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

[Lee Roberts]

Neil, fix a nice plate to both bearings on your choice of master rail, then pop a clock dial on via a mag base featuring a long reach arm/boom to get to the other rail with the clock, then traverse the master rail via the plate and bearings dialing in your second rail as you go.

Ideally you would want to do this with out the bearings and plate and so just moving the mag base along the master.

That's how I always do it for the machines I build from wood .

.Me

[njhussey]

I've decided to cut the 20mm piece of Ali I currently have to the correct width for the bed which will leave me a 100mm (ish) wide strip 1000mm long (ish) which I can use for mounting blocks. I'll cut a piece 200mm long and machine a carriage block...



Then after attaching the carriages on the master rail I'll move it up and down and clamp the rail ready to drill.

I've made a small drill guide to go in the rail so the drill bit is kept at 90° (or as near as damn)




I've put a piece of 10mm Ali plate on the bed and moved my Pillar Drill on to it to drill the holes, a bit like below...



Should make drilling easier (but slower) and I hope not to snap any more drill bits as I snapped one in an end hole on the rail

[EddyCurrent]

Neil, It's obviously best to drill the holes spot on but if they are tapped at an angle it's wasted effort, I like your drill guide so maybe a similar thing is reguired for the tap or maybe you could just open out the drill guide hole slightly.

[njhussey]

Neil, It's obviously best to drill the holes spot on but if they are tapped at an angle it's wasted effort, I like your drill guide so maybe a similar thing is reguired for the tap or maybe you could just open out the drill guide hole slightly.

Funny you should say that....I've just made a tap guide as I had that very thought. Will be tapping them by hand, shant be impatient and use a drill!

[Jonathan]

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.

[EddyCurrent]

Sliding carriages along the rail gives some indication of the straightness, but very little indication of the twist.

He's right, I forgot about that. Neil just go and buy a straight edge I remember putting one across the top of my rail bearing beams to find they were leaning out slightly. This was due to the welding process but the epoxy job brought it right again. I did however put the straight edge across the top of my rails once fitted to ensure they were still level. Obviously if they are out and you bolt down the gantry cross member there will be a lot of stress put on the Hiwin bearings.

[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

[JAZZCNC]

so it's arguably OK to use but you will need to have realistic expectations of the accuracy.

Bingo he's Hit the nail on the head.! . . . . . . . People are getting silly on this forum regards the level accuracy they are trying achieve or THINK they are achieving with what is essentially Cave man tools in engineering terms.

Be realistic and remember it's a router based machine that will probably spend most of it's time cutting materials that have high variations of in-stabilty that far excede the accuracy machine can cut too.!

If you take your time to align the rails with sensible means IE: Clive S suggestion of taught wire along with feeling of bearings etc you'll be very close if not spot on for the use of the machine.
Yes rail alignment error will affect performance and live span of the rails but with care and patience the level of error will be so small to make little difference at DIY levels. Even in small/medium scale production enviroment it will take good few years to have any affect on wear if care is taken on setting up and alignment.
Just throw them on and you'll pay the price but with careful setup and sensible attention to detail you won't go wrong.!! . . . . Stop over thinking it and take sensible precations with checking straightness/twist along with feeling your way and you'll be fine.!! . . CRACK ON