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  • Long internal keyway

    I need to make a 3/16 keyway in a 1 1/2 bore approximately 5 inches long.
    What would be the easiest way to do it. I have nothing at present that I think is capable. Would a broach & arbour press work?

  • #2
    Originally posted by klemchuk
    I need to make a 3/16 keyway in a 1 1/2 bore approximately 5 inches long.
    What would be the easiest way to do it. I have nothing at present that I think is capable. Would a broach & arbour press work?
    possibly with some special bushings and shims. The different sizes max out at different lengths buts a lot less than 5, maybe 1.5". The problem is because its a progressive cut when things get too long, your taking to much DOC. However, you can make a bushing and engineer a set of shims such that only the last tooth or two cuts on each pass it should work.
    in Toronto Ontario - where are you?

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    • #3
      Originally posted by klemchuk
      I need to make a 3/16 keyway in a 1 1/2 bore approximately 5 inches long.
      What would be the easiest way to do it. I have nothing at present that I think is capable. Would a broach & arbour press work?
      The short answer is yes. You will need to make a special guide for the broach.

      BTW, 3/16 is quite narrow for a 1 1/2" bore or shaft.

      You may want to consider using a lathe or a vertical mill to cut the keyway. You would want to use as large of a boring bar as possible and manually cut the keyway with the carriage or the quill as appropriate.

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      • #4
        Step one - Get some 3/16 square HSS tool steel. You might already have some.

        Step two - make a bar.
        Get some 1" round bar stock long enough to be clamped in your lathe and reach the end of your 1-1/2" bore with some extra.
        Drill a hole through one end of the bar just large enough for some 3/16 square cutter bit to fit through.
        Drill and tap a hole (at 90 degrees to the previous one - either in the end or from the diameter side - doesn't matter much) that intersects the first hole. This will be for a set screw to hold the tool bit in place.
        Slip the 3/16 bit through the hole so it sticks out a bit more than the depth you want it to cut and tighten it in place with your set screw. Probably want to cut any excess off the back side (if you have any) so it's flush with your bar.

        Step three - mount your piece in the lathe chuck and the bar into your tool holder in the lathe, pretty much just like you'd use a boring bar except you want the tool bit centered in the middle rather than the upper edge of the bit.

        Step four - lock the chuck in place or put it into your lowest gear. Maybe even unplug the lathe in case you think you might turn it on accidentally.

        Then just use your carriage to feed it through the bore. Feed it into the material in the bore a thou or so per pass. Left-right-feed out-left-right-feed out-left-right, etc.....until it's to the desired depth.
        Prolly want a few spring passes (no feed) when you get close.

        Congrats! You just made your lathe into a shaper. And got a bit of exercise at the same time.

        p.s. Don't have the exact stuff I described in the steps? No big deal - just improvise. Obviously need to grind the tool bit to a workable geometry, and can grind a larger bit down to 3/16" if you need to, etc. etc. etc.
        Last edited by tyrone shewlaces; 05-12-2010, 11:33 PM.

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        • #5
          Yes, you can do it with a push type broach. You will have to make or buy a bushing that is 5" long, buy a 3/16" broach if you don't have one and make several thin shims longer than 5".

          It would be a good idea to make the slot in the bushing a little deeper than stock so it don't take a heavy cut on the first pass. Then with several .020" shims adding up to get the correct depth of keyway you can start. You will have to use a bar to finish pushing the broach through the bore. You should also broach it from both sides on every other pass.

          I have even used two standard bushings in a bore rather than make a long one. You have to have three or four hands at times doing this so you may need a helper.
          It's only ink and paper

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          • #6
            Originally posted by klemchuk
            I need to make a 3/16 keyway in a 1 1/2 bore approximately 5 inches long.
            What would be the easiest way to do it.
            I would cut it with a end mill ,plug it with a key and weld it and turn the OD.

            Not for high precision but i done it that way many time

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            • #7
              Not a very clever idea to make it with a standard keyway broach (like the ones from DuMont). They only can take a cut of a certain length. Even if you do make your own bushings and take more passes.
              The reason is, there isn't enough room for the chips. A longer cut makes a longer chip. It will fill the room between the teeth and then the tooth will break.
              Only a quick way to ruin you expensive broaches.

              A single toothed broach is a different storry, a slotter is the solution. You could do that on a shaper too.


              Nick

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              • #8
                Originally posted by MuellerNick
                You could do that on a shaper too.
                Slip across the border and I will sell you a 16" G&E shaper.


                ME

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                • #9
                  ... and I will sell you a 16" G&E shaper.
                  Nice toy!
                  My big shaper has 650mm (25" for the metrical challenged ones).


                  Nick

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                  • #10
                    I am starting to run out of room. I have 4 shapers, 14, 16, 24 and 28" I just picked up a Reid 6x18 surface grinder recently and a kiln that I will add better controlls to make a heat treat oven. So, something has to go cause I don't want my shop to be as crowded as Mcgyver's.

                    shapers

                    ME

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                    • #11
                      Originally posted by MuellerNick
                      Not a very clever idea to make it with a standard keyway broach (like the ones from DuMont). They only can take a cut of a certain length. Even if you do make your own bushings and take more passes.
                      The reason is, there isn't enough room for the chips. A longer cut makes a longer chip. It will fill the room between the teeth and then the tooth will break.
                      Only a quick way to ruin you expensive broaches.
                      whether its clever or not will be determined by whether it works and no one loses an eye (or broach). It's doable and i've done them longer than they broach is supposedly capable of (although i haven't done 5")

                      You just have to plan the shims so that your not overloading things. A broach is taper and is normally designed to take a bit off on each tooth per pass, the shim gets changed a second pass is taken. The idea for this job is to create much small steps using a lot of different shims - you engineer it such that the its not taking off more than it can handle, load or clearance, in once pass. If that means 5 thou a pass on one tooth or retracting the tool to clear the chip half way, whatever...its still doable...essentially turning the the broach into a one or tooth slotting tool. For that matter, make your own cutting tool and avoid buying the broach if there's only 1 to do - if its only a single tooth broach, easy enough to do.

                      A pita with all those shims? maybe. less than dragging a 16" shaper across the border or acquiring a vertical slotter
                      in Toronto Ontario - where are you?

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                      • #12
                        Do it like you are line boring in the lathe, only have the tool bit locked into position parallel with the travel of the saddle. Now mount your work to the saddle, with tool bit in bar that is between chuck and center. Moving carriage back and forth, advance part into tool bit.

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                        • #13
                          As I said I have made keyways longer than what is considered standard with the Dumont broaches and the critical thing is chip size. For that reason you can't use more than a .010" to .020" shim AND you have to deepen the slot for the broach so the first cut will not be excessive.

                          Yes, it takes a lot of time but if your only doing one or a few it is cost/time effective.

                          I agree Nick, if you have a shaper or a single point keyway cutter it's better but home shops and small machine shops have to take the best and cheapest way for them.
                          It's only ink and paper

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                          • #14
                            How about making a long bushing with a tapered slot. Taper magnitude 1/2 the broach taper. Set the broach into the tapered slot then push broach and bushing through together. Shim and repeat. This will reduce each tooth DOC by half.

                            To reduce chance of bore damage from galling select bushing material accordingly and use plenty of lubricant.

                            Note that I have not actually done this but seems like it might work.

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                            • #15
                              You just have to plan the shims so that your not overloading things.
                              Load is one thing. But length of cut is what makes the volume of every chip.
                              Just a quick check on a Hassay 4mm broach:
                              Height difference between one tooth to the next is 0.07mm. If you want to reduce chip volume, you have to shim in smaller steps than 0.07mm. So you wanted to suggest to shim in 0.02mm steps? Would require about 100 cuts for a 4mm keyway.

                              You may do as you want.

                              Nick

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