Chisel and Plane Iron Tolerances for flatness and square

[Tom Ellison 8]

All,

I am relatively new to serious woodworking. I have recently upgraded to a small set of LN bevel edge bench chisels. I am very meticulous with my tools; even more so with tools that have the appearance and price of LNs. My question is :

How meticulous is too meticulous when it comes to the flatness of the back of chisels, the squareness of the bevel to sides of the chisel and if the microbevel is parallel to the primary bevel?

If you hold a straight edge or square to check any of these characteristics and you can see a little light when held up, is this a big deal? What kind of tolerances are allowable before you start to see unfavorable results? Are these tolerances the same for plane irons and chisels?

Are there are benefits to getting as close to perfect as humanly possible or if the point of diminishing returns is reached fairly quickly?

I have sharpened and honed these chisels a fair amount since I received them so they are no longerror as pristine as they were when they arrived.



I appreciate any responses very much.

Thank you,

Tom

[ken hatch]

All,

...the point of diminishing returns is reached fairly quickly?

...
I appreciate any responses very much.

Thank you,

Tom

Tom,

Yes :-).

Square? If it looks square it is close enough, I think the boat builders term is "if it looks fair it is fair".

The back and the bevel need to meet with the smallest angle possible for the iron to be sharp, so small it will not reflect light. The most consistent way to have that happen is to have the back as flat as you can get it.

ken

[Shawn Pixley]

If I put a known straight edge (say a good square) and saw light, i would flatten it. For chisels, a bit of hollow in the center is not as bad as light at the edges. Typically, LN and LV are square and flat when new. I only end up polishing the backs of chisels and plane irons (as opposed to flattening) on the stones. With old Bailey irons, I have had to do some serious flattening or to remove corrosion pits. Realistically, I look for the polish on the back pattern to deturmine flatness rather than a square. I use an Atoma to flatten my stones. I don't use the "ruler trick" and the back only sees the stone again to ensure the burr is gone after the highest grit on the bevel.

[bridger berdel]

If I'm taking a chisel or plane blade to the grinder I keep a small square at hand to check frequently as I grind. Once it gets to the stones I no longer bother. If it's out of square enough to catch my eye I'll check it, but unlikely I'll need to do anything about it until the next grind. Planes have lateral adjusters, so camber is much more important than square. With chisels, being very square would only matter if the chisel is making a cut where the blade is tightly constrained in a cut. The main such cut I can think of is a mortise, but having the bottomf a mortise be very accurate isn't necessary.

[ian maybury]

As above - but i can't claim long term expertise. This is an issue likely to bring out differing views.

Squareness of the cutting edge to the line of the tool/blade isn't hugely critical, but still needs to be close. It's not too hard for some misalignment to creep in during honing, so checking regularly with a square is advisable i think. (presuming the side of the tool is straight) A plane iron needs to be square enough to be well within the range of the available side to side tilt adjustment. I'd argue that a chisel used for chopping needs to be square, especially if it's a bit wider - so that within reason it cuts through across the full width of the cut without the need to tilt the chisel. i.e. if upon checking with a square against a light there's any gap visible (other than intentional camber in the case of a plane blade) then it's probably best to sort it out - before moving to the finer finishing stones.

Back flatness is often argued as not being functionally critical behind the first say 3/4 in or so from the edge. The point though is that the back on a good modern chisel is probably flat within a few microns all over when new (will cut all over in a few minutes on a 1,000 grit waterstone), and if it's not then cutting it back on something coarser and then working it up on frequently and accurately flattened waterstones can bring it into that range - and without any special attention keep it there over successive sharpenings.

That may well be overkill, but the potential issue if some degree of out of flatness is let creep in during sharpening or a tool is not properly flattened from new is the likelihood that the situation will subsequently get worse - because of not having had a large enough flat reference area from which to keep it accurately and consistently aligned on the stone. Presuming frequent flattening of the waterstones it's not hard to keep a back flat when starting from a flat surface, but once the possibility of instability/rocking on the stone creeps in then a lot of care and skill is needed to prevent it likely getting worse...

It's to my mind a bit like many working practices. It adds very little to keep flatness and squareness right, and while some minor inaccuracy won't necessarily immediately cause a problem in use it's best avoided/sorted out ASAP as it avoids the risk of unknowingly sliding into troublesome territory...

[Jim Koepke]

Howdy Tom and welcome to the Creek.

As far as edges square to the sides are concerned, some of my plane blades do not have parallel sides.

With chisel blades for me it matters more that they are sharp. Some of my chisels are a bit off square. I just try and adjust for that any time they get sharpened. It doesn't correct the situation all at once. To me it is more important to get it back to work.

My only requirement of my tools is that they do the work asked of them. I like pretty tools, but the ugly ones can do just as good of a job at the bench.

jtk

[Tom Ellison 8]

Thank you everyone. I am new here and it is nice to see so many responses so quickly!

[Jim Matthews]

When I can shave endgrain on soft pine, my chisels are sufficiently sharp.

When I can round over endgrain on soft pine, my planes are sharp enough.

Results are what matter. How you get there is a matter of preference.
I prefer sharpening methods that are compact, quick and repeatable.

[Brian Holcombe]

I like paring chisels and mortise chisels to have flat backs, since they are used a reference. For bench chisels I just work the last 1" ~.

[Pat Barry]

Are there are benefits to getting as close to perfect as humanly possible?
Tom

Tom, its not a life or death situation. Do they cut? If yes, then you're done.