I have no experience of the Proxxon, but I am in the slow process of doing a 3 axis lathe conversion to do a similar job of engraving the outside of pens.

The Nema 17 motors use in the Proxxon conversion are tiny, with very little torque. I would strongly advise that you check the torque requirements of the machine you are to convert. The torque needed to apply an axial force with a leadscrew is roughly as follows (from 'Ondrives&#39:

Torque (N.m ) = Axial force (N ) x Pitch (mm ) / (2000 x PI( ) x thread efficiency )

Where: thread efficiency = 0.35 for conventional threads and 0.85 for ball leadscrews and PI( ) = 3.1415

The axial loads you will need to consider are:

1. Table friction, both 'stiction' and the smaller dynamic friction.
2. Required acceleration of the table
3. Cutting forces ( these will be tiny compared to the acceleration loads )

It is close on to impossible to guess the friction and stiction loads, so a spring balance pulling the table with the leadscrew removed is needed. You might just be able to calculate the torque by applying a load to a lever attached to the leadscrew drive handle and hanging a weight off.

OK that's one minor technical bit considered. The most important bit is being completely clear in your mind what you want to do. Is it just to create spirals? Or any type of engraving? How fast? How capable. It is an easy field to waste money in, as I have. I wanted to engrave and cut threads for pens, so bought a 4 axis gantry machine, and discovered the zeroing and repeatability of the gantry was such that the thread cutting was insufficiently concentric. For the engraving, it was adequate. But.. The multi start thread cutting on a conventional lathe is close to beyond me as I need up to 5 starts at really wierd pitches, which is one reason why I wanted the CNC. So, one answer is to convert a lathe, which is now what I am slowly doing.

Hope this sets you thinking

Regards

Richard.

I bought one of those Proxxon tables to go with a small drill press, also a Proxxon, and it was money wasted. The quality of the table and screws is poor and it's very small. You would be surprised how much space is taken up by your headstock and tailstock and how little is left for for the work.

If you want to the CNC route I suggest either converting a small lathe by adding stepper drive to the headstock, cross-slide and leadscrew; or a small mill such as the X1 from Arc, or a Chinese gantry router – though Richard found its accuracy poor for threading it might be perfectly satisfactory for your purposes..

And depending on whether you want to get lost in Arduino programming as well as all the mechanics, use an established CNC controller such as Mach 3. Actually what you want to do is best done with a mill controller such as Mach 3 Mill as it can drive 4 axes – 3 linear and one rotational.

Can I recommend looking at this thread John **LINK** It is the best step-by-step introduction to using an Arduino to control stepper motors that I have seen, with pictures and descriptions of all the components required, and was the first Arduino project I attempted. The program (sketch in Arduino terminology) includes keypad, display and stepper control, as well as some arithmetic to set the angles, so it is a handy program to tinker with.

The only caveat is that the little blighters are addictive – but with a pack of 3 Elegoo Nanos (The Uno has funny pin spacing whilst the Nano plugs straight into a breadboard or can be socketed or soldered to Veroboard) costing less than £10 on Amazon, it isn't an expensive vice.

Brian

there are several reasons why metal lathes will not give you the gearing required – 1st is the size of the banjo usually used – second is the torque required to be transmitted thro the gear teeth to drive the screw thread driving the cutting tool many times faster than the speed of the chuck

you are into wood lathes where the cutting force is generally considerably less than for metal and the required accuracy is generally lower – the now discontinued Trend router lathe would appear to be the basis of what you want – however with low cost generally comes lower accuracy and it is not clear that you could reset passes on this to give the accuracy you seem to want – the Trend + similar devices would appear to have been aimed at spindles for banisters etc for low production volumes – these days the large professional CNC lathes would turn out such at cost much lower than the skilled labour cost of manual production – however you are looking at serious money here – you may well find it useful to visit Axminster tools who seem to sell into this market but have a deep cheque book.

Edited By Frances IoM on 24/06/2018 12:44:33

The Sieg C2 / Chester Conquest style "7×14" mini-lathe is just about large enough for the size you mention. Often available on eBay at prices 300 – 500 squids.

The book on making the Quorn describes setting up the lathe to make a spiral groove in the main column. IIRC a Potts spindle on the carriage driven from overhead with a slot drill; leadscrew driven by a handwheel and geared down to the headstock. Worth a look perhaps to see how the gears were done.

Mach 3 – you can get everything you can want and more here. It's an application that runs on a PC to control a CNC machine tool. In its standard form it outputs pulses via the parallel port that can drive stepper motor drivers directly. It is programmed either by providing it with G-code or using its internal wizards. M3 Turn however assumes that the spindle is turned in the normal way, if you drive the spindle with a stepper it becomes a "rotational axis" which is best handled with M3 Mill.

IIRC = If I Recall Correctly

You could just buy the ARC KX1 which is the CNC version of the X1 suggested earlier and that even comes with the stepper for a 4th axis pre wired so easy to add a rotary table as your forth axis spindle. Plus it has a high speed spindle which you won't get converting a standard mill without extra work with gears or belts.

Arc do a 4" rotary table as a plug-in (the 6" version would be a bit big for the KX1)

https://www.arceurotrade.co.uk/Catalogue/Workholding/Rotary-Tables/4-Rotary-Table-with-Stepper-Motor

I've got this part and it does work very well.

The prices really have shot up – getting nearly double what I paid about eight years ago and I got Mach3 and Cut2D bundled in the machine price.

Jim.

Edited By Jim Guthrie on 25/06/2018 09:24:42