The Shop > Tools
Alexander Engraver to CNC Miller Conversion
philf:
Having been mainly an observer on the site for some months I have been coerced into doing a post of my own.
Some years ago I acquired 2 Alexander manual engraving machines for the princely sum of £100. They looked like a suitable basis for a CNC conversion and, at the price, I couldn't resist them.
Even better was that, a matter of weeks after acquiring them, I saw an ad on Homeworkshop.org for a spindle for an Alexander engraver. I replied and was offered £100! The spindle was despatched and thus the machines were free! The pantographs and copy tables were taking up too much space and went to the tip.
Some time last year I decided to unsheet the machines which had been stored outside and drag the best one into my workshop.
Before I retired I managed to acquire a good assortment of very high accuracy ballscrews off redundant equipment. The mounting of the nuts wasn't conventional but they were too good not to use. I spent a lot of time drawing out parts of the engraver and eventually found a convoluted way of using them. (Keeping the y-axis screw protected from swarf was a major issue.)
Unfortunately I didn't take any photos during the conversion but this is the finsished machine:
The spindle is home made and is supported on an arm fabricated from 4" thick wall square tube with a piece of 4" x 1" mild steel welded to the end. From a distance the welding looks OK but it's only after milling off the lumps and filling in the holes with Plastic Padding! I could do with attending the Rob Wilson School of Welding! The face was machined square to the arm in the lathe.
I designed the spindle to take ER32 collets directly and wanted it to be capable of up to 10,000 rpm. The bearings are precision preloaded double row angular contact at the bottom and at the top two deep groove shielded ball bearings which are preloaded together but can float relative to the bottom bearings to take care of thermal expansion. To get to my desired 10,000 rpm top speed the bottom bearings had to be oil lubricated and hence the drip feed lubricator. The 'coolant' nozzle isn't connected to a coolant pump - it's connected to a fairly quiet diaphragm compressor to blow chips out of the way as well as cooling the tool. Sticky materials like CZ 108 brass still need lubricant but I apply that with a paint brush.
The spindle is driven from a new 0.55kw 3,000rpm inverter class motor which runs from an inverter at up to 5,000 rpm. The 3 step pulleys are Poly-vees giving ratios of 2:1, 1:0.8 and 1:3. My lowest speed is about 250 rpm. Embedded in the spindle pulley is a magnet for a hall-effect speed sensor. At 5,000 rpm the motor develops over 1hp which will be enough for my needs.
The controller for the machine is built in a 19" rack which I managed to blag from an old work colleague. The badge on the front was one of my first jobs on the machine. Excuse the labelling on the front - I need some Traffolyte to make some nicely engraved ones.
The drivers are 4.5 amp microstepping drives running at 8 microsteps. The steppers are 23 size 3 N-m. The x and y screws are driven directly whilst the Z axis acme screw is driven via the original 1:2 bevel gear and a 1:4 belt reduction. The power supplies were an Ebay bargain and run at 43v at 9.9 amps. The breakout board came from Hungary and is fully opto isolated.
For finding datums etc it's useful to be able to control the axes manually. An XBox 360 handset is excellent for rough positioning but lacks sensitivity. For very fine control the Contour Shuttlexpress video controller is superb. Both are catered for in Mach3 (my choice of control software).
The marks in the table aren't my doing - they were already there.
Before I finished the machine I built a 4th axis. The spindle is held in relatively massive taper rollers and uses a Harmonic Drive (again from a piece of redundant equipment) which has a 200:1 reduction with negligible backlash. The nose is 'a la Myford' with a 1.25" register and 1.125 x 12tpi thread and 2MT. (I have Myford collets and chucks left over from when I sold my Super 7.) I have yet to do anything useful with it but I'm sure (hope) it will be indispensable.
The last thing I made for it was an auto tool height setter. This interfaces with Mach3 to zero on to the top of a workpiece and then back off to a safe height. The drill in the collet is broken - CNC isn't forgiving of typing mistakes!
Finally a picture of some parts completed on the machine which are for a 3 1/2" gauge Lion loco. These are all in mild steel and are up to 3.2mm thick.
I've not yet tried using a big cutter to test the rigidity of the machine. If it is a problem I can easily brace the machine across the swan-neck. (The other machine didn't have the swan-neck but was in poor condition - or so I thought.)
Even though the basic machine cost very little the drivers, stepper motors, power supplies, motor, software etc etc soon added up to about £700.
Jobs still to do are to replace the Z axis leadscrew with a 25mm x 5 ballscrew and possibly take some of the weight with a gas strut and improve the sealing to the spindle to make sure that the waste oil goes down the drain tube and not as a line across my clean shirt when I turn the spindle on!
The taper on an ER32 collet is very similar to a ISO30 taper and I have dreams of making an auto tool changer...............
Hope this has been of interest.
Phil.
Brass_Machine:
Nice! I love CNC conversions.
I have questions, if you don't mind :dremel:
1. I am going to do the X-box controller for my conversion. Hadn't thought about the shuttle express... are those controllers expensive?
2. I would like to know more about the auto tool height setter. In fact, I want to make one. Did you design it yourself or did you use plans?
Again... very nice job!
Eric
Rob.Wilson:
:clap: :clap: :clap: :clap: Now thats a very nicely done CNC conversion, very tidy Phil
What CAM software are you using ?
I also would like to no a bit more about the Tool hight setting doo dad :dremel:
Those loco parts look cracking .
I am pleased you took the time to post,, good read :D
Rob
philf:
Hi Eric,
Shuttlexpress controllers crop up regularly on EBay - I think I paid about £25. New, they're anything from £35 upwards in the UK. They're a dream to use for edge finding.
The height setter is my design - it's very simple. The top is spring loaded to allow for overtravel. (Mach3 will decellerate the motors to stop after seeing the sensor. Stopping instantly might lose steps.)
The drawing was done just for me to make it so isn't very detailed. It's all made in stainless. The three springs give continuity between the platform and the body as the DU bushes don't conduct. I've added a few notes.
One connection goes to the pin shown the other to another pin pressed into the body (not shown on the drawing).
I don't connect these directly to the breakout board. I have a plastic box with a couple of AA batteries, a switch, an LED and an opto-isolator. It's the opto-isolator output which connects to the breakout board. (The earth to my controller is different to the machine so I didn't want to risk blowing anything up.)
Hope this helps.
Cheers.
Phil.
Rob.Wilson:
Thanks for sharing you design Phil :med:
I am sure i have a Glacier bush suitable for the job .
Rob
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