Help with workholding on a 5C head grinder
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  1. #1
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    Default Help with workholding on a 5C head grinder

    Guys, I need a bit of help.
    Right out of the gate, I am not a grinding house!!!
    I do some surface grinding for internal needs, but that's it.
    OTOH, have never touched an ID/OD grinder ....

    Until now!
    I have gotten a hand-me-down Covel 512 unit.
    Came from a customer that have replaced it with something new.
    The unit is complete with the 5C head, tailstock, ID attachment and a few hubs. Fairly clean state and everything seems to work.
    Was told that it holds a few tenths without any issues.


    So, my question is: I have 3 pieces of shafts to make, and I figured I'll test my hands grinding 2X bearing journals on each.
    I only have to hold .0005 total, but they also need to be concentric w/in .0002

    So, I was thinking to just put it between centers and go ....
    Problem: I don't know how to drive it on the head side?
    I thought there were some 5C face drivers ... No
    Then perhaps some straight shank face drivers ... No

    So the question: How do I drive it with the 5C head?

    Thank You

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    I'm not familiar with the Covel - does it provide the option/do you intend to run with dead centers?

    If not & you have a Hardinge 5c "dead" center collet, the extension is long enough to grip with a dog, and drive a bent tail dog on your work. Or a barrel-wrench type gripper on the collet center extension. Or for light work, a hose clamp, etc.
    Always touch up grind the center before setting up the work since it will be live in this app.

    If you don't have a regular 5c center, then on the live end (drive) all you have to do is put a suitable collet in the headstock, and grip an on-size blank round. Pre-turn a 60 deg center, but touch it up in place. grip a dog or other clamp onto the extension as above and drive a dog on the work. Or hose clamp, etc.

    If the Covel has dead center capability at both ends, you're probably going to have to find or make the proprietary pieces.

    If you use the dowel-in-regular-5c-collet method, it can be useful to have a shoulder so it can't push back.
    It is also good to have some diameter if it will be used as the driver as described.

    Solid 5c collet bodies can be had with MT sockets to use taper shank centers.
    Or, with an ID grinder, can be made from a blank solid 5c tool body....

    The above assumes you simply don't want to wait or afford going rates for face plate &/or drive center?

    OK, so these are a little pricey, but you can see the options to look for:

    https://shophardinge.com/productGrid.aspx?catID=11198

    Or roll your own:

    ShopHardinge - 10150000000000

    Somebody at the factory has a sense of humor, but this is what they look like.

    ShopHardinge - 57 0000296

    smt

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    Wow Stephen, that was a mouthful!
    Thank You!!!

    Hardinge was my absolute first stop, thinking everything 5C + Grinding = Hardinge.
    Saw the center you've linked to, and saw the pricetag .... thankfully it is out-of-stock!!!

    The back end is a dead center, so I will need to drive it with something a bit significant...

    I do have 2 pieces of the 5C solid blank collets, and if no other off-the-shelf option comes up, that is the way I'm going to go.

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    It would be nice/good to have a pair of straight shank centers that one could put in a pair of precision V blocks for checking a bearing fit job setup, so to mock bench centers. But I don't know where straight shank centers can be bought,

    Checking off the shaft out of a good V block is Ok if one knows the shaft is straight.

    likely the customer may check such a part in bench centers.

    I have run precision shaft OD bearing fits out of a V block on a surface grinder..and out of a pair of v blocks with the part set in two close-fitting bushings and the out end bumping a dead stop..and with a set of 4 bearings that acted like a V block...again with checking the shaft to be straight...because likely the customer won't check off the shaft, but between bench centers for straight and size..

    Live centers grinding is tricky because you take off one part side and leave on the other side with any centers error...live centers should be dead-on perfect....0001 on to get a .0002 part.

    A between-centers fixture about 3 feet long so to be set in the SG cross direction would be nice to have.

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    Hi Seymour Dumore:
    Aside from the excellent posts by Stephen Thomas and michiganbuck, I have the following to add:
    Grinding shafts accurately between centers is a bit trickier than it looks, and as michiganbuck pointed out, if you have a rotating center at the headstock end it must be perfectly concentric, so as Stephen Thomas commented, the common protocol is to kiss the center with the grinding wheel before the work commences to ensure it's as good as the headstock bearings are good.

    To avoid all of that, cylindrical grinders commonly have "Dead Center" capability, as Stephen Thomas also points out...this is an arrangement where the center in the headstock does not turn, but a collar around it does, and that is where you mount a post that can engage a drive dog.

    Look for a way to disengage the spindle from its collar on the Covel...it's a feature of just about every cylindrical grinder ever made so I'm sure there is a way on your machine too.

    As soon as you spin a shaft between dead centers, the quality of the center holes in the shaft starts to matter a lot...grinding houses that do a lot of shaft work have dedicated machines for dressing those centers to make them as perfect as they can be.

    So they need to be as good as you can make them beforehand...even if you choose to drive the shaft with a collet or chuck, or on a live center at the headstock end, but doubly so if you are grinding between dead centers.

    A center drilled hole alone, is not really good enough for fine work...at a minimum these should be single point turned beforehand with a little boring bar to get them round and concentric.

    Next and super important, is that your tailstock center MUST be spring loaded and the tailstock barrel needs to be free to slide back and forth under spring pressure but not have enough clearance to wobble.
    This is so the workpiece can expand in length as it warms up without loading the centers and inchworming.

    Again every cylindrical grinder with a tailstock will have that provision, but a lot of them are totally worn out, and will drive you nuts trying to hold size and cylindricity.
    Some of them also get seized up with crap and dried coolant, so make sure yours still runs back and forth properly.
    You can help a beater by shoving a spring loaded pad under the tailstock barrel to take up the slack by forcing the whole barrel upward, but it's a terrible bodge that will just barely get you out of a pinch and not much more.

    Last, flood coolant is your friend when cylindrical grinding...it's so much easier to hold size when the part stays cool, and it makes for a much nicer finish too.
    It goes without saying that the coolant should be clean...you don't have to be anal about it for your task, but skanky, smelly blobs of crap in your coolant will not help you, and for extremely fussy grinding, the filtration systems get pretty elaborate.

    So that's about it...all I can think of for the present...I'm sure michiganbuck and Stephen Thomas (and others) can add a lot more details to the conversation.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    I think with not having an OD grinder running a .0005 size and .0002 tir part would be better done on a lathe with the head center ticked in a chuck, rather than a jury rig set-up on a surface grinder. if the lathe is good for .001 then crocus cloth to size would not run out .0002.

    It is not uncommon for a better collect to run out .0002, and a good 4 jaw to wobble over 0002.

    Even many poor lathes can do better than that with the part on dead centers.

    A tickled soft/miled center in any chuck runs near zero.

    I think .0002 is a mile for a precision bearing shaft.

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    I have a Covel 512.
    Yes my workhead is 5C but I do not believe
    you can make it where you have a dead and
    not rotating center on the workhead. The
    spindle has to spin in its bearings.
    I know my Brown and Sharpe #13 you can lock
    out the spindle and the belt drives the
    faceplate to engage the dog, so with it
    you can have true dead centers. The B&S
    is a 100 year old design, and mine is a
    1983 model. But to my knowledge, the
    Covel can not grind on 2 dead centers.

    ---Doozer

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    A tip for improving your centers, though it may or may not help you in this particular situation: in a shop I worked in previously I used to do a bit of OD grinding work and I found that for getting good centers, setting up a steady rest in the lathe and tooling the centers like Marcus suggested worked well but was finicky and slow. I mostly used that method for the larger centers like #6 and up.

    For smaller centers I would still set up the steady but just center drill then run a center lap in the center hole right in the lathe by hand. To do this, buy a center lap with a female center in the end, place the lap end into the workpiece center and place the tailstock center into the other end of the lap. Bring the tailstock up until the lap can just rotate by hand, then while holding the lap with a wrench or something similar, rotate it by hand with some good cutting oil at the cutting/lapping surface. Make a few turns, then check and see if you've cleaned up the old surface all the way. Continue until you have cut a full new surface and you're done. I found this method to be quick, easy and fast, with great results. Always got nice round and true parts with that method. It does depend on the lathe not being a worn out junker though.

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    Wow I just lost my whole post with trying to add an eBay link ..darn
    my bad..should have written it on a document first.


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