View Full Version : Will steel angle work for a decent machine?

03-06-2015, 03:31 PM
Hi guys. Before I get into sketchup(never used it) and stuff I'd like to run through a few ideas.

First off, i've never built a cnc machine before but have general skills, i'm always trying to build bits and bobs, I cant weld though.

Will 50mm angled steel be good for the base and also the gantry using only bolts, no welding. I have the usual tools, drills, angle grinder, taps etc. No pro stuff available though.

I've got 20 massive photocopiers that I can get my hands on for big steppers, bits, and possibly use the power supplies??

I want to use ballscrews to drive the gantry and router. I'm hoping it would be good enough to cut wood and ali to start of with and later modify the cnc to cut thin plate steel by getting a spindle etc later on. I'm hoping it will cost less than 1500 to build but most of all be reliable and accurate to around 0.05mm, is that possible?

For the size i'm hoping to make it 1.2m x 800mm.

Boyan Silyavski
03-06-2015, 11:19 PM
No, steel angle is not good, neither U or I profile. Square or rectangle box have much bigger moment of inertia than the before mentioned. 60x60 is minimum, 80x80 is best for normal machine. I prefer 100x100x3 or 4mm, as the bigger the better, but the design must be cleverer also. take a look at my first build, link in signature

No, steel is out of question. You need a mill for this. As a last resort the machine must be fixed gantry with moving bed and short Z. and very very rigid.

You will need 20 size square supported rails /Hiwin or similar/ with the longest bearing blocksblocks, xxxxxHA, not xxxxxCA

Basically with the money you say you have, you can buy the steel, the rails and ball screws and that's all. And thats my advice, make a small 300x300 or up to 400x400mm machine with fixed gantry, invest in proper bearings and ball screws. The slowly finish it whenever possible.

04-06-2015, 12:38 PM

I agree with Silyski. Reviewing what you want to start with:
> 50mm angle iron baseframe and gantry
> Simple bolt together, no lathe/mill etc.
> Steppers and electronics from (big) photocopier
And what you want it to do as a specification:
> 1200x800mm
> Cut wood, aluminium, possibly thin steel
> Hold 0.05mm tolerance
> Be a 'decent' machine
I think you cannot even come close to meeting that specification with the approach you are looking to take. So you have 2 choices -
1. Make a simple 'learning machine' with the 'wrong' bits and get yourself up to speed with what is important etc. Be prepared to write off the hours and costs involved. There is something to be said for this if you go in with that in mind.
2. Actually build a machine capable of what you want (and by the way 0.05mm is tough at this size, even if you do a really good DIY build) by getting some of the bits made for you.
My experience is that I have made 3 major evolutions of cnc machines over the years, with tens of minor improvements to each of them along the way, and I can tell you that I started with a machine a little better than you are proposing (but would not come close to what you want it to do) and worked my way up to a pretty solid machine now (which would almost match what you want to do).
Hope this helps and I know it can be disappointing to be told that something won't work but it is said with the best intentions of having been there, or done that, or seen it done that way and failed.

04-06-2015, 01:37 PM
No. You guys have been a massive help. Saving me loads of time money and a lot of disappointment in the end. Think i will try and build a aluminium extrusion cnc slightly smaller instead with less expectations of accuracy. Thanks for the brilliant detailed answers. Time to trawl the internet for some designs that are possible on my budget. Cheers

04-06-2015, 08:05 PM
Don't want to scare you away! Have a look at the build logs on this forum > machine building > gantry style

In general the general DIY builds on the 'internet' leave a lot to be desired in my view. The builds on this forum, plus some of the cnczone ones, are much better having benefited from the collective wisdom and continuous feedback over a number of years.

For ideas about a deceptively simple but solid machine (using some extrustions) have a look at this recent build:

Finally, if CAD is not your thing then you could post links to a couple of other people's ideas you like and get feedback on those. But the CAD trip is well worth it in the end so I do encourage you to try.

05-06-2015, 06:01 PM
No, you haven't scared me away, just given me a lot to think about. hehe

Gunna have a long look at the builds, cheers.

Yea, I think I will get into CAD before I lift a single tool, but first, I definitely need to do far more research.

On a side note. I've taken a nema 23 stepper out of one of the photocopiers, its 2.8v and 3A and weighs about 1.12kg. The length without the shaft is 78mm and I think it has around 270 ounce-inch holding torque. Does this sound about right?

Will this stepper be O.K for an Ali gantry?

05-06-2015, 07:37 PM
I wouldn't like to say for sure on electrical bits but comparing what you have with popular steppers for general CNC work:
Yours.....vs...Typical (e.g. SY60STH86-3008BF)
1.9 Nm..........3 Nm
2.8 V............5.46 V
78 mm..........88 mm
?.................3.2 mH (inductance - important value to get right)
3 A..............4.2 A
I have a stepper close to your spec on the Z and it works OK but I wouldn't use it on the X or Y (gantry) as it's a bit low on torque etc. M60STH88-3008DF is another popular choice with a similar spec. I'm giving you this info so you can build up your library of knowledge and have a look around - don't buy these sorts of bits yet until the design is ready!

05-06-2015, 07:53 PM
No. Not thinking of purchasing anything yet. Just thought I'd have a look at one of the steppers I have from the old photocopiers. Looks like I'll need to buy some then. Oh well. Thanks for the great information.

Boyan Silyavski
05-06-2015, 08:50 PM
Steppers are one of the smallest expenses you are to deal with. Plus these steppers are possibly much more modern than the one in the photocopier. Plus the shaft may be is bigger and so on. Another thing worth noting is that most people drive them at 70V.

Here (http://www.cnc4you.co.uk/Stepper-Motor/Nema23-3.1Nm) you will find them / the 3nm motors/ fairly priced.

05-06-2015, 10:05 PM
and later modify the cnc to cut thin plate steel by getting a spindle etc later on
'Thin' makes me wonder if the requirement is for cutting out 2D/flat shapes, which might make a plasma cutter a viable option. It's often attractive because the lack of contact with the work piece means that the machine doesn't have to be nearly as rigid.

If there's a need for 'engraved' features on plasma cut work, then one option is to etch it with acid. If you've seen a brass and enamel sign, chances are it was produced this way. With very thin materials it's even possible to cut out shapes by etching from both sides. Etching is faster (specifically, it's great for area, but rubbish for depth) and cheaper than CNC but does involve some fairly nasty chemicals.

Yea, I think I will get into CAD before I lift a single tool, but first, I definitely need to do far more research
That CAD experience will pay off when you've got a CNC machine, and you need to prepare jobs for it.

If plasma cutting sounds like it might meet your requirements, BTW, then I think there's a few machine designs in the plasma table forum.

05-06-2015, 10:52 PM
Thanks for the link. Are they a decent company/reasonably priced?

Yea, its only a 7mm shaft on the stepper I have. What voltage could my stepper be run at?

05-06-2015, 11:08 PM
Thanks jess. I wouldn't trust myself with chemicals, played around with them too much when I was younger!! :hypnotysed:

Think I'm just gunna make one for wood and ali now. I just wanted to see if steel work was viable at my price point, it wasn't essential. It would have been handy to make a few bits for work, but it's no big deal.

Boyan Silyavski
06-06-2015, 09:12 AM
Thanks for the link. Are they a decent company/reasonably priced?

Yea, its only a 7mm shaft on the stepper I have. What voltage could my stepper be run at?

I believe so.

I personally buy them from Zappautomation (http://www.zappautomation.co.uk/electrical-products/stepper-motors/nema-23-stepper-motors/sy60sth86-3008b-nema-23-stepper-motor.html) , cause at the time it happened that he responded faster my email. Plus he is active here at the forums. If i was in UK i would buy all from him. Now i buy a lot of stuff directly from China, due to the low euro/gbp and shipping costs involved of receiving materials here in Spain.

But if i learned one thing with the CNCs is that the main and most important thing you buy is the support, so many times saving a couple of $$ could result in weeks frustration and inability to produce during that time.

06-06-2015, 12:47 PM
Thanks. Shall check them out too.