Jim Wilkins wrote:
On Aug 21, 4:11 pm, (DoN. Nichols) wrote:

...
And 4130 is *far* from "free machining S1214" (which is probably
a version of one of the LedLoy alloys above).
...
Enjoy,
DoN.


Speaking of 4130...
I have a sample pack of 4130 N tube & rod from Aircraft Spruce to play
with, ie practice threading and TIG welding. The lathe is old & worn
and I have trouble with carbide chipping, so I'll likely machine it
with HSS and brushed-on cutting oil. Any advice?

jw


Yup! Espescially if the carbide tools were of the brazed variety.

My advice is this. "It's about bloody time!"

High speed steel works very well, and is quite forgiving. The carbide
(brazed) tools can save your butt when you have a bit of work hardened
stainless to deal with, or similar, but generally need to be ground to
get decent performance out of them. Grinding a decent edge onto brazed
carbide is tougher than getting a decent edge on HSS, IMO, and requires
a far larger investment in wheels for the grinder as well.

Take a good look at the thread form diagrams for the threads you are
cutting. More like than not, there is supposed to be a flat on the tip
of the tool. This flat makes the thread turn out the correct shape, and
makes the tool even tougher to destroy. Both good things!

Get a decent magnifying glass to look at your tool tip with! A good
quality thread gage is a real boon too! Cheap thread gages are mostly
punch-cut or sheared, and have ****ty edges to compare to. Tough to get
a nice clean, straight line when you don't have a decent straight side
on the gage. Good thread gages are pretty cheap, and they don't wear
very fast.

One of the things I show guys in my shop, is to grind a long straight
30 degree line from the front left corner of the tool blank. The 30
degree grind in the other direction then is a very short, easy touch
against the wheel. It makes it quite simple to cut up to a shoulder,
when you do not have to grind a great bloody hack out of the bit to
clear it. It also makes for a very fast return to working after a crash,
as most of the tooth form is there already.

I have, on occasion, ground threading tools using one of the existing
straight sides of the tool bit (just add some releif) and a 60 degree
grind across the end. It has to sit at 30 degrees (tool bit is aligned
with the compound, rather than at 90 deg to the axis of the work), but
works fine.

Sharp sharp sharp! Sharp tools cut well!

Cheers
Trevor Jones