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I suggest the type of corrosion called de-zincification. The zinc has been preferentially dissolved leaving the copper - hence the copper colour. The photo shows a similar failure in a garden tap fitting.

Rod.

The maximum tensile stress (tangential direction) in a rotating disk with a central hole occurs at the cylindrical surface of the hole (i.e. minimum radius) and reduces as the radius increases (to about 1/4). Removing a concave dimple near the inner radius will increase local stresses further (stress raiser). If the material has a sufficiently high fracture stress compared to the peak local stress - no matter. But why unnecessarily increase maximum stress? The only possible purpose I can think of is post-manufacture balance. One then wonders whether the manufacturer knew his business. I encourage further investigation beyond the retailer.

Here is a good book that covers the topic. Holes, Contours and Surfaces Richard F. Moore, 1955 Predates DROs etc. The second book at the link is also highly recommended.

**LINK**

John Stevenson’s comment about 60/63 being used “instead of” 120/127 might, for some, leave the impression that the approximation comes about because 63 is the closest integer to one half of 127 and is, in comparison, compact and hence more convenient. But not so – the error would be one part in 126 (or 127 for their reciprocals). As stated in other posts, a 127 tooth gear will produce a mathematically exact metric pitch on an imperial lead screw, being the exact number of mm in 5 inches and the lowest integer pair that expresses this exact relationship.

For metric pitches using an 8 tpi leadscrew, the exact desired conversion ratio is 25.4/8 mm per one leadscrew pitch, or 25.4/8 = 127/40 = (127/100) x 2.5 = 3.175 (exactly). It just happens that this is closely approximated by 200/63 = (80/63) x 2.5 = 3.174603…, just 1 in 8001 smaller (12.5 microns per 100 mm, or 0.0005” per 4".

Notice though, that whereas the 127 tooth gear forms the numerator (a driven gear), the 63 tooth gear forms the denominator (a driver gear). It is not performing the duty of an approximate 127 tooth driven gear (i.e. not 63 x 2 approx. equals 127). The actual comparison is between the ratios 127/100 and 80/63 (ignoring the 2.5 common multiplier).

Since 21 and 3 are factors of 63, a 21 tooth gear can also serve as a driver, with the factor of 3 formed by other train gears. For example, a 1 mm pitch from an 8 tpi lead screw requires a lead screw to spindle turns ratio of 63/200 = for example (21/40)·(30/50),  or, as per Roderick's table, (45/40).(21/75)

Edited By Rodney Entwistle on 14/01/2016 06:36:48

Edited By Rodney Entwistle on 14/01/2016 06:37:28

Edited By Rodney Entwistle on 14/01/2016 06:58:45

Edited By Rodney Entwistle on 14/01/2016 07:00:14

Here is a hole-basis chart. Not sure of its origins, but readily available at many internet locations.

Hi Hywell, Good job. Recommend that the new leads from winding ends to junction box also be laced to the existing windings to avoid movement and fatigue. Then some varnish on all modified wires. Polyurethane would be better than nothing.

Thanks Clive. I started making the 'Duplex' hacksaw, as a starter project, when I first acquired my lathe. It took a long time to finish it (other projects intervening) . In the mean time, I came across a garage-sale bandsaw for a good price and bought it.

I find I use the small Duplex quite a lot for small items that are difficult to easily support in the bandsaw. There is also the additional satisfaction of using a self-built tool (or am I weird?). The bandsaw, of course, handles the larger cross sections much quicker.

If I had the bandsaw at the beginning, I probably would not have started building the Duplex. But now having both, I'll keep both of them!

Rod.

My version of the ME Duplex (1950) powered hacksaw cuts on the in-stroke, as per the original design. As the carriage arm pivot is above the crank, this adds load to the cut on the in-stroke and relieves the cut of the out-stroke. The added load depends on the mass being accelerated, and the arm pivot to crank separation distance. While built for the fun of it and learning various machining procedures (I also have a bandsaw) it is in regular use.

A NVR (No volt release) is a good idea for any/all workshop machines. Should the electrical supply be interrupted, even momentarily, the NVR will open and the machine cannot restart until you do it manually, i.e. knowingly. The most dangerous situation (IMHO) is when the supply fails for a few seconds and is then restored. In that few seconds, one is working out what is going on and has time to place a hand where it should not be, just in time for it to restart. Not good.

My workshop has two RCDs on the supply, one each for the light and power circuits. The power circuit also has a NVR. In this way, every machine is protected against unexpected restarts. NVRs on each Individual machine is another alternative.

This may help? See this link at the bottom of page 3.10.

**LINK**

It gives the cos^3 expression, indicating it to be an approximation, and then gives the "accurate" expression in terms of the involute function (tan(x) - x), where both helix angle and pressure angle come into play. No mention of the size (PD) of the cutter.

There is a paper by Andrew H. van de Ven entitled:
Nothing Is Quite so Practical as a Good Theory.

True!

Just a note of caution....before running a lathe at high speed, check that maximum allowable speed of your chucks. (Of course high speed = small collet chuck or similar, but worth saying, just in case.)
Rod.

Be careful not to place a cold morse taper into a warm spindle. Its expansion will make it a very firm fit.

Edited By Rodney Entwistle on 12/10/2010 05:27:14