Small Mill very early design stage

[leadinglights]

Why do I need accuracy? I am afraid the best answer I can give is, in the words of Sir Edmund Hillary, "because it's there". In constructional hobbies, and this is my hobby, most people strive for some principle in what they make: elegance, simplicity, beauty etc.. For me, the principle is accuracy.
As far as expence goes, what is a reasonable price to pay for a CNC milling machine? If you regard Arc Euro Trade's KX1 at £2350 as reasonable, then I think that I can build something quite special for less than that - especially as I have controllers, stepper motors etc.
What will I make with it? Clocks, small but accurate tools, a co-axial brushless DC motor for a model aircraft, wax models for investment casting, you name it. How long will it take? A couple of months if I work on it all of my spare time, a year ot two if I only spend the time "She Who Must Be Obeyed" allows me, but probably somewhere in between. Will it be worth it? If you are in business the answer must be "Hell no!" but if you are a hobbiest then the answer is "Damn yes!"
Regarding the idea of using Peltier temperature control. After the normal suspects, backlash, vibration etc., thermal differences in the workpiece and machine contribute a lot to errors. Controlling the temperature of bits that get hot such as the spindle and table, and bits that are long such as the upright bits of the gantry with Peltier devices is cheap - about £5 for a 90W device and somewhat less than that for the bits to control it, a few pounds for heatsinks and tubing and perhaps £20 for one of the water cooled radiators sold to computer modders. Including fans and concertina hose to dump the stepper and spindle motor heat outside the case I think there should be some change from a couple of hundred pounds.

[Robin Hewitt]

Hmmm

Perhaps confidence is that feeling you get just before you understand the problem? :whistling:

I don't think you have to worry about heat quite yet. I suspect you are losing the plot and zooming off on a tangent.

You need a lot of iron and the cheapest way to get it is an older machine that you tart up. Scrape the slides, add ball screws etc.

It may seem a good idea to buy a shiny new wonder mill aimed at the CNC hobby market, but an older industrial or (better) ex-school machine is probably a much better bet, not so pretty but considerably cheaper and with more possibility for improvement.

I suggest you aim for 5 micron accuracy, the resolution of your everyday digi-caliper. You will then get 25 microns fairly easily. You will then realise 25um it isn't enough.

If you shopped with 5um in mind you don't wind up replacing the whole works like I had to.

Robin

[leadinglights]

Hmmm
...
I suggest you aim for 5 micron accuracy, the resolution of your everyday digi-caliper. You will then get 25 microns fairly easily. You will then realise 25um it isn't enough.
...
Robin

Hi Robin,

1 thou , 0.001 inch, 25 microns for the youngsters, is quite easy over a small distance with a well adjusted machine, but gets progressively harder over long distances. I have aimed at this over the 200mm by 200mm by 100 mm range, quite tight enough - and even if I get close it should be good.

I have rejected converting an old milling machine on a simple basis, space available is of the order of 1000mm by 600mm including access so say 600mm by 600mm.