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  1. #1
    Join Date
    Sep 2016
    Posts
    44

    [PCNC 1100] Y-Axis Gibb Issue

    Hi Guys,
    My Y-axis gibb removed from the new Tormach PCNC 1100 seems to be noticeably bowed on the scraped side only. The other side (not sliding one) is perfectly flat. My table has quite bad slop/play even with the gibbs over-tightened (with backlash out of spec). The issue probably comes from this bowed surface. I just like to confirm with other experienced Tormach users that this curve is not made by a design. I know that there should be a taper on the gibb, but curved surface? Can you please confirm that for me?


  2. #2
    Join Date
    Mar 2008
    Posts
    256

    Re: [PCNC 1100] Y-Axis Gibb Issue

    It's not by design, but it's not designed to be much better. Yours may be worse than average. I was also dissatisfied with my gibs, but ended up having to remediate them myself. It made a big difference.

  3. #3
    Join Date
    Sep 2016
    Posts
    44

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Thanks flick for the confirmation. This is hand scraped right? Why manufacturer didn't bother to make it flat. Is there something else behind this poor finish, any explainable reason? It looks like I'll need to scrap the centre of this surface but it's just hard to understand why it's poorly made this way.

  4. #4
    Join Date
    Jun 2016
    Posts
    26

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Have you sent this picture to Tormach? If you have not then perhaps you should, as it is, like you said a new PCNC1100. The more feedback they get of issues on "New" machines the better. One would hope they communicate this back to China were they would implement stronger Quality Control or is that just wishful thinking........ :roll eyes:

    That being said I am sure going by your picture they would send you a replacement one.

    G.

  5. #5
    Join Date
    Sep 2016
    Posts
    44

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Quote Originally Posted by GBru View Post
    Have you sent this picture to Tormach? If you have not then perhaps you should, as it is, like you said a new PCNC1100. The more feedback they get of issues on "New" machines the better. One would hope they communicate this back to China were they would implement stronger Quality Control or is that just wishful thinking........ :roll eyes:

    That being said I am sure going by your picture they would send you a replacement one.

    G.
    I'll send them images and some data, to highlight the issue. I'm not expecting a gibb replacement. The gibb has to be made for the particular machine and it's not replaceable part without an additional treatment.

  6. #6
    Join Date
    Feb 2006
    Posts
    7063

    Re: [PCNC 1100] Y-Axis Gibb Issue

    NEVER start scraping without knowing what the problem really is! If you scrape the gib flat, you will very likely make things worse. If you suspect a problem, you need to get some Dykem, and test to see what the actual contact pattern is. That is the ONLY way to have a clue what, if anything, needs to be done to make it right.

    Regards,
    Ray L.

  7. #7
    Join Date
    Sep 2016
    Posts
    44

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Sure thing Ray. I'll wait to hear back from Tormach guys. The non-invasive trials with Dykem sound like a good idea in the meantime.

  8. #8
    Join Date
    Jun 2006
    Posts
    3063

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Quote Originally Posted by flick View Post
    I was also dissatisfied with my gibs, but ended up having to remediate them myself. It made a big difference.
    How did you do that?

  9. #9
    Join Date
    Oct 2008
    Posts
    11

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Count on the Chinese to hand scrape and fit a machine properly??? Haha


    Sent from my iPhone using Tapatalk

  10. #10
    Join Date
    Aug 2009
    Posts
    610

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Quote Originally Posted by CNCer__ View Post
    Hi Guys,
    My Y-axis gibb removed from the new Tormach PCNC 1100 seems to be noticeably bowed on the scraped side only. The other side (not sliding one) is perfectly flat. My table has quite bad slop/play even with the gibbs over-tightened (with backlash out of spec). The issue probably comes from this bowed surface. I just like to confirm with other experienced Tormach users that this curve is not made by a design. I know that there should be a taper on the gibb, but curved surface? Can you please confirm that for me?

    Well you know that scraper can get pretty heavy after one has worked consecutive 80 hour weeks hand scraping in a "state of the art factory" in China-especially so in the summer months. I think that you just need to invest in better precision angle gauges and 1-2-3 blocks that have also been made in China- everything would look good "on average" then :-). I mean come on look at what you are using right now. There is a sticker on the one triangle thingy with some sort of number...why would one ever want their QC tooling serialized? All dripping sarcasm aside I am sure that the folks at Tormach will work with you to understand what went wrong and how to get your machine to specification. Keep us posted.

  11. #11
    Join Date
    May 2014
    Posts
    170

    Re: [PCNC 1100] Y-Axis Gibb Issue

    I dont care what they say, these machine are not hand scraped one machine at a time. I would bet they are not hand scraped at all. But rather they are ground and flaked to look as if they were. Same thing that was done to a lot of old machine that have been "rebuilt". How would you even manage to do that by hand .001 at a time, blue it, .001, blue it. And you certainly would not get that if it was truely mated to that way. As they might like you to think

  12. #12
    Join Date
    Oct 2008
    Posts
    11

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Go watch MuellerNick on YouTube, what he does to scrape in a machine. He actually took a brand new Chinese lathe and showed how disgustingly off it was. It's best you learn how to scrape and more importantly, how to measure and check your work, and do it your self.


    Sent from my iPhone using Tapatalk

  13. #13
    Join Date
    Aug 2013
    Posts
    980
    Great input, as always, Ray.

    Quote Originally Posted by SCzEngrgGroup View Post
    NEVER start scraping without knowing what the problem really is! If you scrape the gib flat, you will very likely make things worse. If you suspect a problem, you need to get some Dykem, and test to see what the actual contact pattern is. That is the ONLY way to have a clue what, if anything, needs to be done to make it right.

    Regards,
    Ray L.

  14. #14
    Join Date
    Jun 2016
    Posts
    57

    Re: [PCNC 1100] Y-Axis Gibb Issue

    What I bet has happened here is the gib was hardened then ground in a clamp down fixture with the angle built into it. The bow was introduced at heat treat and when it was clamped down it was fairly straight. When it was released from the fixture, the bow re-appeared and was not caught due to non existent quality control. If you tighten that gib enough the bow will flatten out a bit but not all the way. So you get excessive friction and play because it's only contacting the way at the one point and the rest of the surface has clearance.
    Remedy: have the gib thermally stress relieved (not annealed), then re-ground at the proper angle if there is enough mat'l on it to do this. The key is to surface grind it in a non-distorted state so it doesn't spring back when it is released from the fixture. You may have to add Turcite to the sliding side if you have taken off a lot of mat'l to get it back flat.

  15. #15
    Join Date
    Sep 2016
    Posts
    44

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Quote Originally Posted by Welder2022 View Post
    If you tighten that gib enough the bow will flatten out a bit but not all the way.
    What interesting, the gibb is not bent, only the scraped surface has curvature. It will not flatten out as the non-sliding surface is perfectly flat.

  16. #16
    Join Date
    Mar 2008
    Posts
    256

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Quote Originally Posted by MichaelHenry View Post
    How did you do that?
    I scraped one side flat with reference to a surface plate. Use Prussian Blue to find the high spots. I'm not sure if Dykem (mentioned above) makes Prussian Blue, I've only seen their layout bluing, which is a much different product.

    I scraped the second side to the proper taper with reference to the way itself. For this operation I used whiteboard marker to find the high spots. It was the opposite process as the Prussian Blue - the whiteboard marker is applied to the gib, and it comes off the high spots where the gib makes contact with the dovetail.

    Highly labor intensive, but it got the bow out of the gib and improved machine backlash, geometric accuracy, and rigidity immensely. I did both the X and Y.

  17. #17
    Join Date
    Feb 2005
    Posts
    24

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Quote Originally Posted by flick View Post
    I scraped one side flat with reference to a surface plate. Use Prussian Blue to find the high spots. I'm not sure if Dykem (mentioned above) makes Prussian Blue, I've only seen their layout bluing, which is a much different product.

    I scraped the second side to the proper taper with reference to the way itself. For this operation I used whiteboard marker to find the high spots. It was the opposite process as the Prussian Blue - the whiteboard marker is applied to the gib, and it comes off the high spots where the gib makes contact with the dovetail.

    Highly labor intensive, but it got the bow out of the gib and improved machine backlash, geometric accuracy, and rigidity immensely. I did both the X and Y.
    You can get a tube of Prussian Blue made by Permatex for about $5 thru Amazon or your local auto parts store (Autozone or O'Reilly can order it for in store pickup as think most FLAPS can)

  18. #18
    Join Date
    Jan 2012
    Posts
    97

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Very Interesting, as Arte Johnson would say. ( link for those of you not old enough to know of him: https://www.youtube.com/watch?v=krD4hdGvGHM )

    I have suspected a bow or at least a tendency to bow in my x axis gib for some time. If I tighten the locking screws more than finger tight while adjusting per Tormach's recommended procedure, I have noticeable play in the x axis. I can twist the table noticeably in the x-y plane and if the table is moved to the right of the home position by more than 10", I will observe a lifting of the table on the right. I have more reasonable performance if I tighten the screws to just slightly more than snug.

    It is my feeling that the gib is bowing in the center, causing binding and a subsequent lost motion increase while the extremes of the gib have more play which permits the twisting and lifting that I experience.

    I did talk with Nolan Serink, Engineering Manager and John Wallner, Technical Support Specialist at Tormach during their Open House last July. I asked about getting a replacement gib as UI don't want to screw my existing up any more than it might be now. We left it that it might be possible to have Tormach order a replacement with the understanding that it would be a raw piece and have to be scraped in to fit properly.

    Other activities have kept me from following through but it is my intention to try to resolve this issue.

    R J

  19. #19
    Join Date
    Mar 2008
    Posts
    256

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Quote Originally Posted by CountrySmith View Post
    It is my feeling that the gib is bowing in the center, causing binding and a subsequent lost motion increase while the extremes of the gib have more play which permits the twisting and lifting that I experience.
    I'm certain you're correct. My conversations with Tormach (about 3 or 4 years ago now) revealed at the time that they were aware of the bowed gibs but did not find them to be cause for concern. They said that the bow should come out with minimal thrust on the adjustment screw. I'm sure that's true, up to a point, but I wanted my machine to work better than that approach would allow.

    I think you're wise to scrape in a spare gib, rather than the original. I was without my machine while working on my gibs, and it's an arduous process for a beginner like me.

  20. #20
    Join Date
    Jan 2012
    Posts
    97

    Re: [PCNC 1100] Y-Axis Gibb Issue

    Quote Originally Posted by flick View Post
    I'm certain you're correct. My conversations with Tormach (about 3 or 4 years ago now) revealed at the time that they were aware of the bowed gibs but did not find them to be cause for concern. They said that the bow should come out with minimal thrust on the adjustment screw. I'm sure that's true, up to a point, but I wanted my machine to work better than that approach would allow.

    I think you're wise to scrape in a spare gib, rather than the original. I was without my machine while working on my gibs, and it's an arduous process for a beginner like me.
    Interesting that Tormach was aware of bowed gibs. That was never mentioned in my several conversations and e-mails on the subject. I bought my 770 in December, 2011 so that fits the time frame.

    Generally speaking if you push in on the ends of a bowed bar, it will bow more, not less, so I don't buy their theory about tightening the adjustment screws to straighten the gib.

    R J

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