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T-nut dimensions

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  • T-nut dimensions

    I need to make some t-nuts for a t-slotted drill press table. I watched the Tubalcain 2 part series (#102 & #103) and got a few good tips. The only topic not covered is how long should it be. I have noted (internet but no specific sites I can post) that
    milling the opposite sides of carriage bolts to fit the t-slots is discouraged since it concentrates the forces onto too small an area.

    Is there a formula to suggest a suitable length... for example, if the table slot is "x" wide then the length should be "y" times that dimension... or any other suggestions?

  • #2
    Just a guess: I say four or five diameters. I have some on the front porch, just too lazy to get up.
    I can give you a real answer tomorrow.


    • #3
      These images might help:

      Paul , P S Technology, Inc. and MrTibbs
      USA Maryland 21030


      • #5
        I just made some for my new to me rotary table, and I suggest you make one long strip tee nut and then cut them to size when done, much quicker, I made it long enough for 12 Tee Nuts.
        Agua Dulce, So.California
        1950 F1 street rod
        1949 F1 stock V8 flathead
        1948 F6 350 chevy/rest stock, no dump bed
        1953 chevy 3100 AD for 85 S10 frame have a 4BT cummins motor, NV4500
        1968 Baha Bug with 2.2 ecotec motor, king coil-overs,P/S


        • #6
          Originally posted by Dunc View Post
          Is there a formula to suggest a suitable length... for example, if the table slot is "x" wide then the length should be "y" times that dimension... or any other suggestions?
          Paul's already shared them, but all of the common standards are in Machinery's Handbook plus a ton of other useful data. There's everything from "machine not cutting" checklists to design standards in there, searching the index is usually faster, easier, and more likely to be correct than the internet.
          "I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."


          • #7
            Yeah, my copy of MH sits & gathers dust. I "know" it has the answers to everything but I can never remember to look until I get a gentle reminder.
            Thanks for the replies


            • #8
              I have made some, and measured the slot dimensions first to make them the closest fit possible. If I was going for bolts, I would either reduce larger ones, or make them out of solid.


              • #9
                Short, long and extra-long.

                Short for when two t-nuts have to butt up together or when one has to come close to, say, a vise or fixture key.

                Long for normal use.

                Extra-long for when you want a t-nut to extend out past the edge of the table. Two or more holes. Often find a need for this on the rotary table, to fix a work stop to the mill table, etc. If you're extending it out past the table, this is the time I'd be very careful of the table slots.

                I wouldn't worry about the short nuts breaking out table slots. It's always better, though, to have the fixture or workpiece against the table, so that the action of the t-nut is more to compress the table ledge than to lift it. More t-slots are broken out by bottoming out the stud or screw than by anything else.

                When making t-nuts, I make them in long strips, and keep some strips for something that might come along in the future. Once you're set up to make them, it doesn't take long to make more than you need.