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  • Centering work on a rotary table

    How do you center your work on a rotary table, when all you have on the work is a mark where it's supposed to centered to?

    Albert

  • #2
    roughly centre it by eye, now bring a stationary pointer over the mark & rotate the table, adjusting as needed. When you get to the point where the table rotates but the mark doesn't move - you are there!
    Tel

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    • #3
      Good question. I am interested in seeing some ideas myself.

      I turned a tapered plug on my lathe that drops into the center hole. The top of the plug has a 0.500" diameter end that I aligh with a 0.500" edge finder that I place in a collet in the headstock.

      This allows me to quickly find the center of the table to about 0.002 to 0.005" if I am in a hurry. Once set, I zero my X and Y counters on the DRO.

      To locate work on the table I install a pointer in the mill's headstock and use that to point the work or I can use the edge finder and subtract 0.250".

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      • #4
        If you centerpunch the mark, you can use a wiggler to indicate it. Center the table first of course.
        I picked up a Blake Coaxial indicator on eBay for $35.00. Great little tool for centering on milling machime.
        One of the Lautard books had article on making your own. I did one of these too, and it works as well as the Blake.
        Jim H.

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        • #5
          Depends in part on how accurate you need to be. The ideas given above are pretty much what I'd do, probably.

          Expanding a bit on debequem's idea: I've got a center plug with a 1/2" dia. hole in it, about 1/2" deep. I've also got a selection of smaller 1/2" dia. plugs that can drop into that hole, with various diameters turned on their tops. That way, if the workpiece has, say, a 1/4" hole in it that needs to be centered, I can drop in the small plug with the 1/4" projection and set the work onto it. If I need some size I don't already have, it's a trivial matter to turn up another small plug out of 1/2" rod. It's probably accurate to under 0.005", which is usually good enough. If it needs to be better, I take the time to use an indicator.

          ----------
          Try to make a living, not a killing. -- Utah Phillips
          Don't believe everything you know. -- Bumper sticker
          Everybody is ignorant, only on different subjects. -- Will Rogers
          There are lots of people who mistake their imagination for their memory. - Josh Billings
          Law of Logical Argument - Anything is possible if you don't know what you are talking about.
          Don't own anything you have to feed or paint. - Hood River Blackie

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          • #6
            Use an indicator on round parts and an edge finder on square. Quick way to get close on round parts is to use the edge finder. Touch on the surface and zero your DRO on the incremental setting. Move in this axis only and touch the other side. Take the reading from the DRO and move half of the incremental distance towards center for this axis. You will be close to center in that axis. Now set zero in the absolute screen of your DRO for. Repeat for the other axis and you will be very close to center.

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            • #7
              Thanks for all the ideas. I was hoping that there was some nifty trick, but I guess sometime there no shortcut.

              Albert

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              • #8
                One of the best tools I've got is a centering scope. There are so many uses for it ~ in fact I discover another use almost daily! It can be used for re-setting tailstock on centre, picking up centre popped drill positions on the drill press, checking qaulity of small drill regrinds (by looking into the spot drilled into a piece of scrap) ~ and of course for centering work in the mill.

                Once you've got the table centred (as amply described in previous replies) and then moved x (or y) co-ordinates to the desired radii of operation; now comes the tricky bit, especially if you have an odd shaped piece of work. I would suggest you blue up and scribe 'mark out' lines, or centre pop, as the job requires; the centering scope fits into the tool holder and the work can be positioned 'spot on'.

                I see Enco have a 45x Centering scope, with 3/8ths straight shank, for $170ish. I'm sure in auctions these can be found for a lot less, as not many people would recognise one if it whacked them in the face. I bought mine, buried in a box of drills for آ£10. It turned out to be a Zeiss (worth about آ£200 second hand).

                RR

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                • #9
                  RR,

                  That's one that I didn't think about. I can see that working quite well. Does your centering scope have focusing control?

                  Albert

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                  • #10
                    Albert,

                    The Zeiss centering scope has a pair of cross hairs, with concentric rings at 0.2mm pitch with a major mark at every 1mm. The field of view is about 8mm (5/16ths) ~ focal length is about 1" and the eyepiece has a focussing facility. What I do is to bring the work up to about the focal length ( by table z axis), if the cross hairs are fuzzy, an adjustment on the focussing ring brings the cross hairs back into vision and a final adjustment is made to the focal length via the table Z axis.

                    One other use I found was the set up of work in a 4Jaw, with the 'scope held in the tailstock, any odd shaped (or even round!) work can be centred in next to no time. I would fully recommend anyone to purchase one, they are without doubt a very useful tool. I'm sure you North Americans could even modify a rifle 'scope???

                    Some 'scopes come with a ring of 'pee wee' bulbs to light the object. They are usually 6 volt so can be powered by a remote lantern torch battery.

                    RR

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                    • #11
                      I ordered one of the "import" centering scopes, and sent it back. I found it unsatisfactory. I expect one made by Zeiss, however, would be a totally different experience....
                      ----------
                      Try to make a living, not a killing. -- Utah Phillips
                      Don't believe everything you know. -- Bumper sticker
                      Everybody is ignorant, only on different subjects. -- Will Rogers
                      There are lots of people who mistake their imagination for their memory. - Josh Billings
                      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
                      Don't own anything you have to feed or paint. - Hood River Blackie

                      Comment


                      • #12
                        RR

                        Zeiss? Better be good, Duh! Even their wooden cases are awesome. I think you are spoiled - have you snuck that Schnaublin in yet? If the wife complains remind her that she has that stove, fridge, washing machine, dryer, television, and house and all you have is her and some tools to reminder you of her. (a tear running down the cheek here would be ideal - Habanero sauce works for me)

                        Comment


                        • #13
                          Thrud,

                          Unfortunately, or not as the case may be, the 'scope came at the bottom of a bin of old odd sized drills and other flotsom in a factory auction. I delved into the bin just prior to it going 'under the hammer'. I saw the end of the 'scope and took a gamble on what I thought it was. The wooden box for it must've perished along with the factory records in a good old bonfire ~ or some guy has it to keep parts of his fishing tackle in! Just goes to show that some of the auctioneers don't know what they're dealing with when assembling lots.

                          Still working on the good lady for the Schaublin ~ how big a bunch of flowers do you think I need??

                          RR

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                          • #14
                            RR
                            Red roses - 2 dozen & Belgian chocolates.

                            Auctioneers are real twits sometimes. I was lucky enough that when they found the gears for my lathe they kept them for me at no charge. Other times they break up stuff despite your protests to put them together because they are matched - can't win them all.

                            [This message has been edited by Thrud (edited 09-15-2002).]

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