[rogue-insight]

I started with the Shapeoko 2, but the plastic v-wheels made me angry. I didn't see how they were even good enough for using the machine on wood. I then set off on designing and building my own. The details are in the description. What I did differently was move the entire gantry up and down for the z-axis. This required two z-axis drive motors and ballscrews. This makes the machine stiffer because the gantry is always behind the spindle, and the moment arm doens't increase as the spindle moves downwards. I think it simplifies the design as well. Everything attaches to the gantry plates, which are just flat plates with hole patterns in them. There's no need to make right angles, etc to put things together.

Here's some assembly pics:
- Album on Imgur

And here it is cutting into aluminum:
https://www.youtube.com/watch?v=KfcmfX-xigI

[wizard]

A very interesting machine. More pics would be nice. This kinda reminds me some old planer mills and vertical turret lathes I worked on in the distant past.

[jueston]

how do you verify your gantry is perfectly level? do you have to level it manually every time you start the machine or do you zero it with limit switches?

it is sure a unique idea, and i can see some advantages, you could have a very large z-axis travel and without the loss of accuracy most long z-axis machines face.

[LeeWay]

Nice work. Looks great. I find that slaving the axis with two motors works very well. I think that is even less critical on the Z axis for flatter work pieces. That said, if it is out much on larger pieces, it will certainly show. I have long dado's in plastic parts that have to be pretty much perfect. I don't think such a design would be good in my case.

[rogue-insight]

how do you verify your gantry is perfectly level? do you have to level it manually every time you start the machine or do you zero it with limit switches?

it is sure a unique idea, and i can see some advantages, you could have a very large z-axis travel and without the loss of accuracy most long z-axis machines face.

Before I locked the z-axis ballscrews nuts to the gantry, it was resting on the bed with gauge blocks under each end (left and right), so that set the gantry beams level to the bed. I then locked the ballscrew nuts to it, and only moved the gantry with the stepper motors, which are slaved. As long as they don't miss any steps, it'll stay. Eventually I'll put a belt between the two ballscrews, so they'll be mechanically sync'd. It's the same methods used for dual ballscrews on a Y-axis.

[LeeWay]

You don't really want to have a belt between the two. That is old school and has issues when something misses a step.
The best possible way to keep them inline is with switches.

[rogue-insight]

I think the belt would solve the missed step issue. If one of them screws up, the working motor will turn the ballscrew that normally would stay still during that moment. Technically I could drive the gantry up and down with only one drive motor that powered the two ballscrews, so long as they were sync'd mechanically. So following that logic, belt would be a viable backup mechanical connection.

[ger21]

I think the belt would solve the missed step issue.

The only thing that solves the missed step issue is not missing steps. If any of your motors are missing steps, you're machine will be basically unusable.

Just don't try to go faster than your motors are capable of, and you won't miss steps.

Too many people try to find the magical cure for missed steps. Keep your machine withing it's limits, and it's not an issue.

[jueston]

my Y-axis is squared using switches like leeway suggested, i think switches are the best option and allow for easy adjustment.

as you have it right now, if you have the machine off, and vibration allows one side to go down it will remain that way when the unit is powered back on. this might not be a big problem if doing a lot of 2D work, i do a lot of 2 sided work and having my z perfectly level is important.

how much Z-movement do you have right now?

[rogue-insight]

my Y-axis is squared using switches like leeway suggested, i think switches are the best option and allow for easy adjustment.

as you have it right now, if you have the machine off, and vibration allows one side to go down it will remain that way when the unit is powered back on. this might not be a big problem if doing a lot of 2D work, i do a lot of 2 sided work and having my z perfectly level is important.

how much Z-movement do you have right now?

I must admit I dont' understand how to use the switches. I'd have to place them so very accurately that I don't think it makes sense. As far as the gantry sliding down, I do have that concern, but i haven't seen it move at all yet. With the residual friction from a two stepper motors, it's enough to support the weight. If i mechanically sync'd them, then it would solve that problem too

[bhurts]

The switches don't need to be perfectly aligned. Just tell each side to back off the switch a different amount based on being square. They don't have to be the same although close would make things easier.

Ben

[ger21]

The switches don't need to be perfectly aligned. Just tell each side to back off the switch a different amount based on being square.

Can UCCNC actually do that?

[pippin88]

Nice work.

Similar designs have been used for large gantry mills. I have a design in mind for a gantry mill, though I think I would have the gantry on the front of the uprights.

[bhurts]

To be honest ger21 I don't know. I didn't even pay attention to what control he's using. My bad. I use k-flop and kmotion on my router. I am not using dual motors but I know k-flop can do it. I just assumed they all should be able to. If I'm wrong sorry. It seems that it should be doable though.

Ben

[wizard]

A couple of other options exist to deal with the axis parallelism issue (if it is even an issue here).

One would be to do away with the dual motors ant to mechanically connect the two axis. You could do this with belts and not do too bad with slop between the two verticals. Another option is two right angle gear boxes and a large diameter shaft between them. Both of these approaches require some sort of mechanical phase adjustment too get everything parallel. I know this is often dismissed but it was common in the past when electronic solutions didn't exist. If you get the results you need it is far less complicated than some approaches.

A second alternative is to use electronic leveling. In this sense you would be using a high precision switch to probe the table height (parallelism to the gantry) on the left and right sides and adjusting one or the other axises to keep the gantry parallel to the table. Interestingly the RepRap guys have invested efforts in methods to do this on machines with very similar mechanics. This probably will require custom coding though as I'm not sure of a normal CNC platform that supports this natively.

I suppose a third option would be to use a comtroller that supports mapping in some way to compensate for axis errors.

On some CNC injection molding machines, with belt driven dual lead screw axises, the leveling method (as advised by the factory) was simply to jump a tooth on one of the lead screw pulleys. A rather course but effective way to achieve the parallelism required. How effective this would be on a router type machine depends a great deal on the lead screw pitch and the accuracy required.

In any event I just wanted to point out options. There is an array of solutions from simple to complicated.