Lapping

Excerpts from The Message Boards

Bill Tindall: We have found that diamond paste or powder charged on some flat substrate provides cheap and rapid lapping and sharpening of tool steels. I initially dismissed diamond as too expensive for mortals to use, in spite of the fact that all the abrasive manufacturers suggested it for steels of Rockwell 60 and higher. Turns out it is very cheap. It takes but a few cents worth to turn a piece of cast iron into something equivalent to an expensive diamond bench stone, a very pleasant surprise.

3V steel can be rough ground with any abrasive suitable for tool steel (I use ruby wheel and others use ceramic wheel or belts). The Makita powered water stone abrades it at an acceptable rate, but much less rapidly than high carbon steel. I will report on an optimized procedure that is cheap and fast.

Some very preliminary work has been done using acrylic (plexiglas) as a substrate for diamond powder. The results looked promising, particularly considering the very cheap cost of an acrylic plate. Further evaluation of acrylic is needed, but I am not highly motivated to do it as I have settled in with cast iron. However, if no one else does, my curiosity will get the better and I will likely do it.

I have been pleased dealing with Reentel.com for diamond powder. Only $1 per carat. We are in the process of settling on what grits are really essential. It turns out less than for grinding hard rocks. Maybe as few as 3 or 4 to go from serious material removal to near mirror.

I have such limited experience with waterstones as to not be of much value making comparisons, except to say that they are a vastly greater cost than diamonds on a plate of some sort. And I don't like the fact that they are only 8" long. Now used to 12" lengths I cannot go back to shorter sizes.

If a plastic is used for a substrate it needs to be as hard as possible. Hence, acrylic could be the preferred choice as it is one of the hardest plastics readily available. Also it is readily available from MSC etc in an optical grade which means sufficiently flat for sharpening. I have not had any experience with phenolic resin for a diamond substrate so I can not comment. It is fairly hard.

Amen to the great difference in abrasion resistance of modern tool steels compared to simple carbon steel. It is a simple fact that the alloy carbides are greatly harder and hence more abrasion resistant than iron carbide.

Bob Woodburn: I'm not so sure about the generalizability of "lapping = convexity". It's possible that you and I are merely members of a race of men for whom that's true in certain circumstances...using certain methods and techniques...and in our present uncertain state of development. I don't completely discount the idea that you or I might someday emerge from a cocoon and fly off with the others.

There was a ton of "Pond" posts on this topic in years past characterized by much testimonial and no consensus. Even here and now, various WC members routinely describe or imply the "flattening" either of plane soles or of cutter face/backs by, in effect, lapping. I often wonder if 1) they are somehow simply gifted, or 2) they never bother to put a good straightedge inspection to their work. Either way they seem happy with the outcome.

Just last night I needed to true up a water stone. In effect, I lapped the stone against an EZE-lap diamond plate. In less than 2 minutes I could wring them together so tightly Hercules himself wouldn't separate them by pulling. I lapped the sole of the Spiers plate flat...I thought...on the cast iron lapping plate. I lapped it smoother with a 123 block wrapped with abrasive paper. What I can't seem to do successfully is use what amounts to the "Scary Sharp" method to get things flat.

A couple years ago, I lapped 3 plane soles together in the tradition method of "originating" a flat surface: abrading A to B, B to C, C to A in long series of iterations. I wanted to see if it could be done. It seemed to more or less work.

Three ordinary block planes:

I've marked these with a little tag of tape so I don't mix up A and B and C. Clover compound, for those of you who don't know it, is basically SiC in grease. It comes in various grits. If you recall the look of this workbench from the infill pictures, this is the bench surface 2 years ago. Appalling, eh? Incidentally, for those who don't recognize it immediately, that odd looking, gray, pre-Columbian mother earth looking object is a hunk of clay. At the time I thought I'd model the next generation ergonomic plane handle, become rich and famous, and retire to a secluded paradise. I dropped the idea when I realized I'd get lonely, bored and paranoid.

There may be intervening photos, but I don't find them. This is the result of an hour or so of A/B, B/C, C/A rotation of rubbing the soles together (like rubbing your hands together on a cold day). A little dab of Clover compound is all that's used as abrasive. Every once in awhile I'd clean and spot the three of them to see how much progress I'd made. This is probably where I stopped.

I think this was poplar.

A nice piece of mahogany.

Steve Elliott: My experience is the same as yours. Scary Sharp methods using abrasive papers have always given me a slightly convex surface, especially at the edges. It's the edges (some of them) that I especially care about: the leading edge of the mouth on a plane sole, the business end of the back of a plane blade.

Using waterstones, I tend to get a slightly convex surface using the coarse stones, but as the stones get finer, the surface gets flatter. By the time I'm done with 8000x, the surface is almost optically flat clear up to the edge. (Not that I go to 8000x on a plane sole, but I can get it as flat as I want.)

Using a cast iron lapping plate and 1 micron diamond compound, the results fall between the other two methods. Not quite as flat as the waterstone method, but way better than abrasive papers. I use W/D paper on a granite surface plate to flatten my waterstones, which probably leaves the edges dubbed a little. That doesn't matter, the stone still gives me a flat, non-dubbed surface on my blade.

I use waterstones to lap the backs of my blades and to remove the wire edge that forms when I hone the bevel, and use a lapping plate with diamond for the bevel. That combination gives me both speed and accuracy.

Bill Tindall: I probably should say diamond grinding plates, at least for the coarse sizes. I talked with a person who makes his living polishing precious stones. he was most helpful and supplied the following information.

How do you charge cast iron lapidary wheel (presuming charging a cast iron plate will be equivalent)? Answer: Brush cast iron surface with wire brush. Then, scratch perpendicular to lapping direction. Use razor blade and scratch every 2 mm. (This operation provides a place for the diamond paste to lodge)) Smear on diamond paste with finger, not too thick.

What grit do you use? To find optimum grit start with the coarsest grit you intend to use. Then step directly to finest grit you need to use. If this fine grit is too slow at removing scratches of previous grit then split the difference with an intermediate grit. Usually 3 is all that is necessary. (but he does not start with very coarse grits. he steps from 6 to 1/2 micron for stones. Metal should be vastly easier to grind than precious stones)

Are their substrates other than cast iron that could be useful? Answer: Tin alloy but it will probably be too soft. Ceramic for the final grit cuts very fast and stays flat. He highly recommended it for final grit. (I have ordered a sheet of ceramic for evaluation) Finally he said that Corian has been used with success. (Corian is acrylic filled with some mineral and pigment filler. This information makes me think that Plexiglas (acrylic) may well be the most cost effective substrate for our use- $3 for a 3 x 12 x 1/2" piece from MSC.

To make this discussion clear let me define bench grinders, LV sharpening system, belt sander, hand crank grinder, etc. where the abrasive particles move past that to be sharpened at relatively high speed as "power grinding". When the object is moved by hand at slow speed across the abrasive i will call it "hand grinding". And, we will not further define what we are doing-lapping, sharpening, etc. and just lump it all into metal removal.

The most important thing I have learned in sharpening is that all of the worn edge must be removed to establish a new sharp edge, be it planes or scrapers. Therefore, the objective of the first stage of sharpening, "Step 1" is removing enough metal to remove the old worn edge. Formation of a burr indicates that this objective has been achieved. The rest of the sharpening process(I will call these steps "Step 2") consists of removing the scratches of the previous grit size to establish a finer scratch size. This process continues through successively finer grits until "it's good enough". Compared to Step 1, very little metal is removed in all of Step 2

These steps can be easily followed with a 10X lens and it is informative to do so. Fundamental Principle** If in Step 2 the reduction in grit size between steps is not huge, these steps require very little abrasive action(time). If you have read our article on sharping with abrasive sheets (Articles Section) we show that only a few hand grinding strokes are necessary to remove previous grit scratches and the abrasive lasts a long time. The secret is to not make big jumps in grit reduction.

It seems to me that power grinding has its greatest benefit in Step 1 where a relatively large amount of metal must be removed. The turning community enthusiastically employs this practice. If the scratches in step 1 are coarse and the goal is very small scratches at the final edge, then two approaches are possible. Big reductions in grit size can be made with the need for a lot of grinding at each step ( and resultant great wear on the abrasive).Either power grinding or tedious hand grinding would be required. If relatively smaller steps in grit size reduction are used in Step 2, very little time is required at each step. Hence, the desired result is easily and cheaply achieved with hand grinding. The "cost" is the necessary inventory and inconvenience of more abrasive devises (stones, paper, lapping wheels, whatever) to cover all the required steps.

Diamond cuts much faster than any other abrasive we have tried. Hence, the steps between grits in Step 2 can be bigger, maybe much bigger, that we recommend in the abrasive sheet sharpening article. For aluminum oxide and silicon carbide a size reduction of about 30% per step is recommended. For diamond a factor of two is recommended and our preliminary work suggests a factor of 4 is possible for tool steel.

I don't know if the following will work, because I have not tried all the steps and materials in a controlled fashion. But I think it has a good chance of working based on what has been done. I mention this information to encourage others to experiment with what I think could be an effective approach that doesn't cost much to implement.

Step 1- power grind with something that will quickly establish a burr.

Step 2- Using cheap diamond charged on cheap 3 x 12" acrylic plates, or more expensive cast iron plates (more on this in a later post), take about 5-10 hand strokes using 60 or 30 micron diamond. 30 vs 60 will depend on how coarse the scratches are from Step 1. Repeat with a grit 4 times smaller. Continue until it is good enough. I have been stopping at 6 micron but most will want to go to 3. My planning objectives are such that I have no useful information as to whether even finer grits can be beneficial. Most of us already have a power grinder to achieve Step 1 objective. If one sharpenes more often than I tend to do, Step 1 may not even be necessary. Less than $100 will purchase the acrylic and a near lifetime supply of diamond paste or powder necessary to achieve Step 2. (12 x 12 acrylic plate is about $12 and diamond paste is about $15 for 5 grams paste or $24 for 25 carats of powder).

do have a fair amount of experience using the above approach for lathe tool sharpening and have found it quick, effective and cheap(I stop at 15 micron for fine turning work). I am about to do a lot less latheing and more planing and chiseling so may have more to say later. bottom line to this long winded answer, I think it makes more sense to power grind on the coarser grits and hand grind for the smaller.

Robin Frierson: Bill I have switched over to diamonds exclusively for the backs, and wonder what type of efforts you take to prevent contamination between grits? Do you wipe the iron between grits or take more action, like washing them. I have found it easy to get the coarser diamonds into the finer diamonds unless the iron is cleaned between grits, as the oil based binder clings to the iron. Do you also find the diamonds embed themselves in the cast iron, or can you easily clean the plate and reuse it with a different grit?

Bill Tindall: ESSENTIAL! I wash the tool with mineral spirits that I keep in a handy dropper bottle and then wipe with clean paper towel from the paper towel rack my wife thoughtfully provided. It is believed that the diamond does embed in the cast iron and that is why it works and regular iron works less well. By embedding it becomes stationary while the tool rubs back and forth. All reasons why acrylic could be attractive. At $3 for a 3 x 12 sheet I wouldn't feel bad throwing away a contaminated plate. I am sure the lapidary people have some means of dealing with contaminated pates, but I failed to ask.

Lyn J. Mangiameli: A great presentation for this forum. While I recognize in this setting you are limited in how widely you can cover all factors (and why readers should also read your referenced article on abrasive sheet sharpening), I'd like to emphasize, however, that some of your recommendations and conclusions are also affected by factors that at some point would be wise to integrate into any current discussion. The first is heat production (influenced by many factors including abrasive size and shape, speed of power grinder, and cooling medium) which for some steels will have considerable influence on edge life. This may affect choice of power grinder, as the heat generated in step may become a dominant factor, irrespective of later edge refinement.

Second is the ability to achieve repeatable presentation of the tool to the sharpening media, whatever that might be (singularly or in combination). Your statement of rapid removal of previous scratches can only be achieved if the tool is consistently presented to the abrasive. Any variation in presentation (either by change in bevel angle, change in approach to the bevel, or lack of consistent shape of the abrasive substrate [that is, flatness or variation from a defined curvature]) will require additional removal of steel to achieve the slight change in geometry in addition to the scratch pattern refinement. (This relative repeatability, of course, is the feature of such power units as the LVPSS, the Tormek, and the better hand honing guides. Interestingly, the size of the abrasive particles themselves can cause mild geometry changes in fixed carriage systems).

Third, is the issue of flat vs hollow grind achieved in your step one. Flat grinds on a large tool (particularly with some of the more abrasion resistant steels) are going to require additional time during your stage two to refine scratch patterns and will influence how large a step between abrasive sizes is advisable. My experience with non diamond abrasives is that with the more abrasion resistant steels, it can actually take a considerable amount of time using a finer abrasive to effectively remove a prior coarser scratch pattern.

A short simple discussion of optimal sharpening practice is almost impossible to perform, though I think you have offered one of the better brief discussions. I am probably most concerned with maintenance of a single desired geometry throughout all the abrasive steps, and ease with which it can be achieved. This is one of the major reasons why I am rather fond of both the Tormek and the LVPSS.

Again, none of this is intended to take anything away from this presentation, which I think is thoughtful, based on sound observations, and practical. It is just my desire to place it in a bit larger context

Bill Tindall: Couldn't agree more. No doubt I would own a low speed grinder if I would afford one. I think the perfect arrangement would be Tormek and then 15 micron diamond, or even less. And it would take but a few strokes to remove the Tormek scratches. Complete sharpening would be less than a minute.

If I had many plane iron backs to do I would take them to a machine shop and surface grind them once and for all. With a magnetic chuck one could do a bunch with one set up, certainly in less than a machine shop hour of labor.

Tim of San Leandro: So far I've had very good results using cold rolled 1018 carbon steel as the substrate for diamond paste/mineral sprits....I did lap the steel plates flat using abrasives and a granite reference plate. I stopped the lapping at 120 micron paper and used several circular laps as the very last passes to give "ridges" for the diamond. I'd suggest contacting customsandingbelts.com to get zirconia and AlOx papers at affordable prices for lapping steel or cast iron plates. I've got a Tap plastics down the street from me, I'll have to stop in and see if they've got any acrylic plates to try.

I get very good edges with this and still use the same techniques for sharpening as I did with waterstones....but the diamonds cut MUCH FASTER than my King waterstones and the plates have so far stayed flat. I do nothing before the diamonds....I'm not an antique tool junky. In fact, I just unloaded the few antique metal bodied planes I had and got some wonderful planes from Steve Knight. Hence, all the cutting tools I sharpen are already in decent shape. I thought about an 8 inch grinder but have since relegated that tool to the bottom of my want list. The rougher diamonds really cut steel (A2, O1 and Japanese steels are what I'm sharpening) FAST.

I start with 325 mesh (45 micron, IIRC) and go to 50,000 mesh (0-1 micron). I have a bunch of sizes in between - 600 mesh, 1200 mesh, 8000, 14,000? I got a package of different grits. By far, I use the 325 anf 50,000 the most. 325 for starting sharpening so I can quickly get to fresh steel and 50,000 for the final polish. My guess is that I could get away with just 325 or 600, the 8000 and the 50,000 alone. IIRC, Joel recommends only 3 grits for diamond compound sharpening.

The steel plates have been holding up really well, especially for the finer grits. The 325 grit plate definitely shows scratches from the diamond so I'll have to keep a close eye on that plate for dishing.

David Barnett: Exactly so.The lapidary use of acrylic (Plexiglass, Perspex, Lucite) is entirely limited to oxide polishes:

• Cerium oxide for quartz, beryl, tourmaline
• LindeA (alumina) for topaz, garnet, tourmaline, peridot

The heat generated with diamond further softens the acrylic, enveloping the grit. While the price seems attractive, there are better substrates.

Lyn J. Mangiameli: With regards to the fine honing compounds, if they are wax based sticks, then I suggest applying them to a comparably sized abrasive sheet like the 3M microfine .5 and .3 micron PSA films. This has resulted in an even and durable adherance of compound to the platter.

Those abrasives that come without a binder, or with a lighter binder (such as light oil) are more of a challenge, as you have found out. My current technique is to use a PSA backed mylar film such as LV provides (even thinner version that the LV are desirable but not always easy to obtain) adhered to the platter. Then create a very thin slurry of powder and water, which will make it a lot easier to work with the superfine powder. Apply the slurry to the laminated platter, and use a clean roller (for example a lacquered maple dowel you dedicated to this purpose and grit size) to press the particles into the surface of the mylar. Let the water dry, tap off the loose particles, and you have an effective platter which can be recharged with the same techiques.

I'm just getting ready to extend this technique to powdered diamonds, but haven't yet had the chance to experiment with dry and paste slurries of diamonds, but suspect they will adhere about as well.