Messages

Rich,
Thanks, I've read that document several times. I was going to try and build a semi automated drill sharpener with a computer controller. But then if found and decided to just get a Tormek. I have to many other things to do right now. However I have a lot of bits to sharpen so being efficient is a key right now. Once I get them sharpened, then I can spend time occasionally resharpening as needed. That resharpening will go faster if I write down the primary and secondary angles on the box of bits.

I made a plastic guide that looks like a bigger version of the Tormek primary face angle guide and 3d printed it. It actually didn't turn out very well, my printer nozzle was getting clogged up with something (dirt most likely). Its a +20 degrees to primary angle guide. (27, 29, 31, 34 degrees). That was pretty close to the secondary angle I was getting by just setting the secondary angle manually. I then made a +13 degree guide, which I'm trying out right now. So its 20, 22, 24, and 27 degrees down from perpendicular to the grind stone.

Dan,

The document, "Drill Bit Geometry", by Joseph Mazoff is a truly great reference about drill bit geometry.  Here's a link:

http://www.newmantools.com/machines/drillpoint.html

May not answer your question, but it is the best I've seen yet.

Kind regards,
Rich

I'm new to the forum. I've had a DBS-22 for about 2 weeks, but I've been sharpening all my metric and standard bits (about 300).  On  a T-7.

The secondary angle grinding is somewhat random. Its based on setting the slider table at a not quite horizontal position. I've been setting it by putting the drill bit holder onto the secondary position and bringing the table up so the bit starts to hit the grinding wheel. Again this is still somewhat random based on the protrusion of the bit from the bit holder and the size of the bit and the position of the adjustment for the primary facet grind.
The secondary face just needs to be at a greater angle to the cutting edge than the primary angle. Using the recommended procedure I would guess that the secondary angle is about 28 degrees (very rough estimate) down from perpendicular to the grinding face. The jig gives us settings of 7, 9, 11, and 14 degrees down from perpendicular to the grinding face.
So i tried sharpening some of my good german metric bits with a 130 point angle, and using the 9 degree primary facet angle, then setting the secondary angle at 14 degrees. (5 degree delta) I also tried 9 and 11 (2 degree delta) but the line between primary and secondary faces is not really discernible so its hard to get a good center point.
Advantages: 1. This allows me to have a very repeatable secondary angle, so in the future I will hopefully be able to grind on the bits less to achieve both a new sharp primary facet, and the secondary facet.
2. I can set the DBS-22 base plate angle, sharpen one bit, primary, then adjust angle for the secondary facet, and using the Primary Stop, finish the 1st bit; then immediately start on the second bit with the secondary facet. When that is finished, I turn off the machine, reset to the primary angle and finish grinding that bit, and then start on the next bit. This saves a lot of time in resetting the DBS-22 table 2x for each bit. Instead of setting the angle 2x for each bit (primary and secondary), I only set it 1x for each new bit, thus saving time.

Problem:
A.  I noticed that while the angles were cut, the bits didn't seem right. The secondary cut heel (lowest part) wasn't really the lowest part of the bit. So the bits weren't cutting, they were riding on the heel of the secondary cut. I attribute this to the curved surface of the grinding stone and the long edge at the outer edge of the bit, and the low secondary angle.

So I went back to the original method, and recut those bits with a larger secondary angle. They work great.
I think the secondary angle needs to be more than 5 degrees, and probably more than 7 degrees (7-14=7), because I tried that set up too.
So how much difference is required between the primary and secondary facets when using a DBS-22 on a T-7 type machine?

I 3d print stuff. So I'm going to make a ~ 20 degree delta plastic guide (27, 29, 31, 35) and maybe a 28 degree delta plastic guide and try those out. In the mean time, lets hear some thoughts.

If you have the time and energy to try welding this back together, try it. The only thing you might loose is your time and the cost of a welding rod. Arc welding will probably have the highest chance of success if you can get a good welding rod match. You see arc welding in the field for the repair of bulldozer blades and backhoe shovels all the time. Same basic steel arrangement- The body of the drill should be a "tough" steel to deal with the loads of drilling. The front cutting edges should be hardened steel to deal with hitting the concrete. So you should be able to weld the body of the bit together with more success. But welding produces harder material in general which is brittle, so the bit will likely break at the weld in the future. You can increase your success by changing the steel in the weld zone with follow up heat and cool. But local to the weld zone, not the hardened tip. Heating and cooling the tip will soften that steel and make the bit dull very fast. What exactly is needed is anybody's guess. You would really need to talk to a materials engineer who is versed in steel to find the right temperature to heat to (which is the key), then cool fast in water.
Alternately You can try hammering the weld with a ball peen to toughen it and reduce some of the stresses. Which is part of the arc welding cleanup, so that's another reason to use arc welding.
FYI, this is my 1st post on the forum. But I have a BSEE, and one materials engineering course, and my brother has a MSME in materials, so I do know a little about the subject.