Denford Software & Machines

hi im looking for advice on a 4th axis to fit to my triac running on mach3.

ive seen a load on ebay that look like the stepper holds the chuck in place by a belt ,which looks like itll be jumping around . ive also seen advertised gapless harmonic drive versions which have the same pic as above so im a bit wary.

i just wondered if anyone can recommend one for reasonable money that they have bought

cheers

If you are engraving on the centre line you can use a direct drive, but once you move from centre the cutting force is multiplied by the distance from centre so you need a proper worm and wheel type. The cutting loads with drilling and milling is far too great for any other type.

There are some nice small 90 degree low backlash gearboxes on various web sites at good prices it may be worth sticking a chuck and motor on one of these.

Just make sure what you get has a metal worm and wheel set, wiper motors are plastic, no good.

My advice for FWIW is to buy a reasonablby priced 4th axis direct drive or belt drive type, the worm and wheel type wear very quickly unless you pay big money for a high quality one. I have a Sherline one on a Triac and it really isn`t very good, when I get the chance/time to get back into my workshop I will be doing a Servo driven either belt or direct driven one !!

On the belt type, nothing wrong with that at all, remember your X,Y and Z axis are already running with belts and the backlash is minimal, there is usually more in the ballscrews
Direct drive speaks for itself, no issues with either belts or worms so if you have the space for one, remember it may foul your enclosure if you have one.

Now, as Mach3/4 is outputting a step/direction signal you can fit a small say 100watt or 200Watt Servo motor instead of a Stepper depending on how hard you want to machine on your 4th axis, the reason for this is that you can buy Servo motors that have a Brake built in so when the axis stops the Brake is applied which gives a much more stable and accurate position to machine against
Downside of the Servo with Brake is you may need an extra small power supply for the Servo Drive as it will be different to your Stepper drives PSU and also a small low voltage supply for the Brake, usually 24volts DC on the Brake.
You will need to get all the relevant dimensions and double check just how far the motor with Brake will stick out, they are quite a bit longer than a normal servo and way longer than a Stepper

Just my ideas on this and from what I have researched it isn`t terribly expensive, not cheap but not going to break the average bank

Hope that helps.
Regards
Rob

Lone_Ranger wrote: ↑

Wed 15 Apr , 2020 16:55 pm

My advice for FWIW is to buy a reasonablby priced 4th axis direct drive or belt drive type, the worm and wheel type wear very quickly unless you pay big money for a high quality one. I have a Sherline one on a Triac and it really isn`t very good, when I get the chance/time to get back into my workshop I will be doing a Servo driven either belt or direct driven one !!

Worm and wheel is a good option, but I would never hold anything Sherline as even an average example of sound engineering.
The big draw back with worm and wheel, is if you're using a stepper motor, rotation speed is pretty limited.

On the belt type, nothing wrong with that at all, remember your X,Y and Z axis are already running with belts and the backlash is minimal, there is usually more in the ballscrews
Direct drive speaks for itself, no issues with either belts or worms so if you have the space for one, remember it may foul your enclosure if you have one.

But the ball screws give you a lot of mechanical advantage. The issue with direct or belt drive, is you're relying solely on the motor, which unless you use a very large motor, there is always going to be some 'spring' in the drive, along with limited holding torque, so you're limited to ever decreasing depth of cuts as you increase diameter.
Adding a brake is a valid option, but then you're limited to the 4th axis simply being a glorified rotary indexer, which for a lot of work is likely to be good enough.


I do have some sketches done for a 4th axis for my Triac, but I've just never got around to building it.
My plan is a worm and wheel, with suitable adjustment for backlash, and running using about a 200W servo, however one of my key requirements is being able to pass a length of bar through it like a lathe headstock, which is why I opted for worm and wheel.
If I didn't want the hollow spindle, I'd probably opt for a harmonic drive setup.