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IndustryArena Forum > MetalWorking Machines > Tormach Personal CNC Mill > Lost motion/backlash...gonna have to dive in.
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  1. #1

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    Lost motion/backlash...gonna have to dive in.

    Happy New Years guys,
    I knew I'd be having to go down this path. Did some lost motion tests and that rabbit hole just turned into a bottomless pit. I did some searches here and followed a thread by Jake-something. and quite if you chimed in and through a lot of digging, I think ballscrew/nut and angular bearing got him fixed up. Anyway, grabbing my table, I got enough movement that you could actually hear the oil on the dovetails making their suction sound. Tried tightening x to the point of it jamming, it wasn't X Moved onto Y. It's acting all kinds of crazy and after reading this thread, I decided I'd like to just pull the X and Y saddles and clean/inspect everything.
    I suspect debris in the dove tails, I might even expect a loose ballnut where it connects to saddle.
    Anyway, I don't see a diagram in my manual, any points/heads up would be helpful. I don't currently have the spanner wrench for the angular bearing adjustment, figured I'd just make one. I watched a video by NY CNC but they had an 1100. Does the 440 have the jut/jam nut on the X and then the bearings adjustment is WITHIN the stepper on Y? Maybe this is how 1100 is too...I'm not sure, He didn't go into Y adjustment. I might even think the ballscrew needs replacement which my machine was sold with one, but I'll have to figure out if its a X or X (I assume they are different lengths)
    Not the way I wanted to start 2021, but after 2020, no surprise.
    Thanks guys.

  2. #2
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    Re: Lost motion/backlash...gonna have to dive in.

    Quote Originally Posted by Tigster View Post
    Happy New Years guys,
    I knew I'd be having to go down this path. Did some lost motion tests and that rabbit hole just turned into a bottomless pit. I did some searches here and followed a thread by Jake-something. and quite if you chimed in and through a lot of digging, I think ballscrew/nut and angular bearing got him fixed up. Anyway, grabbing my table, I got enough movement that you could actually hear the oil on the dovetails making their suction sound. Tried tightening x to the point of it jamming, it wasn't X Moved onto Y. It's acting all kinds of crazy and after reading this thread, I decided I'd like to just pull the X and Y saddles and clean/inspect everything.
    I suspect debris in the dove tails, I might even expect a loose ballnut where it connects to saddle.
    Anyway, I don't see a diagram in my manual, any points/heads up would be helpful. I don't currently have the spanner wrench for the angular bearing adjustment, figured I'd just make one. I watched a video by NY CNC but they had an 1100. Does the 440 have the jut/jam nut on the X and then the bearings adjustment is WITHIN the stepper on Y? Maybe this is how 1100 is too...I'm not sure, He didn't go into Y adjustment. I might even think the ballscrew needs replacement which my machine was sold with one, but I'll have to figure out if its a X or X (I assume they are different lengths)
    Not the way I wanted to start 2021, but after 2020, no surprise.
    Thanks guys.
    Sounds like a project.
    Take lots of pictures, Try to address base twist first. This will effect everything you do. Keen did a good video on how to measure this and address it just a couple months ago. While apart I would carefully clean all the lube system passages and lines also.

  3. #3

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    Re: Lost motion/backlash...gonna have to dive in.

    I'll have to see if I can find his. It's concerning that I can tighten the gibs up and still get torsional movement on bed. X or Y?...I think it's Y. I would like to just inspect everything and clean it up. Any video I watched seems to be on the 1100, and their bearing appear to be separate of motor so some of the tests using a pulley in place of the motor might be unattainable. I'd like to make sure dovetails look good and oil flow is smooth to ball screws (dovetails were plenty oiled.) I wasn't aware of any bed twist, at least not a problem, but I will research this and check. I don't know if anyone really seems to need a write up, but I'll try. I'm one of those jump in types and never stop to take pictures or make notes, though it would be handy even for myself. Well tomorrow is the day I jump in!

  4. #4
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    Re: Lost motion/backlash...gonna have to dive in.

    Sigh....those dammed dovetail problems......now you know why linear rails were invented.
    Ian.

  5. #5

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    Re: Lost motion/backlash...gonna have to dive in.

    So...spent the last few hours taking apart and cleaning/inspecting. Though the wear almost looks like the surface of a record, I can't discern with my fingernail. (trying to make myself feel better) Any good ideas/technique for inspecting with a DTI? Just the base of the machine, lower Y ways. Anything else I can take out, I will put on my manual mill and run a DTI as if it was my mills X table.
    I'm not thrilled with oil distribution. Check valves are really where it seems to be limited. Though air passes one way through them...its very little of the air I'm passing through it that actually makes it. Perhaps these need replacing? Maybe that's how limiting they are supposed to be? I'm thinking I might get another oil pump and separate the Z from the other axis'. I really think that would be huge for oil distribution.
    Gibs look great. They even still show the original "flaking". Odd that the dovetails show the wear over the gibs.
    Hit me guys, what all should I be checking here? I'll post more pics here, but this is about as informative of pictures there are.

  6. #6

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    Re: Lost motion/backlash...gonna have to dive in.

    Continued...
    Attached Thumbnails Attached Thumbnails XballScrew.jpg   XGib.jpg   YbotR.jpg   YBotL.jpg  

    YBallNut.jpg  

  7. #7
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    Re: Lost motion/backlash...gonna have to dive in.

    Hi, a lot will depend on your engineering skill ability as far as metalworking goes.......I would not advise touching the dovetails with anything except an oily cloth as they need to be fitted very closely but still free for CNC work.

    If you assemble the dovetails dry and still get untoward movement as shown by an indicator against the table ends then perhaps a quick course in fitting is on the cards.

    The very simplest move you could make would be to clean the dovetails and apply some mechanics blue to see where they touch or not touching, but that in itself is an art form and needs interpretation to be meaningful.

    As this is a new thread the details of the machine are none existent......what mill is it, how old and how much work done etc etc.

    If you bought it used then someone else might have attempted to "rework" the slideways and failing that just sold it on etc.

    As I'm a fitter and turner (retired) machinery fitting is a trade I followed on and off for the last 60 years or so and you don't learn that overnight from a book.
    Ian.

  8. #8

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    Re: Lost motion/backlash...gonna have to dive in.

    Thanks Wanker.
    It’s a 440 and I’m a hobbyist so I’m keeping this realistic. I do believe there was room to improve with what I have to work with. My wife tells me this all this time!
    Anyway, though most the wear appears to be on the base/Y ways, I did some measuring by mounting to my manual mill and indicating it as parallel with the bed as I could. Though I could see some movement perpendicular to ways, running along length it was pretty solid. I cleaned the hell out of everything and decided to order a 2nd oiler to separate Z with other axis’ to increase pressure.
    If I jog .005 and back to 0 (according to DRO) my DTI matches perfectly. HOWEVER.....and I know this is splitting hairs here.... I have to move about .0015 (.0001 steps) before I see actual movement. Perhaps angular bearing adjustment, but I’ll leave that. The crux of all this, and I did narrow it down to X table, I can apply torsion to table and get about .002” movement. This is where I ended after cleaning/inspecting/adjusting. I don’t love it, but I think it’s the reality and no solid fix for it. I still need to dig into Z just to see it’s condition and clean adjust.
    That oiler system is sketchy, I’ll have to do a search & see what others have done to improve.

  9. #9
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    Re: Lost motion/backlash...gonna have to dive in.

    A DRO on a CNC mill control panel as shown by the movement on the readout is not a DRO per se........it is indicating the rotation of the ball screw and that is as good as a manual mill with just a thread and nut to show movement.

    An actual DRO with a glass or mag scale on a manual mill will indicate actual movement of the table or other slides as opposed to thinking the table moves when in actuality it is the rotation of the screw and the table can be static due to wear or backlash in that case.

    However........if you have suspected wear in the Y axis slides you'll need to blue them up and see where they touch.

    This is not a perfect indication as one slide in a dovetail will match the other but not in a straight line etc but it will give some indication of where the slide is laying......you need actual dovetail straight edges to test the planes of the faces before the dovetails can be considered a fit......this is done at the manufacturing stage and also in subsequent refitting.

    I need hardly point out that if the Y axis slides are iffy, being shorter and so subject to forces from the long X axis table slide, then a refit by a person qualified to wield a scraper etc would be the sane way to go......you cannot expect to work miracles on machinery to new standards without the expertise etc.

    The sum of all expectations would be to be able to have reliable moves in the axes with squareness in 3 planes and no wobble etc.

    I would think that if you can move the table in 2 planes and get squareness with free travel that is as good as it will get......any slop due to slack slides for easy moves will be a cross to bear, that is a characteristic of dovetails.

    I would think that continuous pressurised lubrication "could" possibly make a dovetail slide run on the lube film as opposed to a hit and miss lube where it touches.........big end bearings in an engine are examples of pressurised lube film, but the amount of continuous lube that oozes out of the cracks will make it quite messy.

    You cannot have metal to metal contact without seizing up and an oil film does the trick if it is there.

    If you can live with .01mm tolerances then dovetail slides will be as good as it gets.
    Ian.

  10. #10

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    Re: Lost motion/backlash...gonna have to dive in.

    When I get the secondary oil system in, I will get the bellows back in (giving them plenty of time to dry from the new layer of coating) and run some real world test and see where I'm out, like a 1" circle pocket and see what the X/Y final size is. I think I'm about as good as I can realistically get (without spending more time and money fixing rather than fabricating.) I'll post some final results then.
    Thanks MountainDew and Ian

  11. #11

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    Re: Lost motion/backlash...gonna have to dive in.

    Second oiler

    Attachment 456452

    The shimming was so minute, but when you're using a precision level, it LOOKS like SO much. Think I ended up using .0006" front left, and .0008" right rear.
    Attachment 456454

    Dumped the fixture plate...for a machine this small, unless you're using low profile vise, seems redundant.

    Attachment 456456

    Keen's silicone, bellow coating on front and rear Y

    Attachment 456458

  12. #12
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    Re: Lost motion/backlash...gonna have to dive in.

    Nice Job!
    pictures tend to explain a lot
    I like your extra oiler!
    Hardware stores sell a epdm rubber membrane sheet for shower floor pans. I would buy a section and use that to cover and protect bellows for heavy machine use. Otherwise I just keep them clean.

    funny how your machine requires shims in same locations as my machine and so many others I have seen!
    Thanks for posting your progress!

  13. #13
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    Re: Lost motion/backlash...gonna have to dive in.

    Quote Originally Posted by Tigster View Post
    Check valves are really where it seems to be limited. Though air passes one way through them...its very little of the air I'm passing through it that actually makes it. Perhaps these need replacing? Maybe that's how limiting they are supposed to be?
    That's how they're supposed to be. They are actually Flow Restrictors https://tormach.com/lubrication-oil-...tor-31370.html (Wow, they've gone up in price since I bought some spares from Tormach )
    In another post you mentioned "Seems as if Z suffered as it had upward flow to contend with...the path of least resistance and all that." The idea is to introduce a high resistance to each path so there is no path of least resistance, they're all essentially equal, regardless of whether they go up or down. If you remove a restrictor from the ways you'll see the oil only drips out slowly. I takes 10-20 seconds to feed the oil but that's not an issue.
    The lubrication system is not ideal, at least not on 1100's, but the restrictors are not the issue.
    Step

  14. #14

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    Quote Originally Posted by TurboStep View Post
    That's how they're supposed to be. They are actually Flow Restrictors https://tormach.com/lubrication-oil-...tor-31370.html (Wow, they've gone up in price since I bought some spares from Tormach )
    In another post you mentioned "Seems as if Z suffered as it had upward flow to contend with...the path of least resistance and all that." The idea is to introduce a high resistance to each path so there is no path of least resistance, they're all essentially equal, regardless of whether they go up or down. If you remove a restrictor from the ways you'll see the oil only drips out slowly. I takes 10-20 seconds to feed the oil but that's not an issue.
    The lubrication system is not ideal, at least not on 1100's, but the restrictors are not the issue.
    Step
    Yeah, i thought they were well over priced. I get the purpose, obviously you want the positive pressure to feed the ways and ball screws without it back flowing (probably a bigger issue in Z) I guess just considering the whole system, I think the one tiny pump feed 7 lines? Very little flow, some fighting gravity etc... The new pump does push more volume and now just does the lower half of machine. I have noticed a bit of pooling so I'll need to back off, but if I had to choose between too little and took much....Anyway, I'll find my happy medium.
    I might add the silicone/terp mixture made have made my bellows a bit sticky now, been drying about a 4-5 days now. If they build up,I'll just replace them.

  15. #15
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    Re: Lost motion/backlash...gonna have to dive in.

    Quote Originally Posted by Tigster View Post
    I get the purpose, obviously you want the positive pressure to feed the ways and ball screws without it back flowing (probably a bigger issue in Z)
    Just to be sure, there are not only check valves but are also intended to ensure that each lubrication point receives the same amount of lubrication, independent of the oil line length or height differences. They're sometimes called metering valves. I don't know the 440 pump but I would expect Tomach have done their homework. You don't need lots of oil, the excess will just run off as you've found.
    As far as the bellows are concerned Robin Renzetti just posted a solution to a similar problem on Instagram: https://www.instagram.com/p/CKHFDcvp-EM/. Maybe a long shot, but worth trying if the alternative is to replace them.
    I would recommend the solution proposed by MD earlier. Tormach sell a "Chip Flap" for the 1100 and 770 https://tormach.com/y-axis-chip-flap...100-32780.html but I'm not sure about the 440. I have one for my 1100 but they're simply not wide enough to fully cover the bellows completely. A real shame, but IMHO much better than nothing.
    Step

  16. #16
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    Re: Lost motion/backlash...gonna have to dive in.

    A couple points

    There was a problem with too much oil pressure lifting the table or head when oiling during machining and making out of tolerance parts. This showed up more with the auto than the manual oiler since it was more likely to pump when machining. I think the oiling system has been designed to slowly ooze to avoid that problem.

    From the hip. Table weighs 200 lbs. Oiler without restrictions can put out 10 PSI. Each X way is 15 long 2 inches wide. 600lbs of lifting force, more than enough to pick up the table.

    Several people have reported inspecting ways after years of use and seen undetectable wear.

  17. #17

    Re: Lost motion/backlash...gonna have to dive in.

    I understand the OP has a PCNC 440, and I am not trying to hijack his thread, but I was wondering if any PCNC 1100 owners have noticed
    drain down of the of the Z axis lube oil.
    I have attached a image of the PCNC 1100 lube diagram, and I noticed there is no flow control for the Z-Gib and X-Gib.

    David


  18. #18
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    Re: Lost motion/backlash...gonna have to dive in.

    I installed a check valve on the Z supply line on my 1100, this worked for awhile but occasionally would leak down so I installed a second oiler just for the Z, this has worked fine since.
    mike sr

  19. #19

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    Re: Lost motion/backlash...gonna have to dive in.

    I just ran a test running a 1.25" circle pocket, I read the same measurement on X and Y, though they were both .010 under at 1.24". This is a brand new tool and I questioned myself in setup as I read the diameter at .246 though it's a .250 tool. At any rate, this could account for a 8 thou off diameter, but glad it read same on both axis.
    Another point, the silicone and turpentine mix, water proofed my bellows for sure, but made them so tacky that it was very difficult to get chips off. I think it's a great idea for water proofing, but would recommend a light layer of WD-40 prior to use to get rid of that tackiness. (They have been drying inside the house for maybe 10 days?)
    Overall I think my mill is in better shape now and I have piece of mind on the oiling of all the axis. Hopefully longevity has been improved...more so for the next person I sell to when I outgrow this entry level machine.
    Click image for larger version. 

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  20. #20

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    Re: Lost motion/backlash...gonna have to dive in.

    @David Allen, I know nothing of the 1100, but it is odd that the one axis that exists ABOVE the oil reservoir is the one that they didn't put the check valve on? I still need to do all this same work on the Z axis on mine, so I'm curious to see, but when you pump positive pressure into line, you wouldn't want it back flowing or being negatively pressured on that line as the pump is pulling oil from reservoir. I mean, correct me if I'm wrong here, but isn't it a big oil can? If you've ever pulled apart a Eagle 66 oil can or similar, this is how they work on a smaller scale.
    If I didn't say it earlier, seems like there is plenty of room for improvement on the oiling systems here. Being they are so detrimental on the machine if not working properly....I have a hard time sleeping until this is all buttoned up. Splitting the system into two I feel was a great 1st step. Checking for wear damage and that all lines flowed properly, I feel closer to a good night sleep!

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