Member postings for Sam Stones

Curiously, over a period of several years (before I bought the lathe), I had on occasion to walk past the previous owner’s house.

Over that time, I had actually seen the belt guard of the ML7 hanging from the picture rail of his upstairs box-room workshop. However, I had no idea what piece of machinery could be operating without a belt guard. Furthermore, I could never have realised that one day I would become the proud owner of his Myford.

Besides the issue of seeing the belt guard hanging from the picture rail, the centrifugal switch may have been stuck open for a considerable time, because the previous owner had worn off a substantial amount of paint from the rim of the large pulley, and introduced a sort of polished patina to its edges.

Sam

Hi Phil,

The Crompton & Parkinson 1/4 hp single phase motor fitted to my Myford ML7 used to do the same.

In my case, (and because the motor was uncovered), metal swarf was finding its way into the electrics via the motor’s ventilation holes. The shorting was not sufficient to blow fuses or trip the leaky earth switch, but it certainly made a loud popping noise when it happened. There was also a sizzling noise (mechanical not electrical), which once again was swarf. This time the swarf was rubbing against the rotor. I would guess that steel swarf was being attracted to various parts as a result of the magnetic field(s).

I cured this problem by applying metal fly wire (readily available in Australia), over the vents.

The original lathe owner had a `wonderful’ way of starting the lathe. When I bought it from his widow, the centrifugal switch inside the motor was stuck in the `open’ position. It was clear that the owner (who had removed the belt guard), was using the large pulley to spin-start the lathe motor.

I no longer have my workshop, but fitting a 3PH motor seems to be a very common improvement. See other postings.

Best regards to all,

Sam

Having replaced certain instrument parts which varied in thickness, and choosing to go via the case-hardened mild steel route, the question of final brittleness was always a consideration.

I fully support John Fawcett’s comments about cyanide heat treatment. It can be full of hazzards for both professionals and amateurs, as the following example shows.

The `hardening shop’ I hinted at in my earlier posting on this subject, was a small room next door to our toolroom. It was accessed through a personal door in one corner of the toolroom. As a young apprentice, I could never comprehend that next door to the hardening shop was a fairly large work area know as the drug-store. It must have been the most significant fire risk area of the whole factory, since it was stocked with open bins of finely powdered coal, sulphur, and various other industrial chemicals. These chemicals were openly weighed into bins, which in turn were elevated along conveyors. There were bails of natural rubber too, ready to be cut up and fed to two-roll mills and large Banbury mixers.

Back in the hardening shop were a couple of gas-heated cyanide baths measuring some 18" deep by about 9" diameter. There was also a small electric furnace for hardening HSS. I think it was normally heated to about 1250-1300C. For quenching, there was a bath of hot water, and standing on the floor was a rather large tank of oil which measured about 4' high and 4' diameter. Allowing for the volume of any items to be quenched, the oil tank was kept topped up to within an inch or so of the rim.

It became necessary to harden several cylindrical mould inserts. At a guess, these steel inserts measured about 14" long and 6" diameter. The actual mould cavity was by way of a hole down the centre of the inserts. This through-hole measured perhaps 1.7" diameter. In order to lower these inserts into the cyanide bath, the wise ones in charge made up a hook and had it bolted to the platform of one of those hand pumped stacker-trucks. The idea being that the mould inserts could be lifted from the cyanide bath and then lowered into the oil.

Unfortunately, when it came time to quench the first heated insert, the stacker truck could not be pumped up high enough to lift the insert over the edge of the oil tank. It was therefore necessary to rapidly transfer the red-hot insert from the hook of the stacker truck to a steel wire hoist above the oil tank, the hoist in turn being secured to the steel roof truss. The hoist consisted of two pulleys around which were several turns of twisted wire. The transfer went well, and the insert was lifted up and over the edge of the bath of oil.

Then the real drama began. The hoist hadn’t been used for many years, and as the insert was being lowered into the oil bath, the hoist wire spun around and jammed. This was a perfect situation for a massive fire because, with the red-hot insert half in and half out of the oil, ignition was almost instantaneous. Burning oil began to pour over the sides of the tank, and there was panic. Somehow, they managed to free the hoist and totally submerge the insert, but flames began to leap towards the roof, as sand and all sorts of other stuff was used to try to quell the blaze. Finally, the fire was brought under control. The drug-store didn’t ignite, and the excitement ended with a toolroom full of smoke and several red faces.

Because of the small bulk of the wheel, and thus a fairly rapid return to room temperature, I estimate that there would be about a 60 degree C temperature differential between the `warm’ and the `cold’ conditions.

Sam

A CAD image of the wheel.

 

 

The wheel at two temperatures.

The change of shape is very slight. Will this be enough?

Hi Nobby,

Perhaps a few words about the spherical turning attachment which I hinted at earlier.

This version works in a totally different sense, with the cutter (a short length of round HSS), inserted into the end of the nose piece on the left of the image. The cutter is inclined downwards at about 5 degrees to provide `front’ clearance, while the protruding squared-off tip of the cutter is the `top’ cutting face. In other words, the main cutting force would tend to push the cutter further into the nose piece.

Setting up requires that the axis of the device (holding the bronze bit in the tool post), is horizontal and exactly in the same plane as the horizontal axis of the lathe. The device axis should also be parallel with the cross slide movement. Using the cross slide, the tip of the cutter is then brought into line with the vertical axis of the workpiece so that when the device is rotated with the lever, the swept arc will generate a sphere.

Bingo!