Wormgear 4th axis

[hokkaju76]

Purchased this unit from Singles-day sales in AliExpress. Unit is with 130mm chuck and Nema 34 Stepper.
Everything is pretty much as expected, including backlash issue.

I stripped all to parts and backlash is due fact that worm- and main-gear are not close enough to each others.
Gear and worm seems to fit pretty nicely together



I´m thinking how to create shift main axis. It´s bit thin to machine stuff away and make eccentric bushings.

Also I´m puzzled to weld it.. Most likely its casted aluminum. So just weld bit material on side and machine eccentric location for bearing and sealing.



Outside is easy, just make eccentric cover.



So any suggestions?

Cheers-Jukka

Similar Threads:

• Open Source : 4 axis and 5 axis print with a 3 axis milling in order to have a 5 axis
• Need Help!- 4th axis rotation on x axis chaging to Y axis in simulation
• Source for wormgear system-building rotary stage
• Wormgear cutting

[awerby]

Any gear and worm is going to have backlash. It's necessary for there to be some clearance in there, or the gears will freeze up. When you write "create shift main axis" It sounds like you're going to try to move the shaft closer to the worm, using welding to build up the case and re-machining to restore the mating surfaces . This is a lot more likely to result in a rotary table that won't work at all than one improved in its function. You'd be better off building a rotary table from scratch than in trying to improve this one in that way. If you can't tolerate any backlash, start with a harmonic or cycloid drive. But as long as the thing isn't actually flopping around, it will probably work okay as-is, if you avoid changes in direction, which is where the backlash will show itself.

[hokkaju76]

Yes I know, I´m not looking for 0-backlash its not going to happen in this price range.. I´m just going get max out of my spend $300 + postage.
Just for reference at edge of chuck backlash was like 1/16" or 1.5mm which is too much. Teeth were just about 0.4-0.5mm too far from each others.

But you are right, if I overdo my repair It will be jammed, so there are pretty accurate measurements involved here.

Worst case losses are about 100$, which will mean I need new Chinese NMRV-40 gearbox. So we are not talking here about big $.

[addman16]

Purchased this unit from Singles-day sales in AliExpress. Unit is with 130mm chuck and Nema 34 Stepper.
Everything is pretty much as expected, including backlash issue.

I stripped all to parts and backlash is due fact that worm- and main-gear are not close enough to each others.
Gear and worm seems to fit pretty nicely together



I´m thinking how to create shift main axis. It´s bit thin to machine stuff away and make eccentric bushings.

Also I´m puzzled to weld it.. Most likely its casted aluminum. So just weld bit material on side and machine eccentric location for bearing and sealing.



Outside is easy, just make eccentric cover.



So any suggestions?

Cheers-Jukka

Hi what was the model number for that. Looks great trying to see if I could buy it

[hokkaju76]

Hi what was the model number for that. Looks great trying to see if I could buy it

https://www.aliexpress.com/item/CNC-...70784c4dLz8vqk

Or search AliExpress with 130mm 4th axis.

Actually I got pretty nice idea , it will involve 6906 and 6907 bearings. I´ll do adjustable gear mesh clearance to my drive with smaller ones and bigger ones are for new supported chuck axis.
Lets see what happens, sad that those bearings are not too cheap locally, so I need to wait China Post.

[addman16]

https://www.aliexpress.com/item/CNC-...70784c4dLz8vqk

Or search AliExpress with 130mm 4th axis.

Actually I got pretty nice idea , it will involve 6906 and 6907 bearings. I´ll do adjustable gear mesh clearance to my drive with smaller ones and bigger ones are for new supported chuck axis.
Lets see what happens, sad that those bearings are not too cheap locally, so I need to wait China Post.

Interesting....
I'm seeing some rotary tables with a harmonic drive they are supposed to help with backlash 100:1 reduction same price

[asuratman]

I'm seeing some rotary tables with a harmonic drive they are supposed to help with backlash 100:1 reduction same price

with only 100 mm chuck, no 130 mm chuck

[hokkaju76]

Yes I have seen those also. But there is no data of backlash in numbers and regarding price I was bit suspicious that there is actually planetary gear instead of harmonic gear.
This is just my guess, I have not seen any evidence to either direction. I just know that true nice harmonic gear alone is few hundred $, even second hand.
If you are interested to buy one of those, I´d be very pleased and I believe many others if you could share your experiences.

[asuratman]

For now, I am using the worm gear like yours. But in the future I plan to use harmonic drive. I saw on ali, its not too expensive. I am still confused which part to use.

[hokkaju76]

Bearings arrived, now gear is assembled with eccentric bushings over smaller bearings. It was bit tinkering to find good tuning.
But it seems to be possible to make it backslash "free"... Well at least it not wildly shaking back and worth.
Eccentricity of like 0.3 mm would have been enough, I just took 1 mm by guess and adjustment needed was actually very small in angular vise. Bit fiddling to get it nice and snug still avoiding it to stuck.

[DAAD]

Jukka,

Are you still happy with the rotary axis?

Adam

[hokkaju76]

Jukka,

Are you still happy with the rotary axis?

Adam

Hi. Yes Im am. It works as expected. I build Division Master to run it.

[hanermo]

Fwiw, it IS possible to build worm gears with zero backlash.
Many strategies exist.

E.
One could have a secondary worm wheel behind, on the same axle, but preloaded onto the shaft.

One could have a single worm gear, but preloaded onto the shaft axially, by a small amount.
Like a floating end bearing, preloaded by a belleville spring.

They don´t need to have clearance to work, but the wear goes up if they don´t have any clearance and even worse if they need to slide.
Most gears do not slide - they contact, and as such do not have fast wear.
Auto transmissions are typical examples.

Very complex, multiple shafts, multiple complex gears on each shaft.
Extremely accurate, and last 20 years lifetime with 10 years typical service life, with zero maintenance apart from maybe one change of oil.
The gearbox on a car, small sedan, costs about 3000 €.
The engine costs about 3000 € all-in.
Everything else in a sedan costs about 6000 €.

These are the prices OEM manufacturers like gearbox in madrid charge the auto companies to make say qty 100.000 per year of transmissions for a given normal basic sedan.
The 12k car costs about 16k with taxes and stuff, and then retails for about 28 k with 22 VAT, or 23 k without.
Add dealer margins and advertising costs, typicallly 8% for cars.

[DAAD]

Hi. Yes Im am. It works as expected. I build Division Master to run it.

Thanks for the reply! Do you use the division master with the cncn?
Any idea where you got the excentrinc bushings?

Adam