Accurate Strong Gantry

**vargai** · 07-12-2014

Originally Posted by Ross77

Looks good but you might need a bit more triangulation. The thin gussets only work in one direction so ideally you need them in equal amounts in all 3 planes.

Why is there a bit gap in the middle?

What rails are you using? There are different types and some can handle 4 way loading and others cant so are best mounted on top of the rail. Especially if you are using a heavy moving gantry.

Yes some corrective action should be done .

The gap in the middle just represents the place of the single ball screw in case of narrower machine

regarding the rail I would use one like this which is regular type now
The problem is as you pointed to it at my case only the upper row of ball hold the load but the moment resistance is good that occurs at start-stop and direction change
I have no experience using it but suppose it works -the catalogue also mention it as possible mounting arrangement

Because of my 100kg+ heavy moving gantry I have drooped this design and go with fix gantry where the moving Z will be balanced

**Boyan Silyavski** · 07-12-2014

The Hiwin HGR are double row bearing blocks and there is no difference how you mount them, so don't worry about that.

For a router HGR20 is enough and even a bit overkill, depending on the design. So no worry here also.

**Ross77** · 07-12-2014

Ok, I'm a bit confused. You keep saying fixed gantry but then you show a bed with rails on the side.

Is this the bit that will be moving? If so I would have said that it is not the best way to do it. Moving beds should have the rails underneath and at approx. third points or a quater in.

That way the rails are supporting the load better and are closer together so you can get away with one ballscrew.

As you have drawn it the bed can bend in the middle under load.

**vargai** · 07-12-2014

Originally Posted by Ross77

Ok, I'm a bit confused. You keep saying fixed gantry but then you show a bed with rails on the side.

Sorry for being double meaning.
I have started the thread with the moving gantry principle and as the design and details developed according to the useful comment from the site two days ago especially after having Dean's #41 post I have changed my mind .
My intention was not to leave my earlier ne'er-do-well concept and correct it.
This is the case when the design concept turn to other way so I put this moving gantry into a drawer now and finish this chapter.
I will start a new thread with it when it is actual again.
So I am giving thanks everybody and I am at full pelt with the fix gantry from now on.

**Boyan Silyavski** · 07-12-2014

Nevertheless keep this thread alive, cause that's one of the most interesting things, somebody starts with one idea that evolves in something quite different sometimes.

**vargai** · 15-12-2014

Chapter #2 Fixed gantry

I am back again after aging some thoughts however I could not go too far. I cannot find too much examples for the ideal fixed gantry frame.
Probably I am making the typical mistake and try to reform something that is good as it is.
My viewpoints are:
using hot rolled profile -do not know but think it is better vibration damper than cold formed tubes (SQ or RECT)
using bigger cross sections- to eliminate the bracing and welding as far as possible
setup with 1700 mm total length-just slightly longer than moving gantry

My concern are:

-bolted connection as figure shows-is it is good enough- instead of welding?

-The spindle overhang is quite big -though is fixed in one direction . Is there a better setup to eliminate?

-I would balance the moving bridge on both side with pneumatic cylinders or gas spring that I red here and like this option.
As the spindle moves in Y direction the Center of Gravity moves with it -that seems not too beneficial for the balancing

Figure below shows mainly principles first to make a good machine setup

Thank you for your comments and advice in advance.