where to put glass scale on J&S 540 vertical axis
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    Default where to put glass scale on J&S 540 vertical axis

    Not sure if the question is better here or in the "Abrasive Machining" forum. But I consider this to be part of "machine reconditioning" so will try here first.

    My J&S 540 surface grinder is now my only non-DRO machine and it's getting on my nerves. I was grinding a part for a friend this evening and got a step wrong by about 5 microns, which I should have gotten closer. I don't think I messed up the marks, maybe the lead screw is off by that amount. Anyway, it reminds me that I need to fit a good glass scale on the vertical and cross axes.

    The cross is easy, but the vertical is harder. I was looking at the machine, and can see one good location. If you pull the upper back panel off the machine, the metal casting that carries the spindle is visible (the spindle pulley is right in the middle of this casting). I could attach a 300mm (12") glass scale to the back of that casting, and mount the read head on the (fixed) body of the machine. The read head would be close to the line defined by the spindle rotation axis, but offset along that axis (say 200-250mm, 8-10") from the metal rails that carry the casting up and down.

    It's a good location in terms of dust/coolant/flying bits. Is it a good or bad location in terms of accuracy? Is there a better place?

    Cheers,
    Bruce

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    Al axis have twist.
    Do you know Abbe and her close friend Error.?
    What twists and where? Back side not so great a choice.
    Bob

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    All surface grinders that i have ever seen all have the wheel head cantilevered out over the work......as such only the vertical slide is in play for mounting a direct measurement system....Short of a non contact setup like a laser of
    such where the lens or target was mounted directly to the wheel head , i don't see another way to fit a DRO scale for the "Z".
    Good news is this is a grinder, and when finishing to close dimensions there should be little external force acting on the active members....
    Think if your slides are in good shape, everything running parallel and perpendicular to the table and the gibs adjusted your setup should be fine......
    I would try and locate if possible the scale at a height more or less the same as the vertical slide ways...as opposed to having the scale higher up on the casting....less chance low of
    having issue with the casting flexing...

    If worried you can always chart the real movement and set corrections within the box, provided you spring for a unit that can accept such....

    Cheers Ross

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    Hi Bob,

    thanks for the helpful reply! What location would be better?

    I have read about Abbe errors, but I wonder if the J&S 540 designers knew about them. On this machine, the lead screw is well behind the guiding column and the grinding wheel is cantilevered out in front on the other side of the machine, far from the lead screw or guiding columns.

    FWIW the location I am proposing is almost exactly at the intersection of the horizontal axis defined by the spindle rotation and the vertical axis defined by the lead screw.

    Ross, thank for replying. The location I am proposing is right in between the vertical slide rollers, which are located at the top and bottom of the spindle and spindle motor carrier.

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    Ballen’s question has me wondering about dro’s on surface grinders. Haven’t seen any dro’s on grinders in the shops I’ve been in. Is this unusual? Grit issue? On occasion I use a dti on mine, but a dro on cross and height would be very useful.

    L7

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    Most of the places I've worked have had DRO on at least the head of the grinder if it was used with any frequency.

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    Hi Bruce,

    this is the way we have done it on a ELB Surface Grinder.

    elb-dro-1.jpgelb-dro-2.jpgelb-dro-3.jpg

    greatings Franz

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    Closer to the wheel is better for obvious reasons.
    I mount mine on the front right side of the column much as above.
    I orient the reader head towards the spindle so that the reader head mount arm is as short as possible and make a double L shaped sheet wraparound metal cover over the entire thing to help with dust, dirt and in my case lots of water.
    Many would worry about the life of a glass scale out here but mine have gone 38 years with no failures yet (knock on wood).
    The fanciest I have ever built for someone had 1/10 micron scales on the front and back of the column. Software in the readout would calculate twist in the spindle assembly and interpolate out to where the wheel was in space.
    That IMO was overkill but they had a very big budget.

    A scale, indicator or such simply can't tell you about wheel growth when working or room temp changes.
    Spindle can be in the right spot, bottom of the wheel maybe not.
    Bob

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    Hallo Franz!

    Quote Originally Posted by MASCHRATUR View Post
    This is the way we have done it on a ELB Surface Grinder.
    Thanks for the photo! I like it, that you have the sealing lips pointing to the back of the grinder, to help protect from grit and coolant.

    If I use your location, then the read head will be in the plane of the column guides, but far from the lead screw and from the axis of the grinding wheel. I'm not sure if that's a better or worse location than where I have in mind.

    I think I am going to do some experiments. I'll mount a 0.001mm reading dial indicator on the wheel housing, and indicate the magnet just below the wheel. Then, I'll mount a 0.001mm reading Heidenhain electronic indicator at various locations around the machine, and see which locations give me the least hysteresis/backlash and the best repeatability.

    According to theory (E. Abbe, Messapparate für Physiker, Zeitschrift fur Instrumentenkunde 10:446–448, 1890) the correct place to put the scale is oriented vertically, directly above the wheelhead. Since that's not very practical, I am going to forget the theory and take a 100% experimental approach to find the best location.

    Beste Grüße
    Bruce

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    Hi Bob,

    Thanks for the thoughtful reply.

    Quote Originally Posted by CarbideBob View Post
    I orient the reader head towards the spindle so that the reader head mount arm is as short as possible and make a double L shaped sheet wraparound metal cover over the entire thing to help with dust, dirt and in my case lots of water.
    Please, could you post a photo to help me understand that?

    The fanciest I have ever built for someone had 1/10 micron scales on the front and back of the column.
    The scales I am using don't cost that much: the effort of installing it is the majority of the "expense". With that in mind, I could put one on the left and one on the right and sum them in the counter. That way, if the column "rocks" on the guides the reading will still be correct.

    A scale, indicator or such simply can't tell you about wheel growth when working or room temp changes.Spindle can be in the right spot, bottom of the wheel maybe not.
    True. But since you and others here are able to work to micron accuracy, it must be possible to overcome those effects at the micron level.

    Thanks again for your comments!

    Cheers,
    Bruce

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    Right and left or little use, Rock not the influence on size control as it tends to rotate around C/L and even the 3-5 inches down not a real player.
    It is tilt of the spindle that pucks you as it is loaded or friction on the up/down.
    Part of this is the whole argument of go down and then up to size or down to a size. The system gets loaded differently.
    Ran a production grinder with large core aluminum wheels at low coolant in a non-air conditioned shop. From 6 am to 2 PM I could tell you the temp rise in the building by my size adjustments.
    Was sort of neat to map that and figure the why out.
    Bob

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    Quote Originally Posted by CarbideBob View Post
    Right and left or little use, Rock not the influence on size control as it tends to rotate around C/L and even the 3-5 inches down not a real player.
    The J&S 540 has a pair of round steel rails, mounted vertically, on the left and right. The spindle carrier moves up and down these with four rollers that push against the rails, one top and one bottom on each side. It's not clear to me that these are free of stick/slip. So I can imagine that on small vertical moves, one roller stays fixed and the other moves.

    Is a similar system used on all grinders? Or are there other approaches?

    It is tilt of the spindle that pucks you as it is loaded or friction on the up/down.
    Part of this is the whole argument of go down and then up to size or down to a size. The system gets loaded differently.
    On the J&S, the motor + spindle carrier assembly must weight at least 100kg. That weight is carried by a rear-mounted vertical lead screw. If I mount the scale in the position that I proposed, it will be almost exactly correct (according to E. Abbe) for measuring the position of the lead screw nut along the lead screw, since the scale will be almost exactly in line with the lead screw.

    Since the J&S designers intended that point to be the one where the vertical axis position was measured, they must have designed the column bearings and spindle weight to properly preload the head, so that it follows the motion of that lead screw nut.

    So to me it seems that this ought to be a good location. If the machine designers did their job carefully, the thermal expansion which moves the head relative to the magnet should be the same as the thermal expansion which moves the lead screw nut relative to the bottom fixed point of the screw. That should be the case if the design maintains relatively small temperature differences between the lead screw and the machine base.

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    Don't think complicated, most of the Surface Grinder manufacturers use a Rotary Encoder mounted on the upper End of the lead screw.
    Too much play in the slide in the column has to be fixed
    similar to toothache, it is better to go to the dentist then swallow painkiller

    greatings Franz

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    "the correct place to put the scale is oriented vertically, directly above the wheelhead." why not do that? because it looks weird?

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    Bruce,
    I think that you can understand better what Bob is trying to tell you if you translate it in terms of a surface plate and a precision square.
    Similarly to your vertical guides, the surface plate is fairly flat. However, if you traverse it with a precision level, you will notice movements of the bubble. Now, think about traversing it with a square and consider the deflection from true vertical of the tip of the blade: it will be out of true by a factor that is proportional to the length ratio between the long and the short sides of your square.
    Similarly, the up and down movements of the wheel on your grinder are a combination of leadscrew movements, stick-slip and deflections due to imperfections of your roller and vertical guide multiplied by the ratio between the distance of the wheel from the rollers and the distance between the top and bottom rollers.

    Nothing is strictly perfect. If the errors are mostly on the guides, they're reproducible and mappable, like leadscrew errors. If the eccentricity errors of the rollers is a significant component of the total error, it's much harder to account for.

    i hope it makes sense.

    Paolo

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    I think a DRO is very handy on a surface grinder. Counting turns for a step dimension is tough when one grinder has .125 and another grinder has .100 on a hand wheel.
    DRO saves the time needed to place a scribe line plus many other valuable functions.

    We had a DRO on the 540 and the parker SG and on all the CNC TC grinders...but I cant rember where tha glass scale was. I have run machines that had the DRO read in an odd position that required you to look far from the work and never liked that.
    In my home shop I dont hav a DRO on my surface grindres.

    I also like a screw stop to drop in at my long travel stops.. just a rectangle with a screw and holes for adjustion so I can adjust the long travel to a stop position and so back away as the down feed makes the end of long travel need to be backed off. This for letting the wheel diameter arc be the end on a grind to seporate a part hiight step long ways. you ont see that need often an a part print but designing you own parts and fixtures it can look very nice compared to right angl steps..

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    Hi Bruce, I have a Heidenhain DRO fitted on my 540, the column scale is fitted as per the pictures, let me know if you need more details.

    Nick

    1-c.jpg

    2-c.jpg

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    Quote Originally Posted by nickom View Post
    Hi Bruce, I have a Heidenhain DRO fitted on my 540, the column scale is fitted as per the pictures, let me know if you need more details.
    Nick, thanks, that's almost exactly what I had in mind! Only difference is that I was going to mount mine in the middle rather than to the right.

    I've got several questions:

    - Did you fit this yourself, or did the machine come to you like that?

    - What's the type of the scale and the resolution of the display? For example does it show microns in the last digit, or tenths of a micron?

    - Is it accurate? In other words, if the display says you have taken off 50 microns, is that actually the amount removed?

    - Does starting and stopping the wheel cause the counter to fluctuate a lot (from vibrations)? Has it ever "lost the count" because of that?

    - Is it correct that the scale is mounted on the moving carriage, and the head is fixed to the body? If you could shove your cell phone in there and take a few photos showing how they are attached, I would appreciate it.

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    QT:[ if have taken off 50 microns, is that actually the amount removed?]
    50 microns and wheel loss understood by grinderhands.
    Agree not much wheel loss in .002 take.

    I like that position as it keeps slide out of the grits.

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    Quote Originally Posted by ballen View Post
    Nick, thanks, that's almost exactly what I had in mind! Only difference is that I was going to mount mine in the middle rather than to the right.

    I've got several questions:

    - Did you fit this yourself, or did the machine come to you like that?

    - What's the type of the scale and the resolution of the display? For example does it show microns in the last digit, or tenths of a micron?

    - Is it accurate? In other words, if the display says you have taken off 50 microns, is that actually the amount removed?

    - Does starting and stopping the wheel cause the counter to fluctuate a lot (from vibrations)? Has it ever "lost the count" because of that?

    - Is it correct that the scale is mounted on the moving carriage, and the head is fixed to the body? If you could shove your cell phone in there and take a few photos showing how they are attached, I would appreciate it.
    Hi Ballen,

    I have only just bought the machine and haven't had it running just yet, need to sort out VFD etc and sort out the controls to work with VFDs etc.

    The machine came fitted with the DRO , it was stripped and refurbished by Andmar in 2006 so the DRO could have been fitted by them

    j-s-540-scale-closeup.jpg Here is the part number on the scale.


    here is closer look at the attachment to the column
    dro-slide-attachment-1.jpg

    dro-slide-attachment-2.jpg

    dro-slide-attachment-3.jpg

    As a crude way of checking resolution I zero the dial and the DRO and rotated until it registered on the DRO. it looks like its 5 micro meters.

    here are the pics.

    dro-0.jpg DRO zeroed

    I need to add another post as max number of pics is 5


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