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Building a 4th axis and could use some help/opinions

Anathema

Plastic
Joined
Feb 1, 2022
First, I'm trying to be semi-economical and build a rotary fourth axis I already have a 400w Servo (Stepper Online T6) and I'm looking for a dividing head or rotary actuator to couple it. Then I will design a mount and coupling so I can run an Erowa chuck on it. This is for a small machine so trying to keep it under 120mmish in all dimensions no counting the servo, So far I'm looking at two options neither or which I'm super stoked with.
1. Ebay dividing head, This scares me simply because it's on ebay. Also the reported stats aren't the bes CNC 4th Axis Dividing head Rotary A axis For Metal Reducer 15:1 + 125mm Chuck | eBay
2. Alibaba, rotary actuator. High Quality Hollow Rotary Actuator Table For Servo Motor - Buy Hollow Rotary Actuator Table Product on Alibaba.com same as above.

Am I on the right track with these or do I need to be looking for something completely different. My work is small and light and I would prioritize precision and repeatability over everything else. I've got max around $2000 to spend.
 
What is your time worth per hour, to design and build this? What performance (accuracy, backlash) do you need to achieve? What machine and controller do you hope to connect it to?

Considering time and materials, what would you charge to build a $400 6" vise? If it's more than $400, you shouldn't build it. The same equation applies to a rotary.
 
Sureline rotary with stepper already on it. I think one for sale in the commerce section. Buying new is well in your budget with lots to spare.

The next level up is well beyond your budget.
 
I know low cost rotary tables exist but none that I've found offer exactly what I want. I need one with a through hole in the center and being able to run a tunable servo on it isa big plus for me.
 
What is your time worth per hour, to design and build this? What performance (accuracy, backlash) do you need to achieve? What machine and controller do you hope to connect it to?

Considering time and materials, what would you charge to build a $400 6" vise? If it's more than $400, you shouldn't build it. The same equation applies to a rotary.
If you are time poor then yes you can't afford build it however if you have limited funds and lots of time you should build it. The payoff will not only be money saved you will learn a lot.
 
I know low cost rotary tables exist but none that I've found offer exactly what I want. I need one with a through hole in the center and being able to run a tunable servo on it isa big plus for me.
If you are using flood coolant you will have issues of rusting etc. Are you wanting simultaneous 4 axis movement or indexing.
 
If you are using flood coolant you will have issues of rusting etc. Are you wanting simultaneous 4 axis movement or indexing.
I use alcohol mist for coolant. This will mostly be used for indexing I do manually now. but I would like to incorporate 4axis rotation as part of the cutting operation in the future.
 
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If you have the necessary skills it wouldn't be difficult to build a stepper driven indexer using something like Arduino.
 
If you have the necessary skills it wouldn't be difficult to build a stepper driven indexer using something like Arduino.
I have a Masso running the machine and already installed the servo driver for a 4th axis I need to figure what will get me the best repeatability for <$2000. I can make the fixtures and the mount but it needs to have at least a 10mm through hole but 20m would be better.
 
You know a cnc 4th has a huge brake built into it right?

I've bought 3 different full cnc 4ths, modern ones. 6", 8" and 13". Most I've spent is $1000
 
You know a cnc 4th has a huge brake built into it right?
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I've bought 3 different full cnc 4ths, modern ones. 6", 8" and 13". Most I've spent is $1000
The servo I have has a brake. Not sure that's the same thing but looking in the servo tuning app it looks like it could be used in this way.
 
The servo I have has a brake. Not sure that's the same thing but looking in the servo tuning app it looks like it could be used in this way.

No, it's not. The brake is on the spindle and the same diameter as the face plate in most situations.

If this is just tiny hobby stuff then use whatever junk you want. If you want to mill and drill metal you need a brake.
 
A brake on the motor is not the same as a brake on the table axis. (Backlash over time)
I have put 100W-400W servos on Phase II rotary tables for grinding (very wet). Been doing it for 25+ years. 3:1 belt.
The worm drive lives about two years. Then we just put on a new rotary table. We keep spares in stock.
Accuracy. lash, etc is a function of part size and location as the error is angular. You do not specify largest size and numbers needed.
Think 1/8 inch wide grooving tool located on center vs 6 inch part not on center.

Also brakes. Bought my first 3+2 in the early 80's. Brakes on the tilt and rotate along with super high resolution encoders.
It was Trokey's first tilt/rotary cnc dive into this world. Options where others but I went with this. How hard can it be?
The integrator had a heck of a time with the Fanuc servos trying to tell them not to fight when the brake turned on.
One example here of needing a brake is drilling a decent size hole off center. You can not allow the servo to hunt or move when doing this.

Used tables can be a deal but if that gearing has gone bad you had better be siting down when you price a replacement.
In some of my other grinder heads that is now over $8000 for a new split zero lash gearset.:eek:
Remember the days when it was only $1800. Should have put many of those in stock knowing I will eat them up.

With all these warnings said I built my first as a proof of concept machine to grind threaders and groovers.
A platform to work out the software swinging rads and such and did not expect anything out of it.
Was very surprised.
 
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Let me reframe the question. I'm willing to save up to get the right piece of equipment espcially if I cannot make it. If I raised my budget to $5-8k what would be the most accurate rotary 4th axis with a diameter no larger than 120mm
 
Let me reframe the question. I'm willing to save up to get the right piece of equipment espcially if I cannot make it. If I raised my budget to $5-8k what would be the most accurate rotary 4th axis with a diameter no larger than 120mm
To connect to what machine and controller? That makes all the difference.
 








 
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