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Universal (dividing head + mill)

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  • Universal (dividing head + mill)

    Or in other words, adding a universal dividing head to a universal mill.

    Around this time last year I started a thread on universal mills suitable forthe home machine shop. Around 6 months ago I snagged an old 'NEWS' universal dividing head, managed to repair it and so then looked for a machine to put it on.

    It took some months and lots of running around but I now have a smallish universal mill. My question is (as this is a non OEM dividing head) how are the two linked. I know the hand wheel comes off the left end of the table and a gear is mounted onto the shaft, but I can't see any mounting points on the mill for banjos or other things.

    Has anyone got any pictures or can describe how their set up is done? I suspect I will need to make a couple more gears and some sort of mounting for them but I'd prefer not to overlook the obvious while I devise something more highly complex.


  • #2
    Firstly, I think you'e approached it the right way, by getting a universal dividing head and then looking for a mill to put it on.

    I have a smallish universal mill (Centec), and I guess universal dividing heads just aren't made this size.

    So I've had a roll-your-own-dividing-head project waiting for me to get good enough at welding. The first stab would be a dividing head that doesn't - just the banjos and a frame for transferring geared leadscrew motion to revolving work.

    On the Centec there's a small gearbox for on the far end of the mill table from the handwheel, so getting a feed from the leadscrew will be easy.

    Banjos and the like should be straightforward for me, as I've already been into that, gearing up a non-geared lathe. For you, if there's enough meat on the dividing head's casting to screw stuff to you should be able to cobble up something. You have to collect your range of gears first, decide on bores, and make hubs. I'd have thought the tricky part is getting a feed to the worm.

    And then there's the question of what a universal mill really is. In my view, my mill isn't really universal. You can swivel the whole table, so you can set up an angle between the work and it's movement, and the horizontal arbour, so I suppose it can do helixes (SP ?).

    But what I would rather have is a table that swivels on top of orthogonal (right angle/rectilinear) slideways, so the x-axis is still perpendicular to the y-axis, but the angle of the work and the table has changed, taking over some of the functions or a rotary table.

    Keep us posted, and more details of size of head and mill please.
    Richard - SW London, UK, EU.


    • #3
      No experience but Tony's site

      has a miller section and there are some photos that may give you ideas or help with the design (none I could find were in great detail)

      Adcock and Shipley Universal (photo near bottom)
      Pratt + Whitney 3C
      Elliott Miller, Elliott/Victoria Models U0, U1, U2 etc.

      the "difficulty" is none of the photos are really detailed enough in the correct spot as most just show a bunch of gears, 5 or 6 in some cases; the second thing I found was on some of the older models (of others not in above list) the drive did not necessarily come off the end of the table but rather some sort of intermediate gear box...not that it is a bad idea but no way to know what all was going on inside though some inferences can certainly be made and that has the potential to make the system more complex, but I suppose if done correctly, simpler?


      • #4
        Originally posted by form_change
        Has anyone got any pictures or can describe how their set up is done?
        Find online copies of Brown & Sharpe's 'Treatise on milling' and the similarly-named title by Cincinatti. There are chapters in both that cover this and show pictures of the set-up. If you have Moltrecht's books, they have the same information in (looks as if it's lifted directly from the earlier works).

        I hope I'm not telling you something you already know, but there are two uses for a universal dividing head - let us call them compound indexing and spiral milling.

        When used for indexing, the banjo is on the head itself, the gears go between the spindle of the head and the worm shaft, and are used to rotate the dividing plate, allowing divisions that are not possible with plates alone. This set-up is totally independent of the milling machine - it could be set up on your kitchen table.

        When used for spiral milling, the banjo goes on the milling machine leadscrew, the gears between the leadscrew and the spindle of the head. The worm and plates are not used. Exactly analagous to screwcutting on a lathe, but in a sense back-to-front, you turn the leadscrew a certain amount and the spindle in the head rotates a proportion of this amount.

        A third, fairly specialised use is to gear the head to the spindle of the mill thus allowing hobbing. The challenge here is to arrange the drive so that constant angular velocity is preserved.


        • #5
          I remember that thread! It always bothered me because I know the folks that made my mill were smart fellows... and they called it a "universal" mill even though the table didn't swivel with the leadscrew (see above thread for distinction if confused). It bugged me for a long while, and I finally found my answer a little while back. You don't actually need a swiveling table to spiral mill. All you need is a swiveling vertical head:

          I just wanted to share the discovery for those of us without the swiveling table. This is why I love old books with set-up pictures. I can read the texts all day, but that one picture (Fig.17) opened up a whole new aspect to me.


          • #6
            Originally posted by form_change
            Has anyone got any pictures or can describe how their set up is done?
            Here is one with open gearing so you can see:
            Last edited by Arthur.Marks; 05-21-2011, 02:11 PM.


            • #7
              This may help.


              • #8
                I think rohart nailed it. A true "universal" mill (as I've always understood the term) is one which allows the whole table to be adjusted angularly along the X axis, and it is indeed for the purpose of milling helical gears. The same effect can be achieved by rotating the top of a Bridgeport and using the 90 degree attachment.

                EDIT: In ArthurMark's photo you can see the universal's the tell-tale protractor base visible just above the lower left hand corner (in the shaded area).
                Last edited by DATo; 05-21-2011, 04:05 PM.


                • #9
                  To return to the OP's question... It seems to me there are a couple of ways to attach the banjo depending on your universal head design.

                  1)If you have a solid shaft which sticks out from the head, you clamp the banjo onto that. You can then swivel it on the shaft to provide engagement of the gears.

                  2)If no solid extension shaft on the head itself---or some have a tapered shaft which disallows the above method---you rigidly attach to the table. Some I see attach a shaft by what seems to be a nut in the t-slot. This shaft is then available to clamp the banjo and swing the gearing for engagement. Others have fully enclosed boxes which are rigidly attached to the front or side of the table. Examples in this category are the Aciera shown above in my first photo as well as the Hardinge UM's universal gearbox:

                  (for other views of above, see the following link:
                  The benefits of the latter are that you can position the head anywhere on the table. This may offer you better workpiece support in some instances or the necessary table travel. The variable positioning is possible through a connecting shaft from the box and the universal head. The former method necessitates positioning the head near the edge of the table because a gear is directly installed on the universal head. The latter offsets that gear into the enclosure.
                  Last edited by Arthur.Marks; 05-21-2011, 04:35 PM.


                  • #10
                    Here are some photos Of the gearing on my old Van Norman I built. Had to design and build the banjo bracket and machine all the gears .
                    This might give you some idea of what you will have to do. Lots of work but fun work. and you will have something to be proud of when done.
                    Every Mans Work Is A Portrait of Him Self


                    • #11
                      Arthur.Marks ---- That picture you posted of the Hardinge Mill is so sexy that it should be a fold out page in the Machinist's Handbook *LOL*


                      • #12
                        Attached is a picture of the end of the table in question

                        The dividing head (DvH) is a BS2 sized unit. I've taken the left hand wheel off to show the shaft for the table gear - an interesting thought is that the mill is metric, so working out helix angles may need some maths. Even with the head slid right up to the end of the T slot (that is, as far as it can go) a gear mounted on the shaft would not line up with a gear on the DvH. The two tapped holes on the visible face of the DvH are for the banjos used when differential indexing. My options look to be mount something on them or mount something using the T slots at the end of the table. So - how do other makers do this?



                        • #13
                          Originally posted by form_change
                 interesting thought is that the mill is metric, so working out helix angles may need some maths...
                          I was unaware that angles came in imperial and metric flavours :-). Most of the tables in the books are in term of leads, which are in linear units but are specific to the leadscrew pitch of the machine in question. If you think of it as screwcutting (albeit very coarse threads), the calculations are easy enough (e.g the leadscrew goes round ten times for the workpiece to revolve once: 1:10 gear ratio needed).

                          The more complicated bit is to allow for the table being skewed relative to the cutter axis. You have to modify the pitch by (IIRC) the cosine of the helix angle. You will never get exact gearing for these, so you have to get close enough. For these calculations, it is well worth reading up on continued fractions - there are a few online calculators as well where you can put in a decimal ratio and it gives the nearest fractions. I suspect that Marv Klotz has a program somewhere that does the same thing.

                          Originally posted by form_change
                          Even with the head slid right up to the end of the T slot... a gear mounted on the shaft would not line up with a gear on the DvH.
                          Because you are gearing to the spindle of the head, there is normally an extension shaft that inserts and is secured into the spindle that is then supported near the table (banjo) end.

                          If you get in touch with Sir John, he has available a copy of the Elliott Universal Dividing Heads manual that contains much useful information.


                          • #14
                            The metric comment was because I was reading machinery handbook and the table they have in there to work out leads etc. Recreating the tables should not be difficult but having the gearing ratios established was a nice thought.
                            It's the gearing ratios that are causing me the most thought though. An extension from the back of the spindle is easy enough (although my first thought (without knowing how things were done was that driving through the worm was the way it was done), but I still need some way of gearing up/ down to change helix angles. That means additional gears in the train supported somehow.



                            • #15
                              Read the link I provided. Although the DH is K&T, the differential indexing is done in the same way. BTW, the same gears used in differential indexing are used in spiral milling, although the numbers will probably change a bit for metrics.
                              Your gears, if you don't already have them , should be easier to make. Just a single keyway, not the 6 splines.