My first post (I think), although I've been lurking here and some other CNC forums for ages.
I've decided that I'd really like a CNC machine, to build various little parts for my track day car etc and also because I just like playing with computers anyway.
The problem is that I'm not sure if I'm better off converting an existing mill, e.g. the Arceurotrade sieg sx1 (long table), or one of the sub 500 pound machines from Amadeal, or if I should build my own router.
The materials I'd be cutting into would be aluminium and various plastic - I don't think I'd need to mill anything in steel. The largest part I can see myself wanting to machine is something like a dry sump pan (would need about 25 x 25cm x 3cm for my engine), but the majority of parts would be smaller and thinner than this. The pan would essentially be one big pocket in a block of aluminium (well, not quite, but that gives an idea of the amount of material that needs to be removed).
I wouldn't want the machining to take more than say 8 hours - does anyone know if this is realistic with one of the smaller mills? As my garage is mainly full of a car and various spares, I don't have enough room for a big machine (in fact, I had to sell my centec 2c due to space constraints :( ).
The other alternative that I keep returning to is building a cnc router. I'd be going for a welded steel fixed gantry design with an effective work envelope of maybe 50 x 60 x 10cm.
Do you think this would be a better bet for the kind of projects outlined above? I'm worried that if I buy one of the smaller mills, everything will take absolute ages to make, which kind of defeats the purpose, so which is faster? Router or mill? :)
Any comments appreciated, as I've been procrastinating for far too long already.
I have a long table sieg sx1 under diy CNC control, it makes for a fun project and it is a game little machine. A bit bendy for steel work perhaps but certainly capable of munching aluminium. It is also a pain in the arse.
With respect to your post:
The max spindle speed, 2000rpm, is almost okay for aluminium but I think you need something quite a bit faster for plastic.
Y travel is only 140mm so for a 250mm piece you would need to rotate the work half way through the process.
With respect to CNC:
Z control is random, sometimes the head will dip down a fraction when the screw is driving it up and sometimes the head will stick for up to 0.5mm when commanded down. The ways, guide rails for want of a better description, on the back of the head are just too short, the adjustment way to twitchy, there is no real, long term fix.
The X and Y backlash adjustments do work but are not designed for the sort of continuous back and forth movements you end up asking during CNC operations. Over an 8hour job you'll be able to see the errors starting to creep in.
The ways all around, metal to metal, dove tails with gib strips are likewise not designed for 8hours of continuous motion. The X especially starts to show slop at the end of a hard day.
So, £700 - £800 for the X1 + motors + drivers + home made hardware, quite a bit more if you buy one of the commercially available kits. I'd seriously consider some other options.
You'll be able to build a CNC router capable of machining aluminium for about (ballpark) the same cost as CNCing a reasonable size mill. the X1 size of machine sounds too small for your needs, sounds more X3 sort of size so you're looking at £1200 or so before you start. You'll still need to add ballscrews/motors/drives and like all things retrofitting to an existing table involves some machining operations that are hard if you dont have somehting to do them on to start with (or £2000+ for the commercial kit). Bootstrapping a new build is much easier IMHO. By all means consider an X1 to help build the bigger machine and keep it as a manual unit for those small/quick jobs where setting up the CNC is overkill.
Build this style machine in steel and you wont get cheaper for the same strength (use supported rails thou.!!). It will match any cheap mini mill. Problem with Mini mills and aluminium is the spindle speed.? Far too low to give decent feed rates. Higher spindle speeds are much better in alu and mixed with flood coolant then you can shift some serious material and still have a very nice finish.
Thanks for all the comments, guys. Exactly the kind of real world experience I couldn't find using google :)
That machine linked to above looks fantastic! I think I'll end up building something of similar size to keep as much rigidity as possible.
Just to give a little update to this thread, I actually went and bought a very cheap adcock and shipley horizontal milling machine on ebay instead, ahem.
It is a production style machine, so pinion/rack on the x axis, and also not on the z-axis, but the y axis at least has an acme lead screw with 0.001" backlash.
Compared to my old centec, this machine is in way better condition, with no discernible play on the table, but obviously the x and z axis have to be sorted for it to be sensible.
I'm currently in the process of converting the x axis with a m16 threaded rod (i know, i know), as it's what i had lying around. Obviously not ideal, but a huge improvement on 1 turn = 5 inches :)
My plans for the machine is to use the horizontal part as a little lathe (er40 collet to hold a bit of bar), and i'll also make something to hold a small lathe chuck for non circular work pieces.
I'm also going to build/bodge on a vertical head of some sort, with built in travel, as that essentially sorts the z-axis issue (I can move the z-axis, but it requires gorilla strength).
Might keep this machine as a manual one and use it to build the parts required for a CNC machine, as suggested earlier in the thread, as I'm guessing it's not ideal for CNC conversion, given that the table doesn't sit on rails etc.
As for CNC machines, I'm thinking of starting off with a CNC lathe instead of a milling machine, seems more useful for the bits I need doing for my car hobby.
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