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Best Bottom For Homemade Tools on Surface Plate?

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  • Best Bottom For Homemade Tools on Surface Plate?

    I recently bought a granite surface plate and have been working on some projects related to it, in particular a digital height gauge made from a damaged digital caliper and a surface gauge/squareness gauge/indicator stand multi-use thing.

    Here's my two units I've designed in CAD, the height gauge is 3"x3"x1" base and the other one is 3"x4"x1"



    My issue right now is, I'm using A36 hot roll steel to make these as my machines are small and I have no experience working with tool steel, I also don't have anything more than a propane torch for heating equipment.

    My question is, what would be a good way to handle the bottoms to make them slide nicely on the surface plate? My ideas right now are to mill a clearance and leave a 1/2" strip on each side of the bottom, which would then be sanded and polished flat. I'm worried over time that the soft steel will become marred and start to harm the surface plate.

    Case hardening the bases seems out of my reach as I don't have an oven or the torch required to heat treat them properly. Also I'm concerned they may distort or twist and become so out of shape that flattening it would remove all the hardened surface in the process.

    Another idea is to buy some O1 tool steel bar stock, either 1/8" x 1/2" or very thin 1/16-1/32" x 1/2" and attach it to the bottom of the bases after quench hardening it. It would be done either by small countersunk screws or by loctite adhesive for the thin stuff. Then it would be polished smooth and flat. This would serve as a wear surface for the base, but possibly could make grit or damage to the base even worse for the surface plate?

    The tool steel pad approach seems like it could be a good backup if the plain soft bottom idea failed to hold up over time.

    I've seen mention of people applying small teflon feet to the base to improve the slipperiness on the surface plate, but is that likely to wreck the precision?

    I'm very new to this surface plate stuff and I've never done any work with one before, so tips from some experienced users would be great.

  • #2
    I wouldn't worry too much about the hardening. Just keep everything nice and clean and re-reference often.
    I often use the cheap magnetic ones that I know are not hardened.

    To make one would be a nice exercise but these can be gotten so cheap as to be not worth the time.
    I'd have to look but I think I may even have one to give you if you pay postage and show us your location.

    Welcome to the forum!
    Last edited by KIMFAB; 11-21-2016, 01:39 PM.
    Guaranteed not to rust, bust, collect dust, bend, chip, crack or peel

    Comment


    • #3
      Hi,

      Don't sweat it too much. A36 is fine for this use. Just turn/mill off the bark and your good. Relieving the base is good. Some may prefer a scraped bottom, but again it isn't the end of the world if you don't. A fine milled finish is good enough for very nearly any use.

      I personally prefer cast iron for such bases, but it doesn't bother me to use any steel that is handy

      Dalee.
      If you think you understand what is going on, you haven't been paying attention.

      Comment


      • #4
        The A36 will be fine. I would leave the bottom solid or make a rim all the way around, maybe with a skinny slot for air to escape. You can mill it flat, then put a sheet of sandpaper on a very flat surface and draw the base over the sandpaper several times. You may want to do a cross hatch pattern, go in circles, or figure 8s. At this point it will be flat enough to work fine. Repeat as required if you find dings or burrs. This will probably outlast you.

        Comment


        • #5
          For someone that is a home shop guy I don't think you'll ever use them enough to wear the surfaces to any degree that matters. So I'd make them from what you can work with and just use them. You'll be old, bald and shakey before you pass them on to the next user. And THEY may need to resurface the bases sometime during their life.... but probably not.

          Your idea for the runners being the only surfaces in contact is a good one. And you can "lap" them in for a smoother and more accurate fit by sticking a sheet of fine sandpaper down to your surface plate with water and then wet sand the bases to an even and fine finish. That'll remove or at least crest off the milling marks and make the base as flat as your surface plate.

          I'd start with 320 grit wetordry paper and finish with a sheet of 600 or 800. After you're done clean the plate and parts well and "polish" the bases just with a sheet of common printer paper used as your "abrasive". That'll take off any final micro edges from the finer grit paper. I would not go finer than that as the sheen of a surface from the 600 and 800 grit is a nice one for holding a film of oil for lubricating the movements on the plate and also preventing any rust on those critical running surfaces. Polish to a mirror shine and you remove the small surface trenches that will aid in holding an oil film to the surface.

          You also don't need to remove ALL of the mill marks. You just need to make it so the surfacing marks are covering up around 80% of the runners. Leaving SOME traces of the milling swirls that might be deeper just indicates that you got your flat running surfaces without the need to remove much metal.

          If I were to worry about anything I'd worry about grit picked up on the metal wearing the granite. That's an example of lapping. So ensure the tools are clean and preferably store them when not being used in a nice box that seals out dust. It's a good idea to clean your hands first before doing work on the plate and handling the tools. A "worst case" example would be that you were grinding some items earlier in the session then used your hands to wipe off any dust on the base of your plate tools and the surface plate. There's a chance that grinding dust is in the grime on your hands and just transferred to the running surfaces of your tool and plate. See how that can work? So I make it a practice to go and wash my hands if I'm going to do that sort of work after doing any rougher stuff earlier in the session. And ESPECIALLY if anything I did earlier involved abrasives.

          For this same reason a surface plate MUST be covered up when not in use. And care taken to keep the underside of the cover free from any dust or abrasives when it's not sitting on the plate. Even how you lift the cover off the plate. You want to take the dust on the cover off and away, not shake it onto the plate by lifting it off the wrong sort of way. Oh sure, we clean the plate before every use and clean the tools. But working clean with the tools plate and protective covers and containers should still be a factor.

          Comment


          • #6
            Some good advise above. You really do not have to worry too much about hardening. In fact, I wouldn't. A hardened base would scratch the plate quicker than one that is not. And you should handle any such instrument with care so it does not become scratched.

            Most commercially available instruments that sit on surface plates will have a ground surface. But if your shop is like mine, that is not an option. I guess you could take it to a shop that has a surface grinder. But that will cost.

            I would worry a bit about lapping the base on sandpaper or some other form of abrasive. I can not confirm it, but it is said that lapping will cause grains of the abrasive to be embedded in the surface and they can cut into the surface plate. In this, sand paper may be better than conventional lapping with a metal plate. And if you do this anyway, I would use a generous amount of light oil on the sandpaper.

            I would suggest a form for the base. Most lathes will make a facing cut that is slightly concave. This if because a concave face will not rock on a flat surface. So, if I were making a base to rest on a surface plate I would make it round and face it in my lathe. I would also hollow it out with a cut that starts about 1/8" to 1/4" from the outer edge. You don't have to go too deep, 1/16" or even 1/32" is plenty enough. If you use a light cut on this facing and a tool with a slight radius at the tip, you should be able to produce a decent surface finish that will need only minimal or even no lapping. I would use a free cutting steel.
            Paul A.

            Make it fit.
            You can't win and there is a penalty for trying!

            Comment


            • #7
              Paul, to avoid the issue of the abrasive particles embedding in the metal we simply need to ensure that the opposing surface is softer than the metal being lapped. The sandpaper I've suggested should fill that bill. And buffing it off on some printer paper afterwards should aid in catching and breaking free any other particles that may still be stuck in the scratch marks.

              Lightly oiling the part and rubbing a softer metal like copper or aluminium over the lapped faces would also not be a bad option. The softer metal would act much the same as using a file card or those same metals to unpin a file that was badly clogged.

              I'm not sure it even is an issue from using sandpaper like this. But if it were then these other steps should take care of any slight risk.

              In the end I think it's worth the lapping step as it would remove any slight out of plane effects from using a mill that is not perfectly in tram. The result would be that the tools would contact more evenly over more area than if resting on only a few points caused by any hollow cutting due to any tramming issues.
              Last edited by BCRider; 11-21-2016, 04:15 PM.

              Comment


              • #8
                KIMFAB, sent you a PM.

                Thanks for the replies, it sounds like I'm majorly overthinking it. The idea that a hardened base would scratch the surface plate easier makes a lot of sense.

                I'll see how I fare with getting the surface looking nice and smooth and flat with the fly cutter. I've been soaking the 3x4" base in vinegar for a little over a day now and I'll be scrubbing it tonight to see how well the scale came off.

                As BCRider added, sanding and lapping to eliminate any out-of-tram effects would be a good idea for me. I have a small microscope so I could inspect the surface after lapping to see if there are any inclusions, and can rub it down with some aluminum stock and see what happens.

                And I'll be honest my surface plate is a brand new alleged grade B import plate that only cost $45 CAD. If it gets worn out in a few years in the pursuit of some lessons and relocated to stepping stone duty it wouldn't be the end of the world.
                Last edited by mattthegamer463; 11-21-2016, 04:33 PM.

                Comment


                • #9
                  don't sweat it too much. You don't need to harden them for them for the diligent and less frequent use in a home shop. A36 is not the nicest metal to work, but other than a bit of weight, the material is not called on to do that much. your undercut idea is good. Best finish is ground or scraped, but the objective is that it doesn't rock.

                  Consider buying a surface gauge. To me they are indispensable, but used band names ones don't seem to sell for much.....unless you just want to make it to learn, which is itself valid, its a lot of work for $40 (Cdn)
                  Last edited by Mcgyver; 11-21-2016, 05:14 PM.
                  .

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                  • #10
                    Originally posted by Mcgyver View Post
                    don't sweat it too much. You don't need to harden them for them for the diligent and less frequent use in a home shop. A36 is not the nicest to work, but other than a bit of weight, the material is not called on to do that much. your undercut idea is good. Best finish is ground or scraped, but the objective is that it doesn't rock.

                    Consider buying a surface gauge. To me they are indispensable, but used band names ones don't seem to sell for much.....unless you just want to make it to learn, which is itself valid, its a lot of work for $40 (Cdn)
                    Agreed, and you're right, the learning is a big part of it. In particular I want to add features that would make it handy for squareness comparing and whatever else I can come up with. Getting comfortable with steel is something I need to work on, as my go-to material is aluminum for most things.

                    Plus making things slows me down, reduces my dollars per hour in the workshop. I've gotten too much practice at buying.

                    Comment


                    • #11
                      An hint from a write up on "flat vs smooth" from one of the Machinist's Bedside Reader journals. If your mill is perfectly in tram then which cutter you use matters not. If it has much of any out of tram amount at all all cutters will cut with a slight coving or "wave". Or you can get a bit of a shallow saw tooth wedging shape depending on the direction of tram issues and direction of table motion.

                      The depth of this distortion due to any tramming misalignment is proportional to the diameter of the cut being swept. So using more passes from a smaller diameter cutter will result in less lapping being needed to cut away the high spots and get an even surface. Alternately if you use a small enough cutter, within reason, and run consistent steps between cuts the waves or wedges would provide you with a close spaced and matching set of crests to ride on. Or you can top off the crests consistently and with only a little effort at lapping. So I'd be inclined to flycut the sides and top for looks but to switch to something smaller like a 3/8 end mill for both cutting the center relief and facing off the runners.

                      Another interesting fact was the time needed. One would think that a big flycutter would be faster since there's only one pass needed, right? But to get a consistent finish first off the rotation speed needs to be pretty low due to the larger diameter and maximum SFPM allowable. And due to that and only having ONE cutting tooth you need to use a slower feed speed to avoid raising the chip load on that tooth too much. Then on top of that is the need to fully traverse on and off the face of the work by a whole flycutter diameter on each end of the part. So you need to add the fly cutter diameter to the length of the part for figuring out the length of time for the cut.

                      ON the other hand a small four flute cutter does not need to move as far off the face of the cut. It can also turn faster and with four teeth being fed at the same chip load will perform the pass in 1/4 of the time. In the end it comes down to a wash for time taken to surface a face. So the choice is in the sort of pattern you prefer. consistent edge to edge arcs or a more fish scale like "engine turned" look to the milling marks.
                      Last edited by BCRider; 11-21-2016, 05:05 PM.

                      Comment


                      • #12
                        Originally posted by BCRider View Post
                        An hint from a write up on "flat vs smooth" from one of the Machinist's Bedside Reader journals. If your mill is perfectly in tram then which cutter you use matters not. If it has much of any out of tram amount at all all cutters will cut with a slight coving or "wave". Or you can get a bit of a shallow saw tooth wedging shape depending on the direction of tram issues and direction of table motion.

                        The amount of this distortion due to any tramming misalignment is proportional to the diameter of the cut being swept. So using more passes from a smaller diameter cutter will result in less lapping being needed to cut away the high spots and get an even surface. Alternately if you use a small enough cutter, within reason, and run consistent steps between cuts the waves or wedges would provide you with a close spaced and matching set of crests to ride on. Or you can top off the crests consistently and with only a little effort at lapping. So I'd be inclined to flycut the sides and top for looks but to switch to something smaller like a 3/8 end mill for both cutting the center relief and facing off the runners.
                        You're absolutely right. I forgot about that. Looking to see if my fly cutter was dragging the heel and what kind of marks it was leaving was how I tested my tram after shimming my column a few months back.

                        Comment


                        • #13
                          Sorry, I added a rather lengthy "edit" to my post above. You may want to go back and check the additions that ended up being a lot longer than I planned when I hit the "edit" button.

                          If it is in tram the arcs from the leading and trailing cuts will be matching with neither more than mildly stronger than the other.

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                          • #14
                            Originally posted by BCRider View Post
                            Sorry, I added a rather lengthy "edit" to my post above. You may want to go back and check the additions that ended up being a lot longer than I planned when I hit the "edit" button.

                            If it is in tram the arcs from the leading and trailing cuts will be matching with neither more than mildly stronger than the other.
                            I've taken a preference for fly cutting when possible because it's comparatively cheap, and if time is a wash, I'd rather keep my end mills for the 80% of work that fly cutters can't do.

                            I've been thinking about ordering a cheapo indexable face mill, 1.5" or so, if it does a modest job of roughing a surface and can get the job done a lot faster than a fly cutter, might be worth a try.

                            This kind of thing
                            http://www.ebay.ca/itm/4Flute-400R-5...4AAOSw5ClXw2VW

                            My mill also came with a pretty junky brazed carbide face mill about 2" diameter, tried it once and it didn't seem to work very well. The arbour for it looks very similar to this face mill, I'd have to check.

                            Comment


                            • #15
                              I found the same issue occurred with the face mills that come with the mills. First off the cutters are not always indexed perfectly. I got mine to work way better simply using a dial gauge to set the cutters in the body. But really the whole cutter needs to be done in a tool and cutter setup to match all the edges and angles of the teeth.

                              Have fun with the project. I'll also be watching your height stand with interest since I've long wanted to do something similar.

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