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The Emco UM630 will meet all of your requirements with 5 axis simultaneous capability.

The Denford Triac (cnc mill) almost makes the 300mm X axis only misses out by 10mm and they do come up occasionally with ATC using BT30 or BT35 tooling but may not meet your 10 micron spec, but there are not many machines available that will hold such close tolerances.

Emgee

If worst case 10 micron accuracy is really needed then you're into mid to high range professional machines. Converting a manual mill on the cheap simply isn't going to cut the mustard.

For a start you'll need high end ground ballscrews and ideally low friction ways. Conventional ways have static friction that will exceed your accuracy requirements – ideally you would need a closed loop system with an independent measure of position.

JasonB makes a good point on spindle speed, for aluminium you could easily make use of 10k+ rpm.

I have a Tormach CNC mill. I think they claim something like 1.3 thou per foot basic accuracy based on the ballscrews. I reckon I normally achieve 1 to 4 thou depending upon cutter, toolpath and material. I think the smallest step on the Tormach is about a tenth of a thou, but there is at least half a thou of lost motion due to stiction and probably another thou or so due to backlash.

Some years ago I had a heatsink machined by a professional machine shop as I didn't have the time to make extra ones. Unfortunately they made rather a mess of it. So I ended up making detailed measurements of one made on my Tormach and one made on their professional CNC mills. I had errors around 0.03mm to 0.05mm whereas they were a bit better at 0.02mm to 0.03mm, but still a long was from 10 microns.

You will also need a fairly sophisticated controller. Quite large errors can be caused by changes of direction in machining if the controller and/or the CAM software don't look ahead and change feedrates or make changes to the toolpath to compensate. A simple case to consider is machining a rectangle. The table can't change direction instantaneously at each corner but will tend to overshoot slightly.

One other point, the specified Z movement is far too small. It won't accomodate varying work pieces or simple tool changes.

Andrew

Plus 1 for a Denford Triac.

They're a good machine of about the capacity you're looking for and can be tweaked quite easily to get more out of them.

I haven't systematically done any tests for accuracy, but I think I'm getting around about +/- 0.01mm on the parts I make on mine.

I've added a counterweight to the head on mine for less stress on the stepper motor drive and I've also added a spacer between the column and base to give me more working height.

Mine is running Mach 3, but I want to upgrade to PlanetCNC as soon as possible as that's the controller I use on my lathe and I'm very pleased with it.

Martin.

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It would certainly be easier if you are right, Barrie … but the statement does seem pretty explicit:

“Most work will require precision, +/- 10 microns at the very worst.”

MichaelG.

It would be good to have clarification on whether the OP meant resolution, precision or accuracy…as well as what "worst" means. The lack of current machinery indicates an upgrade of an older CNCmachine would be better.

There quite a number of Denfords around, Novamill and Triac, which might meet the requirement. If you are lucky they would be without the old electronics which is very outmoded and cheap to replace with modern hardware, software and drivers. Denford machines were often bought for education and may well have had an easy time given the lack of trained teachers!

In a similar position to the OP but with a working lathe and big mill I bagged a Novamill without electronics on eBay for 600 squids and built new electronics for less than 200.

I agree with mick above, conversions always seem to me to be a compromise between a purpose built CNC and converted manual machine.

I also have a Sieg KX1 and think it's a great little purpose made CNC mill. I've not inspected every single piece of work it has done, although everything has come out pretty darn good, it is advertised at 0.01mm repeatability. So just under half a thou isn't too bad, not far off the accuracy you are after.

A purpose made machine looks like the sensible option.

IanJ

I bought my KX1 from arc euro over four years ago. Soon after I bought it arc euro had issues with back up and servicing of the machines, so decided to exit the CNC market. Axminster as far as know still sell them under their own banner and colours, in an enclosure. But due to the coronavirus may be having difficulty getting machines.

Can't remember the last time I saw one for sale, I think people keep hold of them because they are good machines.

IanJ

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