Chinese 4th Axis on Ebay

[ArtF]

Please do. I was looking at those last week wondering if I migth be better off with one. They do seem
to be well built and very well hobby sized...

Art

[Richard Cullin]

I got one in my 3040 mill package , its acceptable but the belt tensioner arrangement was badly made ,it needed modifying to make  re-tensioning even possible.  A 4 jaw chuck would be nice too but they are drilled for 3 jaw only , I'm not game to re-drill it yet

[JustinO]

I use my Sherline CNC rotary tables and a Sherline stepper spindles for gear cutting/generating. The tables are 72:1 to the motor, which is a little slow, and the stepper spindles are 2:1 to the motor, which is a little low in resolution.

I've been wanting something in between, but I'll want something that I can use my tooling on. My tables and stepper heads can hold all my chucks, arbors, mandrels, face plates, etc.

I can boost the stepper spindles to 4:1 with another set of cogs, and if I get myself a new computer with more "steps", I get more speed out of the tables.

Between the two, I get what I need for now.

I've been experimenting with three nested rotary axes.

[ArtF]

I see a couple on ebay that are 2 nested axis a 4th nd a 5th..that looks kinda interesting..
Bet I could cut a bevel then... :)
  The toolpaths would be a bitch to calculate, but itd be fun. Too bad there isnt enough of them
out there to make it feasable to do..

Art

[JustinO]

I hand code bevel gear g-code in my sleep. Do you want it for a tapered mill or a straight mill?

[ArtF]

Keep that thought, we can have an in depth discussion on Bevel Gcode when I hit the bevel recoding, Ive never been happy with my approach.. :)

Art

[Mooselake]

@JustinO, those must be interesting dreams.

Can you post some eBay links?  My eBay search-fu just isn't finding them.

Kirk

[ArtF]

I thought these were cool..

http://www.ebay.com/itm/CNC-Rotary-Tabl ... 4d0b1662c8

Art

[JustinO]

Kirk:
Search for this on Ebay:            4th axis engraving machine

[Mooselake]

Thanks!  I must have been having a bad search day.  The two axis version looks pretty interesting.

Kirk

[danmauch]

Don't buy one of those Chinese 4/5th axis combos. The 5th axis has practically no torque even with a 380 oz in. 3.5A  direct drive motor.
They say they are for engraving and that is true. But engraving takes a lot less torque than for machining. They are worthless for machining.
I have been working on my Chinese 4/5 axis to up the torque for the 5th axis. I have been trying to make a hypocycloid gear head attachment but business has slowed the progress.
Here is a video of engraving the letters CNC on a dome using my 5 axis G540+1 control box.
http://www.youtube.com/watch?v=rF67CGlEVK4
If you skip past the 2 minute description of the control unit you can see the 4/5th axis as well as the XZ movements.
Pretty cool.
What is not showing is the machining of the dome/hemisphere. I actually had tohelp with my hand the C axis to rotate to prevent lost steps. So it wouldn't even cut soft pine.
The B axis could easily be increase in cutting force by adding a second ratio and the other thing to do is to mount the stepper motor on the outside for more travel in the B- direction.

My friend wrote the G code using and expensive Cad/Cam program. He had a lot of trouble getting the post processor working right.
We wanted to use Rainea's CNC_Tool_KIt  as a plugin to Gmax but his program was setup to use the spindle 4/5th axis and not the trunion type 4/5th.  He and I posted on their web site a few times to see if they would change the program but no one was interested. As I recall it is open source.

Dan Mauch

I see a couple on ebay that are 2 nested axis a 4th nd a 5th..that looks kinda interesting..
Bet I could cut a bevel then... :)
  The toolpaths would be a bitch to calculate, but itd be fun. Too bad there isnt enough of them
out there to make it feasable to do..

Art

[Dan]

After watching the tangential shaving you-tube video I think it's time to go past 2D gear cutting and into a 4th axis setup.   There are two basic types,  6x1 belt driven and 100x1 harmonic drive reduction.

Do you have a link for a harmonic driven axis? Don't see any on eBay.

Dan

[JustinO]

Dan:
This one mentions "Gapless harmonic drive reduction gearbox. Gearbox made in Japan"
http://www.ebay.com/itm/CNC-Router-Rota ... 3cc129641d

[Dan]

Thanks Justin. That's interesting. I am not keen of the 0.3mm end play. The other disadvantage of this arrangement is it being very long and not suitable for some little machines and there is no through hole for bar stock. Other than that the gearbox sounds like a nice thing. Interesting what's the actual backlash.

Dan

[John S]

Be careful on the belt drive rotary drives as utting forces can easily fore the holding torque of the stepper motor to jump.

I built quite a large one with 1500 oz/ in motor but doing splines with an 8mm cutter just did a spiral toolpath. You could see it jumping as it was cutting.

Finished up scrapping it and converting a rotary table.