8x4 Router build thread

[Jonathan]

I have to agree with mark here...

I predict from your drawings that you will have lots of fexibilty troubles resuling in a really disapointing experience (unless your cutting polystyrene)

Yes! It's interesting though - you've gone for very expensive aluminium extrusion which is good for rigidity and yet very cheap, and in my opinion a bit dodgy, bearings. I think you'd be better off investing that money in proper linear bearings from eBay (look up linearmotionbearings seller and send him a message with the sizes you want - may be pleasantly surprised). What your doing on the X axis relies on the steel strip having a constant width and doesn't account for wear. It would be better with the bearings sprung. There will be a lot of force on each bearing, and due to the small contact area in your design a lot of pressure.

your Z axis travel seems abitious.
... imagine your Z axis at the bottom of its travel, if you put some pressure on it in the XY plane i imagine it would flex millimeters rather than tenths of millimeters:sad:

Again, yes very ambitious... I went for 400mm Z travel on my machine using 20mm thick aluminium plate for the Z axis. It still flexes, not too much but enough to stop it machining metals. A lot of my flex probably comes from the gantry so I'm going to lower that.

It's not really worth thinking about the B/C axis untill the other bits flexing are sorted as it's only going to add more flex/overhang to the design. That's why I've left my B/C axis design for now, still planning it but I'll only make it once I've done the steel frame for my machine. The following drawing shows the general idea/shape. The 'C' shaped bit that holds the spindle will be made with something thinner with a gap between and possibly welded to make it strong enough. I've calculated for the final belts I'll have to use 25mm wide HTD to get it strong enough. Two belt reduction on both axis with 3nm motors. Bearings will all be tapered roller bearings ... etc:



The centre distance of your belts looks too small for the ratio. You should aim for 6 teeth engaged on the smaller pulley.

[Zebethyal]

I replied to the first response shortly after it came in, but my post is still not showing after 2 days.

I appreciate that new members posts are vetted for the first few occasions, but having to wait 2 days for a post to appear is a bit much.

I agree that a shorter X in preference of a longer Y would be more rigid, and this is how it was originally designed. The idea was dropped because of the increased cost. However I have since dropped the profile sections on the Y axis so it should be cheaper again - I am mid re-design on this again to see how it looks and costs out.

I also agree about the potential flexibility of the Z axis, which also has around 400mm of travel, especially with the B/C ideas that could have all sorts of slop in them - a more stable B/C would be a lathe type design on the bed that could either use one of my trunion designs or simply be a chuck geared down to a stepper with a tailstock.

I am also going back to some homebrew versions of the 'CNC router parts' carriages and some thicker steel for them to run on 6mm instead of 3mm, still redesigning the X/Z carriage interface.

Image shows the carriages on the alternate Y axis design.

Zebethyal