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Thread: Accurate hand lapping advice
03-31-2010, 02:39 AM #1
Accurate hand lapping advice
Hi, recently there was a discussion on a woodworkers message board regarding solutions for lapping the backs of plane blades/chisels. Many members suggested sand paper on a granite reference, lapping on flattened sharpening stones, diamond sharpening plates, and one person suggested using a cast iron lapping plate. I figured I would ask the people who probably know best about this, so here I am. What would people on practical machinist recommend? Thanks for your time.
03-31-2010, 02:54 AM #2
I think this is a case where the same word has different meanings in different environments.
Lapping in a machine tool context can produce surfaces with flatness errors measured in millionths of an inch. I'm inclined to doubt that's what you're after.
Your first suggestion (fine sand paper/emery paper on a granite reference surface) should produce results well within your desired tolerance.
03-31-2010, 02:57 AM #3
I'm after getting the flattest surface possible by hand.
03-31-2010, 03:02 AM #4
03-31-2010, 03:07 AM #5
Condition (hardened/stress relieved/annealed)?
Over what temperature range? What temperature gradient across the piece?
What measuring equipment do you have? You'll certainly need a 1/20th-wave optical flat.
What is the accepted limit of error of appropriate measuring systems as defined by NIST?
What experience do you have in precision mechanical measurement techniques?
I'm inclined to doubt that you understand what you're asking.
No offense intended.
03-31-2010, 03:09 AM #6
03-31-2010, 03:26 AM #7
Lapping the back of a plane iron is worlds different from precision machine lapping. A plane iron has to be smooth and quite flat but not so flat as to be measured in millionths. Abrasive sheet lapping is a good as it needs to be although the purists among amateur woodworkers go to laughable extremes and take infinite pains most of which is wasted effort.
Back in the day the best of woodworkers flattened the back of their plane irons and chisels on naturally occuring abrasive stones like sandtones rich in aluminum oxide or limestones containing calcite crytals. When backs of their plane irons were lapped sufficiently they'd seldom touch them again except to strop off the burr.
Now we have a huge range of sharpening apparatus avalable and an endless supply of hair splitters as self-applointed experts. The best sharpening methods are based on efficiency and common sense uing smple equipment. The thing for a neophyte to do is select a method and become practised with it.
When I was working wood by hand I used a bench stone followed by a hard Arkansas to flatten the backs of my chisels and plane irons. With a little practice they became as mirrors showing no roll-off at the edge and were highly reflective as well. Later as they became available I used DMT diamond plated bench stones.
The flat back of keen cutting edges may be made so using abrasive sheet lapping on a granite surface plate or thick plate glass, bench stones and oil, Japanese natural and synthetic water stones, loose abarasive (I prefer diamond lapping compound in a graduated sequence) lapping on cast iron, and lately on a Tormek clone using a rotary water stone.
Here's a tip on sharpening fine cutting edges on woodworking tools: if it takes more than a minute to touch up a cutting edge and more than three to remove a nick your method needs either practice or replacement. The whole idea of sharpening is to restore the cutting edge as quickly as possible and get back to making chips. A simple, efficient method followed by a ten second treatment with a charged strop is all you need.
Here's some more good advice: when confronted with insistant purists of any pursuasion, either ignore them or assult them with loud mocking laughter.
I know guys who spend more time perfecting their cutting edges that they do makng chips. They give me a headache where I sit down.
One last tip, never use loose abrasive or lapping compound on glass. The glass laps several times faster than the steel and the glass soon wears into trough and depressions.
Last edited by Forrest Addy; 03-31-2010 at 09:54 AM.
03-31-2010, 06:34 AM #8
I had a cheap cast iron plane that was pretty bad. I used it for scraping practice. The surface was a bit scary compared to a smoothly sanded or lapped surface, but it worked great. I think the scraping pattern held the paraffin I use for lubrication.
03-31-2010, 07:05 AM #9
I bought a new Darex Work Sharp 3000 at an estate sale recently. It is a motorized sharpener for woodworkers. It uses plate glass disks and adhesive backed abrasive papers in many grades from 80 to 6000. You can put abrasive on both sides of the disks and grind on either the top or bottom of the disks.
They even have slotted abrasives. With the slotted abrasive installed on the bottom of the disk and a light positioned above the disk, you can grind gouges while you actually see where you are removing material. They sell a slotted plastic disk, but the slotted abrasive works just as well on the glass disks.
I sharpened a pile of antique wood carving tools that I had accumulated but not used. The machine worked great.
And it does make plane irons, both front and back, super easy to flatten and sharpen. Think of it as mechanized sandpaper on plate glass. Same idea, but quicker and more expensive. Amazon sells the accessories cheaper than list price.
WS3000: WORK SHARP 3000
Amazon listing and reviews: Amazon.com: Work Sharp WS3000 Wood Tool Sharpener: Home Improvement
03-31-2010, 07:12 AM #10
There is a published method for sharpening microtomes (which make sections for microscope slides, usually between 0.05 and 100 µm in thickness) that sets the blade up on a wooden stand, and uses wooden paint stirrers charged with diamond dust to finish the edges. These are blades that you can almost drop a tissue on lengthwise and the tissue will be sliced open as it falls. And the sharpening uses essentially waste chunks of wood.
There is nothing to say you could not use a cast iron lap to get some sort of shiny surface approaching "machine tool" dead flat. But Leigh's right: It is overkill. Heck, a piece of wood can expand and contract more than 0.001" in a single work session. And so +/-0.00001" is needed, why? Forrest is right, too: The time it would take would not be worth it in the sense that your neighbor (who used emery cloth stuck to plate glass with some water and was done sharpening in 2 minutes) would have an entire shelving unit fabricated and installed while you would still be sharpening your plane!
For a nice flat surface, use water to fix a piece of fine sandpaper (I've used 400, 800, and I think 1500, the black kind) to plate glass with water. You will be good to go, with a nicely flat, shiny surface and a straight edge.
03-31-2010, 07:53 AM #11I think this is a case where the same word has different meanings in different environments.
Lapping in a machine tool context can produce surfaces with flatness errors measured in millionths of an inch. I'm inclined to doubt that's what you're after.
I aslo agree, whats the point in better than a thou for chisel?....but if its out several thou and you start with coarse compound, lapping will work to get it to a thou.
a piece of emery paper on a flat surface is not lapping as i understand the word to mean. Lapping is when abrasive compound is embedded in a lap and deployed such that said embedded abrasive machines the work.
As well as flat to some reasonable degree, you want the surface very smooth as it forms 1/2 of the cutting edge. As lapping can be a process that creates a very smooth finish, I can see why with a tiny bit of knowledge why someone might erroneously think the need it lapped to the highest standards of flatness (like you gotta make hot rod parts out of billet) ....BUT.....what you really need is say it flat to a thou and a very smooth finish.
if its out quite a bit, get it flat by abrading on emery on something plate, thick plate glass or even your table saw....work up to say 600 grit. Then with stones up to 8000 put a mirror finish on. You'll put a great edge on and will be more than flat enough
03-31-2010, 08:10 AM #12
When I was a young man, a "fellow woodcrafter" asked that I true up his all metal block plane. Straight and square.
I put the "as delivered" plane body on to the surface plate and went all over it with an indicator and reference edges and squares in good light. There was not .002" variation from "dead nuts" on that body except at the very heel of the sole. A bit of roll off. I reported my findings and suggested that the plane could be improved very little even at great expense. The reply returned was "just go over all the surfaces to get the look of "machined all over", that is what is wanted.
Flatening backs of blades is one of the difficult tasks in woodworking. We always want to begin with too fine an action. My experience is that like the Japanese style irons with relieved backs, blades need attention to thier backsides whenever the edge is made keen. "Can't just do it once!"
03-31-2010, 10:10 AM #13
Christian, if you've never done this before it's very easy to create a rounded surface (high in the center), what ever method you may use. And then its difficult to remove it. Or it may be like that to begin with. I've found it much easier and quicker to use a small abrasive wheel in a Dremel to create an ever so slight "hollow grind", and then flatten from there. Just lap a little to find the high spots and then kiss them with the wheel, repeat till the plane iron doesn't rock, and then lap flat. I use the Mizzy Heatless wheels.
I suppose the expert machinists here will find this crude and amateurish, but it sure works for woodworkers. Very much like the hollow on the Japanese blades. And if you're going to back off a bit each time you sharpen, be sure that your stone is flat - they tend to dish in the center, especially water stones. Then you're back to a domed surface.
I'm not sure why its so easy to round surfaces lapping on sandpaper, i suspect maybe the slurry formed cuts more aggressively at the edges. Or maybe the center of the paper dulls more quickly.
Just my 2 cents
03-31-2010, 11:49 AM #14
For flattening plane blades, if you plan to be doing it for a few years, a good diamond stone lubricated with water will cost much less in the long run than sheets of abrasive paper. It will also stay flat better than an iron lapping plate. You can also use a diamond stone to flatten your sharpening stones. You want to select a diamond stone that has some sort of relief groove pattern on the surface so the slurry can work on the entire surface. With abrasive sheets, like Richard suggested, you create a buildup of abrasive slurry that cuts faster at the outer edges so there is a tendency for that area to be abraded faster than the center.
Just in case you haven't seen it, the tool sharpening section of this forum will have more information than you will need;
Japanese Woodworking Forums • Index page
03-31-2010, 12:28 PM #15
Artist/woodcarver Bonnie Rasmussen, who does this for a living, sharpens her gouges on a shellac stone with a rolling action side to side, which she feels makes it easier to get a flat bevel. Then she polishes both sides with 1 micron synthetic sapphire abrasive from Micro Abrasives Corp. Welcome. Most of her carving is done with just hand pressure and the more smoothly the chips slide over the blade, the better the control. After polishing the blade, she tips it up to a higher angle and drags it backwards on the stone for only one stroke to give the edge a little tooth. Accuracy and super flatness are not issues, but the high polish is. I should remember what she uses for a lap, but it escapes me at the moment. I know that it isn't metal. Wood or some plastics would work. Paper gives fast cutting but tends to round the edge. Her work can be seen in "3 Dimensional Illustration" by Ellen Rixford.
03-31-2010, 01:20 PM #16
Hey Bill, what is a shellac stone? That's a new one to me.
03-31-2010, 02:21 PM #17
From a desription of Phillipe Dufour's watchmaking process;
Pierre gomme-laque: A block of shellac mixed with an abrasive such as emery. Also known as a shellac stone. Used to create a straight grained finish on steel surfaces such as springs, levers, cap jewels, etc. The process of using the shellac stone is very similar to making flat polish except that the stone is moved across the surface in a straight line. Historically all parts that will be flat polished are first made flat using a shellac stone.
03-31-2010, 02:37 PM #18
As Gordon Long says, they are shellac bonded abrasive stones. Bonnie was selling them at one time. Since she decided that I was carrying on with a young grass widow who lived next to the shop (I wasn't), she hasn't spoken to me, so you are on your own there. They may still be available from
Success Barber & Beauty Supply
113 E Chariton St
Moravia, IA 52571
They give a great finish but they should be reserved for light finishing because they break down easily. They come with rub stones used to dress their surface.
03-31-2010, 02:43 PM #19
Accurate sanding or lapping is similar to hand scraping. there has to be a way to check surface and show where high spots are.
if you have a thin layer of non drying bluing on a surface plate it can be used to transfer blue to high spots. or if you have a surface with surface dyed with a marker you can rub off high spots with a surface plate. you can cover surface plate with 600 grit emery if you are worried about about creating a wear spot on surface plate.
Of course there are tools for checking surface plate flatness. Some use dial indicators and some use a precision level. Electronic levels can be used to create a map of high spots on a surface plate needing lapping usually done with diamond lapping compound and a smaller than surface plate cast iron lap.
a surface gage can be used with a electronic dial indicator and a surface plate to measure height differences (peaks and valleys). When this is printed out full scale of paper it can be used as a map showing peaks needing sanding or lapping. I have done spot sanding before with 600 grit. If I even suggested hand scraping the say titanium bars I would have been removed from ever working on the multimillion dollar equipment ever again. I am talking about measuring surfaces where water moisture, water spots, fingerprints would be 10 - 100 times permissible tolerance. All surface are cleaned with distilled alcohol and allowed to dry for hours.
using ground steel plate 1x2x3 inches and double sided tape to hold sandpaper or use sandpaper with peel off backing and you have a flat abrasive tool using 220 to 2000 grit paper. You can also use mold polishing stones to do spot polishing too. Ultrasonic stone polishers the Japanese have sold for many years now.
on larger objects optical tooling can be used to see if objects are flat to within 0.0001" for short distances and 0.001" per 17 feet. Of course they have lasers now that can easily measure the floor going down 0.0001" when a 200 lb man steps on a sole plate made for a 10 ton piece of equipment.
How you remove the high spots can vary from power scraper and ultrasonic stone polishers to sanding blocks. All require checking surface periodically and this is best done in climate controlled clean room as dust particles can also be 10 - 1000 times larger than working tolerances.
03-31-2010, 03:36 PM #20
Hell i dont plane anything since getting the surface grinder. Does a lovely job on the finnest of woods with a freshly dressed wheel. Its the number of nails i have to hammer into the work to get the magnetic chuck to stick that causes my problem!
Most bits even then check good on the optical flat, well at least till the humidity changes a fraction of a percent!
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