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How to fix finished dimension using thickness jig?

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  • #625618
    Alexander Miller
    Participant

    I’m new here, and new to attempting to learn fine woodwork. My question is about the thickness jig:

    https://woodworkingmasterclasses.com/videos/thickness-planing/

    As I understand it, since the plane iron has to protrude below the sole, the top of the workpiece will be planed lower than the top of the rails on which the sole rides. Hence the depth of those rails does not determine the finished thickness of the workpiece: It will be slightly thinner? And whatever that finished thickness is, in order for the next piece to be planed to identical thickness, the depth of the iron must remain unchanged.

    i.e. the jig cannot accurately determine the finished thickness? Maybe I’m missing something here, but if so, what?

    #625619
    deanbecker
    Participant

    The jig is wide as the outside of the plane if you look at a plane sole you will see the area on both sides that dont cut. The outside edges ride on the depth gauge.

    #625622
    Alexander Miller
    Participant

    [quote quote=625619]The outside edges ride on the depth gauge.[/quote]
    That’s understood; but the plane iron cuts slightly lower than those edges. Hence, will the the finished workpiece not be a little thinner than the full height of the depth gauge rails?

    #625641
    Larry Geib
    Participant

    Well, you have to keep in mind a plane shaving is not all that thick in woodworking terms. You can set the iron quite easily to , say .003” or about.07 mm to get a finished face. With only a little more sharpening diligence, you can make .001” shavings. That’s not measurable with woodworking measuring devices. It takes at minimum a dial calipers or dial indicator to measure that. Traditional woodworkers didn’t use those tools.

    For reference a sheet of A4 typing paper is about .05mm or .002” in thickness. Just put a piece of it under your guides to get to the thickness you want.

    More important than the .001”, or whatever, is that the thickness appliance allows a CONSISTENT thickness.

    #625648
    Alexander Miller
    Participant

    Thanks Larry. You confirmed that my assumptions are a) correct and b) largely irrelevant. I like that. The paper shim is a good trick if I ever get accurate enough to need it. Consistency of the rail heights is understood, but maybe not how I’ll achieve it :).

    #625933
    Sven-Olof Jansson
    Participant

    By committing “blasphemy” of the deepest nature, one can obtain those strips also when one’s planing and rip-sawing aren’t sufficiently evolved.

    Timber yards invariably, I assume, have panel saws and off-cuts of mdf-boards; perhaps not for 1/8”, but almost certainly of the 1/4” thickness. After an offer to buy the off-cut, a plea for ripping off one or two pieces to specified width won’t be refused; and at the end the off-cut is also likely to be handed over without charge.

    Any “heretic” taking advantage of that mdf-boards are flat will of course be enjoined as penitence to the acquisition of dimensioning wood and sawing to a line. Myself, I hope to be absolved once my rip-cutting stops meandering like a river on flat ground.

    Sven-Olof Jansson
    London, UK; Boston, MA

    #625979
    Larry Geib
    Participant

    Good point, Sven . But there is no blasphemy in using known thicknesses to guide your work.

    And another thing you can do is keep a set of thickness gauges around to measure against. Lee Valley sells some but I use a set of shaft keys. I have full metric and USCU key I gathered over the years from the hardware store. The are very accurate and come in 1/64th” and .5mm increments. You can get short lengths or 12” and longer.

    If you are looking for 1/4”, you can often get them by ripping apart old electronics panel racks. Often grounding strips and panel corners are made from 1/4” square stock – even in metric countries. It’s a common modular size.

    • This reply was modified 1 week, 4 days ago by Larry Geib.
    #628470
    Alexander Miller
    Participant

    Dean, Sven & Larry: Thanks for your responses. In terms of ‘not-fine’ or just plain sloppy woodwork I’ve been blaspheming all my life. Just recently I decided to get a bit more religious. It began with a desire to reduce my reliance on machinery; and the attraction swelled after stumbling on some of Paul Seller’s very inspiring you-tube videos.

    But after discovering how difficult it will be to develop the necessary skills at my advanced age I’m pondering how devout a convert I really want to be. Most likely I’ll be like one of those religious folks a bit flexible day-to-day about which commandments they’ll bother with.

    Well, enough of that analogy! I’m having a lot of trouble with ‘where to start?’ The thickness gauge question arose in the context of building a ‘poor man’s rebate plane’ which I actually started before realizing it was far too ambitious for now. I lack the necessary skills (which I will practice), enough quality tools (which I can ill afford), and quite likely the longevity to acquire many of these things; I’m 82. Plus I find that most of the tutorial projects are about items I won’t have much use for, so I want to come up with my own while incorporating skill-building techniques from the videos.

    I could get very long-winded here (!) so I’ll quit. But I need to find my way around the forum and go ask some questions about saw sharpening.

    #628544
    Sven-Olof Jansson
    Participant

    Thanks Larry,

    You wouldn’t by chance be referring to the blocks I was recently presented with as a birthday present from my better half (please see attached photo). In total, I now have three metric ones and one imperial. They are simply too handy to have just one of.

    Sven-Olof Jansson
    London, UK; Boston, MA

    Attachments:
    #628588
    Larry Geib
    Participant

    Hi Sven.

    I was specifically referring to the expansion set on the right of your picture, but they are all useful. They reside in a candy tin, not those nice boxes lol.

    I gathered up my collection from shaft keys and other bits before Veritas made theirs available. And I made my own 1-2-3 block when I got access to a friend’s milling machine one day.

    Even a collection of small blocks made of hardwood will help on a project.

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