My 1st Homebrew CNC has started.

[Kammo1]

Hi guys, after many months in fact it seems more like years I have finally started my 1st CNC build consisting of 20mm MDF,Oilite bushings and ground linear rails.
Well have to admit given the chance to start again and recommending what I have learnt and messsed up I certaily would not use the oilite bushings ever again, they are most unforgiving and if you think that you can drill 2 holes a said distance apart like I did and get it right 1st time "WRONG!" literally every piece of the build I had to make 2-3 times very frustrating and very annoying, to be honest if I had taken the angle and skatebearing approach this machine would have been finished as regading all the linear motions working ie X Y and Z.
I started with 2 X 1 metre long 20mm OD ground steel rods for the X axis ie forward and backward motion, 2 X 600mm long 20mm OD ground steel rods for the Y axis left to right motion and 2 x 16mm OD for the Z axis, I thought I would have a generous size machine capable of cutting a good size of work when it comes to showtime.
I started the machine on Monday and have built the main gantry as well as the Z axis and again without alot of frustration with the bushings have now got the machine moving by hand very smoothly and there is virtually very,very little play and should eventually once its showtime cut and produce some accurate results, although I will only cut wood parts it should be more than adequate but again we will see as mister "sods law" hasn't reared his ugly head again. The Z axis should have a range of between 3"-4" inches of travel more than I need.
I will use for the X axis motion the skatebearing/angle approach as I cannot for the life of me go through with the problems that I had with the rest of the build and I am almost 100% positive this will produce a beautiful smooth motion for quite a reasonably heavy gantry. I will try and get some pics up tomorrow so I can show you all how its turned out and have to say its quite a thrill to be making my own CNC as I have trawled this forum endlessly searching for tips,plans etc,etc although I have quite honestly not worked from any plans but built and measured as I have gone along and have enjoyed it very much.
I will be starting to think about leadscrews and the drive components so would like any help I can get in what would be reasonable components to use. I have thought about using 8mm threaded rod which I can get here in the UK from my local Screwfix or B&Q depot and using a skate bearing to hold the rod in place as its a perfect fit "BUT" for the life of me I cannot think how to fix it in place ? I know that when the stepper motors are fitted I will use an adapter from 1/4 inch or 6.35mm to 8mm but how do I fix it at the ends of the rods to keep it spinning freely and keep it in place without moving ? I have tried to look at other builds but cannot for the life of me see any pictures of what I need to do. I thought I would ask here as I do not want to drill any unecessary holes and risk making errors as I do not want to go about making what I have got moving perfectly again which I know will present me with problems, any help and advice will be greatly appreciated.
I guess the main thrill for me is learning what to do and not to do and have this machine build me my next one which will be an awesomme task and more accurate and I have loads more other questions but I'll save them for later.

[irving2008]

Kammo,

Attached is a sketch I did for 10mm x 2mm trapezoidal threaded rod turned down to fit into 22x8x7 skate bearings... but the same idea could be adapted for 8mm threaded rod...

the circlip could be replaced by another nyloc nut, the idea being to lightly grip the two bearings in the block to remove the end-float... The dual-bearing is at the far end, the sliding bearing at the stepper end...

Skate bearings aren't great at handling axial forces, individually they have a lot of end-float. The approach above addresses that moderately well but introduces quite a lot of friction unless things are lined up perfectly.

Alternate (and better = more expensive) options are
- the shaft should be supported by one bearing with a thrust bearing either side to manage axial forces (the thrust bearing being a ring with embedded balls)
- the bearings shown should be replaced by angular contact bearings set with opposite tapers. Angular contact bearings handle axial and radial thrust well....

hope this spawns an idea or two...

[fatal-exception]

Irving has it right as how to lock the screw in place, but if you decide to use nylock nuts, drill and tap them or they will be a perpetual annoyance when they loosen and introduce a ton of backlash to your axis'.

Check out nookindustries.com. They show how the profesional stuff is done. Glean your own ideas from that.

8mm might be a little small for a driving lead screw. Think more like 16mm...

Paul