Member postings for Andrew Johnston

I don't understand why that should be? Cast iron, particularly the continuously extruded stuff, is fairly soft. Cast iron is also one of the few materials that is happy working against itself. So why would cast iron swarf be abrasive? Of course if there's sand or slag in the mix from a casting that would be abrasive, but not the cast iron.

Andrew

I use both HSS and insert tooling. Nothing special, tool geometries as for low carbon steel, speeds similar, or slightly slower, and feedrates the same. Cut dry, cast iron swarf plus coolant equals a horrid black sludge. To some extent it depends upon the source of the cast iron. if it's continuously cast then it is soft and easily machined with any tooling. If it's a casting then inserts might be better choice as some castings have hard spots or surfaces depending upon the foundry technique.

Andrew

Nobody went round and changed all the transformer taps in the UK or Europe. The authorities simply decreed that the supply was 230V +/-10% thus encompassing both 220V and 240V without the need to actually change voltages.

Andrew

Never heard that one? In my experience most rechargable lithium cells come discharged. For shipping lithium batteries are divided into two basic categories. Those containing lithlum metal (non-rechargeable) and lithium ion (rechargeable). Both are capable of causing a fire if faulty or abused, but the regulations are much stricter for batteries containing lithium metal. Combustible electroyte is one thing, an alkali metal fire something else.

I'd concur that the electronics between battery and motor is for controlling the motor. The battery protection functions are normally built into the battery iteself and are not accessible. Otherwise some people would defeat them. The protection circuits normally protect against short-circuits and undervoltage, but not over-voltage.

Charging lithium ion batteries is somewhat involved. If the battery voltage is below a threshold (deep discharged) the charging cycle starts with a constant current charge at a reduced rate, often C/10. Once the battery voltage exceeds the threshold then charging switches to constant current at a higher rate, 1C or more. As the battery voltage nears full charge the charging switches to constant voltage so the charge current falls off as the battery voltage rises. At a set voltage charging is turned off. Lithium batteries don't like trickle charging as often used with lead acid batteries. The voltage thresholds are critical, they need to be better than 1%. There are some really nice linear and switcher based charging ICs available. The ones I've used seem to perform well over long periods without fudging the batteries.

There have been some reports in the press recently about fires caused by replacement batteries bought on the cheap. In general you get what you pay for but with batteries you may well get an additonal "bonus" surprise.

Andrew

That's interesting, my plug in mains monitor currently (!) says the voltage is 243.8VAC.

Andrew

Over the last couple of nights I've been machining the hole for the balanced valve and body, and one of the steam passages into the HP valve chest, for the governor on my cylinder blocks. The result isn't easy to photograph and it's just a hole! So a section of my 3D CAD model of the cylinder might be more informative:

It's not a disaster if the hole breaks into the HP cylinder bore as a thick liner will be fitted. But it's a case of satisfaction if it doesn't. The large 1" hole was machined with a slot drill, usaing the knee rather than the quill to set the precise depth:

The oblong slot from the bottom of the balanced valve to the HP valve chest was drilled 6mm at each end. The middle was then "drilled" using a 6mm slot drill with a fair amount of stick out:

Finally the slot was cleaned up by machining from side to side with a step down of 1mm. Machining the slot is not as bad as it looks. The first 1" is fresh air and once engaged the cutter is contrained on two sides.

Eventually there will be two drilled passages from the HP valve chest to the top of the balanced valve, but they will be done after the valve body is finally fitted.

Andrew

That is interesting. Their tables look just like mine in many of the details:

I bought mine secondhand on Ebay some years back. I didn't fancy the tables with lugs and two axial bolts. They'd move in an instant with my thud and blunder machining. I also wanted a large table as it would need to support a cylinder for a 4" scale traction engine. The table I ended up with is bigger than I intended, at 9" by 18", but it just fits on the mill table. The top and T-slots are in a shocking state but the table operation is smooth and everything that should be flat, square or parallel is so.

Andrew

Paul; welcome to the forum.

Now for the bad news. The Smart and Brown L is a plain lathe. Although there was a toolroom version it was primarily intended for second operation work. In other words simple repetitive operations to finish a workpiece. Smart and Brown are long gone although there is a UK company (Bracehand) just down the road from me in Shefford, close to Biggleswade where the S&B factory was located, that deals in Smart & Brown (and Pultra) lathes. However in my limited contact he doesn't have much in the way of spares. It is highly unlikely that parts from other lathes will fit. Even the collets were proprietary. In short what was essentially a production lathe is of little use without tooling.

Interestingly there are some S&B collets on Ebay, but they are not dead length collets, so not intended for use with the L lathe.

Personally I'd pass and look for a more general purpose lathe with screwcutting and power feed capability.

Andrew

Copper has an appalling resistivity temperature coefficient, about 0.39% per degree C.

As alluded to by Andy those pesky electrons will follow the path of least resistance whatever one does. So one would need to be very careful with the positioning of the clamps to ensure that the area that needs heating is in fact the area that does get heated.

Andrew

Rectangular ground flat stock is ground on the wide sides only. The narrow sides are as sawn.

Andrew

I never twigged that, thanks for putting me straight! Sadly, as far as I'm aware, there are no full size logging locomotives of any type in the UK.

Looking at pictures of the Climax the tooth profiles all seem to be symmetric whereas the Kozo gears are definitely not. They're straight on one side and curved on the other. In one of the Climax pictures the teeth on the pinion are definitely straight exactly as per a normal bevel pinion. In another the pinion teeth are at a slight angle. Presumably the works made a design change at some point. Looking at the design parameters for skew bevel gears the teeth on the bevel gear are straight when pointing at the shaft intersection. So if the teeth on the pinion are at an angle my working assumption is that the pinion is not located at the theoretical shaft intersection.

Andrew

I agree with Ramon, there's nothing difficult about grinding HSS tools. It's simply a case of understanding the angles. None of which need to be precise, just done by eye. I use a 5" Slibette (bought by my father 50 odd years ago in Cooks of Bedford) for grinding. It's got a coarse (46 grit) aluminium oxide wheel on one end and green grit wheel on the other end for grinding TIG welding electrodes. I also have a 8" Wolf grinder with an 8" wheel, but that's very fine and doesn't get used much. If I need to remove a lot of material I'll mill the toolbit first.

I use a lot of rectangular steel section, but mostly hot rolled rather than cold drawn. My conrods were hogged out of hot rolled bar on the horizontal mill before turning the taper and transition curves on the lathe:

I've never built any of the Stuart models so it's time for me to drop out of this thread as I can't add anything pertinent.

Andrew

None of the above. I broke them deliberately (Widlarised is the technical term *) as the threads they produced simply didn't fit together properly whatever I tried. I can't remember the exact details but I got so fed up making, and scrapping, parts that didn't fit that I binned the taps and die. I then bought a 5/8" UNF spiral flute tap from a commercial supplier (probably Cutwel as the brand is YG) and screwcut the external threads. I no longer use the ME supplier from whom I orginally bought the taps and die.

Andrew

* After the legendary analogue integrated circuit designer Bob Widlar. Having found a duff component during debug his advice was to smack it with a hammer, for two reasons. One, it makes you feel better, and two if you leave it lying around someone else will use it and then have to go through the same debug process.

Bother, due to finger trouble I've just lost what I was typing. Just as well though as I was beginning to ramble. I can now start again with a better idea of what to say. On the plus side it's just started raining so I can abandon plans for weeding the garden and hit the workshop instead.

The OP needs to decide what he wants to make before buying taps and dies. I'm building a relatively large (4" scale) engine but the most common threads are 1/4" BSF and 2BA. Smaller engines will most likely be metric, BA or UNC/UNF depending upon where and when they were designed.

I mostly use metric threads for work related design, but my engines are a mix of metric, BA, BSP and BSF and even one part which is 5/8" UNF. Internally on my engines I use metric threads and commercial socket head bolts/screws. But for visible threads I reverted to the original BA and BSF threads after a brief period of aiming to convert everything to metric. I use commercial BA nuts and small BA screws from EKP. I understand that small scale metric fasteners are available from European suppliers. But I use so few that I make my own. I was unimpressed with commercial fasteners for the larger threads so I also make my own; 2BA bolts and M4 nuts:

1/4" and 5/16" BSF studs:

And matching nuts:

Of course it helps that I've got a repetition lathe; once set up it's very quick to turn out multiple parts.

To summarise the ramblings; decide what to make and then buy taps and dies as needed. There are two rules for buying taps and dies, and any type of cutting tool:

Rule 1: Don't buy cheap

Rule 2: See rule 1

I buy from professional tool shops for taps and dies I use a lot. For odd sizes I won't use often I tend to buy from Ebay, but only branded names such as Dormer or LAL and from UK sellers.This is what happens to cheap tools, bought from a UK ME supplier, that were not up to standard:

They get recycled!

Andrew

I'd agree with Martin, use hardened dowel pins rather than make them. For the plain holes I'd probably use a chucking reamer in a collet. But experiment first on an offcut. Reamers are a bit hit 'n' miss when it comes to fine fits.

Last night I used a 1" slot drill to "drill" a 1.4" deep hole in my cylinder casting ready for the governor valve. The resulting hole measures 1.001" according to my internal micrometer. Fine for my application, but not much good for a precision fit. So I wouldn't use a slot drill in this application.

If I was going to be a perfectionist I'd make a D-bit, do a trial and cylindrically grind the D-bit as needed to sort out the last few tenths.

Long ago I designed a fixture plate for the Tormach/Bridgeport of similar size to the OPs. I bought the jig plate ...... but never got around to making the plate. I don't miss it in the least. I hadn't thought about it for ages until this thread appeared.

I can't find the CAD model and drawing I created. But I'm pretty sure the tapped holes were through and the plain holes had a small through hole. I alternated tapped and plain holes along each row, offset by one space between rows.

Andrew

I have been known to use dies; just made some custom D-type connector lockscrews for a client and I used a die to cut the external 4-40 UNC threads as I already had it. Albeit using a quick release holder on the repetition lathe so I could thread up to a shoulder at 500rpm. I prefer to use Coventry dieheads for more than one offs. They cut really nice thread forms, are fast, don't wobble or wander and are simple to adjust to size to fit mating parts.

Andrew

Quite so and very impressive work. I've recently been sent a copy of his article in Livesteam. The teeth are cut on the slant and the tooth profiles are clearly asymmetric. What interests me is that on some logging locos this is clearly not the case. The tooth profiles are symmetric and the teeth do not lean over. So while the gears by Kozo are a tour de force what really interests me is how were the gears as depicted on the full size engines designed?

The publication I have found starts by stating that the pinion can be a normal straight tooth bevel gear. The key seems to be that for the bevel gear the tooth profile at the outer edge needs to expand, in much the same way as normal and tranverse DP in helical gears.

There has been some discussion of skew bevel gears recently on MEM including some pictures of the gears in production at the Lima Locomotive Works. It's clear that the teeth need to slide as well as roll over each other. Consequently it seems that in real life the gears had poor reliabilty. Apparently after Lima switched to cut gears rather than cast they offered a two year guarantee on the gears.

Andrew

Thanks for the welcoming comments. Looks like I've made the right decision to return. As before I'll have a few informal rules about posting. Some electronics threads in the past got a bit heated, so I intend to generally stay clear of electronics. It's my profession, not my hobby, so I have an approach to design and debug which probably isn't appropriate here.

Inevitably in the current panic there have been a lot of posts recently about import machinery, the pros and cons and what are best buys. I've never used any import machines and know nothing about them, so I will be steering clear of such threads. That's not to say I won't comment on machining issues involving said machines; the cutting process is not machine dependent.

Andrew

If you don't actually need M5 or 10-32 then use 2BA. It's within a gnats whatsit of 3/16" and 32tpi. Taps and dies are readily available from commercial suppliers. I'm not a fan of ME threads. They're useful when fine pitch threads are needed in larger sizes and I use them on the smaller fittings on my traction engines. But I screwcut most external ME threads and internal ones where possible as I've found the modern taps and dies available are not great quality or particularly accurate on diameters.

Andrew

I use insert tooling for general turning but use a lot of HSS tooling for specials. On the repetition lathe I exclusively use HSS toolbits as that is what it was designed to use. The internal grooves in these eccentric straps were machined with a HSS tool using the numbers on the dials rather than measure and cut:

Likewise the mating sheaves were machined with a HSS tool:

I used a groove micrometer as a sanity check on the groove widths.

Like Ramon I make one off tooling using silver steel and gauge plate:

If I've done it then I'm happy to explain how, if I haven't then I keep quiet.

Andrew