Surface Plate & Height Gauge recommendations

I now have three 'surface' plates (four if you include a plate glass one). I'm not recommending that as a practice - but these things do seem to accumulate over time. I use them all to a greater or lesser degree and for different purposes.

My first plate was a casting from CES, which I machined before surface grinding at college many years ago. It is about 10" x 8" (I think) and is used for general marking out. I have several vernier height gauges but very rarely use the large (24" ) one - preferring an old 9" vernier gauge (set in a base block) as it's much more convenient. How accurate this plate really is, I don't currently know (I plan to change that). I have a several small surface gauges that are also used for marking out in some instances.

I then have a large cast iron plate, about 18" x 22" which is too heavy to lift/move around easily and gets used as required in my large workshop - mostly for checking machined parts for accuracy (something I've become a bit more fussy about over time). This is done with a surface gauge and dial indicator. The plate was purchased from the college and has certainly had some use and must be worn to some degree. However, using an indicator on a very solid arm & base I cannot detect much (any) surface variation - although I suspect a professional would find some with the right equipment. It's good enough for my purposes though, offers a large surface area but is also very heavy, enough that I don't try to move it often. So it cannot be used in both workshops

Recently, I purchased a small granite surface plate from Rotagrip which wasn't too expensive (they have 20% off at the moment). Including shipping, the one I purchased (the smallest one) was just over £50, which I think is reasonable for a good quality surface plate for use in a hobby shop.

Rotagrip Granite Surface Plates

It's 12" x 9" - so my small cast iron plate can now be checked on it. This will be its main use (as my 'reference' plate) for scraping various small machine/tools parts that I'd like to be as flat as I can sensibly make them. I can pick it up (not for too long) as it is just on the borders of what I can comfortably manage to lift these days.

I've also had a piece of plate 1/2" glass about 12" x 24" set in a wooden base for many years and this was originally used for marking out but now is only really used for frame assembly work. I've never checked it for accuracy but it seems OK for what I need it for. It's kept in the inside (Winter) shop with the small cast iron plate.

I've very been fortunate to being able to accumulate these plates over the years at no great cost.

So - for marking out, a plate glass or small suface plate and Vernier gauge is fine. The size required will depend on the kind/size of work required but you can normally mark out larger parts on a smaller plate if their bottom edge is reasonaly flat & square. However, for checking parts for accuracy, a surface plate with surface gauge and DTI is required and here you really need space to be able to navigate around the part to check it fully/accurately - so a larger plate is a better bet.

Finally, how 'flat' your surface plate needs to be, obviously this depends what you are using it for. My granite plate will be used to check/compare the flatness of other parts and small tools - so I need it to be as good as possible without breaking the bank and also (in my case) to be able to move it without breaking my back (as it will be used in both workshops) - so weight was a key issue.

Surface plate size, weight (portability) and cost all need to be considered in relationship to the work it's going to be used with. However, if I was starting over - the granite one would be my obvious choice now.

Regards,

IanT

Edited By IanT on 31/05/2020 16:13:31

I used various granite work tops for years, 3 years ago I treated myself to a granite surface plate, 450mm x 450mm x 90mm.

I probably don't really need it, but I do like it!

Jim

Hi Lee, Guys,

When I wanted a height gauge I made one ! I used a digital vernier, one of the cheap Aldi one that they sell for about £8. A few bits of scrap, a couple of salvaged bearings from an old hard drive. More than accurate enough. My surface plate is a piece of broken granite headstone.

Here is a picture, I did a build log for this a couple or so years ago.

That brass knob drives the M6 leadscrew. A nice fine 1 mm per turn which you can actually measure on the readout.

A close up view.

More pictures in my album.

Not sure, how tall you want the Height Gauge, or how big the Surface Plate, nor how much you are prepared to spend..

HEIGHT GAUGE

If you are going to buy new, Arc Euro sell three Digital Height Gauges, a 150 mm one at £39.10, an 200 mm one at £79.31 and a 300 mm one at £94.03

If you buy secondhand, (possibly a bit late now, but when Industry changed over from Imperial to Metric, you could find Imperial ones in quite good condition fairly cheaply, because they were no longer wanted. My Height Gauge was condemned, because it had a 0.002" error over 18", which is acceptable for the work that I do! )

SURFACE PLATE

Some years ago, I made a surface plate for The WaterWorks Museum in Hereford., 18" x 24" x about 1.5" thick. A Kitchen Work Top / Grave Headstone maker, in Wisbech, cut me a piece of granite for £30.

You might be able to find an offcut cheaply, and make a base to suit.

If that seems expensive, an industrial, Mitutoyo 6' x 4' x 6" would have set you back over £3K at the time!

So, relatively, I got a bargain; for less than a third of the price an Industrial quality one.

I made up an angle iron frame, with a leveliing screw at each corner. The legs extended above the frame, to provide a loose location for the plate. On this frame, was placed a plywood support which was coated with a moist layer of plaster / Polyfiller, onto which the marble was placed. Being fluid, the filler could flow, so that the granite was uniformly supported, and not stressed.

Finally, a plywood cover was made, varnished and fitted.

An Industrial Surface Table, like the one mentioned above was ruined, by being leaned at an angle against a wall.

It sagged and bent!, Hence the need for a table to be stress free, as much as possible.

(No point in trying to work to greater accuracy than your measuring equipment, which includes the flatness of the Surface Table )

HTH

Howard

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I have a Digi height gauge from M-DRO & a 18" x 17" x1.5/16" polished granite sink cut out from a kitchen manufacturer... free gratis after I told them what it was for.. suits me fine for the accuracy I need.. as for flatness.. measured with digi gauge from corner to corner ( 4 corners ) & measured to '0' with a 0.0005" fall off at one corner, just fine for me.

George.

Yes, but beware!!!

If there's a need for repeatable accuracy better than 0.01mm you can't just buy second-hand and hope for the best. Checking against a 1" standard is a good first move, but have you got a 1" standard? With a certificate? Do you know how to use standards properly in the 0.001mm region?

Unfortunately, checking high-precision instruments at only one point on their scale isn't good enough either - they have to be calibrated across the entire range. Whilst a micrometer thread might be in excellent condition at the 1" end, it could be badly adrift towards zero where most of the action is.

Instruments in this class can't be trusted until their accuracy is confirmed. Best not to be led astray by a quality brand with fine graduations and a good feel. Sod the fantasy, get it calibrated! If it's good, hurrah, otherwise no tears please. In the bin with it.

Comes back to what the tool is for. At best I suspect most Imperial model engineers work to ±0.001", and most Metric model engineers about the same at ±0.02mm. Working to 0.01mm is comparatively unusual and a home workshop cutting to ±0.001mm must be a rare beast indeed. Don't get sucked into miserably chasing accuracy that can't be had outside a properly equipped tool-room.

Dave

Repeatability and accuracy are not the same thing. Generally the former is easier to achieve than the latter.

Andrew

S O D is right.

Probably, most of the time, we are happy to work to +/- 0.001" or 25 microns.

If we want better than that, we are going to start thinking in terms of lapping the mating parts together.

You can't work to single figure microns outside a temperature and humidity controlled Standards or Calibration Room, and only after everything has soaked for at least 24 hours.. And the measuring instruments used will be traceable back to a NPL standard!

Even a Rabone 6" rule is marked "At 20'C" , and modern micrometers, and length standards, have insulating pads on the frame, so that hand heat does not affect the size, to give the clue.

To see the effects of hand heat, hold an Aluminium Piston with its Gudgeon Pin in place.. After a few minutes the Gudgeon Pin will fall out of the bore, because of the expansion from the small temperature rise above ambient resulting from the heat of your hand.

Howard

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Photo above shows the evolution of my marking out tools, on the right is a homemade surface gauge built when I must have been about 15 on the Unimat3, can't remember what I used it on but may have just been the formica worktop but got a Stuart 10V and Beam made with it.

Next is a bought surface gauge that I must have got during the Minnie build and that would also have been use don some if the early Fowler TE too.

The 6" digital height gauge was not brilliant with an uneven base and scriber that pointed upwards but a bit of work flattened that out, don't use it much now but it is handy on the mill when setting up a casting to check heights as it's small size fits under the column and does not need much table surface.

The vernier one saw a bi step up in accuracy of my marking out though now not used so much as I tend to layout holes and faces with the DRO but it comes in handy some times and a few scribed lines act as a double check when using the DRO.

Currently using a polished porcelain tile as a marking out surface, with a smallish shed it's easy to put it out the way if the bench space is needed and it also makes a good background for photos of small parts.

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Barrie,

I am not trying put off anyone.

We all work to whatever standard of accuracy we can can attain, or are prepared to accept.

I was merely implying using common sense.

If you don't need to work to 0.005 mm, don't, unless you want to boast of your prowess, and are prepared to spend the time and money so to do.

A bolt made to a length within 0.005 mm will, all other things being equal, clamp no better when then the nut is tightened, than one with a 0.5 mm tolerance. It will just be much more costly!

Normally, +/- 0.025 mm suffices for my work, but last week, I had to make a part that would seal against petrol. So I had to work to an interference fit on the OD and size and size for the ID.

Fitness for purpose has to be the watchword.

Howard

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Very true, Andrew ... and I suspect that Dave tries to avoid tautology

‘repeatable accuracy’ however, comes pretty close to a working definition of ‘precision’

MichaelG.

Never fear. I am not put off (good luck with that - must try harder)!

And please try to refrain from getting personal with one another, particularly on my account.

After watching Stephan on YouTube, it's hard not to be inspired to work more accurately. At least to some degree. But I'm not going to kid myself. I am unlikely to buy (maybe make?!) a lathe mounted tool grinder or a surface grinder or even a shaper, so measuring to a degree where I need to account for if the ambient temperature of my workshop is currently 15°C or 20°C is highly unlikely.

It would be nice to have the capability (in terms of tooling and competence) to work to 0.001mm, but in reality we're talking at least an order of magnitude less precise than that. Talk of industry standards and certification are so far beyond my aspirations, they're not even worth contemplating (at this stage ).

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Lee,

As you can see from their remarks, different folk here have different needs - and it's not always clear what these are when they offer advice (which will naturally be influenced by their personal requirements). For my work, I don't need to measure microns and (frankly) none of my machines are capable of reliable/repeatable cuts much below a couple of thou anyway.

I still mark-out my work (I've no DROs fitted) and try to do so as accurately as possible. Convenience is also important to me and a surface plate and Vernier are generally ideal for this work.

My machines are mostly old and occasionally I also need to check (and correct) wear or damage on a machine surface I therefore need a reference 'flat' to check against. A surface plate is obviously a very useful tool to have when doing this. For checking related surfaces (or machined work) - a dial test indictor and stand is preferable to a height gauge in my view.

Please note that I'm often checking surfaces by comparison - Is this machined surface parallel? - Is this table flat (enough)? I'm certainly not going for any extremes of metrology - I'm just trying to get a machine to work a bit better or make something that pleases me (which is generally anything that doesn't end up in the bin).

However, you originally enquired about a surface plate and height gauge.

A Rotagrip granite plate and a mini-height ( 6" ) gauge from Arc would probably suit most hobbyist needs and cost about £100 new. There are cheaper alternatives available but these are certainly tools that I use regularly - and I can't claim that for all of my purchases I'm afraid..

Regards,

IanT

Absolutely. Which is the reason I posed the question here. To obtain a varied plethora of views, opinions and experiences from a wide collection of knowledgeable enthusiasts/professionals. And boy, you guys did not disappoint. So, thank you to everyone who as (and who will) participate in the conversation. I've learned a lot from you all.

Still not entirely sure how I will end up proceeding. The immediate plan is to keep all 20 of my phalanges crossed for some eBay gems. Failing that, I might have to purchase new from one of the regularly mentioned retailers.

#notsponsored

To get back to the original subject, a while back I bought a biggish piece of float glass (around 60 x40, maybe a bit bigger and about 20mm deep) to act as a 'cheap' surface plate.

When I got it and did some checking, I found that it varied by around 0.5mm in height over the area. I raised this with a colleague and he told me that this was within tolerances! One of his roles as an engineer was quality control in a glass factory so I guess he know his stuff.

I'm not saying that a piece of glass can't be accurate to within the sort of tolerances we need, but I am saying it may not be.

Iain

Quite right! I hope it's correct, but this diagram shows how I remember the difference between accuracy, precision and resolution. Using a bulls-eye target to illustrate accuracy and precision came from Neil Wyatt I think. I've added resolution. Apologies for the colours; red's fairly obvious but blue isn't good on my screen.

Resolution is how finely a particular instrument can read. It's not the same as the graduations, which are often over optimistic. However, assuming the operator has a good touch, successfully avoids parallax, and corrects for temperature, the resolution of a 0.001mm micrometer is limited by the state of its threads and anvils. The instruments ability to measure down to 0.001mm is compromised as it wears. Not possible to repair worn threads and anvils in a home workshop, and the professionals rarely bother either. It's cheaper to replace. Serious measurement requires ruthless reduction of all sources of error, and having a good looking but untrustworthy instrument laying around is asking for trouble. Calibration rejects are one source of ebay bargains.

The diagram represents the actual dimension with cross-hairs. Ideally measurements would hit the bulls-eye every time but it's impossible. Minimising measurement errors gets progressively more difficult and expensive. Consequently engineers should be mindful that good enough is good enough. Time and money is wasted on a grand scale when quality is pursued without justification.

The picture has three examples.

On the left bulls-eye, the instrument gets close repeatable results but is persistently off target. It's precise, but not accurate. Not bad news though, because the error might be due to incorrect zeroing, and in any case precise measurements can be corrected by calibrating the instrument. I wonder how many forum members working to better than a thou bother to correct their micrometer readings, or even need to? But calibration and subsequent correction of readings is certainly necessary for serious measuring!

The centre bulls-eye shows an instrument scattering measurements around the target. On average the instrument is correct but its individual readings are all untrustworthy. This is typical of practical measuring, and it doesn't matter provided the scatter isn't too big for the purpose. The instrument is accurate but not precise. Again, the scatter matters for serious work, but how many of us take the trouble in our workshops to average several readings before proceeding?

The bulls-eye on the right is measurement heaven. The instrument reads accurately and precisely. But note that none of the measurements is spot-on. Magnifying this chart shows it has the same character as the central diagram, but the instrument is better because it measures with less scatter. Unfortunately this kind of performance is expensive to buy, tricky to apply, and expensive to maintain. Screw micrometers inevitably lose precision and accuracy because they wear slightly every single time they're used. For that reason serious micrometers are checked periodically against standards and dumped as soon as they exceed specified tolerances. The gauges used to check micrometers also wear, making it necessary for them to be regularly checked against even better standards and replaced too. At the top of the tree is the standard metre, defined from the average of several high-end atomic clocks. There's an enormous gap between the standard metre and my £30 micrometer! Fortunately for me, a £30 0.01mm micrometer is 'good enough' for my purposes, and I don't need to apply any of the disciplined methods made necessary by working to close tolerances.

When buying tools I feel it's important to separate utility from desirability. Understand your reasons. On the down-side, a £30 micrometer looks and feels cheap. There's no pride of ownership in it and having to use it carefully wastes time! My workshop meets my needs but it wouldn't suit a time-is-money professional or the type who enjoys 'quality' tools.

But please don't tell beginners struggling to start on limited money that only the best will do, especially if the best is second-hand, condition unknown, and is over the top. There's a great deal of fun and education to had from imperfect equipment, and one can always upgrade later.

Dave

Edited By SillyOldDuffer on 01/06/2020 11:05:31