Cincinnati Hydrashift Head disassembly help.
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  1. #1
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    Default Cincinnati Hydrashift Head disassembly help.

    Anybody out there ever disassemble a Cincinnati Hydrashift 15 lathe Head?
    I could use some advice.

    Thanks, David

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    I've had the headstock on my Hydrashift 12-1/2 torn down to the bare casting, and reassembled with all new bearings. The smaller machines (10", 12-1/2", and 13") are slightly different from the mid-range units (15" and 18"), but basically the same.

    100_0263.jpg

    What do you need help with?

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    Default Gear cluster out of position

    Well, I have a gear cluster out of position. I am assuming a location pin broke. See pictures. In the one picture you can see the pin is a roll pin, and it is in a blind hole, so I am thinking it was not supposed to be a roll pin - maybe a pull dowel? In the other picture the assembly has been rotated about 180 degrees and you can see the key is about to come out but is stuck. This is on the shaft directly below the clutch shaft. I have not gotten to far into trying to take this all apart yet. Anything special needed? Anything I should be careful of?

    Pictures are upside down for some reason.

    Thanks, David
    Attached Thumbnails Attached Thumbnails 20210718_110453.jpg   20210718_110431.jpg  

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    In the second image, there's something odd about that key. The factory parts catalog shows the 15" lathes using a length of square keystock in that location, and the smaller lathes like my 12-1/2 use a Hi-Pro key (sort of a Woodruff key with ears), but that key in your photo doesn't look like either one.

    As to the roll pin, it is correct. DO NOT USE a solid pin. The trick to removing it is to drive the roll pin farther into the gear (you have to do this step to de-couple the gear body from the shaft in order to drive the shaft out of the headstock - the factory manual sort of explains this procedure). The roll pin is short, less than the diameter of the shaft, so once you drive it into the shaft, clear of the inside diameter of the pressed-on gear, it will clear the gear body and allow it to be pressed off the end of the shaft. Once the gear is off, then the roll pin can be driven out of the shaft, which is drilled all of the way through - it's only the gear body that has a "blind" hole. When installing the gear on the shaft, use a NEW roll pin of the correct length, and drive it flush with the outside diameter of the gear body as shown in your photos.

    Here's an illustration from the factory manual. Note Item 10, which is the stubby roll pin, and the bore of the hole through the shaft, which allows you to drive it in clear of the ID of the gear body (Item 8).

    screen-shot-2021-07-23-6.17.00-am.jpg

    No special factory tools needed. You'll need an adjustable pin spanner for the locknut (Item 3), and some sort of puller (I use a slide hammer) to remove the plugs (Items 1 and 2) in the headstock at each end of the shaft axis, but that's about it.

    One suggestion: before removing the shaft (and with the gears positioned in neutral), put a dial indicator on the machined face of the pressed on gear and see how much runout you have. On my lathe, the shaft needed a bit of tweaking once it had been removed and disassembled to restore an acceptable runout. And I replaced the bearings, too, which were common single- and double-row ball bearings (not like the uber-special and expensive flanged tapered roller bearings that Cincinnati used in other locations). Cheap insurance.

    The bad news is that you'll have to remove this shaft assembly from the headstock to do this repair. The good news is that you should be able to remove it without disturbing the other shafts.

    Did that "key" thing somehow walk out the end of the slot in the shaft/gear? If so, then all of the torque would be on the roll pin, which would likely shear and allow the gear body to rotate on the shaft. If that's the case, then you'll have to line up the hole in the gear body with the hole in the shaft (it's 180 out from the key slot) before you can drive the roll pin fragments into the shaft. And figure out why the key walked to begin with: is it the wrong key type? Maybe the wrong dimensions (keys come in over- and under-sizes)?

    If you don't have a copy of the factory service manual / parts catalog, I recommend getting a copy; it's invaluable for the exploded parts diagrams.
    Last edited by Elwood1968; 07-23-2021 at 11:28 AM.

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    Great advice Elwood. The key in the 2nd picture looks like a Woodruff key turned up. It's a good thing you opened it up when you did or it would have come out and stuck in a gear and would have had a major crash. You better remove the shaft as I suspect the keyway is wallowerd out. You may have to recut the keyway to a larger size.

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    This is a big help. The drawing shows it all clear. Maybe this serial number had a Woodruff key. (?) When I get it apart I'll no more. I'll let you guys know how it turns out. It might take me awhile - I don't have that much spare time.

    Thanks...


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