Runout of grinder spindle

Discussion in 'Horological Tools' started by karlmansson, Jun 25, 2019.

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  1. karlmansson

    karlmansson Registered User

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    #1 karlmansson, Jun 25, 2019
    Last edited: Jun 25, 2019
    Hello!

    I just got myself a used tool and cutter grinder, a German made Kirba UG2. The seller did not understand how to package the machine unfortunately and the grinding wheel guard was cracked and shattered partially in transit and the spindle was bent. The runout was about half a millimeter at the end of the 40mm long shaft.

    I’ve been reimbursed for half of what I paid by the seller and I’m keeping the machine and I’ll try to salvage it as well I can. There are spare parts available but they are no longer being made and so are quite expensive.

    I’ve coerced the spindle down to a few hundreds of a mm of runout. My question is: how much of a runout can be tolerated in a spindle designed to run at a few thousand rpm? I’m guessing “next to nothing” but in numbers? Since the wheels arent mounted with sub micron precision and are turned true with the holder it seems to me that there are other sources of error than the spindle runout that can cause greater vibration.

    All help appreciated!

    Best regards
    Karl
     
  2. karlmansson

    karlmansson Registered User

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    Pictures of the listing and the result of the machine laying on its side, weight bearing on the guard and three layers of cardboard as padding.

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  3. DeweyC

    DeweyC Registered User
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    Karl,

    That is truly a shame. The runout will cause vibration. I would send it back and get the Deckel because parts are available. Is the maker still in business? Can you find an old distributor?

    Do you have time for another project? The runout will quickly cause uneven wear on diamond wheels.

    It looks to me like the center at the thread end is now lost so mounting it between centers is not an option.

    A skilled machine repair shop may be able to get it back in shape; but $$$$.

    Or, make a new spindle.
     
  4. karlmansson

    karlmansson Registered User

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    Yes, I got this machine in the context that yes, it was a fairly expensive piece of equipment but it would save me time on doing things I don’t enjoy doing in the shop. Such as hand sharpening cutting tools. When I realized that this was going to be another one of those things that would need solving and time and energy my heart just sank... It would have been so easily avoided too. Just remove the shield and the wheel and the spindle would have sat far enoug back behind th edge to be protected.

    The runout pictured is as the machine arrived. I did manage to bend the spindle nose back into something resembling concentricity using brass lined parallel pliers. My thinking was that by levering against the seat on the spindle (that did not run out) I could take the load off the bearings. The spindle is press fit into its bearings and I didn’t want to risk messing it up even more by pressing it out. I used the wheel hub that was a good slip fit on the arbor as a surface for gripping on as well as a magnified surface for measuring in the flat. I got the flat to within 1/100th and the axial to within 4/100th of a mm. Then when I measured the spindle itself I still had a 10/100th runout at the tip. So maybe something gets lost in translation with the hub.

    My thinking now is to get the axial runout back down to below 100th and then try to grind out any unevenness in the flat using a stone. 1/100th on the actual plane shouldn’t be a problem whereas I risk introducing a taper or a loose fit on the spindle nose if I try to grind on the radius.

    A spare part is available for about the same price that I now ended up paying for the machine. I’ll try to go down this route first.

    Regards
    Karl
     
  5. DeweyC

    DeweyC Registered User
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    Karl,

    The refund covers the spare spindle? And you want to spend time instead? Have you just come off a 36 hour rotation? Seriously?! Plus, you can service the bearings.

    Buy a couple diamond wheels and you can make your carbide tooling from broken endmills as I do; both lathe bits and gravers. Even micro boring bars. I know you know how to handle the dust.

    BTW, it is a cute machine; looks more compact than the Deckel. You are going to find other uses for it so you would like it to be correct. I even used it once to modify a locking jewel.
     
  6. karlmansson

    karlmansson Registered User

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    With all due respect, I’ve still not gotten an answer to the question I asked. How much runout is to be expected and how much is acceptable? Without knowing that, I don’t know if a new spindle will yield better results. 0,01mm runout on a face diameter of 40mm seems decent to me. But I don’t know as I don’t have a machine in good condition to compare it to.

    Sure, I could brand this spindle “damaged”, call it a day and order a new one. But without knowing that I will be better off with a new spindle (which by the way is sold in a bundle with new bearings), that’s 350 dollars I’d rather put towards tooling for this grinder, the mill and the lathe.

    The time is already invested in it and it didn’t take much. An hour or so with careful manipulation. I can’t imagine the same about of time won’t suffice to bring it the final few hundreds into concentricity. Do you think I took up the hobby of restoring watches because I enjoy leaving broken things be broken? :)

    Regards
    Karl
     
  7. DeweyC

    DeweyC Registered User
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    Karl,

    I understand your frustration. But the exact answer to your question has to be: whatever you consider "good enough". I had the bearings in my Habegger replaced when I realized it was jumping during parting. I had good results until then. It was "good enough".

    I reject out of hand machine tools with decentered spindles. It is like bed scraping; sure an individual can do a one off; but the job is better and done quicker by someone who does it every day. Same reason I had a pro install my Habegger bearings.

    To me, attempting to repair a bent spindle when new is available is like trying to straighten a balance pivot on a precision watch when the staff is available. I have other things that require my time.

    If you look in the files section of schaublin lathes you will find manuals for deckel and Agathon. The specs may be in those. My Deckel license Alexander has about .004 mm runout at the face when measured with a parallel on a diamond wheel. I use it for touching up hand gravers. My Agathon does not even move the needle and is my goto for precision grinding.

    Both are good enough for how I use them.

    I suspect you can get away with quite a bit using non diamond wheels that can be dressed. The only way to judge vibration is to try it. But then you are not using it for carbide.

    If you like the challenge, go for it. You already are aware of my respect for you.
     
    karlmansson likes this.
  8. karlmansson

    karlmansson Registered User

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    Cheers Dewey! The feeling is mutual.

    That’s quite the challenge then... Another concern with changing the spindle is pressing the bearings and arbor in and out. I’m afraid I’ll mess up a brand spanking new spindle. I don’t know anyone close to me that repairs machines such as this.

    I’ll post updates!

    Regards
    Karl
     
  9. karlmansson

    karlmansson Registered User

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    Speaking of which, how DO you dress a diamond wheel...?
     
  10. DeweyC

    DeweyC Registered User
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    I prefer formal wear.

    Actually, I have not. This is why spindle condition is so critical. You DO unglaze them with a white (ALOX:???:) stick that is cheap. But I find letting it get glazed puts a nice finish on the carbide.

    For the Agathon, you actually returned the wheels to the maker. But today it is just as easy to buy new and I expect the wheels to outlive me.

    BTW, think crystal grinding!

    Working on updates and photos now. Will have something to send soon.
     
  11. Dr. Jon

    Dr. Jon Registered User
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    I have a new grinder from Shars. It is a Chinese model that they claim they inspect and assure it meets standards. I have not measure run-out but it does run very smoothly. Be sure to order spare daptors fro it so you can either change wheels more easily of adapt the adaptors for finer diamond wheels.

    Used grinder differ from used tools like mills and lathes since fgrinders spend their lives immersed in abrasive.

    My Shars does well on gravers and I use to make carbide spade drills. I get very well centered drills that find center, The Shars unil comes with a lot of stuff and sells for under $1K. It comes lashed to a pallet so it is not going to get busted in transit.
     
  12. karlmansson

    karlmansson Registered User

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    Got the grinder up and running last night. The spindle is within 0.04mm runout over the length of the shaft now. I modded the electrics with a capacitor to make it run on single phase. Seems to work! I’m probably losing a bit of torque but for a grinder such as this I think I’ll be fine.

    There is some vibration in the spindle, you can feel it when laying a finger on the nose of it while it’s running. I used a fine stone to knock off any burrs that may be present on the shaft and the stone felt smooth while running against the shaft while it was running at high speed.

    Decided I wanted to test it with a stone in it and placed the cracked shield back onto the machine for safety. Didn’t want to go through the trouble of patching it up if it turned out the rest of the machine was shot in some way.
    Took a couple steps back and flipped the switch. The machine ran at full speed for about 30s during which time I could feel more substantial vibration in the machine housing. Didn’t do a very good job at centering the stone on the arbor probably. Then the stone exploded.

    I forgot that that was the stone that was mounted on the machine when it took a hit. Probably had a crack in it and tore itself apart when it spun. I was wearing PPE and the shield took the hit, never got any on me. The shield popped off but seems to have held up, no more shattering.

    I’m going on vacation for a week now and I’ll think about how to proceed with the spindle. It might prove problematic to proceed with this one...

    Regards
    Karl

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  13. karlmansson

    karlmansson Registered User

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    Yeah, I didn’t realize at first but this machine is coated in a layer of grinding dust mixed with grime. Nasty stuff.

    While first got the motor running, it too took off in cloud of dust. This machine has seen some use of the years. Lots of use and no dust extraction by the looks of it...
     
  14. karlmansson

    karlmansson Registered User

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    Yeah, I didn’t realize at first but this machine is coated in a layer of grinding dust mixed with grime. Nasty stuff.

    While I first got the motor running, it too took off in cloud of dust. This machine has seen some use of the years. Lots of use and no dust extraction by the looks of it...
     
  15. DeweyC

    DeweyC Registered User
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    At least no injuries. Have fun.
     
  16. karlmansson

    karlmansson Registered User

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    Yeah, but still what I would describe as a “laxative experience”. There is a LOT of energy in those wheels when they reach marching speed.
     
  17. karlmansson

    karlmansson Registered User

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    The further I continue with this machine, the more it starts looking like a sack of woe.

    I was thinking I would have the appropriate collet sizes with it, as it came with quite a few. Turns out, those were really on the higher end of the size spectrum. The largest is 20mm and the smallest 6mm. So I need to get some more collets for smaller bits. Most of the tooling I use is 3/16th sized. Turns out this is something of an oddball of a collet. A lot larger than what comes with the cheap Chinese grinders that are sold today. It has the looks of an R8 but with an external thread and larger in size. I’ve done some research but I can’t seem to find any matches. The closest I’ve come has been an expired listing for an identical machine to mine that says it came with a set of “LID collets”. No info on those that I can find. I asked the company (that apparently has stopped manufacturing this machine) about a week ago and no response. Only one collet has the logo that is in the pictures and that I don’t recognize. The others just have the sizes.

    If anyone knows what type of collet this is, please let me know!

    Dimensions are:
    Shank diam: 23mm
    Thread diam: 22,8mm (although it very much looks like a 50% thread), 1,5mm pitch
    Overall length: 93mm
    Start of taper: 32mm
    End of taper: 24,5mm
    Length of taper: about 10mm

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  18. karlmansson

    karlmansson Registered User

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    A thought that occurred to me was that I might be able to make a secondary spindle to fit inside the largest collet that could use 6mm collets for finer work. That spindle could then be used as an endmill grinding jig as well, provided it was made long enough and with a close enough fit into the 20mm collet.

    Regards
    Karl
     
  19. karlmansson

    karlmansson Registered User

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    Well, the grinder is now in working condition albeit with some discussable vibration. Not having seen any other grinder up close I don’t know what is normal or not. The option of getting a new spindle is still there.

    I took the articulated arm for the tool head apart, as well as the tool head itself. Some wear but overall I managed to get it back together with no play in the tool head spindle. It’s a rather simple contraption, two straight bearing surfaces and a frontal, flat flange. If it proves difficult to find the collets for this one I think I’ll make a new spindle that will take 5C collets. The hard part will be the hole circle for the graduated stops around the spindle nose. I think I might be able to kill two birds with one stone though: take care of wear in the spindle and make something where parts availability will not be an issue.

    I have since my last post become aware of the “Deckel collet”, which by all means except size is identical to what I have. The Deckel collets are 20mm in shank diam. where mine are 23. Maybe this company was looking to take Deckel on for the grinder market? Doesn’t seem like they won though...

    Regards
    Karl

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  20. karlmansson

    karlmansson Registered User

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    Well, turns out the collets are proprietary, very short in supply and the few that the manufacturer still has go for 75 euro a pop.

    What I'll do is to make a new spindle for the tool head. It's pretty straightforward, with straight bearing Surfaces. I don't Think it's hardened either. While I'm at it I'll make a new spindle for the grinder as well. I got the old one out of the bearings and it has similar features. A straight shaft that is preloaded by a compression spring at the back and retained by a C-clip ad the front. The pulley is machined integra with the shaft though. I'm thinking I might get away with making a separate pulley and pressing it on, to minimize machining. The shaft of the spindle is 20mm and the pulley is 50mm.

    I'll also modify the design a bit and att a nose taper to the spindle and make corresponding Wheel holders. As it is it's just a straight shank that is a slip fit into the holder that came with the grinder. Which I'm now pretty convinced is a lot too thick for this machine, the Wheel is protruding out of the sheild adding to the runout problem by additional stick out.

    This has turned into something of a monolouge. I'm mainly updating this for posterity and for anyone else that would happen to buy a Kirba grinder.

    Regards
    Karl
     
  21. brian fisher

    brian fisher Registered User

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    karl,

    i am sorry to see that no one has responded to your thread. i have never seen collets nor a grinder like the one you have there. however, i would really like to see your progress in making a new headstock.

    i don't think that spindle should have more than a thousanth (.001) of runout. i would suggest selling the collets you have to recoup your costs. even if you sell them for half the price of new, that would be a good chunk of money.
     
  22. karlmansson

    karlmansson Registered User

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    Thank you! That's a good suggestion. I was contemplating keeping all the original parts should I sell it and someone wants to restore it to original dimensions.

    I'll keep updating this thread as I go along.

    Regards
    Karl
     
  23. brian fisher

    brian fisher Registered User

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    i guess my thought is that the runout on your machine is so bad that it seems almost unusable. i don't think i would ever try to sharpen anything with the wheel flopping around like that. i am pretty sure you can buy new chinese r5 collets for like 5 us dollars each? seems to me that you can buy a complete set for the money you could recoupe from the ones you have on hand.
     
  24. karlmansson

    karlmansson Registered User

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    Since my first post I've brought the runout down to a couple of hundreds of a mm so "flop about" it does not. But it does vibrate somewhat.

    There are two different parts I'm discussing here, the first is the actual machine spindle, where the runout is present and where I Think I can make a new spindle with a taper nose to increase concentricity on the holder both in the flat and in the round.
    The second part is the tool head which takes the collets. This part doesn't have much runout at all after I serviced it and tightened up the spindle nut. The reason for making that is to make one that takes 5C collets.

    I'll post some Pictures later to clarify.

    Regards
    Karl
     
  25. brian fisher

    brian fisher Registered User

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    #25 brian fisher, Aug 1, 2019
    Last edited: Aug 1, 2019
    sorry. i meant to say 5c and not r5. by the time i realized my error, it was to late to edit.

    judging by photos you posted above in your first entry, when i compare the dial indicator readings, it appears that your runout is about .44mm and not .04mm(as you state in entry #12)? it looks to me that one turn of the dial is 1mm? you have almost a half of dial of runout there it appears. when i do the conversion, i believe that comes out to .017"? no offense, but man....that is a crazy high number. i think that this tool should have about 10x less. i think i might be scared out of my wits running a stone at high speed with that much eccentricity.

    presumably, this is a grindstone insert that goes into the collet spindle and it appears you are saying that the actual collet spindle has much less? if you are using the same dial to check the rest of your machine, just make sure you are interpreting the values correcly.
     
  26. karlmansson

    karlmansson Registered User

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    If you read through the thread you would see that I bent the spindle nose back and ground it, getting the runout down to 1/100th mm in the flat and about 4/100th in the round.
     
  27. geo.ulrich

    geo.ulrich Registered User

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    A brake truing fixture, its basically a rock wheel that holds tension on wheel as the two spin with each other. also indicate wheel as close as you can before truing and mark wheel and spindle so when you change you can index them back in same place
     
  28. geo.ulrich

    geo.ulrich Registered User

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    also if spindle to enough of a shot to bend spindle I would take a good look at bearings for flat spots
     

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