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johngoodrich
14-08-2017, 05:44 PM
http://www.ebay.co.uk/itm/152304246962?_trksid=p11400.c100710.m5035&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1% 26asc%3D20170110123657%26meid%3Db8a7809b599a46e8b7 35e7c22e5e0a4d%26pid%3D100710%26rk%3D1%26rkt%3D2%2 6sd%3D152304246962&ul_noapp=true

i'm looking to machine wood only on it, no metal and maybe some plastics. do you think this will be ok. Tolerance is not too important as it will be all arty type stuff. opinions please

Chaz
14-08-2017, 06:06 PM
It *should*. Accuracy will likely be the issue however if this is not too much of an issue for you, might be fine.

There are many of these around, I'm sure ive seen them cheaper.

johngoodrich
14-08-2017, 08:28 PM
hi chaz. any idea where you have seen them cheaper. the only place I have seen is china and then you get vat and import on them so doesn't work out

paulus.v
15-08-2017, 12:34 AM
cheaper (https://www.aliexpress.com/store/product/EU-Delivery-K12-100mm-4th-Axis-CNC-dividing-head-Rotation-Axis-Tailstock-for-Mini-CNC/704350_32821915007.html). shipped from Germany as well.

what about this one (https://www.aliexpress.com/store/product/CNC-Rorary-axis-A-aixs-4th-axis-Gapless-harmonic-reducer-Gearbox-3-jaw-100mm-dividing-head/704350_32338368636.html)? harmonic drive they say.

I cannot see any accuracy problem, maybe only in the axis alignment. the issues are resolution and torque. with the 6:1 reduction, at 100 mm diameter one full motor step will translate in 0.27 mm of movement.

harmonic drives are in a different league, if they are for real inside..

Desertboy
16-08-2017, 07:47 PM
hi chaz. any idea where you have seen them cheaper. the only place I have seen is china and then you get vat and import on them so doesn't work out

When I ordered my ballscrews the import tax should have been 68 when they arrived they were marked as 2nd hand ballscrews with a value of $10 each, customs didn't buy this but only put 15 in import tax on.

Import tax is luck of the draw but personally from China I'm pretty lucky anything from the US I get screwed on to the full value.

Robin Hewitt
17-08-2017, 10:52 AM
I thought these bolt to the bed rotating chuck things usually came with a worm drive and an index wheel/pin.
Sticking a stepper in place of the index handle is a CNC conversion.
Replacing the worm wheel with a toothed pulley sounds like a Chinese CNC conversion. More for selling than using.
Maybe you want to engrave toothpicks and this is exactly what you need.
Alternatively, maybe if you bought it as an incomplete conversion, played with it, decided what resolution your usage required, replaced their timing pulley with a nice anti-backlash worm from HPC gears, tried it with the stepper then replaced the stepper with one of those singleton servo drives doing the rounds on eBay.
That could work.

magicniner
17-08-2017, 12:17 PM
I have one of the type in the first link in the OP, I chose it for the decent through capacity which you don't get with harmonic drive versions, it worked well enough as standard but I added a link bar and bearings outboard at the back behind the belt to take bending load off the stepper shaft and was then able to add a belt tensioning pulley bearing.
A few hours work and a few quid in bearings yielded something which is up to 4-axis machining in Ally and Steel using tooling up to 12mm and 7000rpm.

I had a good indexing head but I believe that a converted/ home brew worm/wheel job is more of a bodge than pulleys, belts & bearings because long term under CNC use gears and plain bearings will require more maintenance, more expensive maintenance and more complex maintenance.

- Nick

magicniner
17-08-2017, 12:17 PM
Double Post, Sorry guys, gremlins on the interface!

Robin Hewitt
17-08-2017, 04:54 PM
What is a harmonic drive? Do they mean epicyclic?

Gary
17-08-2017, 05:13 PM
Harmonic is a brand name and people recognise it just like hiwin,but yes its epicyclic.


What is a harmonic drive? Do they mean epicyclic?

magicniner
17-08-2017, 06:42 PM
Er, no they don't and no it certainly is NOT!

https://en.wikipedia.org/wiki/Harmonic_drive

https://en.wikipedia.org/wiki/Epicyclic_gearing

Both have teeth, that's about it for similarity.

Gary
17-08-2017, 06:52 PM
I stand corrected.
So its a Strain wave gearing.

Er, no they don't and no it certainly is NOT!

https://en.wikipedia.org/wiki/Harmonic_drive

https://en.wikipedia.org/wiki/Epicyclic_gearing

Both have teeth, that's about it for similarity.

paulus.v
17-08-2017, 07:01 PM
Harmonic drives are the perfect solution for high gear ratios, high torque, lightweight, and the most important, they have no backlash. Widely used in multi-axis cnc, articulated robots, etc.

There are a lot of them on ebay, SH from Korea, the only ones at an affordable price...

I was surprised that the Chinese claim to have 4th axis with harmonic drive... possibly used ones fitted inside..

A_Camera
18-08-2017, 10:32 AM
http://www.ebay.co.uk/itm/152304246962?_trksid=p11400.c100710.m5035&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1% 26asc%3D20170110123657%26meid%3Db8a7809b599a46e8b7 35e7c22e5e0a4d%26pid%3D100710%26rk%3D1%26rkt%3D2%2 6sd%3D152304246962&ul_noapp=true

i'm looking to machine wood only on it, no metal and maybe some plastics. do you think this will be ok. Tolerance is not too important as it will be all arty type stuff. opinions please

I have been considering something similar for quite some time now, but can't make up my mind about it. In theory it would be very useful for me, it would save time because it would turn around the work piece automatically, but maybe the work piece would vibrate too much so it would be useless for what I am doing, so I am not sure. Never the less, there are plenty on eBay as well, shipping from Germany most of the ones I found.

Anyway, I am interested in the subject, as well as the use of it and the experience people have.

Robin Hewitt
18-08-2017, 11:26 AM
Has anyone bought one of these harmonic drive index chuck thingies? Are they any good? Is the lack of a through shaft putting you off? Who will Magicniner contradict next? So many questions, life is too short for all these questions.

magicniner
18-08-2017, 12:25 PM
Who will Magicniner contradict next?

As you clearly prefer your information to be of the non-factual variety I'll leave you to it :D

A_Camera
18-08-2017, 12:57 PM
Has anyone bought one of these harmonic drive index chuck thingies? Are they any good?

I am sure they are pretty good otherwise they would not be sellable.


Is the lack of a through shaft putting you off?

Yes. That and the fact that it is considerably more expensive.


Who will Magicniner contradict next?

I found his comments very informative and valuable. I don't know what you see was wrong with his comments or choice of words, but I did not find them contradicting, quite the opposite. I would actually be interested in hearing more about his experience and the modifications he did, as well as how he is using it.


So many questions, life is too short for all these questions.

...so why did you ask the last one then? It was pretty rude and unnecessary. His comments were pretty valuable, as opposed to your last question... :disturbed:

Robin Hewitt
18-08-2017, 04:27 PM
I...so why did you ask the last one then? It was pretty rude and unnecessary.

Don't worry, he's a Yorkshireman, he's already retaliated.

johngoodrich
18-08-2017, 09:33 PM
magicniner, do you have any photos of the mods you have done to your 4th axis. I would like to see it. from your experience with these, do you thinkit would be ok for 4th axis wood milling as is, or a bit of modding

magicniner
18-08-2017, 10:54 PM
John,
I have an early pic of the "proof of concept" I knocked up with what I had lying around,

22607

I've subsequently re-worked the spacer support with alternate bearings to reinstate the through capacity of the spindle, it does what I need in brass, bronze, aluminium and steel.
I don't think it would have been up to much without the tensioner to remove backlash, without the support the stepper shaft bends if you tension the belt,
Regards,
Nick

johnsattuk
20-08-2017, 03:00 PM
I chose it for the decent through capacity which you don't get with harmonic drive versions, - Nick

Picked up this harmonic drive some time ago for a 4th axis project, not yet got round tuit. 50 -1 with 25mm through and pre-loaded cross roller bearing on the output ring

22615

Robin Hewitt
20-08-2017, 03:13 PM
I just found these things existed but I already feel a deep need to own one, was this an e-bay find?

magicniner
20-08-2017, 03:53 PM
Picked up this harmonic drive some time ago for a 4th axis project, not yet got round tuit. 50 -1 with 25mm through and pre-loaded cross roller bearing on the output ring

22615

Yeah,
Harmonics with through capacity exist but are not fitted to the Chinese eBay 4th axis models under discussion here, nice thing to have in the parts drawer, please post some photos when you've completed a project with that,
Regards,
Nick.

johnsattuk
20-08-2017, 04:39 PM
I just found these things existed but I already feel a deep need to own one, was this an e-bay find?

Yes, came across it after I had bought a 5phase stepper with 50-1 harmonic drive ( 25000 steps /rev ) which I was going to belt drive a head 2-1 so that I could incorporate a through hole. I also have some very low backlash 5 phase 10-1 (5000 steps/rev ) epicyclic drives that I thought I might use with perhaps ~4-1 belt drive.

2261622617

Robin Hewitt
20-08-2017, 06:03 PM
I have now bought a 50:1 harmonic to play with, eBay item number: 291926642351
I thought maybe connect it to a shaft using my favorite Myford change wheels. Not easy to cut the middle out 100% concentric so I would have to spring two together, that seems to do the trick if you want low backlash with Myford wheels. I think I could enjoy this. Somewhere in my junk boxes I have a new pair of 40mm self-aligning, flange bearings, featuring grub screws on the extended inner race. They could easily become a part of this.

johnsattuk
20-08-2017, 06:15 PM
They come in various sizes, 11 is quite a small one, do you know shaft sizes

Edward
20-08-2017, 09:13 PM
I use lots of harmonic drives for my motion control rigs. I buy them second hand from ebay, but I have also bought a couple of modern brand new ones from the Harmonic Drive rep in the UK. They are very expensive new. HQ is in Germany but usually made in Japan, they own the monopoly, so the cheapo Chinese contraptions may not live up to expectations re. "zero" backlash, quality of bearings and so on. A brand new size 25 HD will usually cost a couple of thousand. I paid 1500 for each size 11 for a camera rig. They are beautifully made.

The one above from Johnattuk is a proper one with very good angular bearings. These usually come from small robotic machines that are decommissioned, a lot from S Korea, and a bit old, but perfectly usable. Some work perfectly, some have seen better days and will work, although they may be a bit bumpy at certain speeds, which you wouldn't probably notice on cnc rigs, but you do notice in motion control where perfect smoothness throughout the range is paramount.

The one you bought, Robin is too small, being size 11, with small bearings. You need at least a size 25, with size 14 being a bit marginal. Typical price for a good decent second hand size 25 with hollow shaft is around 450.

Here is a render of one of mine showing both ends

Edward

22623

And this will give you a perspective on sizes. Size 11, size 14 and size 25

22624

magicniner
20-08-2017, 10:23 PM
I thought maybe connect it to a shaft using my favorite Myford change wheels..

Surely you'll be using Anti-Backlash gears from HPC Gears as it would be a strange choice to add backlash in the primary drive (regardless of how small an error this would introduce) of a system designed specifically to avoid backlash?

Jonathan
20-08-2017, 10:25 PM
And this will give you a perspective on sizes. Size 11, size 14 and size 25

Lightweight ;), here's a size 50:

22644

I had two of these sitting in my shed for 5-6 years - like Robin I found out about them and immediately decided I must have two. Then I got very sidetracked, so I sold one recently and held on to the other. I think I'm more interested now in coaxing a high torque motor into a direct drive axis, as the cost of encoders is decreasing. Seems more elegant.

One interesting point with harmonic drives is that although they don't exhibit backlash (if well made), they still do have some hysteresis. Still, beats buying a chuck driven from a stepper motor via a rubber band.

magicniner
20-08-2017, 10:32 PM
Still, beats buying a chuck driven from a stepper motor via a rubber band.

It could, but I've been making parts with my "rubber band" for a couple of years, how's it going with your "Doorstop" ?

Robin Hewitt
20-08-2017, 10:40 PM
They come in various sizes, 11 is quite a small one, do you know shaft sizes

I think it is 6mm in, 12mm out.

Jonathan
20-08-2017, 10:48 PM
It could, but I've been making parts with my "rubber band" for a couple of years, how's it going with your "Doorstop" ?

Well enough:

https://www.youtube.com/watch?v=lVuBEEceWJ4
http://www.mycncuk.com/threads/3341-4th-Axis-running-as-CNC-lathe-using-milling-machine
http://www.mycncuk.com/threads/11220-Mini-lathe-as-a-4th-Axis

Unfortunately I ran the stepper motor on the rotary table into my milling machine column (wasn't looking) last year and bent the worm gear, so I do have another doorstop! I'm now wondering if these are better than the price suggests:

http://www.ebay.co.uk/itm/Precision-HV6-Rotary-Table-150-mm-Horizontal-Vertical-Milling-Indexing-Dividing-/222515565808?hash=item33cef614f0:g:VYsAAOSwZ4dZHZk C

The problem with the direct belt drive method is the stiffness of the belt is quite poor compared to a harmonic or worm drive. Of course, it can be useful but that depends somewhat on the diameter of the material, your accuracy requirement and other factors. If the rotary table above is any good - i.e. "most" of the backlash can be adjusted out, then that plus a 1Nm stepper motor seems like an attractive option.

Robin Hewitt
20-08-2017, 10:49 PM
Surely you'll be using Anti-Backlash gears from HPC Gears as it would be a strange choice to add backlash in the primary drive (regardless of how small an error this would introduce) of a system designed specifically to avoid backlash?

Wow, it almost designs itself.

Edward
20-08-2017, 10:50 PM
Robin if it's like mine in size 11, then it's probably 6mm in, 10mm out.

And Jonathan, I also have a size 50 monster that I use on a crane rig, weighs a bit that one:)

Edward

magicniner
20-08-2017, 11:26 PM
Wow, it almost designs itself.

That's extremely fortuitous then ;-)

Robin Hewitt
28-08-2017, 11:17 AM
I just took that harmonic drive apart, one screw head decided to snap off, one had to be drilled off.

Much as expected, only remarkable thing is how fine the gear pitch is.

These gears are about 28mm diameter...

2268522686

Edward
28-08-2017, 11:26 AM
Not just the fine pitch but also the fact that they are flexible to mesh and I am not totally sure about the inner workings, but I think they have one more tooth than the gears they mesh with, or vice versa. Incredible concept and I guess very difficult to machine such precision.

Edward

johnsattuk
28-08-2017, 11:59 AM
Not just the fine pitch but also the fact that they are flexible to mesh and I am not totally sure about the inner workings, but I think they have one more tooth than the gears they mesh with, or vice versa. Incredible concept and I guess very difficult to machine such precision.

Edward

Need 2 teeth difference and because of the fine pitch, need a bit of care when reasemmbling as it is easy to be one tooth out, do not force. :eek:

Robin Hewitt
28-08-2017, 12:14 PM
I have to get those headless screws out before I can reassemble.
M2.5 and darned close to the bendy cog. I don't have anything suitable to grab them with.
Any ideas?

johnsattuk
28-08-2017, 12:19 PM
Have you tried two or three nuts locked together perhaps with heavy duty locktite retainer as well

johnsattuk
28-08-2017, 12:33 PM
You may need to dissasemble further to avoid damaging the flex ring ( bendy cog ), if you dissasemble further it wil give you more ways of gripping the screws, perhaps a heat cycle on the screws would help quick blast on the top of the screw till red and let cool before trying to remove.

Need to be very clean on reassemby, because of the very fine pitch quite small foreign bodies will quickly ruin the drive.

Robin Hewitt
28-08-2017, 06:53 PM
Broken studs removed, new tool shopping opportunity sadly missed, drive reassembled less screws, M2.5 taps ordered to clean out threads. Gave it 50 turns without noticeable sticking points so probably okay. Having arrived, been taken apart, looked at and reassembled it has probably achieved it's purpose and can now comfortably rest in a drawer until my son finds it after I have snuffed.

machpoet
21-06-2018, 10:49 AM
cheaper (https://www.skysmotor.com/category-55-b0-4%E8%BB%B8CNC%E3%82%B9%E3%83%86%E3%83%83%E3%83%94% E3%83%B3%E3%82%B0%E3%82%AD%E3%83%83%E3%83%88.html) . shipped from Germany as well.

what about this one (https://www.skysmotor.com)? harmonic drive they say.

machpoet
21-06-2018, 10:50 AM
hi chaz. any idea where you have seen them cheaper. the only place I have seen is china and then you get vat and import on them so doesn't work out