I have been noticing that except for a couple places there isn't as much available in 5/16 as 1/4. I was wondering about that since so many cheap mini lathes come setup for 5/16 now. Then I realized, they all want you to spring for a quick change tool post kit right away. A quick change tool post is definitely in the immediate future for me (or some custom tool holders made on the mill), but when the lathe arrived I just wanted to cut something. I wonder if that is marketing or if there is some other reason.
(Yes I know. Grind your own and don't worry about it, but I wanted some good standards to cut to match from since I don't have one of those fancy grinding/sharpening machines.)
I believe there were at least a couple of dealers selling the 8-piece 5/16" pre-ground sets, not long ago.. if that's what you're referring to.
I guess too many mini-lathe users are trying to struggle along with brazed carbide or inserts, and the pre-ground 5/16 HSS weren't popular enough to keep in stock. The pre-ground HSS sets have a couple of cutting tools that wouldn't be easily made. They were offset/dogleg in shape, as ground from a larger piece of HSS.. not an extremely difficult task, but time consuming.
The 8-piece 1/4" HSS sets, such as those sold by Walden Specialties would be suitable for use wih a mini-lathe, but they end up being too low to the cenerline. Instead of fuzing around with a bunch of shims, a friend showed me how to make a few "adapters" that allow the cutting tools to be height adjustable.
By taking an appropriately sized section of square stock, and milling a ramped slot in it, this allows for some height adjustment of the cutting tool. When I got my 9x20 lathe, I made a set of three of the gizmos, each with a different taper in the bottom of the trough. I had 2 sets for 5/16" and 3/8" for my other lathe.
I've emailed Walden and LMS to see if they have any of the 5/16" sets.
For hand grinding blanks, you might want to consider a small project for holding the blanks while you grind. I've found them to be very worthwhile.
One very handy accessory that can be made for a lathe, is a boring bar holder. They're versatile for holding boring bars made from worn out taps or reamers.
Or even a bench type belt sander with a correct belt. If you have the belt/disk combo sander you can get fine grit disks at most auto supply stores that sell body working supplies that will put a mirror finish and razor edge on the tool after roughing on the belt. FWIW even tools directly from the belt sander are perfectly acceptable.
For a hand honed edge without the hassle, get a blue nylon abrasive bristle brush for your drill press. Hardware store ones will have a 1/4 shank. A quick pass is all that is required.
Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).
---------------------------------------------------------------- Bob A 'fancy grinding/sharpening machine' may be nice to have/use but is _not_ required . For the basics of 'How To' take a look at the following Sherline URL.
I started with a Sherline (still got/use it) and found the Sherline site to be a wellspring of information. When I moved up to an 11" Logan the majority of what I learned from them was aplicable(sp), including grinding my own HSS tools.
I used an "American" or rocker style tool post and Enco's "Armstrong" type bit holders for years. until I found a cheap second-hand quick- change one. They work fine, they are just slow to adjust. The tool post was one of my first projects. I made it out of a large bolt.
You can grind HSS bits to the same shape as brazed carbide bits or triangular inserts, with the tip rounded a little more. Really the horizontal profile doesn't matter much as long as it cuts a chip. The angle on the end of a new HSS bit is about right for the vertical relief angle below the cutting edge, though you can get away with much less.
An ancient bench grinder with the original generic wheels about half wore out, and one dressed down square.
Actually I am looking at setting up a chuck for a 3" diamond wheel on my lathe, and using a Wilton style 3 axis vise mounted on a slide to get the same results as a fancy sharpener for a fraction of the cost.
not on this computer, I have a photo of grinding a threading bit to the correct angles in a fully articulated Univise on my surface grinder, but I grind all normal HSS turning bits by hand on a cheap 6" bench grinder I bought at a yard sale. They simply aren't worth the trouble to set up a fixture for the front rake, then the side rake and finally the top rake each time I want to touch up the edges. The bits were all ground differently to solve some new problem and the angles aren't written on them, so I'd have to carefully measure them first.
Besides, the acceptable tolerances are huge. You really could take a new bit, grind the bevel on the end for a few seconds to sharpen the top edge and start cutting with it. If you ground a similar bevel for a short distance along the left side of the end it would work pretty well to turn a cylinder. Tighten the angle between the left and end cutting edges somewhat, say to 80 degrees, and it will cut up to a square shoulder and then face it.
It's difficult to grind an edge lengthwise along the bit, like the AR holder:
The easy alternative is to grind off both corners to make a spear point, like the BR or E, and rotate the bit in the tool post. As long as the angle between the cutting edges is less than 90 degrees it can cut up to a shoulder in both directions, parallel to the ways and straight out.
These were all ground freehand:
roughed out the discolored one with a 7" angle grinder and you can see the finish it left on the narrowed shank. I cleaned up the smaller internal threading bit with a 1" belt sander, for my resume kit.
The round-nosed one at the top was the traditional shape of forged carbon steel tools for general turning. That one makes half-round pulley grooves. The one under it rounds the end of freshly cut threads with the left end and digs most of the metal out of deep narrow grooves with the 30 degree point on the right. I ground the concave surface with a slightly tapered stone in a die grinder.
Notice that the rounded bits have flat tops. Top rake makes a bit cut better but it is NOT essential, and is generally left off formed shapes like those to preserve their geometry.
Probably the hardest part of freehand grinding is judging the angle of the steel against the wheel. I set the bit the way I want by pressing it against the motor housing and then shift over to the wheel with my legs, so my arms don't move. I let the bit float a little to keep the whole surface in contact and get a hollow grind that's easier to touch up with a whetstone.
I found free-hand grinding, especially of the 1/4" bits which I use exclusively, a "bit" too much. None of the bench grinders that I looked here came with a decently adjustable tool-rest, except the DeWalt.
I spent $50 on the Veritas adjustable tool rest. I liked it so much that I bought another one for the second grinder.
The other big help was clamping the bits in the Taig toolpost to hold them.
Have you ever read my long post on grinding HSS tool bits?
All you need is a (proper) grinding wheel with a protective shroud. I don't even recommend a work rest, which is nothing but in the way.
Understand that the wheel commonly found on pedestal or bench grinders is not even remotely suited for grinding HSS. Also, pay close attention to this. Ed Huntress, long ago, expounded on the use of green silicon carbide grinding wheels for HSS, saying they serve quite well. What he failed to mention is the fact that silicon carbide dissolves in ferrous alloys at high temperature (like when you grind), dulling the abrasive rapidly. The dulling, of course, causes the wheel to slough off quickly, constantly exposing fresh grain, which, in turn, is also rapidly dulled by dissolution. The net result is a poor wheel life, and a life threatening cloud of silicon that can be devastating.
Choose the correct grade of aluminum oxide, along with a desirable size of abrasive and wheel hardness and you can grind HSS almost effortlessly.
Bad idea. Diamond is NOT an acceptable grinding media for steels unless it is applied at low speed, so no red heat is created. If you are hell bent on doing what you suggest, you should shift your attention to a CBN wheel. Further, I suggest you lose the idea of grinding on a lathe. The swarf created is very damaging to the machine. It's fine and gets under wipers, where it accelerates wear.
Best of all, read about off-hand grinding HSS tool bits using a proper aluminum oxide wheel. It takes a little effort up front, but once mastered, you are set for life. You will never be free until you have mastered the art.