Flying Gantry 2' X 4' CNC Design - Comments please

[alien_X]

Hi

I have been designing a flying gantry design, based around many, many builds I have seen on the cnczone (Gadget47, Model D, Micke H etc. - I hope you don't mind)

I am aiming for a 24 " X 48 " cutting area, and my build will be in metric (Apart from the cutting area

I will use linear bearings on supported rail for the X (Longer) axis, Skate bearing truck riding on aluminium angle for the Y axis, and probably some more linear bearings, oilite bushings, or an iko/thk slide for the Z axis.

The frame will mainly be built from mdf, but there is an aluminium extrusion.

I am designing all the precise pieces less than 300 X 300mm, since that is the cutting area of my model A (when it is done). The long wood length which creates the I beam type structure will be cut in 4 pieces, on my small cnc - so it will be accurate and make assembly a piece of cake (hopefully).If the build is made from wood I will most likely use aluminium angle to reinforce certain places. I will also add some support under the base (Maybe torsion box style) and it will be built into a table-like freestanding structure.

Enough rambling, here are some exported jpgs from solidworks (not the best quality I know)

On the skate bearing trucks, the angle the bearings are attached to is 3/4" and the rails are 1"

I am stuck on how I will do the Z axis, as it stands the bottom of the Y axis carriage is about 200 mm higher than the table (The y axis carriage is 230 mm wide for reference), so I will need a reasonable amount of travel, but it will need to remain sturdy and cheap - So please, any help or ideas ARE VERY WELCOME!

Also, if anyone can see a problem, then I am all ears,

Thanks








Alien

[abomb55076]

Thats a pretty good start. It looks like the bases of the gantry are wide enough too to support the weight without getting top heavy. One thing you might want to think about is the slides for the axis on the gantry. It looks like if you get too much weight on the front of that, those slides could become unsturdy.

[Grunblau]

Consider the opportunity to 'cap' the whole gantry with the MDF piece that holds the aluminum angle. I believe this would add a lot to stiffening the assembly...




Aren't the star shaped holes for threading a bolt into them? Unless this is an aesthetic choice, I might use these for a connection point.

[alien_X]

Thank you for the comments.

Abomb, what would you recommend I change to remedy this problem? Are you referring to the weight of the Z axis assembly and spindle pulling the sliding carriage forwards/down?

Grunblau,by "capping" do you mean adding another piece on top of the opening and exposed endgrain where the extrusion fits (on the gantry sides)?
Also, did you mean a seperate piece, or part of the aluminium angle fixing section?
And regarding the exposed extrusion end, I thought it would be stronger to have it sitting in a groove than held up by bolts, I was going to slide T slot nuts into the section, and using some threaded rod fix the extrusion to the fronts and backs of the gantry sides.

However, you have built one of these, so what is your opinion?


Thanks for all the help so far!

Here is some pictures of the Z axis I have been working on, it uses 16mm rails (300mm long) and oilite bushings. At the moment I think this gives me too much travel, so I will maybe shorten the rails and raise the height of the gantry sides. Please could you give me some comments on this assembly, thanks alot!

the extrusion is 45 X 90 mm, is this large enough?

[Grunblau]

Originally Posted by alien_X Thank you for the comments. Grunblau,by "capping" do you mean adding another piece on top of the opening and exposed endgrain where the extrusion fits (on the gantry sides)? Also, did you mean a seperate piece, or part of the aluminium angle fixing section?

If you thought of the top piece of MDF as an H in plan. I see no reason not to as this would strengthen the side gantry boxes and also continue the potential for t-bolts all the way to the end of your extrusion...




I think that the extending the extrusion through the MDF is better if the ends aren't perfectly 90 degrees. if they are 90 degrees, you could benefit from pulling the end of the aluminum extrusion against your side pieces... this will always be a tighter connection than any slot you could cut to fit especially after a bit of wear...

[alien_X]

Thank you for the very good suggestion and explanation, I will definitely be adding these into the design.

The long length which the angle attaches to is going to be cut in multiple pieces around 300mm long, so I can cut it on my first machine. Do you reckon this will add much weakness to the assembly, and whether this would affect the strength of your elongated H beam?

I was thinking of adding a joint shaped like this (And obviously a socket shaped inversely on the opposite end) :
_ _
| |
| ----
| ----
| |
---

Or something similar to the end of each of the strips in order to lock them into an aligned shape, what are your thoughts?

Also, Does anyone see any problems with the length of the moving plate on the Z axis in regards to the bushing spacing?

Thanks alot for all the input so far!

[alien_X]

I have now added the H shaped beam to the design:

[shadowless]

where is the best position to mount the x-axis leadscrew?

[alien_X]

Hi

I have had alot of feedback on another forum about getting rid of the gantry sides and having the X axis rails above the bed. Much like the solsylva 24 X 48 design.

So I will start to redesign this completely, any thoughts on this?

Thanks for all help Regards