Hybrid gantry

My cnc machine has a classic raised moving gantry which works very well for cutting balsa, liteply, and ply. This layout gives great access for loading materials.

But on the rare occasion I've cut aluminium I needed to take slow shallow cuts because the sides are not super stiff. A better machine would be one with raised X axis rails, like the one posted by Florian some time ago, plus Jonathan more recently. These are without doubt superior machines, but I wondered if there was a middle ground with the stiffness of the raised X axis, but the easy access of the raised gantry.

Here is an idea I had recently along these lines. No plans to make anything like this, just though I'd post it to see if anyone has ever seen or made something similar.

Attachment 5795

I've seen others mention they don't like the raised sides because of restricted access and I dont understand what the problem is or the concern they have.??

I've built several machines large and small with raised sides and it's just not a problem loading and removing material like your probably imagining. The advantages are very very much worth the slight and I do mean slight restriction and unless you have servere restrictions like ONLY being able to load from side then there really isn't an issue at all in my 4yrs experinece using my machine.

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Originally Posted by JAZZCNC

I've seen others mention they don't like the raised sides because of restricted access and I dont understand what the problem is or the concern they have.??

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Same here... wouldn't have been able to put this 100kg sheet of 20mm thick aluminium on my router ready to cut if loading was difficult! As I see it the main advantage of having a raised bed is in addition to the rigidity gain from not having flexible gantry sides, you gain rigidity by using a raised bed and as a result minimising the Z-axis extension. With your design as soon as you raise the bed the easy access is lost.

Humm, not much i can added really. When i designed my machine i gave myself enough "room" to work with material of a max hight of around 100mm with about 70-80mm travel on the Z, the machine was designed for working with thin sheet materials.

I thought that i should pay attention to keeping the X axis center as close to where the cutting action was taking place as i could, as was the same for the other two axis's, i've seen a number of diy machines where they seem to have made the z axis longer/higher/taller (whatever) than would ever really be needed, some having 200mm + travel and then dumped it on an x axis so far away from the Y that i really couldnt understand the point of having such a tall Z?

I dont know, but i was under the impression that we should be trying to keep the cutter as close to all axis center's as we can, Dean ?

.Me

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Originally Posted by Lee Roberts

i've seen a number of diy machines where they seem to have made the z axis longer/higher/taller (whatever) than would ever really be needed, some having 200mm + travel and then dumped it on an x axis so far away from the Y that i really couldnt understand the point of having such a tall Z?

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My Z-axis is 400mm...I've not got anywhere near to using the full travel yet, but it doesn't hurt to have it since I have the adjustable height bed. The reason I made it with so much travel is to give room for 5-axis (XYZAC) machining which shouldn't be too far away.

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Originally Posted by Lee Roberts

I dont know, but i was under the impression that we should be trying to keep the cutter as close to all axis center's as we can, Dean ?

.Me

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This is were I think it can go wrong or be mis-understood.? It's 2 completely different issues or reasons.

The main reason for trying to keep all axis close to centres etc is more because of even weight distribution and loadings on bearings than for cutter performance.
High sides design is for strength and ridgity by not having flappy gantry sides so less resonance hence less chatter at the tool where it matters most, thou really to make best use of these high sides you should have an adujustable bed.

Regards long Z axis extensions well this is a personal choice and also dependent on machine use. Most of my machines never have more than 200mm Z extension unless special reason like foam block cutting. The main reason why I design and build machines with high sides/adjustable bed other than the said strength gains is for flexabilty.
As well has allowing a greater range range of materials sizes It allows the use of vices, 4th Axis, large Or odd material size or shapes, long drills or long cutters for materials like foam all without sacrificing strength or introducing to much flex and therefore chatter at the cutter.

The negatives which I persoanly find hard to find any are massively offset by the gains.!