[G-Spot]

OK finally got past rails and bearings level design and onto screws.

The total weight of my x and y axis is only 155Kg minus the weight of the screws and motors.

If I could realistically get 200 N/um from the bearings I would go for 35mm screws. But I think I have more to gain realistically by taking advantage of the low weight to stiffness ratio of this design on the milling plane and use 20 or 25mm screws instead.

Using a gantry design of this stiffness and you must be looking at having to move at least 500kg on your x and z axis.

Also this design lives and dies on the X axis length, All measurements are derived from that. And it is almost impossible to change or upgrade. In this case the inner diameter of the torus, so I wont be making accurate drawings of anything until I have the X-axis components in my hand.

I am now going to focus on assembly methods until I have the bearings and screws in hand, take some drawings to the engineers, I know that milling a 1.6m x 1.6m plate is a lot more expensive than if it is less than 500mm, I could split the end plates into sections and save myself a lot of money.

[G-Spot]

Got the bearing stiffness data, see attached.

So it turns out the 35mm bearings are more than good enough for 173 N/um, according to that paper, number of axis plus connected objects, in my case a multiple of 5, means the bearings need to be 865 N/um

Then I had a eureka moment while I was wondering how to deal with the 6 months needed before the concrete would be stable. I was designing a connection system that would always stay true and if the cement shrunk you would only lose stiffness and not alignment, then you could remove the plates put a thin layer of grout then reattach the plates.

Then I realised that because I have shrunk my original work-area dimensions down to 300 x 400 x 400, I could now afford to get the concrete core cut from a solid piece of granite.

I replaced the concrete core with a granite core in my FEA and the stiffness lept up to 370 N/um.

Tomorrow I am going to look for granite blocks, I might get lucky because it is used by the trucking companies as a no loss load, trucks travel down to the port to pick up loads, often empty, instead of traveling empty they pick up granite blocks and get paid enough so they are not making a total loss on the journey.

Not going to go to the many granite companies but try the quarries and trucking companies first. I don't need it polished as I would put a thin layer of grout between the granite and plates when I bolt together.

Cut rough straight from the quarry would work for me.

[hanermo]

Very ambitious.
Good luck.
My scratch built VMC has less than 100 N/um,
and it´s a portal, and uses 35 mm rails, and is version 5 over 10 years.
Measured deflection by standing on the spindle.

Granite is about 3x more flexible than steel.

Got the bearing stiffness data, see attached.

So it turns out the 35mm bearings are more than good enough for 173 N/um, according to that paper, number of axis plus connected objects, in my case a multiple of 5, means the bearings need to be 865 N/um

Then I had a eureka moment while I was wondering how to deal with the 6 months needed before the concrete would be stable. I was designing a connection system that would always stay true and if the cement shrunk you would only lose stiffness and not alignment, then you could remove the plates put a thin layer of grout then reattach the plates.

Then I realised that because I have shrunk my original work-area dimensions down to 300 x 400 x 400, I could now afford to get the concrete core cut from a solid piece of granite.

I replaced the concrete core with a granite core in my FEA and the stiffness lept up to 370 N/um.

.

[G-Spot]

My scratch built VMC has less than 100 N/um,

Thanks
And if you put the design into FEA what is its stiffness?

[G-Spot]

Talking of lightweight machines that are 100 N/um stiff.

It will NEVER be a gantry design because with a gantry design you have to spread your wide geometry all over the place. You are taking the mountain to Mohamed, instead of taking Mohamed to the mountain.

While a portal design keeps the large geometry close to the work piece.

Here's an all steel version of my portal minimum 100 N/um stiff and only 786kg the frame is only 500Kg.

That's like half the weight, and cost of a gantry system.

Attaching the CAD files for it.

Using this same design a 50 N/um machine that would weigh less than 500kg using only steel is possible.