Design Study: Rail Inline With Ball Screw

[Bravin Neff]

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.

I might not be understanding you correctly, but I think you have in mind either gussets between the horizontal and vertical plates, or what I have been imagining, a small vertical detail that connects the horizontal plate with the Gantry, which would fully box in the ballscrew mount and ballscrew. I have been leaning away from that, because the design as is leaves that surface (the horizontal one that the ballscrew mount attaches to) fully exposed on a vertical machining center, making it easy to backside machine. In other words, I am trying to balance the design with ease of Machining these details.

If you can imagine this entire Gantry as one welded fabbed unit, then putting it on a vertical Machining Center, upside down, makes the rail Carriage surfaces easy to machine flat, and then you can back side machine the opposite side, making the ball screw Mount Services flat as well.

[Robin Hewitt]

Is this your first design? What is it supposed to cut? How big is it?

[Bravin Neff]

Is this your first design? What is it supposed to cut? How big is it?

Yes. Wood and aluminum. Roughly 950 x 630 x 135.

[Robin Hewitt]

If you are trying to put the screw close over the linear blocks, why don't you sink the nut in to the plate and drop the screw down? How are you going to keep the cuttings out of the screws? You have made it from heavy section to cut aluminium but that will not help you get the speed to cut wood efficiently. If your gantry weighs 50 lbs then you need 50 lbf plus the cutting force to accelerate it at one G.

OTOH I think you need to build something wrong and then fix it with the Mk2. Understanding CNC design does rather come with experience. Getting it wrong is not actually a bad idea.

[Bravin Neff]

If you are trying to put the screw close over the linear blocks, why don't you sink the nut in to the plate and drop the screw down?

I don't follow you here. Do you mean machine a pocket into the plate in order to get the ball nut lower (i.e, closer to the linear carriages)?

How are you going to keep the cuttings out of the screws?

Guards, covers, bellows. They aren't shown.

You have made it from heavy section to cut aluminium but that will not help you get the speed to cut wood efficiently. If your gantry weighs 50 lbs then you need 50 lbf plus the cutting force to accelerate it at one G.

I don't follow you here. You seem to say it won't be fast enough by saying it won't accelerate enough - is that what you mean? Regardless, I assume there is always a servo strong enough. Some of the machines I sell (for my day job) weigh over 30,000 kg and can accel at 1G. Of course those motors are huge... I'm personally looking at the Clearpath servos. Nema 23 and 34 frame sizes.

OTOH I think you need to build something wrong and then fix it with the Mk2. Understanding CNC design does rather come with experience. Getting it wrong is not actually a bad idea.

I think that's sage advice. What part are you seeing that is wrong?

[magicniner]

Basic Engineering Design revolves around Triangulation, without which you will never have optimum rigidity for the weight of your design.

[zvon]

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.

you're on to something there but as the otehr members said the weak point is the upright plate with no bracing for side to side loads. here's the same concept with one form of bracing added to what you initially drew
i like the idea it's very clever & done right could be quite sturdy

[zvon]

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.