Which 4th axis?

[ohiococonut]

I've been looking at adding a 4th axis to my home made machine for some time so I'm asking if anyone has added one or have any recommendations.
My machine has a cutting area of 49"x49" running on ball screws. I'm using (4) nema 23 270oz stepper motors with a Gecko 540 4 axis controller and a 48v power supply. I've completely wired the machine so there's no problem and I plan on using "A" axis to drive it and run it along my "X" axis. I'm also using Mach 3 and Aspire so software isn't a problem.

Suggestions or recommendations anyone?

[ozymax]

I made my own rotary axis for my router, so I can't offer any specific product.
I decided to use the Probotix motors and boards when building my machine and I have noticed that they started offering a rotary axis for their machine now.
Might be worth a look. Their boards and motors have worked perfectly for me.

http://www.probotix.com/accessories/

[cac67]

Take a gander at this one.

http://www.cncsharktalk.com/viewtopic.php?f=12&t=1521

[ohiococonut]

Thanks for the suggestions!

ozymax, right now that one is at the top of my list because I've read your other post concerning it. My other option was to buy one of the Chinese models and replace the stepper motor with something a little more substantial.

cac67, that is probably at the bottom of my list. I took Bob's simple 4th axis and modified it considerably with the intentions of modifying my Shark Pro Plus HD to run just it and cut dovetails. Unfortunately, the controlling software for the Shark is severely lacking and if I'm going to make a 4th axis for my larger machine I don't want to use wood. I actually bought a few components, rods, bearings and aluminum angle to begin the modification but decided to just build a larger machine that could do what I want, and I haven't even run the Shark since then.

Thanks again. Still looking for more suggestions to follow up on.

[mike1966]

I made a indexer/lathe using a planetary gear motor from automation technology and a 960oz stepper motor and bought a headstock from Grizzly $8 and had a machine shop drill a 1/2" hole so I could put it on the gear motor.The tailstock is $35 for a Grizzly 16"lathe.
for the bed I used 2 10ft pieces of 2in x 4in channel welded together with a 1 1/2in gap so the tail stock can slide like a regular lathe.It was realy easy to build and way cheaper and more sturdy than any I have ever seen.
If you are interested in building an indexer I can send some pictures

[martin54]

You might want to ask this question on the mach support forum as well as here, will give you a wider range of answers. I've always found it very helpful, unfortunately I can't put a rotating axis on my machine without carrying out major surgery.

[ohiococonut]

Mike, sent you a PM. Thanks!

Martin, I've been looking at most of the sites I know about and googled 4th axis until I'm google eyed
Surprisingly I'm not finding a whole lot of helpful info. Some of the designs I'm seeing are for steel milling machines and way too big. Others need to have pieces machined and I really don't want to go to the expense of buying a metal lathe/mill combo to make the parts, although before I decided to go with a wood cnc router I almost bought one. I'm a tinker by nature and always looking for a challenge.
Roughly 3yrs ago when I started this venture into wood I knew absolutely nothing about wood cnc machines so I need to keep the design within the parameters of my machine because when I built it, it WAS major surgery for me. Everything I've learned came from the web and the community here has truly been an inspiration and I'm glad to be a part of it.

It's just a matter of time, so please keep the suggestions and recommendations coming. Thanks again.

[ozymax]

Here's another idea.
Try and pick up one of those little cheap wood lathes from ebay for the basis of the axis.
Then modify the head stock to take a toothed belt reduction and mount a stepper to that.
You can probably machine up a motor mount on your router.
I use a 6:1 reduction on mine and that gives me good resolution. I bought my components https://sdp-si.com/eStore/Catalog/Group/346.

Here's my little axis that I made. Admitadly I have milling and turning machines to work with, but it may just give you some ideas.

I basically just use a flat face plate that has either 3 or 4 angle brackets that pivot and I use screws to hold the work.
I have a max dia of 90mm and a length of 650mm.

Here is my first ever test cut after I finally got the Mach3 settings correct.

[ohiococonut]

oxymax, thanks! Another idea to ponder.

[AlbertaClipper]

Hey Mike1966, I would be interested in some pics of your set-up if it's not too much trouble.
mcquadem@shaw.ca

Thanks

[Greolt]

Here is another idea.

And a video. Sorry you don't really see the axis until a couple of minutes in.



And this one shows a bit better. near the end.

[ohiococonut]

Greolt, Interesting build and thanks for sharing. I'm still putting ideas together.

[IslaWW]

Coconut...
You might want to determine your gear/belt reduction based on the diameter of your turnings. If you look at the attached chart, showing a 200 step/rev (1.8*) stepper with a 3 to one reduction, you can see that the step resolution changes with the diameter of the part. In some combinations of reduction and driver settings you can see that at certain (larger) diameters that the rotary axis returns unacceptable step resolution.

FYI, the step resolution is the smallest amount the indexer (with that combination of step setting and reduction) would be capable of moving (at that diameter)

This would make one think that you should strive for the highest microstep level that you could use, but there is such a reduction in holding power that this is not the case. I personally like to add mechanical reduction 15:1 or greater and keep microstepping set to full (200 native) or half (400), never more than 1/4 (800) to ensure that the indexer has the ability to hold its position. See chart below for reduction amounts.

[ohiococonut]

Gary,
Thank you so much for the info!
I was thinking about a 20:1 and don't plan on turning anything larger than 4" round. Speed (cutting time) is of no concern to me if I get the results I'm after since this is just a hobby.

[IslaWW]

Coconut...
Here are the numbers for a 20:1 reduction: