Refurbishing a Surface Plate?

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello All,

I have a 12 " x 18" surface plate. It is the real McCoy with the box type ribbing underneath and it weighs …… well I have difficulty in picking it up!

The surface is a little bruised here and there and has had some very small amount of surface rust in its life. It could do with a bit of attention. Am I correct in assuming that a lick over with a surface grinder will do the trick or is there more to it than that. I have seen some very old surface plates that seem to have been scraped flat, looking at the tooling marks on them. This one seems to have been ground flat.

Advice would be most welcome.

Andrew.

Edited By Andrew Tinsley on 28/02/2013 20:22:22

Edited By Andrew Tinsley on 28/02/2013 20:23:05

[Andrew TinsleyParticipant @andrewtinsley63637]

[DustyParticipant @dusty]

Hi Andrew

Yes a lick with a surface grinder will produce a useable surface plate, however because of the way surface plates are made it needs to be clamped to the table of the grinder, it cannot be pulled down on a magnetic chuck due to the three small feet on which it sits (the mag chuck would not have enough area to hold it down) Thus it will not be cheap. Scraping is probably a non starter as you will need two more surface plates and the three would then need to be scraped together. I am afraid you are between a rock and a hard place,unless you have a friendly local engineering Co. I wish you luck

[Michael GilliganParticipant @michaelgilligan61133]

Greetings Andrew,

A lick over with a surface grinder will give you a decent "marking out table", but I doubt if it would qualify as a "surface plate"

Have a look at how Whitworth made his …

MichaelG.

[Paul LousickParticipant @paullousick59116]

If you cannot hold the surface plate to a magnetic chuck because of not enough area of contact can you first bolt it to a steel plate and then use this plate for mounting to the magnet.

Edited By Paul Lousick on 28/02/2013 20:52:12

[Andrew TinsleyParticipant @andrewtinsley63637]

So what sort of flatness is one talking about for a surface plate? Datum leval plus or minus what ? Just curious!

I reckon it is a decent marking out table as it stands. As far as I can measure, the worst bruised area is a maximum of 3/10 of a thou low, but quite difficult to measure with any degree of certainty.

Andrew.

[MadMikeParticipant @madmike]

Andrew how are you measuring the "bruise" depth at 0.0003? If you are to use it as a true surface plate then flatness over the whole area is the real measure, in simplistic terms I might add. Whole papers have been written on the subject and frankly you will never get anywhere near the accuracy levels measured in micro inches. If you are model making, or even doing other stuff, I would suggest that a good clean is all you will need. Surface grinding, unless done carefully and professionaly, may now cause deflection in the prime surface and then you would be far worse off than you are now.

In reality you need to decide what you are going to use it for. Perhaps you would let us all know as it may then change some views on what you should do with the plate. After all if you only intend to use it as a marking out table then a simple clean will do you I reckon. HTH.

[Sub MandrelParticipant @submandrel]

Hi Andrew,

At first approximation, the surface plate only needs to be as accurate as you are able to work. If you can only work to the nearest thou, then it needs to be flat to better than a thou.

However, he problem is that small depressions could cause things to tip slightly – a small angle may create a significant error in the parallelism of lines with the base, or on a tall workpiece.

Ultimately, if you are aware of any problem patches and can avoid them, you might do better living with minor comsetic issues.

Neil

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Andrew ,

Surface plates are graded according to their accuracy . Several different definitions of accuracy have been used in the past but easiest to understand and use is unilateral deviation from a true plane . Typical value for a medium grade workshop surface plate would be 0.0004 inch .

A modern day surface grinder will produce a surface so accurately flat that no further correction work is usually nescessary .

Surface plates for general use were I worked were routinely reground . Usually the big ones were just mounted on the grinder deadweight – no fixing at all apart from a couple of safety dogs fore and aft ..

Surface plates do not have to be exactly flat everywhere . A surface plate which is generally flat but with small pits is quite ok for most purposes . There is a type of surface plate for special purposes which has a pattern of deep cut slots in it deliberately .

Perfectly possible to scrape surface plate true but you would need use of a large master plate to test against . Using the alternative three plate method would probably take you the rest of your life .

Best advice would be to carefully remove any actual upstanding burrs and then leave yours alone .

Ask any questions you wish .

Regards ,

Michael Williams .

[DMBParticipant @dmb]

Ian,

I think the "knickers ad" was CH4. Its an on-going series of ads telling a story, much like one sometime ago featuring a courting couple and coffee. This one starts off with the back of her dress getting caught in the lift doors and latest one she falls over on pavement….

As Harold (Steptoe) used to say, "you dirrrty ol` man!

Edited By DMB on 28/02/2013 23:21:21

Edited By DMB on 28/02/2013 23:22:56

[Clive HartlandParticipant @clivehartland94829]

Michael mentions a surface plate with slots cut across its surface at right angles to each other, its a, 'Lapping plate' and I have used one to dress up a surface plate.It was along tedious process and dirty to boot. Using diamond paste and some Kero. It was rotated in figures of eight and regularly reversed in position and motion.It cleaned up the surface and using auto collimation to check the surface it was found to be very flat and even.While doing it it showed all the pockets that were worn.The only thing was, it left it in a Matt surface condition.This made moving devices across it a bit slow.

Initially, the Lapping plate was used for dressing the steel standards of theodolites to get the tilting axis true.

Clive

[colin hawesParticipant @colinhawes85982]

If you want to regrind your surface plate it should first have bumps and burrs removed with an oilstone using paraffin as a lubricant. This may be enough to give a good result. If regrinding is still desirable the stoned surface can be laid on the magnetic chuck and any rocking shimmed out before skimming the feet.Then it can be stood on its feet to regrind the working surface.

Note that a ground surface plate is likely to be unsatisfactory due to measuring equipment "wringing" to it and difficult to slide. This is a key reason for scraping surfaces such as this and machine slides. Colin

[jason udallParticipant @jasonudall57142]

..Colin Hawes …."Note that a ground surface plate is likely to be unsatisfactory due to measuring equipment "wringing" to it and difficult to slide. This is a key reason for scraping surfaces such as this and machine slides. Colin" ..

Guess I am lucky our height guage hovers over the plate when needed to move….oh joy…… probably just as well since the plate is less than prestine

[AB658Participant @ab658]

Andrew, it may also depend on what options you have locally. I had stored a similar plate for many years & resurrected it about 6 years ago; there were no visible dings but plenty of surface rust most of which came off with kerosine. I looked for surface grinders that would do what you're seeking, but none within a sensible driving distance had a machine big enough to do the job in one sitting (or is that setting?). But I did find a specialist lapping company that took it on. The m/c they used had multiple rotating heads that rotated in-unit, like a fairground "whirler". They gave up at £40's worth (many hours), as we agreed that the micro-pits (~0.5mm) were not worth chasing. Otherwise, a bang-up job looking all the better with the sub-structure in black hammerite. I have no kit capable of testing the accuracy, but I am trusting their reputation…..

Adrian

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Andrew Tinsley on 28/02/2013 21:04:52:

So what sort of flatness is one talking about for a surface plate? Datum leval plus or minus what ? Just curious!

Andrew.

.

Andrew,

For one reasonable specification … see para. 2 of this

MichaelG.

[HopperParticipant @hopper]

Another reason surface plates were hand scraped to a final finish was so they transfer bearing blue better. A precision ground surface may be too flat to allow room for the the marking medium. So the old timers always said.

Scraping of course needs a master plate to mate the job to. The old boys where I served my time used to aim for about 30 bearing spots per square inch across the whole surface, using straight alcohol as a the marking medium, which allows you to see the metal-to-metal contact points. Don't think there are many of those guys left today.

[Author]

Posts