It’s A Compressor, Jim, But Not…

[Nigel Graham 2Participant @nigelgraham2]

Thankyou.

I’d gone straight to the ‘Lens’ web-site, which is intended for ‘phone use. I’d not known Google more generally offers the application more directly.

Anyway I’ve sent the images to a friend who can use ‘Lens’ or similar.

 

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Incidentally, does anyone remember that very strange circular slide-rule(?) with “random” fractions and 16-times table, that totally foxed us all a few years ago? I wonder if these identifying tools might help solve that, if anyone still has the photo. It appeared on here before such search-tools existed, or were readily available.

[Michael GilliganParticipant @michaelgilligan61133]

Photo included here:

That Strange Calculator Again

MichaelG.

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Edit:

Google’s AI overview [in lens] does a pretty good job of analysing the image, and offers to help further.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Nigel, if you mean the one in MichaelG’s post, Google Lens search

Regards Nick.

[Michael GilliganParticipant @michaelgilligan61133]

and here is the image … cropped to remove the extraneous wood

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MichaelG.

[Nigel Graham 2Participant @nigelgraham2]

That’s the wee beastie!

I had copied the photo but seem to have a lost many, despite all care, including that one. I think MS’ attempt to put them all on its “Cloud” was one factor.

I asked slide-rule and drawing-board makers, Blundell-Harling, and organ builders Harrison & Harrison. Both firms were intrigued by had never seen anyhting like it, and H&H said it’s not connected with musical instruments.

 

Anyway, back to our air-pump.

Working in better light – the bright sunshine outdoors – helped.

I found the “oil screw” does lock the journal in place. The better lighting showed the thread extending down into the brass.

Tried to remove the pulley from the shaft, but started to damage it. Eventually, a large mallet and soft drift pushed the pulley, crankshaft and journal out as one assembly, allowing the piston to slide out of the end.

This revealed the four ports in the double-ended cylinder’s wall are rectangular so must have been cast in, despite being only about 5/16″ square, if that.

 

So that’s how it works…  I realised.

I’m going to pose it as a puzzle.

How do you think the shaft drives the piston?

It’s beautifully simple but not intuitive. I can see what happens but cannot really conceive the geometry, and have not encounted the mechanism elsewhere, physically or in text-books:

1) The piston and crankshaft axes are mutually perpendicular but co-planar, their housing being a Tee-piece.

2) The double-ended piston both reciprocates and oscillates about its axis by about 20-30º per revolution.

3) The piston is a plain cast-iron bar with two pairs of keyway-like channels as ports.

4) It has a plain, fixed, bronze bearing-bush lining a central hole, across its diameter. There are no slots, cam abutments, etc. This bearing cannot revolve or otherwise move within the piston.

5) The crankpin is a plain pin projecting forwards, overhung mode, from the end face of the shaft, 1/4″ from the axis to give the 1/2″ stroke. It is a close sliding fit in the piston bush, and its length is nearly the piston diameter .

 

What is the critical detail I have omitted….?

 

I have taken photos but will add them with the answer.

However, I did try to sketch (artistic meaning) simplified versions of the two parts in Alibre to give a better idea here. Not very well though. It was harder than I thought it would be.

I’ve represented only one of the four air channels, and it should be either 90º or about 135º round the axis.

Not properly to scale.

Again with the secret omitted, although this view would not show it anyway.

 

[Nigel Graham 2Participant @nigelgraham2]

No-one rose to the challenge?

 

The secret is that the crank-pin is ball-jointed, a bit like a centre-finder, so can partially rotate the piston while reciprocating it. The motion also obviates any sliding parts in the drive other than small reciprocation of the pin within the piston bush. Herewith the complete machine in bits, and close-up of the crank within its journal, and piston with its central crank-pin bush and the air channels.

 

[Michael GilliganParticipant @michaelgilligan61133]

Clever stuff, Nigel … we really should find who designed it … credit is due !

MichaelG.

[renardiere7Participant @renardiere7]

That is cunning. It puts me in mind of the engines of Charles Redrup with his various axial wobble plates, swash plates etc.  Wouldn’t be surprised if he was the originator of this pump as he was a prolific designer.

[duncan webster 1Participant @duncanwebster1]

Is this the chap? https://en.wikipedia.org/wiki/Charles_Benjamin_Redrup

I must say a rotary engine on a motorcycle with the engine whirling round between your shins doesn’t appeal. probably good for cooling tho’

There’s a book about him as well

[renardiere7Participant @renardiere7]

That’s the man. Highly recommend the book as well.

[Michael GilliganParticipant @michaelgilligan61133]

Well done, Gentlemen

… a very likely candidate.

MichaelG.

[Nigel Graham 2Participant @nigelgraham2]

Indeed – I would love to know my compressor’s history, or at any rate who made these and when. There are no identifying marks anywhere on it; but the makers’ label could have been on the long-lost motor or tank.

Anyway it’s all back together now, with some sealant in the broken gasket. The finishing touch was servicing the flat-belt tensioner.

….

Seeing that Redrup designed swash-plate drives reminded me I have a neat little oil-pump, I think it was, I had thought was swash-plate driven. So I dug it out….

Careful opening showed it is ingeniously cam-driven instead.

Its body is less than two inches square by one-and-a-half over its surface-ground cover-plates.

The shaft, protruding from both sides, drives a steel rotor containing seven longitudinal “cylinders” – drilled and reamed through parallel with the axis- whose “pistons” are pairs of bearing balls separated by light coil springs. The balls protrude from the rotor ends by about half their diameters when they align with the hollows in a fixed, two-lobe face cam on the inside of each cover-plate. The combined stroke when the lobes push the balls towards each other, is perhaps 1/4″. Or 6mm: it might be metric.

The connections are two 1/8″ BSP unions, but I have not determined flow direction and control. It might be bi-directional. A little port-block on one cover may have served a pressure-gauge, relief-valve or air-bleed valve.

It’s a fine piece of precision-engineering but of blocky, purely functional appearance, unlike my mystery compressor that has a certain elegance to its cast base and body.

Despite some arcane numbers and letters, its origins and intent are untraceable; perhaps continuous-flow lubrication to some machine.

I might incorporate into my steam-wagon to lubricate its enclosed engine, driven from the feed-pump reduction-gear or even manually rotated from time to time, as simple “oiling round” would be sufficient. It takes an appreciable effort to rotate.

[Andrew EntwistleParticipant @andrewentwistle]

Looks like a match for the Valve-Less Air Compressor made by The Dental Mfg Co Ltd, apparently originally supplied with a Bakelite pulley.

https://www.hobby-machinist.com/threads/bakelite-pulley-disaster-ideas-wanted.10225/

Andrew.

[Mark P.Participant @markp]

<p style=”text-align: right;”>Andrew this is the same compressor I mentioned in  earlier that my dental technician father had</p>
<p style=”text-align: right;”>Mark P.</p>

[Andrew Entwistle]

On Andrew Entwistle Said:

Looks like a match for the Valve-Less Air Compressor […]

Nice one, Andrew !

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

[Nigel Graham 2Participant @nigelgraham2]

That’s the thing!

Simply a slightly different layout, mine having a single inlet rather than two.

Thankyou very much Andrew!

All I need now is a new motor but the chances of finding one like that are pretty remote. I think it would need mounting on a base-plate with the motor to one side.

 

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I have tried finding how to find things by Google Lens, but to no avail. Every attempt ended in wanting me to “sign in” to something I don’t have – including Google itself, let alone an “account” with it.

 

[Andrew EntwistleParticipant @andrewentwistle]

Hi Nigel, in Google Chrome browser I just right clicked the first image you uploaded and selected the ‘Search this image with Google Lens’ option, cropping it tightly. The first result was the hobbymachinist page. Cropping to remove all but the engine from the search was the key.

Andrew.

[Andrew EntwistleParticipant @andrewentwistle]

I tried logged out of my Google account and the image search no longer worked.

[Nigel Graham 2Participant @nigelgraham2]

Ah – I see I’d have to install Google Chrome first!

These big IT corporations don’t like to make things easy and need you jump through a lot of hoops, and their uses of “account” implies wanting an open-ended, non-numerated subscription.

 

 

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[BazyleParticipant @bazyle]

Jason will surely advise but isn’t there a small steam engine design based on this kind of ‘twist and throw’ crankpin.

[Grindstone CowboyParticipant @grindstonecowboy]

Not sure why you are having issues with Google Lens, I’m running Windows 10 and Firefox, not logged into any Google account, and I just go to the Google page (www.google.com), select the photo icon I described earlier, and it just works with no prompting to do anything further.

Rob

[Nigel Graham 2Participant @nigelgraham2]

Bazyle –

That rings a bell with me, too, but I forget the details.

The compressor’s motion is reversible. When I pushed on the exposed piston heads the crankshaft did revolve. I don’t think it would be very efficient that way round though; rather like trying to drive a Scotch Crank from the reciprocating part.

 

Grindstone –

Thankyou for that tip. I’ll try again.

[pauses to grapple with Google…]

Cor! I made it work for me! (Software and I have a relationship best described as “awkward”.)

So thank you very much.

 

We now know what my compresor is, so I fed it with that photo of the strange circular “slide-rule”.

Google tells us it is a BriCal adding-machine invented in 1905-6 . “Our” specimen was a variant released in 1908, as its date says, for British currency with its fractions of pennies, etc.. The 16-times table facilitated pricing quantities by weight in ounces.

More accurately, we see only its fascia. The operator rotated the dials by a stylus inserted into the appropriate holes, and a complicated gear movement behind them did the actual sums. We can’t tell if the photographed specimen is still complete or just the dials.

Even so the values displayed still seem extraordinarily complicated, until we consider that the farthing was in regular use >100 years ago, and I can recall odd prime-number prices like £19. 11s. 6d., in the 1960s.  (Most of a week’s wages, were that!)

 

[Trevor Drabble 1Participant @trevordrabble1]

Nigel , have sent you a PM . Trevor

[Nigel Graham 2Participant @nigelgraham2]

Thankyou Trevor. Have just replied to it.

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