Thread: Removing the headstock of a Hercus AR

If you go the replacement ring, you will need to either use the lathe you have or be able to get a lend of one.

If you put your lathe back together it can be used without the back gear in place.

I would recommend if you use your own lathe that you change the motor pulley to a smaller size, maybe half of what it is know for the machining as the lowest speed you have will probably be to fast for the diameter in cast that you will be turning.

I would suggest you make a mandrel so you can slide the back gear on, in this case a tapered mandrel wont really work well, a parallel mandrel with shoulder and nut would be better or a tapped hole in the end with a heavy washer and set screw.

Holding it in a good 3 jaw or 4 jaw with a centre might work ok.

You will need to measure the ID of the ring in 3 or 4 places to see if it is round and also so you can note the size/s of the bore.

Once you know the ID size you can then give the allowance for the shrink fit, rule of thumb .001" to the inch, in this case around .003".

Your finished size for the back gear should be .003" bigger than your measured ID of the replacement ring.

After you have machined the back gear and remove any burrs you can then heat the replacement ring until it fits over the machined back gear.

Cant tell you a temperature but if you have a pair of inside calipers set them to .001" to .002" larger than the OD of the machined back gear, when the calipers drop through the replacement ring it will be good to go.

I would suggest that you put the ring onto the back gear rather than the back gear onto the ring.

If you can support the machined back gear on two pieces of material that are flat then the ring can be dropped over the machined area and the flat surfaces will align it with the machined back gear.

After the ring has cooled enough ( probably 1/2 to 3/4 of an hour you can then if required or desired drill for one or two roll pins that will then stop any rotation of the ring on the machined back gear.

If needed a repaired back gear with replacement steel gear will set you back about $70.00 on an exchange basis.

Originally Posted by pipeclay

If you go the replacement ring, you will need to either use the lathe you have or be able to get a lend of one.

If you put your lathe back together it can be used without the back gear in place.

I would recommend if you use your own lathe that you change the motor pulley to a smaller size, maybe half of what it is know for the machining as the lowest speed you have will probably be to fast for the diameter in cast that you will be turning.

I would suggest you make a mandrel so you can slide the back gear on, in this case a tapered mandrel wont really work well, a parallel mandrel with shoulder and nut would be better or a tapped hole in the end with a heavy washer and set screw.

Holding it in a good 3 jaw or 4 jaw with a centre might work ok.

You will need to measure the ID of the ring in 3 or 4 places to see if it is round and also so you can note the size/s of the bore.

Once you know the ID size you can then give the allowance for the shrink fit, rule of thumb .001" to the inch, in this case around .003".

Your finished size for the back gear should be .003" bigger than your measured ID of the replacement ring.

After you have machined the back gear and remove any burrs you can then heat the replacement ring until it fits over the machined back gear.

Cant tell you a temperature but if you have a pair of inside calipers set them to .001" to .002" larger than the OD of the machined back gear, when the calipers drop through the replacement ring it will be good to go.

I would suggest that you put the ring onto the back gear rather than the back gear onto the ring.

If you can support the machined back gear on two pieces of material that are flat then the ring can be dropped over the machined area and the flat surfaces will align it with the machined back gear.

After the ring has cooled enough ( probably 1/2 to 3/4 of an hour you can then if required or desired drill for one or two roll pins that will then stop any rotation of the ring on the machined back gear.

If needed a repaired back gear with replacement steel gear will set you back about $70.00 on an exchange basis.

Looked like only two of the ring gears left on Friday last week. Doesn't look like they are a fast moving item by the surface rust but certainly a good fix. Price was $20 from memory.

Originally Posted by neksmerj

Hi Stephen,

I presume you replaced your bearings with standard grade, which should be ok.

I priced Timken precision 3 bearings some time ago. A complete set was over $1000.

Ken

Hi Ken, and for those who have the model AR, last week when I posted that I had bought a new set of bearing for the headstock of my AR, I just paid $114.40 and didn't take any notice of what bearings they were and as they had to order them I presumed they'd be the generic. I got a phone call last Friday to say they were in so I called in today to pick them up and I couldn't believe it, they are Timken so it looks like they're a very good price and the pick if you're replacing headstock bearings.

Cheers
Stephen

The price you paid for those bearings is about right.

As mentioned earlier, those bearings come in different grades of precision.

For the amount you paid, they would be standard grade. I'm pretty sure Hercus used precision 3 bearings, and that's where the price sky rockets up to over $1000 a set.

For a home hobbyist, I don't think bearings worth $100 or $1000 will make much difference.

Ken

Ken there was nothing special grade about the bearings Hercus put in there from new. They were schmuck grade, and definitely not $1000 ultra-precision bearings.

I just went through the exercise with Timken technical engineers as to what difference higher grade bearings would make from the same manufacturer, as I was looking to increase the spindle stiffness by running higher preload. The bottom line is the only difference will be in the roundness of the work, and on lathes like this we probably have bigger fish to fry in regard increasing the precision.

I've pulled the spindle a number of times on both my Hercus lathes and the Type 0, and just use a pipe as suggested by Mal. Indeed I've just used PVC pipe as it's just in compression. However it's definitely a tight fit and the poor old PVC must be right on the limit, with the potential for it to turn ugly it definitely wouldn't be my material of choice! However the principle is quite straight forward, and a suitable size aluminium tube or similar would be ideal, along with some all thread. One way or the other definitely pull the spindle off and on, and don't start hammering away of the poor old bearings.