Quick Change Lathe Tool Holder

Harold Hall

This just leaves two tasks for the lathe, the Height Adjuster Washers (3) which needs no comment and the Locking Spindle (5). For this, take a length of 12mm diameter and set to run true in the four jaw chuck with about 40mm projecting, turn to 6mm diameter over 9mm and to 8mm diameter over a further 21mm. These diameters should be a close running fit in the body.


With that done, off set the part by 0.35mm in the four jaw. This giving a total indicator reading of 0.7mm, Photo 26. Keep reducing the diameter over the 10mm length shown on the drawing until a new diameter is fully made. This, nominally 7.3mm diameter.


The easy way to detect when the diameter is fully machined is to cover the initial diameter with marking blue, then, as the depth of cut is increased the width of the blue surface will reduce. When this becomes narrow, say 6mm, reduce the infeed by very small amounts, say 0.025mm, and repeat the cuts until the blue is completely machined away. Leave the part at this diameter whatever, the 7.3mm above just being a guide.


Do not part off at this stage to produce the 15mm high head as it just may be necessary to return the Locking Spindle to the lathe to reduce the diameter of the cam. Remove from the lathe and cross drill hole A in the head for the Tommy bar


Photo 27 shows that I used my Hemingway Kits cross drilling jig which normally I use on the top slide where the vee in the side lines up with the lathe's spindle. The hole can then be started with a centre drill, the position of the hole being set using the cross slide. In this case I used the jig in its other mode, that is on the drilling machine. A drill bush is not needed for each drill size but first drilled using a smaller bush, this then removed and the hole opened up to the required size.  


Now insert the Clamp Assembly into the Body and the Locking Spindle ( as made so far )into the Body, fit a Tool Holder and check that this tightens securely.


If the Locking Spindle will only turn so far but not secure the Tool Holder adequately then the cam diameter needs reducing, say by 0.05mm, no more. To do this, return it to the four jaw and set the cam to run true, reduce as above and retest.


Whilst very unlikely, if the cam rotates fully without adequately securing the Tool Holder then add a thin shim between the Tool Holder and the Spacer, increasing its thickness until a secure hold results. In this case add a new thicker Spacer as the test indicated.


Workshop Projects

Dial Indicator using
Cross Drilling Jig "Hemmingway kits"