Gantry idea

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18 Jan 2021 09:34 #195761 by OxxAndBert
Gantry idea was created by OxxAndBert
Hi all - planning my first DIY 1500x1500 table and have been looking through my collected junk for materials that might be useful.

Came across a long pneumatic linear actuator that might be useful for a gantry. The extrusion is roughly 80x75 and weighs about 8kg/m.


Normally it has a double acting piston like this:

Apart from the good size 40mm bore what caught my eye was the nice dust seal method and how easy it would be to attach some linear rail.


My plan for the X axis was to use a rack and pinion with reduction gear drive, but maybe I could use a ballscrew inside the bore of the extrusion, all nicely sealed up by the original seal, and very simple to support/align in the bore at each end.
Should be pretty simple to attach the ball nut to the original drive lug and seal guide, but I'd need to gear it up 1:5 to get 25mm travel per stepper revolution.

Does the idea have any merit, or should I just stick with using it as an extrusion and bolt on an external rack?
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18 Jan 2021 10:16 #195764 by tommylight
Replied by tommylight on topic Gantry idea
From the above asuming the ball screw is 5mm/rev so that will limit the max velocity a lot, but it might also be enough for what you need. Also adds a lot of weight to the gantry.
Rack and pinion is ok and also needs reduction.
A 10mm wide GT2 or 3M belt would be ok with 1:3 to 1:5 reduction.
As a general rule, everything on the gantry as lite as possible.
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18 Jan 2021 11:40 #195771 by OxxAndBert
Replied by OxxAndBert on topic Gantry idea
Thanks Tommy.

I also have some 50x50x3mm steel tube here which would be about half the weight of that extrusion. I see that is about the size that was used for 4'x2' build by HomemadeNJ in the DIY sticky.
Guessing I'd be better to use that, and put the extrusion aside for another project?

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18 Jan 2021 12:07 #195773 by rodw
Replied by rodw on topic Gantry idea
I think your 50x50 would be OK. I used 80x40x4 aluminium. I think the ally is more dimensionally accurate. We get 50x50x2.6 steel parts laser cut and sometimes parts do not fit well becasue the tube is construction grade by definition.
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