Member postings for John Fielding

The only error with the schematic is that the emitter of the 3055 should be connected to the negative supply rail, the bottom line under the transistor. The diode connected to the collector of the 3055 is a catch diode which with the parallel capacitor serves to protect the transistor from back EMF transients generated by the switching due to the PWM signal applied to the transistor base.

Yep-----well covered in the brazing books.

The important thing is to heat the cast iron well above the normal brazing temperature to burn off the graphite and then let it cool. Then wire brush vigorously and apply flux. This brings the surface to more like low carbon steel. Done this lots of times to repair broken castings etc.

OK - seems 12 holes is a bit too simple.

How would you generate a plate with 48 holes without a master gear, DRO and nothing more than a ruler?

I wonder if anybody has made division plates from scratch without using a master gear?

I have never seen this technique used but the principle is quite simple.

Suppose you needed a division plate which has, say, 12 holes, how would you make such a plate without a dividing head or a master gear?

Let's see what the Brains Trust comes up with!

A possible solution if the 127T gear is too big to machine is to change the DP. If the DP is chosen to be 40 then the gear will be half the diameter of a 20DP gear. It would of course mean you would need a similar transition gear to mate with it which is also 40DP and to compound it with the other gears in the train. Whether such gears are readily available from a supplier is another moot point!

A reasonably cheap source for a surface plate is scrap grave headstones. These are normally ground by the stone masons. We have a local gravestone refurbisher and they often have broken headstones they have to replicate. I popped into them a while back and asked if they had any small offcuts they would be willing to sell. When I explained that it needs to ground flattish and what I intended to use it for they were most helpful. Seems for a few quid equivalent they would supply a piece 75mm thick and 300mm square, but I would need to collect it!

The Grayson gears are nominally 11mm thick, probably 7/16-inch, I see I typed 1mm in my earlier post. Finger trouble on a cold day!

Hi Savinay,

I haven't seen that type of suffix, but as Andrew said they are most likely manufacturers site and or year/week codes and I would agree with that assumption. I also don't recognise the manufacturers logo - probably Far Eastern ? There are so many small places churning these products out and I prefer to use manufacturers I know and trust, like International Rectifier, which incidentally is now owned by Texas Instruments!

That is a clone of the old Motorola 20N50 Mosfet.

IIRC the 20 refers to the drain current 20A and the 50 is the reference for a 500V device.

The package style is the TO-247 which is an industry standard. Take a look at the IR website for equivalents, plenty of modern devices available.

International Rectifier www.irf.com

Edited By John Fielding on 11/06/2016 16:39:09

Hi Dave George 1,

The Grayson change gears and the Myford ones are interchangeable, again seems Myford copied the Grayson design.

The only difference is the Myford ML7 ones have a keyway in the bore whereas the Grayson ones do not. They instead have one or sometimes two dowel holes in the boss. This takes a dowel pin to couple two gears together for compounding.  One both types the bore is 5/8-inch. They are are both 20DP and similar thickness, the Grayson ones being a tad thicker. Nominally 1mm thick against the 9.5mm for a ML7 but not an issue.

In the picture the Grayson gear is on the left and the Myford on the right.

Edited By John Fielding on 11/06/2016 16:26:32

I would definitely go for the 1/2hp 1500 rpm option.

A 1500 rpm motor is a 4-pole machine and since power = rpm x torque then the torque will be much higher. That means the lathe isn't going to slow down as much on a big cut. The one thing you need on a machine tool is lots of torque.

Although most of the time the extra torque isn't needed, when do need it is available without running the risk of overloading the motor.

my 2c worth!

Hi Dave George 1,

I see you are making good progress. It's looking good!

The chuck end of the Grayson spindle is identical to the Myford ML7 and later series, seems Myford copied that when they bought Grayson. The thread and register collar should be fine as they were made of good steel in those days. On mine the front bearing portion had been badly chewed up and I had to resort to metal spraying and then regrinding to salvage the spindle.

So any chucks or other bits which fit the Myford range should also fit. The headstock bronze bushes on mine were easily removable and I did make new ones as the originals were pretty shot when I got it. IIRC there are minute dowel pins that hold the bush in place, but it is a long time ago when I last played with the old girl.

Please explain what you mean by "the hole is not straight"? Are you attempting to drill the hole without drilling a pilot hole first?

A word of caution when you mention "Chinese" tools. There are in fact TWO China's. One is the mainland China, which is the communist ruled part and they are called PRC -People's Republic of China. The other Chinese country we know better as Taiwan, which is a more westernised and generally have better quality products at a fair price. Taiwan is officially called ROC - Republic of China.

So if the name plate has PRC it is mainland China and ROC is Taiwan.

One of the things people forget about is the steam space in a boiler. Typically the boiler will be 3/4 full of water and the remaining space is for the steam. If you take a 3-inch diameter tube it has a cross sectional area of 7-square inches. So a boiler 12-inches long has a total volume of 85-cubic inches. When 3/4 full of water the steam volume is only about 21-cubic inches, which isn't a lot if you are drawing off a lot of steam.

However, for a small engine running with no load the steam consumption will be low. If you load up the engine to maximum you can expect the steam consumption to increase considerably, perhaps as much as twenty times, hence you need a larger reserve of steam space to cater for this. You will also need far more heat output from the " furnace" to keep the steam generation up to the required volume being drawn off if the pressure is not to fall.

The problem with English is like all modern languages it evolves with time. Ian SC mentioned Afrikaans, which originally was high Dutch, but today it has moved considerably away and has many other words adopted/made from other languages. Similarly true English is a mixture of many other languages, and new words are added on a regular basis. If we could go back 500 years and hear English as she is spoke then hardly anybody would be able to comprehend what the person was saying. And dialect and accents play a huge part. For a southerner to try and understand a geordie speaking is comical.

When I first emigrated to South Africa I had to get my head around some of the words used. And these were so-called english speaking people. I was directed to find a place and I was told to go up the main road to the first robot and then turn. What the hell is a robot? It is what British call a traffic light! Roundabouts are called circles, which when you know that makes sense.  In Yorkshire traffic lights were known as "To-go-stops".

Then there was the predominance of posting everything in English and Afrikaans. The most famous was "Slegs-Only", which until you learn a little Afrikaans is truly puzzling. Slegs in Afrikaans means Only.

The company I worked for made radio equipment for the local defense force and everything had to be in both languages. This meant that all instruction manuals had to printed twice. Typically the English version would be compiled and then the Afrikaans version would be translated from that one. In the Afrikaans language certain words don't exist and have to be "invented". We had a Prof at Rand Afrikaans University (RAU) who was the official government language consultant and he invented new words when needed. As he was appointed by the government then whatever he deemed the new word was law. It so happened that the Afrikaans for Voltage Standing Wave Ratio (VSWR) didn't exist, so he was asked to invent the new word. When it came back as the literal translation is was about 50 letters long and sounded like the railway station in Wales. Thankfully it was discarded and the troopies had to learn the English word.

Edited By John Fielding on 02/06/2016 16:58:05

And on the subject of old mechanical engineering terms and how they have changed over the years.

In an old textbook I have from the mid 1800s is a treatise on adjusting holes to size with a "rimmer", today that has become reamer.

The other thing that often causes confusion is the American terminology and the English for the same item.

Drill rod = silver steel/tool steel, as it is/was used for making drills and cutting tools.

Wrist Pin = Gudgeon Pin

Piston Pin = Little End Pin

Circlip = Snap Pin

And there are dozens of others.

Hi Tim,

He's lost his bottle' started (as I understand it) in Birkenhead in the Wirral, where ships are (were) scrapped using oxy-acetylene cutters. The origin was not quite the same, as is common with such expressions, rather it was 'His bottle's gone' - ie he has run out of gas.

You could be correct but from my experience of the Birkenhead shipyards, mostly Cammell Lairds, they did do a lot of ship repairs and building but almost no scrapping. The most used scrapyard for vessels was Inverkeithing in Rossythe in Scotland. Today the hulks get towed to India (Bombay aka Mumbai) for cutting up. My late grandfather (who died before my birth) was a plumber at Cammell Lairds during the war converting liners into troop ships.

I thought that was cockney slang - bottle and glass - a**e. So lost his bottle would mean brown underpants, but I could be wrong.

Clive you are quite correct. As I was born and brought up in the London area Cockney rhyming slang was in everyday usage. Some others are:

Whistle and flute = suit

Apples and pears = stairs

and Porkies comes from Pork Pies = lies.

There are dozens of others which some will remember but are slipping out of common usage today as London becomes more inter-racial. In the poorer parts of London in the olden days the population consisted of a high percentage of Jewish people and their slang inter-woven with the locals made some interesting combinations!

And old and wizened foreman I worked with when I was an apprentice was well versed in "Knockometry" or "Tapestry" and he had a selection of hammers in his tool bag for "minor adjustments to machinery". He was the person to show me how to dislodge stuck tapered joints on my motor car using a big hammer on one side and a smaller on the other. Just one well aimed biff had the ball joint jumping out of the steering arm. I have never forgotten that trick. He called a hammer a "Birmingham Screwdriver".