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PWD
22-05-2012, 09:41 AM
I have been nosing around with companies on Alibaba. Have managed to be in communication with this company. Basically looking for a machine with a 4th axis to mill 2mm alloy tube . I think this would suffice with the 2.2 or 3 kw spindle. Has anyone an opinion on these machines. Not wanting to buy something that's going to be frustrating or hard to set up as my CNC experience is virtually ..well is 0 . It is on "offer" for about 1800 delivered (plus imports and handeling etc which will add around 450 extra)6023602460256026 which does seem cheap...so if you know of something better for slightly more would be grateful as well as any heads up on likely problems I may run into once I plug it in .Many Thanks

Web Goblin
22-05-2012, 10:52 AM
I dont have any experience on these machines but looking at the pictures I would seriously think about it before buying it. The 4 axis looks a bit thrown together,
the nuts used as spacers to pack up the chuck, the rather thin base plate its mounted on and the slide that the tail stock is on looks like someone hacksawed the end off to get it to fit. I also hope its just sitting in this position to show it rather than this being how it fits to the machine for working purposes.
Just my opinion.

Regards

Ian

Jonathan
22-05-2012, 11:18 AM
Yes the 4th axis does look a bit thrown together. Also it's just belt driven from a stepper motor with a single reduction, so the available torque and thus holding force will not be much. It would be ok for light work in wood, but would struggle to do anything serious (such as aluminium) due to the lack of stiffness.

The machine frame looks sturdy, however due to those nice covers we can't actually see what type of linear rails are used on X and Z. We can see that Y is 25mm supported rails, which is good. The pdf says the others are 20mm, but are they supported or unsupported? Perhaps ask for a picture without the covers on...what are they hiding?

The gantry has a piece across the bottom to link the two sides which strongly implies there is only one ballscrew on the Y-axis (I'd normally call that X, but they called it Y). This can cause the gantry to deflect when the cutter is towards either end since it is less well supported. The big spacing of the bearings helps, but it's still not as good as it could be.

There is a very large overhang between the tool tip and where the spindle is supported because they have put the rails on the gantry carriage, not on the actual Z-axis. Again this is adding weakness and potential for resonance.

Also they say they used 2510 ballscrews on X and Y. They would get a much higher feed-rate and acceleration with 1610 screws and on this size the critical speed wont be a problem, so it seems a bit of a waste of money to use such large ballscrews. 7-8m/min is good, but notice how they state the resolution is only 0.05mm - perhaps it's geared up a lot to gain speed at the expense of resolution.


Overall it clearly depends what you want to do with the machine. If cutting a lot of aluminium I certainly wouldn't recommend it. Anything else, well it's less clear cut but still not a good machine in my opinion. The problem is you'll struggle to find much better than that without either spending a significant amount more, or making it yourself.

PWD
22-05-2012, 11:31 AM
Thanks for that I appreciate your time it took ...will dismiss it and look again. Have just been sent more info from a Chinese firm so will post again shortly.. and also and have been in touch with a UK firm called STRIKE CNC ..anyone heard of them ?

Jonathan
22-05-2012, 12:02 PM
Thanks for that I appreciate your time it took ...will dismiss it and look again. Have just been sent more info from a Chinese firm so will post again shortly.. and also and have been in touch with a UK firm called STRIKE CNC ..anyone heard of them ?

No worries, yes we've heard of Strike CNC on this forum. I'll leave you with this:

http://www.mycncuk.com/forums/showthread.php/4155-Strike-CNC-(My-first-CNC-router)

It's a long thread, but worth reading for the explanations of common faults with CNC router design.