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... ;)
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.!
Last edited by JAZZCNC; 25-01-2014 at 02:33 PM.
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!!!
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.
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.
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.....
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?
These lot, make you think too much.... think less........
Just do the best you can do with the tools & experience you have. I spent ages in my build worry about this very point, in the end I just got one rail spirit level flat, and set the other one up off that. BOSH
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.!
The Following User Says Thank You to JAZZCNC For This Useful Post:
Cheers Jazz ;)
My cunning plan is to get some of my 10mm 6082 plate I have and make a plate to go across the X axis and bolt it to the carriages like so....then put some 100x50 section on it to stiffen it....
Then I can drill one hole one end of a rail and then using digital callipers (accurate enough???!!!) get the hole at the other end the same distance from the rail side, move the carriage to one end and drill a hole on the opposite rail at that end, slide the carriage up to the other end and mark the hole and drill that. Then by sliding the carriage up and down and nipping the bolts up I should be able to get them parallel to each other. I can then move the carriage near the middle and mark, drill and tap those holes. Once I've a sufficient number of holes drilled and tapped (every other hole?) I should be able to see if it slides freely or if it binds? If it slides freely......happy days, if not then epoxy it is! Sound like a (convoluted) plan?
P.S. I know the bolts should be allen head socket bolts and counter sunk but I couldn't be bothered to draw any.....sorry!
Last edited by njhussey; 27-01-2014 at 04:55 PM.
although the amount of deflection mentioned by jonathan may seem small, it would be noticeable over a large machine base, or if your surfacing or engraving anything bigger than 500mm.
In his build, he shows you how to use epoxy to get it level, as close as you would need it.
I also fly RC planes. If you considering cutting wing profiles, you will notice even a small deflection. All depends on what your doing.
IMHO, for the sake of £ 45 for the expox, and a few hours ( no expencive tools needed ), do the resin thing, get it as accurate as possible.
Imagine doing a glider wing profile from foam, 1000mm long each, a small amount deflection on your rails would ruin the wing.
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