Granite surface plate/flattening/where to buy?

[ali27]

I regularly fit kitchens with granite worktops and I would be surprised if a standard 30mm thick worktop is not flat enough or rigid enough to cope with flattening the sole of a plane.
Offcuts are always available from granite suppliers locally who would be happy to cut to size and polish the stuff.

Bob

Hi Bob,

From the information I have read, kitchen granite worktops
can be less than flat up to 2mm in length.

I don´t know how much difference that means in a
40 inch long granite worktop.

Have you checked with a reliable straightedge?

Ali

 

[Benchwayze]

Ali...

Have a look at this, and make some enquiries of the seller. Maybe they can fix you up.

Ebay.co.uk Item No. 360267337709

HTH

John

 

[ali27]

Ali...

Have a look at this, and make some enquiries of the seller. Maybe they can fix you up.

Ebay.co.uk Item No. 360267337709

HTH

John

Hi John,

thank you for the tip. The plate is too short unfortunately.
The seller has larger ones, but they are so big and shipping
would be very expensive.

I don´t know for sure, but I think there would be interest
in a granite surface plate which measures approximately
24 inches long, about 6 inches wide and 2 inches or
so thick. If my math is correct, such a granite surface plate
would only weight 15kg! Whereas a 24 x 18 x 4 plate is 90kg heavy! Try moving that(if necessary).

The length is good, but the extra width is not needed. I doubt
you would need a 4 inch thick plate to have adequate stiffness.

Ali

 

[ali27]

How much would a machinist charge for calibrating
a granite surface plate?

Maybe I could just buy regular granite tops(which aren´t)
really flat and have it flattened by a machinist.

Another option. Using MDF plates. They are quite flat
I think, but they lack rigidity. What if I put 3 or 4 thick MDF
plates on top of each other, would that provide sufficient
rigidity?

Ali

 

[Benchwayze]

Tufnol is also extremely flat. Not dirt cheap, but cheap enough.

Flat enough for a plane sole, and for sharpening. Just araldite some 10mm tufnol to a 25mm thick piece of MDF and that will also be inflexible.

HTH too.

John

 

[ali27]

Tufnol is also extremely flat. Not dirt cheap, but cheap enough.

Flat enough for a plane sole, and for sharpening. Just araldite some 10mm tufnol to a 25mm thick piece of MDF and that will also be inflexible.

HTH too.

John

John,

I had never heard about tufnol. This is the info I found about
how flat it is:

Tufnol Sheet - Flatness Tolerances
The below table is the maximum deviation from flat for Tufnol Sheet over a distance of 1000mm using a straight edge.
Sheet Thickness Variation
1.6mm to 3mm up to 18mm
3mm to 6mm up to 10mm
6mm to 8mm up to 8mm
over 8mm up to 6mm

http://www.tufnolsheet.co.uk/tolerances.ph

Here some more info on this matter:

Flatness test.
If a sheet is bowed, it is tested as follows:
1. The sheet is laid, concave side up on a flat horizontal surface.
2. A lightweight straightedge 1000mm or 500 mm long is laid on the sheet in any direction
and the maximum gap under the straightedge is measured with a slip gauge or feeler
gauge.
Light weight
Maximum gap straightedge
(measured with a
gauge)
TUFNOL SHEET
Permissible tolerances:
The maximum gap permitted is as follows:
Maximum gap under Maximum gap under
Nominal thickness of sheet
1000 mm straightedge 500 mm straightedge
Over 3mm up to 6 mm 10 mm 2.5 mm
Over 6mm up to 8 mm 8 mm 2.0 mm
Over 8mm 6 mm 1.5 mm

According to this source it bows very easily(am I correct?), but I don´t know what the tufnol will do if you stick it on top of MDF.

Ali

 

[ali27]

Maybe if there is interest, we could do a group buy
for this:

http://www.axminster.co.uk/product-Axmi ... -20297.htm

And then have it sawn in 3 pieces. 24 inches long, 6 inches wide.
I don´t know how much the sawing would cost to be honest, but I
guess at least 50 pounds?

So 96 GBP(if it picked up and not shipped) for the plate,
about 50 GBP for sawing=146 GBP. Divide this by 3 and
each plate would be less than 50 GBP.

Ali

 

[jasonB]

I have just taken one of my granite kitchen worktop samples, levelled it on the carrage of my lathe and then traversed it along its 300mm length with a dial test indicator on it.

Over the 300mm length I get 0.0003" ( 0.000762mm) difference but that is a constant movement of the dial due to me not being bothered to get it totally level.

I think we can say that an off cut of kitchen worktop will be more than adequate for your needs as I said at the start of this post.

Also I would strongly advise against bonding two different materials together such as Tufnol/MDF any change in humidity will make the MDF expand/contract and your Tufnol will go concave or convex. If you must bond to MDF then glue the same material to both sides.

Jason

 

[Benchwayze]

Ok Folks...

I bow to superior knowledge on Teflon. I just hope no one tells my plane soles, water-stones and irons! Or maybe I am lucky in having stable humidity in my workshop. Can't say I ever had any problems. (Not even with rust.)

Of course it could be that I am not an absolute perfectionist when it comes to sharpening matters. If a plane is flat, for a decent area, at the toe, around the mouth and at the heel, (i.e. those three points are in the same plane, all the way across the sole,) I am happy. Mine are generally better than that, but there's my minimum. Neither do I go to the extent of having mirror finishes on the backs of my edge tools. If they are 'satinised', and give me a reference reflection, again that suits me.

As for performance I am happy with that too. Freehand honing on water-stones is my way. What I am fussy about is having an edge that is at 90 deg to the side of the iron, and a water-stone that is as flat as I can get it. Both of those are easy enough to attain.

Ali,

If you are after close to zero tolerances then maybe a properly finished granite slab is the best option, that or a piece of 25mm thick float glass. Hopefully you can find suppliers for these nearer to you. I agree shipping is going to be a problem, on top of the cost.

EDIT:
I have used the cast-table of a table saw in the past, but I don't have one any more. I suppose any cast machine table would be flat enough for a plane sole. But I could be wrong again...

HTH

Regards
John

 

[beech1948]

I have just done a google search for Granite Surface Plates and come up with 30+ in the UK. You should try the same search in your country and maybe a nearby country.

I think all of this discussion about granite counters, cemetry granite etc etc is probably a waste of time as the surface accuracy of the end product is unknown and unverified.

So seek out a suitably sized proper granite surface plate and buy it 3 or 4 inches thick.

If you must cut it down then try a paving slab cutter with a diamond blade. A slightly ragged cut line will not affect surface smoothness.

regards
Alan

 

[Lons]

I regularly fit kitchens with granite worktops and I would be surprised if a standard 30mm thick worktop is not flat enough or rigid enough to cope with flattening the sole of a plane.
Offcuts are always available from granite suppliers locally who would be happy to cut to size and polish the stuff.

Bob

Hi Bob,

From the information I have read, kitchen granite worktops
can be less than flat up to 2mm in length.

I don´t know how much difference that means in a
40 inch long granite worktop.

Have you checked with a reliable straightedge?

Ali

Hi Ali

Just checked my own worktops with a straightedge and I would be perfectly happy to use it, (if the wife would allow ).

If you go to a granite supplier, they will allow you to choose your offcut and check with your own straightedge before purchase.
As well as natural granite, there are types which are reconstituted with a resin plastic and these are also worth looking at.

As far as cutting - Very easy to cut with a 4 1/2" grinder if you use and ultra thin cutting disk (1 -2mm thick). Not too much dust or too expensive in lieu of water cutting equipment.

Tufnol / teflon etc.

My background is plastics including these, and whilst their composition differs, they are both unsuitable IMO. I could show you samples of both - very bent.
Tufnol is great for components and gears as well as templates but is far from flat.

regards
Bob

 

[ali27]

: Lons wrote

Hi Ali
Just checked my own worktops with a straightedge and I would be perfectly happy to use it, (if the wife would allow ).

If you go to a granite supplier, they will allow you to choose your offcut and check with your own straightedge before purchase.
As well as natural granite, there are types which are reconstituted with a resin plastic and these are also worth looking at.

Thanks again for answering Lons a couple of questions if you allow me:

1)how long was the straightedge
2)Is it a reliable straightedge
3)how much was the gap between the straightedge and the plate

I will follow your advice to take a straightedge with me to a
granite supplier. Nothing to lose doing this and perhaps there might
be a rather flat plate available.

How much do you think it would cost to let the graite supplier
saw an offcut to specific size?

Thanks again.

Beech I did check for granite plates in my own country. Very
expensive I am afraid.

Jason,IF I UNDERSTAND YOU CORRECTLY(which I think am not) that would mean that a granite kitchen plate is flatter than a certified granite plate which is impossible unless you got one piece that is incredibly flat by coincidence/chance.

Ali

[/b]

 

[jasonB]

I'll take a video of the dial gauge as the granite moves under it, will be later today as I'm off out soon.

As I said granite worktops are ground in the country of origin on very high spec machines and most granite suppliers in this country could not grind to such tollerance, they tend to just buff up the surface to remove any small marks that have got into the stone during transport and cutting. This is usually done with handheld Flex grinders with diamond pads.

Had this discussion with my usual granite supplier a while ago when I wanted the whole draining area at the side of a sink dropped rather than just grooves, said he could not achieve the same level of finish as the factory surface.

Jason

 

[Lons]

: Lons wrote

Thanks again for answering Lons a couple of questions if you allow me:

1)how long was the straightedge
2)Is it a reliable straightedge
3)how much was the gap between the straightedge and the plate

I will follow your advice to take a straightedge with me to a
granite supplier. Nothing to lose doing this and perhaps there might
be a rather flat plate available.

How much do you think it would cost to let the graite supplier
saw an offcut to specific size?

Thanks again.

Beech I did check for granite plates in my own country. Very
expensive I am afraid.

Jason,IF I UNDERSTAND YOU CORRECTLY(which I think am not) that would mean that a granite kitchen plate is flatter than a certified granite plate which is impossible unless you got one piece that is incredibly flat by coincidence/chance.

Ali

[/b]

A stabila 1200mm spirit level

Obviously can't certify the correctness of it but I moved the edge along the bench, turned it around etc and looked good to me.

I also have a 500 x 200 x 30 bit which I use withe abrasive and I checked that with several steel rules and showed no depressions. i haven't bothered to check with my dial gauge as I said I would be very happy with the results - doesn't mean you would! - You pays your money etc.

I could never say it is the equal of a certified granite plate, just that I would be happy with it!

Cost of cutting an offcut - depends how the guy feels but always can be negotiated.
I bought a 900 x 900 offcut of blue pearl last year for £50 for the centre of a coffee table and they polished and bevelled the edges for another tenner.

regards

Bob

 

[bugbear]

According to this source it bows very easily(am I correct?), but I don´t know what the tufnol will do if you stick it on top of MDF.

It will be as flat as the MDF, which is also the case for glass layered over MDF.

Don't forget that the so-called-lapping process involves quite high forces.

BugBear

 

[Lons]

Ali

Don't take this the wrong way, but isn't it a bit OTT when the plane surface you have flattened will expand and contract naturally anyway depending of heat / cold / humidity.
And - the wood you use it on will move even more. :lol: :lol: :lol:

Mind - if someone accused me of being OTT over my car - I would become very defensive so I'll probably be put firmly in my place over these comments :lol: :lol:

regards

Bob

 

[ali27]

Ok guys. I took my straightedge and went to investigate
the flattness of granite(kitchen), glass and mdf.

A 20mm piece of glass was the flattest,but I could
still see clear light. Granite(thick piece) and mdf
were both clearly not flat.

I have read much about MDF being flat, but it really
wasn´t.

I used a very good straightedge(Groz brand).

Ali

 

[Mohammed Imran]

Hi Bob,

I have 13 years of experience in surface plate lapping and polishing in India.
Do you have any idea where and how can I apply for the job?

I also worked in kitchen Granite worktop.

Thanks
Imran

 

[Trainee neophyte]

A random thought: have you considered concrete? Make your own mold using a certified (by you) flat piece of melamine or similar, and then you could get exactly the surface you want. If it isn't 100% perfect you can actually abrade it yourself. I would use 2:1 sand/cement mix, and make a wooden surround for it because it may well be brittle. I would also cure it submerged in water for at least a fortnight, but I would check for and correct any lack of straightness in the first couple of days, when it would be marginally easier to work.

No idea if this is a workable idea, but it would be cheap. Very, very cheap.

 

[MikeK]

Prior to this morning, the last post in this thread was nearly 11 years ago. Perhaps Ali has found a solution by now.