SB 16 gearbox/leadscrew hard to turn
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  1. #1
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    Default SB 16 gearbox/leadscrew hard to turn

    SB 16 countershaft - Album on Imgur

    Having some issues with engaging the leadscrew. With the leadscrew engaged I can turn the spindle by hand, but after about half a revolution there is resistance. Things moved a lot freer before moving, but I have leveled the lathe in its new position.

    The gearbox countershaft seems to be recessed excessively in the one side and proud on the other.

    Before I take the leadscrew/gearbox off, does anyone have any ideas what's broke?

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    Sorry. I don't own a 16. But for a dumb idea, maybe get your smart phone under the gearbox to take a few snaps? or an inspection mirror? Maybe you can see what is binding before taking it off. Does the countershaft resume normal position if you hand roll the spindle backwards? Seems as if a pin has sheared.
    Just some lame-brain thoughts.
    Good luck.

    PMc

    PS: I'll throw this photo up here in case it might help, but I suspect it looks nothing like what's on a 16. Just trying to help.

    gearbox-4.jpg

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    https://i.imgur.com/D3zLuhC.jpg
    From what I've been reading the two lever quick change are all very similar.

    It's looking more and more like I have to yank it apart

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    Before yanking it all the way off, try breaking loose the mounting hardware for qcgb. Then roll by hand. Qcgb has an alignment adjuster bottom right, two set screws and a bolt you tighten. Loosen that bolt too.

    All that hardware just crack loose, so that hardware is just barely snug, not backed all the way loose. Use adjusting set screws to help with alignment.

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    Hey adjusting screws and parallelism worked!

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    Forgot to mention it, maybe you did it anyway. You might crack loose the leadscrew end bearing, on tail stock end, same as you did for qcgb. If you already tightened qcgb, maybe crack that bearing loose, roll lead screw a few turns. Tighten it back up.

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    Unlike trump, texasgunsmith is actually out here doin something!

    Good call Tex.

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    False success.

    I pulled the apron, for some reason there are grease zerks on there that I'm assuming aren't factory.

    With the VFD turning slow it seems that the primary tumbler will lock up on occasion and stall out, this is worse in positions B and E. Reversing the VFD seems to un-bind and then occasionally bind in the other direction.

    The secondary tumbler doesn't seem to have any effect on stalling.

    I had suspected the lead screw may be the issue, it appears to have a slight bow when running as shown in the video, but with the apron removed there's nothing potentially binding there.

    Guessing that there's a lot of wear in the gearbox, time to pull it apart and check alignments. Just need a second hand to get the lead screw and gearbox off.

    Most of what this lathe will be used for is facing castings, I can forego a lot of accuracy in the turning direction.

    Lead screw and rear gear train - Album on Imgur

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    Here's my .02 worth. All gearing needs to be cleaned (side gears,reverse gears...set side and reverse gear "axles" with lube holes at top,Disassemble QCGB and clean and check for wear and install new felts upon re-assembly). Now, the apron. Those zercs DO NOT belong there.You need to check your worm gear bushings. I suspect they are bad or adjusted improperly. This could be causing your binding...
    Probably why the zercs were installed. I'm pretty sure your problem is with the worm gear, but, everything needs cleaned and re-felted anyway. Good luck. PB

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    Definitely not the worm gear on the apron, the qcgb binds occasionally at low speed with the apron removed. The oiler cup for the qcgb is mashed, so it may have been greatly neglected. Seems like I bought a bit of a dud. Good learning experience though.

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    Quote Originally Posted by packardbill View Post
    Here's my .02 worth. All gearing needs to be cleaned (side gears,reverse gears...set side and reverse gear "axles" with lube holes at top,Disassemble QCGB and clean and check for wear and install new felts upon re-assembly). Now, the apron. Those zercs DO NOT belong there.You need to check your worm gear bushings. I suspect they are bad or adjusted improperly. This could be causing your binding...
    Probably why the zercs were installed. I'm pretty sure your problem is with the worm gear, but, everything needs cleaned and re-felted anyway. Good luck. PB
    In his album link, there is a a vid of the leadscrew. It does appear bent. I've not tried straightening one, not sure about that, or might replace leadscrew.

    However, if I was just writing it off, I would surely experiment. Maybe two horses in parallel with a press. one on each side. Spaced two or three feet apart. Point bend upwards. Wood block on threads. Use press incrementally to see what might give me a favorable result.

    I'd like perfect, but if I could halve the bend, might not bind after that.

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    Would the leadscrew being bent like that bind the lathe up occasionally like it does at low speed? Even with the apron removed? I figured having it free turning while still occasionally binding would point to the qcgb?

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    Quote Originally Posted by Rockmonton View Post
    Would the leadscrew being bent like that bind the lathe up occasionally like it does at low speed? Even with the apron removed? I figured having it free turning while still occasionally binding would point to the qcgb?
    You are correct. I missed that detail.

    If you pull gear off left end of head stock side. The gear thats usually keyed onto a shaft of qcgb. Not looking at a pic, but at end of banjo, that gear right on outside of qcgb. . .

    With that removed. Roll qcgb by hand. Change gears while your inspecting. You might find a dinged tooth on a particular gear while looking up inside the qcgb. Maybe a piece of debris or something.

    Or leave reverse tumbler in neutral. Use that gear to help roll qcgb by hand. However you can manage rolling by hand is how I like to find issues.

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    I tried rolling by hand in neutral for a while and could not recreate the binding, it feels like the gears in the levers "climb" until they bind. I'll update when I get it off and inspected

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    In the ongoing comedy of "what not to do"....

    SB 16 continued.... - Album on Imgur

    Well, found the problem. Shift rail was bent, worn badly, retainer was chewed up.

    Tried to get the shift rail out, couldn't get it to move through the first selector with a big drift in the centre point and 2lb sledge.

    Put it in the press, got it to move some..

    And the learning lesson: make sure the bar you're pressing with is smaller than the shaft minus the keyway. Pressed on the key and shaft and smooshed the casting very quickly.

    Might try to move things back into place and braze it up, try boring in the mill and fit some bushings. Surprisingly for having been poorly oiled the ball bearings were in decent shape.

    Anyone got a qcgb casting and a good shift rail/levers they would part with?

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    Had to look up your first thread to see if it was a double tumbler or not. I think this is what you want, but can't tell from the pics entirely:

    South Bend 16" Lathe Dual Tumbler Quick Change Gear Box Bare Casting | eBay

    Taper pins are size specific. By measuring the old one you know which to buy. Measure large end, small end, and length. Somewhere they sell them in individual, need to google. But as example as in package form:
    McMaster-Carr

    They also sell size specific reamers for each size. In case you need a new drill hole. drill to small diameter size, or under. Run the reamer by hand till the taper pin fits.

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    Definitely a dual tumbler, unfortunately haven't found someone with a casting or whole GB that ships to Canada yet, I'll keep looking.

    Brazing rods are cheap and I need to do the crack on the rear gearbox cover too. Should see what the local machine shop would charge for a line bore.

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    Hmm, brazing, boring on mill and fitting some self-aligning ball bearings seems to be the plan right now.

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    Got the keys on the handle gears I mangled in the press cleaned up.

    Fixing handle gear keys SB 16 - Album on Imgur

    Decided on boring out the gearbox ears and shift lever ears to hold 1.25 OD, 1.125 ID bonze impreg bushings. Going to use a 1.25 PGS and two small steel blocks to align everything while brazing, make a new 1.125 shaft and retain with a snap ring.

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    Had a few minutes to pull the rest of the GB apart and measure for bushings

    Widths and I.D as follows:

    Handles 11/16" w x 1-1/8" di 4pcs
    Case main 1.5"w x 1" di 2pcs
    Case secondary 1-5/16"w x 1-1/8" di 2pcs

    SB16 gearbox teardown continued SB16 gearbox teardown continued - Album on Imgur

    Definitely didn't see much lubrication


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