Advice sought on new Mill build

[Blackrat]

pouring aluminium into the tube will just make a loose slug, the ally wont bind to the column

[JAZZCNC]

pouring aluminium into the tube will just make a loose slug, the ally wont bind to the column

It could also distort the column with the heat coming from it.!!

[Jonathan]

You want the X-axis rails attached directly to the bed, not the bearing blocks. It'll save material and keep the bearings (i.e the support) in the same place in relation to the spindle regardless of the X-axis position. The same goes for Y - orient the rails like on the machine Jazz posted.

You've mentioned using 25mm ballscrews, but it's a bit early to be deciding that yet. On a router we'd say use 16mm screws, as the critical speed isn't a limiting factor for this size machine. However on a milling machine it can be worth using bigger ballscrews if the increased stiffness is beneficial - but you can only know that when the frame (etc) is designed.

pouring aluminium into the tube will just make a loose slug, the ally wont bind to the column

Yep, and it won't do a lot for damping either, which is the purpose of the epoxy...

[embraced]

Thanks for the advice everyone.

I will tackle the column design first.

So from the suggestions, I've moved from RHS (rolled hollow section) to a welded plate construction. the rear of the column has pockets to put the E/G mixture into, and to perhaps have another plate bolted on to seal the pockets and act as a torsion box.

Am I on the right track?

[Boyan Silyavski]

What is the exact column length and what is the head height? Having in mind what Dean said that the head looks too narrow.

[embraced]

Column width is 250mm at the narrow end, 500mm at the bottom end. length is 1100mm, and the depth is 250mm.

[Boyan Silyavski]

So from the suggestions, I've moved from RHS (rolled hollow section) to a welded plate construction. the rear of the column has pockets to put the E/G mixture into, and to perhaps have another plate bolted on to seal the pockets and act as a torsion box.

Am I on the right track?

Bolted? Forget about bolted. Welded sounds better . If you want to pour later E/G , just make pass holes prior to welding the pieces.

Making all braces same distance is not a good idea vibration wise. Introduce some progression or irregularity, in distance i mean.

What you call a torsion box will not function properly if braces are same thickness as the large plates. Plates should be thicker, or the side braces should extend more. Otherwise instead of torsion box you are creating weak spots.

Beware with that side braces cause they must be braced also between them IMO.

[embraced]

The reason i'd like it to be bolted is so it can be disassembled and lifted without more equipment. It's also easier for me from a manufacturing standpoint.

Good suggestions on the irregularity. I'll do that.

I should mention that I'm more interested in HSM, not ploughing through plates with gigantic cutters - hence the 12000rpm spindle. I would put one of those high-speed ATC integrated spindles on it if they could measure up to the performance I would get out of the servo-spindle.

[Boyan Silyavski]

I guessed so, about the HSM i mean. Your choice seems very good to me. Will it be 1:1 driven or variable puleys

So how you plan to move the counterweight? I mean could it be better that the counterweight slides on a cheap round rail or something, for the sake of perfection? Inside or outside?
Inside would be better, cause it would not be seen and at the same time you have to make the beam bigger, so that means stronger, tough also means heavier.

I believe that for a proper build you should forget your worry about moving the thing. I have made various mistakes thinking like that in the past. You will make it perfect, it will make money, so who cares. Any way making something more than 120kg needs special planning when moving and possibly a machine to lift it. It would cost you exactly the same if you move 200kg or 350kg or 800kg, so concentrate on the final characteristics you need.

[embraced]

Good suggestion regarding the weight.

For the spindle, the motor I will be using has a max speed of 8000rpm. The spindle has a max speed of 12000rpm.
I will put a 60T HTD5M pulley on the motor and a 40T on the spindle. I will still get a large amount of torque on the bottom end - 15.7N.m. I don't really imagine I would need more than this, given that the BF20 I have only has 3.6N.m. with a 1.8kw servo - and I have not managed to make a cut using all the available power yet.

As for the counterweight, originally I was going to have the counterweight slide on a round or HIWIN rail at the back of the column. With the new changes on the column I am starting to think that I may be better with a gas spring next to the ballscrew to push the column up.

Thoughts?