 

[phaxtris]

The included angle of the tip is not really super critical, 110 deg, 118deg heck 140 degrees all will drill, what is really important is the support behind the cutting edge, to steep it will drill like a banshee for about 2 holes before chipping or dulling, to shallow and it either doesn't drill at all or takes a massive amount of pressure

Take a look the side of the cutting lip of some factory bits, try to emulate that angle, being able to get that right is what separates a good sharpen from a bad one, a long lasting shapen to a 2 hole wonder

Once you get the hang of it you can modify the included angle and support angles to suit the material you are drilling

Edit: a note about both cutting edges being equal, it will drill if they are unequal, the bit will just wander and not drill a straight hole, best to make them as even as possible

 

[CWret]

Bit sharpening is not that difficult with practice and a steady hand.
Start with a good quality (80 grit, brand name like Norton) medium grit balanced wheel. Decide if you want 118 angle (general purpose) or 135 angle (harder metals). A bit gauge is a big help. A balanced wheel is very important.
Here is a set up to balance the wheel:Here is using a diamond single point cutter (in a jig) to make the wheel round:Also should check that the two bit corners are engaging the work evenly. Here is a couple samples of 3/8”hand sharpened bits (as others said, bigger bits (over 1/2”) are easier to hand sharpen).

https://www.amazon.ca/Drill-Angle-Gauge-Sharpener-Measuring/dp/B079FS4MS5/ref=mp_s_a_1_2_sspa?crid=MVYXOHG9FTSK&dib=eyJ2IjoiMSJ9.q9ql0Hgp3z4F42Ga-QWoT8TydXRZNG5AFwubuls06oUEbJZTBfzW1sevkXPx42VV0varKerZNbNtJU932gwjPlPQ0GCrMku1m3pHonG7QBiaKXzJg8rrM3a5Y5Eb24cJyDFbSNKSVtWf4-_LZEW16IVyradFXkCe9AoOeLJMYhZlgwmUiqpZne3GUvBxvyO252X64P_VBwh3zJx__827_Q.c33r0wGS2n66gNDczoFUOC6SYEgj-VYeCDB1iAS9fMI&dib_tag=se&keywords=3+piece+bit+sharpening+gauge&qid=1744827734&sprefix=3+piece+bit+sharpening+gauge%2Caps%2C203&sr=8-2-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9waG9uZV9zZWFyY2hfYXRm&psc=1

 

[CWret]

Don’t be afraid to try hand sharpen an EM too. Here a link to a post from a couple months ago.
Thread 'End mill brought back to life'
https://canadianhobbymetalworkers.com/threads/end-mill-brought-back-to-life.14286/

 

[phaxtris]

This is the make or break angle, if you don't get this right it doesn't matter if the included angle is correct, to steep it dulls and or chips, to shallow it cuts like crap or not at all

Hundreds of drill bits by hand, plenty of those with an angle grinder in a vise (your setup is not that important) , you get that angle correct it will drill and last

 

[mickeyf]

The included angle of the tip is not really super critical, 110 deg, 118deg heck 140 degrees all will drill

Yes, but... in general you want a sharper angle for softer materials (plastic, wood). I think 118 deg was "scientifically" determined to be a pretty good compromise.

The issue with uneven lips is not so much that the drill wanders, but that because as the drill advances it pivots around its point. If the lips are not the same length then the hole will effectively be cut to the radius of the longer lip, thus creating an over sized hole. This is why even a factory fresh drill may make a larger hole than claimed, and no drill will ever make a smaller hole than it's nominal size (total mislabeled garbage excluded, of course!). If you are aiming for exact hole size then same-length lips are more important than the exact cutting angle.

An angle gauge is definitely worthwhile. There are several types available. Even the simplest, least expensive one is a good tool to have.

I have always ground all my drills by hand, but just like when grinding HSS tool bits you want a container of water handy to cool them periodically. Good drills in general are made of hardened steel that you don't want to take the temper out of. Sometimes you find some that are made of softer stuff:

 

[phaxtris]

Yes, but... in general you want a sharper angle for softer materials (plastic, wood). I think 118 deg was "scientifically" determined to be a pretty good compromise.

The issue with uneven lips is not so much that the drill wanders, but that because as the drill advances it pivots around its point. If the lips are not the same length then the hole will effectively be cut to the radius of the longer lip, thus creating an over sized hole. This is why even a factory fresh drill may make a larger hole than claimed, and no drill will ever make a smaller hole than it's nominal size (total mislabeled garbage excluded, of course!). If you are aiming for exact hole size then same-length lips are more important than the exact cutting angle.

An angle gauge is definitely worthwhile. There are several types available. Even the simplest, least expensive one is a good tool to have.

I have always ground all my drills by hand, but just like when grinding HSS tool bits you want a container of water handy to cool them periodically. Good drills in general are made of hardened steel that you don't want to take the temper out of. Sometimes you find some that are made of softer stuff:

View attachment 63301

Yes, I believe you just rehashed my post, other than missing the most important angle of the entire bit, the cutting edge support, a 118 bit will drill stainless or plastic, a 135 deg bit will drill stainless or plastic as well, not ideally, but it will work, screw up the support it may not drill at all

yes you want the angle on both sides as close as possible to the same angle/length, or it will wander/corkscrew and make an even more oversized hole. But...it's a drill bit, they are not precise, not even close, not rigid enough

 

[Don Sipes]

I use a Drill Doctor for small bits. For larger bits I need to hone my drill sharpening skills. I only have one grinder at the moment and the wheel has a very coarse grit. Seems like I should start with a smaller grit wheel. I actually have an older but good white much finer grit wheel so I think that is probably a good wheel to try? Comments?

I just watched a sharpening video at it seemed like the grinder was turning at a much slower speed, total guess but looked like < 1000 RPM vs. my 3600RPM, since I need to get or make a grinder for this white wheel is there an ideal RPM for sharpening?

What about fixtures to maintain the correct angle, unnecessary or a good idea?

I definitely need some pointers. Thanks in advance.

I don't have a grinder with a wide enough stone to grind large drill bits either. So I use my belt sander and it does a good enough job.

 

[Mike R]

Sometimes you find some that are made of softer stuff:

hahaha - I recognize that as very possibly one from a set of Princess Auto extra long wood boring bits. Mine is still "straight" but I untwisted it such that it reverses the helix half way up!