Thread: Advice sought on new Mill build
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24-09-2014 #1
Hi,
You need a miny version of my recent aqusition.!! . . . .
The column won't be the weak link thou it could be made much stronger.! It will be the narrow head and weak base. Would look at making the Head have wider foot print by either using wide section or placing wide think plate on front of Section.
The base is far too Flimsy IMO and will require much more substance and bracing to avoid twist and stress from every thing above. You shouldn't rely on fastening the base to a frame for strength because this will introduce error in the frame by pulling and twisting. The base is the foundation and your starting with crumbling bed rock.!!
Look at the base of the machine above it's one Solid cast Iron lump with coolant tank built into it so it's very very heavy and dense to resist the forces from above.
From the outside the column looks like hollow box section but it's actually made up of 5 Thick steel plates welded and braced. If you look and zoom in you can see thru the lifting holes just how thick the material is. You can also just see the Red counter balance weight which is a Big lump of steel on round linear guide. That head is perfectly ballanced and I can lift it with one finger.!!
Personally I would forget using section and Epoxy Etc for the strong parts and make a weldment machine using thick steel plate and lots of bracing. If you do go down the Hollow section route just fill the Section with Sand it's much easier and dampens resonace good which is what your wanting. It's also easy to remove when moving.!Last edited by JAZZCNC; 24-09-2014 at 10:52 AM.
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24-09-2014 #2
Hi Jazz,
I can't see the attachment.
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24-09-2014 #3
pouring aluminium into the tube will just make a loose slug, the ally wont bind to the column
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24-09-2014 #4
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24-09-2014 #5
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.
Yep, and it won't do a lot for damping either, which is the purpose of the epoxy...
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26-09-2014 #6
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?
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26-09-2014 #7
What is the exact column length and what is the head height? Having in mind what Dean said that the head looks too narrow.
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27-09-2014 #8
Column width is 250mm at the narrow end, 500mm at the bottom end. length is 1100mm, and the depth is 250mm.
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27-09-2014 #9
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.Last edited by Boyan Silyavski; 27-09-2014 at 09:35 AM.
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27-09-2014 #10
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.
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