Based on this machine.
VM32 Variable Speed Milling Machine | Belt Drive Milling Machine | Bench Mill | Quality Metalworking Mills
Justification - in the UK the 80kg lighter AMA20 style machine is £1200, this machine is bigger, heavier and stifffer for £1450. The next bigger machine is an RF45 type but that is £2100 - with CNC parts that makes it too expensive, also the weight may be too much to dissemble and rebuild in my garage. I am tempted by a RF45 type though for the extra stiffness..
This is the list of parts
Mounting Hardware - price of alloy maybe expensive due to some large parts, end plates will be alloy, I may use steel for the saddle mount, will have to wait and see. I strongly considered some of the kits available but I wanted to use different (better grade) ballscrews, also they are in the USA and my machine may well be different to say a PM30 so the parts (or some of them) may not actually fit, and I'd have to pay for shipping to the UK (for parts that may not fit) so I will make my own. I have a small manual mill at the moment so can make parts on that.
Mach 4 £160 - Just because I use windows..
3 Nema 34 4nm closed loop and drivers £400 Justification - quite a lot of thought gone into this. I don't want cheap drivers and believe steppers are still on par or better for accuracy (I want the machine to be accurate), I used the motorcalcs excel spreadsheet to try and estimate max torque and figures come out very low - 0.26Nm cutting with 150mm/sec and 75Nm force 5mm pitch ballscrews. Most torque appears to be needed for acceleration at high speed - this set-up can reach 3000mm/min in the spreadsheet, it may be a lot better than that because of the use of closed loop steppers.. I may also consider some lower Nm steppers but I wanted plenty of reserve if I want tight gibs and ballscrews to improve accuracy...
3 power supplies 120 - just std switched 60v supplies
C5+ ballscrews For me I'm not happy with C7 accuracy so will pay a bit more and go for C5 (new parts) or better than C5 (2nd hand parts)
Ballscrew machining TBC
Double preload balnuts 90 This is based on the quote from Fred at BST on Alibaba I think - no name ballscrews but they are double with adjustable preload. I'm expecting I may have to reball if they are too tight on the shafts I have and also adjust the preload (any info on how to do this is welcome)
Electronic Case 30 - planning to use a computer case from the electronics
Toolco VM32 1450 Mill
Breakout Board (smoothstepper) ethernet 160 I need to understand what this does, if it's necessary or if cheaper alternatives will work well..
£36 for Dunlop 3 double sets of angular contact bearings.
£?? unknown for a spindle speed control - can I tap into the machines spindle speed controller and do this easily/cheaply?
Total is around £2540 at the moment.