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  • centering help

    What tool or technique do I need to center this housing on my mill? I need to bore the bushing that fits in the end.Click image for larger version

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    san jose, ca. usa

  • #2
    It depends on how accurate you need to be. I'm assuming that you want the finished hole to be 90 degrees to the flange that is on the table.

    Quick and dirty is to put a bull nose center in the quill and move the part around till the center is firmly seated in the hole.

    A more precise way is to use an edge finder to probe the edges in the x and y axis, but that can be clumsy. The idea is that no matter where you touch the edge of the hole, the center will be 1/2 of the distance between the left and right reading.

    A wiggler works really well for quick and dirty too. You lower the wiggler probe into the hole press the probe against the side. Then you sweep the diameter by hand. The probe will be moved to the position that matches the edge that is closest to the spindle center. Rotate the spindle to find the edge where the probe has the most clearance and move the table 1/2 the distance. Do this 3 or 4 times and you will find that the probe is touching for a full resolution. A wiggler can be used with very little free room between the spindle and the work.

    An indicol holder is a step up from a wiggler. You do the same process as with a wiggler, but using a test indicator to measure the offset. Can be very precise.

    A coaxial indicator is like an indicol that lets you see the indicator dial as the spindle rotates. It can take a lot of Z room.

    I believe that you can get within .005 tolerance using any of these methods.

    At the end of the project, there is a profound difference between spare parts and left over parts.

    Location: SF East Bay.


    • #3
      I am not sure I follow your question. You need a test indicator with a stem clamped in your spindle, but I bet you know that already. Preferably an indicator should have a long needle allowing you to reach deep into the bore. Put the spindle in neutral and rotate it with the indicator . When indicator reading stops changing, you are on center of the bore. Do it on several depth positions to see if the bore is sitting perpendicular to the table.

      You can try to clamp the casting directly to the table (remove the vise first). It is high, but hopefully you have enough rigidity to take light cuts with a boring head. If you never used a boring head on this machine, I would suggest you try first on a piece of scrap. Do you have enough vertical room to fit a boring head with the tool?


      • #4
        Where the task is something that is likely to be repeated and frequently enough to make the investment worthwhile, a tool like the Blake "Coaxial Indicator" is one way of centering on a mill. I have an original Blake. Less expensive import copies began to appear on the market a number of years ago - back at the time I noticed complaints about the imports, but there may have been improvements since then. Others here may be able to comment.

        For a one-off task, alignment can be achieved with simpler tools like Wigglers, Edge Finders and even through basic techniques of "touching off" with a cutter or drill blank against a piece of paper of known thickness and then determining center coordinates from edge locations.

        Keep in mind that alignment is necessary in the vertical, as well as the horizontal plane.

        Edit: As danlb & mikey553 point out, vertical clearance is at a premium for this set-up. Questionable whether there is enough to accommodate a Co-Ax indicator .
        Last edited by EddyCurr; 01-16-2022, 12:37 PM.


        • #5
          If you have enough Z height, a coax indicator would be useful. Otherwise, turn a steel plug which fits the existing bore in the work one end and in a collet at the other, and then clamp the base of the work down. You could clamp the work down first and then use the X Y and Z to get the plug lined up perfectly.


          • #6
            thanks guys, the room is the problem. I can borrow a co ax, never used one but could figure it out. but no room. I have indicators but the leg isn't long enough. I have never seen an indicator with a long leg. will google indicol holder.
            san jose, ca. usa


            • #7
              ok I have one of those indicol holders, it moves around too much and doesnt fit in the space well. I think I need to reframe the question.

              I need to press a bushing into the tail shaft housing, this bushing has to be finished to size some how. normally I'd have someone hone to fit on a sunnen rod hone. unfortunately, the people who could free hand this and get it right no longer exist around here. how can I do it. too big for my lathe.(tried that first.) if not done right, it locks up the output shaft. I appreciate you taking the time to respond. I did try the xy back and forth to center but this lightweight machine is sloppy, and I'm not a machinist.
              san jose, ca. usa


              • #8
                The picture looks like you have quite a bit of room, how much do you have from the quill to the housing? Danlb has great ideas, can you try any of those? Do you need to size the inside of the bushing when pressed in or the housing to put the bushing in to the tranny. By the way what car are you working on, Morris Minor? My car of choice...

                When you say it won't fit in the lathe what size of lathe do you have? This should be able to be done (if the lathe is big enough) by jigging the housing on the ways to center of the tail bushing then run the hone in the chuck of the lathe. Take the tailstock off and it should give you enough length to set up a mount of some kind. The other idea would be use the tranny support and build a 90* brace off it to run the hone with the mill or with a guide on the 90* a drill motor.

                Just me thinking outside of the box for good or bad results..

                Mr fixit


                • #9
                  I'm assuming that a the opening at the end of that casing is bigger than your centers.

                  I think I'd make a quick and dirty bull nose center on your lathe. Turn the shaft to match your favorite mill collet. It will look something like this, though the diameter needs only to be slightly bigger than the diameter of the opening.

                  To use it, mount the center in the spindle and position the casting under it. When you lower the center it will hit one spot on the opening. Shift the casting until the center seats all the way around. Lock the table and proceed to the next step, which mill most likely be a boring head.

                  Click image for larger version

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                  BTW, a wiggler is pretty easy to make too. No precision needed. Here's a $10 set at shars.

                  At the end of the project, there is a profound difference between spare parts and left over parts.

                  Location: SF East Bay.


                  • #10
                    I bought a coax gauge about a year ago. It's an import one sold under the Accusize name. The results with it were excellent the 3 times I've used it so far. But it does use up a lot of vertical room.

                    What about taking a bit of time to make up a holder for a DTI or dial gauge? Most of the DTI's come with a dovetail to round stem adapter. It should be pretty quick to make up a round bar that fits into your boring head adapts to that stub. That turns your boring head into an adjustable gauge holder.

                    If you have a DTI and given the size of the hole you are trying to center on I'd go with this first option.

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                    Missing from the picture is the roughly 4" length of 1/2" rod you need that will slip into the horizontal hole in the boring head. Into one end of that bar you'll drill a hole to accept the stem and a second hole which gets threaded for a set screw. Or you can split the bar for some length through the stem hole and use a clamping screw to pinch the stem.

                    Don't have a DTI? But have a dial gauge? Then have a look at this picture.

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                    It won't reach down deep into the hole but you should be able to get the end far enough in to read the bearing seat. For a quick and dirty holder we're looking at a length of 1/2" round again to slip into the boring head's cross hole. But this time on the end add a hinged leg about 2 to 3 inches long drilled to fit the finger's extension housing and another set screw hole. The hinged leg will give you some leeway for setting the indicator's finger angle.

                    You're in a hurry, right? So just knock this out from some 1/2" round bar and cut the hinge "D" ends for the overlaid hinge with a hacksaw or bandsaw and file to somewhat semi true then drill and tap for a hinge screw that also locks the joint. Drill the other end so it fits the round finger housing and fit a set screw. Don't grossly tighten it or you will find that it distorts the housing and pinches the finger. But lightly tight is tight enough.

                    Best of all with the gauge face in both cases facing upward you can easily see the readings as you sweep the hole. And with either option I can't see it taking more than 20 minutes to make the holder. It won't be pretty, but it'll work fine. And it uses the same boring head that you'll be using for the actual cutting. Of course if you like this idea and it works out but is a bit rough then the sky is the limit on how fancy you make the next similar boring head gauge holder.

                    For later on if you have a DTI a second very short holder could be made to fit into this picture. A short stub of 1/2" bar with a hole for the stem which is offset as shown so the finger is close to the center line? This one would not work for the size you need this time. But perhaps another time? For the few minutes it takes it's worth keeping in mind.

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                    That setup is going to result in a pretty tall setup with not a big footprint. Any chance of rigging some temporary braces off the back column and a second brace for the other direction off some other thing to either side? I'm thinking even some 2x4's pipe or bar stock of some manner that won't whip around is going to help. A patch of thick plywood with a hole saw cut that fits firmly over the OD of the end of it would make for easy attaching of the braces?
                    Last edited by BCRider; 01-16-2022, 02:26 PM.
                    Chilliwack BC, Canada


                    • #11
                      It looks like you have too much of an advice and not enough experience. Forget about all expensive tools you supposedly need to have. You can do just fine without a coax indicator or Indicol. All you need is a test indicator with a long leg to indicate deep inside the bore and the way to mount it to the spindle.

                      But before you even go there you need to decide if your mill has enough vertical room for your casting, boring head and a tool. Do you have a boring head and at least one appropriate boring bar? Does your mill have an auto down feed? If you can say "yes" to all these questions, try the boring head on some piece of scrap aluminum to see if you can do it. Only after that start looking for an indicator. By the way, they exist with long legs. I have one with 1.4" long leg. The indicator body can also go inside a bore, if bore is big enough.

                      The casting looks like it is made out of aluminum alloy. If you heat it in an oven, you can drop the cold bushing in the bore to create a shrink fit. It is better and safer than pressing the bushing. Most likely the bushing ID will change after assembly so you will need to finish it on the mill or some other way.


                      • #12
                        Looking at his picture it sure looks like there's room for a boring head with a short bar. Thankfully the bushing doesn't need a very deep cut. It'll be tight though. If the housing was another inch longer I'm thinking that it might not be a big enough machine.

                        No power downfeed isn't a deal breaker either. Just wind the handwheel smoothly and slowly so he gets fine chips. It's one of the old round column mill/drills. So it has a slow advance hand wheel in addition to the drill press style feed arms..... Or at least it would have the drill press arms if they were screwed in.....

                        Gambler, I'd certainly suggest that you take heed of the heating the housing and cooling the bushing trick mentioned above.
                        Chilliwack BC, Canada


                        • #13
                          Originally posted by gambler View Post
                          thanks guys, the room is the problem. I can borrow a co ax, never used one but could figure it out. but no room. I have indicators but the leg isn't long enough. I have never seen an indicator with a long leg. will google indicol holder.
                          The round Cast Cap on top of the round column can be removed to gain a little more Vertical Travel.


                          • #14
                            1. I don’t think I have the room Click image for larger version

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                            san jose, ca. usa


                            • #15
                              Sprite race car transmission is what it’s from.
                              san jose, ca. usa