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    Default tolerance requirements for grinding machine ways

    Hi all am looking into having my Schaublin 135 bed reground. There is a mixture of mystique and magic around these machines but I would like to get a good handle on the facts without the BS. What do I need to require of the grinding house to achieve the performance this machine is capable of by design.

    I am a fairly experienced mechanical engineer but do mostly analysis have never done drawings for grinding or all that much GD&T for that matter so it seems like the people actually do the grinding might know more about what goes into getting the results.

    Those of you who do precision way grinding what are the typical ways of defining the result (straightness over a distance, flatness ... ) surface finish (Ra etc)

    This is in Europe but I can deal with inch dimensions (being born and raised in the USA)

    Once setup, scraped, leveled etc the machine should be able to cut extremely straight (say 0,002mm over 200mm) or 0.0001 inch in 8 inches. The bed is going to need to be better than that I presume, so something like 0,001mm over 500mm with a very fine surface finish (RA 0,4 or better)

    Any thoughts?

    thank you

    Luke

    the bed in question is shown in these drawings: Schaublin 135 Bed.pdf - Google Drive

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    Good luck finding someone to grind to the specifications needed
    Ruemema tried to outsource the grinding in Germany He never got the results he wanted
    The only shop I would thrust is indeed Ruemema
    If you want to bring that machine back to original specs be prepaired to buy €20000 or more in new parts
    its not only the ways and saddle that make these machines this accurate


    Peter

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    Get it from the horses moth and call these German companies that I taught scraping classes at. One thing to remember when your grinding that close is you have to scrape the part that mags to the chuck flat first to avoid twisting the part when they pull it down.

    Go to post 40. Call that company as hey do amazing work and way grinding.
    Specs for super precision grinding and then match fitting is .00005/12'

    Call these companies and see what they can offer.

    http://www.practicalmachinist.com/vb...25/index2.html

    these guys specialize in precision grinding a scraping:

    Der Spezialist fur Retrofit, Spindelservice & Sondermaschinen

    go to post 11

    http://www.practicalmachinist.com/vb...2015-a-304431/

    More Precision shops who scrape in Germany and Switzerland.

    http://www.practicalmachinist.com/vb...s-pics-301415/

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    wondering how you came up with 2mu over 200 mm. i doubt any lathe is capable of doing that, for many reasons. with tail or without?

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    Thanks Richard, I will add those to the list of grinding houses to talk to.

    I have a couple options already but I still am looking for hard numbers as to what I need to ask for and at what point does the price gets insane (ok more insane than it already is)

    thanks

    Luke

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    It is a number measured by someone I know here in Norway that I have no reason to doubt the truth of. And yes that would be without a tail stock.

    Luke

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    One can get anal on precision especially on a lathe where you have mechanical devices that use bearings and tool bits, Push away, temperature control issues, etc. Say you grind a bed and scrape it to .00005"/12" and your cutting a 1/2" part, outside of a air bearing inspection instrument how can you measure it? And why. You can over do it.

    How's your German? If I were you I would check a sales catalog and see what the factory says it can hold.
    I found this one...there must be others...you can look it up
    http://www.schaublin.ch/app/webroot/pdf/cat/5.pdf

    Schaublin 125 lathe

    You achieve consistent sizes I would suggest a CNC Swiss Screw machine or OD grinder.

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    [QUOTE=Richard King;3121624][lots of good info deleted] "... Specs for super precision grinding and then match fitting [at a recommended company] is .00005/12' ..."

    That ought to be good enough for my 1948 9A, don't you think?

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    connelly (in sec. 26.75) recommends 0.0008/12" in the turning test for a tool room lathe. im always very proud people figure a schaublin will be 10 times better, because its swiss. between centers its half of that, btw.

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    0,02mm per 300mm (8 tens per foot) doesn't seem like a very good result. I would hope for considerably better than that from a tool room lathe. A part that turned out with 0,04 in about 250mm is why I am regrinding this machine. I don't want to get too caught up in numbers but am just looking for reasonable requirements to ask from from the grinding house. I can't just say make it good, as that doesn't mean anything. Richard's 0,001mm/300mm for the grinding is probably a good requirement or at least a starting point for conversation with the grinding house.

    L

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    Quote Originally Posted by whidbey View Post
    0,001mm/300mm for the grinding is probably a good requirement or at least a starting point for conversation with the grinding house.
    You have to be joking. That's three times tighter tolerance than a grade 00 surface plate.

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    Quote Originally Posted by ewlsey View Post
    You have to be joking. That's three times tighter tolerance than a grade 00 surface plate.
    Not entirely a fair comparison unless you have a surface plate that is 30mm wide, think more of straight edge tolerances.

    also maybe that is too tight but it is a starting point.

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    Quote Originally Posted by whidbey View Post
    Hi all am looking into having my Schaublin 135 bed reground.
    According to this Ruemema web page:
    Generaluberholt statt Neu - Drehmaschinen von Ruemema
    their Schneider JoH2 way grinder itself is accurate within 3 microns over 2.4 meters.

    I would contact Ruemema, and ask if they will (just) regrind the bed for you. One advantage of dealing with them is that they specialize in Schaublins, and have reconditioned a lot of machines which are of the same type as your lathe. So you will not need to get them any tolerances or drawings or other information. Just agree on a price, and ship them the bed. They will do the rest!

    Cheers,
    Bruce

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    Like I said To rebuild a machine like that to factory specs you need to buy a decent amount of new parts
    So grinding the ways is just a small part of the costs
    I know of 2 compagnies who can do it and have the proof they can do so That is Schaublin and Ruemema
    If you want to do the rebuild yourself ask Ole steen and Edvind (ole can get you in contact with Edvind)
    They have done one

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    Quote Originally Posted by Peter from Holland View Post
    Like I said To rebuild a machine like that to factory specs you need to buy a decent amount of new parts
    So grinding the ways is just a small part of the costs
    I know of 2 compagnies who can do it and have the proof they can do so That is Schaublin and Ruemema
    If you want to do the rebuild yourself ask Ole steen and Edvind (ole can get you in contact with Edvind)
    They have done one
    I know both Ole and Edvind and know what they did on their machines, where they had there machines ground (which I am not supposed to share) etc. I need to replace the screw and nut in the cross slide but otherwise there is a bunch of labor and not so many parts. The bed/saddle and cross slide are the main components along with the spindle the contribute to accuracy and that is mostly a matter of careful measurement and scraping after grinding them. (lots of time, not so much parts cost) The spindle is good as far as I can measure but that may need new bearings or at least adjustment but that will wait until the bed is good. There is no way to get to 20k euros in parts, maybe half that if I buy a new Biax scraper.

    The rebuilding process, viability etc is a different discussion. I am trying to understand this one part of it which is the tolerance requirements on grinding the ways. Everything else literally rides on the bed so if that is off nothing will be correct no matter how many other parts I replace.

    Luke

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    Quote Originally Posted by ballen View Post
    I would contact Ruemema, and ask if they will (just) regrind the bed for you.
    Everyone have the same idea... Trying to cut costs by having done only what one thinkthe *crucial* operations are, and taking care of the rest.

    Can't say for now, but in the past, that was clearly NOT an option at Ruemema.
    Rüdiger Kramer has his way of doing things, and I bet he will strongly advise you NOT to try to overhaul your machine this way (be it with him or anyone else).

    Reason is he has a very deep knowledge of what it takes to have a 135 or a 150 at its full potential.
    There's a lot lot more to it than just having the bed reground.
    And Mr Kramer is not the kind of bloke who does things halfway. There are no shortcuts to perfection and perfection is his aim in everything he does.

    You may tell him that you would be satisfied with a just a little less than perfect result, trying to convince him. I must admit I thought about it for myself.
    But I bet his answer would have been "why bother with a Schaublin 150 then ? Buy a Weiler ! " or something close
    Wich indeed, makes sense.
    That's the reason I didn't even ask.

    Beauty is more than skindeep they say...

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    Hi Tien,

    Quote Originally Posted by TNB View Post
    Rüdiger Kramer has his way of doing things, and I bet he will strongly advise you NOT to try to overhaul your machine this way (be it with him or anyone else).
    Well I don't know Kramer and you do, so I am sure that you are right. Personally, I would have hoped if sent just the lathe bed, and asked to regrind it in the best possible way that he could, that he would agree to do this, since he is not being asked to do something less than perfectly. But it's certainly his right to refuse.

    Cheers,
    Bruce

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    Yes Bruce of course, but his business is not simply about fitting or grinding.

    He does not only sell particular operations but rather a global know-how, totally aimed at very narrow selection of machines.

    Otherwise he could widen up his market instantly, by offering rebuilding services for any machine the customer would like to pay for.
    Don't you wonder why he does not ?

    As I see things, it sure took a lot of time and dedication to build that reputation of perfection on his name.
    In that regard, I think that to accept to have his name associated (be it closely or vaguely) to projects he wouldn't manage completely would probably be short sighted.
    I'm quite sure that's the way he feels anyway.

    And indeed, it makes sense again.

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    Again the issue is not finding a skilled grinder, there is nothing magic about schaublins or any particular rebuilder/grinding house. I can find a number of grinders who can legitimately meet and document a set of requirements, at a price of course. Yes experience with a particular machine will make that easier but there is nothing unusual about this bed compared metal lathes of the type. It is a careful if straight forward job from the feedback I have heard so far. The question comes down to just exactly how careful do I need them to be and what makes sense from a price to performance standpoint.

    L

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    Quote Originally Posted by TNB View Post
    Don't you wonder why he does not ?
    Because there are plenty of rubes who will pay $40,000 for a rebuilt lathe under the illusion it will hold 1 micron over a meter...


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