X4+ 4Axis Backlash

[Martin Long]

I have recently been using the 4Axis to engrave a scale on a 30mm dia bar, I found the when producing the numbers they appear to be, not quite right, sort of on an angle of 1-2deg. On further inspection I found quite a lot of backlash in the rotary table, so no big deal to adjust the worm and wheel to eliminate this, I thought!
The worm wheel is not truly a worm wheel, it is a helical gear, with teeth which looked like they have been cut with a rusty nail, the burs on each tooth were so big, when I used a cloth to wipe the grease away they tore the cloth into shreads, OK, made in China you may say!!!
After tidying the teeth with a needle file, cleaned up and re- greased, I re-assembled the unit into the housing, I still found that I was having trouble adjusting the backlash, I could adjust the worm to eliminate the backlash at zero position but in 180deg. position it was too tight, or running in clockwise was ok but in counterclockwise is was tight.
On the rotary table side of the wheel assy. there is a thrust surface with an eccentric oil groove, however on the opposite side there is only a check nut without any form of thrust bearing or washer, the checknut face is not only running direct onto the housing casting, it is also machined out of square to the bore. This explains why it will run in one direction, but in the other direction it has no decent bearing surface.
To overcome this I have ordered a needle thrust bearing which is 5mm thick, I can machine the checknut by 3mm to accomodate the bearing whilst still ensuring to keep the checknut within the bottom surface of the housing.
I will take some photo's and post the bearing numbers etc. as I continue to try and make a silk purse out of a sow's ear.

Martin

[jalessi]

Simple solution.

http://tinyurl.com/4qnu3f

http://tinyurl.com/3ry7la

Jeff...

[Martin Long]

Jeff,
Thanks for your constuctive comment.
US$304 = AU$460
Shipping from USA to Aust. = US$70-100
Appox. total cost AU$600
One needle roller bearing AU$20

I will try my way first.
Please understand I'm not whinning about Chinese manufacture, I'm aware of what I purchased. I'm only trying to assist others, so they don't have to waist time investigating the problem.
Martin

[jalessi]

Martin,

I really welcome your efforts, it would be nice to have a inexpensive rotary table solution.

Please keep us posted.

Thank You

Jeff...

[Martin Long]

Further to my earlyer post.
Note the worm wheel has straight teeth.
Checknut with the shinny witness mark on one small area.
Location of where the checknut sits against the housing.
I should have the needle bearing tomorrow and will post my progress accordingly.

Martin

[iGG1e]

I hope you do find a solution. I'm just about at the stage where I want to use the 4th axis and getting it to run properly seems to be first on the list!

Please keep us posted.

[PEU]

Early this year we shown the Syil X4+ w/4th axis at a local expo, we ran a demo using the 4th axis all day long and I can vouch for its repeatability, the key setting IMHO is low speed, I had it set up at 2turns per minute and never had a problem.
Also you need to true it before using it, that will improve accuracy too.


Pablo

[sharpshooter90]

Our company had a Shoptask with 4 axis CNC and the Shoptask CNC rotary table. It used a worm gear on an eccentric to adjust the backlash. It ran zero lash and was smooth all the way. The table was made in India, and the quality was surprisingly good. The shoptask design also allowed manual use and use of dividing plates as well. Look at www.shoptask.com under "tooling" part # ST32

[Martin Long]

Fixed the backlash, but still not getting the quality I would like from my engraving.
Zero's appear slightly on an angle, Im using BobCam V21 to produce the text, vectorizing, then creating G code programe in BobCad.
As a newbe to CNC there must be something I'm missing, should'nt the two axis's X and A move in an interpolation and not as separate movements (ie I&J command)?
O()
G90 G80 G40 G54
G53 Z0.
T0 M06
S1600 M03
G90 G54 X0. Y0.
G43 H0 D0 Z1.
M09
G00X13.5965A34.3373
G01Z-0.2 F50
F200
X13.7252A34.8275
X13.8275A35.3972
A36.2428
X13.9694A36.7942
A37.3517
A37.9215
A38.4974
X14.0737A39.0734
A39.6493
A40.2313
A40.8072
A41.3832
A41.953
X13.9694A42.5105
A43.0619
X13.8672A43.6072
A44.2076
X13.7252
A44.7407
X13.5965
A45.1818
X13.4481
X13.2841A45.6413
X13.1089
X12.9288
X12.7492
X12.5787
X12.4211A45.1818
X12.2812A44.7407
X12.1681A44.2076
A43.6072
X12.0241A43.0619
A42.5105
A41.953
X11.9067A41.3832
A40.8072
A40.2313
A39.6493
A39.0734
A38.4974
A37.9215
A37.3517
A36.7942
X12.0241A36.2428
A35.7036
X12.1681A35.097
X12.2812A34.564
X12.4211A34.1229
X12.5787
A33.6695
X12.7492
X12.9288
X13.1089
X13.2841
X13.4481
A34.1229
X13.5965
G00A34.3373Z1.
M05
M09
G53 Z0.
M30

[iGG1e]

Not being exactly what you'd call experience in CNC either, but isn't it down to the configuration of the CAM program and the post it uses to implement the likes I and J commands in the final G code?

Was it the bearing fix that sorted your backlash out?

[Martin Long]

iGG1e,
I will wait to see what response I get from the post regarding the program.
Yes, I have fixed the backlash, but not entirely, I think there is some eccentricity in the wheel, there is a tight spot in the wheel, when I set it up so it drives ok over 360deg, there is a small amount of backlash in some areas. If I remove the backlash totally the motor stalls in some locations, I'm hoping with time the worm/wheel will bed in at the tight spots so I can re-adjust the worm accordingly.
With the needle bearing in place it certainly drives consistant in both directions. The bearing is slightly too big in the bore by 1.4mm, I will make a sleave to centralise the bearing at a later date. I had to turn the checknut thickness down by 3.3mm to keep it below the housing face, this also left just enough meat for the locking screw to be effective.
I can post photo's if anyone wants?
Bearing no. Torrington (not sure of the spelling)
1 @ AXK4060 (Bearing)
2 @ AS4060 (Washers)
AU$21
Martin

[ataxy]

photos are always good! please do.