Chinese Lathe woes

[Astrobits]

About 12-13 years ago I was living in South Africa and purchased a Chinese 3 in 1 lathe, coded HQ500. Some years later I returned to the U.K. and brought it with me. It has done well for me ( very light use ) until about 1-2 years ago when the auto feed stopped and the auto feed speed change lever jammed. I continued to use it on and off without the auto feed until recently when I decided to sort it out. Examination of the manual and the machine itself did not show any reason beyond something within the headstock was broken. A query to the U.K. agents for this machine, for help in dismantling the headstock went unanswered. I therefore had to attack it blind. The first item was to drain the oil out. There is no identified oil drain plug in the manual or on the machine so finding that was guesswork. I opened up the rear panel on the headstock and, apart from oil everywhere as I had not drained it through the correct bolt, easily identified the problem. Two of the gears were plastic and one had lost some teeth--hence no drive to the auto feed. Removing the gears was relatively simple, there is only one obvious way to do it. I identified the gears and ordered replacements from the U.K. agents who responded to an order within hours! The gears were reasonably priced at £25 each but clearly had to come from China as there was a £30 airmail charge on the invoice. I decided to replace both plastic gears although only one was broken. It took nearly 5 weeks for me to receive the order so perhaps I had to wait for the manufacturers to make more stock.
I was surprised to find plastic gears within the headstock as they are not replaceable easily nor quickly as other, external, plastic gears are on other lathes are. In a previous life I was a research scientist in ICI's Plastics Division and it just so happens that the performance of Nylon ( as are the gears in my headstock ) in an oil environment was a project that I was involved in. In brief, Nylon in oil slowly looses it's strength so the failure of those gears is inevitable. Nylon should not be used in such an application.
The headstock opened showing the two nylon gears:



The two gears removed showing lost teeth on one, and their replacements:


Nigel

 

[paulrbarnard]

I wouldn’t be surprised if metal versions were available from somewhere. They seem to be available as upgrades for most Chinese lathes.

 

[ScottandSargeant]

Try HPC … we use them when gears are needed.
https://www.hpcgears.com/

 

[clogs]

Tuffnol is a very good material for this job....
Prob with metal gears is that if something goes wrong the power just smashes everything else up on these cheapand cheerful machines.......

 

[Sandyn]

Prob with metal gears is that if something goes wrong the power just smashes everything else up on these cheapand cheerful machines.......

As Clogs said, this is a safety design feature.
Tufnol.com
"In abnormal stall or excessive overload situations, the laminated gear will usually strip without causing undue damage to the metal gear or other parts of the equipment."

 

[Astrobits]

I doubt that this is a safety feature. If it is then there are better places to put such a feature.
As this is a belt driven lathe then I would expect that the belts would slip before damaging steel gears. Also, the headstock gears drive a shaft to the outside and another train of steel gears that ultimately drive the feed screw. It would be logical to put Nylon gears there to absorb any stall and they would be very much easier to replace ( after all they are swapped around for different threads ) as they are in other lathe designs. Any stall that stopped the chuck also stops the drive to the headstock gears as they are driven directly from the chuck shaft.
I do plan to get replacement gears in steel ready for the inevitable failure in the future. Perhaps I should think about getting some Nylon gears to replace one or two of the external steel gears.
Nigel

 

[Sandyn]

sounds sensible, but it is a common practice to use tufnol gears which are designed to fail if the mechanism stalls somewhere. The ones on my pillar drill would be a nightmare to replace, they are deep inside the gearbox.

 

[Fergie 307]

I have to agree with Astrobits. If it was a safety feature then you would have one plastic gear, not two. Most lathes use a sacrificial pin or similar in the outside drive train, that will let go in the event of a crash. The better ones use a clutch which will slip in the event of a stoppage. I suspect it is more to do with noise suppression. Metal gears are very noisy. A good example is Ford's use of a fibre intermediate gear on gear driven camshafts, like the 3.0 and 2.8 V6. This was done purely to reduce noise, but they do fail. Fortunately it's a non interference engine so no harm done when they do go Standard practice in tuning these was to replace it with a solid steel one, as the standard part won't take the strain of a higher lift cam and stiffer springs etc, but the steel ones make a good old howling noise at speed. Ask anyone who has a Harrison lathe with all steel gears in the headstock, they make a right old row.

 

[Daniel2]

I have to agree with Astrobits. If it was a safety feature then you would have one plastic gear, not two. Most lathes use a sacrificial pin or similar in the outside drive train, that will let go in the event of a crash. The better ones use a clutch which will slip in the event of a stoppage. I suspect it is more to do with noise suppression. Metal gears are very noisy. A good example is Ford's use of a fibre intermediate gear on gear driven camshafts, like the 3.0 and 2.8 V6. This was done purely to reduce noise, but they do fail. Fortunately it's a non interference engine so no harm done when they do go Standard practice in tuning these was to replace it with a solid steel one, as the standard part won't take the strain of a higher lift cam and stiffer springs etc, but the steel ones make a good old howling noise at speed. Ask anyone who has a Harrison lathe with all steel gears in the headstock, they make a right old row.

Yep, my gear head lathe (Chinese), makes an awful racket at higher speeds.

 

[Fergie 307]

I have a lovely 1970's American Toolkraft pillar drill/router Great machine but uses steel on steel gears between the motor and gearbox, makes a HELL of a noise. And the Harrison really sings when it's going at full chat.

 

[sawtooth-9]

There are certainly some Chinese machines that are ok
BUT most are "cheap and nasty "
You get what you paid for - and it's always a false economy
Reputable makers know how to run metal / metal or polymer gears - they have actually heard of shear pins !
If its not a reasonable quality when new, why bother repairing it !

 

[Fergie 307]

There are certainly some Chinese machines that are ok
BUT most are "cheap and nasty "
You get what you paid for - and it's always a false economy
Reputable makers know how to run metal / metal or polymer gears - they have actually heard of shear pins !
If its not a reasonable quality when new, why bother repairing it !

If it's served well then repairing it is perfectly sensible. I agree entirely about the quality of many Chinese machines, although they have improved considerably. At the end of the day you can still turn out good work on these things, just much harder work than a really good machine would be. What does get me scratching my head is how Warco etc sell machines in the 4-5k range. At this price you can buy a decent used Harrison, Colchester or Boxford machine. Like a Rolls Royce versus a Cortina. I suppose it is the attraction of something arriving in a crate with all accessories thrown in and , allegedly, ready to go. But lots of corners cut in the quality of the design, and build quality is often pretty poor. I have an Amadeal 25 mill, and had a look at his lathes as well when I was there. These do seem to be at the better end of the Chinese machines. One thing I found frustrating was that build wide they seem to just assemble the components in the right order and chuck it in a crate. Nothing on my mill was adjusted remotely correctly. Having spent some time after installation going over it and making sure everything was set up properly, it now works very well, and the quality and accuracy of the machined surfaces is pretty good. I can't blame Amadeal, at the price he can't afford to unpack every machine and spend a couple of hours adjusting it. The only real criticism I have of it is that it does have some backlash in both x and y feedscrews. They are both regular type threads rather than square or acme, a very common cost cutting feature in many Chinese machines. I have a dro on mine so doesn't cause me an issue. So in summary good value at £1200 if you have the knowledge to set it up properly, but if you expect to just take it out of the crate and use it you will be disappointed. I helped a guy out recently who was getting awful chatter with his brand new mill. Partly it has to be said down to poor working practice, he didn't realise that you should lock axes that are not in use for example. But the main issues were it wasn't trammed correctly and the gibs were loose on both table axes, hence the table having a nice wobble, like a good panna cotta, ok a bit of an exaggeration, but you could actually see it moving when the tool got to the work. With these issues sorted he was chatter free. He had assumed that as a brand new machine it would be good to go straight out of the box. This was a Warco, if I remember correctly, so I think you can safely assume they all suffer similar issues.

 

[Keith 66]

sounds sensible, but it is a common practice to use tufnol gears which are designed to fail if the mechanism stalls somewhere. The ones on my pillar drill would be a nightmare to replace, they are deep inside the gearbox.

That sounds like an Arboga, lord knows how you ever get at the gears in one of those if you strip the tufnol ones! I have a manual & it looks difficult to say the least.
As for the chinese ones they are nylon because they are cheap!

 

[Daniel2]

That sounds like an Arboga, lord knows how you ever get at the gears in one of those if you strip the tufnol ones! I have a manual & it looks difficult to say the least.
As for the chinese ones they are nylon because they are cheap!

With the added benefit of noise reduction.

 

[sawtooth-9]

That sounds like an Arboga, lord knows how you ever get at the gears in one of those if you strip the tufnol ones! I have a manual & it looks difficult to say the least.
As for the chinese ones they are nylon because they are cheap!

There is a very simple principle - someone put it together, so someone can take it apart.
It usually just takes a little thought, patience - and perhaps a "puller" or two.
It's not rocket science, just plain old basic engineering.