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!!

JIm

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.

Dave

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.

JA

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

Howard

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.

Nigel B

I think Portsmouth is probably on chalk, if it was granite round there it might be a bit more stable.

Mike

The chalk at Portsmouth is at Portsdown hill, about 2 miles North of the harbour which is alluvium.

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.

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.

One of the helicopter companies had problems measuring the jig they made the helicopter body in. Using a Leica N3 level for measuring, it came back 3 or 4 times to me for calibration and was withing the fine tolerance we had. More complaints and the Tech rep. visited and found the shop on the bank above a tidal estuary and stayed long enough to prove that as the tide came in it heaved the concrete base and affected the jig and levelling. They would level before lunch and come back and find all levels and measuring points all over the place as the tide receded.

Two things….

1/ Where I did my apprenticeship, at Saunders Roe (later became BHC) East Cowes IOW. The machine shop was about 25…30 feet away from the sea wall. The company designed and built a large mill to machine the wing spars for the Princess flying boat, the mill had a bed 60 odd feet long, but only about two feet wide. This machine was installed in the corner of the building nearest the sea wall. When I was in the Millwrights dept I had to do some work on some equipment adjacent to this mill. My curiosity was aroused by the tide tables on the wall near the machine. I asked my boss, George the full time machine shop maintenance man about the tide tables and he explained….due to the proximity of the sea the machine bed moved up and down dependant on the tide state, there was only one guy who knew how to make accurate parts. He depended on the tide tables, and as the cutter traversed the bed, the cutter height had to be adjusted to suit the tide state. He did this with chalk marks on the bed with arrows to indicate "up" or "down" and a number to indicate dimension change. The expert had retired before my time, but was called back when there was a need. The last job was Vickers Valiant wing spars, apparently there was a giant corporate sigh of relief when the Valiant was scrapped!!

2/ I also worked at Vosper Thornycroft at their Southampton yard. The yard was established in the 1870s, the centenary of the yard was celebrated whilst I was there. In the machine shop the was a huge lathe designed purely to machine propeller shafts for destroyers. The whole yard knew when this machine was being used as there was a very low frequency rumble which could be heard and felt all over the yard

The Saunders Roe/BHC and Vosper Thornycroft sites where I worked are now pretty much closed. They both seem to be car parks……

cheers

Bill