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

[njhussey]

Depends on whether you have a gantry to use as a gauge? I had built the structure of my gantry in advance for this purpose, so I bolted down one rail along the box section centre line, placed the second rail on its box section, and attached the carriages to use to align the rails. I think, in essence, you are doing the same thing but you will then pick off the rail spacing dimension to finalise the gantry. Hiwin recommend aligning the rail against a machined step but where this is not possible you align the second rail from the first. My only reservation is how you guarantee the straightness of the first rail but I think you can finally adjust this by test cutting. I hope so, anyway!

Looks a nice epoxy job.
To fit the first rail I clamped a good wide straight edge on top of the beam then butted the Hiwin rail up to it, like Neale said about the machined step. Then I mounted the gantry and used the bearings themselves to line the second rail, just nipping the bolts up slightly. Before fully tightening the second rail down I put the straight edge up to it to make sure there were no kinks. After that I also checked the distrance between them at points along the length just too make sure they were parallel.

Thanks guys.....

I'm going to do a similar thing to both of you. I don't have a good straight edge that I can butt the rail up to so I'm going to use the first rail as a reference and use the dummy gantry to get the second rail square to the first. Regarding striaghtness of the rails I might look at using a small laser pointer that I have to shine along the length to check for any bend in the rail, not sure if this will work but don't see why not in principle?

Got some more cutting discs (and G clamps to clamp the rails) on the way in to work this morning so I can cut the second rail to length. Looks like it's going to be lots of drilling and tapping today, hope there's not too much proper work to get in the way of doing this...!

[JAZZCNC]

But how do you know the first rail is striaght.???

I wouldn't waste any time setting the second rail without the gantry on the machine. Set the master rail straight and parallel to frame then run set slave rail using gantry running up n down feeling your way along as you tighten up the rail. . . Feel for binding is a very good guide in setting up.!

[njhussey]

But how do you know the first rail is striaght.???

I wouldn't waste any time setting the second rail without the gantry on the machine. Set the master rail straight and parallel to frame then run set slave rail using gantry running up n down feeling your way along as you tighten up the rail. . . Feel for binding is a very good guide in setting up.!

Dean, how do I make sure one rail is straight without buying a proper striaght edge? My frame is not straight enough to align the first rail, or at least I don't think so as it's just plain 100 x 50 x 4mm steel, with any sort of accuracy?

I was thinking of getting some of my 10mm thick Ali and using the milling machine machine as much as I can down one edge and then turn it round and then using my edge finder set it parallel again and machine the rest to give a straight edge. Would this do?

[Clive S]

Dean, how do I make sure one rail is straight without buying a proper striaght edge? My frame is not straight enough to align the first rail, or at least I don't think so as it's just plain 100 x 50 x 4mm steel, with any sort of accuracy?

I was thinking of getting some of my 10mm thick Ali and using the milling machine machine as much as I can down one edge and then turn it round and then using my edge finder set it parallel again and machine the rest to give a straight edge. Would this do?

How about using some fishing line stretched very taut along the length. ..Clive

[njhussey]

How about using some fishing line stretched very taut along the length. ..Clive

Wouldn't that be a little flexible? Plus I've got an end stop on one end so can't wrap it round the rail, would have to accurately drill a hole through the steel.

Just looking at a Veritas straight edge http://www.axminster.co.uk/veritas-steel-straight-edge which I could clamp to the rail to keep straight?

[Clive S]

Wouldn't that be a little flexible? Plus I've got an end stop on one end so can't wrap it round the rail, would have to accurately drill a hole through the steel.

Just looking at a Veritas straight edge http://www.axminster.co.uk/veritas-steel-straight-edge which I could clamp to the rail to keep straight?

You could clamp the line to the rail with a spacer say 1mm between the rail and line then do the same at the other end with spacer. With the line tight you can then measure with a feeler along the length after fixing one end first. ..Clive

[Neale]

As Jazz said, sliding a carriage along is a pretty sensitive test of whether or not the rail is fairly straight - you quickly feel the graunching sensation if it isn't! My design uses an aluminium block with two carriages bolted to it (gantry then bolts to these later) and having two carriages fixed in line is even more sensitive. No way am I going to buy a 1.8m straightedge for alignment purposes.

Just bolting it down by eye (I loosely bolted one end of mine, then wiggled it a bit to let it find its own line) is probably good enough for a first pass, with a sanity check of running the carriage up and down. It's not going to be many thou' out, I reckon. I then set the second rail to this, knowing that it's probably not absolutely straight but good enough to work, and will then fine-tune it by cutting test pieces once the machine is in a state to actually cut something. It's another example of the "you can't build it accurately enough but you can tweak it afterwards" home-workshop approach...

[EddyCurrent]

Got some more cutting discs (and G clamps to clamp the rails) on the way in to work this morning so I can cut the second rail to length.

I rarely use metal cutting discs so I bought these after reading the description, I was amazed how good they are; quick, little mess, cuts rails like butter. !00 times better than the thicker type.

http://www.toolstation.com/shop/p39737

[njhussey]

I rarely use metal cutting discs so I bought these after reading the description, I was amazed how good they are; quick, little mess, cuts rails like butter. !00 times better than the thicker type.

http://www.toolstation.com/shop/p39737

I've got some 1mm thick ones, as you say they cut through the rails like a hot knife through butter. I've got the Y & Z axis rails to seperate (curently two rails 1100mm long with 4 blocks on each soon to be split.....) but now thinking of making the Y axis rails longer to get the carriage spacing wider. Just re-drawing it to see if I can get away with slightly less Z axis travel.