Do fine wheels need better balance than coarse?
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  1. #1
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    Default Do fine wheels need better balance than coarse?

    Just got a 5SG80 wheel for my Boyer 612 and it seems out of balance. Dressing hasn't completely helped- I can feel the vibration through the handles. Surface finish sucks and is wavy, maybe 0.1" period. Light cuts, 0.0005" max. I haven't had the same problem with my well worn coarse white "sugar" wheel. I've never used a fine grit wheel- are they denser and in more need of balance? Seems odd. I'm going to make a balancing flange and see if that helps, but this seems contrary to all the people who never need to balance 7" wheels.

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    Balance is one of them strange things on 7" wheels, for ages it won't matter then it does, then on a different wheel it does not. Some grinders seam way more sensitive too it too. My jones and shpiman is a mixed back were my old heap of poo surface grinder with ways so worn it could grind the curved template for banana gauging could have anything on its damn spindle and grind a beautiful mirror finish!

    80 grit is a fine wheel too, just jumping to 60 grit seams to really change how they grind. Have you really dressed enough off to get it true? Sounds odd, but it can take more than you think, have you also dressed the sides as that can really help too at times. Finer wheels also need finer dressing to really see a benefit, but if your 100 thou pattern varies with table speed, dress is good and you can feel some vibration on the spindle, yeah its probably a out of balance wheel.

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    Did you dress the sides of the wheel.You may be confusing wheel wobble for a balance problem.If you are using an SG wheel you need a really good sharp diamond not a worn out mushroom. It makes a big difference.Yes a balance ring can help.

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    Give this gentleman a call and he can help you with a diamond for SG wheels. Braemar USA Tempe Az. 480 966 9311.

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    Finished my balance ring tonight, but still have to modify the wheel guard. It came to me with a sheet metal outside cover and I need to rework it a bit to clear the new balance system. Ain't runnin' it without a cover! Wish I could find a factory cover, but they seem pretty rare and there are several styles- mine's round, not rectangular.

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    Surface finish variations certainly show up more in finer grits and this is not the most rigid spindle in the Sg world.
    While you can band aid it one can't really fix in/out balance problems with a balancing adaptor so dressing the sides may be needed.
    Very easy to overcome the axial preload on this spindle which is why they hate grinding on the back side.
    I tend towards 6 inch and smaller wheels on these size grinders.
    You can indicate in the side to side runout if you use a large rounded tip and a dial indicator. It will bounce but you can tell what is going on.
    Sometimes they just do not mount up right.

    80 grit is not that fine and the machine should not shake so something is not right and you should not need a balance ring.
    Spindle taper, wheel adaptor and spindle nut are all good? (yes, the face of that little spindle nut matters and can override the taper)
    I have seen bad wheels but this problem is very, very rare.

    I do not balance wheels in this size at standard rpms even if 1+ inch wide and problems end up getting traced elsewhere.
    How are you going to "adjust" your new balance ring?
    Bob

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    I haven't checked side-to-side and will do that. The B-S spindle was cleaned and inspected by me, so I know the preload is working right, but as you say, more rigid spindles have certainly been built! Heck, more rigid grinders have certainly been built. I used to use a small Harig 612 size at work and in 30 years I don't think anybody ever had a balance problem with a wheel there. The problem follows the wheel- my standard white wheel works fine. The balance ring allows me to add screws and weights (12 positions) and being a test equipment nerd, I'll put an accelerometer on the thing and dynamically balance it. I do like to understand the root causes of things (which is why I never get anything done) and this wheel does have me a bit mystified. Given the price of the thing, I would have expected it to fix any problems inherent in the machine or my technique. BTW, I noticed it had an 8/14 date, so it's been sitting at McMaster for a few years.

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    OK, success! I did a 4-run balance with a trial weight and used the spreadsheet I've referred to here in the past. It took 4.91 grams on a radius of 3.36 cm to bring the thing into perfect balance. I actually did a couple cycles, dressing the wheel in between to be sure everything was running right.

    It made all the difference. I'm probably at the limit of the spindle bearings now, which are "tired", but no waviness or surface problems. I don't know if 16.5 gm-cm out of balance is considered a lot or a little, but it's certainly enough to screw things up on the small Boyer Schultz.

    The wheel was purchased by somebody else for a specific job, but if I had bought it myself I would have complained and sent it back. BTW, it does seem to run true on the sides, and I didn't dress them.

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    Quote Originally Posted by Conrad Hoffman View Post
    being a test equipment nerd, I'll put an accelerometer on the thing and dynamically balance it.
    How expensive and what is involved with your balance rig?

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    I've got an embarrassment of riches, having collected electronic test equipment for many decades. For this adventure, I used a Wilcoxon accelerometer and an ancient General Radio Corp. Sound & Vibration analyzer. 3600 RPM is 60 Hz, so that was the filter setting. I just set the accelerometer on the table. Pretty much anything that's sensitive enough to measure the vibes will work, but you usually need a filter to get rid of anything not related to the vibration frequency. I've no doubt a phone app would do the whole thing. You make four runs with a trial weight at specific locations, measure the amplitude of the vibs, and from that the correct weight and location gets calculated.

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    I think balance is like chatter on a boring bar in that above a certain level it excites it's self and goes to crap, but keep below that level and you never have a issue. thats at least my experience with it and grinding, bellow a certain amount the machine can just hang onto it, go a bit above and all hell lets lose finish wise.

    Have balanced mine before when a bad wheel that was giving me crap with nothing more than a old DTI on the table touching the furthest out part of the wheel head and looking at the flutter. its surprisingly fast once you can actually put a kinda value - quantity to it to play better or worse and get it down low enough to no longer be a issue.

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    Quote Originally Posted by Conrad Hoffman View Post
    You make four runs with a trial weight at specific locations, measure the amplitude of the vibs, and from that the correct weight and location gets calculated.
    Do you do that calculation yourself, or does the device do it for you? If you do the calculation yourself, could you please tell us how it works, or show us the calculation that you did as an example?

    Cheers, Bruce

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    Grab the second item here- Conrad's Free Stuff and note there are two tabs- first one for instructions, second one for the actual calculations. All you need is a vibration amplitude, a trial weight and the location from an arbitrary mark. Oh, and a scale to weigh the weight!

    Though my grinding results look good visually, I'm still suspicious of the wheel. Heck, and the grinder. I've heard so many reports on this forum that the SG wheels are the only way to go, and that wouldn't be the case if these sorts of problems were common.

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    All wheels need to be balanced on 7" grinders in my opinion, as most in that size range show ripples in finish due to vibration. Finer grit wheels show vibration more than coarser wheels.

    If you think an 80 grit wheel is bad, try a 150.

    Sent from my XT1053 using Tapatalk

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    No thanks on the 150! I finally ground the small pins that started all this and they came out well. The 80 wheel gave me a decent small radius on the steps between different diameters.

    After getting advice from one of our machinists who has a lot of grinding experience, smaller feed steps, only approaching the wheel from one side after dressing and a few other things, I ground a test flat. Though it still has some visible imperfections that I think are wheel bearings and/or a trace of vibration, it's better than anything I've done before. Ran it on our profilometer and got an Ra of 0.013 um in the wheel direction (with the lay) and 0.040 um across. OK for a $100 magnetic chuck that came with a free grinder.

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    Quote Originally Posted by Spyderedge View Post
    If you think an 80 grit wheel is bad, try a 150.

    Sent from my XT1053 using Tapatalk
    I have a 120 but it only ever gets used for sharpening HSS bits on the surface grinder and im talking light tickles at that, personally i don't find the finish that vastly better than i can pull of a 46 grit wheel thats dressed smooth and used with sub 20 thou step overs. Generally if i need finer than ground finish its the edge of a cutting tool and diamond lapping is so dang fast from a ground finish in anything i have had to do its a non issue. Simple low speed diamond lap impregnated with 5 micron diamond lubed with WD40 will take any item i have needed from a good 46 grit whel grind to mirror like in under a dozen revolutions. I do more than a few cermaic water valve cartridge faces on the diamond lap too, its really usefull, great for HSS form tools in plastics too!

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    Quote Originally Posted by adama View Post
    I have a 120 but it only ever gets used for sharpening HSS bits on the surface grinder and im talking light tickles at that, personally i don't find the finish that vastly better than i can pull of a 46 grit wheel thats dressed smooth and used with sub 20 thou step overs. Generally if i need finer than ground finish its the edge of a cutting tool and diamond lapping is so dang fast from a ground finish in anything i have had to do its a non issue. Simple low speed diamond lap impregnated with 5 micron diamond lubed with WD40 will take any item i have needed from a good 46 grit whel grind to mirror like in under a dozen revolutions. I do more than a few cermaic water valve cartridge faces on the diamond lap too, its really usefull, great for HSS form tools in plastics too!
    I have never been able to produce a finish as good as a 150 grit wheel with a 46. 60 gets close. How do you do it? Even with a very slow, shallow dress I can't do that.

    Light stepovers might leave a slightly better finish but tend to produce more heat than a wide stepover pass. For me, and those I've talked to, sub .0001" downfeed (looks like 50 millionths or less on the dial) and wide .100" or more stepover is best. I don't know my exact feed stepover percentage, I just crank both hand cranks together.

    This was from a 46 grit wheel. I don't have any pics of a 150 grit grind, but it's nearly glass smooth. 46 still leaves some tooth unless you take loads of spring cuts, in which case the finish ends up looking like a poor creep feed pass.

    Sent from my XT1053 using Tapatalk

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    After some more experiments last night, I'm more convinced than ever that balance is critical on a small grinder with a full size wheel. No idea about bigger better ones, but they're probably more rigid.

    My machinist friend that used to grind large numbers of 8" square Invar plates to a near mirror finish suggested the following- Very small step-over, 0.001" to 0.005" max. Takes for freaking ever. Only feed on one side of the wheel- don't come back the other way at all. Keeps the far side of the wheel in the best shape for the final finish. Very fine wheel dress, not the aggressive one I usually use! Brush part with oil- he used Moly-D on the Invar. I was using a spritz of WD-40 with the white wheel, but the SG wheel doesn't work well with it. Monroe Cool Tool II seems to work well. A mist attachment would probably work better yet if it kept the contact area clean.

    His method did work well for me, but for most things it's overkill. I get about the same finish as the above photo with a 46 wheel, much better with the 80.

    edit- found this previous thread, very similar to what I did, Dynamic (Grinding) Wheel Balancing Method using iPhone Vibration App and SHCS's
    Last edited by Conrad Hoffman; 09-14-2017 at 02:52 PM.

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    I have also noticed that WD-40 and kerosene are poor choices for grinder coolant.

    Small surface grinders are actually very flexible, and that's why wheel balance is an issue. On my DoAll dh612 I can move the wheel up and down a few tenths fairly easily by applying some force onto the column. The DoAll isn't a very small grinder, either.

    Small crossfeeds are good for removing lots of material, and is often the best choice to prevent burning.

    Sent from my XT1053 using Tapatalk


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