Doubts while flattening old irons - Woodworking Talk - Woodworkers Forum
 
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post #1 of 7 Old 11-06-2017, 12:30 AM Thread Starter
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Doubts while flattening old irons

Good evening folks,

I'm in the process of restoring some old wooden planes. One is a jointer, two are smoothing planes and one is a rabbet plane. Now the blades are in pretty bad shape and they're giving me a bit of a hard time to restore them to a point were I say I'm satisfied with them. Most of them got some real bad hollow spots on the back up to the edge.
I'm not a very experienced person when it comes to grinding nor do I own or have access to an electric grinder or belt sander, so it's my extra coarse DMT diamond stone, the irons and me against time.
While grinding the back I realized that different movement directions revealed different high/hollow patterns, which seems weird to me.

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I made this picture to try to illustrate what I'm talking about. I actually started this on a coarse sand paper on glass a while back and went back to it today. The first thing I noticed was that grinding on the diamond stone revealed completely different spots than on the sand paper with glass, which seems weird to me. Was my glass plate bent? Is my stone not flat?
The green section showed high when grinding straight forward from bottom to top of the stone. The orange section was ground afterwards rotating the iron sideways and rubbing it up and down the length of the stone. Then I got curious and made a circular movement which yet revealed a different high spot. Is this just normal? What am I viewing here? Apart from still having a lot of grinding left to do this made me doubt about me failing hard on the back grinding or something like that.

Another detail here would be that my stone got a goldenish color to it after grinding these irons. The rabbet plane iron looked really old and black, could that be the reason? Now when I took the photos I realized the other irons actually got this tone to it also, which is not notable with the eye. (It sure looks awesome on the photo). Is this something to be concerned about? Should I try to clean my diamond stone or can this be ignored?

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"Earth is paradise, which nobody cares for" - From a Mexican folklore song

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post #2 of 7 Old 11-06-2017, 08:29 AM
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The metal may be flexing under the pressure of your hands. Do you have a flat block you can attach the blade to so the pressure on the blade is perfectly even?
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post #3 of 7 Old 11-06-2017, 11:34 AM Thread Starter
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I do apply quite a lot of pressure indeed. I will see today if I can find something flat to use as a push-down and I'll also try to not apply pressure and let the grit do the work and see the difference. That might as well take days to get some of those irons flat though.
Any ideas on the goldish coat?

"Earth is paradise, which nobody cares for" - From a Mexican folklore song
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post #4 of 7 Old 11-06-2017, 11:52 AM
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if there's a high spot the iron will 'rock' on the high spot....it only takes a micron or three of gap and the scratch pattern can change.

eventually the high spot will wear down and you should see an even pattern.
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post #5 of 7 Old 11-06-2017, 05:15 PM Thread Starter
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I thought it might be just a very little high spot, I suppose it's still a lot flatter than before I took it to the stone. No ideas about that patina?

Actually here's another doubt I have. The huge iron of the jointer is coated in black for most part. Is this what they call black rust? Or some kind of antique patina? Should I leave it? Should I try to clean it?
Doubts while flattening old irons-jointer_iron.jpg

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post #6 of 7 Old 11-06-2017, 05:52 PM
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the black could be left over from heat treat, if they did that - an oil quench can produce a nice black patina.
or a chemical dip ala anodizing. like blackened grill/stovetop grates for example. note that the little nicks and dings show a thickness more than what one would expect from patina - i.e. could be paint?

the brownish / multi-colored is likely plain ole' oxidation - perhaps with a bit of color from a preservative oil coating that has dried up?
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post #7 of 7 Old 11-06-2017, 08:29 PM
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When you sharpen a tool on a "stone", move it in a direction that makes the scratch lines run the length of the tool. If you do a cross pattern the edge will be more fragile. Diamond "stones" work best under water. It allows the sharf to be floated away. As long as the tool is flat at the cutting edge, you don't need to do more grinding. A hollow grind on the cutting edge via your bench grinder will make it much easier to get sharp. Just get it straight across.
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