Thread cutting on the lathe by hand crank

[19brendan81]

Hi guys,

I was reading one of Anorak Bobs threads where he mentioned threading on the lathe using a crank and no power. How does one go about doing this? What speed do you have the lathe in to make it easiest to turn? Do you put the crank on the leadscrew or in the spindle? Seems like a good way for doing very fine threads.

Brendan

[welder]

Not 100% sure but I think you put the lathe in neutral and turn the spindle. I thought a crank handle was a great idea and am half way through making one.

[pipeclay]

At a guess with never doing it this way,I would think you would have the lathe/headstock in neutral/belts disengaged.

Your method of rotating the spindle would be attached to the spindle.

Your gear train would be set to the desired pitch/tpi.

Your gear train would be attached to your spndle drive gear/stud,as per the normal method of screw cutting.

There would be no logical reason to have the lathe set to any spindle speed,you would want the less resistance possable when rotateing the spindle by hand.

[Ueee]

Hi Brendan,
I pretty sure BT uses carbide threading tools, and maybe a comment from him would clarify, but i would use HSS if turning by hand. As we all know, carbide doesn't like being stopped in a cut and i don't know whether the unevenness and speed of hand turning would risk breaking a carbide tip off.
Somewhere i read about turning the leadscrew by hand or powered for doing really big pitch threads, as the gearbox/geartrain effectively gears down the speed of the spindle.

[Dave J]

You can chip HSS as well, but carbide chips easier.
If your having trouble threading to a shoulder you can shape your HSS threading tool like the picture below to give you more room.

Dave

[19brendan81]

How does one attach a crank to the spindle to turn it?

I havent done a lot of threading to a shoulder, but should the need arise I would like to know how to tackle it.

Thanks for the pic dave - I ground up one like that the other day for a job I was doing.

[Big Shed]

This is still on my "todo" list, but basically you make an expanding mandrel that fits inside the spindle and expands by turning a nut.

See here, about 2/3 down the page

9x20 Lathe Modifications - Stellar Technologies International

THere are also 3 different versions on this page

http://www.toolsandmods.com/library/ralph-patterson

[Anorak Bob]

Hi Brendan,
I pretty sure BT uses carbide threading tools, and maybe a comment from him would clarify, but i would use HSS if turning by hand. As we all know, carbide doesn't like being stopped in a cut and i don't know whether the unevenness and speed of hand turning would risk breaking a carbide tip off.
Somewhere i read about turning the leadscrew by hand or powered for doing really big pitch threads, as the gearbox/geartrain effectively gears down the speed of the spindle.

I do use carbide simply because I'm lazy. The inserts I use are not capable of cutting large threads, say 1 1/2" x 8 but for most small stuff they have proven satisfactory. I use HHS for internal threading.

I have the belts loose and I don't use back gear. Here is a link to some photos of the crank and expanding mandrel I insert into the spindle. I have mentioned this before, having a removable handle sure beats a fixed handle.

https://www.woodworkforums.com/f65/th...2/#post1496597

BT

[scottyd]

How does one attach a crank to the spindle to turn it?

I havent done a lot of threading to a shoulder, but should the need arise I would like to know how to tackle it.

Thanks for the pic dave - I ground up one like that the other day for a job I was doing.

Ive done it before on a geared head 260. I was cutting a 45 x 4.5 for four revolutions up to a shoulder. I put it in the fastest gear and switched the machine off and unplugged it (so if i accidentally bumped the power, it wouldnt go to hell in a hand basket!), which made it pretty manageable to rotate just using the chuck key. I was cutting 2011 alu though, a fair bit easier to do than most steels...ymmv.

For what its worth, to make it easier to cut such a large thread by hand, I cut it in three stages of depth. After I went in 1.5mm on the compound @ 20º, I returned to the start point and moved in with the cross slide some to begin cutting again. Only when I got to the end of the third stage did I bring the "multi start" thread back into one. Much easier on tooling, not to mention your arms when youre hand cranking!