Thread: Metric threading on an imperial lathe

Not sure you would probably have to test it.

Would test it anyway before attemting to Screw Cut.

If the lever engages easily every time without getting caught in theroy I believe it should be ok,if on the other hand it dosent engage everytime you probably wont be able to use that method.

Vernon,

Without having seen the leadscrew reverse on a Nuttall, I don't think that will work. I think you need to reverse the motor and turn the spindle and the whole gear train backwards to maintain the correct relation between spindle and leadscrew. Once you break the gear train between the spindle and leadscrew I do not think you will be able to pick up the thread again. I tried it once using the tumbler reverse to reverse the leadscrew on the old Brackenbury and Austin lathe and it did not pick up the thread afterwards.

I do not have a reversible motor on the B & A lathe. I normally cut threads on it using the back gear, and prefer to cut metric threads on the other lathe where possible because of the non-reversible motor on the B & A. When I need to cut metric threads on the B & A, to wind the carriage back I disengage the back gear, but do not lock the headstock pulley to the headstock spindle. This makes the spindle easier to turn and does not disturb the relation between the spindle and leadscrew. Then (temporarily I hope, until I find a reversible motor), I use a portable electric drill to turn the spindle and geartrain backwards until the carriage has moved back to the start position, then re-engage the back gear for the next cut. I know some people have made spindle crank handles to do this, but the electric drill is easier! The right answer is the reversible motor though.

Added later: By the way, should you decide to use a 37T and 47T pair of gears for your metric conversion set like I use on the B & A lathe because there is not enough room for a 50/127T set or a 63/80T set, your excellent change gear programme tells me that these can also be used in the gear train individually to cut good approximations to a number of BA thread pitches as an added bonus should you ever need to do this.

Frank.

Some of the Southbends have a lever in the change gear train that can provide conventional feed, no feed, or reverse feed. It achieves this by inserting an extra idler gear in the train for reverse, or seperating the train for no feed. From memory the normal feed gear on the lever is the first driven gear in the train, driven by the spindle pinion.

The way this works, it is intended as a set and forget for the job at hand, ie set to normal position for normal feed or reverse for reverse feed. The control lever is locked into place with setscrew once set in the required position.

If the Nuttall uses a similar system, I would suggest that there is little chance of keeping synch by using this mechanism.

If your thread is not too long, it is fairly easy to hand crank the spindle to rewind back to the start of the thread for the next cut.

EDIT

After much searching I found a pic of the gearcase of a Southbend, added labels for the relevant bits, and explained the drive sequence. This is in the PDF attached below.

I doubt it will go back in sync as it will move when u swap it as its only ment for cutting left hand threads

Thanks for the feedback guys. My gut feeling is that changing the reverse lever will NOT keep sync (as seems to be the consensus), however I might, as Pipeclay suggests, try cutting a dummy thread using it and see what happens.

The lathe is 3 phase, so I can easily set it up to reverse the motor, however there is a clutch between the motor and the geared head that does like going in reverse (trust me I know this from experience ).

BTW, does anyone have a copy of a Nuttall manual (for a 6 1/2)? I know there was/is a bloke selling Nuttall gear, but he doesn't seem to respond to emails.

Originally Posted by Vernonv

Hi All,
I have a question regarding cutting metric threads on an imperial lathe. The lathe I am wanting to use is my old Nuttall. Now lets assume I have the correct change gears to cut the metric pitch (I don't currently have them, but I will get them).

Now correct me if I am wrong, but normally to cut a metric thread on an imperial lathe you have to keep the half nuts closed at all times and power the carriage back to the start of the thread for each pass. The thread chasing dial can't be used.

Here is my issue. On the Nutttall lathe you can reverse the feed direction of the carriage, however that doesn't change the direction of rotation of the chuck (ie you are not reversing the motor, simply reversing the gearing to the feed).

Does anyone know if it's possible to use the feed reversing lever on the Nuttall lathe to take the tool back to the start of the thread while keeping everything "in sync"?

Or is there another way to achieve the same thing?

are you trying to use the thumble reverse? if so then no it wont work you are disconnecting the gear train the usual way it to reverse the motor drive so the chuck spins anti clockwise and the tool moves back in the threads you are cutting (you pull the cross slide back a turn at the end of the treads)

To eliminate having to actually cut a thread for testing,either use a piece of dowel,nylon,or metal of some type.
Set up a Felt pen or pencil in your tool post and check it that way.
If it works once I would repeat at least 6/12 times just to be sure.

If you have a clapper box type tool holder like a shaper does, you just have to bring it to a halt at the right spot, maybe with a mechanical brake or a speed controller brake and then stick it into reverse to the start again and everything will stay in sync and the tool will not cut when in reverse as it just lifts up and rides on top of the shaft to be threaded.



which is discussed here:Shop Made Tool pics - Page 2 - Practical Machinist - Largest Manufacturing Technology Forum on the Web

I'd put money on the Nuttal NOT having a syncronised leadscrew reverse.
Some of the old Macsons did though. Was great to use. you'd just wind the tool out at the end of the cut, flick the lever over (with the spindle still turning), there would be a bit of a pause and then the leadscrew would reverse. repeat when the saddle was back at the start of the job.

bollie7