Hi,
I guess the ground C5 and support bearings is the most cost but out of curiosity what the heck you are doing Craig and you need such a precision? Perhaps a machine shop?
No, nothing like that. I made a mini-mill (travels 180mm x 180mm x 180mm) with 20mm C5 ballscrews, 15mm linear rails on cast iron beds eight years ago. I made it mainly for making
circuit boards but wanted to be capable of milling steels as well. It was just barely capable of milling steel, despite being all cast iron and steel construction the cutting forces caused enough
flexure to interfere with cutting accuracy.
I could perhaps have modified it to overcome most if not all of its shortcomings but really wanted to build anew incorporating what I had learned. It was always my intention to get cast iron
axis beds cast for me, and that rather set the tone throughout the design and build. My previous mini-mill also cast iron axis beds, but I milled them out of large cast iron elevator weights
I bought from the scrap yard. They worked out pretty well but the cast iron of a weight is pretty poor, it had inclusions and a really hard and abrasive outer rime. I swore the next time I would do
better, and I did but the cost....oh crikey... the cost!! The castings (3 at 115kg each) cost $3500NZD, and the machining and stress relieving cost another $6000NZD. I sort of have to consider
that I did not control the costs as I should have, and that could be considered a failure, however I've got a superb result and that's what I paid for.
Finding the ballscrews I mentioned was another important part of the project. Ground C5 ballscrews are really expensive, that I was able to find three matching ballscrews in near new condition
for 1/5-1/3 the cost of new allowed me to proceed. Because the ballscrews are all the same length the travels are cubic, that is to say 350mm x 350mm x 350mm. From the same Korean company from
whom I bought the ballscrews I also bought three matching pairs of 20mm HSR (heavy duty) linear rails by THK, they were new old stock, and was able to buy at a much better price than new.
I decided that I wanted servos for this build, so bought a 400W Delta B2 series (160,000 count per rev) AC servo. It far exceeded my expectation of performance, so I then bought three
750W B2 series servos, one with a brake for the Z axis. They have proven to be superb.....and they EAT any stepper ever made!
This is still a hobby mill, but I use it daily for work. Mainly for making circuit boards, for which its is overkill, but also for many small parts in brass, aluminum and plastics for automotive instruments,
but I now also have genuine steel and stainless capacity, which was always my intent starting eight-nine years ago.
Craig
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