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View Full Version : Drill bits , what do I do wrong ??



stragenmitsuko
08-23-2007, 08:59 AM
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
08-23-2007, 09:44 AM
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
08-23-2007, 10:20 AM
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
08-23-2007, 10:43 AM
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
08-23-2007, 10:48 AM
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
08-23-2007, 10:49 AM
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
08-23-2007, 12:36 PM
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
08-23-2007, 12:54 PM
"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
08-24-2007, 11:23 AM
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
08-29-2007, 10:26 AM
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
08-29-2007, 11:16 AM
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
08-29-2007, 11:23 AM
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

One of Many
08-29-2007, 01:24 PM
Another peek and I would suspect the secondary relief is not a flat angle grind, but a radius of the wheel where in the runout(near tangent, but not quite) meets the heel of the primary grind while it also reduces the negative rake at the web center blend of the opposite flute.

The center may not neccesarily cut, but it could help stablize the drill from wander?

DC

Deusrexmachina
09-14-2007, 05:34 PM
Hello to all, this is my first post. :þ

You've to also forgive my crappy technical explanations if there'll be something I won't express properly, mainly because I've never learned these exact terms in my almost 8 years as a CNC lathe operator starting from scratch, and on top of it my past school background differs from my job, so what I've learned is grounded directly from the workshop.
We've recently changed two supervisors, and our working methods have changed for the better, providing us -finally!!- with appropriate tools. Some past techniques still remain though, like grinding drills by hand and/or using the grinding machine in a slightly different way. I've learned, for instance, to sharpen unevenly the cutting edges; the result is to have a bigger hole from a minimum of 0.05 [mm] up to 0.4 [mm]. It's good for deep drilling so the diametrical cutting edge of the drill bit doesn't friction during the path, wearing it and in the worst case destroying it.
Example:
Material 1.2311, drill Ø8 x 83 [mm], drilled automatically with the lathe (can't recall the feed nor the rpm, sorry); I've drilled 54 pieces without the need to sharpen more than once (before starting); the hole wasn't important so it could have been almost up to Ø9.
Sometimes if drills are too precise, well, they just don't fit for the job. Of course I'm not talking about those modern bits with inner refrigerant holes, eh?

Erm, didn't want to show-off nor be a smart-ass, just wanted to share a little info I THINK might be useful. :p

chipsinpan
09-22-2007, 01:30 PM
Is That an old Gallmeir Livingston grinder ? Looks a lot like mine .
Anyway , that jig in your photo is not meant for drill grinding . I think you are just grinding a cone that "looks" like a drill point .At best , you are grinding an end mill with a tapered end . Suggest you get a cheap drill grinder , like a drill doctor and see how it gyrates the drill to get a variable angle that changes from the point , out to the O D lip. You will be able to split a point , or do a facet grind on a masonry bit with this setup , but you will never get consistant results as a properly ground drill.

Mcgyver
09-22-2007, 03:32 PM
I think you are just grinding a cone that "looks" like a drill point .At best , you are grinding an end mill with a tapered end . Suggest you get a cheap drill grinder , like a drill doctor and see how it gyrates the drill to get a variable angle that changes from the point , out to the O D lip. You will be able to split a point , or do a facet grind on a masonry bit with this setup , but you will never get consistent results as a properly ground drill.


chips, why do you say that? most I've heard or read says the faceted point is as good or better than a conical point, which has also been my experience. imo a cheapo drill doctor can't hold a candle to a properly done T&C ground 6 faceted point. the good conical point sharpeners are thousands and still don't do a better job.

Pat, couple of things,

i take it from your explanation that you are moving the univise instead of indexing the drill 180 degrees? This is a bit problematic in that it's difficult to set the univise with any angular precision, meaning that the two sides might not come out exactly the same. much better to be able to index the drill.

I designed a drill holding head to go onto a univise to do this - to be able to hold any sized drill, index via a tooth rest and have find adjustments on both tooth rest and the longitudinal position of the drill. here's some pics.

http://bbs.homeshopmachinist.net/showthread.php?t=25540&page=2

Finally, the first picture you posted, is a 6 facet cut. Note the acute corner of the drill lip has been ground down a bit. This is not essential, but does make the faceted grind a lot tougher, probably better tracking. What sort of accuracy are getting with the holes? i still impress the hell out of myself with 1" drills that only cut 2 thou over. :D