Hey all,
I’ve just got a piece of granite work top that i wanted to use with wet/dry sandpaper as a lapping plate to flatten my waterstones and to check the bases of my planes.
I can just about see some daylight beneath a straight edge in a few places. I don’t know if this is flat enough or would it have to be to the thau…
This might be a ‘how long is a piece of string’ type question but I really expect my tools to be, as we say, bang on. Is there any guide lines I should know?
Eoin
Replies
Depending on the source of the granite slab, I might wonder about my straight edge.
Granite can be ground to around .001 I believe with modern grinding techniques. But that doesn't mean the granite work-top you got is ground to those tolerances. And if it is just standard kitchen top granite I would seriously doubt it.
But with that said... if you can just see day-light the question I would ask myself if in your shoes would be....
Watcha' waiting on.... get to sharpening and be done with it so ya can make something. :>)
Sarge...
I have no idea but I have picked up more than a few chunks of scrap granite. A place near me puts them out for free for you to try and lift and get into the car/truck.
I'd bet they have a video cam to watch this old man trying to lift the scraps durnig coffe break for a good laugh!
Most no larger than about 24 inches by something.. Even the so called scrap is flat!
I wonder if it really matters, if MOST of it is flat.. I'd bet the blade never notices the so called low spots.. If it were a 'bump' a different matter.
Just my thoughts...
Hey Will -
Where is this place if it is not your personal secret? I have been looking for a place like that.
Joe
Just seeing a glint of light could be 1/4 to 1/2 Mill. The silicon carbide paper can be that much off. I wouldn't worry about it.
Work Safe, Count to 10 when your done for the day !!
Bruce S.
If you want to quantify it then get a feeler gauge See what you can slip in the space. Or even use a piece of paper as a rough gauge.
OK, it appears I've been a little too up tight. I can't even get a piece of standard writing paper into the space. Good idea to check that way. I'm guessing from what people are saying here that with the addition of the sand paper that this space becomes irrelevant. Thanks Guys
Edited 12/18/2008 1:18 pm ET by eoinsgaff
It is amazing how small a crack of light is visible!
I dunno, but I guess that the wet & dry paper will compress more than a thousanth, the water film or glue you use to adhere it to the granite will vary in thickness more than a thousanth.
I'd give it a go as it is and see if the results are acceptable to you. The whole straightedge/light method of gauging flatness is likely not especially accurate because it is subject to variables like how straight your straightedge is, as well as how flat it is on its face. If it is even slightly bent across its face, less than .001 over the length of the beam, If you aren't dead plumb when you measure, tipping it only slightly, will show a gap that's visible.
Even on good straightedges that are graduated, grit can become lodged in the markings and can disrupt the surface of the edge causing errors. DAMHIKT
One knock against something hard will disrupt the straightedge's edge where it meets the face, jacking it up enough that you'll see daylight under it on a mechanically flat surface.
Of course dust and grit on any of the surfaces will introduce errors.
What really matters is does it work? I bought some big box granite floor tiles that I used for a couple of years, they worked beautifully. I'm sure they're not perfectly flat and therefore the back of my chisels and plane irons aren't perfectly flat either. But it is close enough.
Give it a shot!
David
Would advise a small surface plate, probably <$75 & good to well over "tenths" (.0001").
Inspection x sight can be frustrated x interference (dust, dings etc), parallax and diffraction.
For deviations ~.0005 - .001 use feeler gages, they're cheap.
Routs to .001
Check your straightedge for straight against a known reference point. Most table saw tops are pretty good for a start. If the straightedge is straight, then go down to the local autoparts store and get a spark plug feeler gauge (not the wire kind) and measure the gap.
Me, I don't worry about a dished stone--it gives me the very desired cambered edge should I want one!
T.Z.
If you are talking thousandths of an inch table saws aren't even close to flat.John White
Steel City has one that is... :>)
Regards John...
Sarge.. john t
Depends what kind of saw we're talking about: I have a several decades old Unisaw and I have a 24" rule from my Starret tri-square that I can put on the tabletop and not see daylight. I also have a Grizzly 1023 that I can do the same thing with a similar 12" Starret rule. I'll agree that these rules may not be laser straight, but they're pretty good. In fact, I would say they're good enough for woodworking, eh?
Now, if you're talking about the $80.00 tablesaw special at the Borg, why, you're going to have to use the 50 cent imported rule you got at the kiosk at the local "special" tool sale at the mall. You may have to flip the rule a few times to find the right bow of the rule to match the bow of the tabletop.
Seriously, there are a lot of saw tops that are that (or nearly) that good.
T.Z.
I used to be the shop manager at Fine Woodworking and tested dozens, if not hundreds of saws over the years, and I never saw found a table saw that had a flat table. All but a few were flat enough for woodworking but none of them were flat enough to be used as a reference surface for testing other tools for straight or flatness. My first choice would be a granite surface plate, small ones are fairly inexpensive, and lacking that the tables on most jointers were almost always much more reliably flat than a table saw.John White
When you're honing/polishing a bevel on a chisel or plane blade, a few thousandths off flat on your waterstones will make utterly no difference whatsoever. However, a few thousandths out might very well frustrate you when initially flattening and polishing the back of the blade. I'd note that the a chisel or plane blade back doesn't really need to be flat (at least within a few thousandths), just polished so that the bevel and back meet at a sharp, uniform edge without significant scratches.
The problem you might have is if your successive grits of waterstones aren't flat, and are differently convex/concave. Then what happens is that the width of a blade is uniformly scratched by the 1000 grit stone, but when moving to the 4000 grit stone, you notice that one or more spots are highly polished, but not all the way across the back, and it takes an inordinate amount of work to get the uniform polish all the way across. That can also be a symptom of bad technique, though. In my case, I prefer a granite surface plate because they're cheap and they eliminate a potential source of trouble.
Eoin,
A good guide line is what Routerman has said.
Offcuts of "kitchen" granite may or may not be flat enough- the main criterion for their existence is not flatness-it is more to do with appearance and durability.They are not issued with a calibration certificate like engineers granite plates are so you takes your chances unless you have an accurate means to be sure what you get is flat.
Philip,
I applaud your focus on the need for flatness of granite plates. IF you have three granite plates and a bunch of silicon carbide lapping grit, you can get the three plates extremely flat. If you have just two, you can use this technique to get two of them to match, but that does not mean they are flat. It takes three. When I worked at NASA, I ran across a lot of granite "optical surface plates" that were used for high precision optical work. Each plate has a sticker affixed to it which gives the last time the plate was checked for flattness to the given standard. Every once in a while, you'll find a high tech company which is selling off some equipment. Back in 1971, I bought four of these for $5 apiece from the Link Division of the Singer Co in Binghamton, NY. . I used them in the back of my pickup truck as extra weight to increase traction while driving in snow. Two years later, when I moved to Florida, I didn't need them any more, and I sold them for $25 apiece to a small high tech startup firm, who was thrilled to get them for that price. They were going to have a specialty firm bring them back to within specifications using the "three plate technique" that I mentioned above.Of course, it takes a lot of elbow grease to get the three granite plates really flat. So it helps if you have a really strong wife or girlfriend who is really interested in woodworking. Have fun.
MelMeasure your output in smiles per board foot.
I worked for a while years ago in a machine shop that had many granite slabs ground very flat. It would be nice to have such a surface in my woodworking shop, but the only granite available here is countertop material and tombstones - neither will be as flat as toolroom grade granite slabs. An alternative to the extremely flat toolroom granite is simply a piece of plate glass - the thicker the better. I use a 3 foot long piece of 1/4" thick glass on top of my tablesaw with a strip of 100 grit sandpaper from a roll glued down to flatten butt joints perfectly flat. This makes joints fit together extremely tight and no light can shine through. I haven't tried using it to sharpen any tools on, I don't even own a hand plane. The glass will deflect slightly if you press hard, but I don't put much pressure on it normally. Lot easier to move around too!Steve
http://www.stevengarrison.com
Steve,
I just checked out your website. I am overwhelmed. Your sculptures are fantastic. You are one of the best around. Very creative. I wish I could see one up close. Is there one around Washington, DC? After seeing your sculptures, I have no interest in talking about lapping plates. Great work is much more interesting than sharpening. How big a piece of wood do you start with to get a 12" shell? Do you use any power carving tools, or gouges? What do you use for smoothing? I would guess you use some sort of sander, like the Guinevere that is sold by King Arthurs Tools. I am merely a hobbyist. I don't sell anything, so you don't have to worry about competition from me. Besides, I don't have your talent. But I know what I like, and I like your work.
Merry Christmas, and good luck with your carving business.
MelMeasure your output in smiles per board foot.
Philip,A question for you. I don't know flat from a hole in the wall but I figure if the granite reflects my image evenly and without distortion, that would serve as a fairly good indication of flat? Okay, gimme a lesson.
BG,
You might look better if there is some distortion in the reflection... <g>
Best wishes,
Metod
Eoin,
Don't talk thousandths with these guys; drives 'em up the wall. I learned my lesson. I am staying out of it.
you are on your own . . . enter here at your own risk and heaven help you amen.
: )
I will say wet/dry is for polishing. Not the best for cutting. Takes too long.
roc
The only reliably "flat" (I think most woodworkers use "flat" to mean within 1 thou) items are surface plates.
As various people have pointed out, bit of granite, table saws, bits of MDF are only "flattish".
BTW, I also think that lapping planes flat SUCKs.
BugBear
bugbear,
Yeah, there is a concept of 'flat enough'. The sad thing is, that (observing various posts) many folks do not realize that additional flattening, while improving the 'numbers' does not improve the quality of the cut. I really should re-flatten all my planes to +/-.0000000666".
Best wishes,
Metod
I've never seen a convincing complete analysis of how flat a plane sole needs to be.The notion that it ought to be within a single shavings thickness of "true flat" has always sounded reasonable to me, but I ceratinly can't prove it.I am sure that planes that are "too flat" are "flat enough" :-) BugBear
Japanese planes have two very shallow concavities, one in front of the mouth, the other back of the mouth. They do great work with them. Maybe they have a good comprehension of what is important. :-) Sadly lacking in many instances :-(
Best wishes,
Metod
"Japanese planes have two very shallow concavities, one in front of the mouth, the other back of the mouth. They do great work with them"..
I've got an Indian #7 that has two very shallow concavities, one about and inch in front of the heel and one about an inch rear of the toe and it does great work too for probably a lot less invested than the Japanese planes. I guess anyway as I really don't know what Japanese planes cost?
I suppose I shouldn't have mentioned this as I certainly don't want to stir up any trouble in the eastern hemi-sphere with the peace and harmony that currently exist there. ha.. ha... ha..ha..ha..
Merry Xmas and Happy New Year, sir Metod....
Sarge..
Sarge,
I do not have any Japanese planes, nor have I tried one. I did have (I do not remember which web site) a close look at their geometry, and found it of interest.
And warmest wishes for great Christmas and much goodness in the coming year.
Metod
Thanks for the greeting Metod. I was just spreading some Holiday humor with the post to you. I have never looked at a Japanese plane close up but I can tell you shallow spots in non register spots (toe.. heal.. mouth or outer perimeter of sole aren't going to affect a thing.
For that matter I am not totally sure that an entirely flat sole is a major requrement anyway as I have seen many that aren't that close to being totally flat get the job done. Perhaps the current trend is to worry about minor details that wouldn't have been a concern 20 years ago but results aren't really any different. Perhaps... :>)
Regards for the Holidays to you and yours...
Sarge..
The soles of Japanese planes are shaped very accurately indeed; they're just not flat. BugBear
Yup, three coplanar regions on the sole. :-)
Best wishes for Christmas and the coming year,
Metod
Metod,
When you get an electron microscope and a proper laser measuring device, you will be able to use nano technology to rearrange the molecules of metal on the base of the soles of your planes. That is the only way to achieve REAL flatness. I figure that any serious woodworker would be willing to pay about $200,000 to fettle his planes properly. Heck, if you are using a bunch of Holteys, they are probably worth more than the measly $200,000. I continue to try to devise ways of making big money in woodworking. I am now thinking about starting a new church -- The Church of the Holy Woodworker, for those woodworkers who think of woodworking as a religion, and who pray at the altar of the sharp iron, and before an ikon of the flat sole. If they can be convinced to make their soles really flat, maybe I can convince them that they should make large donations for me, in return for weekly sermons on such matters. Joyeux Noël,
MelMeasure your output in smiles per board foot.
Mel,
For some it would take 'transcendental' efforts to understand what is important in a particular task and what is less relevant.
Much joy, goodness, and Grace at Christmas - heck, why not on the rest of the days as well.
Metod
I took your suggestion and worked on my Anant Camel today with the electron microscope thangy. Thanks as it is really... really flat now. But... should I wipe the sole after each pass to clear any dust or shaving residue off to avoid ruining the transfer of flat force to the stock?
Just wondering as I don't want to actually start a project using it until I am totally convinced it is flat and I can follow proper operating procedure to maintain efficient results... ha.. ha...
Just kidding Mel...
Merry Xmas and Happy Holidays to you and yours...
Sarge..
Edited 12/23/2008 6:04 pm ET by SARGEgrinder47
Sarge,
I was in at Woodcraft the other day, and I opened the package that a granite plate comes in. They are from China. I wanted to see just how flat they are. We have a four foot long straightedge that we keep for measuring the flatness of machines, such as the jointer beds. I put the straightedge on the granite plate and put a light behind it. The straightedge has a thickness that I can't remember, but at lease a quarter inch. With the light behind it, I could see light almost all along under the straight edge. THen I wiped the dust off. The sucker was flat.So wiping the dust off,as you mentioned in your post, is necessary if you are using precise measuring instruments. Well, I hear my wife in the kitchen, and I smell the food. Time to think about something more important than dust.Merry Christmas,
Mel
Measure your output in smiles per board foot.
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