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

**JAZZCNC** · 24-01-2014

Originally Posted by njhussey

I started cleaning up some of the welds but there's a lot of that to be done as my welding is rubbish! I also put on (at Jazz'z suggestion) a piece of 50x6 flat on the end of the rails to act as a stop for the gantry when it goes vertical.

At the moment my machine is back on it's feet for some recent repairs and I can tell you I really miss it being vertical.?
Not just for the space but for my Back has leaning over the bloody thing to fasten material has been killing me. Didn't realise just how easy it does make fastening and accessing material while it's working.
Also having to deal with clearing chips again is a pain in the arse and again you don't fully appreciate how much differance it makes until you have to go back.!!

You haven't experienced using flat so you maybe won't fully get what I mean but you will if you ever use it horizontal after being vertical. . .Lol

**njhussey** · 25-01-2014

Originally Posted by JAZZCNC

You haven't experienced using flat so you maybe won't fully get what I mean but you will if you ever use it horizontal after being vertical. . .Lol

I'll take your word for it jazz lol I'm beginning to wonder if I'll ever get it finished. I just never seem to have any free time...

Looking forward to finishing the frame off next week, getting quite into the fabrication side of things again!

Question for people. How is the best way to DIY cut 20mm Ali accurately? I'm running out of money (wedding is end of March so bills are coming in fast!!). I was thinking of cutting the Ali for the gantry myself to save a couple of quid (plus I like the challenge!) as I don't like the prospect if telling the wife to be that we're not having a cake as I spent the money on machining... ;)

**JAZZCNC** · 25-01-2014

I cut 20m Ali plate full depth on my table saw using a carbide tip blade that is so tired it complains at cutting hard woods yet munchs thru Ali.??
(Wear eye protection and cover all exposed flesh has the chips are red hot and hurt like hell.!!)

For shaped parts make some MDF templates and use large router with bearing guided carbide cutter with very shallow passes.! That's how I made my first machines gantry sides and that was with a 12mm cutter.!!!! . . . Which wouldn't recommend so go for 6 or 8mm max.
Other than being a little daunting it worked a treat.!. . . . Thou I will say I was very very experienced with using a Large router free hand so if not used to routers then be careful has they can be a handful.!

**EddyCurrent** · 24-01-2014

Looking good, I like the look of the smaller box section for the bed and triangulation. Are you going to block off the ends of the box with those plastic caps ?

**njhussey** · 25-01-2014

Originally Posted by EddyCurrent

Looking good, I like the look of the smaller box section for the bed and triangulation. Are you going to block off the ends of the box with those plastic caps ?

Thanks Eddie, I'm pretty pleased with how it's turning out...no I'm going to weld plate the ends and grind the welds smooth. Will probably put 20mm thick bits in the bottom and drill and tap M12 for adjustable legs just in case I do leave it horizontal at any time. :)

**njhussey** · 27-01-2014

Couldn't be bothered to set up the bench to do grinding today so though I'd get out the linear rails for the X axis and see how flat they were. Took a quick video (apologies for it being upright!) and the rails are pretty flat.

My question is.....do I need to epoxy then level as they seem pretty damn bloody flat to me as they are now!!!

**Jonathan** · 27-01-2014

Forget the spirit level thing - it's nowhere near accurate enough to provide useful readings for rail alignment. When I measured the error on the rails in the recent build log, we were measuring height error to 0.01mm and angular error (rail twist) to 0.003 degrees...I'm not saying you have to do that, but it gives an idea of the tolerances that can be involved if you try and do it properly.

The rails will conform to the surface you bolt them to, so regardless of how straight the rail is to start with, if you bolt it on to a surface which isn't flat, the result will be a rail that isn't flat. Hence you should use epoxy to level the surface.

**Wobblycogs** · 27-01-2014

I'm not sure your test of flatness on the x-axis bars is valid because the rails weren't bolted down. If there's a dip in the bar the rail will probably span it but get pulled into it (slightly) when bolted firmly down. I think you'd need a long straight edge and feeler gauges to really figure out if it was flat enough.

As for cutting aluminium my SCMS went though that 10mm you gave me like it wasn't there using a positive rake cross cutting blade - about the worst blade you could use for metal cutting - and left a mirror finish. With a negative rake aluminium blade I'm sure you could do 20mm easily. Watch out for those chips though, as Jazz says, they are bloody hot. As for routing to shape you might want to try a router table instead of a free hand, I think you'd probably get better control over the depth of cut and a finished face this is more perpendicular. The downside of of a router table is that the chips will fall onto and potentially into the router which may not end well. You can pick up a router table insert for very little as long as you don't mind the height adjustment being completely manual.

**njhussey** · 27-01-2014

Oh well.....still quite chuffed that I managed to weld them pretty damn level

Will carry on grinding and welding and getting ready for pouring the epoxy (best buy some I guess!!) OK another question :) Is it better to drill and tap the holes before epoxying or after? I was thinking before as we have a mag drill at work and that would make drilling the holes much easier first, but then would need to fit the bolts and make sure epoxy doesn't stick to them and then there's the question of the miniscus round the bolt?

Now playing devils advocate here....how much accuracy do I need? There's a CNC router I know of that looks a bit like this.....

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which has supported round rails bolted straight to what looks like steel rectangular section and that machine seems to put out some nice accurate shiny aluminium bits

I'm mostly going to be cutting balsa, ply, carbon fibre, wood engraving and the odd piece out of aluminium (probably upgrades for the machine itself if most build threads are to be believed...!) so just wondering to what degree I go to with the levelling? I've got nothing to measure the accuracy of the epoxy once it's set and have no way of accurately telling if the rails are flat. I don't want to go out and spend a small fortune on a surface plate or engineers bevelled edge 1300mm long sop suggestions on a postcard please?

**JAZZCNC** · 27-01-2014

Originally Posted by njhussey

Now playing devils advocate here....how much accuracy do I need? There's a CNC router I know of that looks a bit like this.....
so just wondering to what degree I go to with the levelling? I've got nothing to measure the accuracy of the epoxy once it's set and have no way of accurately telling if the rails are flat. I don't want to go out and spend a small fortune on a surface plate or engineers bevelled edge 1300mm long sop suggestions on a postcard please?

Excellent point and your 100% spot on.!!. . . . He's talking Bollocks.!! . . . . Measuring to those tolerences needs expensive highly calibrated equipment which I doubt he has either.!

For what you want to do then if those rails are on the same plane then you will be perfectly fine.!! . . . . Fact is this is DIY Level precision and to attain higher level precision cost's lots of Money or Lots of time and frustration.!!. . . . . .KEEP IT REAL. . . it will be PERFECTly fine for wood.!