Machinist

[Lawrence London <lfljvenaura@gmail.com>]

THREADING WITH HLV-H  |  Is the HLV-H the only threading mechanism of his kind?
http://www.practicalmachinist.com/vb/general/hlv-h-only-threading-mechanism-his-kind-336896/

He's saying he prefers to keep the halfnut engaged and just reverse the spindle. Good accurate method on a toolroom lathe or an oldtime conehead, not so much on a gearhead. An HLV has a stop collar that kicks the feed out of gear when you reach it. I never cared for it because if you hadn't already made a thread relief it finished the thread with a complete revolution of the threading tool--in other words, a stress concentration.

On a Hardinge there's a lever that reverses the acme drive screw to return the carriage to the start, the spindle never reverses, the halfnut never has to be disengaged. Hand cam lever on the compound retracts the tool and then back into position in one shot.


It's hands down the fastest threading manual lathe I've ever threaded on.

He's saying he prefers to keep the halfnut engaged and just reverse the spindle. Good accurate method on a toolroom lathe or an oldtime conehead, not so much on a gearhead.

Some situations call for this method, cutting metric threads on an inch machine for instance, or, if the machine does not have a thread dial. I ran a machine once where the half nut linkage was really sloppy from damage or wear, so I decided leaving it engaged was safest to get the job done. But I don't see a point it doing this as a matter of course. It's painfully slow, and offers no advantage other than working around the obstacles mentioned above.
On the other hand, the threading feature that Hardinge uses is pretty slick. As mentioned, the spindle does not need to be stopped and reversed. I know I've heard of other companies using a similar idea, Rivett maybe??? This is still only practical on very shot threads.
I can reverse the lead screw on my Reed Prentice from the apron, same for some other lathes I've run, but I'm not sure if it will pick the thread up just or start anywhere. I usually just use the dial.
I've done a lot of threading on a Bullard VTL. They used a single tooth clutch design on their threading attachments so the feed can be disengaged and reengaged without the use of any type of thread dial.

Any true toolroom lathe has a single tooth dog clutch and reverse to the leadscrew on the apron. Hendey also used it, and I have seen LeBlond, L&S, American Pacemaker, R&P and the 16" Sidney at work has it. Ignore the thread dial. Go to the end, the stop will kick out the leadscrew. Reverse the leadscrew at the cariage to back up to the start, engage fwd again and off you go. Great on short threading. Long threads, dial is faster.

Forgot to add P&W...

The Cincy made Pacemaker, L&S and Sidney lathes don't have the lever retract, but they have a ball stop on the cross slide that performs the same function. Zero the tool on the work and set the stop. Now, feed with the compound and the cross slide can be retracted three full turns, then go back to the stop and take the next cut.