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I have used a 12”x9” granite block to fettle the #4 I use bit recently acquired a #5 that belonged to my great uncle. It looks good, and I’m looking forward to cleaning it up, but I assume that I need a flat surface that is longer than the plane sole. Is that correct? Thanks, John

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    In theory yes, but I would want to use a significantly longer surface if I were lapping a plane sole. That's not a problem though, there are numerous other surfaces you could use as the base for the abrasive, but that may not matter anyway because the first thing you should do is check whether the sole of the 5 needs any work. Depending on how you set it up even if the sole is way out of flat the plane could work fine, see Answer. – Graphus May 10 '18 at 12:06
  • This is helpful, thanks. It is an old plane so needs some clean up on the sole. I am planning to check for flatness when I do that. Either way, I will look to get a longer granite plate to use for this and future projects. The article you shared is helpful, thanks. – johapatro May 12 '18 at 16:32
  • Welcome. I wouldn't necessarily go with a granite plate for this, they are certainly one option but they are heavy/very heavy, can be expensive and a sheet of float glass such as a glass shelf, laid on any solid surface that is reasonably flat (e.g. a workbench) can be an exact equivalent. And as a reminder, kitchen countertop material can be more than good enough for lapping if you don't mind doing the work there. – Graphus May 13 '18 at 15:10
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Yes, assuming you're talking about using the granite block (surface plate I presume) as a backing for abrasive paper of some description. You'll want to use the diagonal (15 inches) which is just about as long as the sole and limit your overhang during each stroke to a couple inches. There may be some tendency to produce a concave surface, so you should check the sole for progress frequently. You can reduce high spots more quickly (perhaps on the ends if concavity appears) by concentrating your downward pressure above those points, probably one at a time.

Do establish a feedback loop which allows you to monitor your progress and get a feel for the effectiveness of your technique. Feedback here meaning measuring the flatness against a reference every couple minutes or so. Unfortunately your best tool for that may be covered with sandpaper just when you need it (the surface plate itself), but perhaps you have another straight-edge available that will suit. Use rocking (or the lack of it in the end) and perhaps feeler gauges to locate and measure spots not making contact.

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  • The method you described worked well. I used the diagonal and the plane cleaned up nicely. It did not seem to require much of any flattening, but I’m sure I’ll find out how right I am about that soon enough. Thanks much! – johapatro Oct 23 '18 at 2:49

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