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Thread: Lapping a plane base: recommendations for glue to hold sandpaper?

  1. #1
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    Lapping a plane base: recommendations for glue to hold sandpaper?

    I've been using several rolls of aluminum oxide PSA sandpaper to lap the bottom of bench planes that I've been restoring.
    I use an 18" x 18" granite tile as my flat surface, and have discovered that when removing a worn-out piece, the PSA adhesive leaves sticky residue on the tile that I must scrape off with a razor blade and some solvent. So I solved that problem by first wiping a rag across the tile with a quick spray of WD40 followed by a wipe with a dry paper towel before laying down the next sheet of PSA sandpaper. Doing this causes the sandpaper to stick well enough for use, but will still pull off without leaving behind any gummy residue.

    Now to my question.
    The aluminum oxide sandpaper just doesn't last when sanding cast iron. I bought these rolls (80 and 120 grit) at an estate sale for next to nothing, so I'm happy to continue to use them up, but it's wasting time to constantly replace the worn-out sheets.
    What I would really like to find is PSA zirconium oxide sheets that would last much longer sanding the cast iron. But after scouring the web, I cannot find any vendor that makes such a product. So, the other day when I was browsing the bargain bin at my local ACE Hardware, I found 5 packages of zirconium oxide sanding belts of various lengths at 2 bucks per package - cool! So I bought all 5 of them and intend to cut them into 18" lengths to use on my granite tile.
    So what is the best glue to use for this application?
    These belts all have a cloth backing on the underside that the glue would need to adhere to as well as to the smooth granite surface. Plus I want to be able to pull off a used piece without a lot of sticky residue to clean off the surface.
    Any suggestions?

  2. #2
    I presume you've got a straight edge, if you don't have something suitable and not a ruler,
    how do you know the tile is flat?
    Every granite tile I've came across was convex on the polished side.
    Was very disappointing to find this out and evident even without a straight edge by butting a engineers square against something similar to a 123 block and pushing it across the surface,
    as a gap inbetween becomes evident with a good light behind.

    Just saying, as most videos you will see use methods which rely on the lap being flat as they never check afterwards.
    Those methods no good for convex soles, especially long ones, as there is no way of flattening only where you want to!

    Using a lap longer than the plane is, if the sole happens to have has a convex surface, it will pivot/see saw about in the middle and make the ends of the plane thin,
    Lapping on a larger area than the work is, will always favour dubbing the edges, no matter how clean and taut you can keep the abrasive.
    (Evident on many an add on the bay and where ever you might see job lots of planes, it's not wear from through the years, as they still have full length irons.)

    You must treat the edges as being very important for reference.

    So going back to your question, and presume you have a flat surface and straight edge.
    I have some 3m stuff that is very fancy self adhesive, although I don't use it for lapping per se.
    I use the fancy stuff to check for flat with three rubs,

    I have it stuck to the lap so it can hold another smaller than the plane area in question is, layer of cheap abrasive.
    This keeps the plane suspended off the grit, so won't blunten as quick, and the abrasive is more effective because of more contact with the work.

    The loose sheet (smaller than the area of the plane) of abrasive, will never need to be stuck down as 100% of it is held down by the plane,
    spot work beforehand is done with a shorter strip again,
    Very much a removal of only what you want type deal.

    A few do it differently and stick some abrasive to a wee block instead, but its basically the same principal or targeted areas first, and checking often.

    Either way will save you needing to replace the abrasive often on a lap.

    Once you've got it flat, you can simply do a few rubs with your fancy abrasive or stuck down with spray adhesive abrasive, or even clamped with blocks from each end abrasive
    and it will do the job,
    Basically saying you don't really need to be pulling off abrasives and refreshing it, as it makes little sense to use it like you might have watched on youtube.

    Tom
    Last edited by Tom Trees; 01-14-2021 at 4:05 PM.

  3. #3
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    I agree
    I got a few 36" of granite cut off and neither of them were flat. Both convex as well.
    I had a piece of float glass cut which was flat, buy smashed it when I fell over one day.
    I was searching for something flat to lap on and a old piece of 3/4" MDF or particle board cant remember? That came out of our pantry is believe it or not, dead flat to the best of my ability to check and I use that.

  4. #4
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    In my experience most planes do not need to have their soles lapped. Many of those that do are because someone tried without knowing what they were doing.

    Is there a clear need for the soles to be lapped?

    IMO, if a plane can take a fine shaving for its size, without difficulties it is likely the sole is fine. If you are a perfectionist, think about finding a machinist.

    Some of mine have needed a light application of steel wool or sandpaper to remove rust.

    A few have actually been unusable due to a warped or misshaped sole. Careful lapping on an abrasive sheet was able to turn them into good users.

    My setup uses a hunk of granite acquired from a monument maker. (gravestone carver) This one is a little over four feet:

    Granite on Horse.jpg

    This has likely cleaned up more rusty chisels than plane soles.

    Removing the adhesive left by the sandpaper is fairly easy with a 4" wide putty knife or wall taping knife. Before removing the tape it can be heated with a hair heat gun. (maybe a hair dryer)

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  5. #5
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    I lap plane soles without glue. Have rolls of sandpaper with no adhesive backing, and instead clamp down one end of the paper on the bench, below the surface of my granite block. Since Iīm only flattening when pushing the plane away from me clamping one side is enough.

    Maybe not as precise as your setup, but a plane sole does not need machinist precision flatness in my opinion. Not concave, not twisted, not too convex is enough. A minute dubbing on the edges does not really matter.

  6. #6
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    I brought a straightedge with me to Menards to check the flatness of the granite tiles I was looking for, and tossed aside a dozen or so before I found two that were flat to my satisfaction.

    I use Gorilla spray adhesive because that's all I cound find at the time. A little goes a long way.

    I have used 3/4" mdf clamped to the the CI top of my table saw, and stuck the paper to that, but I try to avoid getting any of that spooge near my saw table.
    Last edited by Marc Fenneuff; 01-14-2021 at 5:30 PM.

  7. #7
    Quote Originally Posted by Jim Koepke View Post
    In my experience most planes do not need to have their soles lapped. Many of those that do are because someone tried without knowing what they were doing.

    Is there a clear need for the soles to be lapped?

    IMO, if a plane can take a fine shaving for its size, without difficulties it is likely the sole is fine.
    I totally agree with this. If it worked then, it should work now.

    If you _did_ somehow want to lap a plane sole, know that bench planes tend to bow convex in normal use, particularly the longer ones (than a #4 say.) And that even on a perfectly flat lapping surface, there is a tendency to accentuate convexity (raise either end.) So what you may be doing is shortening the effective length of the plane, or inducing an “artificially” concave surface to the wood. If you’re okay with this, then fine, but it’s not how things are really supposed to work with that particular plane.

    Which is why I’d suggest leaving it alone, just local derusting and a wax job. Truly warped planes are for the parts bin.
    Last edited by Doug Dawson; 01-14-2021 at 6:23 PM. Reason: Spell checker doesn’t like plane terms

  8. #8
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    Thanks everyone!
    The next time I'm in the workshop (a.k.a. garage) I'll check the flatness of my granite tile.

  9. #9
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    Next question.....does that plane actually NEED it's sole lapped? ( do not bother with feeler gauges,,,,save those for when you are settings points on a vintage cars engine..)

  10. #10
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    Some interesting points raised. The curving up at the ends and effective shortening of the plane is a good observation. Yes polished granite is rarely flat and reference pieces are small. Itís one of those tasks you can start kidding yourself it will make it better. It becomes educational as you learn why itís getting worse! The education is likely the only improvement you will see.
    A new plane will be flat or send it back, an old plane you bought chalk up to experience. If the plane has several contact points along its sole length it should work. If you have lots of planes already that are flat will you really use the Ďimproved plane very oftení?
    There are three old guys with a machine shop to make NASA jealous round the corner, thatís where I go. Seriously they must have won the lottery!
    ​You can do a lot with very little! You can do a little more with a lot!

  11. #11
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    +1 to what has already been said.

    I have 1 plane in my arsenal that truly needed lapping, and i did so with sandpaper on glass and it corrected the issue.

    I would clean the plane up and try it first before you attempt the painstaking task. You may br surprised.

    Another note is to check the iron for defects as well. I had one iron that was ground convex so it was taking heavier cuts on the edges than the middle. Once this was corrected it takes really nice shavings. Its not always the sole that is the issue

  12. #12
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    3M 45 spray mount. You can pull the paper off easily without leaving the backing behind.

  13. #13
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    Wax the granite first. The PSA will stick but peel off fairly easy. It will hold plenty tight for lapping. When you’re done you can take the wax off with mineral spirits.
    Sharp solves all manner of problems.

  14. #14
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    Some water under the paper will hold it due to surface tension, not as light as adhesive but it works. I bought a granite lapping stone at woodcraft that was cut specifically to be flat, wasnt that expensive if I recall correctly.

  15. #15
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    To follow up, indeed my granite tile was slightly dished in the center . Thank you for pointing that out!
    So I took a drive to our local granite countertop factory and they let me dig through their dumpster in the back alley for a piece of granite scrap - no cost. I found a decent looking piece, polished on one side, 1 inch thick, which I checked with a straightedge. I could see no deviation from flat with my eyes, so I'm accepting that as a successful upgrade. I'm planning to get out the liquid nails and glue it to a piece of plywood with a couple of hand-holds cut out so it will be easier to move it on and off of the workbench.

    And yes, I don't need the planes to be perfectly flat. However, if there is shallow rust-pitting on the bottom of the base, I prefer to lap the base to try to get rid of at least some of it, if only for aesthetics.

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