Lathe jumps out of gear

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Lathe jumps out of gear

This topic has 27 replies, 17 voices, and was last updated 30 December 2022 at 11:04 by Bazyle.

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28 December 2022 at 12:18 #626459
Gary Wooding
Participant
@garywooding25363
I've had my Chester 12×36 geared head lathe for about 20 years, with no problems until now. I was turning a bit of aluminium when there was a clattering noise and the spindle stopped turning. The motor turned fine, but not the spindle.

I took the gearbox cover off and noticed that a gearwheel cluster wasn't in line with the corresponding gear on the spindle. See attached photo. The cluster revolves fine but wasn't turning the spindle.

Further investigation revealed that the gear cluster can move sideways by itself, without the turning the control knob. I think there should be a detent to hold it in any one of its 3 positions. The knob, the shaft, the fork, and the gear all move as they should, but when the knob is released there is nothing to maintain its position and the gear can drift sideways and disengage the drive.

I removed the two grub-screws in an attempt to remover the knob and discovered that there is a spring behind the left-hand one (not sure about the right-hand one). And the knob didn't come off – it must be the roll-pin that retains it. I figured that adjusting the grub-screws would do the trick, but the only effect it had was to restrict the full movement of the gear. I haven't tried removing the roll-pin.

Any ideas?
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28 December 2022 at 12:18 #34138
Gary Wooding
Participant
@garywooding25363
28 December 2022 at 12:57 #626469
Brian Wood
Participant
@brianwood45127
Gary,

Until you can get to see what is actually behind the control knob you don't know the full story. I would expect a ball bearing detent of some kind.

Regards Brian
28 December 2022 at 13:01 #626472
JasonB
Moderator
@jasonb
I would second some balls under the springs, do you still have the manual? parts diagram may show what should be there and could be something a simple as the grub screws coming loose over time so there is no longer enough pressure on the balls
28 December 2022 at 13:04 #626473
not done it yet
Participant
@notdoneityet
Hi Gary,

I am not a user, but I would guess there is a ball bearing in front of each of those springs, one of which should slip into a slot for each position of the gear. I’m guessing that if the gear ‘locks’ in one position, but allows it to float in the other, one detent (ball?) is stuck or worn, or the spring is broken.
I suggest you fish out those springs and see if the ball, or whatever is behind them, is to specification. If not it looks like removal of that roll pin will be necessary to determine any damage to the casing.
28 December 2022 at 15:01 #626495
duncan webster 1
Participant
@duncanwebster1
If the gear cluster can move sideways without moving the handle, it sounds as though the there is a disconnect between the handle and the shifting fork, or between fork and gear cluster. If you move the gear cluster by hand does the cross shaft rotate? Does the shifting fork move?
28 December 2022 at 15:24 #626500
SillyOldDuffer
Moderator
@sillyoldduffer
A few pictures from different angles might help. I think the shiny cross-bar is hiding the forks that move the gears. A few shots of the fork mechanism might reveal all.

For example, the two spring adjusters may be for fine adjustment after the fork has been set about right first, and after 20 years the shift mechanism has shifted or worn enough to take the coarse set-up out of range. If so, the coarse setting needs to be reset, probably by centring the gears in position 2, and then tweaking the fine adjusters as necessary to shift cleanly from 1 to 3. How exactly does the fork connect to the knob?

Dave
28 December 2022 at 15:43 #626505
Nigel Graham 2
Participant
@nigelgraham2
There might also now be wear-grooves between the locking dimples, exacerbating the effect of sticking or relaxed springs or a worn detent.
28 December 2022 at 15:54 #626511
DC31k
Participant
@dc31k
The ABC lever looks to be identical to the 123 lever, so if that is working correctly, you have something to compare against.

Looking at the photo, there are two grub screws with lock nuts on the shaft. I think that releasing these would allow the shaft to come forwards out of the headstock without beating on the roll pin. Hold a rag under the lever as you withdraw it or springs and balls might disappear into dark corners.

It could be that the rear, red one of these is slipping or ratcheting on the shaft so that is worth examining.
28 December 2022 at 17:07 #626518
Clive Foster
Participant
@clivefoster55965
My Smart & Brown 1024 has similar balls and spring arrangements to give detents on the basic movements.

When I got it the springs were well mashed up so the detent system didn't operate making it very hard to select the gear required. New springs fixed it. No significant wear on the casting between the detent holes and no evidence of it having been disturbed and damaged during re assembly.

I can only assume that such spring mash-up things can "just happen".

I would have expected something a little more positive than simple balls and springs to keep a gear engaged tho'. The S&B lever has to be pushed down to unlock things.

Clive
29 December 2022 at 12:12 #626599
Gary Wooding
Participant
@garywooding25363
I've investigated much closer. I removed the grub-screws, springs, and balls from the selector knob and removed the knob from the shaft. Neither the springs nor the balls showed any signs of damage or wear. The detents in the gear housing also looked fine. I made a cardboard template that fitted on the selector shaft and contained holes that revealed the detents in the housing. The following photos shows the detents and the cardboard template.

I also took a photo of the selector knob showing the positions of the holes for the two spring loaded balls.

I then found a short length of bar that fitted into the rear of the selector knob, and positioned the cardboard template on it to give a view as if looking from within the gearbox, outwards to the rear of the in-place selector knob. The three holes in the template representing the the three detents. I was then able to see how the detents aligned with the balls when the knob was rotated in its three positions.

I position 1, the detent at 9 o'clock lines up nicely with the hole in the knob. In position 2, the detent at 3 o'clock lines up nicely, but in position 3, when the detent at 8 o'clock is aligned with the knob hole, the 3 o'clock detent is nearly aligned with the other knob hole, which has the effect of both detents trying to align the shaft.

Because of this slight misalignment, the gear in the following picture gently drifts to the right.

Seems like a manufacturing fault to me. In the meantime I intend to adjust the fork to the best compromised position. Any ideas about a solution?

***EDIT*** There was no noticeable wear on the fork.

Edited By Gary Wooding on 29/12/2022 12:15:08
29 December 2022 at 12:29 #626602
Brian Wood
Participant
@brianwood45127
Hello Gary,

I might be tempted to bore out the rogue hole, fit a slug of metal to fill it and re-machine that detail to correct the situation. You can then reset the fork to the original position.

Regards Brian

Edited By Brian Wood on 29/12/2022 12:30:52
29 December 2022 at 12:32 #626603
Howard Lewis
Participant
@howardlewis46836
Looking at the pictures,both the forks, and the lever hub appear to be located on the shaft by grubscrews with locknuts.

Are both these tight and firmly in place?

On my lathe, a Far Eastern, belt driven head model, seemed to have a problem with belt slip. The actual problem was found to be that the dimple in the shaft for the clamping grubscrew was not deep enough, allowing the lever to "float".

Having deepened the dimple, the problem has not recurred.

Howard
29 December 2022 at 12:38 #626605
Simon Williams 3
Participant
@simonwilliams3
Whoa up chaps

Original description stated that the lathe has been operating successfully for 20 years. Then suddenly we have a wandering gear selector. This isn't a manufacturing fault it's wear and tear.

Don't go modifying anything just yet, there's something as yet unexplained.

Rgds Simon
29 December 2022 at 13:08 #626609
Keith Long
Participant
@keithlong89920
Gary, +1 for what Simon says above. Looking at your pictures the selector lever has 3 positions, with the holes as they are the detents will engage in 3 positions, if you alter then spacing as suggested then the detents would only engage in 2 positions.

Look further into the situation before you even THINK of modifying anything.
29 December 2022 at 13:09 #626610
DC31k
Participant
@dc31k
Posted by Brian Wood on 29/12/2022 12:29:36:

I might be tempted to bore out the rogue hole, fit a slug of metal to fill it and re-machine that detail to correct the situation.

Please look very well at the photos he has posted and reconsider your advice.

In one gear, the left hand hole is used and lines up correctly. In the second gear, the right hand hole is used and lines up correctly. In the third gear, the left hand hole is used (again) and lines up correctly but half of the right hand one is showing.

So which one do you suggest he fills? If it is the left hand one, he looses two out of three gears. If it is the right hand one he looses one out of three gears.
29 December 2022 at 13:10 #626611
Jeff Dayman
Participant
@jeffdayman43397
+1 for Simon's thought about 20 yr operation vs problems now occurring. Suggest looking at shaft float on the selector shaft – is the rear bush on the headstock worn, allowing excessive knob / detent free play? maybe worth trying a shim at the rear to take up play.
29 December 2022 at 13:35 #626614
Simon Williams 3
Participant
@simonwilliams3
Forgive me if I'm being thick, but the cardboard template with three holes is mimicing the stationery part, you need a piece of card with two holes the same as the two in the selector lever hub. The the one with two holes slides over the (stationery) one with three holes.

There's got to be three unique positions of the detents else it would never have worked from new. The stuff about a detent covering half a hole doesn't make sense.

Have you dismantled the selector cross rods and forks to check that there isn't a flat or a hole that's smeared and is sticking but moving erratically?

Keep us posted, do

Rgds Simon
29 December 2022 at 14:58 #626621
Dave Halford
Participant
@davehalford22513
Gary,

You've never said the control knob was loose only that the gear drifts, nor that the arm started pointing to the wrong sector.

Therefore it's one end of the selector shaft or the other that's loose. First thing I would have done is hold the fork and try to move the selector. Like your Centec there should be no sideways forces produced by the gears though I suppose if the shafts are not quite parallel that might cause it.
29 December 2022 at 15:01 #626623
Brian Wood
Participant
@brianwood45127
I did only say I might be tempted to carry out surgery, honest!

Maybe it would do no harm if Gary removed the ball and spring selectively from one hole at a time to see if the location 'conflict' resolves itself by doing so.

Retiring to my bunker now

Brian
29 December 2022 at 15:19 #626626
Howard Lewis
Participant
@howardlewis46836
Re reading the O P; the gear cluster can move sideways without moving the control lever

This suggests

1 that either the fork is worn, so that it no longer locates the cluster precisely enough, or

2 that the fork is not firmly secured to the control shaft, or

3 that the control shaft is not firmly secured to the control lever hub.

Howard
29 December 2022 at 16:06 #626634
SillyOldDuffer
Moderator
@sillyoldduffer
I wittered on about coarse and fine adjustments in an earlier post. I've marked two lock-nutted screws in blue which I'd investigate.

The one at the rear attaches the fork to the actuating rod, and the angle of the fork is probably adjustable. It may be the nut grips the shaft directly and has shifted, or it sits in a notch that's worn, also allowing the fork to shift.

Dave
30 December 2022 at 07:46 #626692
Gary Wooding
Participant
@garywooding25363
Thanks for all the suggestions. Here are some answers to the questions.

There is absolutely no play between the knob and the selector fork – the knob is attached to the shaft with a roll-pin and the lock-nuts at either end of the shaft are good and tight. The are are no flats on the shaft. The slightest twist of the knob results in a corresponding movement of the fork and there is no lost motion. The play between the fork and the gear it moves is no more than would be expected.

When the gear drifts to the right, the shaft, fork, and knob move in unison. There is no lost motion. It certainly appears that the fork moves the gear.

Although the lathe is more than 20 years old the the gears are very seldom used for speed changes 'cos I use a VFD just about all the time.
30 December 2022 at 09:43 #626705
Brian Wood
Participant
@brianwood45127
Hello Gary,

That is all very helpful information and it takes the cause of your problem straight back to the indent balls and their fit in the dimples in the housing.

One of the pair that are close together is the dominant one and I think the only way to determine which it is will be to remove the springs and balls in those two positions, fit the lever control and make some careful observations with a good light down the drillings when the gear is shifted into the two positions it takes.

Then you can act knowing what needs correcting. With the new information you have added on the lack of use the mechanical gears have had in the time you have owned the lathe, it all points to a fault built in during manufacture, just as you suspected.

Regards Brian

Edited By Brian Wood on 30/12/2022 09:50:12
30 December 2022 at 10:26 #626714
Andy_G
Participant
@andy_g
Posted by Gary Wooding on 29/12/2022 12:12:16:

in position 3, when the detent at 8 o'clock is aligned with the knob hole, the 3 o'clock detent is nearly aligned with the other knob hole, which has the effect of both detents trying to align the shaft.

I suspect that the issue might be that that the '3 O'Clock' (looking at the lever) hole has wallowed out a bit, and shouldn't be able to align with the detent ball in this position – there is visible wear in this hole in the original photos (the hole is at 9 O'Clock when looking at the lathe). If the detent is '1/2 a hole' out, it shouldn't engage.

How well do the balls fit in the holes in the handle? If they have room to wander, they will be able to engage in the detent holes sooner than they should. (If they are loose, the holes in the handle may be able to be reamed out to take a slightly larger ball, or a small, round ended dowel – made to suit.)

My 2p, anyway.

Edited By Andy_G on 30/12/2022 10:28:56
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