Building Harold Hall's Simple Grinding Rest

[pontiac428]

If you don't mind me continuing to post in your thread, I managed to find a way to cut a quartered single flute (I think). I'll heat treat this W2 blank countersink and give it a shot grinding with the setup as shown. If this works, I can grind all of the other surfaces of the tool to finished size... and make 20 more to cover the included angles that I am missing.

 

[stioc]

Nice! I don't mind at all...post as much grinding related stuff here as you (or anyone else) would like.
May be we should have a thread called "GOTD - Grinding of the Day thread"

 

[pontiac428]

Success! While not what I would consider a precision piece, it will work. I'm going to have to churn out a few more if these.

If I'm to pursue tool making, even at a putterer's pace, it's going to take a bigger, more capable grinder. Probably one that runs coolant. Hmm, maybe not right away.

 

[stioc]

Woah! that's a great looking countersink, looks like the real deal. So I have a question, how did you cut that curved drill-bit like flute?

 

[pontiac428]

The curve comes from the intersection of two cylinders. The grinding wheel is a cylinder, and the tool is a cylinder (in its primitive form). It's only one cut, the plunge of the dressed face of the wheel to make the cutting edge. The back side of the cut is whatever is left over from the procedure, which is a curve in this case. It looks neat. I could cut a second flute on the opposite side, but I think it would defeat the purpose (low chatter and good centering tendency) of a single quarter-cut flute. Anyway, now that I've got the bugs worked out, I would like to try to make some more angles in this 1/2" size and order up some 3/4" steel to make some larger ones.

 

[stioc]

Ahhh! I see it now, it does look neat. What steel are you making these out of?

As an aside I personally like zero flute countersinks because, for me anyway, they don't create any chatter at all.

 

[mattthemuppet2]

how did you get the relief behind the cutting edge of your countersink? I thought that single flute countersinks were ground using a cam based set up to provide back relief for the cutting edge that went the whole way round the tool

 

[pontiac428]

how did you get the relief behind the cutting edge of your countersink? I thought that single flute countersinks were ground using a cam based set up to provide back relief for the cutting edge that went the whole way round the tool

I used W1 water-hardening tool steel.

I used a single-facet design. The cutting edge is ground by first indexing the cutting flute to the horizon, then setting 15 degrees of lead into the spindexing head. The work is moved toward the wheel just enough to make a small flat. Then the work is rotated another 15 degrees, the work is infed into the wheel about .015" (the back relief), and rotated through the remaining 240 degrees of the cone.

I made a craptacular drawing below using paint, because that's all I have on this computer.

 

[bikr7549]

Hello, new member here. I have purchased Harold's book and plan to start making the simple grinding rest but have the same ball material question asked early on, what type of plastic is used for the ball? McMaster has nylon and delrin in the 1" size, not expensive but I want to get the right one. Any suggestions? Do not have a ball turning fixture, yet.

Thanks,
Bob

PS, Harold is not accepting correspondence. Not sure how recent that is but I just looked at his website (was planning to ask him my question) and saw that he has stopped writing.

 

[Technical Ted]

For this application, I don't see where it would make much difference between the two... Delrin might machine a little nicer.

I made mine out of steel with my home made radius cutter (ball turner) and it works fine.

As I have posted on this site previously, I made both the advanced and simple fixtures and between the two, the advanced is much better hands down. Much easier/quicker to setup at the required compound grinding angles.

Ted