Z axis idea

[davida1234]

Hi Peter, yeah, that is within the name too....

Though, there are other samples:











Or, I could just change the name of the machine to Krygtomattænen...... no idea what it means but sure sounds better than "wiki/vertical-lift_bridge"

[davida1234]

Couple more ideas for the name:

PowerGantry

Z_Gantry

XZ Gantry

LiftGantry

Lifting Gantry

Elevating Gantry

Elevator Gantry

[peteeng]

Hi David - Mills seem to call the cross structure a bridge and routers call them gantries. So I'm going with lifting bridge for my mill and lifting gantry for the router. Peter did a quick search and mills use gantry as well so perhaps "lifting gantry" for all !!

[NIC 77]

I have one with an active gantry.

About a month ago, I was trying to figure out what these types of machines are actually called so I could look up some more examples of them.

I read your post and was like, oh, active gantry! Now I know!

There are many large scale rising Z axis machines, but there does not seem to be a common name for it.

Crap!

Here is one showing the machine cutting the top of a 14" cube:

Yeah, that's certainly an advantage. You get better performance when the gantry is low, which is probably most of the time, and can drop your feeds and speeds with it high, doing things like cutting your cube. That's great!

Your design looks very familiar to this one:



The main difference looks like you have rack and pinion while they have leadscrews. This design concept may not have caught on with CNC routing, but it looks like it's doing OK with some 3d printing even though it's not super common, while variations of it are.

The first CNC I built had the same kind of hardened steel guides and v-groove wheels (but the gantry didn't move in the Z direction). Made by PBC Linear. That's funny, because in the background of the video I just linked to there is a PBC linear banner. My experience with their stuff was that some of it was OK, and other stuff was crap.

It's nice that this subject has come up just as I am in the process of finalizing my latest machine, which I am currently in the process of collecting parts for.

IMO, Moving gantry in the Z axis and moving bed, there are so many advantages with this kind of design. It's the next standard "mill" design concept that allows for larger travels than a traditional mill does. I don't know why I didn't see this before. No, I'm not actually making a "mill" to cut metal, in what I'm doing now, but the advantages of this design concept have become apparent in my research.

When you start moving the gantry in two directions, things become more complicated, especially if it's for something like a mill, cutting metal, and you loose a few of your advantages.

[nlancaster]

David, fantastic.

[peteeng]

Hi All - Heres a lifting gantry machine with moving Z. Everything moves. The lifting gantry is called axis W. I posted this somewhere else in the forum couldn't find it...

Peter

[peteeng]

https://www.youtube.com/watch?time_c...ature=emb_logo

Here's another one - Peter

[ger21]

While it does allow you to cut very tall objects, it's potentially more limiting for cut depth.
Say you have a conventional Z axis with 12" of travel, and a gantry with 12" of clearance. You could potentially cut 12" deep.
With a lifting gantry, you can only go as deep as the gantry clearance allows, which would be at best 1/3 the depth of the conventional Z axis.

[davida1234]

Gerry, I am not sure I understand your comment as the cutting depth is
just a question of Z travel length which should be same in both cases.

The important item is the difference of concept for a conventional gantry vs. a lifting gantry.

With a conventional gantry, increasing the clearance height of the gantry (higher gantry location)
increases the path of load transfer from the Y/A-carriage to the tip of tool (cantilever/leverage).
Load has to be transferred up to the gantry and then come down to the tool tip.
The more you move down with the spindle, the more cantilever it creates.

With a lifting gantry, it is just the opposite. The more the spindle moves down, the less cantilever there is.

As the material to be cut is seldom more than 1", the lifting gantry provides the better compromise, IMO.
You get more accuracy with sheet goods and less with the occasional over sized material.

I hope the diagrams below explains the differences:

[ger21]

Gerry, I am not sure I understand your comment as the cutting depth is
just a question of Z travel length which should be same in both cases.

Say you want to cut a 12"x12" cube so that it's only 2" high at each end, and 12" high in the middle.
More than likely, your lifting gantry will hit the part at it's high point before it can cut the sides.

With a conventional gantry, you only need to have clearance for the Z axis, which may allow you to make the deeper cuts.

It really depends on the type of parts you are cutting, but for someone that needs to make very deep cuts, on a regular basis, I don't think it will work.

[davida1234]

Thanks, I see now what you were thinking.

[peteeng]

Hi Gerry - I think all configs have limitations and that's why special machines exist to cope with special requirements. Obviously a 6 or 7 axis robot is the go then!! But the conventional gantry will have difficulty with the 12" cube problem as well due to collet clearance or Z axis nose clearance. Such a shape is done with long tooling which is typical of 5 axis machines. A conventional machine needs a Z travel of twice the tool length which can be huge. A lifting gantry is stiffer over this distance. A recent inquiry of mine wants to cut 150mm thick kaizen foam. Which means he needs a 150mm cutter ie a 300mm z travel. He has conceded and will use 75mm foam in two slabs. But the lifting gantry in this case will do this if a special machine is built. A 300mm plus Z conventional even for foam needs to be seriously stiff. Peter

So the conclusion maybe it needs to be lifting gantry with a moving Z axis like the two machines in prior vids...

[davida1234]

So the conclusion maybe it needs to be lifting gantry with a moving Z axis like the two machines in prior vids...

That would be the best, definitely.

30" of total z travel with two lifting columns on the gantry and an additional conventional Z- axis. A bunch of linear rails, bearings and 6 motors.

I am waiting for an order......

[peteeng]

Hi David - Yes think BIG... speaking of which I came across this. Big cars.... Peter

[cyclestart]

An image search for 'plano milling machine' turns up machines of this type of configuration. Possibly because the design resembles a moving table planer ? https://en.wikipedia.org/wiki/Planer_(metalworking)
I worked in a shop with such a beast but it was cnc in xyz only, the y bridge was raised by large acme screws which were synchronized but not cnc controlled.
The bridge was seldom raised as the machine was primarily used to drill flat bar. Lots and lots of flat bar