End of Saddle Lifted on SB Heavy 10" Lathe
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  1. #1
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    Default End of Saddle Lifted on SB Heavy 10" Lathe

    Hi,

    I've noticed recently that my surface finish on a turned piece was rather rutty. Everything I tried to get a better finish did not work (slower feeds, lighter cuts, larger radius tool tip). On inspection I noticed that the right rear portion (facing the lathe) of the saddle is lifted up slightly. I can push it down with my thumb and it is lifted at least maybe 0.020". I do not yet know if there is any gap in the rear gib but I would think that the saddle should sit down on the "V" ways under its own weight. Is this true?

    I do not yet know if there is something stuck under the saddle that could be lifting it up. This lathe was restored by a previous owner (ways re-scraped, etc.) and I have not used it enough to have caused excessive wear. I have crashed the lathe a couple of times (tool ran up against a piece when trying to knurl) but it did not seem to have caused damage to the lathe.

    Could the saddle be warped or what may be some of the reasons for this point of the saddle to be lifting? Should the gib on the back of the lathe be tightened to remove this or should the saddle not fully rest on the ways under its own weight?

    Thanks for the help and suggestions to this issue!

    hepburnman

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    1) Off all the badness that could happen I do not think a crash would warp the saddle.

    2) Yes the saddle should sit down under its own weight and no you should not use the rear gib to pull it down. It likely would be very hard to move if you did. I'd guess the rear gib should provide very slight clearance/minimal contact.

    3) Have you ever leveled the lathe. It would seem to take a pretty severe twist in the bed to result in what you are seeing but bed twist would naturally cause what you are seeing.

    4) 0.020" is a lot. Does the saddle really rock that much? With that much warpage I'm surprised the rear gib is not hard up against the bed already. I'd remove the rear gib and perhaps the toolpost/compound/cross-slide and lift the saddle slightly to check for any chips underneath and see if perhaps it's just the very end that you can see that's relieved somewhat. At the same time you could really evaluate how much rock you are getting.

    5) I know this is a new condition for you, but there is no telling how qualified the previous owner was to re-scrape the bed. You may have to do some of your own assessment of the bed condition.

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    Hi- Thank you for the reply!

    I will recheck the level/twist of the bed. When I set up this lathe originally I used a very sensitive machinist level but will check it again.

    I'll also try and look under the saddle where it rides on the rear way to see if anything may have gotten trapped there. May have to wait until the weekend though. I'll let you know what I find.

    Thanks!

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    If the bed was refurbished by regrinding then scraping, then the saddle would have to have been built up as well. Same with the tailstock. Turcite is added to the underside of the carriage to bring the carriage back to its correct height. Some of the material used to build the carriage up may have come loose and fallen off.

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    My floor changes with the seasons. Check the twist first.

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    Quote Originally Posted by SLK001 View Post
    If the bed was refurbished by regrinding then scraping, then the saddle would have to have been built up as well. Same with the tailstock. Turcite is added to the underside of the carriage to bring the carriage back to its correct height. Some of the material used to build the carriage up may have come loose and fallen off.
    Hi- Thanks for this idea. I guess I will have to remove the saddle to check for this.

    Now, how to do this? Can the lead screw and the gear box be easily separated? If not I would probably need to remove the two together and then slide the lead screw out of the apron?

    Where can I get small pieces of Turcite if I need to?

    Thanks again for the comments! My floor by the way is poured concrete so it shifting/settling to disturb the lathe bed I hope is not a likely issue.

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    just securely block up the apron, no need to pull gearbox/leadscrew.

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    As Iwananew10K says, separate the apron from the saddle, there are two big screws, remove the hold down bar in the back, the saddle lock in the front and if you have one, the taper attachment. You should be able to lift the saddle off.

    Tom

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    Well, I've now removed the saddle and the issues appears to be just that the rear gib(?) bolts were not snug enough. These can be tightened to the point where it will clamp the saddle to the point it will not be able to slide on the ways. With the bolts just snug they remove any lifting of the backside of the saddle. Without this gib(?) in place the backside of the saddle lifts noticeably. I think this is normal due to the weight of the apron attached to the saddle.

    I guess these rear bolts loosened over time and i did not notice until I was last taking finish cuts. I will take some finish cuts later to confirm that was my only issue. Let's hope.

    Also, I've meaning to replace my cross-slide and compound lead-screws. Does anyone know of a good source for these?

    Thanks for the support and replies!

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    The four contact point on the carriage should be in the same plane. The backside gib doesn't hold down the carriage, per se (like you are thinking), but instead just prevents it from being inadvertently lifted. The gibs aren't really needed, as the forces are all down into the bed. Your carriage might be warped some way.

    There used to be a guy here from Kansas that made the cross-slide and compound lead screws and nuts.

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    Quote Originally Posted by SLK001 View Post
    The four contact point on the carriage should be in the same plane. The backside gib doesn't hold down the carriage, per se (like you are thinking), but instead just prevents it from being inadvertently lifted. The gibs aren't really needed, as the forces are all down into the bed. Your carriage might be warped some way.

    There used to be a guy here from Kansas that made the cross-slide and compound lead screws and nuts.
    It would seem to me that the weight of the apron, when it is attached to the saddle/carrier, with it being off center to the ways, would tend to pull the front end of the saddle down while lifting the back end of the saddle off the way there.

    My lathe doesn't have a taper attachment so there is not this weight to act as a counter-balance to the apron's weight.

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    One would think that way, but if the saddle is properly fitted to the bed, it won't happen. If you thoroughly clean the under side of the saddle and place it on tailstock end of the bed where is less likely hood of damage or wear to the bed, it should fit snugly. You should not be able to rock the saddle by pressing down anywhere. You can go further, stone the bed ways and wipe clean (tailstock end). Coat the ways with a thin film of Prussian bluing and rub the saddle on the ways. When you remove the saddle you will see where the saddle fits to the ways, there will be a transfer of the bluing. In a perfect world, the bluing will be spread uniformly on the saddle ways.

    Tom

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    Quote Originally Posted by hepburnman View Post
    Also, I've meaning to replace my cross-slide and compound lead-screws. Does anyone know of a good source for these?

    Thanks for the support and replies!
    Naru on this forum does this. He made a new cross-slide screw for my SB13 a while back. He used to sell this service through ebay as stedea_71, but I don't see any listings lately.

  14. #14
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    Hi- As an update I did remove my saddle and found that there was nothing caught underneath that lifted it up slightly. I also used layout blue on the grooves of the saddle and it did show signs of wiping on all areas although slightly less where it appears to be lifting slightly with the apron attached. I do need to slight snug the rear gib to be certain of saddle contact with the back way.

    With this gib slightly snug or no appreciable gap my finish issue has resolved.

    The saddle could be slightly warped but it is what it is unfortunately. The lathe still performs well and with accuracy.


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