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  1. #1
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    Default Surface Grinder Sporadic Table Lift

    My Kent KGS 200 seems to be occasionally taking a heavy cut.
    I assume this is caused by the table lifting.

    This is a simple manual machine, the table rolls on balls and the cross-slide slides on plastic V-ways.
    The manual oiler feeds the V-ways and the balls run in a lanolin fluid applied a couple of months ago after cleaning.

    There appears to be a systematic lift of the table on the far side when the cross-slide is parked at the limit on the near side.
    The hypothesis is V-way wear allowing dropping of the front of the cross-slide when the C-of-G is near the front of the ways.
    This is probably 5 micron that I can allow for, and manage.

    The real problem is an occasional heavy cut in the middle of a job.
    This is spoiling work.
    The error is probably only 5 micron, but as I am running dry, the extra cut is quite noticeable.

    The coolant system will soon be operational.
    Is it reasonable to assume that the coolant will prevent, or at least reduce, the effects of the occasional heavy cut ?

    If I lift the cross-slide and clean the V-ways, what special considerations need to be implemented ?

    John.

  2. #2
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    John you really haven't provided enough information to help diagnose the problem(s), but instead I'd suggest proffered assumptions on the cause.

    In the first case I would be looking at the cross slide and not the table if the cross slide is "parked" at its limit. It's possible a stop etc is forcing the axis out of alignment when it's driven against it. It's not good practice to operate any machine at its physical limits like that, so just waste out the last few millimetres of machine travel.

    I don't agree with your hypothesis, but without seeing the machine can't be sure. Any form of rocking should be easily detectable by pushing on the table with a DTI to confirm in any case.

    Your heavy centre cuts could be caused by, sorry to say, "operator error". Again, without seeing what you're doing it's difficult to say, but you would need to start from the wheel dress and type and work from there. Coolant is not your solution, and tens of thousands of grinders are operated around the world dry, including mine, without difficulty and definitely not part spoilage! On wide/thin work the secret is to be patient and keep heat out of the work. A big grinder with copious amounts of coolant will let you get away with more, but if a person running coolant doesn't understand how parts move, get sucked down, change shape with heat, etc, it will eventually bite them too. Don't get me wrong, I'd love to swap, and have a much better grinder with access to coolant, but some of the highest class of work I've ever seen has come off dry grinders. If you don't believe me have a look at Newbould's channel https://www.youtube.com/channel/UCSk...iEnxEFUKuImr9A On the other hand if you're running production and need material off fast, you absolutely need coolant.

    Try and give is some more information John, preferably with video, and I'm sure we can all put our heads together and figure it out. Scrapping parts is never fun!

  3. #3
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    Coolant won't help your problem.

    It might be that the ways are worn in the middle, so when you get to the ends it lifts slightly. That doesn't explain the occasional heavy cut in the middle of a job.

    Grind something flat and check it against a surface plate.

  4. #4
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    The first thing I would be doing is removing the table and checking the ways and bearings - making sure there is not a lump of grit or something (even a small piece of dried out grease) that is lifting the table. Strip it down and clean (and relube) first.

    Michael

  5. #5
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    I were watching Stan (Shadon HKW) on youtube a while back and he mentioned the table lifting slightly as it hit an extra oily section. Perhaps as the guides get a squirt of oil there is a momentary lift? The comment is in one of his grinder rebuild videos.

    https://m.youtube.com/user/shadonhkw

  6. #6
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    Pete,
    The machine is not operated with the cross-slide at the front limit, just parked.
    The suggestion of the rear cocking upwards when the cross-slide is parked against the front stop is a good one, I will not in future come all the way to the front stop.

    The DTI test is on the list of investigations, but removing the cross-slide and cleaning the V-ways is probably a good idea anyway.

    The job is a tool to be used on a wood lathe to hollow out bowls.
    It is 11.5 thick, 50 wide and 150 long with a welded-on stub shaft to take the handle.
    The job is mounted across the chuck because of the weldment.

    This mass of metal will not heat up quickly enough for that to be the issue.
    After the dig-in, a quick traverse back to an area just done moments before also takes a big cut.

    Very light cuts successfully got the first side looking great last week.
    This week, even after wheel dressing, I cannot get from one side of the chuck to the other without a dig-in.
    Something has changed.

    Thanks for the confirmation that I should be able to get a good finish without coolant.

    I accept that I am frequently guilty of operator error, but I do not think this is the case here, considering success last week.

    Note that the dig-in doesn't scrap the part, just means a redo to clean up the slight burn.

    I will try to get a video

    Ray,
    Test pieces done weeks ago came out in perfect condition and checked very good on the surface plate.

    Michael,
    I agree, a strip down and clean is necessary.

    The problem could be dirt pick-up into the table rollers as they are now running in a lanolin fluid as against grease when I got the machine.
    The table is open underneath and wind-blown contaminants could be drawn under the table, especially as it traverses back and forth.

    The Kent manual is silent on roller lubrication, and the way rollers are not piped into the one-shot oiler.

    Similar SGs in the Kent range have the table rollers connected to the one-shot oiler.

    I am pondering the choice of lanolin versus grease when I re-assemble.

    John

  7. #7
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    Rather than lanolin or grease, are you better off with oil (perhaps a thicker variety). Grease what ever the type never appeals to me for these sorts of jobs as it can pick up particular matter so easily and instead of sinking to the bottom as they would in oil, the grease tends to hold them in position.

    Michael

  8. #8
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    I would say it is heat related.
    If it happens suddenly I would say the force created by the heat differential top to bottom trying to bend the work piece has overcome the magnetic clamping force and the centre lifts.
    I would try laying the work piece on a diagonal so as to shorten the grind path and to distribute the heat across the work piece as well as along it.
    The ratio thickness to length has a lot to do with what is happening.
    Also I would dress the wheel very coarsely when roughing. ie. traverse the diamond across the wheel rapidly.

    Robert

  9. #9
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    Quote Originally Posted by electrosteam View Post
    The job is a tool to be used on a wood lathe to hollow out bowls.
    It is 11.5 thick, 50 wide and 150 long with a welded-on stub shaft to take the handle.
    The job is mounted across the chuck because of the weldment.

    This mass of metal will not heat up quickly enough for that to be the issue.
    After the dig-in, a quick traverse back to an area just done moments before also takes a big cut.

    Very light cuts successfully got the first side looking great last week.
    This week, even after wheel dressing, I cannot get from one side of the chuck to the other without a dig-in.
    Something has changed.

    John
    John I don't want to tell you how to suck eggs, as I can't recall how much grinding you've done, but heat is definitely an issue with grinding, and the fact that you considered it wouldn't be for this part (or any part) further suggests to me that we need to investigate this possibility further. To give you an example of just how much it can affect things, consider grinding the mag chuck. The mass in that is probably as high as that particular grinder will ever see on it, yet they are notoriously difficult to grind really accurately. The centre of the chuck will typically go high as it's ground, just with a very small amount of heat differential, and it really requires a lot of patience to do a good job on the grind.

    With parts the same thing can apply, but when you're grinding thinnish parts (as you are) you need to also consider the chuck sucking down the part if it's not perfectly flat on the face on the chuck. The thing with grinding is the distances we're talking about are real weeny, and something we may not think is an issue on a milling machine can be a major source of frustration on a grinder. It may be possible for example that your part is heating and changing shape, that change is enough to pop it partly off the chuck in parts, so it bows up in the centre.

    A way to tell if that's your issue is to go to the point that it gives a problem and then walk away for 30 minutes. Leave everything running and just go have a cuppa for 30 minutes. If you can then do the next pass without an issue then heat is causing a problem.

    Never underestimate just how much metal moves when you're down in the little people's world of grinding and scraping

  10. #10
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    Got the opportunity today to discuss the problem with a fellow machinist not too far away with a smaller manual machine.
    His advice was that one has to learn how the machine responds to set-ups and commands - be patient and work the problem.

    I need to deliver this job tomorrow morning, so I tried one last time.

    Three things changed:
    - the job moved from the middle of the chuck to one end,
    - the cross traverse swapped from outgoing to in-going,
    - the right hand trained to adjust the cross traverse step by using two fingers at the top of the wheel gently in the X direction. No up/down inputs of the handle.

    The result was much better, not perfect but deliverable.

    Michael,
    Oil obviously does work, witness Kent models with oil feed.
    Just how to get oil into this machine would be a challenge, but probably doable.

    Robert and Pete,
    I hear you loud and clear on the heat.
    I certainly had issues with that trying to do exercise pieces on the SGs at TAFE.
    But, I really do not think that is the issue here, witness a successful run tonight.
    I cannot change the job orientation on the chuck because of the welded handle.

    My intention now is to prepare a test piece close to the size of this job and then explore the effect of the three changes listed above.

    Pete,
    Your gentle suggestion on 'operator error' might have some legs, in that with a worn V-way up/down inputs into the cross-slide via the handle may be problematic.

    John

  11. #11
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    I think Robert nailed it, i have had this happen many times despite huge amounts of flood coolant. You simply cannot keep the point of contact with the wheel cool.

    One thing that does effect the amount of heat put into the work is traverse speed. A slow traverse may seem easier on the machine but it allows for a lot of heat build up. I am assuming the traverse is manual and the speed is entirely up to you?
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

  12. #12
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    Quote Originally Posted by electrosteam View Post
    Pete,
    Your gentle suggestion on 'operator error' might have some legs, in that with a worn V-way up/down inputs into the cross-slide via the handle may be problematic.

    John
    As I said in #2 John, and I think it's pretty much unanimous now, I believe you need to completely eliminate heat as a source of the problem before assuming it's an issue with the machine. It may not be as simple as the part itself merely expanding, but if it's warped to begin with and the mag chuck is sucking it down, the heat could be enough to partly pop part of it off the chuck and it will change shape as seen by the wheel much faster than the mere heat expansion alone. The clue here is what you first said "The real problem is an occasional heavy cut in the middle of a job." That can cause the precise problem you described, especially if the work isn't flat to begin with.

    As also mentioned there, I'm having trouble with your hypothesis of a worn way causing this and somehow tipping from one side of the V to the other (as I understood what you meant). What that would mean is the centre to centre distance of the ways have changed and the ways simply don't wear like that. As Ray mentioned, they will wear in a banana shape, but that won't cause the issue you mentioned.

    You mentioned that it seemed to be better traversing in the opposite direction, but did you dress the wheel immediately before this job? If you didn't, normally feed in one direction and then changed the feed direction, you're effectively putting (almost) a new dress on your wheel. That can have a very significant effect on how the wheel cuts and may cause false conclusions in regard the machine.

  13. #13
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    There's a lot of skill and technique in surface grinding, just dressing the wheel, speed of traverse, spark-out, how much downfeed the pass is. It takes time and skill to get consistent results.

    For reference I suspect that the problem might be grinding too heavily and part orientation if you are having a problem with heat build up, As Ewan says, even with flood coolant, there are limits to how much you can take per pass. I usually don't downfeed more than 5-10 microns, maybe 1-2 microns if finish grinding, Then longish spark out.

    The part orientation issue can be trickier to resolve in a general sense, I have a number of custom made mag transfer blocks for some jobs. If it's clearing the socket on a chisel, then you could block it up with a couple of plain transfer blocks to lift the part higher. Don't forget to skim the transfer blocks first if you are grinding parallel. If that doesn't work you can always set up with a grinding vise and parallels.

    In some sense grinding setups are easier than milling setups, because the loads involved in grinding are much less. However it always pays to block the part in with pieces front and back in the direction of traverse.

  14. #14
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    I delivered the part and the customer was quite complimentary, with the promise of another one just like it next week.

    I managed to get a DTI set up to detect table lift with the cross-slide at several positions over its full range.
    The DTI showed absolutely not a quiver, even when I leaned on the handles as hard as I could.
    Couldn't get a reaction even when I tried lifting, frankly the lack of movement is impressive.

    The DTI tracked along the table as it was rolled over a typical range with acceptable deflections, a general slow change due to a non-skimmed chuck with typical bumps from the sliding tip.

    I have to accept that the table may not, in fact, be lifting.
    So, I have to improve my operating techniques to get on top of this, with over-heating high on the list.
    All of the suggestions made will be reviewed and a list of the key points made to keep with the SG documentation for future reference.

    Thanks guys for pushing me in the right direction.

    I think part of the problem was geometry, in that because of the first stop and re-start, then repeated a few times, the job was slowly being shaped with a taper, which looked like a heavy cut when the wheel hit the step.

    In future, if I get a heavy cut, I will swap ends and come in from the opposite side.
    This learning game is frustrating, but fascinating.

    John.

  15. #15
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    Quote Originally Posted by electrosteam View Post
    The DTI tracked along the table as it was rolled over a typical range with acceptable deflections, a general slow change due to a non-skimmed chuck with typical bumps from the sliding tip.
    John.
    Even after you skim the chuck you still won't know if it's flat or not, it will just be that the surface of the chuck follows the wear pattern in the ways.

    Quote Originally Posted by electrosteam View Post
    In future, if I get a heavy cut, I will swap ends and come in from the opposite side.


    If you take the part off the chuck and put it back, you usually have to start over, I often blue the surface I'm grinding, find the high spot first, and touch off from there.



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