Re: Lapping long planes - long response *LINK*
Derek Cohen (in Perth, Australia)
>Hi John
There are a number of options from which to choose when seeking to flatten the sole of a plane, principally those of scraping and lapping.
As has been stated, the important areas to level are the front and rear of the plane, and the front of the mouth.
Bubbear has written a tremendous article on the art of scraping, and it is a must-read as it will open you eyes to the difficulties and dangers of lapping plane soles. The link is below.
Personally, I have ascribed to lapping in the past, and continue to do so under conditions that are unsuited to scraping. Such as the Stanley #7 Type 11 I am working on. The sole of this plane has a low spot in front (and, less importantly, at the rear) of the mouth, which means that the whole sole has to be flattened. Scraping was not an option.
Today I received Zirconion Oxide belts (80 and 120 grit) following a recommendation of Bugbear, having experienced the futility of using ordinary sandpaper. The problem is not that it wears out too quickly, just that it does not remain sharp enough for a plane the size of a #7. This may sound tautological but it is easy to demonstrate in practice: there is a point where one can still lap a #5 while a #7 does not cut at all. This has to do with the downward pressure on the lapping surface reducing in proportion to the increasing size of a plane. Consequently, the larger the plane, the more sandpaper you will go through. Unless ... you use Zirconion Oxide sanding belts.
Don't use a cast iron tablesaw surface on which to do this. Not only is it not flat enough, it is too high to achieve sufficient downforce.
My lapping table is a 10 mm thick sheet of float glass that runs 1m long by 300 mm wide. It rests on a 18mm thick sheet of MDF and this is supported on a waist-high bench (my assembly table) that is equally flat. I have run my Starrett flat edge across it quite obsessively. (Sometimes I wake in the middle of the night, and check it some more). Because of the height of the table, I can press down on the plane, rather than push it. I try my absolute best not to do anything that might lead to a curvy sole. What you must NOT do is try and push the plane in the same way you would use in to produce shavings. If you do this you will cause it to move in an arc, and this will lead to the sole being likewise shaped. When you push on the plane (which has, as you know, frog attached and blade inserted but retracted), hold it as much near the centre as possible. Do not hold it by the totes as this may unwittingly encourage you to push it like a plane.
I'm either good at this or lucky. Probably lucky. I've done quite a few planes this way and I've been lucky with them as well.
Regards from Perth
Derek
Bugbear's article on scraping
