Expectations of Chinese Lathes 12 x 36 or smaller vs. Taiwan units

coolidge said:
Not correct, a QCGB can reduce the number of change gears and how often you need to swap those gears around to cover all the threads and feeds a lathe supports. But it's rare that a QCGB can cover 100% of the threads and feeds without changing any gears. I think I came across a single lathe that can do that but your talking a $25k lathe. Note also feeds, the QCGB and gear configuration is also about covering the full range of feed rates a lathe supports not just the range of threads.

A great example of two quick change gear boxes are the Grizzly G0709 and the G0824....

G0709 - has only 5 change gears. Only 3 of those ever need to be changed to cover the entire thread/feed range. And there are only 3 configurations total hence the factory configuration covers a lot of the most common threads and feeds without having to swap change gears at all. Also, all the change gears are installed on the machine. You don't have a stack of extra change gears to store on shelf.

G0824 - has a whopping 9 change gears and complaints by people who bought the thing not knowing what a pain it was going to be having to swap change gears all the time. I'll let you read up on the G0824 if you want more details.

Grizzly has very detailed manuals, specifications sheets, and parts lists. Everything on the lathe has a part # down to screws and bolts which you can search for on their website to see if it's in stock. I purchased a number of spare parts for my lathe straight away. Two of the lead screw brass shear pins for example because shearing one of those and not having a replacement on hand in the middle of a job blows. Headstock cover gasket because freaking leaks. Extra brass thread dial gear etc. ALSO if there's one thing that would put me in a bad mood is having to wait months for a spare/replacement part to arrive from China. Grizzly's USA part supply was also a factor in my decision. I can't speak for PM's spare parts supply but a lot of these other machine sellers just sell the machines, they don't maintain spare parts inventories.

Variable speed vs fixed speeds vs back gears - Starting with back gears PM lathes with high and low belt pulleys does double the number of fixed speeds. For example my G0709 has 8 spindle speeds. If it had the high and low motor pulleys (back gears) I'd have 16 spindle speeds and if I remember correctly some of the PM lathes have exactly that so advantage PM. That said a lathe is not a mill. Mills have spindle speeds from 50 to 30,000 RPM's. Lathes are a completely different animal. I discussed variable speeds with my brother before purchasing. He owned a $250,000 Mori CNC lathe and never exceeded 2,000 rpms. Different feed rates sure, but you don't need infinitely variable spindle speeds really. It can help in certain situations, tweaking to eliminate/reduce chatter (squealing) for example. Typically variable speed lathes use 3 phase motors which run smoother vs single phase motors which can produce finish issues. But there are other methods for dealing with chatter. Isolating the single phase motor from the lathe completely. Larger shank tools. Smaller radius tool tips etc. If money were no object I might have opted for variable speed but honestly the 8 speeds the lathe has pretty much covers anything I would do so I spent the variable speed money on tooling and chucks instead.
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there are some <$2K lathes that cover 100% of the threads without change gears (ELS)
 
 
dabear?? linked lathe Claimed threads producible .5>3mm, 10>44 tpi
Difficult to tell what they are saying other than Auto switch between metric and imperial.
Photo of change gear selections. Makes me wonder?

An electronic lead screw could produce "any" thread but not sure that fall within this discussion.
CNC machining centers can also produce most any thread.
 

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Larry$ said:
dabear?? linked lathe Claimed threads producible .5>3mm, 10>44 tpi
Difficult to tell what they are saying other than Auto switch between metric and imperial.
Photo of change gear selections. Makes me wonder?

An electronic lead screw could produce "any" thread but not sure that fall within this discussion.
CNC machining centers can also produce most any thread.
Click to expand...
an ELS is a direct replacement for a QCGB, how does this not fall within this discussion?
no gears (at all) in the z travel of the lathe all threads are programmed into the device and every possible thread / feed rate is available at the push of a button (well maybe several). the gear change chart is an artifact and does not apply (function of Chineasysum manufacturer) lot of good reviews of this system (and others) Clough42 has a DIY version he added to his grizzly lathe.
 
Larry$ said:
Why is this the range? What keeps me from turning 8 tpi or 4mm? or 56 tpi.
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Because it wasn't considered important. Or the lathe is too "weak" to cut coarser threads. My 10x22 only supported gears for 8-72 TPI. I have cut 4 and 5 TPI using my ELS, but honestly, it's pretty much at or slightly beyond the capability of the lathe. It also requires a bit of torque from the lead screw. I've had the stepper stall at 4 TPI. Fine pitch threads are easy to implement. I have 25 imperial threads available at one time, simply due to display considerations. Likewise I have 24 metric threads available. But I can recompile and add any thread I want, because I wrote the code and have the source files.
 
Larry$ said:
Why is this the range? What keeps me from turning 8 tpi or 4mm? or 56 tpi.
Click to expand...
have you looked at the lathe i posted? LOL the ELS is not the issue and that lathe was to prove my point, there are many more implementations of this tech and it works (works good), i'm not going that direction because by the time you implement this system you are a step away from true CNC.
 
I made an ELS, because I didn't want to go CNC. Simply didn't have the experience in manual machining, so no point for me to go CNC.
 
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