Fixed Gantry Design - Input Appreciated.

[Electroconducive]

So, After spending a lot of time working through quite a few designs, many hours in CAD and reading lots of build logs. I have settled on a fixed gantry style design. I only need 500x500mm of working area and quite a high Z of 250mm. The machine is being built to mill aluminium, copper and plastics. So, strength is more important to me than size. I intend to use it mostly for electronics enclosures and PC watercooling blocks. Given I have no current machining capability, I have been designing with that limitation in mind(epoxy level all the things).

I have settled on two Z designs. The standard 25mm alu tooling plate design and the novel steel gantry.








The frame measures 1000x800mm. It is made of 100x100x4mm welded box section, with the gantry bolted to the base via two 10mm thick steel plates. The steel Z is 60x60x5mm box section. All alu is 25mm thick tooling plate.

I am wondering, which Z design would be the best for my application?

The overhang of spindle from the main gantry is 35mm more in the steel design than the aluminium. However, I would just like to go with the best option given my current capabilities. I am not competent enough to do a thorough FEA analysis of the options. Besides, I thought I'd ask those with the real world experience.

What do you guys think?

[A_Camera]

I think that the first, traditional design is the best. The second one will be too complicated and it must also lift not only the Z and the spindle, but also the whole gantry. I also think that squaring the second one, and also driving up and down, would be too complicated and difficult. So my vote definitely goes to the traditional design, which is similar to mine. Milling aluminum will not be a problem.

[Electroconducive]

I think that the first, traditional design is the best. The second one will be too complicated and it must also lift not only the Z and the spindle, but also the whole gantry. I also think that squaring the second one, and also driving up and down, would be too complicated and difficult. So my vote definitely goes to the traditional design, which is similar to mine. Milling aluminum will not be a problem.

Thanks for the reply :)

You're right, the second one with the moving steel box section would be harder to square. I'd be driving the z with two 1605 ballscrews a belt and either a nema23 or 34 to avoid racking. I was thinking, given that I would really like to maximise the Z height as much as possible.

Would the steel version be more rigid at max z extension? Or, would the additional distance of the spindle from the fixed gantry in the X direction negate any rigidity advantages?

I am willing to put up with a little bit more of a complicated build for a stronger Z at full extension.

Then again, maybe I am conceptualising this all wrong and it's pointless to even attempt the steel Z.

[njhussey]

Hi, if you're after maximum rigidity I'd go for the twin ballscrew design. If you're not limited by space then put the ballscrews on the outside of the frame and drive with a single stepper and belt like you say. There'll be no problems squaring it with simple tools and once squared it will stay that way.

Sent from my HUAWEI VNS-L31 using Tapatalk

[Electroconducive]

Hi, if you're after maximum rigidity I'd go for the twin ballscrew design. If you're not limited by space then put the ballscrews on the outside of the frame and drive with a single stepper and belt like you say. There'll be no problems squaring it with simple tools and once squared it will stay that way.

Sent from my HUAWEI VNS-L31 using Tapatalk

Thanks, Putting the ballscrews either side will also let me shave 10mm off the overhang. Weird Steel Z design it is then.

[A_Camera]

Thanks, Putting the ballscrews either side will also let me shave 10mm off the overhang. Weird Steel Z design it is then.

I definitely like the idea, even if I think it will be more difficult to make it than the conventional type. I hope you will continue to post regarding the progress because I am certainly interested in following this up. My machine is also a fixed gantry type (conventional Z design) and I am interested in every possible way of improving it.

[Electroconducive]

I definitely like the idea, even if I think it will be more difficult to make it than the conventional type. I hope you will continue to post regarding the progress because I am certainly interested in following this up. My machine is also a fixed gantry type (conventional Z design) and I am interested in every possible way of improving it.

When I finish the initial CAD design I will start a build log. I am very happy to let others learn from my mistakes, and hopefully have others help me avoid making too many of them.

I have a budget of around £2K. I already bought an AC/DC Tig welder and have secured the use of a garage for the project. So, I will hopefully be making real progress soon.

[Clive S]

When I finish the initial CAD design I will start a build log. I am very happy to let others learn from my mistakes, and hopefully have others help me avoid making too many of them.

That would be good and in the spirit (pardon the pun) of the forum it also keeps all the questions and answers in one place. Good luck with the build.

edit. don't forget the pics