Thread: Gears, Fears & Tears...

I posted this originally in another forum, so sorry for the Southbend references...

As follows...

Okay... I have owned an Australian Hercus 9AR (copy of a Southbend) lathe for maybe twenty years now.

At first, it only ever got a little rudimentary use, but as time has passed, it plays a larger role in my work.

Great little lathe, and when I bought it all those years ago, it came with every conceivable Hercus accessory you would ever need, including a STACK of change gears.

Now, here's the thing... I am wanting to learn threading, and I have ALL of the equipment, and a little knowledge, so it should be fun, but... I am still not sure if the gear train I am running (which I have NEVER changed), is in actual fact, the set factory correct gear train.

I have spoken to Hercus here in Adelaide, South Australia, but they are of no help, and don't really want to help.
I have scoured the net, and believe I have found what is purported to be the STANDARD gear train for the Southbend, which is as follows...

The typical set-up for the quick-change gearbox is
20 tooth stud gear,
80 tooth idler gear,
56 tooth gear on the input shaft of the gearbox,
40 tooth stud gear used for very course threads
(This gear is used in place of the 20 tooth gear and stored as a spacer on the input shaft of the gearbox when not in use).

This makes sense, sort of, but WHY, do I have all of these OTHER gears, as well as a 127 tooth for metric?

Can someone perhaps demystify the correct FACTORY set-up, for the imperial lathe I have, as well as somehow, explaining to me WHICH gears I need to change, to cut metric threads, and how?

Even a picture would help.

I have the second edition copy of the Hercus manual, but it doesn't really elaborate that much I'm afraid...

I think I'm missing something here, or over analysing.

Cheers

Ian

All the information you need for cutting the Metric pitches as shown in your book is there,you just need to be able to understand it.

The chart in the book lists the gears required to cut different pitches and tells where they are placed.

What can be confusing is when they show lever positions.

The lever positions are for the quick change gearbox.

The levers (both of them) have to be set up in the correct position to cut the TPI listed(Imperial) for the Metric pitch you wish to cut,

eg select metric pitch,set levers to cut the nominated number of threads on your gearbox,change stud gear,change compound and change screw gear.

Cheers, yes, you are right, but what I am more worried about, is what is the factory standard gear placements on the lathe, incase what I have has been altered with.

I have a LOT of spare gears, and the Hercus book makes no reference to these, it talks of 127 and 100, and I'm still stumped as to how I actually configure those. So many places I could put them...

I am quite mechanically minded, but it all seems a bit ambiguous to me at this stage.

If someone could post a picture, showing the STANDARD gear train, denoting the names of the gears, and their teeth number, then I can compare, to see if my set-up is standard... or not.

Cheers

Ian

Originally Posted by pipeclay

All the information you need for cutting the Metric pitches as shown in your book is there,you just need to be able to understand it.

The chart in the book lists the gears required to cut different pitches and tells where they are placed.

What can be can fusing is when they show lever positions.

The lever positions are for the quick change gearbox.

The levers (both of them) have to be set up in the correct position to cut the TPI listed(Imperial) for the Metric pitch you wish to cut,

eg select metric pitch,set levers to cut the nominated number of threads on your gearbox,change stud gear,change compound and change screw gear.

Not sure what you are having problems with.

Someone else may take the time and effort to re arrange there Imperial drive chain to all the different Metric configurations and take a series of photos for you.

You already have the correct gears and placement for Imperial threading.

If you wished to cut Metric threads you would do as described previously.

If you confusion lays with the positioning of the 127/100 compound gear,it is placed in the position of where your 80 tooth idler gear is at present.

The 127 tooth gear meshes with the Stud gear displayed in the book/chart for the particular pitch and the 100 tooth gear meshes with the gear stated in book/chart for the screw gear.

You will have to use either a small gear or spacer on the screw shaft so as to allow clearance for the 127 tooth gear to turn freely.

You may also have the 127/100 tooth gears currently as single/seperate gears,you should have a small bush and key,this is used to combine the 127/100 together forming a compound gear.

This message relates exclusively to the issue of what you do to get metric threads from an Imperial model of the lathe when you have the 127 tooth gear and 100 tooth assembled together as a compound gear. (It sounds like you have the 127 and 100 separated, but they have to be locked together into the one compound gear, assuming you have the bits and pieces to do that.)

Two versions of the change gear configuration charts for Hercus 9" Model A lathes.

Hercus Metric Thread Chart for Model A lathe.JPG


Metric Thread Chart for Hercus 9 Lathes Model A.png

As those may be too small to read, if you log in to the forum, you can then click on each image to see each in a new window at larger size.

It might be possible to clarify your circumstances if you photograph the current change gear setup and photograph the serial number on the bed and photograph the manufacturer's plate on the gearbox with the model (if any).

I might be wrong, but looking at the charts above, there are no configurations in which the stud gear should be 20 teeth, and it seems from what you write that you have a 20 tooth gear on the stud gear position. The stud gear can be anything from 28 to 48 teeth, depending on the result you want. The screw gear should always be a 56 tooth gear.

If you know enough of the maths behind it, you can do things however you like that works, forget about the charts, there is more than one way of doing the same thing given enough gears.

Donald

I know you know what your gears are for, but some of the new owners need to know. I include a diagram of the standard Hercus model 9A gear arrangement, so people can just print it out. No direct bearing on your question, the others have answered that. model-9A-standard-gears.jpg

Originally Posted by allterrain50

I know you know what your gears are for, but some of the new owners need to know. I include a diagram of the standard Hercus model 9A gear arrangement, so people can just print it out. No direct bearing on your question, the others have answered that. model-9A-standard-gears.jpg

Actually, that photograph, was EXACTLY what I was looking for!

You see, I wasn't sure, if the gear train had been changed, in all the time I have owned the lathe. Thank you for posting.

I did manage, to work out, what the standard configuration is, thanks to some help from another forum. I ALSO, managed to work out the ratios for metric, which equates to all the spare gear sets I have, so home and hosed.

I also, managed to cut my VERY FIRST THREAD!!!

3:8".jpg

Originally Posted by Ian Bee

Actually, that photograph, was EXACTLY what I was looking for!

You see, I wasn't sure, if the gear train had been changed, in all the time I have owned the lathe. Thank you for posting.

I did manage, to work out, what the standard configuration is, thanks to some help from another forum. I ALSO, managed to work out the ratios for metric, which equates to all the spare gear sets I have, so home and hosed.

I also, managed to cut my VERY FIRST THREAD!!!

3:8".jpg

Well done Ian, a lot better than my first effort.
Mal

Originally Posted by Ian Bee

Actually, that photograph, was EXACTLY what I was looking for!

You see, I wasn't sure, if the gear train had been changed, in all the time I have owned the lathe. Thank you for posting.

I did manage, to work out, what the standard configuration is, thanks to some help from another forum. I ALSO, managed to work out the ratios for metric, which equates to all the spare gear sets I have, so home and hosed.

I also, managed to cut my VERY FIRST THREAD!!!

3:8".jpg

Hi,

Looks good.
Which method of cutting the thread did you use? Ie, chasing dial or reversing etc, plunge cut or offset?

Thanks Ben.