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Bore Measurement Again

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  • Bore Measurement Again

    OK, so instead of hobby jobs a paying job comes into my home shop. I have several hubs that have to be bored for bearing races for tapered roller bearings.

    Measuring bores with extreme accuracy has been trying at times and if possible, I make a shaft first, then fit the bore to it, using is as a gauge. This is OK for running and light push fits but for press fits falls short because I can't tell how much smaller the hole is than the shaft. In any case, that method won't work for me on this job.

    So, I'm faced with a few choices. I can try to use my inside caliper or snap gauges which thus far haven't proven to produce extreme repeatable accuracy, or I can try Oldtiffe's "Stick Method" mentioned in a previous thread and also described in Guy Lautard's books, I can purchase a Bore Micrometer or Dial Bore Gauge set which just happens to be on sale at Enco right now with free shipping. I've also considered making a "go gauge" turned carefully on the lathe to fit the bore when it reaches a size for a "light press fit" as described in South Bend's How to Run a Lathe and "sneaking up" on the diameter of the bore with the compound offset about 84 degrees which would prove quite time consuming because no actual amount of material to be removed is known. It would also require the manufacture of two "go gauges" because I have two different bore dimensions. Further, I have no Tool Post Grinder available so grinding the gauge isn't possible, it would have to be turned with a fine finish and perhaps polished with emery cloth & oil.

    I believe accuracy within .0005" would be sufficient for this project. I would appreciate any thoughts on which method I should use before I get started. I don't mind purchasing the Dial Bore Gauge, if it will do the job. Owning good tools that work is always a good investment in my opinion. On the other hand, I don't want a "gadget" that isn't any better than what I already have. The thought here is to obtain the required precision with the least effort and time investment.

    Thanks for taking time to respond.
    Last edited by firbikrhd1; 01-13-2010, 07:18 PM.

  • #2


    What is the diameter of the bore and what class of fit is required?

    A lot of this data will be in the bearing manufacturers or distributors web site.

    If you can't find the data or tolerances, post the nominal diameter and class of fit.

    I will be surprised if your limits are closer than 0.001" or 0.0005"

    "Class of finish" is just as important as class of fit as the "tops" of a comparatively rough finish will obviously not to the job as well as a better finish at the same size.

    Are you going to press the bearings in - or not? There is a good reason for my asking as the class of fit had a limit range that is from the largest bearing in the smallest hole (tightest) to the smallest bearing in the largest hole (least tight). If the bearings exist and/or you have them and can measure them accurately you can use the "unused" limit from the bearing and use the over-all limits instead of just those that apply only to the bore and so have a wider tolerance with an easier job foe the same end resultant class of fit.

    The "stick" method WILL work. All or any others are only variations of it - bore micrometers, inside micrometers etc. etc.

    As you say, boring accurately is much harder than turning an outside diameter to the same limits.

    For those not aware of what the "stick" method is - here it is:


    • #3
      In my (limited) experience the dial bore gauges are good for measuring taper in a bore but are hard to use to measure accurately the diameter, you have to set them with a mike or standard first...I wouldn't try to use mine to measure to half a thou. The inside mikes, however, work nice. CDCO also has inside mikes, and inside sets with interchangable rods, that are reasonably priced and (my copies, anyway) measure with good accuracy... // video_man


      • #4
        It wasn't clear if you have some of these, which don't cost an arm and a leg and should get you to 0.001" if not better. Of course, you'll need a good mic to measure them with.


        • #5
          I'm partial to real inside micrometers. Like an outside mic, but has jaws that fit the inside of the bore. They provide the same feel as a standard mic, and come with setting rings.

          Page 629 top of page.

          I have models sold by CDCO.

          Search for SKU 32101, much cheaper, but for the occasional use, they work fine for me.
          If I checked, with a good outside mic and standards, readings to within a tenth are very probable.

          AVOID calipers.


          • #6
            You said they are taper bearing races and those races are not critical to bore dimensions like a ball bearing is.

            Don't try to use a dial indicator bore mic on a bearing race bore because the bore is not long enough to get a good reading.

            Inside mic's or telescopic mic's are the way to go. For the taper bearing race a telescopic mic will get you in the tolerance you need. For closer work use the bore mic.

            When I use a bore mic I get the bore mic set to the hole and then use outside mic's to get what the bore is. The reason is it's easier to calibrate an outside mic than it is a bore mic.

            When I do a bore for a bearing I use telescopic gages to get within .010" or so and then start using a bore mic for the final size I want. Sometimes I use a flapper sanding wheel in a die grinder to finish the bore to size and smoothness, just leave about .0005" to .001" to polish out to size.

            What ever you do don't depend on dial calipers, digital calipers or telescopic gages to get to the finish size. Use mic's.
            It's only ink and paper


            • #7
              Best Thing

              Telescopic Gauges and Knowing how to use them will enrichen youre Machining Career. I have used mine to super close bore tolerances many times . They are the best thing to use for youre Job.


              • #8
                I hate snap gauges... and I do know how to use them... Good for getting "close", but I don't rely on them for "exact". I have a nice bore gauge that gets me "in the zone" also.

                And.. If I really need to know... I have many sets of gauge pins.... 3 pins and you can measure a "diameter" very nicely. Boring without a taper - that's another issue to keep an eye on.


                • #9
                  For super precision bores, without expensive bore gages, I prefer
                  to use an adjustable Parrallel and two dowel pins.
                  put the pins on top and bottom of the bore and the parrallel inbetween.
                  Slide it until the feel is snug, and lock the scew on the parallel so the setting is kept.
                  withdraw and mike the assembly at the bench.

                  Because you are using the pins on the surface exposed to the bearing races (later) surface finish issues are nullified

                  Super acccurate for few $$
                  Last edited by Rich Carlstedt; 01-13-2010, 10:18 PM.
                  Green Bay, WI


                  • #10
                    Rich, that's a great idea. All you have to do is measure the adjustable parallel and add the diameter of the two pins to get the bore size.

                    That's an interesting trick.
                    It's only ink and paper


                    • #11
                      Aren't there items similar to an adjustable parallel but ground on top and bottom to function as both the parallel and the pin?

                      Seems like I have seen them in a catalog.

                      Those telescopic things are a mystery to me... I can't get them to repeat within 5 thou, let alone a half thou. It's my considered opinion that they are a fraud, right up there with "sea bats"............. Obviously everyone "in the know" sees they are a fake, but nobody will admit it to outsiders.
                      CNC machines only go through the motions.

                      Ideas expressed may be mine, or from anyone else in the universe.
                      Not responsible for clerical errors. Or those made by lay people either.
                      Number formats and units may be chosen at random depending on what day it is.
                      I reserve the right to use a number system with any integer base without prior notice.
                      Generalizations are understood to be "often" true, but not true in every case.


                      • #12
                        Just for your enlightenment how 'bout you guys that call a telescopic gage a "snap gage" Google images and "snap gage"?
                        Telescopic gages in experienced hands are quite capable of .0005 accuracy.


                        • #13
                          First, thank you to all who have replied so far. I really appreciate your input and will try to comment on your posts.

                          Lakeside, your feelings regarding snap gauges are like mine. I believe I can use them accurately, but I can't afford to mess up on this job so I wanted something "foolproof" if it existed.

                          Madman, I agree they are part of what a machinist should have in his bag of tricks, the comments to Lakeside relate my concerns regarding them.

                          Carld & Oldtiffe & Video Man, your comments are well taken, I appreciate the advice regarding dial bore mics. It looks like a telescoping mic or telescoping gauges are probably the answer. I'll check with the bearing manufacturers regarding bore requirements and tolerances, perhaps I'm overly concerned with the tolerances required.

                          Mechanicalmagic, I like the bore mics you suggested, but in the case of the outer bearing they won't reach deeply enough to measure the bore which contains the bearing. There is a larger outer bore in which a bearing cover is pressed. I would like to have a couple of those mics though, but for now may end up either using the telescoping gauges I already have or buying a telescoping mic set, maybe the tubular type.

                          Mtngun, sorry if I wasn't clear, yes, I already have and have use the telescoping gauges you mention.

                          Oldtiffe, the bearing will likely be driven in with a hammer and brass drift. These are automotive wheel hubs and most mechanics I know don't use a press to install them. As for tolerances I was going to do a few things, one, I have a sample hub provided by the client already bored. If I can accurately measure that I can reproduce that fit, second, I can look at the bearing webs sites and find recommended bore diameters and third I have the races so I was going to measure them and deduct the amount recommended for that bore size for a light press fit as indicated in books like How to Run a Lathe or other machinist literature I have. I may try the "stick method while doing this just to gain experience and confidence in the process. It just seems cumbersome to use multiple times.

                          Thank everyone again for your input. You are who makes this site terrific.


                          • #14
                            Originally posted by firbikrhd1
                            Mechanicalmagic, I like the bore mics you suggested, but in the case of the outer bearing they won't reach deeply enough to measure the bore which contains the bearing. There is a larger outer bore in which a bearing cover is pressed.
                            If the bearing bore is machined prior to the bearing cover, the mics suggested might work. If this is a cast item, needing a skin cut, all bets are off. You will need to perfect your telescope gauge technique.


                            • #15
                              Just a smidgen

                              Originally posted by madman
                              Telescopic Gauges and Knowing how to use them will enrichen youre Machining Career. I have used mine to super close bore tolerances many times . They are the best thing to use for youre Job.

                              I have all these and more:

                              I prefer the spring internal calipers and a micrometer. I can hold 0.02mm (~0.0008") easily, 0.01mm (~0.0004") and closer with quite a bit more effort. It was a mandatory required skill as an Apprentice and stays with you - like riding a bike - but its best to have a couple of "dummy/practice runs" to see that your (my) "hand" and "feel" are still "in" - "just in case ..............!!!).

                              At this level its best to use slip guages and set the micrometer to the guage and then use the micrometer as a comparator.

                              Here are one of micrometers, slip guages and digital inside caliper (0.01mm ~0.0004") accuracy: