Thread: Lathe crash - help needed

I would be checking what the leaver is connected to and whats inside that before the gearbox is pulled apart, it seems more like something to do with that or something wasnt right when you changed the gears around.

Chin up son! Its just another of life's hurdles and an opportunity to learn something.....
Do as others have said....take pics and go slowly until you find the source(s) of binding.
It will be alot simpler than a bike gearbox, I think.
Good luck.

Sterob

Done a few bike gear boxes myself (the last one about 6 years ago with 3rd gear welded to the shaft) a lathe is much simpler, with that skill level you will have no troubles at all fixing this, it's just something new to you.

Dave

OK, thanks everyone for replying. I pulled the gearbox off last night, but havent taken it apart yet. I have done some preliminary investigations and it looks pretty grim. I'll answer pipeclays questions, followed by my observations.
　
Can the Leadscrew be rotated when the Lathe has no Gears in mesh. No it couldnt, was very stiff.

On the Quick Change Box is there only 1 Lever? No there is two, each one selects from 3 positions.

You may also find that there is no Sheer pin on your Leadscrew,but if there is ,remove it and check to see what its made of,I often make mine from Brass,you dont want it to be overly tough. Yep, there is a shear pin and its steel and was about half sheered

Take a good look at the Change gears at the rear of your Headstock for any damage that may of been caused or contributed to your problem.Checked these out and they are all fine. no teeth damaged.
　
With the gearbox off I shifted all of the levers around to get everything in neutral. Two of the shafts spin freely but are stiff, two others dont. The one with the 10 gears on it (8 in the pic bryan listed on page 1- the yellow ones) is the worst. You cant move it by hand but it will move if input is provided (i guess the gearing advantage helps things along). It gets to a point where it becomes almost impossible to move, then it passes this point in the revolution and becomes easier, before getting stiff as it comes round to the same point again.

The output shaft to the leadscrew is also playing up. Its very stiff and wont move by hand, but will move when the box is in gear and input is applied. The input pressure required to move the gearbox is heaps, it hurts my hands when trying to do it without a rag.

So, I suspect either a bent tooth or something is in there, but I cant see anything after a thorough look. The other and worse option is that one of the shafts has bent, this would be a real blow.

P.S Dave - Last time I did a bike gearbox it was the exact same prob! 3rd gear welded to shaft on an RM250

The Lathe/Parts diagram you listed,is that correct for your Lathe or similar?

Have you been able to Rotate the Leadscrew at all?

If you cant or it is excessively hard to turn,can you move the Carriage along the Lathe bed?

If you can move the Carriage have a look at the Leadscrew and see if there is any Damage/Burring where the Drive Key for you Cross and Longitudinal Feed comes from.

I understand your need to get the Lathe up and running again,but the 1st thing in my opinion would be to try and assertain what caused or led to the problem.

It would also appear that the safety features to eliminate excessive damaged have failed.

Does it have the Shear key on the Headstock spindle?

The Lathe/Parts diagram you listed,is that correct for your Lathe or similar? The pictures I posted originally are from the manual that came with my lathe, its identical to my setup. See attachment to this post for the whole manual.

Have you been able to Rotate the Leadscrew at all? Yes, its OK. I have removed it at the moment.

If you cant or it is excessively hard to turn,can you move the Carriage along the Lathe bed? Yes carriage moves freely

It would also appear that the safety features to eliminate excessive damaged have failed. Yep.

Does it have the Shear key on the Headstock spindle? Unsure, spindle turns fine at the moment. I can still turn manually, just stressed about losing 90% of the lathes functionality.

The gearbox is rooted...im sure of it. Surely if it was not rooted I would be able to turn the input shaft easily and watch the drive train do its thing...my gearbox for all intents and purposes has seized.

Brendan
If you can fix an RM250 gearbox this should be easy.
When you were cutting the thread were you winding the carriage back by hand or reversing the motor?
I think its a little harsh to say the safety feature failed......steel shear pin sounds like sabotage to me. Still to late wo worry about that now.
Stuart

Reversing by hand, still havent got around to getting one of those drum switches.

What should I make the new shear pin out of?

Note - I should mention prior to starting the threading job I ran the lathe at 2000rpm and used the powerfeed to turn the aluminim down to size. It was only 5 mins or so before the crash. this could have pushed some bushes to the edge and then the threading tipped them over? I was taking beefy cuts because it was a pain reversing the lathe by hand.

Brass would be fine for the Pin.

I only asked about the reversing the carriage by hand so you would know if it was moving freely. If you'd been power feeding it both ways you wouldnt have known if it was tight(i.e the carriage lock on).
The shear pins are normally made from brass.

"because it was a pain reversing the lathe by hand" how long was the cut? shouldnt have been that hard.

Some gearboxs have rpm limits on course thread cutting but I can't find anything in the manual.


Stuart

Did you check the shear key PC mentioned?(Fig 18 and 19 in your manual)

Just went home then, that shear pin is intact. I wonder if it let go a long time ago and someone replaced it with an unsuitable material? Its an ex school lathe so I guarantee its been crashed at some point in its life. The offending student probably just made a new shear pin out of steel or something.

Had more of a play whilst there, the output shaft has definately seized in its bush. As mentioned before too, the shaft with the 10 gears on it has also seized. Either in its bushes, or one of the gears on there has welded to the shaft like what the RM250 did a few years ago.

Ill pull the gears out on the weekend and see what I can do. What happens when a bronze bush seizes? Can I give it a very fine skim in the lathe or do I need to make a new one?

Originally Posted by 19brendan81

Just went home then, that shear pin is intact. I wonder if it let go a long time ago and someone replaced it with an unsuitable material? Its an ex school lathe so I guarantee its been crashed at some point in its life. The offending student probably just made a new shear pin out of steel or something.

Had more of a play whilst there, the output shaft has definately seized in its bush. As mentioned before too, the shaft with the 10 gears on it has also seized. Either in its bushes, or one of the gears on there has welded to the shaft like what the RM250 did a few years ago.

Ill pull the gears out on the weekend and see what I can do. What happens when a bronze bush seizes? Can I give it a very fine skim in the lathe or do I need to make a new one?

It sounds like it ran dry, if it's not the main spindle, you maybe able to clean it depending on the damage.
RM250 you say, the one I did was a RM125 3rd gear,lol
All we did with that was press them apart (it took about15 tons in the press) clean them up and it has run fine ever since in our hands. It was from my nephew running no oil in it when he owned it.
Dave

If after you seperate the shaft and gears and determine what either needs to be replaced or repaired if possable I would then be looking at replacing the Bushes.

If the bushes are worn or Pitted/Scored they should be replaced,as well as looking at the associated bushes I would also be checking on how lube is supplied .

How often and how much lube were you supplying to these bushes and shafts.