Worn Mouth on No 4 Planes

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    William Stanley

    I have a similar issue as Carlos (@CHALS) with a worn mouth on several No 4s that I bought as a job lot (there were 3 No 5s, a 5 1/2, 18 No 4s and a No 3 – all disassembled with the parts mixed up in plastic containers!!).
    I have attached a few images of the problem – on several of the planes, where the mouth is worn on both sides (i.e. towards front and back of plane). From the previous post by Carlos the recommendation was to persevere but after an hour and 1.5 metres of 80 grit I’m thinking of alternative strategies. My options seem to be:
    a) Mechanise (use a belt sander with a jig)
    b) Convert one to a scrub plane and file the mouth
    c) use a thicker blade (Axminster Rider)
    d) Tune the plane and see how much effect the worn mouth has
    e) sell the ones with worn mouths!!
    Any ideas or suggestions would be welcomed




    Larry Geib

    Not every plane has to look like it just came off Lie Neilsen’s assembly line.
    Pick one plane ( a number 4, maybe) and concentrate on that as your smoother You only need one really fine smoother, and keeping a plane at the very peak of condition takes constant attention. Keeping a dozen planes in top shape is a lot of work.

    What you show would be fine for any plane where you intend to make thicker shavings, like jointing, flattening work, etc.
    More important than the last little bit of flat sole, worry more about keeping your irons sharp And the chip breaker set fine for all but a scrub plane. If you use a plane and aren’t getting tearout with whatever wood you are using, just keep using it. If the tearout is small, finish with a smoother.

    The absolute flat sole is really only crucial for taking 1 or 2 mil shavings, and the purpose of most planes isn’t fine shavings, but stock removal. If you try removing wood one thousandth of an inch at a time, you are wasting your day.

    So just do a 4 and one 5 or the 5 1/2 and get woodworking.

    For flattening, You might just have started with too fine a grit.
    Drop back to 60 grit. The goal is material removal first. When the mouth is flat then go to 80 and up
    The rear of the mouth doesn’t make much difference. Just worry about the front of the mouTh.

    And a meter and a half doesn’t sound like much for all those planes. I use that much on one plane. The paper gets dull.

    William Stanley

    Hi Larry,
    Many thanks for your advice/interest. I’m not too worried about looks, although for the planes I want to keep, I’ll maybe make them look nice as well as functional. The rest of the planes, once working to an acceptable level, can hopefully be given a new lease of life with new owners, although some of them are in poor condition.

    My post was a bit unclear, I have only worked on one of the job lot planes so far, but have examined the others to identify how much work is involved to bring them back to fully functional use. That was the real issue for me, just how critical is the shape of the mouth, to the plane’s operation. It’s interesting that you highlight the front of the plane as the key area. I suppose as long as the iron is fully supported on the frog the rear of the mouth is not too important. With regards to the front of the mouth,I have read that this can be made a bit bigger for a conversion to a scrub plane.
    So far the flattening has been with 80 grit. However, I was watching a video by theorboguitarmaker titled “Restoration/Tuning of a block or hand plane to highest accuracy w. files, scrapers, edge & plate” where he starts by filing the sole of the plane, which has a much higher stock removal rate and checking progress using a granite block/bluing. I gave this a try and was able to remove the wear around the mouth after about an hour of careful filing and bluing and checking against a straight edge as well.

    I quite fancy playing with scraping on one of the soles, purely for fun as it is probably ott. What would be interesting would be to flatten the sole using this technique with the frog and blade in place and the lever cap tensioned as recommended by all the plane “gurus” and then remove them from the plane and see if the bluing pattern changes significantly. I have not seen anyone check this out.

    As you say I plan to keep a couple of the No 4s (one smoother and a scrub) a 5 and a 51/2 but I would also like to dedicate a plane for a shooting board (set it up with completely straight blade profile), but not sure whether the 5 or the 51/2 would be better suited.

    Purely for interest, I also weighed all of the No 4s and recorded their casting batch ids and there was a considerable variation in the weight of the bodies (completely stripped down) – from 759g to 904g as shown in table below (apologies for poor formatting) – the underscore “_” is where the number/letter is obscured by paint/japanning.

    Weight of
    cast iron (g)
    body Cast No Other Numbers
    759 6 _Q
    761 F
    762 Q
    767 7 XQ
    772 5 XQ
    777 _ 3Q
    811 Q19
    830 9Q
    830 Q17
    830 Q20
    844 F
    845 12Q
    853 10Q
    856 10Q
    866 Q15
    867 Q13 G12-004
    878 15 G12-004
    904 90 G12-004

    Apologies, but this turned out to be a bit longer than I planned!

    • This reply was modified 2 years, 10 months ago by William Stanley.
    • This reply was modified 2 years, 10 months ago by William Stanley. Reason: Table format
    Larry Geib

    Well, if you are going to go into the plane business, invest in something like a 2×72 belt sander with a Platen longer than your longest plane. it would reduce the time down to minutes. The long belt runs very cool. ( you can also ruin a plane in seconds with one)

    But that would take all the fun out of it. 😉

    It would be interesting to see what they weigh “all up”

    I have a 1903-1906 #4 that comes in a 1430 grams while a WWII model weighs 1560.

    And I have a WWII #3 that is only 40 grams lighter than the older #4. And is only 1/8” shorter.

    To be fair, the old #4 is corrugated.

    • This reply was modified 2 years, 10 months ago by Larry Geib.
    • This reply was modified 2 years, 10 months ago by Larry Geib.
    William Stanley

    They are all assembled apart from the one I’m working on so I’ll try to get out and weigh them when I get a chance. Belt sander sounds good.

    William Stanley

    Finally got the weights for the planes! For the No 4s the lightest are around 1560-1590g and the heavier ones up to 1750g. I have a 1930 USA no 4 which weighs 1494g (surprisingly low) and a UK No 3 at 1475g.

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