Aluminum router build - Could use some input

[Washout]

Here's the last issue I sorted out on my machine: http://www.mycncuk.com/threads/7420-...ith-my-machine
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Some profile rails rather than round rails sorted that on the Y axis. I will likely upgrade the z axis as well at some point and Jazz pointed on my thread, profile rails are a lot better than round due to better resistance to play.
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I didn't have many issues with alignment/binding once I had taken the time to do it properly. I did have a job drilling the ballscrew holes off centre on the left hand corner posts, through the extrusions, but luckily the holes were not critical in diameter and I oversized them so I had some adjustment room when aligning the ballscrews.
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Repeatability is good on my machine and on a part I am milling, which has 56 identical pockets on it, each pocket was within 0.02-0.04mm of each other dimensionally.
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At the risk of "I told you so" from Robin and a debate about capabilities ;) , I am happy with the machine for wood, plastics and ali work. However, there are limitations in using >8mm cutters due to general rigidity and although I have cut 1mm slots accidentally through some holding steel washers, I am planning to buy a commercial milling machine (Warco GH) to convert to CNC and do steel and other harder materials. So I would think carefully about how much ali and metals you want to cut generally as a milling machine conversion maybe better (although you will need custom brackets etc made up, which needs CNC to start with).
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Best of luck with your design and I'm sure others more in the know will give finer advice on your design, which looks much better to my layman's eyes than your first.
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Cheers
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Chris

[routercnc]

To help you get more feedback I've dropped a screengrab from your site into this post - hope this is OK.

Here is your version 1:


Here is your version 2:


If you are keen to stay with supported rails and aluminium extrusion then this is a pretty good layout, and much better than the first one. My view is that you will be able to cut wood easily and accurately, and the occasional bit of aluminium.

But if you end up doing a lot of aluminium then you will find that this machine is not enough. An upgrade to profile linear rails on at least Y and Z is recommended, the gantry sections are too small and not joined to each other (e.g at least a plate over the back), and the X axis stepper motors are mounted off long brackets.

With the layout you have now I would look at moving the X ballscrews outwards and down, level with the supported rails. Then extend the small horizontal plate which the gantry sits outwards and screw the ballnut to the underside of it. There are other variations but you get the idea. This will enable you to mount the motors nearer to the frame, effectively stiffening the X direction when cutting. If this is too big a change then at least make the small plates on the outside much bigger and triangulate up to the motor position.

[Tumblebeer]

I'm pretty much convinced that I should switch to profile rails instead. I guess 15mm should be enough?
Something along the lines of: http://www.aliexpress.com/item/China...489001007.html or http://www.aliexpress.com/item/6-x-H...934543282.html

What should I consider when switching to square rail? Can I mount the rail straight to the extrusion t-slot? Any special considerations?

[JAZZCNC]

What should I consider when switching to square rail? Can I mount the rail straight to the extrusion t-slot? Any special considerations?

If mounting directly on profile then you'll need 20mm because 15mm won't span the slot properly. To be honest 20mm are not much more money and they also give other advantages due to there bearings being slightly higher and giving more support. This esp true when you come to build the Z axis.!

[routercnc]

For info a number of us have bought profile linear rails from 'fa-system' on ebay. They are used but the ones I bought still had plenty of life in them and have been running for a few years without problems. You'll have to cost it all up and make a choice.

Here's an example . . .

http://www.ebay.co.uk/itm/THK-SSR20-...ht_1899wt_1006

[Tumblebeer]

http://imgur.com/a/kszzz

There we go, third iteration. I've switched to square rails, 20mm. The frame is now a mix of 60x60mm and 80x80mm alu profiles. The alu plates are 20mm, except for the backpiece spanning the gantry, that one is 10mm.

The steppers should be more securely mounted, the gantry should be stiffer and hopefully I think it might be slightly easier to assemble.

What do you think? For some reason it just looks "wrong" to me, can't really put my finger on it.

[Tumblebeer]

Made some smaller adjustments, mostly cosmetic, but should have made it slightly more stable as well. Especially the table.

http://imgur.com/a/zyBVw

Any input is most welcome, I'm about to start ordering parts unless someone has any objections and/or improvements...

[routercnc]

Looking pretty good now in my opinion. Again, if you are intent on lots of aluminium with a really good finish and short job times then the raised X-axis designs are really the way to go (i.e. not this layout).

However, with this design as it stands you should be able to cut wood, plastic, and the occasional aluminium without any problems. I'd say it fulfills your brief and will make a nice machine.

I'll just make this comment, which you can take or leave! The extrusion pieces between the gantry sides, rails, and lower plate - I can see why you've done it like that and it will help alot with the corner stiffness. But they look a little unfinished, if that sort of thing bothers you, then one of your first cnc jobs could be to cut out some 6-10mm aluminium plates to go over the ends and tidy it up a bit. The rear end cover plate could easily be larger and join all the gantry, side and lower plates together. In your link the rear view is shown in the 5th picture.

Good luck with the build and post back as you go.

[Tumblebeer]

I got the impression that I'd need either massive amounts of aluminium or preferably a welded steel frame for a raised x-axis to work. Neither would work particularly well for me (since I can't weld, nor work steel), so I think I'll go with this gantry design. I wont be doing massive amounts of milling, just the occasional part.
I'm one of those people that build mostly for the sake of building, not really with any clear goal in mind.

What kind of doc and feed speeds do you think I could expect from this? Something like 0.5mm and 1000mm/min, doing alu and still getting good finish and precision?

As for the aesthetics, I completely agree with you. As a matter of fact, I intentionally left that extrusion end open to have a fun first project to route. I would have liked making the rear end cover cover more (but not so much as to bump in to any high parts I'm cutting), but I'm working mostly with standard lengths and parts, meaning this was way cheaper and in my mind a small cosmetic tradeoff...

Thanks for the tips, I'll probably start ordering next week, need to make sure I'm completely decided first. The building will drag out a bit until the summer is over though.