Reversing leadscrew on small lathe

If there is no provision for changing the feed direction via the feed gearbox then I would expect it to be possible to add an idler into the geartrain driving the feed gearbox. This would reverse the direction. I am not about to download the 47mb PDF file from harborfreight even with broadband to find out.
Lewis Campbell wrote:

i don't think lh threading requires reversing the lead screw. there s/b good info thru google but i would be surprised if you cannot reverse it on your machine. --Loren

Lewis,
Check out these two sites. Both may be of some help.
Regards,
Peter

The tumbler gears reverse the leadscrew on any lathe fitted with them (unfortunately, not the one in question).
Reversing the spindle will *also* reverse the leadscrew, so you are *still* cutting a right-hand thread -- just from the other end.
As already mentioned, adding an idler gear to the train (as long as you can find a place on the crowsfoot to mount it (or whatever the equivalent on the Enco lathe might be)) will accomplish the reversal, if not as conveniently as the tumbler gears on larger lathes.
The actual count of teeth in the gear doesn't really matter that much, since it is just working as an idler -- just find one which will fit between two gears in the existing train.
Good Luck, DoN.

(clip)i don't think lh threading requires reversing the lead screw(clip) ^^^^^^^^^^^^^^ Wasn't there a thread here recently in which the OP wanted to cut RH threads, and was getting LH? He was advised to put the tool behind the work and invert the cutter.

Hopefully you don't believe that would work.
Ted

Start with this:
and then look at his other projects:
A very nice site for the 9 x 20 lathe owner!
Best Regards, Keith Marshall snipped-for-privacy@progressivelogic.com
"I'm not grown up enough to be so old!"

Wow that's a really nice site for anybody. I've thought about the variable speed thing when I was looking at the old unused tredmill/coatrack the other day. It's got a pretty stout motor on it. I'm glad I'm not the only one with this idea.
Thanks,
Russ Wizinsky

Try this:

Many thanks, Keith, this is exactly (well, actually better than) what I was hoping to find.
I really appreciate it.

hoping to find.

nor my Grizzly 3n1 (4015), not too surprising, i guess, but never had a reason to wonder until now. what i thought might be a reverse is simply a clutch which allows you to do manual feed using the lead screw.
so, besides lh threads, what would this reverse mode be good for? probably a dumb question(?). you could take cuts in both directions under power, what else, tram under power? you can reverse the motor for that. Thanks! --Loren

[ ... ]
Sigh!
Well ... I sometimes use it for turning away from a shoulder (after doing most of the work towards it, and moving by hand the last few thousandths. Doing a finish pass in reverse makes sure that the finish from the shoulder on out is the same -- which you lose with hand feeding part of the distance.
Also -- if your lathe has power cross-feed, it allows you to choose between facing from the outside towards the center, or from the center towards the outside. On my 12x24" Clausing, if I want to face from the outside towards the center, I have to reverse the leadscrew. (Same for a parting cut.) I think that this is so you can cut from the end towards a shoulder, then face out to the edge just by switch from power longitudinal to power crossfeed for a finish pass.
Enjoy, DoN.

...>> interesting, and your manual feed likely doesn't use the lead screw, but a linear toothed plate, right? this is a basic design feature that marks the very low end machine, the lack of, i mean. my manual feed requires turning a handwheel on the end of the lead screw. not very handy.
at least the 9X20 has this feature, but makes me wonder about the handle at the head end of the lead screw, likely just a clutch like mine. this makes some sense on my 3n1, since the handwheel turns with the screw. ...> > Enjoy, > DoN.
that's the reason for a 2nd "lead" screw, right? i swear i have seen a 3rd, but don't know where/when. well, this thread has been good for me, thanks to all. Happy Holidays, --Loren

You mean a rack gear on the underside of the ways? Correct.
That also suggests that you don't have half-nuts -- to decouple the carriage from the leadscrew.
Well ... actually, this does not have a second (or third) drive shaft. Some do -- but mine derives the drives from a keyway on the side of the leadscrew, so it does not use (nor wear) the threads during power feed operations. A collar with an internal key slides on the leadscrew, and couples the rotation of the screw into a worm gear, which meshes with a matching gear in the apron.
Then, there is a lever which can connect this gear either to the handwheel (for longitudinal feed), or the cross-feed crank (for cross feed). The actual threads of the leadscrew are only used for threading, thus reducing wear which can make the system less accurate.
On some systems, the coupling to the power feeds is via a clutch. On mine, it is a set of gears that engage or disengage with a lever, which means that you sometimes have to wait for teeth to align before you can complete the lever motion. The lever rotates a short shaft parallel to the axis of the machine (just in the apron), which can either move up for longitudinal feed, or (after sliding the lever to align with a different slot) down for cross-feed.
My memory on this is quite fresh, as I just a couple of hours ago was down in the shop making two 1"x12 thin nuts to complete a storage system for some 16 DB gear tooth cutters -- storing all eight of them on a single short 1" diameter shaft (aluminum) with a nut on each end to keep them together. In the process, I did both power cross-feed (facing the nuts), power longitudinal feed) boring the ID in preparation for the threading, and with threading feed (obviously for the threading). I really don't remember why I selected 12 TPI for that 1" diameter shaft, as I threaded that a couple of months ago, when I got the first two of the gear tooth milling cutters. I now have almost all of them, so I decided to finish the project. Interestingly enough, the #1 cutter (135 tooth to rack gear) is a different maker, and a different diameter than the others, though all came from MSC from the same page and table. :-)
The machines with two shafts which I have seen have a normal leadscrew, and a separate keyed shaft to drive the power feeds.
Those which I have seen with *three* shafts actually use that third shaft (key coupled to a lever on the carriage) to turn the spindle motor forward, stop, or reverse, operating switches inside the pedestal, so there are no wires run out to the carriage. This is more important with a longer bed, which does not allow you to reach both the carriage controls and the switch on the headstock easily -- at least when working near the tail end of the lathe. Very useful when something happens other than what has planned.
Now -- I can picture one with four shafts, or with three shafts without the motor switch lever on the apron, in which there are two leadscrews and sets of half-nuts. One leadscrew would be for imperial threading, and another for metric threading, so you can have both working properly with threading dials. There would have to be a 100/127 gear ratio between the two leadscrews, and I would imagine that to minimize the chances for errors, there would need to be interlocks to allow only one set of half-nuts to be used -- probably selected with a lever on the apron for metric, power-feed, imperial (separate from the half-nuts levers themselves). I might think that putting the metric half-nut lever on one side of the apron, and the imperial on the other, which corresponding threading dials would help reduce confusion.
This would be a machine which *I* would like to have, since I work in both metric and imperial. As it is, I normally do all my metric threading on the little 5" CNC machine (where all it takes is rotating a switch to select between imperial and metric units for all operations. I do have a set of metric transposition gears for the Clausing, but since the leadscrew is imperial, it makes metric threading a matter of leaving the half-nuts engaged (a real pain when threading to a shoulder), or playing games with running the spindle in reverse to get back to the proper point for re-engaging the half nuts -- a bit more of a chance for something to go wrong.
I've only done threading once on a machine without half-nuts -- a ShopTask belonging to a local friend, to test it out, as he was having problems getting good threads from it. Part of the problem is that the spindle speeds don't go low enough to make reaction times reasonable (at least without the optional low-speed pulley set, which he had not installed). The other is that the LED countdown lights are harder to get used to for me than the threading dial, and instead of half-nuts, it has a dog clutch to engage the threading feeds.
And to you, DoN.

there are half nuts, no thread dial. the lead screw is the y-axis feed whether power or manual. if you disengage them, you can move the carridge by hand (literally). right, i have come to understand that what i have is pretty much a kludge. the rack gear would be a real bonus (on low-end machines). it may not sound like i am happy with this 3n1, but i am, for the amount of use it gets and my needs. still, it is fun to think about the better machines and their features. i have not tried to use the lead screw clutch when the motor is on, never had the nerve. if that is okay to do, it might make some things easier.
sounds like a ton of ways for a newbie to break things. i have left the drive belt loose, purposely, as a saftly measure until i get more experience. it has saved me several times already (when running the carridge into to chuck). ...> that makes a lot of sense, and gives me some idea of the variety of features extent. there is a definite safety issue with longer beds. just opening the half-nuts may not always be desirable?
yes, no back gears. same here, but i do have room to do something, some- day. my hope is that the dc motor may mitigate the need for them. another someday project (the motor i ordered is an "open-frame").
this sounds like a newer machine? leds? it seems like half-nuts are a very basic feature, w/or w/out thread dial. i have no thread-dial, so have to keep them engaged while reversing out of the cut. for very occaisional use, okay. for anything more it's a non-starter. --Loren

If you have half-nuts (in the apron), you really need a threading dial. And it is possible to *make* one for the lathe. One quick-and-dirty way is by finding a gear with a tooth pitch which matches the thread pitch of the leadscrew. You'll have to mount it on a shaft at a bit of an angle, to make up for the lead of the screw. Better is to make one which is pseudo-hobbed by a tap which matches the leadscrew, so you have a better match, and so the teeth are angled properly to engage the threads on the leadscrew. The number of teeth on the gear are critical -- and I would have to go to _Machinery's Handbook_ to refresh my mind on the formulas to determine which tooth count you want for which leadscrew pitch. (Of course, if you are cutting imperial threads with a metric leadscrew, or vice versa, the thread dial is pretty much useless, and thanks to the kind of intervals used in metric thread sizes (unlike inch sizes, which are mostly powers of two multiples from a few starting points), you really need a threading dial with (I believe) four different tooth counts, on a sliding shaft.
There was an article in _Home Shop Machinist_ (or was it _Machinist's Workshop_?) on making a threading dial for a lathe which either never came with one, or which lost it. My Clausing, which was used throughout its life as a turret lathe, doing threading with Geometric die heads, did not have a threading dial mounted -- but I found it (apparently unused) in one of the pedestal drawers. :-)
You mean push it along -- no handwheel to move it?
[ ... ]
Interestingly enough -- the Taig (Peatol in the UK) has a rack gear and handwheel -- but *not* a leadscrew. You are expected to do your threading with dies on that machine.
I understand. I started with a Unimat SL-1000 (the leadscrew was the *only* way to move the carriage.) I then got an old Atlas/Craftsman 6x18", which had the rack -- with the handwheel purely manual -- and all power feed was via the leadscrew -- with a basket-of-gears threading setup, and a chart on the inside of the gear cover.
Where is this clutch? The ones which I was talking about are in the apron, used to connect the power derived from the drive screw rotation to either the cross-feed, or the longitudinal feed handles. These engage smoothly, and can be set to slip before you are in danger of damaging your machine.
The ShopTask, however, has a dog clutch (which enages only at one point in the rotation), to couple the spindle's rotation to the leadscrew. (It also achieves reverse, by connecting to a counter-rotating gear with a second dog clutch enaged by the same lever.)
The ones using clutches for the feeds are no problem -- as they can be set to slip before something is damaged.
On my Clausing, in the normal crossfeed direction, if all else fails, you will run out of leadscrew before the cross-slide falls off the carriage. (Fine for facing, but if you're parting, you can run into the remaining part of the workpiece with the tool block. :-) For longitudinal feed, you can run into the tailstock, or the headstock (if you are working with collets, so the chuck is not in the way), and there is a shear pin in the leadscrew drive from the gearbox to fail before something serious breaks.
Not possible to leave it loose on my Clausing. There are three belts in parallel between the free-rotating pulley on the spindle shaft (which is locked to the bull gear with a pin, or coupled via the back gears) down to the countershaft in the pedestal. From that there is a single belt, going on one of five different grooves from the end of the countershaft to the motor spindle. There is a lever which lifts the motor to slack this for shifting belts, but that is way too lose to run. When you move the lever to the side, to engage the belts, the weight of the motor takes over, and won't stop moving the motor until the belt is tightened by the motor's weight. (There is a set of springs to catch the motor if the belt breaks. :-)
If the workpiece is starting to work loose in the chuck, or one between centers is starting to bow, you want to stop that spindle motor *right* *now* -- not just the feed. On one lathe equipped with the carriage mounted lever, there was another panic stop means which was even quicker. There was a stomp bar across the distance between the pedestals, and pressure on that anywhere along its length, would turn power off the motor, and apply a spindle break. (Needless to say, this was *not* a threaded spindle, in which the chuck would be likely to unscrew under such a panic stop. :-) I had to use that only once, but I was really glad to have it. The cut was spewing chips too hot to let me get to the headstock -- or even to the lever on the carriage. :-)
Note that if a large workpiece was starting to work loose in the chuck, I would not want to pass the chuck to get to the controls on the headstock anyway. :-)
Note that you are limited in the torque you can get with just pulleys and belts doing the stepdown. Gears have that nice no-slip advantage.
Hmm ... you'll have to fix *that* feature (with a housing of your own, and a fan blowing filtered air through it), or your motor is likely to stop suddenly, spitting sparks, as some chips get into the brushes. (Unless you plan to only turn plastics and other non-conductive materials. :-)
It was an add-on to an older ShopTask (which is probably not too different from what you have). There is a lot of metal housing the belts and gears, and on the shaft driving the leadscrew, there is a set of reflective markers picked up by the "threading dial" -- an add-on feature which comes standard on the later ShopTasks). It sort of serves the purpose of the threading dial -- especially with the dog clutch driving the leadscrew -- to make sure that you engage the dog clutch in the right position. (Apparently, it is *not* a single position engage, which does not make much difference when using it for power feeds, but it makes a big difference when using it for threading. :-)
As long as you have an imperial thread leadscrew, and are cutting imperial threads, or metric for both, you can use it, with the help of a threading dial. You *can* make a threading dial for the machine. I would check the mailing lists and web-based fora for the model of lathe you have -- I'll bet that someone has made a threading dial for them. (The ShopTask LED "threading dial" was designed and first built by one of the users, to get around just this problem. But the slowest speed is still a potential problem in reflex time. For threading (except very fine pitch threading), I tend to use the back gears. The latest thread that I cut (a 1"x12 inside thread) was cut using the back gears but the same pulley setting which gives me 650 RPM without the back gears -- which works out to be 100 RPM in the back gears. With a coarser thread pitch, I would go down to the lowest belt speed in combination with the back gears, which gives me 35 RPM. I'll also use that if I have a very narrow landing zone when threading to a shoulder, or especially for inside threading to a shoulder.
For a *really* fine thread (e.g. 40 TPI or finer), the leadscrew is turning slowly enough, even at 650 RPM, for my reaction times to work out well.
Enjoy, DoN.

I dont have the machine you mentioned (the 4015), but I looked at their G4015Z picture. The clutch at the left end of the feedscrew should be able to handle changing under power. If you're unsure, you could always disassemble it to determine if you would want to. In a Smithy machine, the clutch is a sliding socket that engages a hex head to engage the feed.
WB .............
snippage

Number of gear teeth = 4 x number of threads per inch of the leadscrew.
for a thread dial marked 0 - 1 - 2 - 3. More rarely, thread dials are occasionally marked 0 - 1, the formula for this is gear teeth = 2 x tpi. If it's metric, I've no idea.
For a typical 8tpi leadscrew, you usually need a 32 tooth gear. Some guy was even selling these on eBay the other day, as a kit for use on 9/10" South Bend lathes, though you could use it on any. It's not unusual for larger lathes to have different leadscrew pitches, a 13" South Bend uses 6tpi, for example...
--Glenn Lyford