DIY Machine Design

[Biggs427]

Hello,

I'm the process of building my second DIY CNC.

Probably made of baltic birch, phenolic. 1000mm X rails and 700mm Y rails.

I was leaning to a classic design with a torsion box base with uprights and a torsion box for the gantry.

Like this:


But while lurking on the forum, I saw a design with no uprights, with the gantry directly on the base like this:


What are the pro cons of both design?

First Design:
- More space for workpiece
- X can be driver by only one leadscrew

Second design
- Might be easier to make it stiffer
- X absolutely needs two leadscrew

Am I missing something?

Thanks

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[Schuimpge]

Not an expert, but:

Both designs as shown would need 2 screws on the X.. Both could also be modified (longer uprights/sides for the gantry, extending below the bed) for a single screw.

Design 2 is easier to make the gantry stiff. The Uprights and the connection to the gantry are typically your weakest point, especially when using wood, so you would need substantial re-inforcement there.
By taking out the uprights, you remove that weak part and your gantry can withstand much higher forces.

Another advantage for Design 2 is that you create a natural enclosure that will help to keep dust to a minimum while also providing a 'safety-wall' when for example you break a bit. Very easy to add a plexiglass or wood 'door' at the front and back to make it completely enclosed.

Design 2 would also allow for a wider gantry outside of the walls, so you could make your Z-axis carriage wider, which makes it stronger to withstand cutting forces.

Cheers,
Luc

[Biggs427]

Thanks for your input!

On design number two, the plan would be to have, as you mentionned, longer uprights that extend below the bed. The CAD screenshot was just an exmaple.

Having only one X lead screw being the only benefit of design 1 seems very little compared to the drawbacks...

[dharmic]

I've seen video of a 5 axis which is a taller version of #2 with a trunnion for A and C axes. It was pretty p0rnstar. I'm waiting to see the downside but, after all, if it there isn't a downside then why does every man and his dog (commercial machines included) tend to go for #1 ??