Microns ...

As said earlier, nanometer resolution is completly different from nanometer accuracy. I used to be one of the designers of machines that put 100,000 spots (100 each of a 1000 different samples) of DNA on 25mm x 75mm microscope slides 200 slides at a time. The feedback for the linear motors had 1 micron resolution. Accuracy was checked with a Renishaw laser interferometer which had nanometer accuracy and included compensation for the effect of air pressure and temperature on the laser light.
The arraying tip (split tungsten pin) position was compensated for thermal expansion of the frame and drive system. A traditional positioner like a CMM was not fast enough, we had a peak axis speed in excess of 3m/s.

Robert G8RPI.

So, how many angels will actually fit on the head of a pin.........................

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Never mind about the microcockup, S O D, next time its my turn.

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I am trimming my pistons on a 1972 Myford Super 7 with 3phase motor VFD controlled with segmented belt drive drive, few would believe me. My smallest reliable cut is 1um on diameter, but have taken 1/2 um cut on diameter when fitting a piston for Glen Lewis. Rob is always impressed by what I am doing off a Myford S7. They had a new one back in 73 or 74 and it was not good enough for their liners or pistons back then. I have however refitted the spindle to bearing assembly, reset the bed clearances, and added a constant gravity oil supply, and refitted the compound slide as well. But nothing that anyone else could not do with time and care. Oh, and made a M8X 0.5mm pitch cross slide screw, but it is a normal RH thread, not the normal lefthand thread that is commonly used. The 0.5mm pitch with the hundred thou dial, makes it read just like a metric micrometer. My lathe is in room at around 20c temp to help with things. So do get there, I have the compound slide on a slight angle, so that 4 thou on the compound is 1um of X axis movement. The original compound as supplied was not capable of this fine enough and repeatable movement, so was reworked to be able to do so. I have a nice 1um 0-30 Tesa micrometer for measuring the pistons with in Combination with small Vee block. It gives a finer reading than just using the micrometer on its own. Another advantage is it allows you to see if the part is round as well. With the liners they are tapered so make for a really good gauge. If the liner is out of round you have to fit tighter to allow for wear etc to get a really good seal. Some piston alloys, even though they are from sintered stock, just will not stay round. So avoid those when possible. Some materials wont keep round to 8 microns or so. Typical taper is 2.5 micron per mm, but some have less taper like 1.2 micron per mm, while other earlier liners had lots of taper like 3.8 micron per mm. The only tool I have found to be able to take the very fine cuts on pistons is the very nice Summitomo PCD insert NF-DCMT11T304N-LD DA1000

Here is a picture of a piston being trimmed before I replaced the rear bearing set and reset the front taper and spindle again. and another just recently. Looking through the exhaust port , you can see the new bearing and refitted spindle is making a much nicer surface finish on the piston. It is hard to see in the 1st pic, but a 1um cut makes very fine sand is the way I describe it. I hand feed at around 0.02mm /rev, it runs around 700 or so rpm, and takes around 1 minute per pass for the less than 15mm length of piston. So that is like around 4 seconds per mm or so or 1/4 of a mm per second how ever you want to work the time/distance out. I don't use power feed as the surface finish becomes junk in comparison and it effects the repeatability of the carriage. Having an old fashion clock with a moving second hand is really helpful in gauging feedrates etc I find. I used to trim with the pison on a fixture and then fitted them to the rod. But with the new press fit pin pistons, the assembly has to be done with the rod in place, so a modified version of the fixture shown with a holder that held the rod and tightened from the back end through the spindle was made. Some days I don't trim pistons, due to temp in the room conditions, or if I don't have the right mindset to do it.

2019

Edited By Neil Lickfold on 07/07/2019 17:09:08

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Neil, you may be interested in a variation of fine feed rates for lathes which I had no alternative but to employ.

We stripped out the leadscrew, apron and rack of the museums Smart & Brown model A for some serious spindle and bush refurbishment. the lathe was still needed for much of the work, so I used the tailstock to push the saddle with great success. The tailstock leadscrew is 8tpi and I had already made a collar for it calibrated 0-125, so a fine feed was actually easier than using the rack.

That is a good idea as an alternative to the carriage wheel. Being centred will have advantages as well.

Thanks for the idea.

Neil

I stand by what I said: "That non-temperature-controlled apparatus thinks it can resolve 1nm repeatably enough to justify the scale's resolution? Delusional, surely. It reminds me of a friend tickled pink by his small bench-top oriental CNC mill. He discovered that his CAD software could work to microns, and sincerely told me that he could now machine things 'accurate to a few microns'."

I can accept that the piezo gizmo can, in effect, change its length by 1nm, repeatably and accurately, but I'm talking about the apparatus as a whole. I'm not clear whether the piezo gizmo is a positioner or a displacement sensor, and if a positioner, whether it's working 'open loop' or 'closed loop'. In any case, the gizmo seems to be attached to a complex mechanical assembly, with a complex, cantilevered shape, which presumably has built-in clearances, etc., and the whole lot is subject to temperature effects. Is the apparatus to which the gizmo is attached dimensionally stable to within 1nm? The chain can only be as strong/accurate as its weakest link. Hence my comment about the CNC mill.

Edited By Kiwi Bloke on 08/07/2019 06:43:20

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But why ?

The whole instrument comprises a standard optical microscope [of the inverted variety] with two Marzhauser stages attached and a digital camera system.

The action of the Z stage can be considered pretty much in isolation, but; as its resolution is sub wavelength-of-light, it may be easier to consider the XY stage ... This has a much coarser resolution, and larger movements, so it might be conceptually more familiar.

Here's another photo of the 'interface'

The diatom, imaged on the screen, is about 20 microns across

The XY control [via the joystick] is 'pixel perfect' on that screen image ... You can use the cross-hairs on the screen to select any point, and the stage will traverse to put that point centre-screen.

This is not 'science fiction' ... these are standard tools used in labs all over the world.

MichaelG.

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https://www.marzhauser.com/en/pim/produktdetail-popup.html?view=details&pimid=a368&no_cache=1&m=null&p=null

Edited By Michael Gilligan on 08/07/2019 08:16:48

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... and that [apparently popular] fundamental misunderstanding is why I carefully chose the subtitle to my thread:

[quote] It all depends on the context ... [/quote]

Your friend's sincerity, and your dismissal of it, are 'two sides of the same coin'

Within the context of something tens of microns in size, it is easy [and neccessary] to work to tenths of a micron.

... and so, ad infinitum

MichaelG.

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Edit: Although it's a different species of diatom; this SEM imaging is worth a look

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0102-33062013000400007

Edited By Michael Gilligan on 08/07/2019 08:56:15

Michael, we seem to crossing swords today - not my intention at all. I admire the nm-resolution (and, presumably, accuracy) of the gizmo, but was suggesting that, unless the rest of the apparatus was remarkably stable, such resolution was wasted, and the achievable performance would be determined by things other than the gizmo. A bit like putting a micrometer head on a micrometer frame made from rubber? Incidentally, could the system be used to check gauge blocks - simpler than optical interferometry, I'd imagine?

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Again we agree ... No intention of crossing swords

The answer to your incidental question is probably "only if they are very small ones"

I seem to be struggling to get the point across [not only to your good self], but

the context is all-important.

MichaelG.

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Edit: This would probably be the most suitable of their stages to use for checking gauge blocks; but obviously would not compete with interferometry:

https://www.marzhauser.com/en/pim/produktdetail-popup.html?view=details&pimid=a272&no_cache=1&m=null&p=null

Edited By Michael Gilligan on 08/07/2019 10:51:31

That's an impressive image of the diatom, the details within it must be right at the limits of optical resolution.

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Diatoms have long been used by microscopists, as a reference 'grid' to test objectives.

Klaus Kemp still supplies an 8 form Test Plate for this purpose: **LINK**

http://www.diatoms.co.uk/pg.htm

... and the best 'light microscope' images I have seen from it are by Osama Oku: **LINK**

https://micro.sakura.ne.jp/bod/typeslide.htm

Even these are completely blown-away by Scanning Electron Microscope images, of course; due to the difference in wavelength.

MichaelG.

It's possible to work to absurd levels of accuracy very easily if you incorporate a feedback loop.

My telescope tracks starts in real time, on a good night with an accuracy of better than a second of arc. It even compensates for the speeding and allowing of stars caused by diffraction as the move higher or lower in the sky - the two clever calculations are (1) finding the centre of the image of a 'guide star' to sub-pixel accuracy and (2) the various algorithms for translating that into a movement of a mechanical mount whilst accounting for backlash and periodic errors in gearing etc.

Neil

I spent a lot of time looking at microscopic fossils, down to about 5 microns - they start getting fuzzy at that size due to the wavelength of light being about half a micron. That was using a fairly standard optical microscope. I got some amazing photos as well.

Neil - I am impressed that you can work so accurately!

I still have, amongst many others, about half a dozen slides of diatoms bought years ago from Northern Biological Supplies to use with my Russian Biolam R25. I gradually acquired most of the accessories for it. Its a shame, I never get around to use it anymore.

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I'm not questioning your claim, Neil, but I would be very interested to know how you demonstrate that.

... are you saying that your 'GoTo' aiming at start-up is accurate within a second of arc ?

MichaelG.

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Edit: Is the method revealed by the solution to Problem 2, here:

https://spacemath.gsfc.nasa.gov/weekly/10Page38.pdf

... or am I missing a trick ?

Edited By Michael Gilligan on 08/07/2019 21:37:34