Plane Lapping Question

[Michael Schwartz]

For Lapping I have been using a granite surface plate, and for anything to large for that a peice of MDF.

I know that using MDF is contraversial and isn't the best method and I am straying away from it at this point for float glass.

I am ordering a peice of Float Glass from Lee Valley and it is about 14 inches long, a few inches longer than my granite plate.

I have a hard time lapping anything longer than a #4 on the granite plate and I mostly use it for sharpening as a result.

I recently did a 4-1/2 with it that I could fit on the diagonals.

Anyway is it apropriate to use a circular motion when lapping? It seems like that might make for more efficient use of the space.

[paul womack]

For Lapping I have been using a granite surface plate, and for anything to large for that a peice of MDF.

I know that using MDF is contraversial and isn't the best method and I am straying away from it at this point for float glass.

I am ordering a peice of Float Glass from Lee Valley and it is about 14 inches long, a few inches longer than my granite plate.

I have a hard time lapping anything longer than a #4 on the granite plate and I mostly use it for sharpening as a result.

I recently did a 4-1/2 with it that I could fit on the diagonals.

Anyway is it apropriate to use a circular motion when lapping? It seems like that might make for more efficient use of the space.

Try this instead:
http://www.geocities.com/plybench/flatten.html


BugBear

[David Weaver]

I guess my issues with flattening planes have been not so much the method, but with getting a piece of glass large enough to do a larger plane - say larger than a #5.

I have a piece of glass a little over 1/2 inch thick - it's 12x18. Inevitably, you're going to run across a jointer that needs lapped, and you're going to be stuck trying to do it on a small plate as I was. I had my 12x18 piece custom made out of tempered glass and it cost $90. I wouldn't do it again.

Yesterday, I called a glass shop with a different approach - asking if they had any scrap float/plate glass that was about 1/2 thick and 36 or more inches long, and low and behold, they said they had over 1000 pieces of similar stuff that they sold for shelves in cabinets. The piece I got is only 3/8ths thick, but I don't use it unsupported - I use it on a sjobergs bench. It was $20 with the edges ground - 8" x 42". Call around if you get glass - there are definitely places who will have something suitable. Keep the MDF as support for the glass if you get something thinner than 3/4ths, and hopefully, you have a straight edge of good quality to test the flatness - it's a useful tool for checking your jointed edges. My new piece of "cheap" glass doesn't have a gap as big as my smallest feeler gauge (0.0015") between it and a starrett straight edge, and that's plenty good.

Another tip, if you're looking for float glass, a lot of places won't call it that - but you don't have much to worry about if it's new glass - not much or none of the new plate glass is rolled, as opposed to floated, so you don't need to spend a bunch of extra to verify that it's float glass.

I don't scrape mine, I just use spray adheisive to bond wet/dry sandpaper to the glass, and then I dump some extra loose silicone carbide grit on the sandpaper for extra bite. It works pretty well.

Also, if you're not using the plane to shoot, you can get away with not lapping the cheeks - they're probably close to square anyway - maybe just not square enough for shooting. If they don't have pitting, and just patina, I use a "sandflex" block to clean them off - it works fantastic, and it's cheap and fast. You can use it to clean the rest of the parts, too - maybe you're already doing that?

As far as motion goes, I think people do the ciruclar or random motions becuase it cuts better - sort of like sanding across the grain of wood. I don't bother with it, but it is probably faster. I have trouble keeping the plane flat with any lateral motion - it's easier to just pretend I'm planing on a longer piece of glass.

I don't think the LV piece of glass is going to do a whole lot of good in terms of size, but you can keep it for sharpening or lapping items that fit on it - like plane irons, etc - and you won't have to worry if you use it for rougher items - it should hollow slower than your granite plate.

[Michael Schwartz]

I never lap the cheeks, I have a LN Low angle jack for shooting. (Although it is set up with a fairly steep microbevel now for smoothing because it is so good at it )

I usualy use scotch bright pads to clean things up, I have a sandflex pad floating arround, I think I will give that a try.

As far as glass, how flat can I expect a 1/4 inch or so peice of tempered glass to be. I am thinking of looking for a cheap coffee table or something at a yard sale for the glass top.

In addition I know a place that has some marble/granite scraps. Is there an industry standard or something for how flat these are ground?

Eventualy I am thinking of getting a narrow steel plate surface ground, but only if I have a ton of planes to lap.

[David Weaver]

The 1/4th glass will be flatter than you'll be able to get the bottom of the plane - the issue with it is if it's not on a flat surface, it will flex. I don't know how thick glass has to be to not flex, but it has to be pretty thick.

The 3/8th piece that I got to lap long planes will actually have a 0.0015" gap under a starrett edge if there's a couple of pieces of 60 grit silicon carbide grit under the end, so the relatively flat surface under the glass is important. In terms of how that shakes out, I don't know what fraction of the lack of flatness will transfer to the sole of the plane, but I'd rather start flat and not have to worry about it.

There are grades for the granite - if it has any legitimate certification, it'll probably be far flatter than anyone needs to worry about, too. See the following link from starrett - there are a lot of zeros before the numbers in the flatness tolerances of lab grade AA and inspection grade A, there's a B grade, too - tool room grade or something - and it is also flatter than we'd need to be concerned with.

The surface plates that come from woodcraft and LV come with a certification that doesn't match anything that I've seen, but the numbers on them in terms of flatness are fine (I think the one I got fell off no more than 0.0002" at any edge).

If you can find a glass top on a coffee table at a yard sale, and you don't mind having it around - just look across the top, and if you don't see any ripples, it's probably float glass and just as flat as you'd need it to be.

If the steel is good and flat, it's probably a good option, but if you have any loose grit that gets under the sandpaper, it'll have a worse effect on the steel than it would on glass. Keeping your eyes peeled for the ideal piece of glass seems like a good option. The issue with steel is the same as cast iron - who knows how much it moves over time. I don't think glass moves any appreciable amount.

Also, some folks on here have used jointer beds and table saw tops to lap - a fine idea if you can confirm the flatness of the table. I think the tops on a lot of the older saws were closer to flat when they were cast - something you can also measure with a feeler. My delta hybrid saw is 8 thou hollow in the depth - too much to lap a jointer plane on it, maybe OK for a small block plane or something.