Metric thread on imperial lathe, without reverse.

[Vernonv]

That arrangement is only for keying the 120 to 127 gears together.

Certainly the case for the idler gears, however that star arrangement is also used on the spindle and QC input shafts.

I figured it would be a simple task just to blind drill a hole into each of the gear hubs, all at the same distance from the centre and use a pin to key the shafts (i.e. have the holes facing each other).

[Oldneweng]

The star shaped shaft is part of the driven shaft on my lathe. It does not come off. Could a 127 tooth gear be made with just a bore to go over the OD of the shaft and then pin the two gears together.

Dean

ps How does the star hub bit lock on to the driven shaft Vernon.

pps I just realised that you are showing the 60 tooth gear.

Is your 120 tooth shaft solid as per mine then?

[PDW]

I've got a set of 12DP 14.5 PA cutters. I'll lend the appropriate one out to someone if they want to cut a gear or 2. ATM I don't have my dividing head set up and I'd have to do direct indexing off of a 127T gear anyway, which is a PITA. I'm also short on time and about to go travelling (again).

Hopefully this time less than 3 tonnes of machine tools will accompany me home.

Anyway the offer of the cutter is there...

PDW

[Oldneweng]

Okay, so my idler gear is 72 tooth not 60 which anyone could see if they looked close at my gear train photo. The gear has 72 cast into one spoke.

My drive gear is 30 tooth.

With the addition of 127, 30 and 35 gears I cover all thread pitches at an error of <0.00001% (a lot are actually spot on).

Do you actually need a additional 30 tooth gear Vernon or was that a typo?

Dean

[Stustoys]

Stuart, albeit I admire your math skills.... but.... is it not more convenient

I say there is a fair difference between "there is absolutely NO way to disengage the half nuts without ruining the thread being cut" and "more convenient".

There is no maths to do while threading*...... do it once and its done.
You're using the thread chaser so an error is no more likely than "normal" threading. If you like, the pick up can be done with the lathe off.

Whats more convenient depends on a number of things, Length of thread and number off would be the big two but the lathe comes into it, as does laziness. I only recall cutting one thread by hand, 6BA I think it was and only about 8mm long, winding my lathe over by hand isnt something I enjoyed.. and my lathe is tiny compared to some here. A handle on the back of the spindle wouldnt be great as you would have to move around the lathe to get to it(though again it would depend). I doubt turning a Nutalle backwards would be anymore enjoyable. YMMV
Being able to open the half nuts may allow you to run the lathe faster so the time between pick ups would be less. Though even at 200rpm its 30 odd seconds - the time to get ready for the next cut - the thread length(in time) - the possible time saving of cutting the thread at a higher speed.

Even if the lathe has reverse being able to open the halfnuts may reduce the pucker factor of threading to a shoulder.


Stuart

*unless you call counting turns of the thread chaser maths. With a custom gear that could be removed.

[Vernonv]

How does the star hub bit lock on to the driven shaft Vernon.

Not sure. I had a look but it was not obvious.

I just realised that you are showing the 60 tooth gear.

72 actually

Is your 120 tooth shaft solid as per mine then?

If you mean the driven shaft, yes it is solid.

[Vernonv]

Do you actually need a additional 30 tooth gear Vernon or was that a typo?

No, the extra 30 is for 1.5mm pitch and multiples.

[cba_melbourne]

> I say there is a fair difference between "there is absolutely NO way to disengage the half nuts without ruining the thread being cut" and "more convenient".

Hmm, I would say in this case it is sooo much more convenient, that trying to do anything else is pure masochism

> Being able to open the half nuts may allow you to run the lathe faster so the time between pick ups would be less. Though even at 200rpm its 30 odd seconds - the time to get ready for the next cut - the thread length(in time) - the possible time saving of cutting the thread at a higher speed.

If worried about saving time, I think the OP would have added a spindle reverse a long time ago.
I concede you may be right if the OP did ask about cutting a large batch of threads of same pitch. But if he is only after a one off or two, I bet in his particular situation it is at least 20 times faster to do it by leaving the half nuts closed and leave the maths alone.


> Even if the lathe has reverse being able to open the halfnuts may reduce the pucker factor of threading to a shoulder.

I can agree with this, but would take it one step further. Why only reduce the "threading to a shoulder" pucker factor, when it can easily be removed altogether?
Just run the spindle in reverse and use the threading tool upside down. That feature alone would make adding a spindle reverse worthwhile.


Chris

[Vernonv]

Just run the spindle in reverse and use the threading tool upside down. That feature alone would make adding a spindle reverse worthwhile.

My lathe has a threaded spindle nose, so that may not work very well (in my situation anyway).

[Oldneweng]

No, the extra 30 is for 1.5mm pitch and multiples.

I should explain myself better. I was running in and out this morning. Out to the shed and back in again to type just to find I had been beaten to the punchline.

My gear train is 30/72/120 or 30/72/127. Sorry about the "60" but I did correct that in post #49.

I could not work out the reason for an additional 30 tooth gear unless you had a different gear altogether. As far as I can tell (this means not much) there is only one position at a time for a 30 tooth gear. This is why I asked.

With the addition of 127, 30 and 35 gears I cover all thread pitches at an error of <0.00001% (a lot are actually spot on).

In addition to which gears other than the idler and 120?


As per your answers to my questions in post #51 just pretend you did not see my questions. I managed to work out what was going on eventually.

This is all academic to me as my lathe is moving to a new home eventually but it is still something that I want to learn. I realised that today trying to get my head around this issue.

I had a quick look at the CY lathe manual today to see what sort of arrangement it has for threading and quickly decided that could wait until it has been installed. I am sure it is easier than it looks at first glance but I want to wait until I am able to put the info into practice.

Dean

[Vernonv]

I could not work out the reason for an additional 30 tooth gear unless you had a different gear altogether. As far as I can tell (this means not much) there is only one position at a time for a 30 tooth gear. This is why I asked.

The extra 30 would be used in a compound situation - for example for a 1.5mm pitch you would have the driving 30 driving the 127 and 30 in compound configuration on the idler, with the 30 driving the 120 in the driven position.

In addition to which gears other than the idler and 120?

The way I've worked it out, the (original) 30 will almost always be in the driver position, whereas the 120 or the 72 must be in the driven position. The additional gears (127,30, 35) will only ever be used in the idler/compound position, as they will not have the correct bore configuration (they will be smooth bore, rather than the star type).

I hope that all makes sense.

[Oldneweng]

The extra 30 would be used in a compound situation - for example for a 1.5mm pitch you would have the driving 30 driving the 127 and 30 in compound configuration on the idler, with the 30 driving the 120 in the driven position.


The way I've worked it out, the (original) 30 will almost always be in the driver position, whereas the 120 or the 72 must be in the driven position. The additional gears (127,30, 35) will only ever be used in the idler/compound position, as they will not have the correct bore configuration (they will be smooth bore, rather than the star type).

I hope that all makes sense.

Thanks for clearing that up Vernon. Perfect sense now that you have explained it. I have doubts that my lathe is good enough now to use for threading to any accuracy but it is all necessary knowledge for future use. I worked out tables for the gear combinations I have plus a 35 tooth just for fun but did not go any further. It became obvious that the 1.25 combinations were an issue.

Dean

[Stustoys]

[QUOTE=cba_melbourne;1713160 I bet in his particular situation it is at least 20 times faster to do it by leaving the half nuts closed and leave the maths alone. [/QUOTE]

I had doubts about the 20 times number, maybe 2, maybe less, it depends how easy your lathe happens to be to turn over by hand. I was going to try it out and see so thought I would set my metric lathe up to cut an imp thread using the same idea. Now assuming my maths is correct I believe this time we can agree its unlikely to be much use. The pick up points are 15inchs apart(dont really have my head around that yet, Ewan come pull my maths into something I can understand lol, its 127 again but its in a different column)

Back to cleaning

Stuart

[Ueee]

My head hurts.......let me think on it for a while. I should be doing bookwork right now.

[Ueee]

Whilst this does not help the imp on a metric lathe directly, it occurred to me that the time taken for the leadscrew to spin its number of times over before half nut re-engagement is the same no matter what thread (i haven't looked at odd pitches yet though) you cut. The carriage movement may change, as may the number of turns but there is one constant-the number of times the spindle revolves from one engagement point to the next. Without doing any maths i bet the number is 127 times.

Stuart, What pitch leadscrew did you work that excel sheet out on?

Chris, unless its a long thread there is no way i'd do this over reversing. For the last 8 odd years reversing is the only way i have cut threads. It would be way slower on short threads. Thanks for the tip of cutting from a shoulder in reverse, i'll remember that one!

Ew