A3 Router Build

[Jonathan]

Another question. What methods do you use when mounting your supported rails to RHS to ensure they are straight, level and parallel to each other and the ballscrew.

Since we can't machine the mounts for rails/ballscrews etc accurately enough for them to be fixed you need to build in adjustment. For instance to get the rails parallel you can start by fixing one down parallel to the frame, then attach the linear bearings/gantry to it and move the gantry back and fourth such that the other rail self-aligns to the first rail. Then put one bolt in it, move the gantry and check it's still smooth .. keep adding more bolts checking each time that there's no binding. That will get the distance between the rails constant, but it wont correct for any bend/bow in the rails. To do that you need a precision straight edge, or tensioned wire to act as an accurate reference from which you can measure to set the first rail. For the majority of DIY machines that's taking it too far.

You set the ballscrew in a similar way. First fix the motor end and ballnut, then run the ballnut to the other and fix the end bearing so that the ballnut aligns. Check it's smooth by spinning the screw by hand and if not adjust. If it's tighter towards the ends of travel that implies the centre height of the ballnut is slightly off, so adjust it...

You can of course do things in a slightly different order so long as there is sufficient clearance or adjustment in the mounts to obtain perfect alignment.

Also have you considered increasing the spacing of the X-rails? That should reduce deflection parallel to X when the tool is near each end of the gantry.

[GTJim]

Thanks for the reply Jonathan, and I will space the X axis rails further apart.
So if I’ve got this right, this process should work.

1. Position one of the X axis rails to the frame as straight and parallel to the frame as possible, using a taught wire or other method.
2. Using a transfer punch mark the fixing positions of the rail support to frame.
3. Drill, tap and mount rail, and recheck straightness.
4. Roughly position second rail and mount a jig/fixture to the bearing mounting blocks on both rails, and slide back and forth adjusting the second rail until motion is smooth.
5. Mark positions of fixing positions onto frame and drill, tap and mount second rail.

Up to this point I think I’m Ok. The problem I see is due to the FK and FF supports for the ballscrew. These don’t seem to allow for any adjustment as the fixing positions would need to be made in the frame prior to fitting?
Maybe I could fix the FK support directly to the frame and amend the design to allow for an adjustable plate at the FF end.
Would I need to have the table made and fitted at this point to attach everything to it?
How would you ensure the rails were level vertically in the Z axis as this could result in the rails being like a wave. Should you shims or use some sort of leveling compound and how would you measure it?

Jim