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Uses for gage/ jo blocks

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  • Uses for gage/ jo blocks

    Every so often I see sets (typically incomplete) of gage blocks come up at auctions. I've always resisted buying any because I can't work out how I would use them. The most obvious use is for setting up a sine bar (but I don't have one). Checking/ calibrating measuring gear is another, although if I needed to do that I could probably more easily get that done with a temperature controlled calibrated set at work.
    For those with a set what other things do you use them for? Are they one of those tools that with hindsight takes up shelf space and doesn't get used enough?


  • #2
    Lots of imperial sets on the market here but most of us would need metric.
    I dont think I could justify the prices being asked for metric for my home shop, although it would always be a nice thing to own.


    • #3
      I sometimes use them to set up zero on a mill or lathe. Use a 1 inch block and when it just fits between an end mill and the work surface, you are at + 1 inch in Z. Same on the lathe for X and Z zero. Carbide cutters do scratch the block after time.


      • #4
        They're quite handy if you have a sine bar/plate or use a surface plate for inspection. Other thing that comes to mind is our QC manager would use them while calibrating micrometers to make sure they were not only adjusted properly, but also reading correctly at several points over their range.


        • #5
          Check slot/key width. Set up sine bar.


          • #6
            Just like the surface plate is the shop standard for "flat", so are gage blocks the last word in dimension. Like most guys here I buy a lot of measuring tools on ebay-my gage blocks allow quick calibration at a few random points in the range of the tool. There seems to be little point to owning micrometers unless you either send them out for calibration or do it yourself.

            As others have mentioned, it is often handy to be able to build up some blocks to make an object of known exact dimension to work from. My mill for example has trays on each axis allowing gage block stacks to be built up. (I now have a DRO though-until then it was a great way to approach jig bore accuracy)

            The other application that I use is with a comparator and a sensitive dial indicator. You wring a stack of blocks to equal the desired dimension, check it with the comparator, then compare that with the part you are inspecting. This gives a direct reading of deviation from the desired dimension.

            Last edited by Greg Q; 06-22-2011, 06:48 PM.


            • #7
              I have a set of gage blocks and find use for them from time to time in setting up, calibrating and occasional other uses. I don't have much invested in them and could do without them.

              On the other hand I also have two sets of gage pins up to 1/2" and find them quite useful for measuring bores and indicating bores in on the lathe. I do not use my telescoping hole gages anymore for these smaller sized bores. These, I consider keepers.
              Jim H.


              • #8
                Good question that has a good answer (IMO) that is not addressed by tool manufacturers.

                Gage blocks can be used for all sorts of things if a guy just had the accessory set. Here's a link to one on eBay:
                Click here

                A few shops I've worked in had these and we used them to set bore gages and the like. They are great for setting up comparative instruments like test indicators to measure a deviation from a target dimension, i.e. set the stack for your target dimension, then zero your gage on it so when measuring you can then get a quantitative measure of how far off of the target dimension your part is so you can adjust things to suit.

                However, as you can see from the link above, the accessory sets typically are extremely pricey for a collection of a couple clamps and things that only need to be flat, in comparison to gage blocks which are flat as well as parallel and accurate in dimension. Seems like somebody would have come up with an inexpensive accessory set which could be used with anybody's gage blocks. Otherwise you're stuck with just a stack of blocks and limited utility.

                Rectangular blocks are the most common, but the rectangular accessory sets are the most rare

                Square blocks (with the thru-hole) are less common and more pricey, but are a bit nicer to use and it makes it easy to stack up what you need very easily.

                There are also round sets which can be had pretty cheap. They have a threaded thru-hole and are easy to set up. Typically I believe they aren't considered as high-precision as the high-grade rectangular and square blocks, but I have a set and use them from time to time. They are handy and you just need to know what accuracy you've got so you don't compound an error with a stack of several blocks. I've never seen an accessory set for those either but maybe they exist?

                Anyways, here's the call to some tool company out there. Make a workable accessory set and sell it for a reasonable price. If they did this, they'd sell more gage block sets ! And we'd use them.


                • #9
                  they do spend a lot of time in the drawer, but there's also lots of uses. In addition to the sine bar mention, you indicate a stack of them on the surface plate with a sensitive indicator then indicator the work - very accurate dimension measurement. The other day i used a version of that to measure the height of my lathe's cross feed screw axis relative to the dovetail horizontals - surface gauge on the way, indicator picking up the OD of the shaft, stack then put between way and indicator.

                  Later I used them to set the taper on the tapered gib. Long spindly piece in the vise with each end sticking out of the vise an inch or so and resting on a stack of blocks on the table. Two gauge block uses in a week - fast times at Mcgyver's shop!

                  low duty cycle, but close to indispensable the occasional time
                  in Toronto Ontario - where are you?


                  • #10
                    Starrett has useful information on the use of gage blocks with the accessory set.



                    • #11
                      Gary.....Thanx for the link. Nice info to have.

                      Much Grass (muchos gracias?)



                      • #12
                        Jo Blocks are for accuracy. Mostly used by tool and die makers in conjunction with a planer gage.Today the Cadillac gage has taken the place of Jo-Blocks, but Jo-Blocks are more versatile for instance when grinding slots. Cadillac gages are not cheap. Jo-Blocks are also used for setting Sheffield Gages to very close dim's for O.D. grinding. If you are a tool and die maker you know how a planer gage works. If not, it would take to some time to explain.
                        Using Jo-Blocks as a stop or for some other purpose not requiring accuracy from thousands to tens and millions of an inch or hundred's and micro in metric is like playing Mozart at a Rock concert.
                        Last edited by Juergenwt; 06-23-2011, 08:07 PM.


                        • #13
                          Originally posted by Juergenwt
                          ... is like playing Mozart at a Rock concert.
                          What... you mean like Eddie Van Halen? Steve Howe? Steve Via?


                          • #14
                            While the accessorie sets are nice, you can basically do the same things you do with the accessory set without one. Instead of using the straight jaws, wring on a couple extra gage blocks and slide them part way off the edge. Or use your caliper jaws. Instead of the half round jaws, use a precision rod (such as a thread wire or pin gage or just a good piece of shafting which you can measure with the gage block set) or ball bearing. etc.

                            It is also possible to make some of your own accessories. In some cases you just need one good flat surface.

                            If you have imperial vs metric, use a calculator. You can get within 0.0001" or 0.00254mm.

                            You can use gage blocks as a height reference on a surface plate combined with a dial indicator or surface gage. If you don't have a height gage, you can use a magnetic base indicator holder (balance so it doesn't tip if using on granite). Make mics/calipers more accurate by using them as comparative instruments. Preset telescoping bore gages (use the extra block trick above). Check the travel on your mill table X/Y/Z axes. Check your skill with a micrometer or caliper. Sine bars, of course. Use them to calibrate your flatbed scanner (computer peripheral). Use them as reference objects when taking pictures. Set spring calipers. Offset a workpiece a known amount. Calibrate a microscope. Tiny parallels.
                            Make go/no go gages. Use instead of inside micrometers. Use with feeler gages to measure in places your other instruments won't fit. Setting buttons.
                            Checking your dial indicators for cosine error in a particular setup. Spacers for use with a square when measuring an object with protrusions.

                            Check your leadscrew pitch:
                            But insert another gage block in that setup. I.E. measure with 1 or 2 blocks not 0 or 1.

                            Checking calipers, mics: if the gage blocks, measuring instruments, and work are made out of the same material, than they will shrink/expand proportionally as long as they are at the same temperature. If they are different materials, calculate the error using coefficient of expansion, length, and temperature.

                            Bear in mind that you can often construct two or more stacks of the same height using a single gage block set, especially if you aren't setting to tenths.
                            This opens up some other uses.

                            Don't have a sine bar? Have a couple pieces of precision rod? Space them a known distance apart with gage blocks then use some more to set angle. Use some parallels. Be creative as to how to hold all this together.

                            You need to consider the errors of various setups, especially improvised ones. Include temperature error when dissimilar materials are involved.

                            If you have access to a good set at work, that is an advantage; you can check that any set you buy is good. You can use the gage blocks as a transfer standard to bring accuracy from work into your home shop.

                            The more things you have around, the more ways you can combine them.

                            Here are some pictures of gage blocks and other measuring instruments in use:

                            You may not use them too often, in part to avoid wearing them out.


                            • #15
                              for those of you that use your blocks for checking the calibration of your micrometers, do you adjust them or just note the deviation and take it into account when measuring?
                              I once learnt how to strip a micrometer and adjust it but I can't remember how it's done now...