View Full Version : Mini lathe as a 4th Axis

16-08-2017, 01:37 PM
I have used a little mini lathe under my gantry router to good effect for vertical mill turning. If I wanted to make it into a 4th axis driven by a spare Nema 34 Could anyone suggest the toothed belt ratios to use please. It seems 50:1 or 100:1 are popular? Any experienced Knowledge gratefully sought.
A source of the t/belt pulleys would be welcomed also please.

Boyan Silyavski
18-08-2017, 05:10 PM
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.

18-08-2017, 05:19 PM
If I wanted to make it into a 4th axis driven by a spare Nema 34 Could anyone suggest the toothed belt ratios to use please. It seems 50:1 or 100:1 are popular?

With a single belt, you'll have trouble getting more than a 4:1 ratio, due to the size difference between pulleys. To get to 50:1, you'd need a worm gear, or harmonc or planetary gearbox.

18-08-2017, 05:23 PM
Boyan - the lathe does not have a gearbox, just a six position belt drive. I anticipate replacing the belt drive with a 20mm timing belt setup. Currently I am thinking 22T driver to 112T driven.
Will only be used for wood plastic and maybe aluminium. Thanks for your information. I have no knowledge of servo`s. Just trying to use what I have at this time.

Boyan Silyavski
18-08-2017, 06:56 PM
You could use the belt calculator web for finding the right belt https://www.bbman.com/belt-length-calculator/ , i asume you know of it, but anyway here is the link.

it seems that 17-18T is better choice as it has 6 teeth in mesh, versus 7 teeth for 20t, so you lose almost nothing. 6 teeth is the minimum recommended for HTD 5 belts, so you are ok there.

so 17x7=119t, which is better as its a whole number of ratio . Its not bad 1:7 ratio . Its 180mm diameter puley, the big one

I can generate you the pulley profile if you need. Thingverse also there is a pulley generator.

18-08-2017, 07:43 PM
Boyan - Have you printed pulleys? I had not considered that option until you mentioned Thingverse. - Could print a 180mm dia. quite nicely in ABS. Got to be a cheap option if it would be serviceable? Thank you for the idea.

18-08-2017, 07:48 PM
You can increase the number of "Teeth in Contact" to at least 50% of the count on the driving pulley by using idler pulleys to generate a serpentine belt path as is done in the automotive industry,

- Nick

18-08-2017, 07:59 PM
Nick - Yes adding a flat side idler would be quite simple. Thanks.

Boyan - Ref. Thingiverse. Did you reference "Customizable Gear4"?

18-08-2017, 08:18 PM
Would you recommend any particular tooth form or pitch please?

18-08-2017, 08:31 PM
Sorry missed that on your reply Boyan. HT5.

Boyan Silyavski
18-08-2017, 09:20 PM
I have printed with great result.Small as GT2. I will advice PETG pulley. PLA will work also. ABS not. Nylon, even better.

HDT5 15mm will work great


19-08-2017, 09:43 AM
Boyan - thanks for your advice. Do you reinforce the the pulley centre, as I will try first with PLA and wondered if it would take the torque from the shaft?

19-08-2017, 10:25 AM
Boyan - Thingiverse/ OPENscad 2x Pully files just now easily and quickly completed. Excellent resource.

Boyan Silyavski
19-08-2017, 04:33 PM
Boyan - thanks for your advice. Do you reinforce the the pulley centre, as I will try first with PLA and wondered if it would take the torque from the shaft?

I print such things extrusion width 0.5mm, with 0.4mm nozzle at 0.2mm layer height , 4 perimeters at least and 50% infill at 90 degree mesh. I don't want to brag, but i consider myself already an expert and i carefully analyze and have in mind many things before a print so results are always working. For things like pulleys and so i will carefully look at the preview to see if there are any unwanted spaces due to object size divided by extrusion width and if needed will change a parameter until i am happy. needless to say when i design something for printing, i will know from the beginning how exactly i would like it printed .

I would have used a nice print, then ream the hole then use Loctite medium or high strength retaining compound for a permanent bond, not superglue.

19-08-2017, 04:58 PM
Boyan - I will follow your advice carefully. There is an interesting new update to Simplify3D which addresses void issues so I will study that to see if it might be used to good effect.
I am indebted to you for your assistance. Thank you once again.

24-08-2017, 09:53 AM
Ik have a 4th axis that I can use as a lathe, it has a 12 nm closed loop stepper.

With help from a friend I can now run it in both positioning mode and continuous mode.
It has a 1:1 transmission and can run up to 1500 rpm, which scares me....:

I use linuxcnc.