The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)

[awemawson]

Yes I think so but the proof will be when I can put 10 bar on the original switch.

I put it all back together again this morning and re-installed it. All seems to work as it should and I’m now going through the myriad of places oil is supposed to emerge checking that they are all lubricated ok

Tiny volumes in some places so not immediately obvious.

[awemawson]

This afternoon I made up a test adapter for the pressure switch - M10 x 1.0mm female to 1/8" BSP Male with a female cone in the end.

Assembling the switch to a test pump and guess what - the switch is INNOCENT - apply pressure switch closes release and switch opens.

I was just packing up and processing the photographs when I realised that there was a possible / probable miscarriage of justice - looking at my photograph of the Fluke meter it was on its next to HIGHEST ohms range not it's lowest 

Of course I'd dismantled everything and put all away, but there was nothing for it, there would have to be a re-rial in the light of this new evidence. I put everything back together repeated the test and OK the accused WAS innocent, and released from custody.

 . . at least I now have a spare pressure switch.

As for the original fault, I believe that the copper wires had corroded where they were crimped - possibly due to the sulpher in the oil, or maybe other causes, and the outer plastic sheath had held the bits in intimate contact, often adequate and sometimes not. Remember that the plastic sheath is retained by the outer crimp on these spade lugs.

[Muzzerboy]

Wow, that DVM came from The Ark! I think I have one of those somewhere although it wasn't badged as an RS product - pretty sure it's a Fluke. I think I got mine second hand in the 80s, which rather dates it.

I recall a time when RS insisted on eradicating any trace of the manufacturer and putting their own part numbers on components instead. That was never going to last. Quite amusing the lengths they went to!

[awemawson]

Oi that's my more modern meter - don't be cheeky 

[Muzzerboy]

Even my AVO is a fairly modern Mk8. I expect you can trump that too!

[awemawson]

I’ve a couple of Avo 8’s but my ex WD Avo 40 recently died from a fatal fall onto concrete

[Pete W.]

I’ve a couple of Avo 8’s but my ex WD Avo 40 recently died from a fatal fall onto concrete

 

I, too, have an AVO 8.  The 15 volt dry battery (high ohms range??) is getting a bit hard to find these days.  I seem to remember seeing mention of a third party DC-to-DC converter to generate the 15 Volts from the accompanying 1.5 Volt U2 cell (aka D-cell).  How it was switched on and off remains a mystery to me!

I rarely use the AVO 8 these days - I have a Fluke 8020A.  My Bank Manager lent me the money to buy it.           One problem with the early 8020A instruments was that the LCD display got 'poisoned' and lost legibility.  Fluke ran a scheme whereby, for a reasonable fee, they would replace the display with an improved version and re-calibrate the instrument.  That was many, many years ago and the replacement display is still going strong.

I remember lots of folklore concerning RAF AVOs being 'destroyed' (or maybe not?) after the 1939-1945 war but that might be considered as off-topic!  As might attempts to trace the evolution of AVOs' manufacturers - Douglas, Automatic Coil Winders, AVO Ltd., Marconi Instruments et al!

[awemawson]

I've been fond of Avo's ever since I was a school in the CCF signals Unit. And when I found that the father of one of my school friends was a Director of Avo I had high hopes - sadly not achieved - of liberating one. He did however arrange a personal trip round their 'factory' in Vauxhall Bridge Road London (mid 1960's) which was a collection of substantial terrace houses knocked together at several levels.

I remember that the Douglas Coil Winders were being assembled in the basement, but also in use winding the non-inductive precision resistors - quite a hive of industry.

Shorty after that they moved to Dover, and I persuaded my parents to buy me the Avo 40 for Christmas from a small ad in the Evening Standard.

[Pete W.]

Like many companies in the electronics industry, the company I was working for between 1966 and 1980 suffered a high 'shrinkage rate' for AVOs.  There were lots of people who claimed to be able to provide me with an AVO on-the-cheap.  However, these offers all dried up when I asked if the deal would include proof of ownership!  I wanted to be able to deploy my AVO in public with confidence.  I eventually bought a new AVO 8 for £32.50 from Watts' Radio in the Apple Market, Kingston-upn-Thames.  I've probably still got the bill somewhere - I must remind myself of its date.

Some years later, Taylor Instruments had the same parent company as the then proprietors of AVO (I guess Marconi Instruments?).  A Taylor sales representative came to discuss panel meters for a current project.  In conversation, he said that when Taylor's manufacturing load was droopy, they'd be tasked with making a batch of AVOs to 'fill the hole'.  He displayed the salesman's consummate skill in keeping a straight face while he assured us that 'of course, a Taylor AVO is better than an AVO AVO'!!!          

[modeng200023]

"Watts' Radio in the Apple Market"

This brings back good memories 

[Sea.dog]

I’ve a couple of Avo 8’s but my ex WD Avo 40 recently died from a fatal fall onto concrete

 

The 15 volt dry battery (high ohms range??) is getting a bit hard to find these days. 


Easy to source and a lot cheaper than when I last looked - https://www.ebay.co.uk/i/273806052629?chn=ps&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&itemid=273806052629

[Muzzerboy]

There are certainly times the AVO has its day, like observing things starting up. By the time a digital meter has got its knickers on and the display settled down (assuming it does), the smoke may have come out. When I was developing SMPS supplies, we used AVOs and panel meters a lot. The DVMs were reserved for precision, static measurements.

At one time I used those little miniclip probes with voltmeters. It was when holding both of them onto a 3 phase supply that I was able to experience the feeling of 3 phase across my hands. Could have killed me I suppose but here I am. I have to say it hurt like f***. Little strands of wire hanging out at each probe aren't clever.

Back then we were allowed to sign equipment out for home use. But we had brain dead a hole managers who thought standing outside the factory door at 5:29pm would motivate the engineers. I signed out an AVO 8 for a homer project and one of said a holes gave me a dirty look on the way out. Consequently I kept it longer than I'd planned and then the company was bought out and closed down, making everyone redundant. On the upside, the all a holes also got made redundant and I still have the AVO 8 in my workshop.

[awemawson]

Sometimes you just get lucky 

Advertised on eBay a couple of months ago were a pair of PCM swiss made powered tooling holders - a straight one, and a 90 degree one. The description was vague, and although they looked to be VDI holders the seller couldn't say if they were VDI 20 / 30 / or 40. A search on the PCM part number of the straight one (as it showed in the advert photo) implied that it was VDI40 as I need but was no means definite. However the drive end of these holders looked to be identical to the Beaver ones that I had had to modify on my existing holders.

Anyway no point in getting too excited - he was asking silly money and had already rejected a more reasonable off that I made a few weeks back. Well, he went through the hoops of re-listing the items four times so last week I made a slightly increased offer and to cut a long story short they have just arrived. A quick inspection shows the bearings to be reasonable and although they need a clean up they are in infinitely better condition than the previous ones that I got that were seized solid and needed new bearings and seals.

The straight holder fits 'as is' directly on to the tool turret with no modifications needed, and the drive engages nicely. The 90 degree one will need to be modified (as I had to with the previous one) as the heel of the mounting face fouls on the centre disk on the turret. About 1/4" needs to be removed - perhaps a bit less - to clear the disk, but I've done it before so can do it again!

. . .so I'm a happy bunny today 

[tom osselton]

You have to love that!

[awemawson]

Since I bought this CNC lathe I've hankered after a collet chuck, which saves all the hassle of soft jaw turning etc. Problem is that the way chucks work on this lathe is rather unusual.

Most hydraulic chucks, be it collet or jawed, have a draw tube co-axial with the spindle which is pulled or pushed by a remote co-axial hydraulic cylinder. On the Beaver the chuck has the cylinder built into it, and has two ports (open & close) in the face of it's rear surface that mate with similar holes in the spindle nose where an O ring is trapped to seal the oil.

Now my main chuck is a Pratt-Burnerd 1749-02780 which I very much doubt was a special for Beaver so it must conform to some spindle nose standard (I assume). The lathe spindle 'seems' to be an "A2-6" standard spindle shape with the two hydraulic ports added.

Anything conforming to this standard is remarkably rare - in the last few years I've found one chuck like mine in the UK that the seller wanted really silly money for, and one rather beaten up collet chuck that was a fair price, but no collets and being in Canada transport killed the deal.

So when a collet chuck using this same system turned up on UK eBay complete with an almost complete set of collets I got quite excited. Conversations with the seller revealed that it was off a Beaver lathe - excitement raising to fever pitch - soon to be dashed when I find that it was off a Beaver TC10 lathe (mine is a TC20) that has an A2-5 sized nose so not directly compatible.

Explaining to the seller how limited his potential market was persuaded him to release it to me at a very reasonable price (£200 inc carriage) which is worth it for just the collets.

So LOADS of googling shows that at least two firms make a converter plate from A2-6 nose to A2-5 nose - they don't have the bores for the hydraulics but if the adaptor plate is fat enough there might be room for some drilling of oil galleries converting from the collet chuck's 60 mm PCD to the spindle noses  84.2 mm PCD. Both are 6 mm diameter.

I envision drilling blind holes into the two mounting faces of the adaptor at the two PCD's with a cross drilling joining them which can be blanked of with a sealed grub screw, but this depends on the adaptor plate being fat enough and actually managing to buy one!

Absolute 'back to the wall' solution is to make the adaptor plate myself, but it has rather a lot of precise features and needs to be absolutely concentric so not something to knock up in a wet weekend.

I have thoughts of 3D printing a model to prove the concept.

. . . the other issue is actually handling the original chuck - nowhere above to put a block and tackle and it weighs 47.2 kg 

[Muzzerboy]

Looks like a fine piece of kit and sounds like a good price too. What I can't understand is how you fit / change the collets - surely you don't undo all 6 fixings?

[awemawson]

Oh yes you do Murray !

Not that bad really with a handled hex driver - usually it'll be for small runs of parts.

Numerous phone calls today are bringing me round to thinking I may HAVE to make the adaptor plate. So if I do I'll pretty certainly  do it on the manual lathe on an expanding mandrel between centres so that I can work on both faces and have some hope of maintaining concentricity.

So where do I find a 45 mm slice off a 170 mm bar of something nice to machine?

[Spurry]

So where do I find a 45 mm slice off a 170 mm bar of something nice to machine?

I've always found M Machine pretty good.

http://preview.m-machine.co.uk/CATALOGUES/metals%20catalogue.pdf

[nrml]

College Engineering do Cast Iron bars for very reasonable prices. 50 mm of a 200mm sized round bar is about £58.72 on their website. https://www.collegeengineering.co.uk/product/200mm-7-87-round/

[vintageandclassicrepairs]

Hi All,
I must be lucky where I live ? There are a couple of engineering workshops close to me where I can buy off cuts
usually a donation to the tea kitty 
When I had a job, the scrap metal skip was never safe LOL

John

[awemawson]

There's a firm on eBay offering 170 mm EN24T 50 mm long for £47 inc carriage - maybe that not too bad 


https://www.ebay.co.uk/itm/Black-EN-24T-817M40-Metric-Rounds-50mm-to-200-mm-various-lengths/193338176672?ssPageName=STRK%3AMEBIDX%3AIT&var=493530085900&_trksid=p2060353.m1438.l2649

[philf]

So if I do I'll pretty certainly  do it on the manual lathe on an expanding mandrel between centres so that I can work on both faces and have some hope of maintaining concentricity.

Andrew,

I'd turn one side, put the necessary holes in, and mount it on the lathe to turn the other side.

Just like finish machining a backplate for a chuck.

Phil.

[awemawson]

Scary CNC machining that second side Phil when you can't even see the work piece

I'd certainly have to make several trial pieces before committing to the final one but I do agree it's the best way of ensuring concentricity !

[AdeV]

Scary CNC machining that second side Phil when you can't even see the work piece

I'd certainly have to make several trial pieces before committing to the final one but I do agree it's the best way of ensuring concentricity !

I've got some big chunks of machinable wax if you'd like to do some trial pieces....

[WeldingRod]

Ah!  So, 3d print the blank for test cutting!

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