Flat Surface

[Russell EberhardtParticipant @russelleberhardt48058]

A bit off topic but reading the above I wonder why anyone would use a granite chopping board for its original purpose.  Surely it would wreck the edge of kitchen knives?  I’m sticking with wood.

Russell

[DalboyParticipant @dalboy]

Two glass chopping boards, keep one as spare. They also have a range of other material boards. Not that dear either

[COLIN MARTIN 2]

On COLIN MARTIN 2 Said:

…. it looks to be pretty flat and is probably ok for what I need it for.

What the flat surface is needed for makes all the difference:

• for rough work almost anything will do.  MDF, Dining Table, and Kitchen Worktops are all “pretty flat”.  Almost everything I need the height of is measured off my bench because ±0.2mm is “good-enough” My bench is a kitchen worktop on top of pine planks.  Steel-rule with loupe accuracy.
• occasionally I need ±0.04mm, done with a digital caliper.  I use my milling machine’s table as the flat surface, usually with a square edge to ensure the measurement isn’t tilted.  When the milling table is too small, or the head gets in the way, I clear the bench and lay my glass-plate on top.  The glass-plate is much flatter than the worktop, but note that a digital caliper isn’t good-enough to get better than about ±0.03mm accuracy.
• once in a Blue Moon, I need ±0.01mm accuracy.  For that a Height Gauge and precision blocks are needed.  For my unpretentious purposes ground parallels make good enough precision blocks.  A more serious player would buy new, not secondhand gauge blocks, and the real McCoy would demand they be calibrated.

A plus point is that it sits on rubber feet so it should be a little more stable than my previous glass pane.

Get rid of the feet!  Problem is the granite board bends under the weight of the workpiece and is no longer flat.  Put a DTI on the middle and press hard with a forefinger to see how much a granite chopping board dishes.  Easily fixed, remove the feet!

 

 

Colin

When high precision and accuracy matter it’s necessary to buy a proper surface plate and support it solidly.  The support can cost as much as the plate, and a set of gauge blocks and other paraphernalia in good condition are also needed.  Costly.

I feel buying old surface plates and gauge blocks is missing the point,  There’s no guarantee ebay bargains are precise or accurate, which what they are for.  The danger is the owner believes he’s working accurately when he’s not…

My guess is that for most Model Engineering purposes a sheet of glass or granite on a flattish bench is all that’s needed.

Dave

[Bo’sunParticipant @bosun58570]

Another vote for ditching the rubber feet on a chopping board (assuming the CB is flat enough of course).  Get some anti-slip matting and a piece of 18mm (or thereabouts) MDF to sit it on.

In those halcyon days, anti-slip mat could be got from one of the “pound shops”.

[COLIN MARTIN 2Participant @colinmartin2]

Thanks for the advice! I assumed that the granite would be strong enough to resist flexing. I will remove the feet and use it sitting on my work bench.

 

Cheers,

 

Colin

[Russell EberhardtParticipant @russelleberhardt48058]

Thoughts on the flexing of the surface under load:

The amount of deflection under a given load is inversely proportional to the Youngs Modulus of the material.  Glass and granite have similar values of the modulus so there will be negligible difference between them.  The deflection of a sheet of the material is however inversely proportional to the cube of the thickness, so it is important to make your surface plate as thick as possible.   A granite chopping board is usually about 1 cm thick.  If you can get hold of an offcut of granite worktop about 5 cm thick it will be 125 times more resistant to deflection.

Putting it on a wooden worktop, however flat will not improve the strength of a 1 cm thick glass or stone plate noticeably.

Russell

[FulmenParticipant @fulmen]

IIRC they made surface plates of glass during WWII to save iron (citation needed). The E-modulus is around 70GPa (same as aluminum) so it’s actually quite bad, but at least it’s hard and won’t corrode. Didn’t catch on though.

The most interesting property is possibly the specific modulus, i.e. the elastic modulus divided by the density. Cast iron has sp.mod around 18.5m2/s2, which is about the same as both concrete and balsa (weird flex but OK).

Both steel and titanium is better at 25, glass even better at 30 while tungsten carbide tops them with an impressive 35m2/s2. That would make for quite the surface plate, eh? But they are all dwarfed by Silicon’s whopping 79m2/s2.

[southernchapParticipant @southernchap]

Honestly? I’d buy a small, cheap Chinese granite surface plate.

It won’t be Mitutoyo granite or Crown Windley cast iron surface plate flat but then you don’t need it to be.

It will likely be just as flat as good quality float glass and flatter than a piece of granite worktop, and it definitely won’t flex. 😉

[Russell Eberhardt]

On Russell Eberhardt Said:

A bit off topic but reading the above I wonder why anyone would use a granite chopping board for its original purpose.  Surely it would wreck the edge of kitchen knives?  I’m sticking with wood.

Russell

Cleanliness!  Wood absorbs fluids, which rot the porous structure, creating a marvellous habitat for micro-organisms. Which is more important: avoiding damage to easily resharpened kitchen knives, OR, discouraging Salmonella, e-coli and Campylobacter.

On Russell Eberhardt Said:

Thoughts on the flexing of the surface under load:

The amount of deflection under a given load is inversely proportional to the Youngs Modulus of the material. …  The deflection of a sheet of the material is however inversely proportional to the cube of the thickness, so it is important to make your surface plate as thick as possible.   A granite chopping board is usually about 1 cm thick.  If you can get hold of an offcut of granite worktop about 5 cm thick it will be 125 times more resistant to deflection.

Putting it on a wooden worktop, however flat will not improve the strength of a 1 cm thick glass or stone plate noticeably.

Russell

All true, except laying the glass sheet on a flat surface isn’t done to improve it’s strength.   The purpose is to minimise bending by taking the load force straight to ground:

In other words, if a cutting board has feet, take them off and support it underneath.

Russell’s point applies to this form of surface table:

Note the thick granite plate, the very sturdy table the plate sits on, and the load-spreading feet.  There are beefy levellers hidden under the plate too.  This is the real McCoy, not only flat to a specification, but designed to take a heavy load without bending.  Accurately measuring an engine block is a far cry from using a sheet of float glass to do some unmeasured lapping.

A sheet of float glass does all I need, and I look askance at chaps buying battered second-hand cast-iron surface-plates, perhaps bent after being leant against a wall.   To my mind they are neither fish nor fowl!  Overkill when ordinary methods are good enough, and insufficient when accuracy matters.   I wonder how many of us happily believe we’re working to tenths when we’re not? The acid test isn’t what our micrometer says, it’s other people measuring our work and getting the same result!  Much harder to do correctly and rarely tested.   Fortunately, accurate precise measurements aren’t required for most hobby purposes:  little need for Model Engineers to apply the American System of Manufacture.

Dave

[SillyOldDuffer]

On SillyOldDuffer Said:

On Russell Eberhardt Said:

A bit off topic but reading the above I wonder why anyone would use a granite chopping board for its original purpose.  Surely it would wreck the edge of kitchen knives?  I’m sticking with wood.

Russell

Cleanliness!  Wood absorbs fluids, which rot the porous structure, creating a marvellous habitat for micro-organisms. Which is more important: avoiding damage to easily resharpened kitchen knives, OR, discouraging Salmonella, e-coli and Campylobacter.

Yes it is a bit off topic, but wood also has anti-bacterial properties otherwise we would all be suffering from chronic stomach infections which we are not so I for one will continue to use my wooden chopping board.

Andy.

[Andrew Crow]

On Andrew Crow Said:

On SillyOldDuffer Said:

On Russell Eberhardt Said:

A bit off topic but reading the above I wonder why anyone would use a granite chopping board for its original purpose.  Surely it would wreck the edge of kitchen knives?  I’m sticking with wood.

Russell

Cleanliness!  Wood absorbs fluids, which rot the porous structure, creating a marvellous habitat for micro-organisms. Which is more important: avoiding damage to easily resharpened kitchen knives, OR, discouraging Salmonella, e-coli and Campylobacter.

Yes it is a bit off topic, but wood also has anti-bacterial properties otherwise we would all be suffering from chronic stomach infections which we are not so I for one will continue to use my wooden chopping board.

Andy.

Some woods!  Pine, Oak, Maple, Teak.  But don’t expect too much of them: many, perhaps most, tummy bugs are caused by Norovirus against which the antibacterial properties of wood are ineffective.

Beware relying on personal experience because it’s far too limited.  That Andrew hasn’t been infected by his wooden chopping board proves nothing. The statistics show stomach problems are extremely common. GPs report about a million stomach bug related consultations each year.    This Manchester University Study (on behalf of the Food Standards Agency) confirms 17 million people suffer vomiting and diarrhoea per year in the UK.

Chopping boards have always caused trouble.  I remember British butchers being ordered to replace their traditional wooden blocks with plastic only to find that plastic was just as bad for different reasons.

Copper is very good because it’s easy to keep clean and the metal is disinfectant.  Granite and glass are effective because they resist scratching, don’t harbour microscopic muck,  and are easily cleaned.  I have three chopping boards: wooden for cutting bread; glass for cooked meat, fruit and veg, and plastic for raw meat.   The plastic board goes in the dishwasher.

Dave

 

 

 

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I don’t know if they still do, but back in the sixty’s/seventy’s, the big wooden tables that Butchers used for chopping and cutting the meats, were all scrubbed down using salt, and then washed off, every day. When my old employer had a canteen, the food preparation tables had to be made with 316 stainless steel. No aluminium cooking pots or utensils were allowed either, and I think knives with wooden handles were also banned.

Regards Nick.

[Neil WyattModerator @neilwyatt]

I use a piece of granite-composite worktop. An offcut from my then sister-in-law’s kitchen install, it would have been free, except I burnt out an angle grinder being a bit too enthusiastic when cutting it to size.

On the plus side, the angle grinder’s gearbox ended up in my electric shunter.

Neil

[SillyOldDuffer]

On SillyOldDuffer Said:

On Andrew Crow Said:

On SillyOldDuffer Said:

On Russell Eberhardt Said:

A bit off topic but reading the above I wonder why anyone would use a granite chopping board for its original purpose.  Surely it would wreck the edge of kitchen knives?  I’m sticking with wood.

Russell

Cleanliness!  Wood absorbs fluids, which rot the porous structure, creating a marvellous habitat for micro-organisms. Which is more important: avoiding damage to easily resharpened kitchen knives, OR, discouraging Salmonella, e-coli and Campylobacter.

Yes it is a bit off topic, but wood also has anti-bacterial properties otherwise we would all be suffering from chronic stomach infections which we are not so I for one will continue to use my wooden chopping board.

Andy.

Some woods!  Pine, Oak, Maple, Teak.  But don’t expect too much of them: many, perhaps most, tummy bugs are caused by Norovirus against which the antibacterial properties of wood are ineffective.

Beware relying on personal experience because it’s far too limited.  That Andrew hasn’t been infected by his wooden chopping board proves nothing. The statistics show stomach problems are extremely common. GPs report about a million stomach bug related consultations each year.    This Manchester University Study (on behalf of the Food Standards Agency) confirms 17 million people suffer vomiting and diarrhoea per year in the UK.

Chopping boards have always caused trouble.  I remember British butchers being ordered to replace their traditional wooden blocks with plastic only to find that plastic was just as bad for different reasons.

Copper is very good because it’s easy to keep clean and the metal is disinfectant.  Granite and glass are effective because they resist scratching, don’t harbour microscopic muck,  and are easily cleaned.  I have three chopping boards: wooden for cutting bread; glass for cooked meat, fruit and veg, and plastic for raw meat.   The plastic board goes in the dishwasher.

Dave

 

 

 

I have just read your link and not once that I saw did it mention chopping boards, unless you have other information that says so

[Grindstone CowboyParticipant @grindstonecowboy]

A scientific report concerning bacteria and cutting boards may be found at

https://www.sciencedirect.com/science/article/pii/S0362028X25001280

I’m happy with wood.

Rob

[Andrew CrowParticipant @andrewcrow91475]

A very interesting article Rob, QED.

All I can really add is that when you’re cutting up food on any board there must be some transfer of the board material to the food, I think I would rather eat minute particles of wood than plastic.

Andy

[Dalboy]

On Dalboy Said:

On SillyOldDuffer Said:

On Andrew Crow Said:

On SillyOldDuffer Said:

On Russell Eberhardt Said:

A bit off topic but reading the above I wonder why anyone would use a granite chopping board for its original purpose.  Surely it would wreck the edge of kitchen knives?  I’m sticking with wood.

Russell

Cleanliness!  Wood absorbs fluids, which rot the porous structure, creating a marvellous habitat for micro-organisms. Which is more important: avoiding damage to easily resharpened kitchen knives, OR, discouraging Salmonella, e-coli and Campylobacter.

Yes it is a bit off topic, but wood also has anti-bacterial properties otherwise we would all be suffering from chronic stomach infections which we are not so I for one will continue to use my wooden chopping board.

Andy.

Some woods!  Pine, Oak, Maple, Teak.  But don’t expect too much of them: many, perhaps most, tummy bugs are caused by Norovirus against which the antibacterial properties of wood are ineffective.

Beware relying on personal experience because it’s far too limited.  That Andrew hasn’t been infected by his wooden chopping board proves nothing. The statistics show stomach problems are extremely common. GPs report about a million stomach bug related consultations each year.    This Manchester University Study (on behalf of the Food Standards Agency) confirms 17 million people suffer vomiting and diarrhoea per year in the UK.

Chopping boards have always caused trouble.  I remember British butchers being ordered to replace their traditional wooden blocks with plastic only to find that plastic was just as bad for different reasons.

Copper is very good because it’s easy to keep clean and the metal is disinfectant.  Granite and glass are effective because they resist scratching, don’t harbour microscopic muck,  and are easily cleaned.  I have three chopping boards: wooden for cutting bread; glass for cooked meat, fruit and veg, and plastic for raw meat.   The plastic board goes in the dishwasher.

Dave

 

 

 

I have just read your link and not once that I saw did it mention chopping boards, unless you have other information that says so

I’m baffled Dalboy, your point is?  The report relates to Andrew’s claim “otherwise we would all be suffering from chronic stomach infections which we are not“.  The report’s about the incidence of diarrhoea and vomiting, not causes.  Look elsewhere for sources, one of which is chopping boards.

Rob’s report, which confirms what I said about plastic boards being problematic too, does the opposite.  In it wooden chopping boards are discussed without addressing incidence; I have no problem with that, do you?

In both cases, information isn’t presented in a complete easy to understand bundle:  it’s our job to dig deeper.  I’m suggesting anyone who wants to know should research the subject rather than relying on personal experience.  I’m not mounting a campaign against Wooden Chopping Boards, I’m pointing out that personal experience is poor compared with other evidence.

Smoking is far more dangerous than wooden chopping boards, yet people still do it.  Many smokers are vehement about their right to ignore the risks.  Up to them, but why do they ignore the evidence?

Dave

 

[fredjscipioneParticipant @fredjscipione]

Re: the sub-topic of measuring the flatness of lapping-plate candidates – Very little is needed to measure cross-diagonal twist to within the resolution limit of your measuring device (feeler gauge, drop indicator, ‘tenths’ DTI, etc.).  Confer Robin Renzetti’s Two-Footed twist measurement on Instagram

 

Moderators Note Your link goes to a general Instagram reels  page not the Robin Renzetti one.

<https://www.instagram.com/reel/CJZIKX8H8ay/&gt;.

Note that it does not require any particular level of accuracy from the spacers or straight-edge/ruler, just repeatability.

Measuring bulges and dips can be almost as simple.  You need two bars to cover the span(s) you are interested in.  One serves as a reference & the other is for the body of a two-footed twist gauge.  The rest is mostly technique.

The reference bar only has to be straight enough to remain within the measuring device’s range.  Measure the reference bar’s thickness variations at the twist gauge’s foot & measurement contact locations.  Absolute thicknesses are not required, only the variations (which can allow better resolution).  Subtract the average of the two foot location’s variations from the measurement location’s to get the reference bar’s ‘bulge’.  Repeat for all spans of interest.

At this point, the gauge readings have an unknown offset from ‘true’ flat.  Take the readings for the top and bottom sides of the reference bar.  Combine them with the ‘bulge’ value to yield the value of the offset (& the top & bottom ‘true’ bows).  Subtract the offset from any reading to get the surface bulge/dip for that span.  Check against the reference bar’s known value after changing to a different span.

[southernchapParticipant @southernchap]

Well, let’s try again and inject some financial perspective into this discussion.

Here’s RDG’s Dasqua surface plate page:

https://www.rdgtools.co.uk/product-category/dasqua-measuring-equipment/dasqua-granite-surface-table/

Amazon page for 200 mm x 200 mm x 60 mm Dasqua surface plate:

https://amzn.eu/d/0dpLlMPI

Amazon page for a 12″ x 8″ x 2″ HHIP surface plate:

https://amzn.eu/d/05orbMh8

Cromwell’s granite metrology items page:

https://www.cromwell.co.uk/shop/measuring-and-test-equipment/surface-plates/c/050501?pageNo=1&pageLimit=50&sort=price-asc

and their surface plates specifically:

https://www.cromwell.co.uk/shop/measuring-and-test-equipment/surface-plates/granite-surface-plate-un-calibrated/f/67538?stockStatus=Show+Unavailable

So relatively inexpensive options for granite surface plates, that are sensibly sized for most of us (most of us don’t need 600 x 400, or 800 x 600 sized surface plates, so we can ignore those).

All of these will likely be notably flatter than kitchen counter worktops, granite chopping boards or even float glass.

I got lucky, and grabbed a Dasqua 400 mm x 300 mm x 50 mm surface plate in a sale, before the prices went up, and I did my best, using Suburban tools’ technique (on their YouTube channel) to workshop test it with an Eclipse surface gauge, a .0001″ dial test indicator and a slip gauge.  If it’s out of the stated tolerance, then I’m struggling to measure it.

But even a 300 mm x 200 mm, or 200 mm x 200 mm surface plate would be adequate for many of us, and you can get them from RDG for £65.

Now, I know, I know, some of our number come from cultural backgrounds where the idea of spending money on a hobby if we think we can ‘do just as well’ with a ‘free workaround’, but we’re not woodworkers, and if we’re working to thou’s, we ought to be measuring to tenths (or maybe a couple of tenths at most).

If we can’t rely on the reference surface we have, to be flat to that couple of tenths then we’re getting in our own way.

How much time could we save in fitting, if we could rely on our reference surface to be flat to a couple of tenths at least?

[alecsParticipant @alecs]

<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.

[fredjscipioneParticipant @fredjscipione]

“Moderators Note Your link goes to a general Instagram reels page not the Robin Renzetti one.”

I am sorry to hear that.  The link works on my browser from the U.S.A.  Anyone having that problem can, of course, do their own search for (e.g.) “Renzetti two footed Instagram” (without the quotes?).

 

To southernchap: The best of both worlds!  The twist gauge method with a ‘tenths’ DTI allows self-certification for all surface plates as well – new, old, used, auctioned, etc.  Throw in a 5:1 lever w/ ‘frictionless’ flexure hinges for 20 u-in resolution!  Also supports those who see making a surface or lapping plate as a hobby project.  Finally, measurements can serve to justify a ‘NO’ decision on a lapping plate substitute just as easily as a ‘YES’.

While a cheap surface plate may be the best ‘substitute’ for a surface plate, OxToolCo makes the case for not using it for sanding.  Once again, for a hobby sanding (& lapping?) plate, an easy & accurate flatness measurement method can be very useful.

[peak4Participant @peak4]

The recommendation given to me, by a friend who was involved in flat surface calibration for NAMAS, was to use new plain float glass, if you didn’t need a cast iron/granite plate.

The bit missing in the previous descriptions here, is to make a stiff wooden box support, line it with something waterproof, say paint or cling film, and float the glass sheet directly on a decent thick layer of plaster of Paris.
This will give full support over the whole surface, with less chance of warping than on a plain wooden base.

Bill

[southernchap]

On southernchap Said:

…most of us don’t need 600 x 400, or 800 x 600 sized surface plates…

Best not to make assumptions; my Crown Windley surface plate is 36″ x 24″ and is definitely not too large.

Surface plates are like milling machine tables. Just because a mill table has X millimetres of travel it doesn’t mean you can mill a workpiece X millimetres long.

Julie

[JasonBModerator @jasonb]

but we’re not woodworkers,

 

And there was me last week adjusting the CAM so the CNC would take an extra 0.05mm off two sides of a WOODEN part. When you are trying to fit 68 of them around a circle the add on effect of 67 being too large means there is no way the last will fit.

As for a 10ths dti I originally managed with a home made one of these, still don’t have a 10ths dti but just 80 odd engines that run. The first built (10V) will still run if I blow into it yet at the other end of the scale is hapy at 1000rpm generating.

My height gauge was from the same book, set from a steel rule. Point was a bit of freehand ground piano wire. Can’t remember what I used as a surface, probably the formica covered blockboard bench I was working on.

 

 

[Julie Ann]

On Julie Ann Said:

On southernchap Said:

…most of us don’t need 600 x 400, or 800 x 600 sized surface plates…

Best not to make assumptions; my Crown Windley surface plate is 36″ x 24″ and is definitely not too large.

Surface plates are like milling machine tables. Just because a mill table has X millimetres of travel it doesn’t mean you can mill a workpiece X millimetres long.

Julie

Might I draw your attention to an important word in my post?

most of us don’t need 600 x 400, or 800 x 600 sized surface plates

😄

That it was you in particular who posted such a correction made me chuckle! When I wrote that part of my post, you popped into my mind as definitely a member of the set that my above quote wouldn’t apply to, thus the use of the word “most”

No assumptions made or implied. 😉

[Author]

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