How flat is a piece of glass?

[justinpeer]

As I have the glass already, I'll send the edges smooth and put it on a piece of MDF and see how it gets on. I couldn't get it to flex with a few bits of paper at the edges so I think it'll do the job for what I need.

 

[Jacob]

Oh the plane's unusable, I think it sat in a box for years. My mum had it after my grandfather died and that's 20 years ago, it's pretty badly rusted but it's an old Stanley, I'm sure it'll come up just fine once it's been sanded clean and flat again.

They don't go bendy with age so if it was OK 20 years ago it still will be, and maybe just need a light clean. Usually rust on the blade, sole or sides isn't much of a problem and pits don't need flattening out - just a few quick passes over a sheet of wet n dry to remove the loose stuff. More likely to be a prob with the mechanism.
Plane "restoration" is another hobby in its own right - but just getting an old plane working nicely might only take a few minutes.

 

[pgrbff]

I have one for flattening my Waterstones but I don't think that would be big enough for a long smoothing plane

I agree. most diamond stones would be far too small.

 

[Limey Lurker]

I think that Phil meant that a diamond stone would be the best way to round-off the edges of the glass!

 

[TRITON]

"How flat is a piece of glass?"

Twice the length from the middle.

No wait, thats string length.

 

[Ttrees]

If your only cleaning up some surface rust, then you might not need anything
more than some sandpaper on a block.
If not the case....just a word of warning if not going to cut that glass.

You stand some chance of causing an error (removing excess material from toe and heel) with such a long bendy length
combined with not having a surface for checking at the same time.

If you don't have something trusty...
I'd try and get it cut, some folk don't bat an eyelid at this,
some like myself haven't had such experiences, suppose it's down to the cutter.

Something a wee bit longer than a no.8 would be nice for checking, and less prone to bend, and likely an offcut of mdf might do the trick.

One way apart from using a straight edge is transversing the length/width
of the plate using two squares butted against each other, with good lighting behind.

Tom

 

[justinpeer]

For those that asked, these are the planes. The wooden one has three names stamped into the front end, one of them is my granfathers so it had a fair life prior to his ownership.

Probably the most accurate straight edge I have is a Starret 30cm combination square, I can use that to get an idea of how flat it is when I'm working.

 

[Jacob]

......

You stand some chance of causing an error (removing excess material from toe and heel) with such a long bendy length

Not if you put it on a nice thick piece or pieces of MDF well supported on the workbench eyc

combined with not having a surface for checking at the same time.

Yebbut how would you check that surface?
Checking by eye is good enough for most purposes. Or pass a straightedge over if you have one big enough. Easy to make one if you have to - just check by eye as you plane it down. Straightening an edge is much easier than flattening a surface

 

[Ttrees]

I wouldn't go mad and just do some spot work with a block,
if the only thing you've got is something which is too short for the job,
and may or may not be accurate even if it were sufficient length, as it's not an inspection tool.

Have you not got a spirit level, I'd guess even that may be more accurate, and that's not really intended for the job either, but from what I've experienced with rulers and the likes, a lot less further out of whack.

You could even make your own straight edges from some straight offcuts of hardwood,
and see how good the level is compared, using the 3 plate method,
which you can do with two beams and a calipers.
Then you can do some hinging/pivoting exercises to check the glass
as it's likely to be troublesome in my view being that length.

Plus just pure awkward to lap out some pitting of your plane irons or whatever.
Be you're own toolmaker and don't trust brand names unless going for the good stuff
made from tool steel, which is a bit OTT .


With all that said, worth noting that having a dead flat plate is no guarantee
that your going to end up with the same, unless you do spot work,
so the question is whether it is going to be worth rigging up a big lap everytime
you want to work something flat, or indeed to a (yet unknown IMO) bias like @D_W has been experimenting with.

Tom

 

[D_W]

For those that asked, these are the planes. The wooden one has three names stamped into the front end, one of them is my granfathers so it had a fair life prior to his ownership.
View attachment 146779View attachment 146780

Probably the most accurate straight edge I have is a Starret 30cm combination square, I can use that to get an idea of how flat it is when I'm working.

that should be fine (the starrett rule). Make sure there aren't any burrs, etc, sticking up along the edges.

 

[Jacob]

......... worth noting that having a dead flat plate is no guarantee
that your going to end up with the same,

It'll be flat enough!

unless you do spot work,

What is spot work?

so the question is whether it is going to be worth rigging up a big lap everytime

Definitely not worth it.

 

[Ttrees]

It'll be flat enough!

I agree, if simply needing to eliminate some crud.

What is spot work?

Identifying high areas what one might wish to deal with, without
taking excess off toe and heel, focusing on those areas with say a block
or a small strip on the lap.
Having something to check with is arguably more valuable than a flat working surface,
that is if it needs more than a lick.

Worth mentioning should there be a twist, or if the plane is a bit thin already on both ends.

Definitely not worth it.

Agreed.

 

[Jacob]

....

Identifying high areas what one might wish to deal with, without
taking excess off toe and heel,

If you just rub it up and down on a flat abrasive it'll show up the high spots in seconds. It's the first thing you do just to check it out before you do any work. If you carry on they'll disappear as the thing gets flatter.

focusing on those areas with say a block
or a small strip on the lap.

Or just keep at it on your flat abrasive surface. A lot easier

Having something to check with is arguably more valuable than a flat working surface,

eyeballs, and a ruler perhaps.

 

[Ttrees]

If you just rub it up and down on a flat abrasive it'll show up the high spots in seconds. It's the first thing you do just to check it out before you do any work. If you carry on they'll disappear as the thing gets flatter.

If you carried on assuming this with a bad case, you will likely end up with a banana profile and thinner ends of the plane than necessary, as abrasion will always favour the edges, i.e toe and heel, and you still would likely end up with a lump around the mouth.

Or just keep at it on your flat abrasive surface. A lot easier

eyeballs, and a ruler perhaps.

Or a plate which you could check things with, whether one does so with abrasives or other inspection techniques, be it feelers, hinging/pivoting, bluing with marker or whatever, much the same kinda thing which you'd need to check the glass in the first place.

 

[Jacob]

If you carried on assuming this with a bad case, you will likely end up with a banana profile and thinner ends of the plane than necessary, as abrasion will always favour the edges, i.e toe and heel, and you still would likely end up with a lump around the mouth.

Very unlikely, barely possible even if you tried!
If the thing was already a touch convex you would of course need to confine the abrasion to the middle. Perhaps work it across the narrow width of your sheet of wet n dry, without touching the ends.... etc .. etc.
It's not rocket science.

Or a plate which you could check things with, whether one does so with abrasives or other inspection techniques, be it feelers, hinging/pivoting, bluing with marker or whatever,

Avoid feeler gauges, hinging/pivoting (whatever that is), blue marker. This is woodwork not precision metalwork engineering. It's not rocket science.

much the same kinda thing which you'd need to check the glass in the first place.

Eyeballs, and a straightedge if in doubt.