Member postings for Georgineer

Tubal Cain's book Drills, Taps and Dies (No. 12 in the Workshop Practice Series) goes into even more detail. For 5 BA he gives:

• 2.80 mm for 59% thread engagement
• 2.78 mm for 60%
• 2.75 mm (No. 36) for 65%; this is his recommended size
• 2.7 mm for 70%
• 2.65 mm for 75%
• 2.60 mm for 80%

While it may seem a good idea to go for maximum thread engagement it gives very little extra strength, and the rate of tap breakages goes up dramatically. Somewhere between 60% and 70% is generally reckoned to be appropriate for general purposes.

This is the real Tubal Cain by the way, not the other one of the same name. I keep Drills. Taps and Dies next to Eats, Shoots and Leaves in my bookcase. Well, it makes me giggle.

George

I don't think it answers your question directly, but this article covers a lot of related ground:

https://www.howtogeek.com/231886/tested-should-you-unplug-chargers-when-youre-not-using-them/

George

An interesting read, Michael, and it confirms my opinion - you pays your expert and you takes your choice. I suppose that in the final analysis it's what works for the individual on their lathe that is the right answer.

It reminds me a bit of the endless discussions in cycling magazines about why there is a left-hand thread on the left-hand pedal (I think I've remembered it the correct way round) with all sorts of theories proposed, contradicted, refuted and argued over. The real answer is that our forebears found that if they used a right-hand thread, the pedal would unscrew itself and fall off.

George

Out of curiosity I've had a look along my bookshelf and find that seven relevant books from 1917 to the 1980s don't mention tool height at all. Of the others, Know your Lathe (Denfords, 1953) is in agreement with the South Bend Book and states that "For ordinary straight turning the correct height of the tool cutting edge is about 5 degrees above centre, or 3/64 inch in diameter of the work… Always place the cutting edge of the tool bit exactly on centre… for every type of taper turning and boring, as well as for cutting screw threads and turning brass, copper and similar tenacious metals."

The Practical Metalworker (ed. Bernard E Jones, undated but probably 1920s) shows similar thinking: "... for other operations [than taper tuning and thread cutting], presuming the clearance to be sufficient, advantage is often felt in placing the point some three or four degrees above the centre, as this affords smoother cutting, and sometimes acts beneficially in preventing chatter. [My emphasis.] Clearance is also affected by the work diameter... the chance of rubbing on a small rod being obviously much less than on the periphery of a large circle."

A quick sketch shows that the quoted value of 3/64" per inch of diameter translates to about 5½°, and that 3 to 4 degrees translates to about 1/32". Those degrees are measured round the lathe centre of course, and are not related to the clearance angle of the cutting tool.

Engineering Workshop Practice (ed. A. W. Judge, 1947 edition) says "In setting tools for turning it is important that the points be set exactly on the centre of the work. If the point be set high… the front of the tool will rub below the point. This is more pronounced on small-diameter material*, and in order to make the tool cut, more clearance would require to be ground, thus weakening the point. With the tool point on the centre, the tool functions most efficiently, although it is sometimes found necessary to slightly lower this in order to eliminate chatter when taking a heavy cut. Should the cutting point be lowered too much… it ceases to cut and merely planishes or scrapes the surface of the work." [*This is the exact opposite of The Practical Metalworker, and can be shown to be wrong.]

The Amateur's Lathe (Sparey, 1984 edition) doesn't mention tool height directly except in relation to taper turning and screw-cutting, though he does suggest that the parting-off tool should be set slightly below centre, not above "as is sometimes advised".

The Myford Series 7 Manual (Bradley, 1982) says that "For all ordinary turning and boring, the tool should be set with the cutting edge at exactly centre height".

At the CEGB apprentice workshops in Penarth (now a housing estate) in 1969, we were taught to put the tool at centre height. My conclusion from all this? You pays your expert and you takes your choice!

George

Edited By Georgineer on 21/04/2023 22:17:30

My thinking exactly. 30 mm is deep for a 2 mm drill, but it should be do-able if you 'peck' frequently to clear the swarf from the hole.

George

Not so! It serves vanity and one-upmanship as well!

George

"Should not" agreed, but there often is. I have measured 19 volts on a system which had passed an earth loop resistance test.

George

That's true, but only after a fashion. I've worked on the century-old oak doors on a local church, and the ironwork looked fine until it came to disturbing it. Behind the fittings the iron and wood had amalgamated into a sort of brittle black mass, and the fixing bolts had almost ceased to exist behind their heads. Reinstating the fittings was quite a challenge.

George

BH?

The sad thing about humorous videos like this is that the un-knowing and un-critical take them at face value. My friend's 13-year-old daughter and her friends spent ages building a solar array to power a motor, for a school science fair. I had the unpleasant task of explaining to them that their solar cell made of cardboard, razor blades (yes, really!) and bits of wire couldn't possibly work even though the one in the video performed well.

Fortunately they took it in good part, and converted their project into a display showing how to make fake science videos. They won second prize!

George

I didn't know Tim Hunkin was still making videos; I shall seek it out.

Tim Hunkin's TV series in the 1980s & early 1990s on "the Secret Life of... " telephones, photocopiers, radio etc. was very interesting and watchable, and I often used it as a teaching aid in Science lessons. He also did a series of scientific cartoon strips in one of the daily papers, and his eccentric machines are a wonder to behold. His "Under the Pier Show" on Southwold pier is great fun, and my teenage daughter loved it.

George

I've read that Kasenit is no longer available. My great-grandfather (an "Engine Smith" ) used a mixture of hoof clippings and leather offcuts...

George

Edited By Georgineer on 27/03/2023 17:57:45

I believe so, but I couldn't see it in the dark. Besides, Mum wouldn't let us stay up late to see it.

George

My brother had a pocket sundial when we were young, but for some reason it wouldn't work indoors.

George

That looks remarkably like 1¼" x ⅜" to me. That's just down the road from me - what a pity I've no use for it!

George

Will it FLASH be possible to FLICK suppreFLICKss the constant FLASH flickerFLICKing and flashing thatFLICK flashes and FLICK flickers all the FLAFLICKsh time on the FLASH new webFLICKERsite?

GeFLICKorge

That and the four-way wire junctions made me suspicious from first reading of the circuit. That style of drawing was superseded by straight crossings and 'blobs' at junctions in... what?.. the 1960s?

George

I presume you know that ML10 changewheels are identical to ML7 ones. I have found Duncan Munro's "Myford ML7 gear calculator" program very useful, and have long since abandoned any attempt to calculate changewheel combinations by any other means. It will not only use the standard set, but will also accept your own list and generate combinations for the pitch you need, and a whole host of close approximations. It's worth remembering that practical thread cutting rarely needs to be very precise, and the metric threads made with some of the 'conversion' wheels, such as the 21-tooth, are surprisingly close to the theoretical values. I have a 127-tooth wheel, and have never found a need to use it.

Duncan's program is at http://metal.duncanamps.com/software.php

George

P.S. Mike types faster than I do.  It's gratifying to see that we are in agreement!

Edited By Georgineer on 13/03/2023 18:37:56

Howard,

The latest ML4 thread was indeed 1⅛" x 12 TPI, Whitworth profile, as later used on the ML7. The register was 1⅛" diameter rather than the ML7's 1¼".

Quote: " I used one of the genuine ML4 gears as a drill jig, by drilling right thriugh and locating this on a stud over the 7 Series gear. Keep away from the keyway! " - Yes. it works, but I found that when using the gear with the new through-hole, the drive pin tends to escape. I ended up putting a grub screw (M3 from memory) to block the hole off again.

George

Welcome, Colin. If you haven't already done so, search this site for ML4, followed by ML3, ML2 and ML1. You will find a wealth of information, some of which might prove useful.

Since your lathe has a serial number, it is most likely to be a relatively late ML4. Earlier lathes weren't numbered, and the ML4 is by far the most common version

George

How many of the posters who have suggested nylon hammers, screwdrivers, lumps of lead, politicians' noddles and so on have actually twigged that none of these is actually a dead-blow device?

How many know but have chosen to ignore the difference and thereby the OP's question?

How many of the readers who come here to learn will go away thinking that there is no difference?

I think we should be told.

George