First threads on lathe

this was my first attempt, the smaller side is 8mm diameter with a thread, the other end is 10mm diameter with almost a 1.5mm pitch, its actually 16TPI which comes out at 1.588mm pitch, so the M10 nut will only go on by a few threads

You don't need the expensive metric conversion set. Didn't check which thread Neil linked but for the Myford there is a thread showing details for metric conversion (approximations) that only uses one small gear change so very much cheaper. JS makes the gear so possibly sells it through ARC. Read the whole thread and follow the later link by JohnF.
If you are not using the angled topslide method (lets not go into arguing about that) when you are using an approximation and the nut is tight just put in a small extra cut with the topside moved along a few thou and you will get clearance. Yes a tad weaker thread but in non stressed parts it's ok.

cheers will try that out thanks

I have also just made my first attempts at screw cutting with limited success.

However when working out how to use the QC gearbox on my S7b I recalled that the lathe came with a loose set of gears. There are eight in total numbered 30, 35, 38, 40, 45, 50, 55, and 60.

Can anyone tell me what they are for?

I would think those change wheels mostly became redundant when the QCGB was fitted.

My lowest speed is 50rpm and I find even that a bit too fast for course pitches. I,d be much happier with about 25 rpm,that would give me more time to run if everything went ---------------------------------!!!

Larry, a mandrel handle should be your next job. Provides variable speed and instant reverse. Also overload protection.

Peter, some of the gears may be needed for metric or BA threads one day. (I'm not saying you won't need additional gears for that). 38/19tpi is often not covered in QCGBs so a 38 gear is needed, but I'm not sure whether the S7b is one of those.

On the insert type of threading tool the fishtail is not needed. Just make sure the shank of the tool is perpendicular to the ways. I use the face of the chuck as a reference.

Bayzle,

I would be curious to know what gearing works for BA threads. Except for the largest (1mm pitch) they all appear to be non-standard pitches in both metric and imperial systems. (It was just yesterday I learned how the BA system was derived. It was here on this forum.)

There's a number of online change gear calculators you could use to do that. With double-compound gearing there is a good chance you could do it within an acceptable error limit.

Good calculator here: **LINK**

For example, the BA thread refered to in the other thread on here is .81mm pitch. Which the calculator says can be turned on a standard metric mini lathe using the standard set of gears by using the following combo: 40, 57,50,65

The number of pitches you can turn with a standard set of change gears is finite, but with compound gearing it is up in the tens or hundreds of thousands  somewhere, so a surprising number of oddball pitches can be made. This includes turning metric threads on an Imperial machine such as Drummond/Myford without any special gears, just the standard set of 20-70 in steps of 5, plus the standard 38.

Edited By Hopper on 24/10/2017 02:34:52

Edited By Hopper on 24/10/2017 02:36:51

try this -works for me -       https://www.youtube.com/watch?v=ksCd9FfjUFQ     &   **LINK**

Sam L

Edited By Sam Longley 1 on 24/10/2017 08:00:23

I would second the idea of a mandrel handle for lathes that won't go slow enough. I made one for my Unimat 3, which is what I did my first screw cutting with. The handle is very useful both for screw cutting and for oversize jobs, anything where you need slow speed and good control. .

The Unimat didn't have a quadrant and change gears, so I made a set of 1 to 1 gears from some plastic gears out of an old can opener. That gave me the ability to cut a 1mm pitch, which meant I could make things to fit the mandrel nose, which was all I needed. It also didn't have a set of clasp nuts on the lead screw, so the technique was to take the cut off and wind backwards to the start.

For my Myford, I made a geabox!

John

As I mentioned in the other thread if your chuck is not going to unscrew then use a tool at the rear of teh work, run in reverse and you don't need it slow as you have the rest of the lathe bed to stop or disengage the half nuts. Did this one at 3-400rpm.

have the rest of the lathe bed to stop or disengage the half nuts

As long as the workpiece does not need support at the threaded end!

Rear toolpost and a bit less time before you hit the tailstock!

You only mention time to stop the cut, as a big advantage - but you can also achieve a much superior finish turning at the higher rpm.

My first ever attempt at threading on the imperial south bend is on the left of the bar at the front of the photo ,the second attempt is on the right and turned out almost perfect. It was a replacement crossfeed screw for the same lathe.

I am at the moment trying to cut s20 x 2 metric buttress thread , ive got the pitch right using a homemade tufnol changegear but the tool shape and feed in for the tool is confusing me.

Hello, some 50 years ago I obtained my first lathe, a secondhand Myford ML4. This machine suffered all the well known failings of the marque.

Screwcutting at that time, was a buttock clenching experience with any thread not a multiple of the leadscrew thread count of 8TPI, and no leadscrew thread dial .

I became aware of the single tooth mandrel clutch, this promised a great easing of the screwcutting experience, so one was made and fitted. All imperial threadcutting became a breeze.

I attach a photo of the ML4 headstock for anyone interested.I will now start anew thread under the heading 100 years on, concerning screwcutting.

paul.

If you want really low speeds, why not make a Mandrel Handle? With this you produce the speed that you want, and make cutting up to a shoulder less fraught.

It may also enlarge you biceps when producing large diameter coarse threads!

Howard

Edited By sean logie on 27/10/2017 10:15:46