New, larger aluminium extrusion

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New, larger aluminium extrusion

Postby cvoinescu » Tue Dec 16, 2014 12:21 am

Prodded into action by Edward's announcement of the next version of Shapeoko, I dug up some plans that I had set aside last year, when I was still searching for a reliable extruder. It's provisionally called MegaRail (an incredibly predictable and boring name). I drew it last night and uploaded it to GitHub.

MegaRail.png
MegaRail profile section (dimensions in mm)
MegaRail.png (15.65 KiB) Viewed 3762 times

MegaRail (ugh) is a linear motion profile that's twice as tall and twice as wide as MakerSlide. It forgoes the T-slots for a significant increase in torsional rigidity (or cost and weight savings, depending on how you look at it).

The essential dimensions (Vs, mounting holes) are the same as Misumi HFS5-4080 extrusion with OpenRail bolted on it in all four corners (only stiffer, lighter and cheaper). The clearances are different, though, and the Vs themselves are wider, supporting not only the standard Delrin V-wheel and the steel RM1 dual-row V-groove bearing, but also the larger RM2 wheel (and a possible upgraded plastic V-wheel). Because MegaRail (sigh) has Vs in all four corners, "dual-X" carriages can run on a single rail. This way, at a small additional expense, most of the off-axis load on the V-wheels (weakest mode) is converted to radial load (strongest mode).

The wall and core sizes are preliminary. The top and bottom faces bulge mostly to help prevent damage to the surfaces of the Vs during manufacturing and transport. Ideally, the core holes would have a star-shaped profile that permits standard screws to form their own threads, but I have to do some research on that.
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Re: New, larger aluminium extrusion

Postby RobCee » Tue Dec 16, 2014 8:55 am

Nice one!
I wonder if you have got round to calculating a rough second moment of area yet for this. It would be interesting to plug is into my stiffness calculator and see how it compares to the deflection of xx/yy rails I have been looking at.
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Re: New, larger aluminium extrusion

Postby cvoinescu » Tue Dec 16, 2014 10:55 am

Very roughly, the area moments of inertia, in mm^4, are 30 * 10^4 and 80 * 10^4. Compare to 1.61 * 10^4 and 6.1 * 10^4 for MakerSlide. So, yeah. It's a tiny bit stiffer (about 15 times). It'll be the same alloy as MakerSlide (6105/6005/6005A), unless I can get 6082 (harder) without paying a lot more.
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Re: New, larger aluminium extrusion

Postby RobCee » Tue Dec 16, 2014 11:30 am

Excellent, that makes it quite a bit stiffer than the Misumi 4080 in the vertical axis, which is 63.3E+4.
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Re: New, larger aluminium extrusion

Postby paul » Thu Dec 18, 2014 9:48 am

That's an enormous increase in rigidity - nice work. Does the big open area/tall side walls result in any resonance (not sure if you've gotten samples for testing yet)?

MegaRail isn't a terrible name, particularly in the world of generally boring extrusion profile names - it kinda sounds like it's from the Judge Dredd Universe....
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Re: New, larger aluminium extrusion

Postby Gadgetman! » Thu Dec 18, 2014 9:55 am

Possibly used in the frame of his Hoverbike? ;-)
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Re: New, larger aluminium extrusion

Postby megeshg » Thu Dec 18, 2014 3:14 pm

You mention there is support for steel v wheels, but mention that it ill be made of the same material as makerslide, will the profile not wear out with the use of steel wheels given the material choice?
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Re: New, larger aluminium extrusion

Postby cvoinescu » Thu Dec 18, 2014 4:14 pm

megeshg wrote:You mention there is support for steel v wheels, but mention that it ill be made of the same material as makerslide, will the profile not wear out with the use of steel wheels given the material choice?

It will wear, unless it's hard anodized. I have a decent quote for that from the fabricator, so it will be an option. It won't be dirt-cheap, but it should still be cheaper than steel rail on a standard profile. There's also the possibility of a larger plastic V-wheel.
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Re: New, larger aluminium extrusion

Postby LouisV » Thu Dec 18, 2014 4:39 pm

That's awesome. Very stiff design. Seems like that would be great to use on the y-axis of my HDX design, or the x-axis for the HD.
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Re: New, larger aluminium extrusion

Postby chamnit » Thu Dec 18, 2014 4:59 pm

Hmm, I'm a little leery about hard anodization. It's usually not very precise and has a tendency to chip when there are high stress concentrations, like when a steel v-wheel on a hard anodized pointed rail. You'd have to always ensure the bearing rides on the flats and never the edge for something like that to work.
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