Straight edge suggestions (for checking flatness)

[jj_sharp]

I am just a simple man.

Maybe someone could provide a simple test procedure for checking straight edges such as triangles and rulers. Perhaps a trueing procedure also.

I know strings pilled tight are straight. Perhaps that is a good reference.

This would be for non machinists, for non critical use such as checking stone flatness.

 

[eKretz]

Erm...buy a new straight edge? Thought we'd already covered that. Just buy it new from somewhere you trust. There isn't much simpler than that. Checking against a string will get you nowhere fast. I could describe a very easy and accurate testing fixture for a straight edge if you'd like. You'd need to purchase some precise round rod. Other than that a block of flat steel or granite and a set of feeler gages and Bob's yer uncle.

 

[bluesman 7]

Hey @eZKretz, ever hear of anyone using the three stone method to check or correct their straight edges? I've not done it, cause I only have two presently, but I've thought a bit about it.

 

[eKretz]

Yes, usually by scraping rather than lapping though.

 

[Alum of Potash]

I am just a simple man.

Maybe someone could provide a simple test procedure for checking straight edges such as triangles and rulers. Perhaps a trueing procedure also.

I know strings pilled tight are straight. Perhaps that is a good reference.

This would be for non machinists, for non critical use such as checking stone flatness.

Plate glass is pretty flat. Grab a sheet and place it upon a support surface. Then reach for some standard 8-1/2" copy paper and cut it into strips so as to avoid wasting an entire sheet of paper. Place the straight edge or rule or triangle in question edge-wise upon the plate glass and attempt to slide one or more of the paper strips between the edge and the plate glass. If the paper slip passes, something is out of whack, either the edge or the plate glass (probably the edge). Pretty rudimentary in the UNESCO create-science-out-of-what-happens-to-be-there sense, but it will at least give you a starting reference or indication.

This being determined, place the relatively straight edge on the stone surface in question. Corner to corner along the diagonals of a rectangular dimension, followed by the X- and Y-axes. Try to slide the paper slips underneath in each case and if they slip underneath, the stone is not true. Then lap until it is.

Come on guys, we're talking about honing razors here. Given that we are finishing or maintaining things on a pliable leather surface in the end, and given all the vagaries of the honing stroke in passing, I'm really wondering why there is such an obsession with flatness to the umpteenth degree.

 

[eKretz]

We have to go over this apparently every time we discuss flattening a stone. Nobody is obsessing over stone flatness. I demonstrated a method of checking flatness used in a machine shop inspection setting. Mainly for those who might be interested in how to check and quantify any error in a straight edge, which one of our members purchased at an estate sale in who knows what condition.

Whether a stone is perfectly flat isn't really all that important. What is important is that all stones used in a sequence be at least pretty darn close to the same in flatness - or not, in the case of say a convex stone - unless you don't care about spending more time and removing more steel than needs to be removed. So checking diamond plates to be sure that they are at least close to each other in flatness is somewhat important to me, since they are used to produce the surface used on those sequentially used stones or hones for honing.

I also use my diamond plates and other hones occasionally to flatten small tools or for things like chisels or plane blades, which I would like to have pretty darn flat as well. All of us would do well to remember that our own ways or needs are not always the same as everyone else's ways or needs...

Edit: I see now that I've responded your post has been changed from "obsession with stone flatness" to omit the word stone, which makes my first paragraph sort of look like I'm off base...guess I should have quoted that.

 

[duke762]

How long ago did you make your straight edge? Did you heat treat it yourself or send it out?

A year or 2 ago. The steel was hardened by a local company, I think it's done in an Argon atmospheric furnace. I've had the steel for years, it's actually a wire edm burn off from the edge of a large die steel that was already hard. Ground flat and squared.

Your home shop is too die for!!!! Lord I could get in so much trouble with your shop!

......Why didn't think of running the indicator on the bottom? Old and slowing down.

Is your equipment all 3 phase? If it is, are you going to do an electric company transformer or 3rd leg in the yard?

How exactly do I send a pm? Is that the start conversation thingy?

 

[eKretz]

A year or 2 ago. The steel was hardened by a local company, I think it's done in an Argon atmospheric furnace. I've had the steel for years, it's actually a wire edm burn off from the edge of a large die steel that was already hard. Ground flat and squared.

Your home shop is too die for!!!! Lord I could get in so much trouble with your shop!

......Why didn't think of running the indicator on the bottom? Old and slowing down.

Is your equipment all 3 phase? If it is, are you going to do an electric company transformer or 3rd leg in the yard?

How exactly do I send a pm? Is that the start conversation thingy?

Yes it's all three phase. I'm going to be using variable frequency drives to convert 1 to 3 phase. Most don't know this but a majority of "3-phase only" VFDs can run on single phase input - they just have to be derated in HP capacity. I have a 3HP VFD (no derating, made for single phase input) for the milling machine and grinder spindle motor, and a 25 HP VFD that needs derating by 40% to run on single phase for the lathe. And yep, PMs here are "start conversation."

 

[stone and strop]

Plate glass is pretty flat. Grab a sheet and place it upon a support surface. Then reach for some standard 8-1/2" copy paper and cut it into strips so as to avoid wasting an entire sheet of paper. Place the straight edge or rule or triangle in question edge-wise upon the plate glass and attempt to slide one or more of the paper strips between the edge and the plate glass. If the paper slip passes, something is out of whack, either the edge or the plate glass (probably the edge). Pretty rudimentary in the UNESCO create-science-out-of-what-happens-to-be-there sense, but it will at least give you a starting reference or indication.

This being determined, place the relatively straight edge on the stone surface in question. Corner to corner along the diagonals of a rectangular dimension, followed by the X- and Y-axes. Try to slide the paper slips underneath in each case and if they slip underneath, the stone is not true. Then lap until it is.

Come on guys, we're talking about honing razors here. Given that we are finishing or maintaining things on a pliable leather surface in the end, and given all the vagaries of the honing stroke in passing, I'm really wondering why there is such an obsession with flatness to the umpteenth degree.

Alan this is why I normally use the ruler mentioned. Its size is convenient for checking smaller things.
It is plenty straight enough to check stones for flattening and tells me whether I need a little more time on the granite slab. Its reasonable inexpensive and plenty handy in the shop. I use it to set calipers for work on the lathe as well.
I am also into high end woodworking tools where dead flat pays huge dividends in performance.

 

[David]

Come on guys, we're talking about honing razors here. Given that we are finishing or maintaining things on a pliable leather surface in the end, and given all the vagaries of the honing stroke in passing, I'm really wondering why there is such an obsession with flatness to the umpteenth degree.

I have to agree. For new guys I can see the need to make sure the stones are as flat as can be, but once you get the feel of things I don’t see the point of Obsessing over absolute flatness. I bought a jnat from Nelson one time that was dished about 1/8” in the center. Cracked me up.

 

[Steve56]

I used to go 6 months between lappings on Shapton Pros, and I hone quite a bit. They’d get dished a little unless I was sharpening a lot of knives.

Dishing increases the bevel angle, like tape. These days, I like to lap my Shapton Glass fairly frequently because I only use them up to 4k and don’t want the ‘coarse’ Stones increasing the bevel angle such that a flat finisher might not make the desired contact with the apex, however little. I think Alfredo laps his SG a little before every use.

Most of my jnat finishers are fairly hard, and if they get dished slightly that’s OK after using flatter pre-finishers.

 

[jj_sharp]

I just found my metal ruller. It walked off to a sewing setup. My first thought is to check it for straightness, as the unauthorized user may have damaged it by running knives along the edge. I have a house full of potential unauthorized users...

I appreciate that some suggest glass as a reference, which will be plenty good for my purposes.

Seems like a lifetime ago since drafting classes. Is it the case that one can draw a line, change ends and redraw the line looking for deviation?

Computer drafting, I think, was not a thing well into my adulthood. Jody

 

[stone and strop]

Hey @eZKretz, ever hear of anyone using the three stone method to check or correct their straight edges? I've not done it, cause I only have two presently, but I've thought a bit about it.

Victor, can you elaborate on the theory of this?

 

[bluesman 7]

Victor, can you elaborate on the theory of this?

Basically if you get edge A to mate with edge B you could have one concave and one convex. If they both also mate to edge C then all 3 have to be straight. Eric and I have discussed this many times with regard to 3 (stone) surfaces. I'll see if I can find a link.

 

[stone and strop]

Basically if you get edge A to mate with edge B you could have one concave and one convex. If they both also mate to edge C then all 3 have to be straight. Eric and I have discussed this many times with regard to 3 (stone) surfaces. I'll see if I can find a link.

This makes sense and I have seen reference to it before but have never seen it explained in detail especially with respect to stones.
How would you go about this? A grid marked and removed by one then repeated by another? This doesn't make sense.
If you can find the link I would appreciate it.

 

[bluesman 7]

This makes sense and I have seen reference to it before but have never seen it explained in detail especially with respect to stones.
How would you go about this? A grid marked and removed by one then repeated by another? This doesn't make sense.
If you can find the link I would appreciate it.

Here is one; https://forum.canadianwoodworking.com/forum/tools/hand-tools/28228-3-stone-flattening-system

The beauty and attraction, to me, is that straight or flat can spring up out of nothing but logic. Think caveman.

 

[stone and strop]

Thank you.
I will have to test this out.

 

[eKretz]

It works. For precision straight edges there is no better way to achieve as perfectly flat a surface as humanly possible. We're getting a bit OT here but three straight edges scraped together (checked against each other as references) can be brought to within millionths of an inch of perfectly flat with no other reference. They are compared A to B, then B to C then A to C. Progress on matching them continues until all 3 match as closely as possible.

On stones and even granite plates I have done this with silicon carbide grit between them to lap both together. You'll want to grid both stones at each pairing and continue lapping until both grids are gone for each step. Once a swipe or two removes most of the grid on all three you are there.

 

[jj_sharp]

I have learned something.
I doubt I will ever need to apply this knowledge, but one never knows.

 

[stone and strop]

It works. For precision straight edges there is no better way to achieve as perfectly flat a surface as humanly possible. We're getting a bit OT here but three straight edges scraped together (checked against each other as references) can be brought to within millionths of an inch of perfectly flat with no other reference. They are compared A to B, then B to C then A to C. Progress on matching them continues until all 3 match as closely as possible.

Well, not completely off topic.
We are still talking straight edges and I'm sure I'm not the only one who finds it interesting.
We're a strange bunch