Wobblycogs CNC Mk2

[Wobblycogs]

I couldn't get off to sleep last night for thinking about the CNC so I decided to get up an do a bit to the design. I wanted to address a couple of issues:

1) the rails didn't mount very cleanly onto the aluminium extrusion
2) it felt like too many parts were becoming sufficiently complicated that I would need access to a milling machine. I know I could get some / all of parts made for me but part of the fun of this project is coming up with a design I can make myself.

With those issues in mind I switched over to using aluminium rectangular section 100x50x6. The other major change was to mount the rails on the front of the gantry rather than top and bottom. I'm not sure if this is the greatest of ideas but I think it'll make the build quite a bit easier.

The shots below show the Y and Z axis together. There's a bit of tidying up to do moving bolt holes but the basic structure is in place.



If vibration is an issue with the box section on the gantry I'll pack one or both beams with fine gravel / sand. Anything shown in red will be tooling plate.

[JAZZCNC]

I couldn't get off to sleep last night for thinking about the CNC so I decided to get up an do a bit to the design. I wanted to address a couple of issues:

Ah ah your officially Addicted . . . .At your first meeting the words to use are " Hello my names Wobbly and I'm an addict" . . .Welcome to the club.!!

Now regards the changes then your making it worse not better.?? . . . Distance from Ballnut to Z axis rear plate is too much and that long bracket will flex and resonate.
I'd just flip the plate to front and cut a slot in it and mount ball-screw on back side so the distance is less, your also protecting the screw and motor. Stick another thin plate on rear and it's fully protected and helps stiffen gantry.

Don't go with your current design you'll regret it in this form.!!

[Wobblycogs]

Yep, I'm completely addicted now. Work is suffering, I'm getting no sleep, the bank manager thinks there's been a robbery...

Lol, when I was drawing that long connection bracket I could hear you in my head saying "that's too long" :-D

As an alternative to mounting the 10mm plate on the front of the gantry could I instead mount the ball screw on the gantry supports like this and put a thin (5mm?) plate with a slot on the front? That gets the screw closer to the z-axis back plate and the gantry gets the full support of a 10mm plate on the back.



I've had to significantly increase the size of the base to accommodate the new rails. I can't really afford a full sheet across the whole base but I've added corner supports all around the bottom and the top has 200mm wide plate running the full length. All plate is 10mm thick and will be thoroughly bolted to the 45x90 heavy extrusion.



I actually feel like I didn't do to badly with the redesign if I only needed to move the screw, perhaps there's hope for this machine yet

[JAZZCNC]

As an alternative to mounting the 10mm plate on the front of the gantry could I instead mount the ball screw on the gantry supports like this and put a thin (5mm?) plate with a slot on the front? That gets the screw closer to the z-axis back plate and the gantry gets the full support of a 10mm plate on the back.

Yes you could no problem but you'll get more support for gantry from that plate if it was on front has the rails will be fastened to it and can't flex in the middle. Has it is now the Box in the middle could flex has the only support is on the back side and the rails applying all the pressure are on the front side.!
You'd be better with it on front and either another thinner plate across back adding bit of support or 2-3 10mm plate braces across back.

[JAZZCNC]

Hold on.!!! . . . . You are having gantry sides aren't you.?? . . . .Your not planning on having it open like those pics show are you.?

I just thought you where showing it like that to save drawing them.!! . . . If not having sides then your in trouble and this won't work very well.!

Edit:

Ok on looking again it's not that bad but think it would be benefit from gantry sides has it would help stiffen things up. Also it would make a better stronger connection to the ballscrew.
Sides and the plate on front would make it quite bit stiffer with less flex.!

The way you have it now this would need beefing up anyway.

[Wobblycogs]

One beefed up gantry with added sides. Now I draw it I can see this is significantly stiffer than what I had, I was relying on the 10mm plate not bending along it's weakest axis, doh!



As you suggest there will be 3*10mm thick plates on the back with the rest covered with a thin sheet. The front will be a full 10mm sheet with a slot for the ball screw. Feel free to imagine bolt holes all over the place ;-)

Thanks again for all the help.

EDIT:

There you go it's drawn up

[JAZZCNC]

It's close very close but not quite Carling.!!. . .Lol

Gantry's fine but those drop brackets for X axis ballnut mounts are too flimsy so make bit wider at top and beef them up a bit and your there.!