|428 forum posts|
Seeing the seismic thread reminded me ...I was talking to a friend of mine , he had a decent apprenticeship with Vospers in the 70's . Their long bed lathes , really big stuff here , he said, only turned (say a propshaft for example ) accurately either when the tide was in or out ? And certain jobs would have to be fitted in around the tide .. Is that true ?
382 forum posts
I have heard of the tide effect from a engineer who worked in a large engineering company, the workshop was situated very near the shore line.
|jimmy b||29/11/2019 14:46:04|
675 forum posts
I have heard this. Could well be true.
Some very highend machines have to have their own "slab" so that other machines vibrations don't interfere with them.
We once had trouble on CNC lathe with surface finish, eventually traced to a big mill at the bottom of the shop!!
|Jeff Dayman||29/11/2019 15:35:52|
|1895 forum posts|
In one firm I worked at, the toolroom was next door to the punch press shop. One really big die for a very large part that ran in the Minster 150 ton press would shake the floor in the area so badly that the turners and mill operators would stop fussy jobs if it was running. Otherwise, there would be marks on the work corresponding to the press strokes! On smaller parts the press did not cause these problems.
There is a story told in Stratford Ontario Canada about the CNR railway shops there, and their neighbours across the road. The story goes that people living in houses next door to the heavy forging shop stored their fine China dishes stacked flat with dish towels between them. This was to prevent them walking off the sideboard and crashing to the floor from the vibration from the bigger forge hammers. If stacked without dish towels, or stood up in the cabinet, there would be heavy damage!
6328 forum posts
The sums are beyond me but I doubt the moon would exert enough force on a large lathe to effect it directly.
But, if a long lathe was located close to the sea-shore, I can certainly believe the weight of sea-water moved by the tide would be plenty big enough to noticeably flex the ground the factory is built on.
Vosper's were based in Portsmouth which has a tidal range of about 4 metres. Guesstimating the Solent to be about 90sq km, that's 360 million tons moving about just outside the front door The tailstock and headstock of a long lathe close to the foreshore might well move at different rates, making it sensible to work only while the tide is on the turn and the ground is still.
The ground also moves itself due to tidal forces. Wikipedia mentions up to 380mm up/down and 50mm sideways, though 40mm would seem more usual. But inland, everything under a large lathe would move at the same time. Quite a few very big lathes are vertical. Dunno if that's to do with the tide, but its much easier to keep a column straight than a beam.
|428 forum posts|
I'll avoid using my lathe then ,if the river is bursting it's banks in the valley down below . It is most likely why bits i make on it are a bit rubbish
|980 forum posts|
My first thought on reading this was gravitational forces but I think vibration is more likely. I do not know the Vospers site but if it was hit by waves at high tide vibration could have been a problem.
When I retired universities, Sheffield in particular, had stated to map out the resonant frequency characteristics of very expensive precision machine tools. One machine would have a large number of resonant frequencies and these could poorly damped (if you are a clock maker, the Q value would be high). Making the machine more massive would decease deflections and change the frequencies but the damping would remain unchanged.
Forced damped vibrations and spring mass damper systems are fascinating if you can handle the maths. I lost that knowledge years ago.
|Andrew Johnston||29/11/2019 17:04:19|
5664 forum posts
The sums are easy if you use Newtons law of universal gravitation. Assuming a mean distance of the moon to earth I make the force on a 8000kg object due to the moon to be 0.265N. Otherwise known as not a lot.
It's more likely that movement due to the weight of water has an effect. But two of the longest items to be turned, propeller shafts and gun barrels, would have been done in naval shipyards. So if there was a problem I would have thought it would be better known?
|Howard Lewis||29/11/2019 17:12:28|
|3608 forum posts|
Possibly, the sea water causes the ground to swell as the tide rises, and dry out (a little ) as it ebbs, so that the ground "heave" distorts the floor, affecting the level or twist in the bed, and hence the accuracy.
Apparently, it was not unknown for the tide water to be seen running beneath the test shop at Weslake's in Rye
|old mart||29/11/2019 17:16:28|
|1991 forum posts|
In areas affected by tidal movements, it would be normal to have machinery sitting on separate foundations to reduce flexure. At the museum, we are on deep soft claylike soil and the building shakes when the Smurfitt Capa articulated lorries next door are passing. This is despite the floor being at least 150mm fibre reinforced concrete. I don't think the lathe is affected much, as it is 3/4 ton and only 20" between centres.
|800 forum posts|
A former colleague (an ex-Asquith fitter) told of having problems getting a floor borer signed off at a shipyard on the Clyde. The onsite installation team was having difficulty getting repeatable alignment figures for the machine so that these could be demonstated to the customer. The problem was sorted by getting hold of a tide table & checking the machine out at the same tidal state, which resulted in repeatable figures & the machine was accepted.
Sounds a bit far fetched, but may be possible if the machine foundation was not well designed ? I did have experience of a machine moving due to an inadequate foundation - a Butler Elgamill that had been rebuilt and retrofitted by my previous company. The alignments were spot on at our works, but variable when returned to the customer. This seemed a bit strange, as the machine had come from a specially prepared foundation where it had operated acceptably for many years before the rebuild. Turned out that it hadn't gone back to the same place in the factory, but had been rag bolted to the floor in a different location that happened to span two concrete slabs - operation of a substantial gantry crane was causing deflection of the slabs as it moved about, which affected the machine alignments. The customer moved the machine back on to it's original foundation & the alignments achieved there matched those seen in our works.
Large machine tools are suprisingly flexible & rely on being bolted to a substantial concrete block to gain rigidity - floor borers and some very large lathes rely on the foundation to keep separate sections in alignment.
|800 forum posts|
Edited By mgnbuk on 29/11/2019 17:31:18
|Mike Poole||29/11/2019 18:45:03|
2745 forum posts
I think Portsmouth is probably on chalk, if it was granite round there it might be a bit more stable.
968 forum posts
Back in the early 60’s went on a college visit to a local foundry that did ferrous and non ferrous, the foundry was the Phoenix Foundry in Lewes in East Sussex. I remember being told by one of the staff there that casting of large items was dependent on the state of the tide, only carried out I believe if the tide was out, the foundry was situated on the banks of the river Ouse, which at Lewes is tidal, foundry now long gone. I am afraid I have long since forgotten the reason why the tidal influence was important to the casting process.
|old mart||29/11/2019 19:56:28|
|1991 forum posts|
The chalk at Portsmouth is at Portsdown hill, about 2 miles North of the harbour which is alluvium.
|428 forum posts|
The friend was based in Southampton , I assumed Vospers were there too. We were actually talking about thread cutting on a lathe , 2 start threads and stuff .. Disappearing indoors , he came out with a 1" dia bolt and nut , in bronze .. "I made this as a test piece when i was at Vospers" says he
It was a 4 start, one turn, over about 4" length acme threaded bolt .
"When it's oiled and clean , the nut will descend slowly down the thread under gravity ...."
Edited By Hacksaw on 29/11/2019 20:39:23
Edited By Hacksaw on 29/11/2019 20:40:05
|vintage engineer||29/11/2019 20:46:24|
254 forum posts
When they built the Shard in London, they had to take a building down first. They were worried about heave when the building was removed as the ground would rise due to the weight being removed.
|Mick B1||29/11/2019 21:01:39|
|1728 forum posts|
They used to say (probably in the Eagle about 1960) that the Queen Mary (81,000 tons IIRC) was 3lb lighter when the Moon was overhead. I can't imagine that a force of that magnitude would have any material engineering effect on a propshaft.
But I've certainly known of a heavy press in an adjacent shop putting a scratch round a turner's work.
|John Haine||29/11/2019 21:03:03|
|3338 forum posts|
I was told of a Netherlands university - Utrecht? - where a large new engineering building was constructed on a sort of concrete barge so it sort of floated in the muddy ground. It has a tower with a microwave dish on a vertical track so that it can be adjusted for the state of the tide, apparently.
|Boiler Bri||29/11/2019 21:39:03|
835 forum posts
Can we do a trail? It would either prove or disprove the theory? I am land locked before you ask.
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