TWO USEFUL DODGES

By Adrian Garner

Dodge number 1- hard to hold

Castings do not always easily succumb to being held in the four jaw chuck or on the face plate.  The answer can be to use a combination of both by replacing one of the chuck jaws with a specially made T-nut (see photograph).

This is easily made from a short length of square mild steel (for many Myford size four jaw chucks 5/8” by 5/8” is perfect).  To make, the bar should be held centrally in a four jaw chuck, faced and the end section turned to a snug fit in the slot in the four jaw chuck.  The bar should then be drilled and tapped.  Mine is tapped ¼” BSF (6mm would be just as good) but for larger chucks a larger thread would be appropriate.  The T-nut can then be parted off and a shallow curved recess filed on the reverse face to allow the T-nut to clear the thread that operates the jaw of the chuck.
Another photograph shows the T-nut in action.  It will happily secure a face plate dog holding the work against the flat surface of the four jaw chuck.  The two jaws in opposition can then be tightened on to the work.  The remaining jaw, however, needs to be treated carefully and only gently tightened against the work.  It will help prevent the work slipping but if tightened to enthusiastically it will move the work under the face plate dog.

A word of warning.  This set up solves some of those awkward jobs but do not take hogging cuts or run at high a speed.  The work is unlikely to be perfectly balanced and the set up is not that robust.

A very useful and successful variation of this approach was suggested by J. L. Ridgers in the Model Engineer, 20 November 1987 for machining Quorn castings.  This involves using the T-nut to secure a stub mandrel set off centre on the four jaw chuck.  Mounting the castings on this mandrel ensures that the two holes required on each casting are the same distance apart and parallel (see photographs).


No 2 - stamping numbers

I must be a masochist.  Who takes up a hobby which includes cutting 360 lines around a dial, of three different lengths, and then tries to stamp numbers perfectly around the resulting disc?  The scope for error is enormous.  But at least when I make a mistake I have the pleasure of doing it all again.

Some years ago I decided that there are better vices (not the metal work kind) than this and I am grateful to the late great George H Thomas who reduced the chance of error in engraving the lines with the Headstock Dividing Head and his version of the J. A Radford’s Graduating Tool.  GHT’s Pillar tool also reduces the risk of error in stamping the numbers as an accessory will hold the number stamps ensuring they are upright and do not slip.  But there is still the possibility of stamping the wrong number or placing it upside down or positioning it incorrectly.

To solve these latter issues I always dap a little blue (not layout blue which dries but the sort used to test how surfaces mate e.g. when scraping) on to the numbers.  They then form a printing press needing only to be pressed onto the work by hand.  If a mistake is about to be made, no worries, just wipe off the work and correct. If the blue printed number looks OK, I repeat the process but with a light tap from a hammer.


 

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