View Full Version : Sieg SX2.7 (Long Bed) CNC Conversion

12-05-2019, 11:16 PM
Okay, it's been a few weekends of work but finally got my SX2.7 under power...


Bench was the original frame for a router I'd intended to build, but chickened out (it was going to be too large for the shed... so became a pretty handy bench). As part of that original design I'd planned around supporting 2 19" racks - using one of these to fit a HP server, the control box (PSU steppers, motion controller) and a server keyboard/monitor - for which the backlight on the monitor finally failed today...


The other 19" bay (out of shot) now simply holds my compressor (a silent 25l ex-dentist job). The central bay just holds stock material.


Z Axis - it's all been done before, I'm just copying others who've converted their 2.7s. Z is by far the easiest axis and the original ball nut holder takes a standard 1605 ball nut. 2:1 belt drive as a general approach to all axis.


Some detail on X - ignore the hack job on the ball nut - I was trying to expose the nut holder's bolt hole in situ to unbind the screw that was slightly misaligned after I'd tightened all bolts. That was a difficult few minutes with a Dremel and none too pretty.


Y Axis - very much like the others. I'm not sure that I like the limit switch so exposed, so might re-do this once I regain my enthusiasm.

Control box is a 800VA 50V dual secondary toroidal transformer; rectifiers and 10,000uF/160VDC caps. With bleed resistors - despite arguments on here to the contrary. Stepper drivers are 2DM860H (4 of to support a 4th axis), Steppers are 3.1Nm 4-wire - just cheap eBay jobs. Motion controller is an UC300ETH with a standard parallel BOB. I finally found a use for the 5/24V PSU that I'd stripped out of a laser printer.

Both Y and Z axis the screws are unsupported, X has a phosphor-bronze bush to support the end of the screw (butchered with a band saw) mounted in the end plate. General approach was limited to hand tools or what I could fit on a Denford Starmill (150x80 table area - somewhat limits options). Oh, and everything with an option to recover the machine back to the original manual control if necessary.

I've tested the machine at 1000mm/min and it's faultless (I shouldn't say that so soon), though my original wet-finger - I didn't realise that UCCNC defaulted to 20% jog speed, and at one point had it running at 4000mm/min - sounded sweet but that's crazy fast for a mill this size, so it's now got a more sensible limit,.

Next is to sort the limit switches properly then consider belt guards for each axis. I've also removed the neutral switching on the e-stop and used the now spare way of the switch to provide the e-stop signal back to the control box. This, and the probe and limit sensors to be routed through a connector mounted into the 8x4" plate on the top/rear of the column.

What I don't have is a solution for the spindle - I've eyeballed the brushless motor controller, think I understand the basic operation but don't fancy reverse engineering that one. I might instead scope the control board in the pendant and see if I can create a closed-loop emulation of the control buttons to get a form of speed control. For now, manual operation of the spindle. I'd be interested if anyone else has a solution for this.

13-05-2019, 09:48 PM
I'd be interested if anyone else has a solution for this.

Well!, that might be easier than I thought... there looks to be a PWM at 10kHz between the front panel control and the spindle motor driver on the main power board. I'll get probing when I can be arsed and it looks like an interface could be easy to interface with a standard 0-10V supply (microcontroller, ADC and PWM driver). Details to follow.