Member postings for Norman Billingham

Thanks to all for some interesting replies. The question of what the bushes are is interesting. They are certainly sintered bronze and RDG advertises them as Oilite but I suspect the term may be being used generically for anything sintered and I'm not sure how one would tell, short of heating them to drive out oil. By chance I had the opportunity to look at a different S7B lathe and that also has the bushes drilled, so I suspect Myford did use plain sintered bronze and did drill them.

You may want to check first that you can get hold of sulfuric acid of the required (quite high) concentration. The explosives precursors and poisons regulations now say that "From 1 July 2018, members of the public who want to acquire or import sulfuric acid above 15% weight by weight will require an explosives precursors and poisons (EPP) licence”. I've no idea how effective those regulations will be, but they may well make life a lot more difficult. Certainly EPP licenses are not handed out easily. You can still buy anodising kits on ebay.

Since the oilite bush thread is drifting off topic can I ask a related question? My Myford S7B runs beautifully smoothly but the right hand countershaft bearing eats oil and has for a long time. I recently dismantled it to take a look and both the shaft and the bearing seem fine, but I bought a new bearing bush anyway. I was a bit surprised to find that the existing bushes are drilled through to connect with the oil cups, given that it was my understanding that these bushes are essentially self-lubricating and I’d assumed the oil cups were simply to keep them topped up. If I put in a new bush, should I drill it?

If you just want a simple NVR switch with green and red push buttons there are lots on ebay - or search for "starter switch" in Axminster tools site

There's a fairly famous study from about 1939 which measured the strength of a torch-brazed butt joint in stainless steel as a function of the gap (it appears as a figure in Keith Hale's book on p. 19). It and several other studies show that the tensile strength falls off pretty linearly as the gap gets bigger, from a maximum of about 140,000 psi at 0.002" gap to 40,000 psi at 0.025" gap. In that study the strength also falls off below 0.002" gap but its been suggested that the reason for that is that a very small gap leads to weakening of the joint due to incomplete exclusion of the flux and the effect vanishes in vacuum or inert atmosphere brazing. In that test the strength was still 100,000 psi when the gap was nominally zero - i.e. the two pieces were in contact

As others have said there has to be some gap or there's nowhere for the alloy to go - but it doesn't have to be much - though even at 25 thou a strength of 40,000 psi is 18 tons psi or 3GPa which is still pretty strong (comparable to annealed copper). Bear in mind that as you scale to model sizes the stresses also scale.

As far as cleaning is concerned, organic contamination like surface grease, oil etc. will very easily burn off at brazing temperatures, so very careful degreasing is less important as long as the flux can spread. However it's so easy to give things a wipe over before putting on the flux that one may as well do it. Certainly Johnson Matthey in their video of the process, which we use in our training course at SMEE, advocate degreasing before fluxing.

The situation is very different for soldering. At the lower temperatures involved organic crud won't burn off so easily so careful degreasing is a good thing.

The Model Engineer and Amateur Electrician originally published by Dewbarn and Ward eventually became Model Engineer. As Frances says, SMEE has pretty much all of the back issues from Vol I 1898 in our library.

The British Library catalogue also shows holdings of the complete run - though whether they can find them may be another question and you'd need to know which issues you want.

I'll leave copyright for others with more expertise. Copyright in written work normally lasts 70 years after the author’s death.

I think you've pulled the LH oilite bush in too far. I've just had my countershaft stripped down for service and there is no fibre washer there. There is a slight step in the countershaft which bears against the end of the oilite bush and the bush is about 1 mm proud of the casting, so the pulley boss can't rub.

Theoretically, the rising knee machine is a better design because putting on a cut involves a screw forcing the table upwards against gravity and is foolproof. Putting on a cut on a falling head machine basically involves taking away the screw support and hoping the weight of the head causes it to follow. In reality I doubt it makes any difference at all as the falling heads are heavy enough. That was the argument which persuaded me in the end to go for a VMC and I've had no regrets. The only caution I'd give is that if you have a small workshop bear in mind that these machines are much smaller in the showroom, or at a show, than they are when you get them home. With either type you need enough space for the table to move fully to L & R without fouling the walls. With the VMC you need enough space to be able to stand on the R of the machine to get access to change speeds.

Interesting to see variacs up for discussion. In my youth we had lots of them in labs, mainly controlling heaters and occasionally motors. They were banned from our labs many years ago on safety grounds following electric shock accidents. Basically a variac is a tapped autotransformer, so one end of the coil is common to input and output. That's fine if the input is correctly wired so that the common side is at 0V, but trouble if the input is accidentally wired backwards. In the proper case, an output voltage setting of say 40V would give 0V and 40V on the output terminals and you might think it safe. If the input is wired backwards you get 240V on one terminal and 200V on the other, so you still have 40V across the load but safety is greatly compromised. I've still got a variac in my workshop collection but I'm always very careful to double check the wiring before switch-on - mistakes are easy to make.

Sodium bisulfate is the material you get by taking sulfuric acid and adding enough base (e.g. sodium hydroxide) to get half-way to neutrality. I used it as a pickle for gilding metal in a silversmithing shop when doing a course. I don't know what concentration it was but the pickle bath was maintained at 50C electrically. Copper alloy black from annealing was gleaming clean in a few seconds and the stuff seemed to have no problem in removing borax flux, so I'd say very good indeed - but we used long tongs and I wouldn't have wanted to get it on my skin. For general amateur use I'd say citric acid is a much safer choice as long as you are not in a hurry.

Chance glass was absorbed into Pilkingtons in 1981 and I assume he's contacted them, though I doubt there is anyone left who does hand-moulded glass.

The company (or at least part of it) re-emerged as Chance Glass in Malvern and (AFAIK) still operates, producing specialty products. They still make microscope slides and precision stuff. Again. I assume, he's contacted them.

In my research days we used a lot of Veridia precision-bore tubing in measuring apparatus. I still have difficulty figuring out how you can make small (<1mm) bore capillary tube with such precision.

The detailed chemistry of anaerobic adhesives can be quite complex and subtle. The adhesives are mixtures of acrylic monomers which polymerise easily by free-radical mechanisms. The free radicals are generated by decomposition of an organic peroxide. However, if there is oxygen around it reacts with the radicals and stops the polymerisation from happening. That’s why the adhesives are stored in polythene containers which allow oxygen to permeate.

The other important factor is that metals like iron and copper are very efficient catalysts for decomposition of peroxides to make free radicals, so that if the liquid adhesive is trapped between two surfaces containing iron or copper then radicals are produced rapidly, oxygen is used up through reaction with those radicals and can’t be replaced, and fast polymerisation (adhesive curing) takes place. Aluminium does not catalyse peroxide decomposition, so if the surfaces are aluminium then removal of oxygen still allows polymerisation to take place but the absence of catalysis means it’s a lot slower. The aluminium oxide is a bit of a red herring - even soluble aluminium compounds are not catalytic.

In reality it’s a bit more complicated because the requirements for long-term storage and efficient curing are challenging and need all sorts of additives to get the required control, but those are the basic principles.

acetylene tetrabromide and 1,1,2,2-tetrabromoethane are synonyms for the same compound, the latter being the modern name. Unusual stuff because it's very dense (nearly 3g/ml). As Keith says, there's a US supplier on ebay but nearly £50 including postage for 30 ml and I don't know about how they could ship it. I'd try Sigma Aldrich - they list it for £24 for 250g (+vat etc). Whether they will sell to a private citizen I don't know - you can only ask. Handle carefully - it's not all that nice.

Wonderful things angle grinders. If you are new to them (or think you are always safe), put "angle grinder accident" into a Google search and click on images - but not if you've just eaten!

Hate to rain on Paul Lousick's parade but PET is a long way from being the most common plastic, useful and widespread though it is. The most recent figures from Plastics Europe (which exclude fibre) show that we used about 3 million tons of it in 2016. The polyolefins (polyethylene and polypropylene) add up to over 23 million tons. Total EU demand for all plastics is about 49 million tons per year, so PET is about 6 - 7%. PVC and polyurethanes both outperform PET.

All depends what you mean by "few". Atomic diameters are in the range about 50 - 500 pm. The LISA experiment can measure down to about 20 pm - about the radius of a neutral hydrogen atom.