Monday 9 July 2018
Eleven years ago, I bought a Vicmarc scroll chuck and also a set of shark jaws. I found these jaws so versatile that I use them for a high percentage of my turning. But as with many projects undertaken, one set of jaws does not do everything. I needed to grip various diameters of cylinders so set about making different sized wooden collets going from 12mm (1/2in) up to 28mm (1 1/2in) in 3mm (1/8in) increments.
These collets were made to fit inside the shark jaws. After much trial and error, I found that they worked better for me when sawn into three sections rather than the normal four sections found on chuck jaws. I also found a simple and inexpensive device to hold them together – an elastic band.
Of course the design can be modified to suit any make of extended chuck jaws and I hope you find them helpful with your turning.
Turning the blank
Steps 1 & 2
The requirement for turning is a blank of any suitable close-grained hardwood, the dimensions for my jaws being 50 x 50mm (2 x 2in) and 40mm (1 5/8in) in length, but adjust this as necessary to suit your jaws. Mark the centre on each end of the wood and mount it between centres. Turn it down to a cylinder with a spindle roughing gouge, and then square off each end using the long point of a skew chisel.
I had to measure in 12mm (1/2in) in from the end nearest the tailstock, make a mark, then to the left of this mark, I turn the blank down to 40mm (1 5/8in) diameter. Next, with a parting tool, make a cut 5mm (3/16in) deep approximately midway, as this will be required for the elastic band which will fit into the groove made by the parting tool. Again, adjust the profile and sectional pattern to suit your jaws
Drilling the hole
Steps 3 & 4
The next step is to remove the turning from the lathe and mount the scroll chuck. You can now insert the turned blank into the shark jaws, and then select a suitable drill bit for the size of hole required. In this particular case, it was a 20mm (3/4in) Forstner sawtooth bit, mounted in a Jacobs chuck in the tailstock. Drill all the way through the blank, cutting at a low speed so as not to generate too much heat. Remember to extract the bit regularly to remove the dust and shavings. Once the hole is cut you do not have to sand the bore you have just cut; you can, if you want it ultra smooth, but this is not necessary
Marking & cutting
When this has been done, remove the collet from the chuck, measure and mark the drilled blank into three 120Â° sections, take it to the bandsaw, and cut it into three parts. By using a fine-toothed bandsaw blade you will keep tearout to a minimum. After cutting, lightly sand the edges of the collet to remove any sharpness or splinters and after this attach the elastic band into the cut recess to keep all the bits together. The collet is now ready for use
Using the collet
Steps 6 & 7
Repeat the procedure changing the cut hole size to create as many different sizes as you require. There are extended jaws available for other makes of chuck, which would also be suitable. Two that I know of are the O'Donnell jaws, and the Nova spigot or long-nosed jaws. You can see a cylinder of wood held perfectly in the 35mm (1 3/8in) collet set. It is important to match the diameter of work to be held to the collet size or you will not have a secure hold. I hope this helps you to make your own. The collets are very handy indeed and don't take a lot of time or money to make.