A collet holds drill bits and end-mills as well as other small diameter work pieces much more securely and accurately than a chuck. Unfortunately collets come in fixed sizes, either in imperial or metric units. Nowadays it is easier and cheaper to get metric sized tool bits, and it is much more convenient to use metric units.
The trouble is that while Taig supplies an optional set of imperial collets and collet holder, and an expensive ER16 metric holder, I cannot find on the market any other metric collet holder which can be screwed directly onto the headstock spindle. The closest I can find is an adaptor collet holder which accepts an 8 mm shaft to be secured in the common chuck. There are 3 sizes available, ER11, ER16 and ER20. ER11 accepts bit sizes from 1 mm to 7 mm and is quite adequate for the Taig, and it is cheap enough.
So I bought an ER11 collet chuck adaptor, and a set of metric collets with it. I can use it as designed, or simply secure the whole thing in the chuck without using an 8 mm shaft. However, there is no guarantee that the adaptor will run true in these configurations, and it almost certainly will not. If it does not run true then the whole purpose of using collets is defeated. I therefore decided to make the adaptor into a holder which can be screwed onto the headstock spindle and aligned to run concentric with it.
Step 1: Materials
One ER11 collet chuck adaptor;
One Taig blank arbour, part No. 1132; and
Some silver solder.
Total cost is less than $10.
Step 2: Design
The design is quite simple. It basically involves attaching the collet adaptor onto the blank arbour for screwing directly onto the lathe spindle.
The blank arbour supplied from Taig is first shortened by about half an inch so that the final product will not be too long which may magnify any initial runout.
The collet adaptor has a stem diameter of about 15.7 mm. The arbour is bored to slightly bigger than this size, say 15.8 mm, to the full depth of the stem. Two flat notches are milled onto opposite sides of the arbour sleeve to accept a wrench for tightening.
The collet adaptor is then inserted into the sleeve and soldered in place.
Step 3: Preparing the Arbour Sleeve
With chucks removed, the blank arbour block is screwed directly onto the lathe spindle. 12 mm is then cut off the blind end with the parting tool. A centre hole is drilled into the blind end of the arbour. From this, an 8 mm hole is progressively drilled to a depth of 22 mm. This is then widened to 15.8 mm with a boring bar. With the two grub screws removed, the collet adaptor should slide loosely into this cavity. The drillled and bored arbour (the arbour sleeve) is then secured onto the cross slide with a long #10-32 screw and a square nut. Placing an 8 mm end mill in the chuck, a notch is milled onto the side of the arbour to a depth of 3.2 mm. The lower edge of this notch is 27 mm high from the threaded end of the sleeve. There is no magic in the choice of this height. In fact, it does not really matter where the notch is precisely placed. It just happens to be handy without the need to set up.
The arbour sleeve is loosened from the cross slide and turned 180° around. A second 8 mm notch is then milled, also to a depth of 3.2 mm. The two milled notches should be parallel to one another. The thickness of the notched section is 19 mm. These flat notches allow a suitably sized wrench to be engaged to tighten the arbour onto the headstock spindle, as well as to tighten the collet holder nut.
Step 4: Solder in the Collet Adaptor
The collet adaptor is then soldered into the arbour. Firstly, a 5 mm feed hole is drilled on the side of the arbour sleeve about 10 mm from the top, in between the two milled notches. This hole allows solder to be introduced into the space between the adaptor and the arbour sleeve. Actual size of this feed hole is unimportant.
The collet adaptor needs to run concentrically with the arbour sleeve. I don't quite trust that the cheap adaptor will run true from the box, so I devised a way to make sure that when the collet arbour is made, it will run true no matter what.
The arbour sleeve is screwed tightly onto the headstock spindle. A 6 mm by 150 mm rod (from a printer) is secured onto the collet adaptor using the 6 mm collet. This rod will form the guide to true up the collet holder. I screwed the Jacobs drill chuck onto the endstock. The jaws of the chuck is opened just wide enough to allow the 6 mm guide rod to slide in when the end-stock is moved into position. This should hold the collet holder off the wall of the arbour sleeve, with a gap of approximately 0.05 mm in between. The soldering surfaces are cleaned with acetone or alcohol and a generous smudge of soldering flux is applied to the surface of the collet holder stem and the inside surface of the arbour sleeve, as well as the inside of the 5 mm feed hole. The collet holder is then slid entirely into the arbour sleeve, ready for soldering.
Protecting the headstock with aluminium foil, I slowly heated the arbour sleeve with a propane torch. When the metal is heated to around 250°C I started to introduce solid silver solder wire into the 5 mm feed hole. The molten solder will start to seep into the gap between the two metal blocks by capillary action, and when enough solder is introduced, some will start to flow out from the side.
This is the critical part for centering the collet holder. The flame is removed and the solder will start to slowly solidify. The Jacobs chuck jaws are slightly loosened. Put some grease on the rod between the jaws. Switch on the lathe motor and allow the soldered unit to rotate. The guide rod should rotate as well as the solder cools and becomes less fluid. As the soldered pieces rotate, the guide rod makes sure that the collet holder is centred while the solder continues to harden. After leaving the joint pieces to cool, the Jacbos chuck can be slid off, and the motor turned on to see how the pieces have joined. If the pieces are correctly soldered the guide rod will run true. I did not use a gauge to measure the run-out, but judging by eye alone, I could not spot any appreciable run-out at all even at the tip of a 150 mm rod.
Step 5: Final Step and Conclusion
This whole project took a morning to complete.
I sanded the surface of the completed collet arbour which has been discoloured by heat. I also dressed clean any excess solder flowing out of the collet holder and sleeve gap.
The applied heat in soldering is no more than 300°C so little if any damage is done to the lathe or the other parts of the collet, as well as the inserted centralizing guide rod.
I used several drill bits and end-mills on this customized collet arbour and ran some test on scrap pieces of steel. The tool bits are securely held and no run-out is observed. I am totally satisfied with this project.
Step 4 was edited on August 29 2017 to show improved centering method and result.