Back in the workshop, a Lathe Problem…
I have a problem with my big Chinese lathe. I was hearing a KNOCK-KNOCK-KNOCK as the main spindle was revolving at low speeds with one setting of the gears.
It is a GBC 1000-400 lathe, meaning that it has a maximum of 1000mm between centres, and it will turn a 400 mm disk. It weighs 2 tons. Has been quite useful when turning flywheels, big lumps of metal, large pieces of wood and so on.
So today I removed the cover from the headstock and had a look. The cause of the knock was quickly obvious.
So, what do I do about this? I need some suggestions, people.
Thoughts so far….
- remove the spindle, remove the gear and bronze braze a replacement piece of steel or bronze, then machine a new tooth.
- same as 1, except use silver solder.
- same as 1 or 2, except do the job insitu (after draining all of the gearbox oil, and screening off the other headstock parts). Unfortunately the missing tooth is close to the headstock case, so filing or grinding a new tooth would be tricky.
- leave it as is, and just avoid using that gear. I can do that. It removes 3 of the 9 gear ratios, including the slowest speed (40 rpm), and is not an elegant, or desired solution.
So what do you think? The gear is most likely made of steel rather than cast iron, from its appearance. The base of the break is shiny, smooth and not porous.
Here are some pics of the ends of the main spindle. It does not look too complicated to remove the main spindle, but what would I know.
I imagine that the main spindle bearings will be pre-loaded, tapered, roller bearings. I certainly do not want to damage them. And how difficult will it be to reinstall the bearings and main spindle? I imagine that it will involve some careful and precise work. Am I taking on a job which is way beyond my abilities? If anyone has experience of this task I would be delighted to hear your views. I have no drawings or plans of the headstock to assist.
(In parentheses, when I was a teenager, I remember my father pulling a Toyota Crown automatic gearbox to bits, identifying a fault, and fixing it. There were bits of the gearbox everywhere. But he fixed the problem. He was not a mechanic, but he had a go at things, and usually managed the task, as in that case. Similarly, I dont mind having a go at this lathe job, but I would prefer not to risk destroying the lathe, so any expert opinions will be welcome. Option 4 above remains a possibility.)