Regrinding surface plate

Here`s someone who can certainly do it.

Unless you need a surface plate accredited to a standard you would be cheaper buying one off Ebay.You`re going to have carriage two ways plus refurbishing charge.Alternatively find someone with a big Lumsden grinder. Mark.

Thanks Mark. I've emailed them for their charges. Fortunately I have a friend who regularly goes 'across' who can take it and bring it back. My plate is at least 50 years old, so it should be nicely stabilized by now, and in any case I have a sneaking affection for it.

Jim Hawkins

Lumsden

Or you could buy two more and use the classic 'three plate' method to scrape them flat. Depends what you want to achieve, but a piece of plate glass is usually adequately flat unless you happen to be NPL Teddington

AWEM

In message , Andrew Mawson writes

How bad is it at present, why does it need grinding?

Mike

Just curious, but is a normal surface grinder not suitable for this job?

After my 'leg pull', you have still to tell us where in the UK your mate will be.

Two items arise- I infer that you are 'doing up' your Myford and also want the surface plate to use as a reference. Following on from this, has your mate access to Tyneside?

Alan Liddle Ltd 0191-4952550 has a big Lumsden and did the top of my ML7 for under =A340 so, no doubt, he could do both items. a big Lumsden does leave a few swirls but at that price?

Cheers

N '

It has patches of surface rust. Nothing that a few thou off couldn't remove, but I've never known how flat it really is, and I presume a regrind would be to some stated surface flatness (without the need for certification of course).

Jim Hawkins

Jim, I have had a few done by Lumsden grinding and they work out fine. Just ask them to place it at the outside of the bed and let it spark out.

The reason is Lumsden grinders use a vertical rotating wheel set slightly off centre to the bed and it leaves swirl marks, If they grind it central you get like a facing pattern in the centre of your plate. it's still flat but doesn't look as nice as if it has more even swirl marks.

I picked a bit arbor press up a while ago and when I collected it the guy said are these any good and pointed to four 12 x 18 plates that had been left outside and were red rust. They were going to sell them but some goon had dumped them outside during a factory move.

I paid £5.00 for all four, dropped them off at the grinding shop on my way home and paid £25 cast to get all 4 reground.

I have sole 3 of the 4 on and use the other for jobs round the shop. It's flat, it works, it isn't hand scrapped and doesn't have a certificate but it's more accurate and flat than most anally retentive's arse's who tell you otherwise.

That only shows that they knew what they did. :-) My reference to the cutter grinder-shop was more to show that you can find idiots for whom a surface grinder is something to make sparks with and money.

Nick

Lumsden's were local to this area. I have the cigarette case presented by the lady staff to the chief draughtsman and his paintings in my dining room.

I have a piece of granite gravestone from a monumental mason, about 1.5" by 18" by 12" - afaict it's flat to well within 1/100th mm over it's 18" length. Cost a fiver.

Apparently they use the same machine for "proper" granite surface plates.

What's the three-plate method?

-- Peter Fairbrother

It's a method of producing surface plates (or straight edges) without a master reference. If you have three plates A, B, C, you blue up A and pair with B. Scrape off the high spots. Do B and C, then C and A etc. etc. Keep going until you get the level of contact you need.

Three are needed because if you just had a pair A and B, the result could be concave/convex. With three, this cannot happen.

If you grind any two rigid materials together in a random manner the mating surfaces will eventually end up perfectly spherical, one convex and the other concave, and with a radius of curvature dependent on the initial contours. Suppose you have three pieces of material, a, b and c. Grinding them together in pairs, a-b, b-c and c-a, taking care always to grind convex surfaces together and concave surfaces together must end up with the three pieces having the only possible common radius of curvature - infinity ! In other words, perfectly flat.

Jim Hawkins

snip

I may go see my nearest soon, could book my personal headstone whilst there to save SWMBO the hassle ;-)

Take a look at

Why cant a car engine refurb place that skims heads do it for you ? I don't mean flycutting, but grinding. I'd have thought it to be near enough flat for average use. bob

That's unusual; I have a "scrap" of granite from ditto, and it had a 1/16" curve in 10"

For "monumental mason" use, as long it's shiny, flat (within reason) isn't important, so they'll happily polish out rough spots, leaving dips.

BugBear

Not the Perfect Ashlar?

I definitely got the impression that a good proportion of all monumental granite was done on the same machines used for surface plates, and should be pretty flat - but I'll ask again, maybe it's just the stuff he uses.

-- Peter Fairbrother

I definitely got the impression that a good proportion of all monumental granite was done on the same machines used for surface plates, and should be pretty flat - but I'll ask again, maybe it's just the stuff he uses.

-- Peter Fairbrother