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Shop made rotary broach for the Rivett

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  • #16
    It's somthing I've never actually tried, if I needed a bolt like that I'd have ended up reworking a cap head Allen screw but watching it makes me want to give it a go, well done, interesting
    Mark

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    • #17
      another Q - I have a QCTP holder with a live drill chuck (turned by a cordless drill). The drill chuck is attached to a 1/2in shaft that runs in oilite bearings, with the front bearing acting as a thrust bearing too. If I made a 1/2in shaft to hold broaching bits, would this holder work? It won't have the ball thrust bearing that I see with most rotary broaches, but the shaft should be well supported. Save having to make a new tool holder too..

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      • #18
        Originally posted by mattthemuppet View Post
        another Q - I have a QCTP holder with a live drill chuck (turned by a cordless drill). The drill chuck is attached to a 1/2in shaft that runs in oilite bearings, with the front bearing acting as a thrust bearing too. If I made a 1/2in shaft to hold broaching bits, would this holder work? It won't have the ball thrust bearing that I see with most rotary broaches, but the shaft should be well supported. Save having to make a new tool holder too..
        Sounds like it would work fine. Worst case, you can reuse the broach in whatever you end up making, if that didn't work out.
        Max
        http://joyofprecision.com/

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        • #19
          neat, thanks!

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          • #20
            Great info! Thanks... I have a couple store bought RB's. Have not used them but wanted to make some broaches for them.. JR

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            • #21
              Originally posted by mars-red View Post
              Sounds like it would work fine. Worst case, you can reuse the broach in whatever you end up making, if that didn't work out.
              tried it, didn't work The holder spun easily by hand but locked solid when the broach was fed into the work (piece of alu scrap). Then I tried to turn it into a holder like yours, by center drilling the end of the broach (1/2in O1) and holder (random steel) for a 1/4in BB. That didn't work either. Again, the broach spun freely in the holder but locked solid under load. The BB was greased and the sides of the broach oiled. Could be that there wasn't enough clearance between the broach and the holder? It's a smooth fit and spins freely, but is tight enough to create a little bit of suction when you pull it out.

              Next option is to create a new holder with the same BB thrust bearing but a cartridge radial bearing. That's quite a bit more work, so I'll probably shelve this project until I get through some others.

              Also, how much front relief or "dish" did you put on your broach? I cut mine at 2deg using the compound but I wonder if that was enough?

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              • #22
                Originally posted by mattthemuppet View Post
                tried it, didn't work The holder spun easily by hand but locked solid when the broach was fed into the work (piece of alu scrap). Then I tried to turn it into a holder like yours, by center drilling the end of the broach (1/2in O1) and holder (random steel) for a 1/4in BB. That didn't work either. Again, the broach spun freely in the holder but locked solid under load. The BB was greased and the sides of the broach oiled. Could be that there wasn't enough clearance between the broach and the holder? It's a smooth fit and spins freely, but is tight enough to create a little bit of suction when you pull it out.

                Next option is to create a new holder with the same BB thrust bearing but a cartridge radial bearing. That's quite a bit more work, so I'll probably shelve this project until I get through some others.

                Also, how much front relief or "dish" did you put on your broach? I cut mine at 2deg using the compound but I wonder if that was enough?
                That's a downer! Have you tried tweaking the alignment? What are the dimensions of the broach body that is supposed to turn inside of the bushings, and how much bushing length do you have? Most of the force should be taken by the thrust bearing (ball, in both of our cases), but there will be some lateral force and if you didn't have enough bearing surface I could see that maybe contributing to binding problems. There could be a lot more lateral force involved than I realized too, with mine the entire sleeve of the body of the tool that fits into my toolpost acts as a lateral bearing against the inner broach holder, maybe 2.5"-3" in length or so. If I had designed mine with smaller bearing sleeves on either end maybe I'd be having the same problem. I wonder if a full bearing surface along the entire length of your broach body would help.

                Regarding the dish at the end of my broach (would that be called the "rake" in the case? I'm not sure, but seems like the relief would be the angle behind the cutting edge of the broach), I formed that just using a drill, so the angle is whatever the tip angle of the drill was. As I recall, I used one of my screw machine drills and I believe that set of mine is 135 degree.

                If you want to correspond by e-mail or even set up a Google Hangout or Skype session to try and troubleshoot this, send me a PM and I'll do my best to help.
                Max
                http://joyofprecision.com/

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                • #23
                  One thing I found when broaching a hex form into steel was the very high pressure required. The broach fitted into the mt2 tailstock and the back gear was used at about 60rpm. It has done no good at all to the thrust bearing in the Smart & Brown model A which is a plain bearing machine with a ball race for thrust. I took out the thrust bearing to inspect and measure. I am fortunate to have found a modern replacement that can be fitted without too much bother.
                  I have ordered an SKF 51109, 45 X 65 X 14 metric to replace an R & M 33B50 (XLT45) which measures 1.77" X 2.674" X 0.627".
                  It will fit fine with a 2mm washer to make up the thickness, the id is the critical dimension fortunately.

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                  • #24
                    Originally posted by mars-red View Post

                    If you want to correspond by e-mail or even set up a Google Hangout or Skype session to try and troubleshoot this, send me a PM and I'll do my best to help.
                    It would be nice if exchanges/problem solving like this would be on the forum to a degree instead of happening behind close doors. Inquiring minds and all that....

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                    • #25
                      Originally posted by softtail View Post
                      It would be nice if exchanges/problem solving like this would be on the forum to a degree instead of happening behind close doors. Inquiring minds and all that....
                      Discussion forums don't exactly lend themselves to real-time collaboration, but if Matt doesn't want to take me up on the offer I certainly won't be offended.
                      Max
                      http://joyofprecision.com/

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                      • #26
                        Originally posted by mars-red View Post
                        That's a downer! Have you tried tweaking the alignment? What are the dimensions of the broach body that is supposed to turn inside of the bushings, and how much bushing length do you have? Most of the force should be taken by the thrust bearing (ball, in both of our cases), but there will be some lateral force and if you didn't have enough bearing surface I could see that maybe contributing to binding problems. There could be a lot more lateral force involved than I realized too, with mine the entire sleeve of the body of the tool that fits into my toolpost acts as a lateral bearing against the inner broach holder, maybe 2.5"-3" in length or so. If I had designed mine with smaller bearing sleeves on either end maybe I'd be having the same problem. I wonder if a full bearing surface along the entire length of your broach body would help.

                        Regarding the dish at the end of my broach (would that be called the "rake" in the case? I'm not sure, but seems like the relief would be the angle behind the cutting edge of the broach), I formed that just using a drill, so the angle is whatever the tip angle of the drill was. As I recall, I used one of my screw machine drills and I believe that set of mine is 135 degree.

                        If you want to correspond by e-mail or even set up a Google Hangout or Skype session to try and troubleshoot this, send me a PM and I'll do my best to help.
                        thanks Max, that's super kind! I'm happy to go through it here though so that others might benefit from it, as Softail suggested. I learn more from my mistakes than my successes

                        I tried from ~2deg (the back rake or relief of the cutter) to 0deg without any difference. The only time the cutter moved was when it got jammed in solid. I tried different speeds to, from a few 100rpm to 20rpm. Even with moderate pressure the cutter locked up solid.

                        Just thinking this through, I'll have to double check that the cutter isn't bottoming out in the holder in anyway. It shouldn't be, but it wouldn't take a moment to check.

                        I'll have to take some pics to show the broach holder (I'm actually rather proud of it). The toolholder that was I repurposing has two 1/2in ID x 1/2in oilite bushings, with the flange of one acting as a thrust bearing. This works fine for my live drill chuck, but I was pretty dubious about it working with the broach holder. The broach holder has a 1/2in diameter by ~1 1/2in hole, with the 60deg countersunk hole for the 1/4in BB at the bottom and the broach is 1/2in x ~2in. The broach is a very close fit in the broach holder, to the extent that it requires a tug to get it out if there's any oil in there. I'm thinking that having such close tolerances might be the problem - any off axis thrust (or even slightly off center hex on the broach) might be enough to jam it solid.

                        I've ordered a couple of 1/2 x 3/4 x 5/16 cartridge bearings for little money (only had 12mm ID bearings in my spares box, grr) and the small OD should mean that making a new holder with 1 or 2 cartridge bearings and a BB thrust bearing shouldn't take too long. It'll give me a nice little project to get one with after classes end in a couple of weeks!

                        thanks for the heads up on the front relief, I'll try and recut mine to give a bit more.

                        To be honest, even though this hasn't worked yet I'm super pleased with how the machining has gone - the broach holder was bang on tolerance and the hex broach came out really well on my DP/mill using my hex ER25 collet holder (love that thing).

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                        • #27
                          No worries, Matt, just wanted to offer in case it would help.

                          Let us know how it goes. As far as the fit, I don't think you'd want any looser. The looser the fit, the greater the angle of the rotating body will be relative to the centerline of the bearings, and that means less effective bearing surface. I think if anything you want as little clearance as you can get while still being "free", to maintain the most bearing surface. You may want to have a bearing surface that runs the entire length, rather than 1/2" on each end.

                          From some of your commentary, it sounds like you are applying oil, which you definitely will want for this application. I really think if you had this same close sliding fit for the entire length of the tool body, and loaded it up with oil, you'd notice quite a difference. Just a hunch though. For what it's worth, I use light spindle oil (3-in-1, in my case) in my broaching tool.
                          Max
                          http://joyofprecision.com/

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                          • #28
                            I wonder about the possibility of using an Allen key with ground relief for the cutter. Seems doable.

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                            • #29
                              Originally posted by softtail View Post
                              I wonder about the possibility of using an Allen key with ground relief for the cutter. Seems doable.
                              I've heard of people doing exactly that for softer metals, and some Allen keys are hard enough that I think you could get away with a use or two in steel. If it's good high carbon steel, you could even re harden it and probably get as much use out of it as the O1 or W1 broaches I've made.
                              Max
                              http://joyofprecision.com/

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                              • #30
                                thanks Max! In the 2nd version the broach rotated (or was supposed to) in the broach holder, with ~1 1/4in of bore/broach contact and the 1/4in BB at the end. I was using grease on the BB and 20W oil on the side of the broach holder bore - probably too thick for this but it spun easily by hand. I'll use ISO32 next time as that's much thinner.

                                I need to check that the broach isn't bottoming out of the bore of the broach holder first, then I'll recut the face of the broach to give it more front relief to see if that makes a difference. No harm in fiddling with it while I'm waiting for the bearings to arrive. Most likely at the weekend as I'm behind in my grading and I have a job to apply to this week

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