Thread: How flat is flat?

Could be wavy and from side to side. And, if the tolerance is plus or minus, surf's up.
Cheers,
Jim

Gents,

I would suggest that, in reality, it hardly matters a rat's delicate little bottom! Think of the variables: pressure, iron sharpness, angle, timber hardness, technique, friction, etc etc. Any we are talking 3-thou? Now if it was our by three HUNDRED thou........

Rather than use expensive stones that groove and get out of flat, I use a glass shelf (toughened, bevelled edges), artists spray adhesive and ordinary wet and dry. You can get a mirror finish (if it is important to you) and then peel and discard the worn paper. Cost about 50c per plane.

Also, easy way to flatten iron and chisel backs - hand pressure on the flat glass surface is all it takes, and several strokes.

BR,

Fraser

Fraser, many of us have used that Scary Sharp method to lap plane soles or plane blades and had inconsistent and often un-flat results. The tendency is to make both convex due to differential exposure of the ends/edges to the abrasive.

Veritas won't let a bench plane leave the factory if it has a convex sole.

Originally Posted by jimbur

Could be wavy and from side to side. And, if the tolerance is plus or minus, surf's up.
Cheers,
Jim

Oh dear, I forgot the smiley face

Wasn't needed Jim, it raised a smile anyway ;-}

Inote that in another thread somewhere here in the handtools section someone flattened there plane sole and used up to 800grit sandpaper before noticing the firction became too much to bear.

I believe you don't want to go past about 240 grit when using this method to flatten a plane sole

Does anyone hear use just water on the glass to hold down the sandpaper instead of glue or spray on adhesive? I've not looked very hard for spray on adhesive stuff yet but it would seem that if water did the trick that would be better...

Water does hold down the wet and dry sandpaper okay, it only takes a few strokes with your plane or chisel to squeeze out the surplus water to give enough to stick.
The problem with this method can be the sandpaper's tenancy to roll up at the edges.

Regards from Geraldton,
Chris

I'm interested in getting a parallel bar for flatness reference. The local industrial supplies place has 9" pair for $85 and 12" pair for just under $100.

Is anyone interested in sharing the cost and buying one?

I know you can buy stone like Granite from different sites including carbatec that is machined down to within .0 something of flat. what's the advantage of the parralell bar?

Cheers Polie for the update, I would not have though even with the paper curling a little that it would be a problem as the plane would push it back flat anyway...

Originally Posted by rsser

How to get flatness on plane soles and chisel backs has been a perennial here. And clearly having flat sharpening stones is important.

So while the figures are in the brain box I offer the following.

The LV website has diamond stones for sale; they're not branded in the labels but a pic shows DMT. Which is what I use. But the site says the tolerance is 3 thou. First time I've come across that.

That's interesting as I've just gone through my ceramic stones flattening them on a coarse DMT.

To add:

Stanley apparently used to claim their plane soles were within 3 thou.
V. say theirs are acceptable to 3 thou but only if concave.

No-one says over what distance

Three thou .... Huh ???
This is woodwork Ern , where we have M , mm , half a mm , and a gnat's tit
And any tool that gets us within a gnat's tit is near enough to true.
.

Anything else is a recipe for stress and all its related health problems .
Boil the billy , make a cuppa , and watch the wood move a gnats tit while you sit there and drink it .

Yes, the slabs are intended for lapping but perhaps if you used paint or bearing blue you could test a plane sole or the like on them.

I want something a little easier to carry around and use. The bars are narrow, something like 3/4" wide.

Bingo post MJ.

I do a lot of chisel and plane iron lapping when rehabbing tools, and have done half a dozen or so plane soles with abrasive paper on plate glass.

It is a real pain to take one of these from Scary Sharp or a stone to the next grit up and find a major mismatch. A plane iron can easily take 1000 strokes on coarse abrasive to appear flat and then on the next grit it takes even more to remove the scratches and 'reflatten'.

It doesn't give me ulcers MJ. Only has to be done once and it's soothing in a way.

I finally got one of the Carbatec granite plates. According to the measurement data that was included, it is significantly flatter than the specificaton (0.0001"). I'll take that as FLAT.....

Polie - there is a trick to getting wet and dry paper to stay on your glass/reference surface, as recommended by the LN demo man

YouTube - Broadcast Yourself.

There are a couple of other LN videos on YouTube that are useful for sharpening tips.

Just as an aside you might try Alox paper rather than W&D next time. I suspect it performs better.

I've used spray adhesive on both glass and the paper to good effect. Paint thinners to clean it off.