Grinding

It's just amazing how Mary Ellen always knows what to get me for birthday or Christmas gifts. Of course, "get" is a relative term. She "gets" it, but I choose it, buy it, have it shipped or pick it up, etc... This one, I told her to not even bother wrapping it!

It's a low speed (1725 RPM) grinder with 8 inch wheels. The wheels are aluminum oxide, which sharpens quickly without overheating the work. The one on the right is 60 grit, and the left one is 120. Nice machine, and not too expensive on sale at Woodcraft, but like nearly all such machines, the included tool rests (not mounted in the picture above) are not very good. Thus, I set out to make some better ones.

I wanted the mounts to be very adjustable, so I decided on a design with slotted arms. I used some metal from an old garage door. It already had several holes for mounting - I just needed to "connect the dots." My first attempt was to just mill the slots, the way I would in woodworking using a router:

It worked, but it was clear the mill didn't enjoy it - lots of vibration, even with small cuts. So, I tried another technique called "chain drilling." Several holes, so you don't have to go so far with each cut. After drilling, I used the mill as before, but with a deeper cut. That worked better, although it was still hard on the milling machine. Here's the chain drilling in process:

I completed the task that way, and then learned what I should have done. I should have drilled or milled a starting hole straight through the piece, and then "nibbled" my way along, moving only about 50 thousandths for each nibble. I learned that from a very fine teacher on YouTube named Tom Griffin, who also has a supporting website at http://tomstechniques.com/.  Anyway, here are the finished side supports for two tools rests:

Once that was done, I needed to make four identical support pieces. That was a good learning experience, to try to get them exactly the same size. Two support pieces per tool rest, with the top one supporting the small table that's the actual surface the tool rests on, and the bottom one giving adjustment via the slots in the brackets.

Once the pieces were made, I drilled and tapped holes for the side brackets and the top rest, and drilled other holes to mount the bottom support. How do you like my "bent bolt" work stop? There are some really neat designs out there for that sort of thing, and I'm sure I'll eventually make a real official one. Incidentally, I'm not tapping under power. I turned it by hand (with the chuck key inserted for leverage) until I had 3-4 turns completed, and then removed the part and completed the tapping by hand with the work held in a vise.

Once all that was done, I put it all together and had something that worked pretty nicely!

The whole point of having this matched pair is so that I can adjust them to the same angle, and then move from the coarse wheel to the fine wheel, and continue at the same angle. I found a tip in a British magazine to use a digital angle guide to set those angles - a nice reuse of a tool I had bought previously to set my table saw blade to exact angles:

So, why am I going to all this trouble? It's because there are times in both woodworking and in metalworking where you want to grind a chisel or tool bit to a precise angle. My immediate application was for a metalworking tool called a "fly cutter." Tom Griffin's instruction was invaluable there too, because he has a long video demonstrating how to use it, and in the reference section of his website he has a precise drawing of how to grind the bits. When you buy the tool, it comes without the angles ground, because different materials require different angles.

It's kind of hard to understand all those angles - a fly cutter bit has three different ones at the tip, and I still haven't quite figured out the nomenclature. But, with Tom's drawing printed out, I could put my tool bit on top of the picture, and decide what to grind and where. Here's an unfortunately blurry picture of my very first tool bit ever:

Once I accomplished that, I mounted the bit in its holder, and mounted that in the mill. I was kind of apprehensive about spinning up that little helicopter, but it spun without mishap:

Finally, I was ready for a test cut. You don't want to take a big bite - I limited my cut to only 0.005".  That's five thousandths, for those of you who have flushed all the math. Here's a picture of the cut in process. You can see how the cutter sweeps across the entire face of the workpiece at once:

After three passes (took that many to get it flat all the way across), look how fine the finish is!

That's very cool. For the sake of comparison, here's a block that I've spent an inordinate amount of time getting flat, square and shiny. I used a 3/4" end mill for those cuts. See the shiny lines? That is the point of overlap for each pass. It makes a very tiny ridge - you can barely feel it with your fingernail. 

Baby steps... if I can learn to reliably control size, finish and angle on this equipment, I can make some pretty cool stuff!