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

[njhussey]

I might go a single stepper on the X axis and use belt drive for both ball screws then.

Got a quote from Chai today for the SBR20 rails/carriages and the 1610 machined ball screws, ball nuts, BK & BF bearings etc. and its very reasonable (just a bit over half the price I worked out getting it from the UK would be) so will get those on order soon. Am moving house this week so will wait till the end of the month till I have done that and unpacked a bit!

Should give me time to go through the design and make sure all dims etc are correct and print cutting lists off for the steel.

[njhussey]

Another question. I was planning on using 3" x 2" x 1/4" Aluminium box for mounting the rails on (X & Y axis) but noticed that others have used steel in their builds. I was always under the impression that steel was not straight enough? I'd prefer to use steel as it's cheaper and I can weld the frame up and I need 3 lengths of it for the existing frame so wouldn't have as much waste.

[JAZZCNC]

Another question. I was planning on using 3" x 2" x 1/4" Aluminium box for mounting the rails on (X & Y axis) but noticed that others have used steel in their builds. I was always under the impression that steel was not straight enough? I'd prefer to use steel as it's cheaper and I can weld the frame up and I need 3 lengths of it for the existing frame so wouldn't have as much waste.

Man wish I'd got £ for every time get asked this.. .Lol

What makes you think Ali box is any straighter or flatter than steel.?. .. It's not.!! Also contrary to popular belief often neither is Alu profile.! . . Steel is far stronger and cheaper and with careful selection can be very straight and flat. It's also very easy to work with if it's not perfectly flat.

There's very few off the shelf materials that you can use without some form of correction for inaccuracies and that includes Alu profile. People think profile is straight and flat but in reality it's often not, yes it can be better than extruded profiles like Alu box but it will still need some form of correction to the surface at some point. It's also 5x the price.

The main area of concern is for the rail surfaces being straight and flat. Extruded Alu like Box is rarely straight or flat enough to use without work so will need some form of correction, either filling or sanding high spots.
This also the same for steel but the difference being steel is quite easy to scrape,file,grind,sand than Ali has being harder it doesn't clog tools etc.
In my experience steel box has just the same inaccuracies that Alu box does but steel is much easier to correct. Often all it needs is a quick run over with grinder knocking off any high spots, Low spots can be filled. Then just shim the rails to get perfect.

If your using the Chinese round type rail then I can tell you with 99% certainty the base will not be flat or straight and will have more error than the steel your fastening it to.!!. . And thats without correcting the steel.!!

Have no fear of steel, it's cheaper,stronger and very easy to work with and manipulate to your needs. Other than being lighter Alu has just the same issues steel does and unless you have special welding equipment is actually harder to work with.
If you bolt together while bit easier to drill alu suffers from crush and hole deformation much more than steel does. Unless it's thick material doesn't hold tapped threads very well like steel does. Steel will easily hold fine threads in 3mm thickness for fastening rails etc and allow decent torque on bolts, try that in Alu.!

[njhussey]

Man wish I'd got £ for every time get asked this.. .Lol

That's £ I owe you then

What makes you think Ali box is any straighter or flatter than steel.?. .. It's not.!!

Just presumed that as lots have it for the Y axis that it was straighter, never used it really so presumed others knew best!!

In my experience steel box has just the same inaccuracies that Alu box does but steel is much easier to correct. Often all it needs is a quick run over with grinder knocking off any high spots, Low spots can be filled. Then just shim the rails to get perfect.

Can do all that in our works, Was thinking of welding some 50x5 flat to the 50x50 box and get a local engineers to skim the surface so it's flat.

If your using the Chinese round type rail then I can tell you with 99% certainty the base will not be flat or straight and will have more error than the steel your fastening it to.!!. . And thats without correcting the steel.!!

Nice, I look forward to that!

Have no fear of steel, it's cheaper,stronger and very easy to work with and manipulate to your needs. Other than being lighter Alu has just the same issues steel does and unless you have special welding equipment is actually harder to work with.
If you bolt together while bit easier to drill alu suffers from crush and hole deformation much more than steel does. Unless it's thick material doesn't hold tapped threads very well like steel does. Steel will easily hold fine threads in 3mm thickness for fastening rails etc and allow decent torque on bolts, try that in Alu.!

I have no fear of steel, it's my preferred material of construction as that's what we use at work to build the oil systems I quote, see the pic of a system we did for Ratcliffe Power Station ID fan blowers.

[m.marino]

Neil,

Nice power station reminds me of the days when I worked as pipe-fitter in Industrial tool trade in the Detroit area. I use AM882's and unless you are planning on going to the feed back loop stepper motor/drive combo I strongly suggest them. They run well and stay cool even after a good long day of cutting (14 hrs). Unless you have access to industrial power supplies I would suggest building one with a toroidal transformer, I get a really nice smooth power off my set up and once the transformer got charged it has been running very nice (looking at adding a fan to cool everything down just a bit, for safety measure).

Nice design and should do everything you are asking of it and more. Hope the move goes well. -Michael

[njhussey]

I use AM882's and unless you are planning on going to the feed back loop stepper motor/drive combo I strongly suggest them. They run well and stay cool even after a good long day of cutting (14 hrs).

I'm not planning on using the feed back loop combo, not sure I'll run the machine that hard as it's for hobby use. For what I want it for the AM882's will be more than good enough.

Unless you have access to industrial power supplies I would suggest building one with a toroidal transformer, I get a really nice smooth power off my set up and once the transformer got charged it has been running very nice (looking at adding a fan to cool everything down just a bit, for safety measure).

I'll probably ask for help when doing the power supply. I think I've subscribed to a thread where one is made but failing that I'll ask for help.

Nice design and should do everything you are asking of it and more. Hope the move goes well. -Michael

Cheers Michael, I'm hoping that I don't get a rush of blood to the head and re-design it again I'm quite happy with the design now, all I think I'll be doing (unless anyone points out any major flaws) is doing the minor details, checking everything fits as it should and then detailing the pieces with the bolt holes, machining etc.

Just been checking the 10mm aluminium sheet I got from eBay a while back (2200mm x 950mm) as I've moved it to temporary storage and after cleaning some dust off I discovered it's 6082 grade so happy with that!! Just waiting for my other bargain eBay bit of 20mm thick Ali to be sent!!