The mill complements the Sherline lathe and many accessories are interchangable. Like all my machine tools, it began with an identified need to do a particular job, or more specifically, to do a job I had been doing by hand more accurately, more quickly, and with a better finish. Once installed in the workshop, I quickly found more and more uses for it.
Recently I have acquired a Sherline
rotary table with a proper worm drive, graduations, and various methods of workholding, and that has proved very useful for jobs like putting rounded ends on connecting rods. The other major piece of equipment is the
dividing head that I made for it, which allows me to make spoked wheel centres and all manner of fittings that have squares, hexagons, or circular bolt patterns.
The mill can be fitted with a drill chuck so that I can drill small holes accurately. A sensitive vertical feed for this would be useful, unfortunately Sherline do not make this as an accessory but I have an idea that one day I might develop.
I had standardized on 6 mm shank FC3 ("throwaway") cutters for the pantograph mill, and I wanted to be able to use the same cutters in the Sherline mill. Sherline sell several cutter holders, but not for this size, so I made my own. The basis is an MT1 blank arbor (not the Sherline one, though it could have been). This was mounted in the lathe, taper outwards, and the taper section was reduced to length, drilled and tapped for the clamp bolt. It was then removed, reversed, and clamped directly into the lathe headstock, so that all subsequent machining would be exactly concentric. The arbor was drilled and carefully reamed to exactly 6 mm diameter, and the outside was turned to shape. The body was then cross-drilled and tapped for a set screw that bears on the flat on the cutter shank and locks the cutter in place. Finally, a small hole was cross-drilled so that it broke through into end of the central hole, to allow the air to escape when inserting the cutter, which is a very fine fit in the holder.
The photo below shows two useful tools for setting up work in the mill. Both are made from 6 mm diameter silver steel and fit into the cutter holder. One is a centre finder. The end was turned to a point with about a 60° included angle (not critical), and can be used to pick up a punch mark in the work to be machined. The other is an edge finder, for which the end was reduced to exactly half thickness by milling, filing, and eventually finishing on an oilstone, and it is used to pick up an edge. Once I know the centre is exactly aligned with the punch mark or the edge, I can use the x- and y-axis traverses to offset the cutter to the correct amount in order to make the cut.
Problems encountered
Recently I found that the x-axis was becoming increasingly stiff to turn, but in one direction only, and the backlash was becoming unacceptably large. Adjusting the gib and the anti-backlash nut did not help at all. Eventually I discovered that the x-axis nut, which is supposed to be held in place in the saddle with a set screw, had come loose. I stripped everything down, cleaned and reassembled it, re-locating the nut. I then readjusted the gib and the anti-backlash nut for minimum backlash, and everything worked as good as new. I've no idea how it happened, but it is something to remember for the future
Bellows
One feature I have never liked is the way the y-axis leadscrew is exposed to all the swarf and chips, which I am sure can get into the thread and accelerate wear. The solution was bellows, made using a fantastic piece of origami.
Here is the pattern for the bellows and the end pieces, together with folding instructions. The only problem was finding the right material for the bellows. The author of the article says plastic, but fails to recommend any particular plastic. After some experiments, I hit on the transparent film that we used to use for overhead projectors, before computer projectors and PowerPoint took over the world. Fortunately I found a box of the stuff hidden away in the stationery cupboard. I think it is a polyester film (for what it's worth), it is sufficiently rigid to hold its shape, and shows no sign of cracking when folded and repeatedly flexed. I thought perhaps that transparent bellows were a bit avant garde for the workshop, so sprayed them matt black. They are attached to the end pieces (black styrene sheet) with double-sided tape and clip into place on the mill. What a brilliant idea.
