AL960b metric threads not quite right

[Maxi77]

Pipeclay, for this bolt I did machine to the end. Just an example as the one I did before it didn't have a chamfered shank. I did have a bolt that was m12 to 16mm shoulder which needed to be done hand(turning chuck)

[casjon]

I also use the chuck key when threading to a shoulder. With a min speed of 125rpm it makes it nigh on impossible to thread to the shoulder under power. I've also used the chuck key method on other lathes that have a much lower speed and never had any problems.

Stuart:
'Every seen a chuck with one side of the square broken out?'. I assume you mean the female square insert in the chuck?

[sossity]

Hello everyone,
i just wanted to ask others who own a AL960b if they have any trouble with their metric threads not being quite right?

i have tried to cut a 2.0mm pitch thread with the 30 tooth change gear installed. It is close but not right. My thread pitch gauge doesn't line up with what it cuts

I am cutting threads in a bit of a 'unconventional' way as I am threading up to a shoulder and the lathe doesn't have a foot break. I have an internal threading bar coming onto the back of the work and running it in reverse so I can leave my half nuts engaged.

If anyone can see what I am doing wrong, please tell me.
cheers

Anthony

It's not essential to have a footbrake to thread close to a shoulder. You can disengage the half nuts at the appropriate point, and let the cutter cut a circle right round, then let the lathe stop in its own time. The trick is to watch the threading gauge and make sure it doesn't do more than one complete rotation after you disengage the half nuts (Doesn't come close with me, but I have to thread on my lowest speed so I don't make mistakes). Then withdraw the cutter so it will clear the thread on the way back. Then reverse the motor and watch the thread gauge come back to the exact number where you disengaged the half nuts and re-engage them. Then the carriage/cutter will travel back. Once it has gone far enough back, stop the motor but don't disengage the half nuts. Then set up you cutter to the correct depth and do the next cut. The big disadvantage of this method is that it is slow but I'm not able to cut threads quickly at the best of times.
Another alternative I read of, was someone made a handle he screwed into the outside end of the spindle so he could manually turn the lathe which might avoid the potential problems with turning the chuck using the chuck key

[Machtool]

I am cutting threads in a bit of a 'unconventional' way as I am threading up to a shoulder and the lathe doesn't have a foot break. I have an internal threading bar coming onto the back of the work and running it in reverse so I can leave my half nuts engaged.

When you are winding back to the start of the thread, are you over-shooting the start position, then running in reverse a turn or two to pick up all the back lash and end float of the lead screw, before you engage your cut?

Regards Phil.

[cba_melbourne]

I also use the chuck key when threading to a shoulder. With a min speed of 125rpm it makes it nigh on impossible to thread to the shoulder under power. I've also used the chuck key method on other lathes that have a much lower speed and never had any problems................

Instead of cutting right to left against the shoulder: Install the threading tool UPSIDE DOWN and run the spindle in reverse. Do not worry, it still cuts a right hand thread. But the carriage now runs left to right and you need not worry anymore about hitting that shoulder. Especially with those lathes that have very hard to open half nuts when under load, like my Emco.

[casjon]

Yes I've googled threading to a shoulder too, there's probably more ways of threading to a shoulder than there are googlers! I've seen a few people using shifters on the flats of the jaws, wedge bars between chuck mounting nuts and spindle, shop made clamps on the spindle outer end, hook spanners and a you beaut plate spanner that locates over the chucks three jaws.

[cba_melbourne]

Yes I've googled threading to a shoulder too, there's probably more ways of threading to a shoulder than there are googlers! I've seen a few people using shifters on the flats of the jaws, wedge bars between chuck mounting nuts and spindle, shop made clamps on the spindle outer end, hook spanners and a you beaut plate spanner that locates over the chucks three jaws.

You may google for a practical problem like threading to a shoulder. But unless you have your own practical experience on the subject, you will likely fail to distinguish between what are good ideas and inherently bad ideas.

If your lathe has a minimum speed of 125rpm, consider the following options:
- make a handle to attach to the left side of the spindle. That gives you speeds as low as you want, as well as tactile feedback and full control of where to stop. The downside is its slow, and in some materials surface finish may suffer when cutting a thread that slow.
- use the threading tool upside down and run the lathe in reverse.
- get a variable speed VFD drive, you can slow down towards the shoulder as slow as needed.
- one could also fit a dog clutch to the leadscrew, much quicker to disconnect than some halfnuts, and no loss of sync

Using the chuck key is simply bad practice. Any of the methods you mention above are bad practice. They may get the work done, but not done well, and risk damaging a good chuck. If yours is an old and rusty worn out chuck you do not care about, that is another story. But dont do that to a good chuck.

[casjon]

I agree CBA, the methods I listed are bad practice, with the exception of a purpose made plate spanner I think. IMHO I think it a better idea than a handle on the left side of the spindle: it places the forces of effort more evenly and I might add it's a lot easier and cheaper than converting to VFD or adding a leadscrew clutch. As you're only turning the last tiny bit by hand, so I think you'd be lucky to pick up the difference in finish with a loupe, not something I'd lose sleep over. That's another thing on my 'to do list', a plate spanner.

It is interesting that you consider using a chuck key as bad practice, and yet,turning with the tool upside down as good practice. Just a quick look at the mounting systems of tool post, compound slide, cross slide, in fact the whole train, should give a clue as to why it is bad practice.

No criticism or offence intended to anyone who uses this method BTW, it's just my personal opinion. I shan't dwell on that any further though lest I start pontificating, pontificating should remain the prerogative of the Pontiff...

[Michael G]

You may google for a practical problem like threading to a shoulder. But unless you have your own practical experience on the subject, you will likely fail to distinguish between what are good ideas and inherently bad ideas.

Agreed. Well said.

... the methods I listed are bad practice, with the exception of a purpose made plate spanner I think. IMHO I think it a better idea than a handle on the left side of the spindle: it places the forces of effort more evenly and I might add it's a lot easier and cheaper than converting to VFD or adding a leadscrew clutch.

Not sure about a plate spanner either. My lathe is big and old so does low speed without issues but with all these "less conventional" ways of getting to a result it depends so much on equipment condition and how much higher forces are going to be than the design anticipated - if you are using a ratty old chuck that is worn and abused then it is more likely to be damaged than gear in good condition with decent wall thicknesses. If the chuck top is thin and there is looseness in the jaws you could have trouble.

Have you considered something that looks like a steering wheel that you attach to the chuck backing plate before threading? (or even a set of holes that could be used to effectively "bar over" the chuck (my chucks are direct mount but from memory a number of them have rear holes to lighten them which could be used for that purpose).

One of the the objections I would have to using a chuck key is the thought that if you leave it in the socket and power up you have a ballistic chuck key. It only takes a brain fade at a key moment - I did it myself only last year.

Michael

[BaronJ]

Another alternative I read of, was someone made a handle he screwed into the outside end of the spindle so he could manually turn the lathe which might avoid the potential problems with turning the chuck using the chuck key

This is the method that I use for cutting threads, with both dies and single point toolbits. It takes a bit of practice to get it right. From experience. My first machine cut thread was an internal left hand one.

I'll take a photograph of mine tomorrow and post it.

[cba_melbourne]

....It is interesting that you consider using a chuck key as bad practice, and yet,turning with the tool upside down as good practice. Just a quick look at the mounting systems of tool post, compound slide, cross slide, in fact the whole train, should give a clue as to why it is bad practice...

Anything that puts side loads onto chuck jaws or chuck key is bad. Chucks are not designed for this. Especially cheaper chucks made of cast iron are at risk of breaking out. Or developing the beginnings of a hair crack... that may then over time grow.... and one day let a chunk go, possibly at high rpm with dire consequences. But also loss of accuracy is a concern. Chuck jaws are very accurate fits to the chuck body - on a new precision chuck, the jaws are actually hard to slide such tight is the fit made. Side loads with a spanner on the jaw will over time loosen that tightness, and what once may have been an expensive precision chuck is reduced to junk status.

It is the first time someone mentions using a lathe tool upside down shall be considered bad practice. Why should that be so? I consider it best practice. It is a very common thing to do when threading to a shoulder. It has the additional benefit that when the tool digs in, it is not pushed deeper into the workpiece but on the contrary it flexes out of it. This is exactly the reason it is also very common practice for parting off, with the lathe in reverse if the lathe has a modern spindle nose, or with the lathe running forwards but the tool in a rear mounted toolpost for lathes that use a threaded spindle nose. It makes parting on not-so-rigid light lathes much easier and safer.

Regarding the VFD, I agree just for threading its overkill. But if you consider all the other benefits, a VFD upgrade is by far the most useful lathe modification of any that I can think of.

[casjon]

Common practice is not always correct, let alone good practice, it is simply - 'common practice'. I think it also worth mentioning that turning the chuck by hand to finish of the last tiny bit of thread hardly constitutes huge forces, unless of course you're turning a 4" diameter thread (not possible on my lathe). But anyway, this is why I would never consider using a tool upside down (parting off accepted - maybe).

A plate spanner that contacts all three jaws is essentially doing the same as a steering wheel on the end of the spindle. And of course applying force to the end of the spindle that wasn’t designed with that in mind can’t be good either. I think you need to look at the forces and mechanics behind using a plate spanner: a plate spanner exerting pressure on the side of all three chuck jaws over lets say a 125mm diameter, IMHO, is a lot less and would cause a lot less damage than that used and caused by mounting a steering wheel type tool in a 25mm round spindle bore (or larger in some cases). That aside, I’m not advocating the chuck key method as good practice, it’s just a methodology I have employed on occasions to an end. Normally I cut a slot in front of the shoulder for the tool to run into – neat does the job right. When I get around to it I’ll manufacture a more appropriate tooling system. But for now it’ll do.

A lathe does what it does thanks in large part to it’s size, weight and rigidity, All that brought about by large blocks of metal resting against other larger blocks of metal using smallish fasteners as locators, When turning steel the normal way, forces are transferred through those large blocks of metal: tool, holder, tool post, compound slide, cross slide, bed, stand, concrete floor, think of it as a series of steps, each step becoming progressively larger thereby amplifying size, strength and rigidity.

Now turn that whole lot upside down (which is essentially what you do when you turn the cutting tool upside down). In effect that aforementioned rigidity now depends on the flat surfaces of those large blocks of metal coupled with relatively small fasteners/locators. So in effect we have a tool hanging off a single bolt (tool post), which in turn hangs off two smaller bolts (compound slide), which in turn hangs off a couple of angled bits of brittle steel (ways and gibs), which in turn hangs off a couple of small guide strips (carriage guides under the bed ways, which were never designed for that purpose. Not as simple as that granted, but that, by and large, is the drift.

For me and IMHO, that is just abuse and not good practice, not far removed from broaching using the carriage (but that’s another argument I’m sure) and unlike your lathe, my lathe is small, new and fast.

‘One of the objections I would have to using a chuck key is the thought that if you leave it in the socket and power up you have a ballistic chuck key.’

Presumably the same could be said for using the chuck key to tighten the chuck! I’m sure everyone has done that – at least once!

BTW, I prefer to think out solutions for myself. Making your own mistakes is far superior to copying someone else's mistakes... Googling is for entertainment value!

I'm sure cutting and threading with the tool inverted has a place in turning (certainly I've seen it done many times), but that place is not in my shop or on my lathe. Again, no criticism or offence intended - just my opinion, I'm quite happy wrapped up in my own folly.

Now look what you have done: I've pontificated. I hate that, pontificating is ignorant, arrogant, rude and just plain boring. So, I take it all back: you’re right, I’m wrong, please accept my humblest of humble apologies. But at least I am happy in my folly.

[cba_melbourne]

...Now look what you have done: I've pontificated. I hate that, pontificating is ignorant, arrogant, rude and just plain boring. ....

I had to look up what the expression "to pontificate" means. To pontificate is to talk in a dogmatic and pompous manner. Now, you probably do not know that for me, English is only my 4th language. I like to think I have become quite good at it. But I can see how someone that does not hear my unmistakeable accent may perceive the way in which I say things as arrogant or rude. In this case it is not my intention. For the record, my first languange is Swiss German, then came Italian, then High German, then French.... and only many years later English. Each language has a different culture, and a different way to say things. Anybody that speaks at least one second language knows that, and is automatically more tolerant in interpreting language finesse.

As for using lathe tools inverted, its pretty much a routine procedure. Just give it a try, chances are you like it both for threading to a shoulder and parting off of larger diameters or difficult to part materials. For the reasons that you mention, it is not a suitable technique for roughing and heavy cuts.

[casjon]

Your English is very good, not much trace of an accent! I studied Colloquial Indonesian many years ago and spoke it quite well, but after 25 years without practice I can't remember a dam thing.

At the time the instructor, who spoke nine languages) told me I should endeavor to think in the spoken language, rather than interpret/convert as you go.

I also speak West Australian, Northern Territorian, and Queenslandian fluently. I do find thinking in Territorian difficult though, you have to down at least two cartons before the brain ceases to function. Apologies to any Territorians (hic).

Parting off is something I have never managed to do successfully without a hacksaw.

[janvanruth]

Common practice is not always correct, let alone good practice, it is simply - 'common practice'. I think it also worth mentioning that turning the chuck by hand to finish of the last tiny bit of thread hardly constitutes huge forces, unless of course you're turning a 4" diameter thread (not possible on my lathe). But anyway, this is why I would never consider using a tool upside down (parting off accepted - maybe).

A plate spanner that contacts all three jaws is essentially doing the same as a steering wheel on the end of the spindle. And of course applying force to the end of the spindle that wasn’t designed with that in mind can’t be good either. I think you need to look at the forces and mechanics behind using a plate spanner: a plate spanner exerting pressure on the side of all three chuck jaws over lets say a 125mm diameter, IMHO, is a lot less and would cause a lot less damage than that used and caused by mounting a steering wheel type tool in a 25mm round spindle bore (or larger in some cases). That aside, I’m not advocating the chuck key method as good practice, it’s just a methodology I have employed on occasions to an end. Normally I cut a slot in front of the shoulder for the tool to run into – neat does the job right. When I get around to it I’ll manufacture a more appropriate tooling system. But for now it’ll do.

A lathe does what it does thanks in large part to it’s size, weight and rigidity, All that brought about by large blocks of metal resting against other larger blocks of metal using smallish fasteners as locators, When turning steel the normal way, forces are transferred through those large blocks of metal: tool, holder, tool post, compound slide, cross slide, bed, stand, concrete floor, think of it as a series of steps, each step becoming progressively larger thereby amplifying size, strength and rigidity.

Now turn that whole lot upside down (which is essentially what you do when you turn the cutting tool upside down). In effect that aforementioned rigidity now depends on the flat surfaces of those large blocks of metal coupled with relatively small fasteners/locators. So in effect we have a tool hanging off a single bolt (tool post), which in turn hangs off two smaller bolts (compound slide), which in turn hangs off a couple of angled bits of brittle steel (ways and gibs), which in turn hangs off a couple of small guide strips (carriage guides under the bed ways, which were never designed for that purpose. Not as simple as that granted, but that, by and large, is the drift.

For me and IMHO, that is just abuse and not good practice, not far removed from broaching using the carriage (but that’s another argument I’m sure) and unlike your lathe, my lathe is small, new and fast.

‘One of the objections I would have to using a chuck key is the thought that if you leave it in the socket and power up you have a ballistic chuck key.’

Presumably the same could be said for using the chuck key to tighten the chuck! I’m sure everyone has done that – at least once!

BTW, I prefer to think out solutions for myself. Making your own mistakes is far superior to copying someone else's mistakes... Googling is for entertainment value!

I'm sure cutting and threading with the tool inverted has a place in turning (certainly I've seen it done many times), but that place is not in my shop or on my lathe. Again, no criticism or offence intended - just my opinion, I'm quite happy wrapped up in my own folly.

Now look what you have done: I've pontificated. I hate that, pontificating is ignorant, arrogant, rude and just plain boring. So, I take it all back: you’re right, I’m wrong, please accept my humblest of humble apologies. But at least I am happy in my folly.

to each his own folly

i couldnt agree more

BUT:

As you explained why turning upside down is abusive and not good practice i cant help but say your reasoning is flawed.
At least in radial turning as in parting.
The tool is a lever.
In "normal"turning a force is exerted onto the tip of the tool in a downwards direction.
The front of the tool is pushed down by the force of the cutting action
The force is going streight down
It will "bend"the side the tool sticks out of, downwards, and thereby forward
In doing so the front will be compressed but the back will be stressed
In "upside down"turning the force of the cutting action will "bend" the side the tool sticks out of upwards, and thereby backward
In doing so the back will be compressed but the front will be stressed
Both forces are equal
Both levers are equal

Only once you get down to the sadle/bed the forces become unequal.