PDA

View Full Version : How to cut left hand thread on chinese lathe



ahidley
03-23-2009, 12:33 PM
How do you cut a left hand thread on a lathe that has power feed in only one direction?

Andrew_D
03-23-2009, 12:48 PM
You need to come up with a way to reverse the leadscrew relative to the spindle. Depending on the lathe you have, try and see if anybody else has done a mod like this before.

Typically, if there is an idler gear in the change gears driving the leadscrew, a reverser can be added. Try looking for mods to the 9x20 lathes. They don't come with a reversible leadscrew, so this is a mod that many make.

Why doesn't a 9x20 come with this option, when a lowly little 7x?? does have it??

Andrew

ClintonH
03-23-2009, 12:49 PM
I just went through this on my lathe as well. What type/size lathe is it? Any pictures of the change gear section? You will need to build a reverse tumbler for your setup, you can take a look at mine Here (http://www.flickr.com/photos/35549096@N07/sets/). It was just a quick setup, I'll be hobbing a gear with a press fit bearing sometime soon.

Andrew D beat me to it. :)

saltmine
03-23-2009, 04:58 PM
I donno. My little HF mini lathe has a reverse lever on the change gears, and the motor is reversable, with the switch.
I've got a 1"X 24 TPI small screw-jack on my cofee table that I made with both inside and external left-hand threads.
I made the screw-jack left hand thread to mess with people picking it up.
I've also got a right-hand thread #5 Acme thread jack that sits next to it.
The hardest part was accurately cutting the tool bit.

camdigger
03-23-2009, 05:37 PM
Strictly speaking, a tumbler gear is not necessary. The lead screw will be reversed by adding in another gear (if there is another stud available so that another gear can be put in the change gear train), or by taking two gears out of the train and substituting a larger gear. Doing this will not change the ratio, the ratio is dependent on the driving and driven gears only. The gears in the middle simply transfer motion (that's why they're called idlers;) ) UNLESS there are two gears mounted on the same shaft - one driven and the other driving the next gear in the train (that's how metric/English pitch translators work).

Really, all a tumbler reverse does is substitute one gear for a pair, depending on the position of the carrier. I think it's called a tumbler because the carrier typically has a spring loaded pin(tumbler) holding the carrier in position. If you were really dedicated, you could make your own reverser...

GKman
03-23-2009, 05:40 PM
Just thread it normally then turn the workpiece inside out. That's how I always do it.

loose nut
03-23-2009, 05:42 PM
Most 9 x 20's have an idler gear that is "somewhat" removable to do left hand threads but it's a clumsy bit of a lash up. Build the tumbler.

camdigger
03-23-2009, 05:43 PM
GK

Can you post a link to a youtube video of that? I'd like to see that!:D

I suppose we'd find it right next to the square hole drill video??

dp
03-23-2009, 05:47 PM
Most 9 x 20's have an idler gear that is "somewhat" removable to do left hand threads but it's a clumsy bit of a lash up. Build the tumbler.

Agreed - mine requires removal of the gear train to swap in the reverse gear. Definitely a nuisance.

rancherbill
03-23-2009, 06:34 PM
I suppose we'd find it right next to the square hole drill video??

Here's the bit. Just put the holder in your tailstock and away you go.
http://i294.photobucket.com/albums/mm100/rancherbill/squaredrill.png


Here the video (http://www.slatertools.com/video.htm) of the general process.

It is pretty neat how they do it.

Don't you hate it when the imaginary is a reality.

MaxxLagg
03-23-2009, 08:49 PM
http://bedair.org/9x20camlock/Micllef.html

or

http://www.bedair.org/Tumble/Tumble1.html
http://www.bedair.org/Tumble/Tumble2.html
http://www.bedair.org/Tumble/Tumble3.html

tattoomike68
03-24-2009, 12:02 AM
Here's the bit. Just put the holder in your tailstock and away you go.
http://i294.photobucket.com/albums/mm100/rancherbill/squaredrill.png


Here the video (http://www.slatertools.com/video.htm) of the general process.

It is pretty neat how they do it.

Don't you hate it when the imaginary is a reality.

Iv seen them work great is screw machines you can threadroll and rotary brooch stuff bullet fast. both at once if you tool up and have fat bucks or a wire edm.

great stuff.

Paul Alciatore
03-24-2009, 01:36 AM
I wound up purchasing a SB with tumbler reverse, but I did consider the import lathes. I have a copy of a internet post by someone named Jack F. that I saved during that process. It is a page of text with some pictures inserted. I'm not sure how good it is as I never built it. From a quick read, I believe he used the gears supplied with the lathe.

If you want it, send me a PM and I will e-mail it to you. I don't have the original web address and it may no longer be there anyway.

ClintonH
03-24-2009, 01:46 AM
Here's (http://www.gunsmith.fuselier.com/tumbler.html) the link that Paul has I think. If you gear train works like the 9x20 lathes that will work or the others posted. But if it is setup like my 10x18 you'll need to build something a little different.

ahidley
03-24-2009, 05:48 PM
OK I saw the pics. Thats great but. My intent was to be able to cut left hand threads. My lathe has a gear set up very simular to the 9x20 . When selecting what thread pitch I want to cut I have to change gears. The problem is I may have to change one or all the gears to achieve the correct feed. Thus to make a reverse work for a particular pitch I cannot just pick any gear, I must use 2 that have the same amount of teeth to reverse rotation and remain with the same feed.

I'll look closely at it this weekend......

Spin Doctor
03-24-2009, 06:48 PM
If there is no compound gearing (two gears of different #s of teeth on the same shaft) in the gear train then it does not matter how many gears are in between the first and last gear. All of the gears in the middle are simply idlers no matter how many teeth they have. A concept I had a really hard time trying to get apprentices to understand sometimes.

BadDog
03-24-2009, 08:28 PM
Yep. The only gears that matter for ratio are the first and last (drive and driven - hard mounted to shaft, no bearing) or translating gears (stacked, 2 turning together; one drive, the other driven).

WilliamG
10-27-2009, 01:55 PM
Interested in how you modified or attached the 'change gear support' to add the reverse tumbler. Any clear photos of this?

Bill

CountZero
10-27-2009, 02:42 PM
If you are referring to ClintonH's modification I think it is an extra 'arm' welded in place holding the extra idler gear. Something I am thinking about doing myself since I have a very similar lathe..

I wouldn't mind seeing a couple of more pictures myself of this, it seems to be the best way to add leadscrew reverse on this type of lathe.

WilliamG
10-27-2009, 03:30 PM
Yes it is ClintonH's reverse tumbler I make reference to. Have the identical lathe purchased in August, however as a senior in my 70's and pure novice I require much assistance to safely complete projects. Like you additional photos should reveal what is really required here. Hopefully someone can bring this to the attention of Clinton. Yesterday I posted a question on grinder arbors. Haven't received a single reply as yet. How sad, this is a fantastic forum when it works!

Bill in Moose Jaw

goose
10-27-2009, 04:17 PM
Just thread it normally then turn the workpiece inside out. That's how I always do it.


That, or what I'll do is thread normally and plunk the finished piece down in front of the shaving mirror.


Gary

Marc M
10-28-2009, 04:17 AM
http://bedair.org/9x20camlock/Micllef.html
...

That is my take on the tumbler reverse setup.


Interested in how you modified or attached the 'change gear support' to add the reverse tumbler.

If you are referring to ClintonH's modification I think it is an extra 'arm' welded in place holding the extra idler gear.

In my version, the only modification made to the lathe itself was cutting a hole for the change lever assembly. The plate that carries the gears pivots on an existing gear stud. It's been a while but IIRC, in the stock configuration, it has a spacer behind a gear. That spacer is removed and the carrier plate takes its place. I breifly looked at the ClintonH version and it appears to be the same, just implemented a bit differently.

I used one of the change gears that came with the lathe for the reversing gear. It was only used for 1 or 2 threads I believe. If by chance I needed that gear, it is easily removed. I wouldn't be able to reverse the leadscrew without it, but it will run fine going forward without it in place.

If there's anything specifically you would like photos of, let me know and I'll try to get them posted here for you. Any other questions, feel free to ask.

Better get back to work before my Whip-Master finds me here!

Marc -

EVguru
10-28-2009, 05:46 AM
A completely different approach would be an electronic 'gear train'.

http://www.homemetalshopclub.org/projects/electronic_lead_screw/els.html