Fair Woodworking

January 31, 2012

Lap a chisel back in 6 minutes

In previous posts Here, and Here. I’ve been discussing the issue (or non issue) of flattening stones. I’ve tried to show how and why many popular systems are not effective, but have neither offered a better solution, nor even proven that it is necessary.

Today, may just be that day…

I’ve put together a little demonstration here. I call it a demonstration rather than an experiment, because I knew what the outcome would be before I started.

Editors note – I’ve noticed that I did not include any instruction on lapping technique in this post. The reason is that you can find it else where, and it really has nothing to do with the speed of my process. It’s all about the stones today.

I found a couple of my old Narex chisels that for whatever reason had never been sharpened, or lapped. The larger is 20mm wide (a little over 3/4″) and a smaller one that no longer shows its size in metric but is about 5/8″. The rules of the game are this. Lap the back of one chisel with my flattened stones until done.

Then lap the second chisel for roughly the same amount of time with some “new to me” stones that have been flattened to a less stringent level.

I know who is going to win in this little game but I want to be fair here, so I’ve chosen the larger chisel for my stones, and the smaller chisel for the new stones.

So let’s get started with the wide chisel. First I just quickly rub the back on my 1000 a couple of times just to see where the high spots are. It looks like there is a hollow in the middle of the blade.

Now I do the same thing, but this time I’m looking to remove the old milling marks. I could go further, but I don’t know if it is really necessary. The blade will register on the flat just fine in use just like this.

Next I go to the 4000. I’m spending about the same amount of time, and again, just trying to remove the scratch marks of the 1000. Look closely at this pic vs. the previous. On the 1000 the scratch marks go from front to back. On the 4000 I went from side to side. It’s easy to see when the 1000 marks are gone. You should also notice that the size of the lapped area has not changed much. That is because the 1000 and the 4000 are almost exactly the same shape so the touched only in the same areas as the 1000 did.

And then on to the 8000. Again I spent about the same time as the other two stones. Again note the absence of the 4000 grit scratches, and that the lapped area has changed little in size. I do see a very thin strip of light on the sharp edge of the blade. I suspect this is a very light burr.

This whole process according to the time stamps on the pictures took 13 minutes. The majority of that time was me fumbling with my camera. I’d say that 6 minutes is more than realistic for a total working time.

Now on to the smaller chisel on the new (suspect) stones. My plan is to work this chisel no more than the last.

A quick swipe on the 1000 to see the lay of the land. Seems to be a little more hollow on this one.

Getting to this point took roughly the same amount of time as the other chisel.

Switch to the 4000, and again a similar amount of work gets me here. The first thing to note is that the lapped area has grown a fair amount. The second is on the blade edge. Can you see that darker grey strip the full length of the edge? This stone completely missed the cutting edge, but removed a bunch off the back further down. Not good.

On to the 8000. This time the lapped area doesn’t change much so we can assume it is the same shape as the 4000, but look at all the scratch marks that are left over from the previous stones, and the unlapped area on the cutting edge now has caught the reflection of the light. It’s still there, this chisel at a glance is lapped, but in truth is not much better than when I started. It’s hard to say what stone was not flat, and it could be that all three were not flat. For sure we know that the 4000, and the 8000 were similar is shape, but the 1000 was not the same.

I wouldn’t bother to try, but if I continued using those stones, I suspect that properly polishing them would have taken at least half an hour or more because of the extra work those stones would have to do removing extra material.

I’ve been accused of being anal with my stones, but the time I take flattening is no where near what I would invest in lapping blades with un-flat stones. Let’s look again at the popular flattening systems in their best light and applicable cost.

Sand paper on a flat surface. Your kitchen counter top would be free, but not very flat. Lets go with the granite slab from Lee Valley. At $36.00 the price is right, and with a tolerance of ±0.0001″ it is the flattest surface I can find (the Veritas straight edge is only ±0.001″). The problem is that sand paper is notorious for not sitting flat, and being costly in the long run.

Norton Truing stone. Video of the Christopher Schwarz method of flattening his truing stone. $29.00 (if you are considering buying one, PLEASE watch the video first!!!)

Editors note – Sadly the link no longer goes anywhere. It was a video of Chris smashing his Norton Truing stone with a hammer. The simple point. It’s a worthless product. WORTHLESS I TELL YA!!!

Diamond plate. Option 1. Diamond stone from Lee Valley measuring ±0.005″ That’s 5 times less flat than the straight edge. $109.00 That’s big money for something that is 25 times less flat than a Veritas blade back. You will be almost guaranteed to mess up a blade if this is what you flatten your stones with.

Option 2. DMT Dia-Flat Diamond Coated Lapping Plate from Lie-Nielsen measuring an impressive ±0.0005″ but at a price of $195.00 you won’t want to loose it, and you will still be 2.5 times less flat than the veritas blade back.

Of all these options I’d say the DMT will give you the best result. I would say that my option is at the very least as effective as the DMT, but I can’t prove it. Why? Because I’m not prepared to drop 200 clams to get something I don’t need.

This post has been rather labor intensive, and I’m starting to fade. I can’t believe that what seemed like a quick little topic has now morphed into 3 going on 4 posts… I hope that at the very least I have provided a decent argument for the value of flat.?

Next time for sure! I’ll show my flattening system.

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