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  1. #1
    Join Date
    Nov 2021
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    Smythesdale
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    21

    Default Hercus 260 Idler Gear Shift Lever Jams

    Hullo everyone. This is my first post.

    I am currently restoring a Hercus 260 lathe. I've had to replace the half nut engagement handle as it was broken. I pulled the unit down. Reassembled it. Confident I put parts back together the right way and setup the clutch correctly. However I notice the cam and the plunger pin tend to jam up. The Idler gear shift lever will go in to the middle position and the pin will go in to the detent in the cam and lock up. I pulled it all down again till I was just left with the cam and the pin and it is not clear to me if this is working as it should. If I wiggle the cam a little from side to side the pin pushes out and slides over. Now many years ago when I did my apprenticeship with one of these lathes I do not recall ever having to struggle with the idler gear shift lever or to wiggle it to get it to shift at all. I definitely don't recall the shift lever locking up. I wondered if the detent in the cam was worn but on checking it more closely it looks to be a nice sharp cutout. Could the plunger be worn? It is hardened steel(?) and I would expect the cam to wear long before it does. Does anybody have any suggestions as to what else might be wrong with this mechanism and causing it to lock up? I see replacement cams are available but the hardened pin seems harder to find.
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  2. #2
    Join Date
    Jan 2004
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    Mackay North Qld
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    6,446

    Default

    Hi mixotricha
    Welcome to the MetalWork forums.

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    Grahame

  3. #3
    Join Date
    Aug 2015
    Location
    Adelaide
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    239

    Default

    Hi, does the pin look like it has one side slightly more worn than the other? I have noticed that on my lathes there is always one side that is worn and I always put that back in to the cam side, the pin is only to lock out one or the other so you would be better with the worn end down to help it move easily.

  4. #4
    Join Date
    Nov 2021
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    Smythesdale
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    21

    Default Pin definitely suspect

    Quote Originally Posted by Tinkerer77 View Post
    Hi, does the pin look like it has one side slightly more worn than the other? I have noticed that on my lathes there is always one side that is worn and I always put that back in to the cam side, the pin is only to lock out one or the other so you would be better with the worn end down to help it move easily.
    When I tore it down again I tried the pin both ways because it is indeed worn more on one end than the other. Not by much but visible. It didn't seem to make a difference in either position.

    Then yesterday I went out and tried rolling the pin on a flat surface and what I suspect has happened is that whatever broke the half nut engagement lever probably bent the pin slightly. The bend isn't visible to my eye but I am going to guess that it is either worn to much or damaged.

    I tried to rotate the pin in the hole and I could feel a very small amount of binding to.

    I still wonder if some of this is just user error. If I slide the pin in to the notch in the cam and I then rotate the cam clockwise' / anti-clockwise' should the pin slide over smoothly and disengage from the cam?

    Out of curiosity I got a 6mm drill bit ( I have no imperial ones ) and slid it in to the hole for the plunger with the pointed end in to the cam and was able to disengage that by rotating the cam with no effort in either direction.

    When I first noticed this problem I went and had a look at australianmetalworkinghobbyist.com.

    I have got a few bits from Mal already.

    But I see that he has the cam but alas I do not see the part number up for the pin.

    Wondering if I should just make one out of an old drill bit or similar .....

  5. #5
    Join Date
    Nov 2021
    Location
    Smythesdale
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    21

    Default

    Quote Originally Posted by Tinkerer77 View Post
    Hi, does the pin look like it has one side slightly more worn than the other? I have noticed that on my lathes there is always one side that is worn and I always put that back in to the cam side, the pin is only to lock out one or the other so you would be better with the worn end down to help it move easily.
    Thanks for the response.

    I think the pin is bent. Not visible to the eye but I think it might be binding in the hole.

    To much friction somewhere.

    It could also be user error.

    I don't have anything else in the apron but the cam and the pin at the moment.

    When rotating the cam with the pin engaged should it push the pin over?

  6. #6
    Join Date
    Aug 2015
    Location
    Adelaide
    Posts
    239

    Default

    It would make sense if the half nut handle had been broken with the gear lever engaged in an operating position, there definitely could be a slight bend causing the issue, the pin should be free the whole way through. You may need to make a new pin for it.

  7. #7
    Join Date
    Nov 2021
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    Smythesdale
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    21

    Default

    Quote Originally Posted by Tinkerer77 View Post
    It would make sense if the half nut handle had been broken with the gear lever engaged in an operating position, there definitely could be a slight bend causing the issue, the pin should be free the whole way through. You may need to make a new pin for it.
    For whoever comes after me ordering a new replacement pin might not do the trick. As what is happening is the combination of worn cam and pin. I think if one replaces one then one needs to replace the other. But then those parts might also be worn unless they are NOS. Also check for any drag under the pin against the housing. I had freshly painted the housing and it was also binding a tiny bit against the new paint. I took it back to bare metal in that location with a file.

    Finally what I ended up doing was grinding a new pin from an old 6mm drill bit. It took me about four tries of old drill bits to get a pin that was just right. The reduced diameter from 1/4" (6.35) enables the pin to wiggle slightly but also took out some of the friction. What I did was to grind the pin so that it was a tiny big longer and also flatter at the 'cam' end where it points in to the triangular slot so that it enters that slot less.

    Note that this is a little different to how they seem to wear. The pin can be worn at that end but because the cam is also worn it can sit to deep in the triangular slot which means to much rotational effort from the cam to shift it.

    It seems to me a bit of a fussy mechanism and the combination of the cam the pin and the half nut engagement lever need a pin that it is 'just-right'.

    I guess if I could help somebody else out I would tell them not to reassemble the whole mechanism until you have verified that the combination of the pin the cam and the half nut engagement lever works nicely.

    Next up is more fussing with the gear box :/

  8. #8
    Join Date
    Jan 2009
    Location
    Holbrook, NSW
    Age
    73
    Posts
    490

    Default interlock bar

    Quote Originally Posted by mixotricha View Post
    When I tore it down again I tried the pin both ways because it is indeed worn more on one end than the other. Not by much but visible. It didn't seem to make a difference in either position.

    Then yesterday I went out and tried rolling the pin on a flat surface and what I suspect has happened is that whatever broke the half nut engagement lever probably bent the pin slightly. The bend isn't visible to my eye but I am going to guess that it is either worn to much or damaged.

    I tried to rotate the pin in the hole and I could feel a very small amount of binding to.

    I still wonder if some of this is just user error. If I slide the pin in to the notch in the cam and I then rotate the cam clockwise' / anti-clockwise' should the pin slide over smoothly and disengage from the cam?

    Out of curiosity I got a 6mm drill bit ( I have no imperial ones ) and slid it in to the hole for the plunger with the pointed end in to the cam and was able to disengage that by rotating the cam with no effort in either direction.

    When I first noticed this problem I went and had a look at australianmetalworkinghobbyist.com.

    I have got a few bits from Mal already.

    But I see that he has the cam but alas I do not see the part number up for the pin.

    Wondering if I should just make one out of an old drill bit or similar .....
    See the attached drawing of the part. The angle of the ends are 90 deg. This is an accurate drawing of the part as supplied from Hercus. I haven't included this on the AMH website, as it's something anyone should be able to make with accuracy.
    Attached Files Attached Files

  9. #9
    Join Date
    Jan 2009
    Location
    Holbrook, NSW
    Age
    73
    Posts
    490

    Default interlock

    Sorry, should have attached a viewable picture rather than a download.
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