Let's Talk Drill Bit Grinders!

[Weldo]

I come from the construction trades. In that world, you learn very quickly that "If the customer likes it, and will pay for it, than that is good enough"

This is good advice! I'm also currently working in construction and sometimes I go overboard on tolerances. I'll be fitting a piece of whatever and it's not quite exactly right and I'll be stressing over an 1/8"! Meanwhile the painters are coming in two days to caulk and putty everything and there's not really even a reason to worry.

Then I go home and play around on my lathe and get jacked off that I missed an I.D. dimension by 0.002"! It can be kinda tough to live in both worlds!

 

[Weldo]

Ground some drills this mornin'!

Here's a few pics of results!

This is the factory Harbor Freight grind. Pretty crappy. The entire set is like this and some of the bigger ones don't even cut at all.

Here's that same edge after grinding in the jig. Notice it still woops up a bit at the end of the relief. Either this is because the jig is not perfectly set up (possible) or the drills are so poorly made (also VERY possible)

Here's the opposite cutting edge. The jig settings were the same but there's no woop at the end of the relief, which leads me to think that these drills are just poorly tolerenced.

I've been resisting for years buying a full set of quality drills since they're pretty pricey for a whole set. These HF drills seems kinda crappy but with a better edge they should be good enough for what I do.

I'm gonna try to use more stick out of the drill in the jig to get a bit more relief angle but I have to drill and tap another hole in my mount to get the travel I need.

 

[Shootymacshootface]

One thing that I noticed after grinding several different drills is that some drills have a much thicker center section between the flutes. This makes a very wide point on the cutting edge. These drills will either need a back cut or just use them with an appropriate pilot hole.

 

[pacifica]

Got my Blue Point clone today!

Spent two hours in the basement crafting a mount, check it out!

Here's the original tool rest. It's just sheet metal so it's got more flex than a drill grinder should have. Also it placed the drill tip almost off the platen.

View attachment 313613

Here's the mount I made. It's a 3/8" angle that someone years ago faced the two outside surfaces down to 5/16". I found this in a bucket with a bunch of misc. tools with my lathe. Can you believe I once contemplated throwing this in the scrap bin?! I welded a flat bar to give me some room for two bolts. All the holes in the big angle were existing. I thought of welding them up but didn't want to risk warpage. They don't harm nuthin'.

View attachment 313614

It mounts very solidly and perfectly square with two 5/16" - 18 bolts.

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Here's how I bolted it. The lower one is a factory flow drilled and tapped piece. The upper one is a chunk of 1/4" flat bar, tapped. No wrench needed!

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The following pics show the jig mounted. Instead of bolt and wing nut I just tapped the base for a 7/16-14 bolt.

View attachment 313612

View attachment 313617

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Turned out pretty well. Haven't done a bit yet though. After working all day and then 2 hours on this I'm gonna relax for a while!

One question on the use of the jig. It says to stick the drill tip about 1/16" past the index tab, so to advance the drill into the grinding wheel are t you meant to use the threaded adjuster at the bit base? This will change the bit stick out slightly. Otherwise you'd have to move the whole jig until the bit made contact with the wheel, and that seems awkward...

My experience:

Got my Blue Point clone today!

Spent two hours in the basement crafting a mount, check it out!

Here's the original tool rest. It's just sheet metal so it's got more flex than a drill grinder should have. Also it placed the drill tip almost off the platen.

View attachment 313613

Here's the mount I made. It's a 3/8" angle that someone years ago faced the two outside surfaces down to 5/16". I found this in a bucket with a bunch of misc. tools with my lathe. Can you believe I once contemplated throwing this in the scrap bin?! I welded a flat bar to give me some room for two bolts. All the holes in the big angle were existing. I thought of welding them up but didn't want to risk warpage. They don't harm nuthin'.

View attachment 313614

It mounts very solidly and perfectly square with two 5/16" - 18 bolts.

View attachment 313615

Here's how I bolted it. The lower one is a factory flow drilled and tapped piece. The upper one is a chunk of 1/4" flat bar, tapped. No wrench needed!

View attachment 313616

The following pics show the jig mounted. Instead of bolt and wing nut I just tapped the base for a 7/16-14 bolt.

View attachment 313612

View attachment 313617

View attachment 313618

Turned out pretty well. Haven't done a bit yet though. After working all day and then 2 hours on this I'm gonna relax for a while!

One question on the use of the jig. It says to stick the drill tip about 1/16" past the index tab, so to advance the drill into the grinding wheel are t you meant to use the threaded adjuster at the bit base? This will change the bit stick out slightly. Otherwise you'd have to move the whole jig until the bit made contact with the wheel, and that seems awkward...

Use the threaded adjuster to advance the bit, usually small amounts so you don"t loose temper on the edges.I use 80 or 120 on my belt grinder.
If the drill is 3/8" or larger it doesn't seem to matter how far out it sticks out. If your changing the drill angle or putting a tip on a broken bit you might want to rough it to shape with a die grinder so you don't loose temper. I eyeball to make sure the cutting edge is vertical. I don't go above 220 grit, finer belts don't seem to make much difference.
If you want to make a great drill, before sharpening put in your lathe and take a small amount off the shank, you can get tir down to .001 and drill shanks are unhardened. sharp bits with minimal runout are the key to straight holes.

 

[pacifica]

Ground some drills this mornin'!

Here's a few pics of results!

This is the factory Harbor Freight grind. Pretty crappy. The entire set is like this and some of the bigger ones don't even cut at all.

View attachment 313669

Here's that same edge after grinding in the jig. Notice it still woops up a bit at the end of the relief. Either this is because the jig is not perfectly set up (possible) or the drills are so poorly made (also VERY possible)

View attachment 313671

Here's the opposite cutting edge. The jig settings were the same but there's no woop at the end of the relief, which leads me to think that these drills are just poorly tolerenced.

View attachment 313670

I've been resisting for years buying a full set of quality drills since they're pretty pricey for a whole set. These HF drills seems kinda crappy but with a better edge they should be good enough for what I do.

I'm gonna try to use more stick out of the drill in the jig to get a bit more relief angle but I have to drill and tap another hole in my mount to get the travel I need.

I sharpen myself and want a drill with known steel and small amount of runout, by the time you get to the end of a
4" drill the runout can be considerable, and that will translate directly into inaccurate holes.

 

[middle.road]

For grins and giggles, I taped up and repaired the manual that came with mine, scanned & OCRd it and uploaded it to the Downloads section.
Thought it might be useful.

Millers Falls #7080 Drill Grinding Attachment - Instruction Manual

Instruction manual for a #7080 Millers Falls Drill Grinding Attachment. Pardon the tape marks, it had a hole punched clear through it.

www.hobby-machinist.com

 

[Weldo]

Some observations.

I tapped another hole to allow my jig to be placed further away from the abrasive belt. This time I tried about 1-1/4" drill stick out and set the cutting edges to be vertical by eye. When I did this I got a very poor relief angle such that the cutting edge was ground nicely but about half way through the relief, the grind stopped making contact, thus leaving the heel proud of the cutting edge.

When the drill is set up against the index according to the instructions the cutting edge is not quite vertical, though it is close. As you look at the drill tip the lower cutting edge is pointing to about 5 o'clock to 5:30. This gave a satisfactory grind so I'll probably stick to that for now. Set the drill just about 1/16" past the end of the jig and have lower flute contacting the index stop.

My drills are still coming out a bit asymmetrical like my above photos but next I'm gonna try a NON Harbor Freight bit and see what that looks like.

Also I noticed that to achieve the rigidity in the jig that I think it requires I had to crank down tight on the pivot screws. It became a little tight to pivot so I think some light grease is in order.

 

[mickri]

I have one of the swing type. An original Craftsman that came in its original box with the instructions. It works for me most of the time. Once in a while I have to redo a drill that I have sharpened. Lots of great info in this thread. Might deserve to be a sticky so it doesn't get lost in the never never land of old threads.

 

[Weldo]

Got some more bit pics!

This time I tried a drill that was unbranded but was stamped USA so I'm pretty sure it wasn't of Harbor Freight lineage. It's 27/64" size.

Here's the bit as found, looks like someone had a go at hand grinding but it didn't go according to plan... or maybe it did, who knows.

The cutting edge curls over pretty bad on both sides. I didn't try drilling with this bit before grinding it but I don't think it would've been very good.

Here's after grinding. Set up was as per the instructions with the drill just about 1/16" past the end of the jig and the bottom flute touched up against the index tab. The drill was advanced inward to the grinding surface with the adjuster screw on the shank end.

The whole process only took about 60 seconds probably.

In the last two pics you can see I'm still getting that slight rise toward the end of each relief. The difference between this and the HF drills is that this one looks more symmetrical. The slight rise is the same on both reliefs, so that leads me to believe the HF drills are ground slightly asymmetrically from the factory.

I'd like to eliminate that rise in the relief but I don't really think it's a problem.

Here's a few shots of a hole made with this drill right after grinding.

Material is 1/4" steel plate, drilled in a drill press at 620 rpm, no pilot hole.

First up is the entry point.

Here's the exit point. Very clean break through, no de-burring was performed.

Here's a look at surface finish inside the hole, it's not great... No lube was used.

It drilled very easily even with no pilot. The hole was made in just a few seconds. Strangely, after the drill had penetrated to full diameter, I observed a long stringy chip only on one side of the drill. Maybe feed was too light?

Finally here's a few of the drill after making that hole. No rubbing is obvious except at the chisel point. The two rises in relief show no signs of contact with the workpiece.

All in all I consider that a success! I'll probably try a few different point angles and see what happens. Like I said, I'd like to eliminate that slight rise in the relief and I'd like to observe equal chips upon drilling but do far so good.

 

[mickri]

The steel plate not being square to the drill might have caused you to only get one chip.