[Talkiet]

[Sorry, initially posted in an inappropriate section - MANY forums here!]

Hi all - first post but I have bought a pretty well sorted 6040 as an exercise to learn about CAM and various basic components of the process and I love it. Now I am wanting to build a MUCH stronger frame using linear rails and dual X axis screws etc. I'm looking at a lot of people's designs to get ideas and inspiration and I wanted to test a theory that I haven't found a good explanation for yet...

Most of the 6040 designs from factory have a very simple gantry design and quite a few of the people reworking them replace the gantry uprights to both increase the distance between the bearings (improves rigidity) and also lean the side supports back so that the spindle ends up being placed equally between the 2 bearings (when viewed form the side). Is this so that there's limited/no torsional forces on the gantry from Z movement? Obviously there will still be the major forces from the tool load as the gantry moves the tool into material - but is the Z loading significant or worth designing an offset set of supports? I have made a quick hand drawn picture to help explain. The blue is the Z axis and spindle, the red is a typical 6040 set of gantry side plates/bearings, and the green is the proposed offset gantry side plates and bearings.

If there are any resources covering some of the theory of frame and gantry design then I would love to hear about them, as well as specific replies to my question here. Even build threads that are well respected and exemplify good design approaches would be appreciated.

Regards
Neil Gardner
New Zealand

[ger21]

I think most people offset the sides just to get a little more travel. You really don't see any commercial machines that do that.
In your green version, you'd be better off bringing the back straight down, spreading the bearings further apart.

but is the Z loading significant or worth designing an offset set of supports?

Depends on what you are doing with it.

This thread has a lot of good info in it.
https://www.cnczone.com/forums/diy-c...cad-posts.html

[Talkiet]

Thanks for that - very useful thread and interesting to know there doesn't appear to be a mechanical advantage (or enough to be useful) in the offset. I see exactly what you mean by bring the back straight down. The wider the stance of the bearings on the gantry carrying axis, the better the twisting resistance. And except for the loss of some travel, it's a free way to stiffen it up at design stage.

Space and weight are going to suck whatever I build, so I might as well just build in some forklift channels or lifting eyes and make it bigger to stance out the X and Y mounts as much as reasonably possible.

The above image was just to illustrate the point - I actually plan on having dual Y axis ball screws and significantly raised sides Might as well get all the height I can in a 100% rigid fashion! I don't see the point in making a lever to help the gantry pivot!

I am aiming for something about this size and design, although not using Granite!!!

https://youtu.be/phphvMno65I

I am thinking that 16 or 20mm 6061 plate for the base, sides and gantry would work, with the sides boxed up with a solid back. There will also be some ribs attached to the underside of the bottom plate running in the same axis as the gantry.



Cheers - Neil G