1st Build, Second machine

[m_c]

12mm alli is pretty substantial, and I'd hazard a guess it would be fine, but I'm sure others will have a better idea than me!

Regarding the rails, I was actually reading about them the other day (can't remember if it was on HSM, CNCZone, or the Mach Forum!), and the general consensus is most hobby builds are majorly over engineered, as there was some big commercial machine running 15mm rails for the long axis. The only reason I was reading about them, is I've got plans for a new machine bubbling away in my mind, and linear rails are featuring.

[Jonathan]

Regarding the rails, I was actually reading about them the other day (can't remember if it was on HSM, CNCZone, or the Mach Forum!), and the general consensus is most hobby builds are majorly over engineered, as there was some big commercial machine running 15mm rails for the long axis. The only reason I was reading about them, is I've got plans for a new machine bubbling away in my mind, and linear rails are featuring.

Looks like we've been reading the same things. I agree that if you calculate based on the load ratings they seem plenty strong enough...I'm going to use them on my machine unless some >15mm turn up cheap on eBay. I think that's the reason most people use bigger, because it's what was available at the time on eBay.
You may need to watch out for the moment ratings, though for the size of your machine it should be fine, just space the rails out on each axis as far as you can.

(That's a bit vague I know, I can give some numbers/examples if required)

[m.marino]

Jonathan are talking to m_c or me on the rail spacing issue? Also you what would you charge to mill the bracket we are talking about for me? Well back to working on the drawing and setting things up as need be.

Michael

[Jonathan]

Jonathan are talking to m_c or me on the rail spacing issue?

I was talking in general really. On the axis the Z-axis is attached to in particular (Y in your case), the further apart the bearings are the lower the force on each when cutting and (to a lesser extent) accelerating. If you take moments in the X-Z plane then it's pretty obvious why...

Also you what would you charge to mill the bracket we are talking about for me? Well back to working on the drawing

I'm not so sure what's required. I can let you know when you've done the drawing...

[m.marino]

Okay,

Let's see if I can get these files up properly.

Sorry that they are jpeg's as it would not let me load the .dwg or .iges file format. That is the bracket I designed to go with a dumpsterCNC anti backlash nut for a 12mm trapezoid leadscrew. Clearance is only 40mm in height. Any opinions???

Also Checking on available box Aluminium in the area but is looking like I have a really good source of off cuts (some over 2 metres) of 12mm Aluminium plate. Any and all views would be greatly appreciated.

Michael

[Jonathan]

How are you joining the two pieces together? That joint needs to be strong so that an axial force on the screw does not bend the bracket. I'd be inclined to either make it out of one piece, or use something thicker for the vertical part.

Also Checking on available box Aluminium in the area but is looking like I have a really good source of off cuts (some over 2 metres) of 12mm Aluminium plate. Any and all views would be greatly appreciated.

Excellent, can I have some ?

[m_c]

Looks fine. If you can't find a bit suitable angle, it could be roughed from a bit solid alu with minimal effort.

Or if you could survive with steel, I might even have a bit suitable angle lying around (I think I came across some 2 or 3" angle during a search for something else the other week!).

Excellent, can I have some ?

I'm nearer and can collect :naughty: