Comments sought on new build: A CNC Router for RC Gliders and Planes

[njhussey]

Sliding carriages along the rail gives some indication of the straightness, but very little indication of the twist. Fortunately for us these rails have very low co-efficients of friction, but when it comes to aligning them this makes small errors in straightness harder to detect as they don't produce much force.

Using an indicator mounted on one rail carriage to measure and fix the distance between the rails is good once you've got one rail straight. If you do if before then, you'll just copy the error - so if one rail is banna shaped the other one will be the same banna shape. To be fair that's still better than having a banna and some other fruit...

From a practical point of view, if you've got the rails aligned well enough that the bearings run smoothly then the bearings should last a long time, so it's arguably OK to use but you will need to have realistic expectations of the accuracy.

Surely the twist will be sorted when the rail is bolted tightly down, that's assuming that the epoxy is perfectly flat of course?

I'm going to use the sliding carriage method to drill and tap the holes, there is a clearance of 0.5mm either side of the bolt in the rail hole so plenty of room for adjustment. When I get the tooling/eco plates I'll be machining a reference edge to mount the carriages to the bottom piece of Ali, then the gantry will have a reference edge to mount the carriage plates to and thus I hope the gantry will be straight/perpendicular/parallel etc. etc. so that when I bolt the carriages to it the second rail will be referenced from the first which will be as straight as I can get it without having a machined reference edge in the epoxy to go on.....if that makes sense?

I think I'll get a straight edge, that will help with twist and straightness....plus the above and it should all be as acurate as it's possible for a bodger like me to get

[JAZZCNC]

Surely the twist will be sorted when the rail is bolted tightly down, that's assuming that the epoxy is perfectly flat of course?

Gezzzz People have too much trust and expectations of epoxy.? You can't beat checking so buy or make a straight edge to confirm if you really think you need that level of accurecy in a router.!!!

When I get the tooling/eco plates I'll be machining a reference edge to mount the carriages to the bottom piece of Ali

Why waste money on Eco-cast if your going to mill the ground surface away.? . . . The whole point is the accurecy of the ground plate and no matter how careful you won't mill to same level as grinding gives.!

What I do with ground plate when I need a ref edge is mill pockets on the ref line and insert aluminium dowels 3mm proud of surface. Then I machine half the dowels away to the plate surface leaving me machined ref edge without disturbing the ground plate.
Like this.

[mekanik]

Have to agree with Dean, can't see the point in going to all trouble of designing your machine, getting feedback from the experienced members and then making a horses arse of aligning the rails at the last hurdle.
No offense intended.
Regards
Mike