DIY CNC Milling Machine From Scratch

[Lee Roberts]

Good start - almost getting jealous!

Correct me if I'm wrong, but it looks like you're leaving the back of the Z column open, so it's a C-shape section not a box? If so then you should defiantly put another plate on the back, as the torsional stiffness of a C-section is very low compared to a box. That's one of the big advantages of putting the ballscrew on the front of the column, not inside - you can have a closed section.

Dito!, Jonathan if he was to close the back up and opt for a box, would it be of worth while benefit to also add some ribs inside the box, I was thinking towards cantilever, an X in a square, the through sections on each plate would also allow then for the filling of the column?

I have a nice solid slab of aluminium as shown in the drawing, about 500mm x700mm by 76mm thick so i hope this will be solid enough.

I was going to fit some of the electronics into the colomn but i am now going to make a stand to house the spindle cooler, electronics, pc and coolant pump, so will probably think about filling the column with something after the z stepper and y stepper is mounted so i know where to fill.

Trouble is the cost keeps mounting up :( best not to take note and hide the reciepts from the missus hahah

Sounds like it would be.

I think its fair to say that making it a box and filling it would be of more benefit to the machine.

Hehe, what's new .

.Me

[totts]

Hmmm yeh true i will add a back the column now, but im not sure on the ribs as if i weld these it may upset my ground face, i may add a couple bars inside to act like rebar. I will get some info on the z axis as im not sure weather to make them out of steel or ally for acceleration.
Ballscrews are 1605 on all axis.

Toroidal transformer is the way i am going for now, just need to do some research.

[totts]

A bit more work done tonight, the beginning of the bed. This is the main body where steel strips will sit creating the t slots, coolant channels on either side. This will eventually be ground.

[Jonathan]

Hmmm yeh true i will add a back the column now, but im not sure on the ribs as if i weld these it may upset my ground face, i may add a couple bars inside to act like rebar.

I don't think adding more than the plate to the back of the column will make much difference, as it's the least stiff parts of the machine you need to target if trying to make it stronger. Intuitively I'd say that's a different part, but hard to say without modelling it, which takes a long time...

I will get some info on the z axis as im not sure weather to make them out of steel or ally for acceleration.

Yes please do. The difference in torque required from using aluminium vs steel is unlikely to be significant, plus steel has better damping properties so I'd prefer steel. Although as Lee has pointed out, there are other ways to solve the damping problem.

[totts]

I don't think adding more than the plate to the back of the column will make much difference, as it's the least stiff parts of the machine you need to target if trying to make it stronger. Intuitively I'd say that's a different part, but hard to say without modelling it, which takes a long time...

Not quite sure what you mean there? Would it be a good idea to add a plate to the back of the column and fill it with resin, or concrete?


Steel it is then! Cheaper too! Does anyone know the realistic weight of a 2.2kw spindle?

I will hopefully be goin to have a bt30 cartridge and motor, but i suppose it wont be too difficult to change the stepper motor of needed in the future.

[Lee Roberts]

Not quite sure what you mean there? Would it be a good idea to add a plate to the back of the column and fill it with resin, or concrete?

Steel it is then! Cheaper too! Does anyone know the realistic weight of a 2.2kw spindle?

I will hopefully be goin to have a bt30 cartridge and motor, but i suppose it wont be too difficult to change the stepper motor of needed in the future.

He’s talking in terms of adding strength to the machine and he’s right but I was really referring to eliminating resonance more than anything, I can’t see that adding ribs/reinforcing plates wouldn’t add extra strength to the column, I think they would help towards stopping any twist in the column at the very least.

I think the problem with concrete is that it’s relatively brittle (though I note your suggestion of using rebar), cracks could form in the concrete and over time it may break down inside the column, I don’t know enough but I’m guessing that it doesn’t really have the same dampening properties as other materials, epoxy resin is a favourite but so is kiln dried sand and the sand is cheaper in comparison.

I think what I will do with mine is to, reinforce the column on the inside, use a mix of aggregate (different sizes, type 2, pea shingle and so on) to then fill the column, then backfill the lot with epoxy resin (filling up the leftover voids) all the way to the top, hopefully creating one solid mass. The idea being the aggregate is just away to use less resin (cost vs. cost) but also brings back the properties of using sand.

.Me

[totts]

Right okay i see now, i think the plan will be to enclose the section in the back which isnt being used by the stepper motors, and fill it with sand, i can always use a resin afterwards if i change my mind.

[Lee Roberts]

Right okay i see now, i think the plan will be to enclose the section in the back which isnt being used by the stepper motors, and fill it with sand, i can always use a resin afterwards if i change my mind.

Exactly, you could run some tests to see the difference with and without sand, you may not even need any.

.Me

[totts]

Back to work with my column to drill more holes haha. The bloody thing is heavy hahah!

[totts]

What is the mass of the Z-axis (head, spindle etc) and what are the dimensions of the Z-axis ballscrew? I've made a script to calculate it more accurately, so if you post that information we can make sure the motor you've chosen is the best option. I suspect you may be OK with one of the 3-4Nm Nema 24 motors. The gas strut makes surprisingly little difference if you try to get a reasonable acceleration...

Okay after managing to get on the computer i have made sure my plates are made of steel, and from what i can find the 2.2kw spindle is around 5.15kgs then the z axis is around 45kgs.