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Making an R8 arbor

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  • Making an R8 arbor

    So I decided to try my hand at making some endmill holders. I bought a length of stress proof to make them from. I set up a yuasa R8 arbor between centers and using an indicator, set my compound to the right angle for the taper.

    Stock is chucked up and center drilled on the end for a live center. I turn the straight portion to .949" x 3" and then cut the taper from .949" all the way out to 1.375". I know that's longer than necessary, but I didn't figure it'd hurt anything. I then drill and tap the the end for 7/16" x 20 for the draw bar. All done in one set up to keep things concentric. After that, I lop it off in the bandsaw at 5.75" total. This gives me enough left to pretty much finish it anyway I like.
    After making the first 5, I finally got the process for the 6th down to about 20-25 minutes. Pretty good in my mind.
    Now here's the question. How accurate does this taper have to be? I got around to bluing and test fitting, and only the first 1/8" or so is getting the blue rubbed off. The taper doesn't stay seated when the draw bar is loosened. Thinking I screwed up, I blued up the yuasa arbor and tried the same thing. It stays seated with the draw bar backed off, but only the first 1/16" or so of the blue is getting rubbed off. By "first" I mean the small end of the taper. It looks to me like my arbors are a slightly better fit than the yuasa, but still isn't quite right. What's going on here? I've got 9 more feet of shaft I want to use before setting my compound back to it's normal position. How should I proceed? Leave them as is and not worry about it? Turn the other 18 and fine tune later? Or change set up.

  • #2
    You would think an end mill holder would want to have full contact on the taper. You certainly don't want to use an arbor with only partial contact.

    Keep in mind you don't have an accurate reference arbor to work with. The Yuasa is not a super accurate brand so it may be off a bit.

    Your spindle could be worn at the large end of the taper.

    I would make the holders with a taper that was as close to full contact as possible in your spindle. That would compensate for any error in the spindle.


    • #3
      No experience but I know I am headed for roughly the same thing (making holders/collets).

      So, question: if you indicate off another arbor, are you not then just copying said arbor dimensions?
      Would it not be the plan to indicate off the hole the arbor fits into?...what I mean is, esp in my case, who is to say that copied arbor is really all that good? Or at the very least indicate both and compare the numbers? and that would tell you where something, if anything, was "off"...

      Personally, I'd check and tweak the set-up slightly esp as concentric is important.

      Edit: had not thought of the point DR brings does it become a question of matching the spindle you have (and could be worn) or making to a specified dimension?
      Last edited by RussZHC; 03-10-2012, 02:57 PM.


      • #4
        Just a thought...

        Are the arbors you've made slitted (collet type) or plain with a locking screw for flats on the milling cutters?

        If they're slitted, you may find that the fit's better with a cutter in place, as otherwise the collet body will distort (because the "jaws" aren't being held parallel) and you may only get contact at the very end of the tapered section? this is not unknown with single-taper collets etc., and is one reason why ER (double-taper) collets can give a better grip...

        Just my ha'pennorth,
        Dave H. (the other one)
        Rules are for the obedience of fools, and the guidance of wise men.

        Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools


        • #5
          Originally posted by RussZHC
          So, question: if you indicate off another arbor, are you not then just copying said arbor dimensions?
          Yes, I'm going with the compare method rather than making to prints because of the tools I have to use. It basically involves an indicator on the QCTP swiping back and forth on the taper and adjusting the compound till the needle stays still. I don't have any other more accurate way to measure a taper.

          Originally posted by RussZHC
          Would it not be the plan to indicate off the hole the arbor fits into?
          If you know how to do that without removing the spindle from the mill and chucking it up in the lathe, let me hear it.

          I blued another arbor, I think it's a jacobs. It showed much better contact, so I suppose I'll chuck it up and run the indicator across it to see what the difference is.

          I don't believe my mill has seen much use, so I don't suspect a worn taper. Either way, I'd rather have the arbors correct so they will fit any R8 spindle. Not custom fit to mine.

          I'm not making collets, these are solid arbors for endmill holders (weldon type) or any other application I can come up with. Holesaws, slitting saws, etc. They're blanks to be bored and reamed on an as needed basis. I'll be able to get about 24 of them out of my $100 chunk of steel.


          • #6
            Gotta say, "I don't know"...the answer was not meant to be flip but I may just be "parroting" what I surmise the would be correct. To me, its just a lathe turned 90*.

            I looked and the largest range of DTI I could find was .200" and if I did the math correct, that is not quite large enough to account for the distance change from the small end to the large end of the taper so...

            I could be entirely wrong, but where I would start...either the table or the mill head moves up and down, so I would use an DTI to find out where the taper starts then apply the same principle to locate where the taper stops (if I am looking at the spec diagram for R8 correctly, there should be a flat "lip" outboard of the slope)...the difference should give you one side of the triangle. Then indicate on the sloping face of the spindle for as long as possible (it does not need to be over entire length since the assumption would be it does not change slope in the middle somewhere) and depending on how much the table or head was raised or lowered, that should give you the angle of the slope so you would then have two sides of the triangle...

            Now that idea may be very, very wrong or not get you the information you seek, sorry, just saying what I would do with the little experience I have...

            Not that is matters but I used this:

            Oh, the bluing way to me is much better than my answer...
            Last edited by RussZHC; 03-10-2012, 05:14 PM.


            • #7
              Originally posted by Boostinjdm
              .... How accurate does this taper have to be? I got around to bluing and test fitting, and only the first 1/8" or so is getting the blue rubbed off. .......... Or change set up.
              I'd change the setup. I turn all my collets and toolholders between centers so I can insure concentricity and yet easily be able to remove and test the fit. I too have had a finicky time getting a taper to perfectly contact its mate when duplicating a "standard" and often resort to a light filing or polishing in the process of bluing and testing fits. Only one thousandth of an inch in diameter on one end the taper will make a large difference in contact area along its surface. That kind of difference could easily come from having set the dial indicator or the cutting tool slightly above or below centerline. Doing it between centers lets me cut the slot for the anti rotation pin, test the fit, and return easily to tune the fit up if necessary. I usually drill or bore the working end in situ so I have perfect running concentricity in the result. If that will be hard to do with your tooling, I would make the working end a bit longer, bore in the lathe, cut a 30 degree chamfer in its hole, and use that for one of the centers when cutting the body and taper.


              • #8
                Well, I redid the setup. Ran the indicator across my jacobs arbor. Had to move the compound just a touch. This arbor read about a thou different from one end to the other compared to the first arbor I used. I now have 3/8"-1/2" of engagement and it will stay seated with the drawbar loosened after snugging.

                I now have 7 R8 arbor blanks that will need fine tuning.

                I have been taking two cuts to make the taper. One really heavy one, and a lighter (maybe .030" on average) cut. Since the little end is engaging first, I may try cutting the taper all in one shot and maybe the tool flex will be enough to make a better fit. Maybe....
                I'm so close on my setup now that I'd hate to screw it up and go backwards.

                The 7 made so far will either have to be tuned up with a file and emery paper or dialed in in the four jaw and re-cut with the compound flipped the other direction. I've been taking some pics as I go and will post 'em when (if) I ever get a good arbor.


                • #9
                  I got 'em all made. Now to come up with a correction plan.
                  I'm thinking maybe a collet set up for quickly mounting since there are 24 of them, and a sine bar to get a more accurate angle setting.


                  • #10
                    I think your method was fine. You found out that the existing arbors have slightly different tapers, when ideally they should be exactly the same. You now have three different brands- the two commercially made ones, and your own. Yours sounds like it is well within the specs.

                    If there was to be more refinement of the angle, the process would then change to making them match your spindle taper rather than conform exactly to the R8 standard.

                    The only other thing that I would consider in making well-fitting tapers is the tool height. The cutting edge has to be exactly on center, otherwise you won't get a perfectly straight taper, regardless of angle. The possible errors might be small, but the goal is to have as close to a perfectly fitting arbor as possible.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                    • #11
                      First one completed and ready for testing. I gave up for the night after cutting my hand on the end mill. I corrected the taper with a few swipes of the file and some scotch bright. Took me about 5 minutes to do. I guess I got lucky. Now the blue gets scuffed so it looks dull, but none rubs through to expose the metal underneath. That says 100% contact to me.

                      I decided to go big on the first one (didn't have the right reamers for other sizes). This is a 3/4" end mill holder.


                      • #12
                        The angle of the cone is typically 16 degrees and 51 minutes (i.e. 16.85 degrees) with an OD of 1.25" (source, Bridgeport Manufacturer

                        See :

                        You may also want to under cut it where it is shown in the pics.
                        You have removed the key, correct?

                        Chuck up a tapered shaft that you want to duplicate. Adjust your taper setup so sweeping a dial indicator from end to end results in zero deflection. Replace the dummy shaft with a blank and machine. tHIS METHOD WAS DESCRIBED BY GKman IN THE Turning a Morse taper... THREAD. This will give you the accuracy of degrees and miniutes as is required for an R8 taper.
                        Last edited by ahidley; 03-19-2012, 10:14 AM.