Drill bits , what do I do wrong ??

[stragenmitsuko]

I've been trying all aftrenoon to sharpen a drill bit
to make it look like the b&w picture .

But the best result I got sofar is like the one in picture nr 2 .
The black stuff on the point is an ordinary marker to make the primary relief more visible . Now these drills cut fine , but somehow they don't look the way I want them .

3'd picture is my t&c grinder .
Universal head can rotated in the horizontal and vertical plane , and the drill bit can be rotated and locked at any angle .

Here's what I do :

1) Set the bottom plate (horizontal plane) to 59° or 70° to obtain a point angle of 118° or 140° , depending on drill geometry .

2) Tighten the drill in the universal head , using the approprate collet .
Letting it stick out an inch .

3) Tilt the universal head at 15° (vertical plane ) for the primary cutting angle .

4) Rotate the universal head until the cutting edge of the drill in line with the horizontal plane . And lock the head to that position .

5) Grind the first edge

6) Rotate the universal head 180° and grind the opposite edge .

7 ) Then I rotate the universal head 20° counter clockwise and tilt it to 30..35° for the second relief

8) Grind the second relief , rotate 180° and grind the opposite side .



Like I said , they're sharp , they cut pretty good , but I'de really like to obtain the point in the b&w picture .

Pat

[mxtras]

Originally Posted by stragenmitsuko 7 ) Then I rotate the universal head 20° counter clockwise and tilt it to 30..35° for the second relief Pat

I would suggest ommitting the "Then I rotate the universal head 20° counter clockwise" part and give it a whirl.

Are you setting a stop to stop the corner of the wheel on center or how are you obtaining the split point? Setting a stop is one method, but more uniform results will happen if you perform a third op on the flank to cut the back side of the flute to create an actual cutting surface at the center of the drill. I don't really know how to verbalize this. I will see if I can locate a pic to clarify.

Can you post a pic of your current results?

Scott

[Oldmanandhistoy]

Hi Pat,

None related but have you removed the guard from your machine for clarity or do you not use one. The reason I ask is that a few years ago I saw a grind wheel explode fortunately no one was hurt.

John

[mxtras]

While T/C grinders have the provisions for the guard, the only time you will see them in place is when the machine is on E-bay...

Scott

[mxtras]

If you are planning on grinding the faceted point and thinning the web, I would suggest using less angle for the primary relief. Something around 8 degrees or so is sufficient. 15 degrees is going to leave the cutting edge suceptable to overheating and chipping - I feel it is too much clearance.

Scott

[Oldmanandhistoy]

Originally Posted by mxtras While T/C grinders have the provisions for the guard, the only time you will see them in place is when the machine is on E-bay... Scott

I have used t&c grinders on and off for 25 years and always use guards.

John

[stragenmitsuko]

To be honest , I don't have the guards .
When I got this machine , it was no more then a block of cast
that remotely looked like a grinder .
Dirthy , rusted , electricly broken , bearings toasted etc .
I've compleately rebuild it , but never gout round to making the guards .
I know , I know ... I shouldn't use it without them , especially with those two big stones .
Good point John !


Scott , I don't understand the comment " give it a whirl " .
There's a picture of the result sofar , the one with the blue background .
I've also tried 8° for the firsdt relief , but then the bits hardly cut .
Remember this is facet grinding not rolled .

[mxtras]

"give it a whirl" - a different way of saying give it a try.

I understand about it being a facet grind. I think that if 15 degrees is the only way you can get clearance then you need to reduce the width of the primary. I would not suggest more than 10 degrees for drill life.

I need to find a picture to describe what I am refering to about the point. It is an additional cut in the web that creates a positive face angle at the point. The way you are grinding, the point will plow - not cut. There is a point method that will allow the point to cut, allowing for beautiful starting and cooler cutting.

I will try to locate a photo that will display the method that Avyac uses for obtaining a faceted split point. This is their site, but they do not show their point style - I think their point style is patented: http://avyac-machines.com/3p32.htm - Drill Grinder from Avyac

Scott

[mxtras]

I attempted to take some photos of the chisel point I am talking about but my camera sucks for up close photos. I can not find a picture of the configuration, either. Sorry.

What is the current status of your grinding efforts?

Scott

[stragenmitsuko]

No further improvement sofar .
Tried a few different angles , I can make it cut a little better or worse depending on primary angle .

But I've stopped experimenting for now . I'm gonna build me some guards first .

Pat

[ImanCarrot]

To photo stuff up close just use a normal convex lens (like an eye loupe- them ones that jewelers use) you will be surprised how good the results are!

Place the lens roughly as far away from the camera as you would use it from your eye- eye loupes are perfect for this as they got the plastic stop and can be held there with plasticine or blu- tac.

Iain

[One of Many]

From what I can see in the pic is that the split point is not stopping at the edge of your wheel. It appears the the secondary relief, to be going past center. You need a sharp corner(possibly even a slight dovetail) on the wheel edge that ends at the web center and a stop set(if you are using the table to travel in towards the center) so that another cutting edge is created there. What you end up with is a bit of negative rake on the root of the opposite primary flute?

I've always done the same edge by hand on a bench grinder. Although I do use a 3/4" wheel and cut a step into the right side to obtain 2 sharp corners to split the point and add the secondary relief at the same time.

If you set the 59 or 70 deg and index the drill 180 to cut both flutes, then reset to get your seconday relief and use the same index, it should all work without to much trouble. Maybe more trouble than by hand, but much more accurate.

Now that I look at it, my methods are for a split point. Not a chisel point as shown. That style may over run center. Hmmmm!

Buy a bit and see if you can duplicate all of its angles?

DC