Mini lathe as a 4th Axis

[Boyan Silyavski]

Depends on exactly what are you going to do and the resolution you will like to achieve. Also if you would use it for indexing 4th axis, slow turning 4rth axis for milling or on top of that use it for lathe 4rth axis altogether.

I keep a mini lathe for exactly the same purpose. What i intend to do is use 750W servo motor with brake so i have more possibilities.

For example if you would use it with stepper motor without feedback, i would say then use it well geared. Do you intend to use it on place of the lathe motor and use the lathe gears or not?


The Inturn mill lathe 4rth axis was geared originally 1:7 if i remember correctly and uses additional 150mm or bigger mountain bike hydraulic brake when indexing, at least before he further developed it. here is some info from the mega duty PDF:

5C collet in spindle nose (draw tube included)
1.25” Spindle thru hole
5mm pitch GT curvilinear tooth belt drive
12:1 ‘back gear’ ratio
4:1 direct drive ratio
Speed range change by quick simple belt move.
Rotating parts balanced for 4,000 RPM operation
7075 aluminum plate frame construction
Reduces mass and draws heat off bearings
Pneumatic internal spindle lock with 100ft-lbs @90psi
Accommodates up to 3HP servo motors NEMA, DIN or OEM


So according to me 750w braked servo motor on the place of the original one and using the lathe gears will fit well my intended purpose for small parts of plastic and aluminum, indexing or lathe jobs. If that does not work and have to direct drive it then 1:10 or what ratio pulley fits reasonably and forget about using it as lathe.


By the way i can generate you any size HTD 5 pulley if you need to machine one. Just drop me aline.