Design Study: Rail Inline With Ball Screw

I'm looking for your comments please. This would be a gantry style CNC router. The Gantry is 150mm x 75mm steel rectangular tube, and the frame is 75mm x 75mm square tube. 1610 ballscrew, 20mm Hiwin HGH20 or similar.

The point of this design is to put the ballscrew directly above the linear guide, with the gantry mount sandwiched between the ball screw and linear guide carriages. I do not believe I have seen this before.

The motivations for this:

1. Ease of machining of the frame. The ballscrew mounts/motor mounts will be machined in the same plane as the linear guide rail surface. Alignment made easy.


2. An attempt to "hide" the ballscrew from inadvertent movement. This doesn't really achieve this, but it gets it away from the outside of the frame.

3. I think it looks cool.

Thanks for your comments.


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Wobbly thin plate with no triangulation adjacent to the Ball Nut is probably the design's weakest point, to resolve this fully triangulate your vertical and move the ball screws outboard.

Would you hold to those comments if I told you the wobbly plate was 9mm thick and fully welded with the gantry?

Incidentally I have contemplated adding a triangulating plate to the inside, which would surround d the ballscrew, and so it would be the one item that isnt welded, but bolted.

Quote:

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Originally Posted by Bravin Neff

Would you hold to those comments if I told you the wobbly plate was 9mm thick and fully welded with the gantry?

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You have a right angle welded joint holding a flat plate with no triangulation with your rails and ball nut mounted to it.
You can make it lighter, stronger or both, given these facts would you hold to calling this a "Design Study" ?
:D

I would. That's what it is. Do you still think it's a thin wobbly plate? Im not being combative, it's an honest Q.

Then it's perfect and you should build it just as you've drawn it :D

One of my ideas was to place the ballnut inside the box section I envisaged for the gantry foot. This would give enough depth for the screw covers to telescope within the gantry. The main advantage of placing the screw outside the footprint of the frame is to keep it away from the incredible amount of flying detritus these machines produce.

Quote:

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Originally Posted by Bravin Neff

Im not being combative, it's an honest Q.

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Honest answer, if 9mm is good in that design you can use less, triangulate and make it lighter whilst still being stronger and more rigid.
Or triangulate and make it far stronger and more rigid for little added weight.

Quote:

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Originally Posted by cropwell

One of my ideas was to place the ballnut inside the box section I envisaged for the gantry foot. This would give enough depth for the screw covers to telescope within the gantry. The main advantage of placing the screw outside the footprint of the frame is to keep it away from the incredible amount of flying detritus these machines produce.

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It's a good point. I've been looking at various bellows and related covers that exist on the market to help with debris, and there is a surprising amount that exists.

Rather than looking for bellows search for "Wire Reinforced Hose" and suddenly there's a huge supply of reasonably priced material suitable for the same job.