Thread: Found cause of noise in Hafco AL-336 gearbox

I has given this lathe because it was too noisy on higher speeds (and its previous owner was given a quieter old Pacific lathe).


Today, I finally took the lid off the gearbox, and had a look inside. The things I found:


IMG_1517.jpg

• It has some oil. The oil smells bad (like an old differential), but I'm not tempted to change it. Maybe just fish around with a magnet to collect any filings, and top it up so I can see it through the window.

•All the gears seem to have their teeth, and there is minimal wear on them

•The middle gear on the right hand lay shaft cluster is a little loose:

IMG_1518.jpg

It is a cluster of 3 gears which are meant to rotate in unison. The large middle one is used for the highest speeds, so has the biggest load on it. A bit of effort was required to remove it (I needed help), but we found nasty wear:
IMG_1519.jpg

There are score marks all the way around the small gear it sits on, and its inside surface (it has been gyrating around the smaller one?). The right hand side of the small gear is unworn.


I spoke to the previous owner. He has replaced the keyway a couple of times. I think a keyway has been dragged around in there.

Called Hare & Forbes. The small gear is $55, so I ordered it. The large one is unavailable (sad for a currently shipping lathe).

We might try brazing or silver soldering its inside surface, then machining for a tight fit over the new gear.







• The right most gear on the spindle is also a little loose. Probably just the keyway. I'll leave it for now - too much work to remove the spindle

I love your clamping rack Nigel, it looks most impressive and very organised. As an added bonus it keeps your tools like new!

Originally Posted by nigelpearson

...The large one is unavailable (sad for a currently shipping lathe).

We might try brazing or silver soldering its inside surface, then machining for a tight fit over the new gear.

I would probably enlarge the bore on that large gear say 20mm (or more) on diameter, weld a piece in and and rebore that to the correct size. Anything softer than the steel and a filler may be pushed around in use (depending on the load).

Michael

Originally Posted by Michael G

I would probably enlarge the bore on that large gear say 20mm (or more) on diameter, weld a piece in and and rebore that to the correct size. Anything softer than the steel and a filler may be pushed around in use (depending on the load).

Michael

+1 although my method would have been to make the sleeve a press fit in the enlarged bore and scotch key it in place.

New small gear arriving today.



I thought about sleeve-ing the larger one, but it seemed like too much work.

The large gear is a tight-ish fit over the smaller gear – I can barely push it on by hand – and with a newer small gear it might be good enough. It is just a rough surface.

My "backyard fix" would be to weld the 3 gears together, to prevent this ever happening again. Just a little TIG blob in a few spots.

Originally Posted by Ropetangler

I love your clamping rack Nigel, it looks most impressive and very organised. As an added bonus it keeps your tools like new!

Could be like the magic pudding. You take one away and magically a new one still in the original packaging takes it's place.

Called Hare & Forbes. The small gear is $55, so I ordered it. The large one is unavailable (sad for a currently shipping lathe).

Saved me buying that one.
And probably crosses Hare & Forbes off the list.

After boring 2mm out of the big gear, got someone to shove some weld in there:
IMG_1684.jpg

and bored it to fit the (new) small inner gear:
IMG_1685.jpg

Last fix is to straighten this slightly bent keyway from the lay shaft:
IMG_1686.jpg

Tried to do that in an arbor press:
IMG_1687.jpg
but that only did half the job. Had to hammer it on an anvil.



So, re-assembled the gearbox, but the lid back on, and spun it up to have a listen;

1. Doesn't seem any quieter
2. On the highest speed, the thing actually tripped a circuit breaker !
   This was when it was cycling up to speed(*), but it has never done that before

So, a little annoyed. Repaired the obvious fault, but short of using feeler gauges, or draining the oil and blueing gears, I'm at a loss.



(*) When turning on at 1400 or 1800 RPM, the spindle gets to about 1000, and speeds up and down for a few seconds, with slight clunking noises, before getting up to full speed.
I'm still trying to work out the cause, but think it is the motor drive belts slipping.
Will try moving the motor down a bit when I can work out how to get to the bolts?

That sounds frustrating.
Can the belts be removed and the gearbox turned by hand?
A shaft bent due the initial problem, now causing the issue?

Beware the random, unrelated problem - eg, the motor has chosen now, to develop a circuit breaker tripping fault. (Unlikely, but as mentioned - beware.)

Time to start on a process of elimination...

One has to suspect it's had a good crash at some point in it's life, but perhaps not.

Take the change gear off the headstock output, thus disconnecting the QCGB and change gears from the equation, run and see if any change.

If no change, take the belts off the motor, run that by itself, and have a feel of the motor bearings. Possibly take a look at the centrifugal switch in the back of the motor as well, can't remember what speed the changeover point is, but I think it would be around the point you're noting issues - could be dropping out too early, or loose and causing shunting and excessive current draw?

Should at least narrow it down to which section exactly the problem lies.

Hi Nigel, Guys,

I don't know if it is the picture, but it looks to have some odd shaping of the teeth on that gear ! Almost as if it had been running eccentrically. Which could also explain the loose bore that you found.

Originally Posted by BaronJ

...odd shaping of the teeth on that gear ! Almost as if it had been running eccentrically

Possible. The gear was a pain to centre in a lathe chuck for machining because it wasn't perfectly round.


If you mean the round wear on one side of all the teeth,

the gear clusters slide left and right axially, and there is a detent on the change levers to locate them, but it is easy to have the gear a bit off from its ideally meshed position. I think at some time in its past it might have run hard when only half meshed. Or maybe that is just the wear from years of accidentally starting between gears.

Hi Nigel,

Thankyou for your post.

It could be the source of the problem ! The loose centre worn because it was running off centre. You’ve re-machined it back to centre so it now binds again.

Those teeth do look a little funny though and I don't mean the chamfering on the side. Pictures can show things that aren’t a problem.

Will try moving the motor down a bit when I can work out how to get to the bolts?

Now you got me trying to remember what I did there. Think I unbolted my now modified splash tray to access. Tray (at least on mine) is fairly straightforward to remove, even when positioned fairly close to a wall.

Three 19mm bolts, only one accessible from change gear side. As Jett said, splash tray had to come off:
IMG_1696.jpg
(although you can save time by only unscrewing the motor side,
and sliding it back on the block that holds the chuck safety shield)


Dropped motor down all the way, levered belt side down as low as it would go, re-tightened. Belts still a little loose (maybe 15mm deflection over the 300mm side length).

At Jekyll & Hyde's excellent suggestion, I disconnected the change gear feed before testing.


Fault still there. Tried with one belt on lower gearing set of pulleys. Fault still there at 1200rpm.


(doing the unsafe thing of) pushing the cover close detect switch while pressing the "motor test" button on the front panel showed one side of the belts shaking when the vibration occurred - the non-tensioned side of the belt.

Thinking about that makes me think it is a spindle gear train fault, because if the motor was speeding up and down, the larger spindle drive train would be pushing it and the tensioned side of the belt would also be shaking?


I also tried the motor on its own. Spins freely by hand or under power, but a little noisy under power (and no quieter when the switch cuts in when slowing down).

I'll check the c'fugal switch next.