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Improving a cheap 4th axis
« on: July 07, 2013, 10:12:02 AM »
I bought a cheap 4th axis and found that the backplate and stepper shaft can flex slightly under load.
By adding a couple of bearings on plugs with a bar bridging them the majority of load is now taken by the bar under compression -



The cap in the stepper end is an eccentric adjuster allowing precise adjustment of bearing spacing.

I'd welcome input as to whether a tensioner a good idea now that belt tension no longer applies significant bending moment to the stepper shaft or axis back plate?

 - Nick

Offline Chaoticone

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Re: Improving a cheap 4th axis
« Reply #1 on: July 07, 2013, 10:45:49 AM »
Looks good Nick!  If it's a good belt (stainless wire braid core or similar that doesn't stretch) you shouldn't need a tensioner.  If I'm seeing it right, might add a lot to put a brace between the brace you have now and motor plate so that it carries all the load.  Looks to me like the brace as is, is dividing the load between shafts.  This would make your back plate a lot more rigid as well.

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!
Re: Improving a cheap 4th axis
« Reply #2 on: July 07, 2013, 04:37:08 PM »
Cheers Brett!
I'll definitely look at tying the brace to the plate, that's a great idea,
Many Thanks,
Nick
Re: Improving a cheap 4th axis
« Reply #3 on: July 21, 2013, 08:41:01 AM »
Here it is finally mounted on the mill -



After a false start with a Chinese 5-Axis board which promised the world and delivered only 3 working outputs I took a look in my existing 3-Axis Routout CNC box, imagine my surprise when I found 3 separate axis control boards and a full breakout board  ;D
By moving the mounts for the 3 vertically stacked Routout CNC axis boards I made space for an additional single axis board. A USB lead collects the required 5v logic supply for the new board from my PC and a connector from Maplin on the back gives my 4th axis output.
While I was in there I replaced the 4-pin inputs connector with a 6-pin connector making all 5 inputs available, then replaced the original home switch wiring and junction box which included a bench level connector for the 4th Axis and an Emergency Stop button.
Isn't alibrating a rotary axis is a wheeze? Get it looking good with 1 turn then try 5, 5 turns then try 10, 10 turns then try 20, 20 turns then try 50, can I stop now?  :D

 - Nick

Offline Chaoticone

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Re: Improving a cheap 4th axis
« Reply #4 on: July 21, 2013, 12:03:25 PM »
Looks real good Nick!  :)

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!
Re: Improving a cheap 4th axis
« Reply #5 on: July 29, 2013, 04:44:59 AM »
Thanks Brett,
It's definitely getting there!
The cheap Chinese 4th axis is definitely a worthwhile purchase as you do a lot for your money, the down side is that like much cheap stuff it's best stripped , fettled and rebuilt.
This one needed the tubular shaft facing square at both ends as it was cut off in a saw resulting in misalignment when assembled and pressed together, the spacer for the rear pulley was a section of plastic pipe cut with a saw which needed replacing with a turned part.
Once reassembled there was still a little runout on the chuck mounting face, milling under manual controll squared this up perfectly.
The chuck will need replacing at some point but for the time being I used 3 heavy springs radially between the jaws to allow the chuck to be tightened whilst open enough to allow grinding of the jaws, with the chuck mounted on my lathe and a Dremmel on the toolpost I was able to make the chuck acceptable for the time being.
Now I just need to make some stuff! ;-)
ATB,
Nick

Offline Tweakie.CNC

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Re: Improving a cheap 4th axis
« Reply #6 on: July 29, 2013, 05:16:50 AM »
Nice work with the 4th axis Nick  ;)

(You need a little shelf, a bit higher up, to prevent the machining chips getting into your Beer  ;D)

Tweakie.
PEACE
Re: Improving a cheap 4th axis
« Reply #7 on: August 03, 2013, 11:31:28 AM »
Hmm,
Cheers Tweakie, I've managed a test engraving of the words "Test Text" 5mm high around a 20mm diameter stainless bar and everything is looking positive, the "Beer Cup Holder" might be a good project ;-)
That'll have to wait a while though 'cos I've been reading through the Mach 3 manual on switch wiring. I've realised I could use the spare input I have (after bringing all 5 available inputs from the breakout board in my Routout CNC box out to the front panel on a new 6-way connector, then adding an E-Stop) to add limit switches;
This shows the original (red) X home switch and my new Y limit switch -



This shows the original (red) Y home switch and my new X limit switch -

« Last Edit: August 03, 2013, 11:40:34 AM by magicniner »
Re: Improving a cheap 4th axis
« Reply #8 on: March 21, 2014, 05:46:20 AM »
I've had a couple of questions about tuning the 4th axis so here goes -
My X and Y use similar steppers, the same settings in Mach3 and my driver boards for X, Y and A are all set the same.
X & Y Steps Per: 645 Velocity: 450 Accell 45
A Steps Per: 35.55 Velocity: 1500 Accell: 80

It will depend on how you have microstepping set on your axes but if you have the driver board for rotary set the same as X & Y then the following should provide a basic start point if you have the same or similar 4th axis:

Divide X Steps Per by 18 for A,
Multiply X Velocity by 3.3 for A
and
Use double the X Accell for A

The Steps Per figure I'm using is only tuned for accuracy over 10 rotations, tape a pointer to the body of your 4th and affix tape with a line on to the chuck to give you a datum.
Align your line with your pointer and Zero A then see how many degrees a full rotation reads, tweak your Steps Per down to increase DRO degress per revolution / up to reduce degrees per revolution.
Once you have one rotation looking good test with 2, 5, 10 and so on until you have the accuracy you want over the number of revs you want, once you are refining for more than one rev you'll be adjusting after the decimal point, at 10 revs you'll probably be adjusting 0.01 in Revs Per to fine tune
Regards,
Nick
Re: Improving a cheap 4th axis
« Reply #9 on: March 21, 2014, 05:54:37 AM »
My controller hardware is once again all British and my 4th axis is running smoother and faster than it was with the Chinese board I used to get it up and running.
For this I'd like to add a quick but big Thanks! to Routout CNC for taking the time to talk to me and find an appropriate matching driver board for my vintage Routout CNC controller box,

 - Nick