An idea for drill sharpening jig

[sorveltaja]

When looking properly sharpened drill bit's grinded surface from the side, instead of being flat, it seems to have some kind of thread-like pitch in it.

Maybe an old idea, but for example, piece of trapezoid or similar flat-threaded would act as a 'jig'.

Comparison between metric drill bit, and thread. Pitch is about 4,65 mm.


My lathe's highest(or is it lowest?) metric pitch is only 1,5 mm, so I probably have to hunt some surplus clamp or vice, that has at least 4,5 mm pitch screw in it, to see in practise, if that idea is any good.

[DICKEYBIRD]

That's a pretty brilliant idea!  All we need is a CNC ballscrew with the 4.5 mm pitch and give it a whirl.    

ps: What CAD program did you use to draw the pic?  Beautiful work!

[sorveltaja]

An evaluation version of Rhino 3D is used. Although it has limited save times, it's possible to make small demonstrations with it .

[John Hill]

Now that is interesting, I suppose one could mount a tool post grinder, set up an appropriate thread pitch and carefully hand turn the spindle half a turn to grind one flute, then, somehow  set it up to grind the other flute.

[sorveltaja]

Another idea how to make pitch adjustable. Red part is a spring, and blue one adjusts its axial length, and its pitch also:

Next thing would be to add part, that follows spring's pitch. I haven't yet discovered how to achieve that.

[Darren]

Why not just use the drills own flute to follow as other manufactures do?

[sorveltaja]

Doesn't the drill's flute have much longer pitch, than cutting surface has?

Once I had one of those horrible cheap sharpening jigs, and just couldn't get any good results with it. Neither I understood, why it was so clumsy device to use.
Theory that I've read about drill sharpening, talks only about degrees, nothing about that drill's cutting surfaces would have a pitch. They aren't flat at any degree.
Or am I missing something ?

[Darren]

Sorry I think I've misunderstood what you are trying to do? I thought you meant sharpening the flute itself....

[John Hill]

Possible procedure.....?

Put drill in lathe chuck.
Set threading gears for required pitch, 4.65mm?
Set up tool post grinder
Turn spindle by hand to take up any backlash while grinder moves towards first flute
Carefully turn spindle to grind first flute.
Disengage threading feed drive at gears or gear box
Carefully turn spindle back half a turn
Reengage threading feed
Turn spindle back to gather up backlash
Turn spindle forward again and (maybe?) it will be in position to grind second flute.

[sorveltaja]

No problem. Just trying to find simple(?) way to sharpen pile of used drills . I guess that sharpening flutes requires highly specificated grinding machinery, so I've skipped it.

[sorveltaja]

Possible procedure.....?

Put drill in lathe chuck.
Set threading gears for required pitch, 4.65mm?
Set up tool post grinder
Turn spindle by hand to take up any backlash while grinder moves towards first flute
Carefully turn spindle to grind first flute.
Disengage threading feed drive at gears or gear box
Carefully turn spindle back half a turn
Reengage threading feed
Turn spindle back to gather up backlash

Turn spindle forward again and (maybe?) it will be in position to grind second flute.

Once first surface is sharpened, turn drill back to starting position. Then turn drill holder(not the jig) 180 degrees, and grind the second half.
Jig doesn't move or rotate during the process.

---
Longest pitch available in my lathe is only 1.5mm, so unfortunately it can't be used for that purpose, unless heavy modding is applied.

[John Hill]

Once first surface is sharpened, turn drill back to starting position. Then turn drill holder(not the jig) 180 degrees, and grind the second half.
Jig doesn't move or rotate during the process.

There is no jig, the drill is in the lathe chuck and there is a grinder mounted on the toolpost.  The requirement is to rotate the drill 180 degrees in relation to the feed mechanisms.  You can not loosen the drill in the chuck as that would loose longitudinal position so we have to turn the spindle in relation to the feed.  If you have a gear head lathe you could put the spindle in neutral and turn 180 degrees by hand then reengage, if no gear box you could lift out intermediate change gear then rotate the spindle 180 degrees and put change gear back.

---
Longest pitch available in my lathe is only 1.5mm, so unfortunately it can't be used for that purpose, unless heavy modding is applied.
[/quote]

[sorveltaja]

It turned out to be too complex to use spring as a guide. So back to the original idea.

Progress so far:


On the left is an old chuck, silver soldered to brass, that has 27 mm(1.06") outer diameter, and 10 mm(~0.4") hole through it.

In the middle are chuck's internal parts. Nothing fancy, but enough to hold the drill bit.

On the right side is the tube that's internal diameter is also 27 mm. Never mind the outer threads, they came as an extra from the scrap yard. Its function is to act as a scaffold.

Essential part is still missing. I'm looking the way to mod my lathe's gears to get 4, or even 4.5 mm thread pitch. Intention is to make two point thread(is that correct term?), one thread/drill side.

Examination is still in process. 

[sorveltaja]

No luck with lathe's gears. Might be another future (side)project.

I found one thing, that has two point thread and its pitch is ~4.7 mm :


Next thing is to duplicate threads to brass part.

[NickG]

I;ve got one of those cheap grinding jigs too and haven't got it to work properly yet, but i do think it uses the correct method. Having said that, this is very interesting if it can produce more reliable results!

Will be watching! 

[sorveltaja]

Here the threads copied. About half turn for both, so                                          When looking drill at the working end, cutting surface   
there is more than enough:                                                                            appears to be ~90 degrees:
                                             

[NickG]

I'm a bit lost with this now! 

What is the rest of your contraption going to look like? Can't quite picture how it's going to work.

With the cheap grinding jigs, you angle the thing up at 59 degrees or whatever, the drill is held against a little thing that contacts the flute, then the jig is swung side to side grinding an arc. I think it depends how far down the flute you set it to hold the drill still that varies what relief you put on the cutting edges! But it'll be interesting if your thread jig removes the need for that, having said that, how are you going to make sure it's in the right position when you start grinding?

Nick

[sorveltaja]

I'm a bit lost with this now! 

What is the rest of your contraption going to look like? Can't quite picture how it's going to work.

With the cheap grinding jigs, you angle the thing up at 59 degrees or whatever, the drill is held against a little thing that contacts the flute, then the jig is swung side to side grinding an arc. I think it depends how far down the flute you set it to hold the drill still that varies what relief you put on the cutting edges! But it'll be interesting if your thread jig removes the need for that, having said that, how are you going to make sure it's in the right position when you start grinding?

Nick

After reading texts that I wrote earlier, I must admit, that it can be quite confusing. 

No other adjustments required, except drill tip angle (for example 59 degrees). Jig keeps drill's touching point with grinding wheel diagonal, if it works as I assume.
An animation of the process could maybe clarify the idea . 

Here are the basepart, and drill holder. Red circle shows broken M3 tap(yet another SS 316 experience). As it is stuck there, why not use it as a guide for brass part's thread grooves:


Parts together with drill bit:

[sorveltaja]

Mock-up, that shows the progress so far:


It needs support for the drill, and locking mechanism, that is to be used by the screw, that shows under the plywood piece.

I guess, that it would be simpler to combine the tube and plywood elements to one part.

[tinkerer]

Trying to wrap my head around this. I am thinking you want to have the trailing edge of one flute at a lower rake than the leading edge. (that may not be what you are trying to accomplish) I believe, in production both, edges have the same rake. I think the most important part of sharpening a drill bit is consistency for both flutes, which is difficult to do by hand, thus the machines. Drills for steels, aluminums & plastics have different angles. plastics-25-30, aluminum, copper & brass 45-50 and steel 40-45. It is very important that both flutes have exactly the same cutting angles, cutting edges and lip clearances. Large dia. drills should have a back cut. To test the drill it should give an equal removal of material from both flutes.

It seems drilling aluminum gives the most problems. A lubricant called Boelube (you can google it and find many suppliers) is used by aircraft manufacturers and airline maintanence. It has a low melting point and lubricates as the heat builds up. I have drilled thousands upon thousands of holes in aluminum with no difficulty using the correct lube and techniques. Using the proper dia. pilot drill, then stepping up to final size with core drills or reamers also. Manufactures and airlines use the sharpening machines with good results and save a ton of cash doing so.

[sorveltaja]

Intention of this jig is to make it easier to grind drill's both cutting surfaces identical, regardless of the tip angle.

In this project, I have abandoned technical terms, that usually relate to drill's sharpening. Instead I have in mind, that drill is like a screw, whose tip angle(and the pitch) dictates, how fast it can dig into certain materials. Something like automatic feed. It also has a pitch. Lower the pitch, higher the feed, and vice versa.

I have clear image in my head about this thing, dirt simple, but in practise... we'll see.

[tinkerer]

Cool. I am still confused about the pitch part unless you are talking about the angle of attack. Kind of like a prop on an airplane engine. Same angles involved on both blade, but appears to screw itself through the air. I'll be watching with interest on how this works.

[bogstandard]

Sorveltaja,

I love what you are doing here.

You are taking a glimpse of an idea thru to trying out a prototype.

To me, it means nothing if you are successful or not.

The fact that you are trying to solve an age old problem by looking at it from another angle is the remarkable part.

I wish you success in your challenge, but don't be disappointed if it doesn't work as you have planned. Think of all the experience you have gained getting this far.

Bogs

[NickG]

Hear hear 

[sorveltaja]

I skipped that plywood/tube -combination, and made it altogether a little more solid component:


Original plan was to make this jig for small (3mm(~0.11") and below) drills, but the chuck is bigger, and so will be the whole device.
  To add even more confusion, I intend to use a small(dia. 13mm(~0.51")), slowly rotating(~100-200 rpm), diamond coated grinding drum for sharpening:


Ordinary grinding wheel would wear on such a low speed. Instead, the thing above seems to last. I have used (and abused) that thing with glass, plastic, wood, HSS, carbide, and various other metals.

Anyway, the jig itself needs still some work to get it ready for testing .