Thread: Hercus Metric Question : Newbie

Hi I'm a complete newbie to turning having had a career in Computer Science. My machine is a Hercus ARLM (15612)
which I'm beginning to think about some thread cutting with. My question(s) relate to gearing and I hope I use
the correct terminology but if not please forgive me.

Let's say that I want to cut a 1.5mm thread. The chart on the gearbox tells me that I could do this in two
ways with a stud gear of 20 (using the C position and the far left gear selector) or with a stud gear of 50 and (using the B position
and the fourth gear selector). Ok understand that and believe my machine is set up with with a stud gear of 20.

When I make a small test cut the pitch is near to 1.5mm but slightly off. This leads me to conclude that my
gearing is slightly off somehow rather than a problem with the gearbox.

My question is what should my gearing look like? I can't find this information anywhere. What I believe I've got
is Stud=20T, Transfer gear=80T, Gearbox drive gear=50T. Is this correct for cutting a 1.5mm pitch using the 20T stud gear
and the aforementioned gearbox settings?

My machine also has an unused 45T tooth gear (gearbox drive). Perhaps I should be using this? If so, that would
necessitate a complete rearrangement of the gears to allow them to mesh.

If the 45 tooth gear is not part of this solution then what is it for?

Any advice would be gratefully received and if anyone knows where there are some photo's of the setups for the metric
gears I'd love to see them as I've searched without any joy.

Thanks

You should have the 45 on the screw gear and either the 20 or the50 on the stud.

If you have a spacer to replace the 50 or the 20 you will only require the 45 and spacer on the screw,and not the 20 or 50 to fill the space.

To adjust the clearance in your gear train or to make the gears mesh if there is clearance you will have to release the banjo clamp,usually a square headed set screw,you may also need to release the idler gear holding nut.

If you need to release any of these you will need to make sure that you allow enough gear tooth clearance,if theres not enough clearance your gear train noise will be excessaive.

Thanks for that Pipeclay. By the time I got your information I'd fiddled about with the configuration and
got it to cut the 1.5mm pitch with the 45T gear . I've also realised there is a Hercus thread so I'll stop clogging
up this one. Cheers

Its been a while since i played with a quick change gearbox hercus...but I could have sworn that the gear that goes on the input shaft to the gearbox should have been a 60T.

Originally Posted by scottyd

Its been a while since i played with a quick change gearbox hercus...but I could have sworn that the gear that goes on the input shaft to the gearbox should have been a 60T.

Yes that's correct, the input to the gearbox (screw gear) should be a 60T. The intermediate or idler gear can be anything you like, it doesn't change any ratios and is there simply to fill in the gap.

Pete

It is possible that you may need a 60 tooth gear but as far as I know this option was not overly common.

With the 60 you would be cutting a different range of pitches.

Seeing that you have the set of gears that came standard with one of the AM models I would say that there is more chance than not that these would be correct and you wouldn't require the 60 tooth gear.

Does your lathe a screw cutting change gear selector plate attached to the quick change gearbox.

Metric machines have 18 and 45 tooth stud gears with a 60 tooth on the box. The 18 tooth gives a decimal range from 0.25 to 2.0 mm, replacing it with the 45T gives a fractional range from 1.25 to 5 mm.

So if you have the Gearbox that requires the 60 tooth Screw gear you then need the 18 & 45 tooth stud gears.

And if you have the non 60 tooth Screw gear gearbox you would use the 20,50 on the Stud and 45 on the screw.

So then this would be correct set up for the different boxes.

Originally Posted by pipeclay

So if you have the Gearbox that requires the 60 tooth Screw gear you then need the 18 & 45 tooth stud gears.

And if you have the non 60 tooth Screw gear gearbox you would use the 20,50 on the Stud and 45 on the screw.

So then this would be correct set up for the different boxes.

By non 60 tooth screw gearbox, do you mean an imperial machine? The sud gears are then 20 and 40, with 45 on the gearbox input.

No just the Metric version.

The above is according to the thread plate on my 260 and the 2 versions of Text Book of Turning I have. The thread plate says 60T on the front.

Jmann,
This is what my metric Hercus 260 gear cluster looks like:

I don't have a clue on the hercus.

This may help though. It is worth while doing a spread sheet with all the combinations and screw constants and change gear in both inches and mm.

DSCN3004.jpgDSCN3005.jpg

Not sure where some people are going with this but it seems pretty off topic.

The original question had NOTHING to do with the Hercus 260AM.