Is this lapping stone level?

[DEATHMgck]

Getting farther into my practice with honing and got to thinking about this.

I use a cheapo lapping stone to level my stones, but i never thought if the lapping stone itself was flat.

Any methods for deducing this? What has worked for people in the past?

 

[musicman980]

What kind of lapping stone is it?

The level at which say a $30 lapping plate differs from flatness from an $80 atoma diamond plate is probably too small detect without some really sensitive equipment.

In reality, lapping plates are never perfect, not to mention you can get a perfect shaving edge from a stone that isn’t perfectly flat.

 

[stone and strop]

Title should be "is my lapping stone FLAT?" not level .
Yes there is a way to quantify this.
Take a known straight edge (tolerances are up to you) Something with a guaranteed tolerance would be good.
Place the straight edge on the hone at 3 different places (at least) along the length and check for gaps with a feeler gauge ( I use a .001 gauge).
Do the same along the width all the way along.
Finally - corner to corner.
If it is not flat there is little recourse. Again, buy something with a guaranteed tolerance if you can.
Basically you can use any straight edge for this. OCD suggests I use others.

 

[cugel]

buy a real straight edge, not a ruler. You have to have a base-line reading for flat. Should cost ~30 bucks from amazon

 

[Twelvefret]

Getting farther into my practice with honing and got to thinking about this.

I use a cheapo lapping stone to level my stones, but i never thought if the lapping stone itself was flat.

Any methods for deducing this? What has worked for people in the past?

I use wet/dry sand paper on a $4 marble floor tile that I know is flat. I used a straight edge at Home Depot before I bought the tile. This lapped the Coticule and Thuringian quickly.

 

[Namkcakram]

Amazon has excellent British made certified squares and straight edges for not too much money. Straight edge on stone and hold up to a light source and look for light leaking through between them. After a while you get pretty good at judging the gap measurement by eye if you always use the same light source.

 

[kohalajohn]

I have also had trouble with lapping plates going concave. I'll be using them and after the fact find out that they were concave and this was the reason for the trouble I was having.

What I do now is have them convex. Convexity is like having money in the bank.

In the past, I'd lap the stone flat, but the moment I had done that, it would start, slowly, going concave again.

I use a very hard, very small, ark made concave by Jarrod. A soft stone like a nani12 gets lapped with this, and this over time creates convexity.

The attached video should show this.

 

[Gamma]

Most lapping stones are not flat and making them flat can be a pita. I use a Starrett straightedge to check flatness, works perfectly. I routinely check each stone in 8 places; 3 places across the width, 3 places across the length, and diagonally. Cheap diamond plates are usually not flat. Atomas and DMTs are usually pretty flat and I think most Atomas will be flatter than most DMTs with the exception of the Die-Flat. IME, the differences (results in both flatness and edge development) between using a cheap diamond plate and, say, a DMT 325x Diafine are notable.

 

[Namkcakram]

^^^

The key words there were “Starrett” and “Diafine”, but you can decide how expensive/precise you are willing to go. It can and does become an all consuming obsession among woodworkers, especially sharpening Japanese tools with wide flat bevels.

For any mere mortal, an atoma/DMT is flatter than any assumed flat surface in your house. You can also find cheaper straight edges that are just as straight, look for certified to British engineering standards or Japanese JIS standards. Shinwa products on Amazon will probably be the best overkill per dollar, but a 12” Starrett is only $60 if you really want certified with a capital C