MASSIVE 2.5M x 4M BED - GANTRY DESIGN HELP NEEDED!!

[woodhouse]

Hi All, and thanks for any advice anyone is able to provide, its greatly appreciated.

We've currently got a project where we are building a massive 2.5M x 4M bed machine with a multi function bridge/gantry.
Its primary use is for a nailgun, for nailing in a pattern but while we are building it it might as well be able to machine as well.

Anyone who isnt sure what we mean just google 'MBA Mobi one' or 'weinmann wms 100' but we intend ours to be much more compact as space is at a premium.

We all ready have the massive overkill NSK 55 profile rails and the bed/frame side of things is not a problem. What we cant decide on is the design for the gantry itself...

so far we have come up with the following...

1) use a large hollow section with the rails tapped into it but would a piece of flat bar be needed under to increase the thickness to get a good tap?

2) use a large c section with the rails bolted through?

3) angle welded flush to face of a hollow section to allow bolting through?

4) smaller hollow welded to produce the gantry?

any ideas and experience of any of these??

I'm assuming that one rail on the front face and one on the top face of the gantry would provide a better design or does it not really matter?

We also still haven't decided on the drive side for it either, whether rack is the way to go or rotating ballscrew?

thanks in advance

Tony

[Blackrat]

option 1 for me please :D, or even use a section that has enough wall thickness , remember this surface must be flat to have an accurate machine, if you weld a plate on, how will you flat it ?

and gearbox with rack and pinion

[D.C.]

Thompson have a ballscrew wizard here you might find useful:
http://www.thomsonlinear.com/website...ing_screws.php

If you don't mind a lot of welding, it might be worth considering a truss type design like pg 178 of this machine design document:
http://www.mech.utah.edu/~bamberg/re...e%20Design.pdf

[woodhouse]

Thanks guys!
The clearance under the router needs to be quite large so there will be quite a bit of leverage on the gantry from the router.

[Boyan Silyavski]

Take a look at my second build at signature for a strong gantry design. May be that will give you some ideas. I go as far to say that its the strongest for the weight i have seen.

Now if that's your first build, i would be very careful, you will either way overbuild it or way under-build it. Both could cost you money and disappointment.


There would be difficulty driving gantry at 4m with ball screw. While the rotating nut is the solution, i dont know from where you will obtain 4m ball screw. I have to speak with Fred from BST but when i was buying from China, the longest 2510 was 3m .

In fact for such a machine i would pay sb to design the gantry for me if i were you. I or some other people at the forum could do that service for you. Just post it at the relevant work quote section. IMO that would be your best bet and save you big money on the build itself and time also, especially if you value it high.


Dont get me wrong, the things you will have to learn to design properly such a big machine are way too much for an inexperienced person. Not to speak of that even welding CNC structures is time costly and needs patience and skill, that the usual welder at a machine shop does not posses.

If you insist going the DIY way, then make a drawing, show it here and we will help you better it with ideas and critics. But speaking without drawing is a waste of time.

[Gary]

Actually anything 25mm diameter or over is available in up to 6M long, the problem is the shipping.

Take a look at my second build at signature for a strong gantry design. May be that will give you some ideas. I go as far to say that its the strongest for the weight i have seen.

Now if that's your first build, i would be very careful, you will either way overbuild it or way under-build it. Both could cost you money and disappointment.


There would be difficulty driving gantry at 4m with ball screw. While the rotating nut is the solution, i dont know from where you will obtain 4m ball screw. I have to speak with Fred from BST but when i was buying from China, the longest 2510 was 3m .

In fact for such a machine i would pay sb to design the gantry for me if i were you. I or some other people at the forum could do that service for you. Just post it at the relevant work quote section. IMO that would be your best bet and save you big money on the build itself and time also, especially if you value it high.


Dont get me wrong, the things you will have to learn to design properly such a big machine are way too much for an inexperienced person. Not to speak of that even welding CNC structures is time costly and needs patience and skill, that the usual welder at a machine shop does not posses.

If you insist going the DIY way, then make a drawing, show it here and we will help you better it with ideas and critics. But speaking without drawing is a waste of time.

[Boyan Silyavski]

Gary,
could you provide such long screws? Its good to know

of course i am not expecting china prices

[Gary]

yes of course up to R5050.

[woodhouse]

I'd already spotted zapp had long enough stock ;)

Yes this is my first cnc machine build so inexperienced form that point of view, not in engineering, electonics or CAD though.

What we need is similar (although on a smaller scale) to what is pictured bellow.



As you can see there needs to be a larger distance under the gantry to a normal board type router, which of course increases the leverage force from the tool to the gantry.

As quite rightly said, I don't want to over engineer it for no gain.

[Boyan Silyavski]

So you need the working table to be separate from the gantry and sides?