Author Topic: Centre marking/indenting larger quantities of square (and round) stock for spind  (Read 4076 times)

Offline macbrat

  • Jr. Member
  • **
  • Posts: 9
I’m often reminded on Youtube videos of how tedious it can be marking up centres of square or round stock in preparation for turning between centres, using centre square tools or straight edges. This is fine for a few blanks but for a dozen or more, time consuming and tiresome. There are many gadgets around, both commercial and DIY. I’ve made a few myself. Where possible I like to adapt/use existing tools that are idle in my tool kit and intended for a different primary purpose. Here are three examples:-

1.   Four jaw self centering chuck method.
Make up a plug with a small centre spike, either threaded (if you can cut your own threads) (Fig.1). or snug fit, to go into the centre of your 4 jaw self centering chuck. For the unthreaded bungs it’s worth having a small base fillet to stop the bung sticking to the stock and being pulled out.
The plug(s) needs to be able to be set level with the front face of the chuck for larger stock (Fig 2), and level with the lower face for smaller stock (otherwise the jaws will not be able to close onto the smaller stock) (Fig 3).
That’s it! Just close in the jaws to a sliding fit and hammer the stock into the spike. Larger stock. (Fig. 4).  Smaller stock. (Fig. 5).

You have centre marked and indented at the same time, ready for mounting on the lathe. p.s. I posted something similar on a different machinists website about five or ten years ago but I’ve repeated it here for good measure.
 
2.   Socket spanner set method.

Socket spanner sets do not of course have the same capacity as the 4 jaw self centering chuck mentioned above. They can typically accommodate square nuts/stock up to an inch or so. Similarly here, make up an unthreaded bung with a centre spike out of metal (Fig. 6), or hardwood, that fits snugly into the square shaft of the best fit socket (Fig 7).
 
You can also use the appropriate sized socket directly in a three jaw chuck to hold your square stock. (As I mentioned in an earlier post this month for metal stock. See ‘holding square stock in a three jaw chuck’).

3.   Ferrule on drive prong method.

Make up a ferrule/collar with an inside diameter that is a sliding fit over the headstock drive centre/spur drive and long enough so that just the teeth of the drive centre protrude (Fig.8).

For centering the stock, the outside diameter should be just a tad smaller than the ‘usable round’ of the work-piece, which can be any cross section shape ( a log in the round for example). Hold the ferrule in the ‘chosen centre’ of the work-piece, carefully slide the ferrule over the drive centre so as not to knock the ferrule off centre and push onto the drive centre Fig. 9. This can also be used for tail stock centre marking.
 
A slip-ring / sliding ferrule is also useful for cutting tenons for holding in specific sized collets. (Figs. 10 & 11). When the correct tenon diameter is reached, the chisel is prevented from cutting deeper by the slip-ring which becomes stationary.

In summary, clearly one has to balance the extra work involved in the making of these ferrules against using the immediately to hand usual tools. e.g. centre squares, straight edges, callipers and diameter sizing tools. It’s all about production quantities / task repetition.