My 1st Hybrid Steel/Ally (1150 x 850 work area) (comments/advice please)

**lebies** · 12-08-2014

Hi all,

My first post after spending much time soaking up some really great ideas.

I must confess though, I'm suffering from information-overload! - there's just too much to take in, and not be able to apply directly.

Anyways, I've always wanted a cnc router - and now I finally get to build one

. So, in preparation I've been trawling forums like yours and without doubt - you guys rock for friendly, solid advice.

The beast:
- I want something that I won't have to say, "damn...if only I had this (longer, wider, 4th axis, etc) or that!" I figure around 1200 x 800 x 300 (X,Y,Z as you guys reference it) would do nicely.
- 4th axis is a requirement.
- Working mainly wood and perspex but must be able to do aluminium as well. I don't mind shallower cuts, slower feed rate and/or more runs to do it, but I must be able to do it.
- As accurate as possible, repeat-ability very important.
- One thing I learned over the years from my electronics career is that when you do something, do it well (as you can, budget permitting) - and don't skimp! If you're investing in something, get the best you can afford, and if you can't afford it, save up for it.
- I've only been considering Hiwin and/or SKF for the profile linear guides and rails and ballscrews.
- Base:
I'm thinking of going 50x50x3 square tubing for most of the frame. I've probably gone over-kill on the supports but what the hell - can't do any harm.
Comments will be most welcome (thanks in advance :))

- Axis:
X (1200-ish):
I was going to use a single ballscrew down the center, until I came across a post(s), I think from jazzcnc, that completely changed my approach (and kicked off yet another design iteration). I think it's a brilliant idea for the 4th axis and so this design based on it.
I'm unsure whether to go with 2 x 12mm or 2 x 16mm x 5 (or 10) for the long axis. SKF (BK/BF) fixed and floating bearings.
Profile rail guides and blocks SKF 15mm profile (LLTHR15 rail, LLTHC1 carriage).
NEMA-23 3Nm stepper motors on either side, reverse polarity on one of them, driven from same driver board.

Y (850-ish):
For this axis I'm thinking of using Ally profile. There's a guy down here in my neck of the woods that has designed and has manufactured a really nice (versatile) 90x45 profile. A big advantage is that the rails (15 and 20) drop right into slots provided, and bolt down via t-bar.
I'm also thinking of a "C-section" to beef it up some (see pics). MUCH more expensive than steel, but then a LOT less tinkering and engineering work negated - which probably justifies the decision. Also, I don't have access to the machinery you'd need to be able to work the engineering.
Profile rail guides and blocks SKF 15mm profile (LLTHR15 rail, LLTHC1 carriage).
12mm x 5 ballscrews, BK/BF end bearings again.
NEMA-23 3Nm stepper motor.

Z (300-ish):
The main decision driver for the 300mm Z-axis is to be able to do up to about 150mm radius wood/perspex lathe work.
Profile rail guides and blocks SKF 15mm profile (LLTHR15 rail, LLTHC1 carriage).
12mm x 5 ballscrews, 15mm profile rail.
NEMA-23 3Nm stepper motor, belt & pulley driven. No idea of ratios!

4th Axis:
100/110mm chuck and tailstock.
90x45 Al profile across the front, provides for a moveable tailstock, running on the profile.
NEMA-23 3Nm stepper, belt & pulley driven. No idea of ratios!

Spindle:
GDZ-80-1 Spindle motor, 12000-24000(RPM), 1.5(KW), 220(V), 5(A), 100-400(HZ) Φ80*188, water-cooled, ER11 Collet

I'd love to buy the following spindle (http://www.cncdirect.co.za/htm/control.html) but it'll have to wait until I can justify the cost! And, there's no local stock at the moment!
I'm a bit concerned with the Chinese spindle having read about guys having had to open them up to properly earth units, sub-standard wiring, and the likes! Hopefully this is not the case on this one.

I'm as yet undecided on the breakout board to use.
I'm very comfortable on Linux and was thinking of going with linuxcnc over mach. I can develop and/or write my own stuff, and/or add embedded controllers if and where necessary. Plus of course, it's free, and I have all resources on the PC available to me if needs be.

Here are some links to the electronics I have in mind to use:
Stepper motors: https://www.robotics.org.za/index.ph...product_id=123
Drivers: https://www.robotics.org.za/index.ph...&product_id=69

And, here are some pics for reference. I would really appreciate all the help and advice I can get.