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use of bearings in rotary broach

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  • use of bearings in rotary broach

    Having read up on rotary broaches on this forum, I thought, I would make one.
    I have two sealed ball races, a double row angular contact and a single row deep groove. sizes are 20X47X20.6 and 20X47X14 metric.
    I could use them together with an ER25 X 20mm shank collet chuck.
    Which bearing would be best on the outboard side adjacent to the chuck?

  • #2
    The deep groove next to the chuck with the double angular taking thrust at the back although one half of it will be doing noting as regards thrust.
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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    • #3
      I know its not what you have but I think I'd go with a set of Tapered Roller Bearings. Far greater load capacity than either of the Ball Bearing units. You could use the sealed Deep Groove at the front as it sealed. Plus the class of the bearing makes a big difference as to the internal clearances.
      Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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      • #4
        It won't make any differance

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        • #5
          You'll also need one ball used as a thrust bearing in the center at the back of your broach. Works just like a dead center. Put grease on the ball

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          • #6
            Bottom line is that all you really need is a moderately capable, simple thrust bearing. ( besides the other ball bearings ) Believe it or not.

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            • #7
              Hemingway's market a rotary broach kit which seems to have a roller bearing and a thrust bearing setup.



              Making tooling looks to be a bit of a pain or would you buy it in?

              Paul

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              • #8
                I built a rotary broach from plans I downloaded. It uses a ball thrust bearing and a radial ball bearing. If you want the drawing PM me with your e-mail address and I will send you file. The original dwg file is dimensioned in metric. If I remember correctly I modeled it in Solid Edge. I could send either the original file or the model.

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                • #9
                  I think Sir John's suggestion makes sense, I don't see the need for a purely thrust element and my piece of metal isn't big enough. The broach will not be used for anything over 1/2". The broach will have a MT2 shank and will be non adjustable, the tool tip extension will be the same for any tool used, easy enough when all the tips will be home made.
                  It looks like I will have to make a wedge with my selected angle to tilt the rotary table / chuck because of height restrictions and no tilting head on a drill-mill. Then I can finish bore for the bearings.

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                  • #10
                    Old Mart. Mine is almost as you described but mine is adjustable. There has to be a way to adjust it to the lathes central axis. Thus the broach tip needs to be on this. If you make yours without adjustment then you will have to move your tailstock off of true center. Not a big deal but a pita. And you will not be able to use it in a milling machine. FWIW.

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                    • #11
                      Also that little angled block that you speak of is what I did. But my block is the size of a hex 5c collet holder
                      I have holders for 5c that are square, hex, octagon, and 12 sided. I think that makes it versatile enough for me.

                      Also don't think that every broach that you make will be the same length. That's like only being able to drill one depth of hole. Each job has different requirements. Make it versatile
                      Last edited by ahidley; 08-28-2016, 07:51 PM.

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                      • #12
                        I intend to make the null point about 1 1/2" in front of the collet chuck which can handle up to 5/8" and 16mm diameter stock, the exact dimensions have yet to be established as I don't yet have the ER25 chuck. I don't think it's likely that there would be any need to go to that depth even. Moving the tailstock off the centre line is too much bother and it certainly will not cant at an angle.

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