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Cutting Internal Keyway in a Lathe

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  • Cutting Internal Keyway in a Lathe

    Several times in the past various posters have asked about ways to cut an internal keyway and good received answers from the highly respected members here; one method often suggested was using a lathe. My search of the site didn't produce any pictures and I thought they might be helpful to some of our newer members, so here goes:

    I needed a special 4 step pulley for a machine so I turned one out of aluminum and needed to cut an internal keyway to complete the job. My 7" Shaper wasn't able to hold this work due to it's length so I used the lathe as a work around.

    Here is the basic setup:

    Pulley in lathe chuck, back gear engaged to prevent rotation and counterweight applied to take up any slack.


    A boring bar is fitted with a tool bit the proper width for a 3/16" key, aligned and centered, ready for the first cut.


    Progress after moving carriage several passes @ .002" cross slide advance per pass


    The completed keyway

    Note: the threaded notch you see in the end of the pulley was no real value. It was used when I used a set screw to affix the blank to a mandrel for turning the pulley. Later the end of the pulley was faced off to the proper length leaving the notch. Better planning could have prevented this but function is not affected.

  • #2
    I wonder if that would work on my 7x12. I've got a couple peculiar project ideas that are hanging up on various permutations of the 'internal keyway' problem.
    ----
    Proud machining permanoob since September 2010

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    • #3
      Well, I searched through my files, links, and many of the other groups I'm a member of but I can't find the damn thing, so I'll have to describe it. I could swear that I remember Bob Wright making one. Anyway, the operation can be sped up considerably by making your own lever action keyway cutter thats mounted to the compound or CS. It works the same way as yours but you don't have to crank the carriage back and forth. You just work the lever and adjust your DOC for the next cut. My guess is that as soon as I post this other members will remember this and post photos. If this isn't in the Shop Made Tools section ..it should be.

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      • #4
        I was thinking about doing it the opposite way

        I was thinking to buy a chuck and mount it on a taper to fit the tailstock. Then I could mount what ever I needed a keyway in the chuck on the tailstock.

        THe reason being then I could use the carriage under power feed to push the tool. The spindle on the head stock would have nothing to do with the operation. The chuck in the tailstock would also be fixed so I wouldn't run into problems with indexing it. Or I could build a mount that would allow me to rotate the chuck and fix it in place to cut splines, etc. ect..

        I think I read about it being done the way I am thinking but don't remember where or when.
        Location: The Black Forest in Germany

        How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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        • #5
          Keyway

          Check out the article on a "Hand wheel for a Lathe" showing the cutting of a 1/8" key way in my lathe. This was done in the vertical plane using a cut off tool. I did not have a suitable tool to use in the horizontal plane and it only took a few minutes to sharpen the cut off tool.
          JRW

          http://www.homemetalshopclub.org/new...ge=6&view=fitH

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          • #6
            Originally posted by Chris S.
            Well, I searched through my files, links, and many of the other groups I'm a member of but I can't find the damn thing, so I'll have to describe it. I could swear that I remember Bob Wright making one. Anyway, the operation can be sped up considerably by making your own lever action keyway cutter thats mounted to the compound or CS. It works the same way as yours but you don't have to crank the carriage back and forth. You just work the lever and adjust your DOC for the next cut. My guess is that as soon as I post this other members will remember this and post photos. If this isn't in the Shop Made Tools section ..it should be.
            I'm pretty sure Evan made one at some point, I remember seeing a picture or two of his.

            JR Williams, I like the use of the cutoff tool. I used a 3/16 tool bit because it was the right width but the cutoff tool would work just as well by moving it side to side to obtain the desired keyway width. Easy to grind too, as you mentioned.

            Madwilliamflint, no reason it wouldn't work. The force required on the carriage isn't much if you take .001" -.002" cuts.

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            • #7
              Originally posted by firbikrhd1
              ....

              My 7" Shaper wasn't able to hold this work due to it's length so I used the lathe as a work around.

              ....
              Interesting example of the versatility of the lathe. It truely is king of machines. Others may do specific jobs better, but the lathe can do more types of work than any other. Perhaps slower, but more.
              Paul A.
              SE Texas

              And if you look REAL close at an analog signal,
              You will find that it has discrete steps.

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              • #8
                thanks firbikrhd1 for the post. Would you please explain how you center the cutting tool and do you pull or push?
                thanks.
                John R

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                • #9
                  I made this gizmo, which works equally well for internal and external keyways, splines and teeth. Doesn't get so much use since I got the Douglas shaper, but still handy from time to time



                  And it will work on a limited range of tapers as well.

                  Tel
                  Senior Member
                  Last edited by Tel; 10-25-2011, 03:48 PM.
                  Tel

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                  • #10
                    That looks like a clever way to cut the key slot, but how much wander and deflection do you get from that length of bar?? it's out there a ways. I guess trying to use a bushing would be out of the question.

                    JL................

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                    • #11
                      Originally posted by Tel
                      I made this gizmo, which works equally well for internal and external keyways, splines and teeth. Doesn't get so much use since I got the Douglas shaper, but still handy from time to time
                      Thanks for posting your version. Yes, yours is similar to the concept I referred too. Have you added it to the Shop Made Tools section?

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                      • #12
                        Originally posted by John R
                        thanks firbikrhd1 for the post. Would you please explain how you center the cutting tool and do you pull or push?
                        thanks.
                        John R
                        Hi John,

                        The easy part first. I doubt whether it matters if you pull or push but I pushed. I think using the inertia of the carriage makes the cut smoother and perhaps a bit easier although it really takes little effort anyway.

                        My method of centering the tool may not be the only way but it worked and only required simple calculations to complete. I used a planer gauge on the flat way of the lathe set to the center height less half of the cutter width slid beneath the bottom edge of the cutter bit. By adjusting the tool holder up and down I was able to obtain a very close height measurement. A feeler gauge or tissue paper could be used with this method in a way similar to that used when setting a cutter on a mill. I did not do that, instead used magnifiers to see the light between the planer gauge and cutter. To get the set screws in the proper orientation I did a similar thing; screwed a straight bolt into the threaded set screw hole until is snugged up against the bolt shank and used the planer gauge set to center height less half the bolt diameter. When the bolt laid flat across the width of the planer gauge the orientation was correct.

                        No doubt the same thing could be done with a makeshift gauge, perhaps a vertical rod with a base, collar and set screw.

                        JoeLee,
                        In response to your question, wander and deflection were minimal. An indication of the straightness of the finished keyway was that the key slid firmly from one end of the keyway to the other without play or hanging up. reasons for this are a few; first, the cut in this case was in aluminum, steel may have caused slightly more deflection but the second point negates that to a large extent. Second point, the cuts are only .001" to .002" at a pass, the tool was very sharp HSS and lastly the boring bar was only slightly smaller than the hole, 1/2" bar and 5/8" hole. Near the end of the depth of cut "spring" cuts were made to insure that deflection didn't cause taper in the depth. During those cuts very little material was removed. The length of cut was about 2.3" long and the bar you see used is only extending slightly more than that from the tool holder.

                        Your thought on using a bushing might work if you used a small boring bar. If done this borders on something akin to the use of a broach and the cut would have to be made in one pass or the bushing would be loose as subsequent passes were made. This would require far too much effort for the lathe.
                        firbikrhd1
                        Senior Member
                        Last edited by firbikrhd1; 10-25-2011, 06:14 PM.

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                        • #13
                          No Chris it wasn't mine. I have plans from The Home Shop Machinist but never made it. I did see one made in either one of the yahoo groups or on PM. Since i bought my SB shaper and a set of keyway broaches it on the way back burner...Bob
                          Bob Wright
                          Salem, Oh Birthplace of The Silver & Deming Drill

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                          • #14
                            Originally posted by aametalmaster
                            No Chris it wasn't mine. I have plans from The Home Shop Machinist but never made it. I did see one made in either one of the yahoo groups or on PM. Since i bought my SB shaper and a set of keyway broaches it on the way back burner...Bob
                            Bob, they say that with age comes wisdom. Perhaps, but along with it comes foggy memories!

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                            • #15
                              ...so I turned one out of aluminum... Progress after moving carriage several passes @ .002" cross slide advance per pass
                              Aluminum is for girly-men! Try steel. Here is a picture of a keyway I cut with my 9" South Bend. It's a steel arbor bearing for the overarm on my (Kempsmith) horizontal mill. The keyway is 1/4" by 3-1/4" long. It took me two nights to carve it out and left a blister on my hand. I used the same method described by firbikrhd1, but had to make multiple passes just to get .001". I also stopped often and ran the bit over my stone to keep it nice and sharp. But when you have more time than money...

                              Tom

                              Tom - Spotsylvania, VA

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