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Thread: Expected flatness (jointing, planing, and table saw)

  1. #1
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    Expected flatness (jointing, planing, and table saw)

    Hi all,

    If I take board thru the jointer / planer process, what should I expect to get as far as any taper or parallelism? In other words, If I took dial calipers to both ends of a 24" board, would I get .010", .020", .001" difference in thickness (assuming every tool is set up correctly)?

    When I use my table saw and fence, I have the same question as above

    My equipment:
    Planer: Delta Invicta 22-650
    Jointer: Delta DJ 20
    Table Saw: Delta (I forget the model, but mid 90's heavy duty 220V / 2 or 3 hp / 10" blade with stock fence)




    PS: I don't have Delta fancy, they just happened to be available for a good price.

    PPS: I set up my jointer using a 50" aluminum bar guaranteed to be flat within .005". I am getting a dial indicator to measure my table saw fence runout. The only thing I can think of to do is to attach the indicator on my sled and run it along the length of the fence.
    Last edited by andrew whicker; 04-18-2017 at 5:11 PM.

  2. #2
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    Your machines should be flat square and true for the projects you build.For instance a properly adjusted jointer should be able to make a face flat and a very good joint on the edge of two boards.when you hold them together there should be no gaps.
    Aj

  3. #3
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    Some of us like to see numbers, others just like to see the product...like Andrew pointed out above. "Hold them together there should be no gaps."

    I don't have any numbers for you but for some perspective, 1/32" = 0.03125", 1/64" = 0.015625".

    Ideally (and IMO), one should set up one's woodworking machines to be dialed in as tight as possible...way more than wood would care about. Remember that solid wood moves--i.e. moisture levels will rise and fall in a given piece of lumber thus changing its dimensions. I like to approach my equipment like a machinist might approach his and dial things in to 0.005" or better if I can, wherever I can. Actually, I think machinists wouldn't be very happy at 0.005" but for wood, I think somewhere around 1/128" is pretty darn good.

    I don't recall many manuals that come with our woodworking equipment that will tell you tolerances for their machines so you have to dial it in best you can and then see how the final product does in your particular project.
    Wood: a fickle medium....

    Did you know SMC is user supported? Please help.

  4. #4
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    I'll stop asking the generic question and ask my specific to this project question.

    As I noted in another thread I started, I am building a coffee table with tons of mortise and tenon joints. I came up with a brilliant idea: Use a tenon jig at 75 degrees (the angle of all the MT joints). Set the sacrificial side that runs parallel with the blade at one location to cut the far T side. Install shim to move piece out and cut near side T. In order to cut the M, place a different shim. So imagine the piece moving right to left when making the T and imagine the piece shimmed in the middle for the M. This way, I'm not moving the jig, I'm simply adding / removing shims. Brilliant!

    But, it's only brilliant if the wood that I cut is within, I don't know, pretty darn good along the entire length. I was pulling my hair out trying to figure out why when I moved the jig .010" I didn't see the results. Then I realized that my pieces have some runout along the length. This one piece has a .020" taper along about a 18" length. In other words, the thickness at one end is 1.500" and the other end is 1.480". So now my shims don't work, my reference distance on the jig doesn't work, etc.

    I'm asking if .020" taper is normal / close to right? I'm going to check everything out tonight.... And note, I'm not talking about flatness. I could make a table top with no gaps showing. I'm talking about taper / parallelism / whatever.

    Anyway, maybe someone has a better idea on how to make these legs because I'm already balding and I don't want to pull anymore hair out.

    Attached are some photos for reference:

    IMG_20170412_120322_775.jpg

    0409172112.jpg

    IMG-20170411-WA0003.jpeg

  5. #5
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    I think I know what you might be facing.First I would like to say that the joint looks good.And the project looks like a good exercise in making bridle joints.My approach to bridle joints or any joint that I want very tight.I face joint and plane my wood 2 or even 3 times and sneak up to my final dimension.Only process the pieces I can work in a day.
    Be aware of snipe at the ends and check for square with a reliable square.
    Aj

  6. #6
    A .020" taper is a lot on a piece run through the planer, so you may need to check the setup. You should be able to get consistent results within .005" end to end and side to side with that planer unless it is completely clapped out. Is the "taper" actually snipe?

    That said, the effect of thickness variations can be minimized by referencing joinery operations from the same face so that the fit of the joint is not compromised. It appears that you are doing that with your tenoning jig, so any variations in fit have to do with inaccuracies in the jig (bar to table groove fit, clamping pressure and the like).

    I don't use bridle joints, but if I did I would probably use a shaper groover or stack dado set for a consistent groove dimension and matched shaper cutters or spaced saw blades for a consistent tenon thickness. On the shaper with a sled, Destaco clamps and a vertical pressure bar I would expect to get a fit that needed no further work for a good glue joint and face registration within .005". A table saw tenoning jig with shims and two cuts on each piece with a single blade are likely to have more variation.

    Yellow glue works well with a thin glueline, about .002". If you can push the joint together with your hat, it is too loose. If you need a hammer, it is too tight. If you can't get a consistent fit with your machinery, aim for a tight fit and work it down by hand with a shoulder plane, sanding block or similar.

    As you no doubt realize, bridle joints are not that easy to cut, and also require clamping in several directions. If that is the look you want, have at it. Personally, I would use an inserted tenon for those joints.

  7. #7
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    I will tell you what I expect from my equipment but you need to know that my requirements are more rigorous than most. I use a CNC router and certain jobs require a really accurate thickness.

    I expect my jointer to machine rough lumber to a consistent flatness of 0.010" or better. Notice I said "flatness" and not "thickness". In my experience, the more passes you use on a board, the more inaccurate the overall thickness becomes. You create a sort of wedge shape. That is why I use a planer to machine thickness. I use a 12 inch jointer/planer combination machine with segmented spiral cutters. I can get a thickness accurate to about 0.005" or 0.007". In some cases, that is not good enough and I will run the material through a well tuned drum sander to obtain maybe 0.003" accuracy. It is noteworthy that several brands of lunchbox planer, including Ridgid and Dewalt, are typically more accurate than cast iron planers. That is because the distance between the bed and the cutters is set by high precision indexing instead of the skill of the person doing a setup job and the precision at which the knives were ground.

    If you have a well tuned table saw with a good blade and a straight fence, you should be able to get a rip consistency of a few thousandths. Accuracy is more than consistency. It is difficult to get really tight accuracy without doing a few trial cuts. Fortunately, that level of accuracy is seldom required. I got very good accuracy with a Ridgid 3650 contractor table saw. The jury is still out on my new Grizzly as I haven't tuned it yet. As for crosscut angle accuracy, you need to take some time and build really nice crosscut and miter sleds. Chances are the miter gauge that came with the saw isn't good enough.

  8. #8
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    Thanks for the replies!

    I am using a dado blade, btw. Frued 500 series.

  9. #9
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    I also adjusted my fence. Much better.

    I think most of my runout came from my fence and... Errr... Me

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