Granite Chopping as Surface Plate

[user 26792]

Hi All

Today I was able to pick up a Granite chopping board from B&M for £8 which I intend to use as a surface plate to flatten the soles of planes, chisels etc, I believe the chopping board to be quite flat and checked it with a straight edge steel ruler and feeler gauge. There was no pass through.

My question is whether there is a more accurate way to measure the overall flatness. I've seen mixed views on the use of granite alternatives to a surface plate. Any clarity and advice would be greatly appreciated.

A little bit of useless background on myself, I have recently reignited a passion for making things in general and decided that I would start with woodworking and build up my skills from there. In doing so I have come across Paul Sellers and I want to be able to use hand tools as much as possible because I think if I can get used to hand tools then using power tools and workshop tools will be a gradual and natural progression. Also I quite like the old style hand tools. As such my intention is not to go out and buy brand new tools but instead use the tools I have and get them into the best state they can be in, picking up the right techniques for calibrating planes, sharpening chisels and irons and setting and sharpening saws and so on. So I'm going to buy the tools to do that stuff hence the chopping board purchase, as opposed to buying new tools for doing stuff as tempting as it is to buy some of them because damn they do look pretty I'm thinking the new Dorchester Saws and Clifton Planes.

Any advice and guidance is appreciated

Thanks

Khuz

 

[Fitzroy]

Welcome to the forum. I use a marble tile for the purpose you describe, perhaps in s few years when we can tell the difference between a 0.05mm shaving and a 0.02mm shaving we may need a flatter reference surface but for now I've not found any shortcomings due to using mine.

F.

 

[ED65]

My question is whether there is a more accurate way to measure the overall flatness.

Don't believe you need to, what you have there sounds more than good enough.

Also I quite like the old style hand tools. As such my intention is not to go out and buy brand new tools but instead use the tools I have and get them into the best state they can be in, picking up the right techniques for calibrating planes, sharpening chisels and irons and setting and sharpening saws and so on.

Good plan IMO, with lots to recommend it.

As far as the need for very very high levels of flatness goes I don't even use feeler gauges to check flatness (can't since I don't own any) and all my smoothers and block planes can take shavings you can read through. This is a little misleading through since three of them could do this without any work being done to the soles

 

[user 26792]

Welcome to the forum. I use a marble tile for the purpose you describe, perhaps in s few years when we can tell the difference between a 0.05mm shaving and a 0.02mm shaving we may need a flatter reference surface but for now I've not found any shortcomings due to using mine.

F.

Thanks for the reply. Very good point, I don't suppose such a tiny variance would make a difference to any project would it.

As far as the need for very very high levels of flatness goes I don't even use feeler gauges to check flatness (can't since I don't own any) and all my smoothers and block planes can take shavings you can read through. This is a little misleading through since three of them could do this without any work being done to the soles

I'm hoping to avoid buying anything until I know exactly what I have in the garage which has tools buried in places I'm yet to discover, I wouldn't be surprised if I found some sort precision gauge for testing flatness my grandad has spent a lot of years accumulating tools for no reason other than it might come in handy lol. That's the only reason I had the feeler gauges, something I found buried deep in the corner under a micro civilisation of webs, spiders and various tiny insects dead and alive.

Appreciate the advice and vote of confidence

Thanks

Khuz

 

[Hot stuff]

I've used exactly the same thing for years now for sharpening and flattening surfaces. Built a hardwood frame and base with gripper tape on the bottom to stop it sliding about on the bench, sorted!

 

[JohnPW]

I believe the chopping board to be quite flat and checked it with a straight edge steel ruler and feeler gauge.

It will be as flat as your ruler! So if your ruler is not very flat...

I presume you've checked in several places, including from corner to corner?

 

[bridger]

depending on the thickness of your granite slab it might be easier to flex than you think. purpose made precision granite surface plates are quite thick for this reason. however, if this plate is as flat as you can measure and the things you make with it are *also* as flat as you can measure then I guess it is as flat as you need right now, and you may never have a need for better accuracy. if you do, you'll find out. until then, give your focus to developing skills from where you are now, with the tools you have now, making the things you want to make now and with the materials you have now.....

 

[user 26792]

I've used exactly the same thing for years now for sharpening and flattening surfaces. Built a hardwood frame and base with gripper tape on the bottom to stop it sliding about on the bench, sorted!

I was thinking of doing a base for it, at the moment I'll be using it on the old workbench which isn't the best base because it isn't flat or level. I'm going to be building a new one soon lol.

depending on the thickness of your granite slab it might be easier to flex than you think. purpose made precision granite surface plates are quite thick for this reason. however, if this plate is as flat as you can measure and the things you make with it are *also* as flat as you can measure then I guess it is as flat as you need right now, and you may never have a need for better accuracy. if you do, you'll find out. until then, give your focus to developing skills from where you are now, with the tools you have now, making the things you want to make now and with the materials you have now.....

The slab is 15mm thick and is pretty heavy, I know the precision surface plates tend to be quite a lot thicker but at the same time I don't think there will be much flex and for £8.00 I have my expectations managed lol. Thank you for the advice, very good point. I'm hoping that if I can start off as precise as possible then my work be better as a result. The skills I'm looking to develop for now is my eye for precision because that is something I've never practiced as much as using a hand saw.

It will be as flat as your ruler! So if your ruler is not very flat...

I presume you've checked in several places, including from corner to corner?

I don't understand what you mean when you say as flat as my ruler's edge. I have not checked several places actually I was planning to then get summoned by the family. I'll have to make sure I do that.

Thanks

 

[bugbear]

It will be as flat as your ruler! So if your ruler is not very flat...

I presume you've checked in several places, including from corner to corner?

I don't understand what you mean when you say as flat as my ruler's edge.

He's saying that you've checked your granite against your ruler. But what have you checked
your ruler against?

Put another way, how accurate is your ruler, and how do you know?

BugBear

 

[novocaine]

short of using a known straight edge that has been tested on a known surface plate all measurements you do will be irrelevant.

in short, if it looks flat, it is flat.

for a more detailed approach, do this, but in reverse

https://www.youtube.com/watch?v=LkdkouWiDFs

 

[AndyT]

If you can pop back to the shop, and if the pieces of granite are not swathed in packaging, you could try putting one slab onto another. Broadly speaking, if they are both flat, they should appear to stick together and you will only be able to separate them by sliding one across the other, not by lifting one off. This is just the effect of atmospheric pressure.

(Apparently it used to be a regular joke to play on engineering apprentices, to surface grind the back of a coin and leave it on a large surface plate. It's impossible to pick the coin up, however much you might want it, to supplement your meagre wages, and while you struggle, the old hands can stand around and laugh at your ineptness. Such larks!)

 

[DoctorWibble]

You can chase your tail on flatness forever. Those in most real need of proving it construct purpose built isolated temperature controlled rooms and use them to house millions of pounds worth of specially mounted metrology equipment. Some manufacturers spend many times that. But even they have to stop sometime and call it flat enough.

So the trick, whatever you do, is understanding how much flatness you actually need. You're likely there already. You're making stuff out of wood not building jet engines or the next James Webb telescope. Relax and enjoy making things. Woodworking tools only need to be flattish.

You do need a good square. In a few sizes. That's it really for bought reference tools. Straight (enough) edges, winding sticks etc can be made out of scrap wood.

 

[user 26792]

Thanks for the responses everyone. I have to say it is reassuring to hear comments which match up to my instincts. In response to an earlier post I checked the edges of the steel ruler against a spirit level which I've been using as my main straight edge reference primarily because it's the best I have at my disposal.

I would like to ideally work my way up to making jet engines and perhaps a batman iron man suit begin a career as a genius billionaire playboy superhero lol. At this point though I'm going to just focus on building a workbench and a mallet lol