I have been lurking around on the site for quite some time now reading all the build logs for various sized machines and the advice people have been offering and it has been extremely eye opening and has change my plans of what I have wanted to build several times over I am finally at a stage where I beleiev I have a reasonable budget to not be scrimping on parts to build something half decent and with the advice of others I can only imagine it will get better!

a bit of background.....

...... my previous experience with CNC was with a 3 axis chruchill matrix cnc lathe which was an enormous beast in comparison with what I am intending to build. I want the machine to be capable of machine hardwoods, aluminium, plastics etc at a reasonable DOC, the mill is not for one specific task as it were as I am always up to all sorts so it needs to be big enough to allow for a wide variety of parts to be made but I am limited in space so it really cant be too big.

Current thinking :

Rough dimensions: 120 x 800 table size

Steel box section construction

2.2kw chinese spindle

x\y running on fully supported rails, z on hiwin profile rails

16mm ball screw (twin drive x axis) singles on y and z

Potential for manual adjustable bed height (bolts out move it bolts back in)


At the moment I am working away in solidworks to develop the design a bit further before sticking it up on here but I thought I would air a few ideas first incase I need to make some changes straight away.


My main issue at the moment is to do with the fully supported rails vs the hiwin style bearings. I know this is always the case and a lot of the deciding factor can be down to cost which is not the only reason for asking this as if I can find a way to use them I will do.

First off making a machine of this size, what size rail would I need in terms of the hiwin rails bearing in mind the main gantry will be a large piece of steel box section at the moment.

I know some peoples opinions of the open ended bearings are that they are terrible, other than using hiwin is there anyway to make them any better? using more carraiges under the gantry 3 per side? 2 above 2 below connected by a plate on the x axis as you would do on the y axis so the openings are opposed?

I would like this machine to be pretty accurate if I am going to the effort of investing time and £££ into it and am I going to be utterly dissapointed with these linear bearings over the profile rails.

Thanks for reading and I hope this thread will come togther to form an interesting build once I get going soon.

Cheers

Francis