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View Full Version : Critique my (steel) chinese machine (AccTek)



the_wildgoose
25-06-2017, 05:44 PM
Hi, I'm currently an owner of a OmioCNC x6-2200L and looking for something a little larger. I looked at a DIY gantry build and thought I would take some quotes from chinese manufacturers to compare.

So - near as I can tell, the chinese options seem to cluster into several main categories (they all seem quite similar, but claim to add their own secret sauce).

a) Bunch of stuff for $4-6K which is made of steel, but tends to max out at 3KW spindle and asking for more spindle or Z height the maker tends to say it's not strong enough for that (however, they visually look stronger than the vast majority of DIY gantry designs I see). 20mm square (or supported) rails at best. Seems like you can easily get a bargain or something which needs a fair amount of work, depending what you order.

b) Jump up to $12-17K seems to get you a fairly big step up in thickness of steel, size of gantry, 25mm Hiwin, TBI screws (and hopefully increased chance it's genuine), Delta servos and a chinese ATC (5/9KW). Quite a lot of variations on options and in this category they seem a little more confident in telling you about qualities of steel and thicknesses of stuff.

c) $22+ gets you HSD spindles, Yaskawa servos, 25mm+ TBI. etc.


So all the above is based on a few emails and some photos, so help me figure out how it's all going to go wrong please... I have talked with Blue Elephant, Omni and AccTek. All were fairly helpful, especially for machines in the second category and above - they passed the smell test in as much as highlighting what you CANNOT do with various levels of machine and didn't simply claim the earth.

I'm not honestly completely sure what I want to use the machine for (more on ideas below), but I wanted to cut the occasional full sheet of MDF, but I don't want a full size machine... So there are two common clones, the 1212 and the 1313 machines which are roughly half sheet. The 1313 machines seem in general to be considered a massive step up in rigidity by the sellers (I don't think any do high end models in 1212 format). AccTek in particular can do ballscrew versions of their 1313 (and the full sheet 1325 equivalent).

So I have had them quote me for a machine in that middle b) kind of spec, but with ballscrews on all axis, so 9KW chinese ATC, 25mm Hiwin HG, 40mm TBI C5 ballscrews (40/40 for the Y, 32/20 for the X, 32/10 for the Z), Delta servos, most of the steel is quoted at 16mm for bed/gantry (and 4-6mm elsewhere...). Gantry is cast iron. They claim to stress relieve everything and claim to grind surfaces flat and CNC drill everything (claimed). Price around the top end of the range I gave above. Delivery is like $80 (!!Had to double check that a few times) and of course there will be many extra costs for customs, delivery to the door, etc (I have some quotes for those)

OK, so here are my concerns:

- So the ballscrew versions of the machines are only single screw on the Y, and so my first question/concern is whether I have any concerns about racking a machine of this size? I would like to be able to cut at the power of the spindle through wood and also cut aluminium to decent accuracy. How will a single screw compromise those hopes..?

- How do I compute theoretical machine accuracy (step size if you like). The ballscrews are at max a 40mm per rotation and the servos are alleged to be these (claims 160,000 p/rev?), and I believe there is a 2:1 step down:
http://www.deltaww.com/Products/CategoryListT1.aspx?CID=060201&PID=225&hl=en-US&Name=ASDA-B2%20Series

To be clear, I don't have any desire to do work of super high tolerances, but I would like to be able to do localised fine work (say PCB) and to be able to carve aluminium with a decent surface finish.

- The spindle supports appear to be "just" plates, ie not a C shape. This would appear to be the most visually weakest point in their design. The single Y axis also implies that the middle of the bed can't be supported, but for aluminium work (and a 1300mm bed) I don't see this to be a practical concern? I'm impressed that the gantry is internally braced. Any other observations on the design?

- How else might this go wrong? What questions should I be asking the seller? Does this look like a strong machine (worth the cost - for the materials used?)

I don't know how to upload photos here, but I have put some dropbox links below. The machine in the photos is the 1325 full sheet machine. I would be ordering a machine half the length (about the same price though!!), and with a linear toolchanger (along the y axis)

Gentle criticism appreciated...

https://www.dropbox.com/sh/kmgdirkdgcyzc6b/AACtzWXQ6FGa_NzO61IM9iKGa?dl=0

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