Member postings for Sam Stones

Further to my previous posting, I have to say that I haven’t been grocery shopping this week. That is the domain of my dear wife.

So, although there have been no requests for a photograph, I don’t have a fresh tub of margarine to demonstrate the action of how metals actually `cut’. Instead, I’ve cobbled up a simple diagram to show what I remember of the so called `cutting’ action.

My hypothetical diagram is based upon a simple cutter (tool bit) shaped like a wide parting-off tool, and placed as if it were installed in a toolroom shaping machine or indeed a planer.

The tool bit is tilted back at an angle of 10 degrees to provide top rake, while the underside (actually known as the front face or end relief angle) is also backed off by 10 degrees. For simplicity, the workpiece is narrower than the width of the cutter. As usual, DOC indicates depth of cut.

This reminds me of the time when I was bending down near a shaper already `cutting’ metal. While searching for some bolts and clamps in a tool box, a very hot piece of swarf landed on my head. As I tried to brush it clear, it wrapped itself around my finger while still hot enough to continue to burn anything it touched. There was a strong smell of burning hair and skin, and my language was not that of a gentleman.

Hi Norman,

Although I have stood for many hours watching swarf in many forms as it leaves various machine-tools, and can remember a little about Mohr’s Circle as applied to metal cutting theory, I cannot venture too far down this burrow. It is unfortunate however, in the context of metals, that we use the word `cut’.

I say this because the action is more complex.

For simplicity, I’m basing my comments upon the action as seen during the surfacing of a round bar of metal in a lathe. 

Let it cool first!!!

It is usual to see a form of rough `shuttering’ or shark-skin on the inside face of the swarf, while the outside face appears `polished’. This polishing is a result of the material being compressed and then burnished as it slides over the top face of the tool-bit. The shuttering is evidence of the stop-start failure pattern.

The shear plane varies from metal to metal, and will also be influenced by the angle of the top rake. Beyond this, and in terms of the energy dissipated, etc., I am out of my depth.

I can however, invite you to explore the action using a fresh tub of margarine from the fridge, and a normal table knife. Between meals and with the permission of SWAMBO, the kitchen is a wonderful place to investigate.

For this test, the knife does not have to be sharp. Taking hold of the knife as if you were about to `butter’ a slice of bread, tilt the blade at right-angles to the surface of the margarine. Starting from one side and with the blade pressed into the margarine a few millimetres, sweep the blade across the surface is if it were a planing tool.

Given that you have got the angle about right, you should see (stuck to the knife) an enlarged version of a piece of metal swarf.

If, for any reason, especially if SWAMBO is hovering around, and you need a bit more detail, I’ll shall be quite happy to take a photograph or two and plonk them into the thread.

Good luck!

Sam

Or has he?

Don’t take this personally Nick, because (I hope) I’m trying to bring attention to an important part of Terry’s original idea.

If it were (all) 3rd angle dangle, sorry projection, shouldn’t the small square of my original PLAN view be dotted? And where should the PLAN view be positioned to avoid this? In the words of `Top Gear' James May "Oh cock!"

While, from a young age, I learned to draw in 1st angle (as a Pomme - English projection comes naturally), I have become `tolerant’ to 3rd angle projection, a method better suited to drawing very long objects such as aircraft and ships.

However, I still maintain (and have taught for many years) that 1st angle is by far the better system for moulds of the injection type. In the plastics industry (especially this country), countless drawings are constructed in 3rd angle, an Australian industry `standard’. Sadly, the views and sections end up in all sorts of weird positions, contradicting the basic rules of 3rd angle, and showing little to no resemblance of how the mould is positioned in the moulding machine. The primary desire appears to be to use up as much space on one drawing, with part of the mould sitting sideways on the bench.

Then along came CAD.

This was the door which opened us up to the wonders of 3D solid modelling but, I believe, caught a lot on the hop. To keep pace with a changing world, they had to learn CAD, and with most commercial software, months of training was often required (and still does).

Personally, other than the cost, I found 3D CAD a delight, and only look(ed) upon 2D as a means of initial construction or when conveying information when my client requested dimensioned (paper) drawings via the plotter.

Perhaps we should wait a little longer for someone to show us other alternative solutions to what has become known here as Sam’s test!?

Best regards to all who sail in her,

Sam

By the way, is a nurd, (nerd, nurd), Imperial or Metric?

Geoff, Thanks for your comment. Bob Sheppard (from Harper Green Secondary Modern School, in Farnworth c.1946) holds a very important place in my memory.

Tony, I think you’re right. Where are all the responses to the test?

Yes, I think you’re right too Steve. It must be too simple a test.

I have another anecdote for those of you who are enjoying Terry's thread. I must preface mine by saying that Melburnians have an expression about exposing ones posterior in Burke Street, so here goes.

In the late 50's, it became necessary to redesign the outer casing of a toilet cistern. At that time, the casing and lid were being compression moulded from a composite of pitch and other reinforcing materials. The `new’ material was the much more modern thermoplastics polypropylene (PP), and had become commercial around 1957. Unlike the pitch compound, PP could be injection moulded. The specification also included that the existing innards of polyethylene ball valve and syphon, and various metal fittings were to remain.

The cistern casing was designed for both `high’ level and `low’ level operation, and for greater adaptability, was identical left to right. It was necessary with this `new’ material to provide parallel wall thickness by local thickening the five inlet/overflow/outlet positions, thus forming `bosses’ on the ends and underneath.

The next task was to design and detail the tooling (injection moulds). Eventually, I had produced about half a dozen sheets of tool drawings for the cistern’s lower half. These drawings, having passed through the checkers hands a couple of times, and gained approval at various other levels, were sent off to a German toolmaker. Two injection moulding machines were duly ordered and installed, and after about 6 months the cistern and cistern lid moulds arrived.

"Have a look at this!" It was the chief draughtsman.

One of the end bosses was missing! But how could that have happened?

It turned out that on the GA and also in detail, (having sectioned the mould through various planes to show the feed arrangement, water circuits, air ejection, etc. etc.), I had inadvertently omitted to show that the cistern was actually symmetrical about the vertical centre line. The toolmakers had gone ahead and worked exactly to my drawing.

Eventually, the problem was rectified, but by this time I had (coincidentally), taken on a new position with a major raw-material supplier. This company supplied PP, the very supplier of the grade being used for the cistern!!!?

Guess what? The bl . . y cistern followed me there with another problem. But that’s yet another story.

They say things come back to haunt you. But surely not twice. A couple of evenings ago, my wife and I were watching a very early `On the Buses’ episode. Bus driver, Stan Butler was replacing their old toilet cistern with a modern low-level version, and as usual, he was getting into all sorts of bother.

You’ve guessed it!

I recall making the brass ring a tight fit onto the (interface) diameter of the steel `sink’ and, before fluxing, I made absolutely sure that everything was clean. An old RAF trade-training catch phrase was `Clean and Tin’. But that was for soft soldering electrical work.

Upon scanning the 1972 ME (five part) article, it would appear that I actually deviated from John Stevens design of a one-piece brass wheel, and followed the bi-metallic design as described by Gazeley. What was I thinking???

I have no real experience of rolling except from forming some 1/16" aluminium sheet into large cylinders about 8" diameter and 5" long. They were casings for the lights of some TV show or other. Again too long ago. However, with respect to its visibility, unless you obtain a truly round wheel, it will look somewhat primitive as it oscillates. That has been one of the issues I’ve had to address wrt the helical balance spring in my clock. In other words, unless the wire of the spring is accurate in pitch, diameter, and held central at both ends it will `wobble’ and look odd.

I think you have started at the right `end’ of the clock, because once you have determined the `beat’, then the gear(box) design should be relatively simple.

Good luck,

Sam

Hi again Richard,

Without too much thought, an obtuse idea momentarily traversed some of my neurons.

Since you have actually contemplated using tin cans, could you apply sufficient brass to a flat strip of steel, and then carefully bend the result (with the brass on the outside), to become your wheel rim? After all, the rim will (normally) be in two semicircular pieces.

I feel sure that you will have already perused the ME Forum for ideas!?

If not, then insert `Balance’ into <Keyword> and `Clocks’ in <All Topics>, this brings up several posting about issues I had with balance wheels and balance springs.

In particular, they highlight some of the `struggles’ I’ve had with the escapement of my skeleton clock.

Clearly, the larger size of your intended wheel is likely to introduce additional challenges, which may not have surfaced during the time I was making my balance wheel, c.1973

As for the spring, that was becoming quite a saga, for me at least. However, thanks to the generosity of one of you gentlemen, I have been sent a spring which has all the makings of a very close approximation to the recommended design.

Second Clue - The wire is 5/16" (0.8mm) diameter steel.