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Bridgeport Mill Clone Spindle Taper

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  • Bridgeport Mill Clone Spindle Taper

    I have a small bench top mill and intend acquiring a larger floor mounted one with adjustable knee and power feed on the quill for general hobby machining.

    I have an opportunity to purchase a good 1985 Bridgeport clone mill advertised with R8 spindle.

    The local machine merchant catalogs that I have seen only list the NTnn range of spindle tapers.

    What are the advantages / disadvantages of the R8 versus the NT30 spindle ?
    For example:
    - is R8 now regarded as obsolete ?
    - are tool holders and chucks for R8 as readily available as for NT30 ?
    - does the R8 have the same or smaller capacity for straight shank tooling compared with the NT30 ?
    - would R8 or NT30 be better for 12 mm end mill or 75 mm face cutter ?

    Happy machining,

  • #2
    Hi John,

    R8 is probably the most common taper on manual vertical milling machines and there is a very wide variety of tooling available with that shank. Check out the various suppliers online like Enco. You can find endmill holders, collets, boring head shanks, drill chuck arbors, slitting saw arbors, ER collet chucks, and the list goes on and on. Hope this helps. BTW, Enco always has a free shipping code every month for orders over $25. Do a forum search for "enco code" and you shouldn't have trouble finding the current one.

    Edit: Regarding capacity, R8 collets go up to 3/4" (they have larger ones, but they're really thin and I wouldn't trust them). Endmill holders are available in larger sizes. 12mm should be no problem. I run 3" face mills regularly and it isn't a problem at all. That's right around 75mm. I take it you live someplace that thinks in metric?

    Last edited by hornluv; 04-25-2010, 09:38 AM.
    Stuart de Haro


    • #3

      R8 is obsolete it some applications but for moderate duty milling it is still probably the most popular.

      Most collets go up to 7/8" capacity and re more readily available than NT 30 at least here in states, not sure where youy are located.

      12mm (1/2") is well within the R8's capabilities. I've got an NMTB 30 spindle on one of my horizontal mills and would consider it a "bit" stouter than R8, not a whole lot more though.

      It all depends on what you plan on doing. B-port made a wholw lot of R8's during their heyday, among others, for industry.
      I bury my work


      • #4
        Adding an iota to the list. R8 hasn't a key or spindle nose drive but the NMT 30 does. Larger drills, shell mills, flycutters etc may slip in the R8 spindle. A little slip once in a great while won't hurt your R8 spindle but you have to be vigilant. The key drive in the NMT30 will not slip. You can reliably drive most any cutter within the capacity of the spindle bearings, available power, and the mechanical trength of the machine's structure and mechanism.

        Handy tip of the week: first thing you do before powering the machine up, locate and remove the spindle index key; the do-dad that engages the keyeat in the collet. Take it out and throw it away. It has no significant torque capacity. It's fragile and the first time you spin a tool (it WILL happen) the little dog point will shear off and the fragment will wedge the tool in the spindle.

        The index key while seemingly useful is in practical terms a huge PITA. The spindle tooling is easily held with one hand while spinning up the drawbar with the other. Once the tool is in contact with the taper it can no longer spin relative to the spindle as the drawbar i tightened.

        The index key takes the form of a dog-point setscrew accessed by removing the spindle end retainer with a strap wrench. There are two short setscrews - one piggybacks the other to lock it against movement. Be sure to remove both.
        Last edited by Forrest Addy; 04-25-2010, 05:14 PM.


        • #5
          Originally posted by electrosteam
          The local machine merchant catalogs that I have seen only list the NTnn range of spindle tapers.
          Please add your location information to your profile. No point in us telling you about Enco if you are on the other side of the ocean.


          • #6
            Thanks guys for the comments on R8/NT30 spindles, you all speak with obvious experience.
            I am now in a much better position to make a value judgment.

            As requested, I have updated my profile to show Sydney as my location (hence metric).
            The profile also now shows that I am a retired electrical engineer with no previous experience of machining - a whole new field of interest.

            The used mill with R8 under consideration is a Clausing/Kondia.
            The new mill with NT30 is a Chinese one badged in Australia as a HM50/52.
            The HM50/52 does not, however, have power quill or knee.
            A quick look through various net locations would seem to indicate that Clausing/Kondia documentation and parts are still obtainable.

            There does appear to be a following for the HM50/52 with the CNC devotees, but my main interest is one-off special pieces.

            Happy machining,


            • #7
              Starting off in OZ


              That HM-52 is a nice machine and only requires 230v single phase power.


              It is my machine of choice when I get rid of my HF-45:


              There are plenty of NT30 adaptors around - expensive if new - so try eBay etc. Here is a list to check out:



              I think that you may find that R8 is very popular in the USA as it was/is a Hardinge (maker of the BridgePort mill) product - which is in wide use in the USA and has a Hardinge R8 taper.

              You may well find that many tapers of that size range in Australia (aka OZ) are No.3 morse taper (aka MT3) and NT30.

              Work your way through this Hare and Forbes - aka Hafco aka MachineryHouse - catalogue for an indication of what is available in OZ.

              I have an interest as I buy a lot of stuff from Hafco and am quite satisfied.

              But if/as you are starting out with machines and tolls, I suggest that you take it slowly and have a look else-where as well as it can - and does - get very expensive.

              I hope that at least some of the other OZ members jump in with advise for you to consider as well.


              • #8
                Hi John,
                I see you joined up here as well, welcome.
                There is a lot of good info and experienced blokes on here that are willing to help out.
                The R8 is readily available in Australia from the big suppliers, as well as people like CTC tooling etc for importing it.