Threading hand crank for metal lathe

[lign]

Hi folks,
I keep seeing mentions of a handcrank for threading on the metal lathes. I see this mentioned even for lathes that run at 60 rpm. Does one open up the gear access door and attach this directly to the back of the spindle like the first pic, or does one attach it to the far end of the threaded drive rod like the second and third pics

As I mentioned in another thread, I'm about to get a metal lathe for multi-lead threading.

Thanks for any help!

 

[lorbay]

Mine attaches the same as the third pic. Infact I have that same lathe, not done any treading on it yet.

Lin.

 

[hilltopper46]

Like the first pic. My guess is the other two pics either do not have a geared (powered) lead screw or the manufacturer provides that crank for the convenience of a slow speed 'manual' feed.

Trying to thread with the crank on the lead screw whoud be like trying tio wag the dog by the tail. the negative mechanical advantage through the gearing would be so great that you likely would not be able to turn the drive spindle

 

[lign]

That makes sense. So is there any easy way to do this? All the ones I find mentioned on the internet seem to involve pretty complicated creation of an expanding rod that goes into the spindle, kind of like some of the closed-end mandrels I've seen. I'm looking at the 7x16 Micromark or 9x20 Grizzly.

Also, any comments on the feasibility of cutting the 3 or 4 lead threads at 50-60 rpm right up to a shoulder?

 

[Texatdurango]

There is a way to keep from spending ANY money!

When I have a blank chucked up and want to cut some threads, usually 3/8" or shorter for either the inside of a pen cap or outside of a lower barrel, I will quite often just grab the chuck and turn it a few times by hand which will give me ALL the control I want and I don't have to worry about turning the threads too far.

 

[lign]

Aha, I see. I was under the impression that you needed a crank to get enough torque. So for small threads in soft stuff, turning by hand is no problem? How about making a tap of something not-too-hard for the inside of caps - say brass or mild steel. Still turnable by hand? Obviously I wouldn't do it that way all the time, but to make a few taps would this work?

 

[Texatdurango]

The reason I hand turn the chuck is to have exact control over where the cutter stops on the blank. Making taps isn't that precise so could just be turned on a slower feed/speed setting.

 

[lign]

George, thanks for the info. Control is definitely the reason why I'm discussing the crank or turning by hand. Have you had any issues with using your Grizzly 9x19 for multi-start threading? I was leaning toward the 7x16 Micromark because I was afraid the 9x19 would not run slow enough for threading pens, which is the main reason for my purchase. For threading pens, do you just run it at its lowest speed and then shut it off when you're close to the end and finish it by hand? Does the lack of reverse ever effect you, or does that only matter for left hand threads?

I've eliminated the Grizzly 10x22 from consideration because belt speed changes are much more laborious than on the 9x19.

 

[Chuck Key]

Does one open up the gear access door and attach this directly to the back of the spindle like the first pic, or does one attach it to the far end of the threaded drive rod like the second and third pics

I like using the lead screw as in the third picture but attach the crank (ratchet wrench) at the head stock (spindle) end.

Like this: http://forum.penturners.org/forum/showpost.php?p=1001940&postcount=16

 

[holmqer]

Like the first pic. My guess is the other two pics either do not have a geared (powered) lead screw or the manufacturer provides that crank for the convenience of a slow speed 'manual' feed.

Trying to thread with the crank on the lead screw whoud be like trying tio wag the dog by the tail. the negative mechanical advantage through the gearing would be so great that you likely would not be able to turn the drive spindle

Wouldn't this really depend on the pitch of the leadscrew and the pitch of the thread being cut?

If you wanted to cut a coarser pitch then the leadscrew, wouldn't the crank there make sense? This would probably occur for pens if you were making a multi start thread.

 

[hilltopper46]

Like the first pic. My guess is the other two pics either do not have a geared (powered) lead screw or the manufacturer provides that crank for the convenience of a slow speed 'manual' feed.

Trying to thread with the crank on the lead screw would be like trying to wag the dog by the tail. the negative mechanical advantage through the gearing would be so great that you likely would not be able to turn the drive spindle

Wouldn't this really depend on the pitch of the leadscrew and the pitch of the thread being cut?

If you wanted to cut a coarser pitch then the leadscrew, wouldn't the crank there make sense? This would probably occur for pens if you were making a multi start thread.

Good point, I'm thinking of 'regular' machining with a small increment per revolution. However, you are trying to drive whatever it is you are threading against the bit, and in my cheapo chinese lathe, the threading gears aren't very robust. I would be very leery of driving the spindle through them. Your mileage may vary.

 

[workinforwood]

I don't have a crank handle yet, but I would prefer the crank handle on the end of the leadscrew because it is closer to the operator, easier to turn being right handed and because it's off to the right, you can see where your threads are at. Being in the gear house is pretty far away from where the work is actually happening and you are working blind in my opinion. On a mini lathe, it probably wouldn't make much difference either way.

 

[rherrell]

Give this guy a call..... http://www.tallgrasstools.com/SpindleCrank.html

He custom made me one and I couldn't be happier with it!:biggrin:

 

[randyrls]

That makes sense. So is there any easy way to do this? All the ones I find mentioned on the internet seem to involve pretty complicated creation of an expanding rod that goes into the spindle, kind of like some of the closed-end mandrels I've seen. I'm looking at the 7x16 Micromark or 9x20 Grizzly.

Also, any comments on the feasibility of cutting the 3 or 4 lead threads at 50-60 rpm right up to a shoulder?

Dave; Don't do it! It is possible to run this way, but far more likely that the tool will reach the end of the thread and dig in, breaking your blank. Manually cut threads have a "relief groove" at the thread shoulder. The tool runs into the groove and you stop the lathe. CNC cut threads don't require this as the CNC machine will stop at precisely the same point every time. Bolts don't have the groove because they are "hot rolled".

When cutting up to a shoulder, there is a special tool bit used called a "half threading tool" (??) If a threading tool looks like "/\" a half threading tool looks like "|\" I've never used such a tool, just have heard it mentioned and talked about.

I have a variable speed Direct Current Drive on my 9x20 and can go down to about 10 RPM with good torque, but would try this out on a scrap piece first.

 

[lign]

Randy,
I've looked at several fountain pens, both kit and regular and they all seem to be threaded right up to a shoulder, with no groove since I'm sure they're all CNC.

Can you give me some info on how you made your 9x20 into VS? I've looked at this briefly online, but it looks like a tremendous amount of work and skill would be involved? That sounds like EXACTLY what I want if it can do 10 RPM.

 

[lign]

Maybe I'm over-analyzing this decision between the 7x16 lathe and 9x20 lathe. I wonder how many of you cut the 3-start threads directly onto your pens right on the lathe using a hand-crank, and how many of you do it with your home-made taps and dies. I assume your dies can cut right up to the shoulder and that you don't relieve the threads as much as factory dies for ease of starting?