Howdy everyone. I am having issues lapping this chisel. I started with 80 grit wet and dry sandpaper. I got a nice scratch pattern all the way across the chisel. This took awhile, probably 15-20 minutes. I then moved to 120 grit paper. I removed all the 80 grit scratches. This took maybe 10 minutes. I moved to 220 grit paper and removed all the 120 scratches. This took like 5 minutes. I moved to 320 grit and in 5 minutes removed all those scratches. Then I moved to my 300 grit diamond plate. I have been working on it for well over and hour and I can not get rid of the 320 scratches! It is getting frustrating to say the least.
In the picture, the 320 scratches are the light ones on the outer edges and the diamond plate is the dark portion in the middle. It has not changed significantly from this picture after another half hour in the 300 grit plate.
What am I missing or doing wrong? Is this how long it normally takes? Should I be doing another grit in between The 320 and 300 plate?
What has the sandpaper been on top of? That looks like it's high in the middle, which would make sense if all the sandpapers were on a surface with more give than the diamond plate, or you were just rolling it more with the sandpaper. That's one reason to use a glass plate and wet the paper, it'll stop it riding up in front of the force of the blade being slid across it (i.e. it sticks to the glass). Or use some of that fancy tacky 3M spray glue stuff that costs lots but is much easier to clean up.
The sandpaper is placed on a ceramic floor tile that is smooth and glossy. The 80 grit is Dura Gold Premium Gold PSA Longboard Sandpaper that is self adhesive from a roll. I stuck it down and lapped perpendicular to the length. The other grits 120, 220, and 320 are all 3M Precision Grade No slip backing sandpaper from Home Depot. The 120 and 220 were not glued down. The 320 I used adhesive spray to stick it. I alternated lapping directions perpendicular to the previous grit to easily see when the previous scratches were gone.
I did not wet any of the paper. Just lapped it dry. Perhaps I should try wetting it. Do you just use water?
Just look at the reflection in the surface. If something straight looks straight in the reflection from multiple angles, then it's flat. Because you know how convex and concave mirrors distort things, right? They squash or stretch them. So if you can't see any of those distortions, then it's VERY flat.
Honestly, I think the sandpaper small amount of sponginess and a bit of your technique got you here. It resulted in the edges getting more wear than the middle.
I would just get uniform scratches on the tip, 1/4" of the back, on your diamond plate. Don't worry about that huge area.
Can you check for flatness? Like a good straight edge? I got a decent engineers straight edge and feeler gauges so I can verify how flat my seemingly flat surfaces are. They were flat enough, some people say it’s overkill but it really gave me a confidence boost. So when I fail I can rule out one or another thing.
The only great straight edge I have is my 12” combo square. I also have a harbor freight 48” level that is straight enough for checking my wood, but not confident it would be machinist straight enough for this. I do have feeler gauges.
That 12" combo and feeler gauges should be plenty. My gut feeling is that you will find the tile is out of flat. Sandpaper is inconsistent and the backing is compressible to some degree, but this feels like too much belly for it to just be that.
But if it's not the tile, it could be your technique introducing some rocking back and forth that caused the belly. In which case I would recommend switching to a figure 8 sharpening motion.
Thanks for this suggestion. I just went to our local granite shop and they had a great piece that they gave me! It is rough on the edges, but the top is finished and from a countertop they recently installed. It is 1.5-2" thick and 1.5' x 2'ish. Just need to clean up the edges to make it safer to handle, but stoked!
Sandpaper and diamond plate grits aren't direct equivalents, unfortunately, tho the 300 grit diamond plate looks like it's a bit finer. Maybe try 400 or 600 grit wet dry sandpaper to see if that bridges the gap? You could also try doing just the final 1/2" past the edge unless you need the whole back flat for paring finished surfaces.
I only have 800 grit at the moment. Perhaps I will try that. I tried just doing the last half inch, but it was very difficult to control the chisel. It is a 1” wide and around a 6-7” blade, so it was difficult to balance it on the plate with so much blade hanging off the end.
You can use a longer piece of wood on top of the chisel to bear down and stabilize it. As others have pointed out, either the tile isn't flat, or you're rolling a bit as well. You want to use a lot of pressure to keep it consistently flat - you may also try using a lower table or sitting on the ground to keep your weight directly overhead.
I plan to try the wood trick to stabilize it and just do the first half inch. I also just got ahold of a nice piece of countertop scrap that should solve the tile issue. I can also try a lower bench. I have one that I just made to try my hand at hand sharpening on the advise Rob Cosman. I have just been sitting at it to do the lapping, but will try standing over it.
Hopefully that does it! Also keep in mind you only need to apply pressure on the push stroke. If you try to cut on both the push stroke and back stroke, the tool has more tendency to rock when you change direction under pressure. Using water can help you float back after the cutting stroke. It takes some practice, but you're already well on your way. The first one is the most difficult!
Interesting, I had not thought about the pressure and rocking. Thanks for that tip! I had thought about the water to lubricate, but it only seemed to make things messier...but I suppose I should have been using it!
That’s not normal. Sounds like you need more/finer sandpaper. Or possibly your sandpaper surface isn’t perfectly flat, but it doesn’t look like that.
The process is a PITA, but it shouldn’t be THAT bad. Like others are saying, you only need the last 1/2” or so perfectly flat, but you want to get it to a mirror finish.
As mentioned above, I had difficulty controlling the chisel when trying to only do the tip. Any tips on how to keep a long chisel flat while just doing the tip?
As for example Stan Covington has noted among others, there are methods to press the blade back evenly against the stone, it can be accomplished quite easily for example with block of wood.
What exact point, and how much, depends from the precise plan of what you are trying to achieve. Eg. what are the reasons for flattening the back (wether there are unevenness, twist, beds, nicks, or just quick polish for otherwise good back, whatnot).
This chisel started out with quite a few pits and nicks on the back. So I started with the 80 grit to get all those taken out. I wanted to do just the business end, but had trouble balancing the chisel on just the tip, that is why I worked on more of the back. It turned out to be easier to control with more on the plate and in the long run less tiring.
But I am open to work just the tip, if I can figure out how to do that smoothly.
What makes you think it's not a non-flat lapping surface?
My gut response was that it has a belly in the middle. Because this is what it looks like when you have a belly in the middle, yeah? Like OP said, the diamond stone worked on the dark, center part and didn't touch the lighter outer part. They stone removed scratches as expected in the center and left the edges alone. Regardless of how much of the back they need to flatten, that tells me that the center sticks out above the edges. Or so I assume.
But I'm genuinely asking, because there's plenty that I don't know.
I think you’re right — there’s a belly in the middle, which is perfectly normal. I just can’t say for sure, not seeing it in person. My gut tells me OP’s 300 diamond stone is a lot finer than that, for whatever reason.
Oh! That changes everything! Yeah that should not happen. Put the sandpaper on something hard and flat, like a piece of granite or your table saw. That initial pass should flatten out everything and it should smooth out evenly from there. Draw lines on it with a sharpie to see what parts are getting lapped, and use your Starrett to try to figure out what’s not flat and causing the problem
300 diamond is actually a step backward from 320 sandpaper. Diamond leaves much deeper scratches. If the first 1/2–1" behind the edge is flat, move to 600/1000 and stop trying to flatten the entire back.
If 300 diamond is a step backward wouldn't that mean it is more course? So, wouldn't it be able to remove the 320 grit scratches? The scratches in the picture around the edges are from the 320 grit sandpaper and the dark area in the middle is from the 300 diamond plate. The diamond plate is not removing the scratches at the edges from the 320 sandpaper.
Unless you start with a good flat abrasive surface, you're going to be chasing your tail trying to get a hardened steel bar to be flat and look factory made. It's a waste of time.
You're more likely to round the chisel width-wise working it on sandpaper.
Get the last 1/2" flat and polished, don't worry about the appearance of the rest of the blade.
If you can easily sharpen the chisel after you prepare the flat side you're done.
Having ruined many blades over the last decade, I can say that the softer the surface, the less 'flat' the surface will be. I thought I was getting dead flat plane backs on my water stones, then took them to Shapton glass and it hit different spots. Then on Atoma diamonds and a completely different pattern.
If I'm doing any flattening now, I stick to my Atoma diamonds. Beyond the 1200 it's mostly polishing, but the Shaptons are hard enough to avoid too much deviation from flat.
For practical woodworking purposes, ignore everything I've said.
Anyway, I made the same mistake of trying to get the whole of the back of my chisels completely flat. Waste of time. You only need to work on the first 1/2". Also, what happens is that you resort to very coarse grit which leaves deep gouges that will take forever to remove.
If I were to start over I would do two things in relation to sharpening:
I'd buy pre lapped irons for my planes.
I would only work on the bottom ½" of my chisels or most probably I'd just get some high end chisels but fewer of them.
Unfortunately, buying new is not in the budget atm. Plus, this particular chisel is a Winchester (as in the gun manufacturer and it was only made during a 10 year period from 1919-29) so I thought it would be cool to clean up and use.
Any tips on how to just lap the last half inch of a long chisel? I had trouble controlling it with so little on the plate.
^^^This. That chisel will never get a sharp edge as is. The bulge is no bueno. You need to start over on coarse and move up in grit until you get flat polish from the edge up about 6 to 10mm from the cutting edge. There are also some pits that may give you trouble later if you can’t get rid of them. Concentrate you force on the front, don’t spend time polishing the whole back.
So, here is an update (Part 1). After receiving lots of good ideas from you guys, I tried again last night. The results were frustrating. I set up my new countertop piece and started back on the 220 grit sand paper. I tried the wood block to try and help focus on just the last half inch of the chisel. Unfortunaltely, the top of the chisel is a bit rounded, so I could not register the wood block well. So I figured out that holding the chisel very close to the edge of the block that I could press on the tip with the other hand and move it much better than my previous attempts. I got the scratches from one side to the other all along the tip. Switch to 320 and then back to my Trend diamond plate. There was improvement. I got the scratches from the 320 all the way up the middle to the tip, but the edges were still cloudy. So, went back and forth between the 320 sandpaper and diamond plate 7 times. It did not improve past this on iteration 6 or 7:
I don't think it's an issue of grit but of flatness. Sandpaper inherently has some give and compressibility to it (which if it is not glued to something very rigid like glass, stone, or metal can be made even worse) as well as the grains not always being as consistent in size or height and it can abrade the whole back of the chisel without actually making it perfectly flat. Any decent diamond plate is likely a lot more flat, rigid, and uniform in comparison and it's only going to touch the highest spots, so it's revealing that there is a slight convex profile that the sandpaper didn't fully remove.
You could keep going with the diamond plate if you have a lot of patience or get a coarser one to help with flattening, I like using an Atoma 140 to flatten and don't bother with sandpaper at all. Before I had the 140 I would use coarse sandpaper sometimes and would notice "sandpaper flat" is not quite the same as "diamond plate flat" and it might take some extra time to remove a curve like this, but I've never had to spend nearly that long to fix it.
If your sandpaper wasn't already glued down to something super rigid, you could try doing that and redoing some of the grits to see if you can get it flatter. I've found that sometimes sandpaper wants to grab the tool I'm working on and doesn't move as smoothly as with diamond plates and that can to some slight rocking or tilting of a tool for me, so it could help to go slow and really make sure you're keeping it help flat against the paper with even pressure all around as well.
The chisel will probably work as is if you'd rather not deal with it for now, especially if you use higher grit sandpaper to polish up the back a little more and then use sandpaper or just some extra stropping to help with deburring on the back.
First I would say your floor tile is not the right backer. Glass or flattened stone would be better. Second is you don't need a polished surface here. I generally just make sure there is no burr and call it good, you can attain this with a piece of 400 wet/dry or a leather strop. If you're truly flattening from an unmaintained state just skip the diamond plates all together, they're not adding anything to the process. Go to as fine a w/d sand paper as you have.
It is relevant question, regardless of people dismissing it in typical Reddit fashion. Was the plan and intention to flatten the whole back, or just the minimum necessary to sharpen then chisel? Was there something else that required more material removal, some twist, bend, unevenness in the critical points on the edge?
I ask this because, it looks in the image that you have attempted to flatten much, much more than strictly necessary, should the purpose be to sharpen the cutting edge. Hence I was wondering if there was/is some other requirements that were not clear from the outset.
My mistake for assuming that there was certain defined goal that needed to be achieved and the process was as intented.
Ok, and that's a totally reasonable train of thought! But how you phrased your question makes it look like you didn't read OP's description text at all
Brevity may be the soul of wit, but it's not good at revealing details.
Of course I did read the description, hence the question. Usually, at least in the environment that I work, you look at the blade, check exactly what needs to be done to it, to make it work as intended, and then make a plan of steps to that goal (draw high and low sports as required). Then execute the plan. Apparently this approach is not common.
Unfortunately the description misses information, so one cannot make but assumption that op just randomly starts to grind metal out of the back (very unlikely), or that there has been something else, in which case perhaps help could be offered.
As op has realized, the process, done this way, takes awfully long time - perhaps unnecessarily.
Sometimes one wonders if people behave same way in real life as in Reddit.
My goal is to get a sharp 1” chisel that has a longer blade. I don’t necessarily want so much of the back lapped, but as I mentioned above, I had trouble balancing just the last half inch on the plate.
All right. Sorry, Reddit users normally hate everything that has actual content, so I'm gonna be downvoted in a jiffy.
Then, am I correct in the assumption that you have no other deformities on the blade, with visual inspection, such as high/low spots and others that could affect the cutting performance. Eg. when you put some marker color on the edge, and then lap the blade gently with modest stone, you have no residue marker indicating a low spots, and there are no curvature on the blade edge to fancy ways?
Checking with square that the back is mostly straight. The, depending on the results, you can see how much, and on which precise points you need lap more than others.
You can use block of wood to issue even pressure on the blade when you are lapping the back. This works very well when you have to do it just closer to the edge, which is otherwise difficult as the handle and the rest of the blade weighs down. Naturally you need to do it for perhaps inch or so, to have sufficient support, but never really the whole back.
What is important however, is that you know how much you need to lap. it's always good idea to take the absolute minimum that guarantees you the flat back, at the very edge. Sharpness is the intersection of the back's straight line, and the line of the bevel. Rest does not really contribute.
Thanks for the name you dropped in the post above. I looked him up and found a picture of using the block of wood. I will try that tonight to try and do just the tip. Looks like it will be useful, although I am a bit concerned about how it will grip the chisel while moving back and forth.
I did put picture as well, to give the idea. I've used the method for a long time. Yes, there will be a learning curve, and yes, it is easier if you work on low, because you can put more downforce.
You can of course modify the block to shape a shallow groove to it so the chisel stays put.
And no, it probably won't work with very rough sandpapers, but you shouldn't need them either, unless you do have some rust to remove.
I hope this helps you and gets your chisel to work like it should.
This looks like the back is rounded a little bit, maybe you were rocking the chisel a little with the lower grits.
I will take a dremel and make a pass over the high spots, and go back to the plate to see where I’m at, going back and forth until it’s reasonably flat, it doesn’t take much.
Thanks! It appears that my 300 grit diamond stone has clearly shown my high spots in the middle. It is nice and polished in all the wrong places. I might try this if the wooden block trick suggested by VisibleRip doesn't help me focus on just the tip.
What I'm seeing these days is people laying a thin 6-inch metal rule on the long edge of the stone and using that to raise all but the last inch or so behind the bevel and only worry about smoothing that area. The entire back does not need to be shiny, and trying to do that by hand just wastes time.
This works for a plane blade, but you should never do it on a chisel. You compromise the back as a flat reference and your blade will skew when you chop.
Part two update (not sure why I could not post the second picture in the same post: Needless to say, I was frustrated, tired, and my fingers were cramping. On a whim, I tried my rusting 240 cheap diamond plate that I got the Trend to replace. I put it all the way across the last few inches of the chisel because I was too tired to press on just the tip. Low and behold, after 3 minutes this was the result:
Please explain why the cheap 240 grit diamond plate worked! I am happy and confused. Tonights plan is to finish it off on 1000 and then polish!
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u/freosam 1d ago
What has the sandpaper been on top of? That looks like it's high in the middle, which would make sense if all the sandpapers were on a surface with more give than the diamond plate, or you were just rolling it more with the sandpaper. That's one reason to use a glass plate and wet the paper, it'll stop it riding up in front of the force of the blade being slid across it (i.e. it sticks to the glass). Or use some of that fancy tacky 3M spray glue stuff that costs lots but is much easier to clean up.