Thread: Flattening the backs

I did try the CBN wheel on a powered grinder in the name of science and... it wasn't a great idea. I'll try it on the hand cranked version in a few days and report back.

In the meantime I dug out the Sigma 120 again (the black brick). It needs to be constantly unclogged and flattened using course silicon carbide grit on glass or similar but once that is done - I'd forgotten what a beast it is. I can't use it without headphones - it's like there's someone's tobogganing a chalkboard down a gravel slope in my brain stem - but it cuts steel like no sandpaper, diamond plate or stone I've ever seen.

I might focus my efforts on making a decent magnetic blade holder, applying even pressure without tiring is probably the main issue.

I got this from Stuart Tierney a decade back, seems he's out of business these days so unsure if they're still sold.

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I can see a CBN wheel being useful if it was horizontal for this purpose.

Got there in the end. Sandpaper wheel on the Dremel plus course silicon carbide grit on the Sigma 120.

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PSA sandpaper roll on a long run of glass or anything flat. No stone comes close, and any that come close in speed will be friable.

Far more even scratches per speed than diamonds (so no strange stray scratches, equating to more speed per finish level).

Setting Up a Random New Mexico Stanley 4 - Part 2 - YouTube

I have used this same lap on at least dozens of vintage irons, possibly 100 and probably 200 vintage chisels.

80 grit sandpaper on the coarse side, 220 on the other then to the stones.

the complement to this lap is a scrap of 2x4 with two bolts through it to hold an iron (I'll fetch a picture) with a slot. You can use hose clamps if you're using single irons (not much of that around in vintage irons, though, at least not in planes worth using). The holder allows you to apply even pressure with two hands and your body weight rather than putting pressure on your figures, and it saves you from burning fingertips on a hot iron.

Any suggestions on sourcing something flat? I do have some thick glass but it's far from flat (though it's tempered). Would offcuts from fabricated stone benchtop supplier work?


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Tempered glass won't be as it is heat treated, you want float glass. Stone countertop should be suitably flat as well.