Flat Surface

[Andy StopfordParticipant @andystopford50521]

A quick search reveals 300 x 200mm float glass is about £25 for 10mm thick.

The 300 x 200mm Dasqua granite (though its not really granite apparently) is 60mm thick for £65. And it probably won’t break if you drop something on it, or bend significantly if not carefully supported.

You pays your money and takes your choice – mine was a Dasqua granite surface plate (actually 300 x 300 – it was under special offer a couple of years ago for about £70, I think).

Note: granite not intended for metrology may not be very flat – stuff intended for worktops, headstones etc., may have been ground using a hand operated polisher on a folding overhead arm arrangement. A skilful operator can make it look perfectly acceptable for its intended purpose, but a laminate worktop may well be flatter.

As for glass/granite chopping boards – I like my kitchen knives sharp, so no, just no.

[alecs]

On alecs Said:

<p style=”text-align: left;”>If you are working to thous, you absolutely dont need to measure to tenths. Ive never had anything but one thou graduated micrometers and dial gauges and managed just fine fo 50 years at work and at home.</p>
And for most home workshops a bit of float glass is good enough. What are most amateurs using it for? Scribing lines that are  two to five thou wide mostly.

If you have some very special purpose for it, a proper surface may be justified, but it’s the exception not the rule.

It’s traditionally considered sensible to measure to a finer resolution than the resolution one is working to.

If one needs to hit a particular dimension with a tolerance in low single figures of a given order of magnitude, then one is rolling the dice a little bit, using a piece of metrology equipment that has a resolution at that order of magnitude.

Okay you can ‘read between the lines’; an experienced person, who knows their measuring tools well, and has decent eyesight, can for example, read a couple of tenths on a micrometer that has .001″ graduations.  That does however, allow another path for potential human error to creep in.

As I implied in my original post, half a thou’ is often a not uncommon ‘higher precision’ resolution used by many hobbyists (Julie, not talking about you here, from what I’ve read of your projects on this forum, I suspect Mahr have probably done reasonably well out of you!😄), but for something like a small diameter bearing, one often ends up with a tolerance measured in tenths.

As many have said on here, it does depend on what you’re working on.  Still, for £65, why not treat yourself to a Dasqua granite surface plate. 🤷

[southernchap]

On southernchap Said:

On alecs Said:

<p style=”text-align: left;”>If you are working to thous, you absolutely dont need to measure to tenths. Ive never had anything but one thou graduated micrometers and dial gauges and managed just fine fo 50 years at work and at home.</p>
And for most home workshops a bit of float glass is good enough. What are most amateurs using it for? Scribing lines that are  two to five thou wide mostly.

If you have some very special purpose for it, a proper surface may be justified, but it’s the exception not the rule.

It’s traditionally considered sensible to measure to a finer resolution than the resolution one is working to.

If one needs to hit a particular dimension with a tolerance in low single figures of a given order of magnitude, then one is rolling the dice a little bit, using a piece of metrology equipment that has a resolution at that order of magnitude.

Okay you can ‘read between the lines’; an experienced person, who knows their measuring tools well, and has decent eyesight, can for example, read a couple of tenths on a micrometer that has .001″ graduations.  That does however, allow another path for potential human error to creep in.

As I implied in my original post, half a thou’ is often a not uncommon ‘higher precision’ resolution used by many hobbyists (Julie, not talking about you here, from what I’ve read of your projects on this forum, I suspect Mahr have probably done reasonably well out of you!😄), but for something like a small diameter bearing, one often ends up with a tolerance measured in tenths.

As many have said on here, it does depend on what you’re working on.  Still, for £65, why not treat yourself to a Dasqua granite surface plate. 🤷

“Traditionally considered sensible” by whom? None of the toolmakers and machinists I ever worked with in the past 50 years.

If you are working on a lathe or mill or hand fitting where the finest tolerance is one thou, you use a one thou mic. Those few working to tenths on high precision grinders use a one tenth mic.

But yes, a precision surface plate is a good buy at 65 beer tokens if you are doing precision work to one tenth such as measuring bearing roller diameters with a tenths DTI to ensure you get a matched set for a lathe headstock or Manx Norton big end etc. Or checking scraped surfaces on machine tool ways etc. I can’t think of much else where it would be necessary in the home shop. Certainly not marking out etc.

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