# G4016 Lathe difficult speed changes



## spumco (May 1, 2017)

As the title indicates, the speed lever is difficult to shift to the outer two speeds.  The range lever (H/L) is fine. The inner two speeds are a little stiff, but rotate the chuck a little and everything drops in place.  Getting in the outer two gears is not impossible but I don't want to break the shift components.

It's _slightly_ easier when I'm in high range, but still a bit sticky.  I can feel the shift lever rod and yoke flexing, and the gears don't 'drop' in to place.  I simply can't get in the outer gears while in low range without exceeding my _"I'm about to break something"_ tolerance.

Note - this isn't a problem with the gears meshing.  Those are fine and there doesn't appear to be too much or too little gear clearance.

Top cover off revealed no obvious problems.  The yoke moves freely through the slack/gap before it tries to shift the input shaft gears.  Drive key is seated - double checked with a brass drift and a light tap-tap-tap didn't get it to seat in the keyway any further.

No obvious scoring of the shaft.  Drive belt tension isn't too tight so I can't imagine how the shaft would get bent.  Oil still clean and full.

So, to sum - the input shaft gears are very difficult to slide to the extreme left and right positions, and a little difficult in the middle two.

Any ideas?  Any adjustments I don't know about?  Put a dial indicator on the shaft and rotate to see if it's bent or buggered?

Thanks,
Spumco


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## fitterman1 (May 1, 2017)

Hi, I would suggest looking closely at the two shift levers and comparing them for differences in stroke or if they require deburring.
Thats my first line of attack. Some pictures may help also.
cheers Alby


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## spumco (May 1, 2017)

fitterman1 said:


> Hi, I would suggest looking closely at the two shift levers and comparing them for differences in stroke or if they require deburring.
> Thats my first line of attack. Some pictures may help also.
> cheers Alby



It's not the shift levers, rod, or yoke arm - they move freely.  It's the gear set on the input shaft that's sticking.  The gears won't slide back and forth easily, especially at the outer limits of travel.  And it's only on the input shaft, not the counter shaft for back gear and direct drive.  Those also move easily.

But thanks for the ideas.  I'll post pics later when I get the cover back off.


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## ch2co (May 1, 2017)

How old is your lathe?


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## fitterman1 (May 1, 2017)

Try another breakin procedure in those specific positions, see if that makes a difference


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## spumco (May 1, 2017)

ch2co said:


> How old is your lathe?



2006 model (I believe), probably first bought some time after that.  I purchased it a year ago from the original owner's estate.  Very well cared for, to the point that he installed a 110V oil circulation pump and filter on the left side to filter out any junk in the headstock.  There was no crap anywhere, or buggered screws, or other evidence that a clown owned it.  It never shifted like butter, but it's gotten worse over the past 3-4 months.



fitterman1 said:


> Try another breakin procedure in those specific positions, see if that makes a difference



The G4016 break-in procedure simply tells you to run it for 10 minutes in each gear, and at this point I've probably run it for 24 hours in each gear - not to mention however much the previous owner used it.  And I do a 10 minute warm-up most times I use it.  Coming up to temp doesn't seem to ease the hard shifting.

I'll try loosening the drive belt on the input shaft tonight and see if that changes things.

-S


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## spumco (May 1, 2017)

UPDATE

It's quite a bit better now, although it's not 'buttery'.  I took the input shaft pulley off and loosened the bearing race cover (three bolts) a bit.  That eased thing slightly.

Second thing was to take the speed shift lever off the front.  I cleaned up some chips behind it and re-mounted it.  I loosened the detent ball spring screw and tightened the shaft retaining screw a bit less vigorously than it was.

Shifted gears a bunch of times in both ranges until it felt better and then snugged up the race cover.  Photos below for anyone's future reference.


Dirty lathe overview.  One of these days I'm going to make some risers to lift the bed off the stands to make it easier to clean underneath.




Input shaft is at the top (connected to shift yoke arm), spindle shaft at bottom of photo.  Input shaft gears weren't sliding left or right easily.  The center two positions were acceptable, but the outer two were almost unusable without approaching the breaking point of some component.



Speed lever at front, range at back.  Little screw on front adjusts the detent stiffness.  Other screw on side is the retaining screw.  These adjustments also helped for some reason.



Input shaft bearing race/cover.  Loosening these screws let the input shaft squirm around a bit and perhaps ease any binding - maybe, as I didn't measure anything.  Snugged up afterwards after shifting gears became easier.


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## fitterman1 (May 1, 2017)

Glad to see its better. What if you rotate the shaft bearing cover (seeing as you can rotate it to three different positions) and test for stiffness.
There may be some eccentricity that may relieve the friction your feeling. Is there a cover on the other end for similar adjustment?


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## spumco (May 1, 2017)

fitterman1 said:


> Glad to see its better. What if you rotate the shaft bearing cover (seeing as you can rotate it to three different positions) and test for stiffness.
> There may be some eccentricity that may relieve the friction your feeling. Is there a cover on the other end for similar adjustment?



There's another cover on the right side, but it wouldn't help.  There's an intermediate bearing to the right of the gears before the shaft exists the right side of the headstock.  Not a bad design since it keeps the input shaft as short as possible.

Honestly, I think the input shaft is slightly bent and loosening the left end let it spring just enough to make shifting not miserable.  The gear set is long enough that even a slight bend would manifest as binding.  And because the yoke has the most leverage in the middle of the travel, it's easier to move it in the middle two positions than the outer two.  If I felt like stripping it down to parade rest I'd bet that the same force is required to move it the whole length of travel and the yoke leverage is why it feels different.

It may also mean that _really_ heavy loads on the lathe should only be taken at the outer two gears since the input shaft is better supported at the ends.  A max cut that bogs the motor taken in the middle two positions may flex the input shaft.

-S


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## fitterman1 (May 1, 2017)

It may also mean that _really_ heavy loads on the lathe should only be taken at the outer two gears since the input shaft is better supported at the ends. A max cut that bogs the motor taken in the middle two positions may flex the input shaft.

This is true. With spur gears there are forces trying to push the two gears apart radially, the greater the load, the greater the forces. The shaft must be designed rigid to take these loads.For example, I used to work servicing wind turbines and one day we had a fault come up which shutdown the turbine. The disc brake on the output shaft that drives the generator came on for some reason (faulty programming? or a power surge) when the turbine was at full speed (1520rpm), this stopped the output shaft which in turn stopped the intermediate which applied a full 2.1MW of power/Torque to the low speed shaft. The gears on the low and intermediate in mesh generated that much force that the gearbox housing was separated at the rear. This is a 20 ton gearbox and we had 470 liters of oil raining down through the tower (it dripped down for weeks). What a mess to clean up. It took over 3 months to get it back to normal, sufficiently safe, to attempt changing the gearbox.


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## fitterman1 (May 1, 2017)

Actually, if you want to measure for a bent shaft, measure the backlash between the gears in multiple positions, ie rotate the spindle manually.


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## spumco (May 2, 2017)

Had the gearbox been designed in Imperial units rather than metric, it probably would have survived...

I think I don't care enough about the shaft to measure it now that it's working, but if I do there's a nice journal between a couple of the gears to drop a DTI in without submerging it.

Thanks for the help.


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