A new hope: Epoxy granite and steel.

[hardenum]

the Z-axis design is narrow and weak which will make all the trouble you'll be going to a pointless exercise.

I thought it's pretty strong, stronger then what I'd get with a U plate and a spindle bolted to it. I based it on dmu 340. In which direction is it weak?

I can see how this would be problematic if you want to mill on the side of long pieces that won't fit under the gantry. With a fixed bed the cutout allows the work piece to extend below the bed. If OP wants to do a lot of those pieces then the moving gantry seems indeed the way to go.

That is what I meant.

[JAZZCNC]

I can see how this would be problematic if you want to mill on the side of long pieces that won't fit under the gantry. With a fixed bed the cutout allows the work piece to extend below the bed. If OP wants to do a lot of those pieces then the moving gantry seems indeed the way to go.

Pro's and cons to both but IMO the cons for having the slightly longer length end machining the price is a too high price to pay in strength terms. There are other better ways. . . For instance.!

For high clearance requirements, I have a design that will work and provide high clearance under the gantry with minimal loss in strength. I've just built a small version with a cutting area of 500 x 500 x 350 that could easily have the clearance and strength increased if required without any impact to it's cutting ability.

[hardenum]

I did a mockup of this design and I had concerns about the depth of cut. It does solve the Z axis problem you mentioned. There's actually this start up that's doing the exact design called Vulcan, that's meant to be sold for around 8k. Here's their structure:

https://scontent-frx5-1.xx.fbcdn.net...d2&oe=5FF33F20
https://scontent-frx5-1.xx.fbcdn.net...58&oe=5FF208F9

[JAZZCNC]

I did a mockup of this design and I had concerns about the depth of cut. It does solve the Z axis problem you mentioned.

Why did you have concerns about DOC.? It doesn't get any better than with this design for a machine with a larger cutting area as the Z extension is never any longer than the tool length, and that is at any Z height.
Some of the largest Gantry mills in the world use this exact design. If you build it strong enough the only limit on DOC will be spindle power.

[hardenum]

Why did you have concerns about DOC.? It doesn't get any better than with this design for a machine with a larger cutting area as the Z extension is never any longer than the tool length, and that is at any Z height.
Some of the largest Gantry mills in the world use this exact design. If you build it strong enough the only limit on DOC will be spindle power.

The main DOC concern was that when I put different pieces with different height onto the vacuum table I'd hit the higher ones with the vertical beam. Like machining the bottom and top piece (http://www.jt-precision.com/uploads/...7293225867.jpg) one after another without actually having to go and change the piece. Sure I could put the higher one to the front, it would work, but knowing me, I'd switch the 2 unconsciously and mess some part of the machine.

Anyway, do you recommend a ballscrew on each column or one thicker in the middle?

[JAZZCNC]

The main DOC concern was that when I put different pieces with different height onto the vacuum table I'd hit the higher ones with the vertical beam. Like machining the bottom and top piece (http://www.jt-precision.com/uploads/...7293225867.jpg) one after another without actually having to go and change the piece. Sure I could put the higher one to the front, it would work, but knowing me, I'd switch the 2 unconsciously and mess some part of the machine.

Anyway, do you recommend a ballscrew on each column or one thicker in the middle?

I suppose it's possible gantry brace could hit if your having very different height materials but I don't think it will be a massive issue and how often are you likely to do that.? It certainly won't be an issue cutting the part you show.
Also there is nothing stopping you having both a lifting gantry for very high parts and fitting a conventional Z axis to this. This way you have the best of both worlds. Again this is commonly done on Large gantry mills, and when I say large I mean something that could mill a full size Car from a billet of steel.!!

Regards the ballscrews then it only works with one on each column. . . . How could you fit a central ballscrew and still have the material move thru the opening.

[pippin88]

The main DOC concern was that when I put different pieces with different height onto the vacuum table I'd hit the higher ones with the vertical beam. Like machining the bottom and top piece (http://www.jt-precision.com/uploads/...7293225867.jpg) one after another without actually having to go and change the piece. Sure I could put the higher one to the front, it would work, but knowing me, I'd switch the 2 unconsciously and mess some part of the machine.

Anyway, do you recommend a ballscrew on each column or one thicker in the middle?

That piece would not be machined assembled. It would be done in two pieces and then the hinges connected.

Your design won't machine that work in one piece anyway. Your cutting tool will be say 5mm, but 50mm higher in Z you will have your full spindle cartridge/Z axis to hit the piece standing up.

How much experience do you have machining / making parts?

Some of the issues you are trying to solve with machine design are actually fixturing issues.

No machine design will save you from forgetting to do something correctly.

[hardenum]

I suppose it's possible gantry brace could hit if your having very different height materials but I don't think it will be a massive issue and how often are you likely to do that.? It certainly won't be an issue cutting the part you show.
Also there is nothing stopping you having both a lifting gantry for very high parts and fitting a conventional Z axis to this. This way you have the best of both worlds. Again this is commonly done on Large gantry mills, and when I say large I mean something that could mill a full size Car from a billet of steel.!!

Regards the ballscrews then it only works with one on each column. . . . How could you fit a central ballscrew and still have the material move thru the opening.

I guess some clever positioning? https://scontent-frx5-1.xx.fbcdn.net...58&oe=5FF208F9

Anyway you have me convinced(https://www.k-mm.com/wp-content/uplo...s_picture4.jpg).

Gonna take a long deserved brake before I dive into the new design. Thanks

[pippin88]

Regards the ballscrews then it only works with one on each column. . . . How could you fit a central ballscrew and still have the material move thru the opening.

I like your new machine, though I think hiding the ball screws like that reduces stiffness too much by cutting into the tubes.

You can have a single central screw on a lifting gantry machine. The screw moves up and down with the gantry. Nut it attached to the fixed top cross beam. Either rotating but with servo attached to fixed cross beam, or rotating screw with Z servo moving up and down with Z.
Pros: Single screw (screw mapping, servo tuning, cost). Cons: A bit trickier to implement. Will have screw sticking right up high when Z fully up.

[JAZZCNC]

I guess some clever positioning?

That's not clever positioning, that's restricting movement and height.!!