Such as bench grinders and belt grinders. The grinding grit thrown downward gets into the sliding mechanisms and causes damage. In the recent training video by Tormek on the BGM-100 use with bench grinders, they commented they don't recommend using the DBS-22 and other jigs. They didn't say why, but the damage I observed is likely part of the reason.
Grinding Grit Wear DBS-22 02-23-24.JPG
I had not done any drill bit sharpening for quite a long time. But enough of my bits had become dull that I was getting ready to have a go at it. I've had diamond and CBN wheels for quite a while and had never really used them for drill bits to any great extent. Recently, on another forum, I was exposed to a different style of dedicated drill sharpening, much like the infamous Drill Doctor, but significantly better. I ended up getting one (Vevor) and feel it is a pretty good machine, but I still like the facets and finishes achieved on the Tormek.
So, in messing with all this in past week, I tried setting up the DBS-22 on my Rikon slow speed grinder, using and FVB and USB. This grinder has an 80 grid CBN wheel, which I though would be great for roughing. It is. But the DBS platform and clamping block are very close to the wheel and the grit is cast downward, collecting on the jig parts and getting into the sliding ways, plastic between the platforms and zinc-on-zinc between the clamping block and sliding platform. I noticed significantly greater scratch marks in the grove and ridge of the latter parts.
I have discontinued using the DBS-22 on the Rikon grinder.
As part of all this I was using the CBN and diamond wheels on T8, trying different approaches to roughing and finishing the primary and secondary facets. The nominal method is to grind the primary facets first and then the secondary, the latter requiring a good bit more grinding. I tried roughing the secondary first and then finishing with the primarys. I sort of like this approach and have figured out that the angle of the platform for the secondary facets is about 20º relative to the top horizontal surface of the T8 case - using a digital angle cube.
The angle for primary facets depends on the relief angle used, 7º relief is about 35º and 9º relief is about 32º. I wanted to know these angles so I could go directly to the secondary first. However, even though I know what the relative angles are for 7º and 9º reliefs are, I still use the Tormek angle template for setting these, it is more consistent and faster.
Further messing with roughing first, I decided to see how the "original" Blackstone (SB) would do, as well as the 10" dia. x 1" wide traditional high speed grinding wheel that I fitted to the T8 would do. I found that I like these latter two as much or better than the CBN and diamond wheels. For one thing, there is less fiddling with wheel changes and given how the DBS sets up relative to the grinding wheels, variation in wheel diameter is much less problematic, compared to angle setting for knife sharpening.
I found the grind finish of the SB wheel equal to that of the DF diamond and there is no worry about wearing out the diamond or CBN wheels, allowing them to be saved for knives.
Jumping back to that "other" drill sharpener, the Vevor, I was thinking it might serve as a good roughing first step, reducing the amount of heavy metal removal on the T8. It does, but it creates a single relief angle by rotating the bit, whereas the Tormek creates two flat reliefs in the primary and secondary facets. There is still a good bit of metal removal to do in grinding the secondary relief after roughing on the Vevor. A combination of the two might work, where the the Vevor is used to rough in what will become the secondary and finishing by grinding only the primary on the Tormek. I tried this, it works. But the grind finish of the Vevor (230 grid CBN) is rough enough that it isn't aesthetically pleasing as when the secondary is done with the Tormek. As a result, I'm now wondering about setting up a platform rest on the Rikon for roughing, the way Jan did back in January 2017 (https://forum.tormek.com/index.php/topic,3226.msg26866.html#msg26866).
Simple_drillbit_jig_2.jpg_thumb.png
Rick
Rick, I'm glad you've posted this. I've also used a bench grinder to start the process of cleaning up a badly damaged drill bit. I knew that I sometimes ground down past the area of hardening, but did not know about damaging the DBS jig.
Quote from: RichColvin on February 25, 2024, 01:31:45 AM...snip... I knew that I sometimes ground down past the area of hardening, but did not know about damaging the DBS jig.
Rich, I'm not clear on what you mean about going past the hardening. Drill bits I have are HSS and my assumption was they were not hardened, just equally hard throughout. I have wondered, however, what is up with "drill blanks", which as far as I can tell are some form of high quality steel but not HSS.
I was bummed to discover the damage as using the bench grinder was very effective.
Rick
I may be wrong, but it seems to me that bits which are much shorter (e.g., ¼" shorter) are not as hard as they were before grinding off that material. At least they need to be resharpened more often.
Quote from: RichColvin on February 25, 2024, 04:45:24 PMI may be wrong, but it seems to me that bits which are much shorter (e.g., ¼" shorter) are not as hard as they were before grinding off that material. At least they need to be resharpened more often.
Well, I'll be... I think you're on to something...
Machinery's Handbook...
Hardening High Speed Steel MH.jpg
I am surprised that a manufacturer, at least of high quality drills, would only heat treat the tips. It does not surprise me that "import" drills may only be tip hardened. While searching in Machinery's Handbook, I found a bit about testing a material for "hardenability", where they heat just the end of a standardized test piece and test it incrementally along its length for hardness levels.
I have to admit, that I haven't had to remove much from the points of drills to have experienced this. On those that I have shortened, I guess I haven't used them enough to find out they dull more easily. OR... All my drills are USA made, Precision Twist Drill brand, so maybe they are full length hardened. Now that I am aware of this hardening aspect, I'll pay more attention.
I've often wondered how they put the "twist" in twist drills. Must be a forging type thing where they heat them to a formable condition, do the twisting, let them cool and then do the grinding functions.
Rick
To beat a dead horse...
Not all drills are HSS (or better, such as cobalt HSS), some ARE made from carbon steel and hardened.
Types of Steel for Drill Bits.JPG
Drill bits remind me of the old John Wayne movie title, "They Were Expendable". As a career telephone man, I worked with drill bits all the time, and, like most of us, frequently abused them. I suspect that abuse is why they seem to need more frequent sharpening and wear down quickly.
Ken
Quote from: Ken S on February 25, 2024, 08:06:05 PMDrill bits remind me of the old John Wayne movie title, "They Were Expendable". As a career telephone man, I worked with drill bits all the time, and, like most of us, frequently abused them. I suspect that abuse is why they seem to need more frequent sharpening and wear down quickly.
Ken
No doubt abuse will cause any tool to wear out or fail prematurely. I think Rich's point was that in normal, non-abusive use (which I'm sure he always practices) a drill bit hardened at the tip will wear and not dull longer than a drill that has been shortened past the area that was hardened.
I think it remains unclear whether the drill bits he is using and having this happen were hardened only near the point and thus are prone to dulling more quickly when shortened. I don't know how one would determine that.
Rick
I have a mish-mash of drill bits which have come from many sources, including inheritance from my dad (who loved Harbor Freight). As I replace them, I but good quality ones from McMaster-Carr.
Rich,
You would like Leonard Lee's advice on sharpening drill bits. For most users, he recommended buying quality US made hss bits.
Ken
I'm at the point where I have complete sets of Imperial, number and letter sizes, and metric bits. If I break a bit, it is usually one which I use often, so I replace it with a well-made one (and buy a 2d for a backup).