In article ,
Jacek Zagaja jzagaja-at-poczta.onet.pl wrote:

Gentelman,

Sorry if my writings are little clumsy. Metalworking is new for me
especially in English

I'm trying to achieve plain (smooth) alloy after turning threads. I've
made special knife with carbon plate so that I can cut as near side as
possible. The problems is in surface quality. My alloy is 2H13 (0.2 C
and 13% Cr and maybe small amount of Ni). Is it possible to get good
surface without polishing?

O.K. Let me see whether I understand you properly -- and offer
some terminology in English in the process.

Given the fact that you *can* communicate in my language, and do
a rather good job of it, but I cannot communicate in yours, that shows
that you are *interested* in communicating. I do have at least one
other language, but not yours, unfortunately.

"special knife" -- threading tool?

For most applications, you don't want to use carbon steel for the task,
but rather at a minimum, HSS (High Speed Steel), or for some alloys,
(tungsten-)carbide inserts. Carbon steel can work with care with mild
steel, but I think that your alloy, with 13% Cr would be rather tough,
and would rapidly dull the carbon steel. For that, I would prefer to
use the special carbide inserts in the proper shank (holding tool) for
the threads which you wish to cut.

Note that the size of the lathe, and the rigidity and power will
determine whether you can use carbide tooling to get a better finish.
Your "2H13" appears to be one of the European steel designations, and I
am not familiar with it. But 13% Cr would probably make that a rather
tough steel. Perhaps Ed Huntress could pop up with a close equivalent
in US steel grades?

It may even be that it would be better to grind the threads
instead of to try to cut them -- but this will require a rather
expensive setup.

Are you doing this as a hobby, or are you in a commercial
machine shop? The tools which would be standard in such a commercial
shop are less likely to be found in a home shop for hobby use.

You'll find mostly hobby metalworkers here -- though there are
some who do it as a job. We really need to know some things about the
task and the equipment. How big a lathe? What thread diameter and
pitch? (I would expect them in metric units given your e-mail address.)

As an indication of the sizes of lathes, Mine is an old Clausing
which will swing 12" (300 mm) diameter over the bed, and somewhat
smaller (at least 6" (150 mm) over the carriage. I consider this on the
large end of hobby lathes, though there are others here with larger
machines. Mine is sufficiently rigid to be happy with carbide tooling
and reasonably tough jobs.

Carbide tools can give a smoother surface to the cut, but they
often require higher speeds and more rigidity from the lathe than
equivalent HSS tooling can.

Carbon steel requires *much* slower speeds or the tool overheats
and looses its temper.

Good Luck,
DoN.
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