Good info, but don't skip over the business about micrograin carbides working better with less-rigid lathes. Traditional C-2 and C-6 can't hold a candle to some of the micrograins that are actually used for
*high-positive-rake* milling in commercial work.
There was, as of three or four years ago, a real shortage of quality micrograin carbides in shapes and sizes appropriate for small lathes. I don't know the situation now. But the materials have impact strength and chipping resistance that traditional carbides can't match. And they can take a *very* sharp edge.
It's a 1965 South Bend 10L, leather belt and threaded spindle, from a trade school where it was mistreated. The 40-position Multifix tool post is very nice with hand-ground HSS bits but I haven't seen any dedicated carbide toolholders for it.
HSS has been fine for my home projects, which are usually made from aluminum, cast & malleable iron, mild steel, drill rod, 12L14 and 303 stainless. I want to understand carbide better for when I use larger modern machines on 4140 and 4XX stainless in clients' model shops.
You can cut either 4140 or stainless with HSS quite successfully. In fact it was the common job shop method of machining nearly all metals up to the 1970's when I left the business. And probably still is in the smaller shops today. Bruce-in-Bangkok (correct Address is bpaige125atgmaildotcom)
O.K. So you need to get the standard shank insert holders. What size can your toolpost's holders accept? My BXA can handle up to
5/8" shanks, and I started using left and right shanked insert holders for negative rake in those. I got a pair of straight ahead (that is 30 degree angle on each side) holders from a eBay auction with 100 inserts per holder, and those work in the BXA-16N -- but the newer TiN coated ones which I listed work a bit better for heavy cutting.
Note that the shanked holders from eBay were actually 3/4" instead of 5/8", so I had to mill 1/8" off of the bottom (*not* the top, so you keep the cutting point height level with the top of the shank).
Your 10L should be sturdy enough -- perhaps for the AXA size tools instead, which means that the inserts would probably drop to 222 or 221 size in the TNMB style. Isn't the 10L also called the "Heavy
10"?
O.K. I've used (or abused) carbide inserts on hardened tools, including the flange of a CAT-30 tool holder to convince it to work in a quick-change holder for NTMB-30 end mill holders. I was amazed that the carbide could handle that with no apparent problems.
Yes, it's a lower version of the 13" lathe rather than a higher 9". This one has worn dovetails so it's a bit loose in the normal work area and very snug at the ends. It's problems may be typical of old lathes, which is why I'm asking here.
O.K. Then you can go with the 3/4" high tool shanks at a minimum. Not quite 7/8" -- but I think that the next size up from 3/4" is 1" anyway. It sounds as though yours was made to metric dimensions,
20mm plus a bit of spare. :-)
Anyway -- the largest shank you can get to fit is the best to use.
Hmm ... the cross-slide and/or compound dovetails worn? Perhaps it is time to redo those dovetails before working with carbide -- or tighten the gibs to work only in the worn center area perhaps while using carbide.
Of course. I thought you were saying that you were going to add carbide tooling so that you could machine 4140 and/or stainless. I was just saying that you could machine both materials with (what I thought) would be the added cost of the carbide tooling.
Bruce-in-Bangkok (correct Address is bpaige125atgmaildotcom)
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