Reversing Drawbar for Hercus A

[BobL]

Recently I purchase one of the fancy parting blades from Eccentric engineering and it has been excellent used in the normal way but I was interested to try it upside down but did not like the idea of operating on the backside of the lathe and of course operating the non-locking chuck in reverse is a bit of a no-no.

Yesterday I took the larger 3 jaw chuck off the headstock and it dawned on me that maybe a drawbar arrangement could be used to hold that chuck on for reverse operations.
So here is what I did.

Step 1
Remove the backing plate from the chuck


Step 2
Insert a 4mm thick spacer over the headstock spindle (behind the backing plate) and screw the backing plate back on
I used a 4 mm thick piece of ally plate - I drilled the 38 mm hole with a Forstner bit on a DP - lots of metho as a lube..


Now with the backing plate proud off the spindle turn a 42 mm OD by 3.5mm step in the backing plate,


Turn up a ring/washer that has the OD and thickness of the step and the iD of the headstock spindle
Reassemble chuck with ring retained inside the chuck


Make up a drawbar that can pass through and sit up against the ring inside the chuck at one end, and the other end in the usual outboard end of the headstock spindle.
This one has the chuck insert end welded onto 12mm all thread and the other end is a stepped threaded locking nut arrangement that mounts like other drawbar locking nuts.


Below is a close up of the partially split locking nut.
I decided to use this arrangement because of the reversing situation.
These locking nuts are used to secure spindle moulder cutters so I figure they should work OK here.
There is no need to do the knurled knob up more than hand tight, once that allen bolt is done up the knob is not moving.


Hardly up to the pro level of finishes and fits but there is nothing here that is critical in terms of fit anyway.

Drawbacks - obviously one can't use the through spindle in reverse but I don't use my through spindle much but can now see reverse being used a lot more often.

I tried it out on a few things, like fast reversing out of a thread being tapped, and I'm loving it.

I've since had a bit of a look around on the web to see what others had done about this and I could not find anything although someone has mentioned using a drawbar but no details were supplied.

[Stephen Gorton]

Very good Bob, you put some thought into that

stpehen

[pipeclay]

If you run the parting tool upside down on the rear of your cross slide the lathe will have to run as per normal. ( anti clockwise ) so it won't come off.

[BobL]

If you run the parting tool upside down on the rear of your cross slide the lathe will have to run as per normal. ( anti clockwise ) so it won't come off.

I an aware of this but that's not possible on a standard Hercus A as the crossslide doesn't go across enough to do this.
On mine the centre of the cross slide barely passes the centre line of the lathe.

[pipeclay]

So you are running it inverted in the normal way?

[BobL]

So you are running it inverted in the normal way?

With the special chuck holding drawbar in I have run the lathe in reverse a number of times but haven't tried inverting the parting blade and running the lathe in reverse.
I have used the EE parting tool in a normal way i.e. not inverted and lathe running forward and it seems to work very well, well much better than a regular parting tool.