Minimill to 4th Axis....

[abfa9358]

Hi
No plans as such because the conversion was bespoke to the harmonic drive I found on ebay. Hopefully, the build thread gives enough detail on what I did.

[Turbo442]

I have a few harmonic drives listed on Ebay right now. They are 50:1 gear ratio with a 6mm input shaft, no backlash. I am kicking around building a 4th axis with a 5C collet holder using one of these drives driven by a Nema 34 for my Novakon NM145. 50:1 gear ratio should give good holding power with out a brake.

HD 14 50 Harmonic Drive Systems Gear GearHead Reducer Conventional Input Shaft | eBay

[SwampDonkey]

Hello,
What kind of harmonic drive? Can you show me? Where is the source of cheap harmonic drive?

I actually have a few with servos attached if you're hunting around for them. Perfectly sized for something like this.

Harmonic Drive Servos 1000PPR Encoders | eBay

Yes, I have them on ebay since I really dont need them. And you'll get the cnczone 20% discount

[Azalin]

Hi,
@abfa9358 I don't know if you are still around but what size of FB type HD did you use on the 4th axis? I have a BF20L CNC mill and will build a 4th axis. I have 17 and 20 size in my mind but could not decide which one to choose.

[joeavaerage]

Hi,
harmonic drives are good but expensive. Additionally if you have a toolpath that requires continuous rotation they are slow.
Lets say you have a servo of 3000rpm and a harmonic drive of 50:1, then the max speed of rotation is just 60rpm. Its going to take a long time for the toolpath to execute.

I chose to use a servo reducer by Atlanta Drives. I got this drive as new old stock for $150. It has a reduction of 19.5:1 and has lash of < 2 arc min. I'm building a fifth axis,
and the drive is another new old stock Atalanta Drive servo reducer of 6.75:1 reduction and a lash of <1 arc min. Cost $180USD about two months ago.

My fourth axis has a 3000 rpm servo for an output speed of 150rpm. Its useable, but I sure wouldn't want it to go any slower. My new fifth axis also has a 3000rpm servo and with its reduction
the free running speed of the fifth axis will be 440rpm.......which will be a real step in the right direction.

Note that the chuck unbolts and I'll substitute a trunnion table with the fifth axis, pictured partly built.

Craig

[GeckoSub]

Hi,
I chose to use a servo reducer by Atlanta Drives. I got this drive as new old stock for $150. It has a reduction of 19.5:1 and has lash of < 2 arc min. I'm building a fifth axis,
and the drive is another new old stock Atalanta Drive servo reducer of 6.75:1 reduction and a lash of <1 arc min. Cost $180USD about two months ago.

Craig

Hi Craig,
(Apologies to the OP for this slight sidetrack)
Have been reading up on the Atlanta Servo Drives prompted by your love for them and I suspect your <2arc min one is a 58 series. Not sure which size, maybe a 5-6, but anyhow here comes the question:

How did you mount the chuck? As far as I can tell, the 58 series only comes with a hollow spindle often with a key way, none of them come with a face plate like some of the 98 series do (I think).

[joeavaerage]

Hi,
you are correct, I have one 58 series (2<arc min), size 4 (63mm between worm center and worm wheel centre), and one 59 series (1<arc min) size 3 (50mm worm centre to worm wheel centre).

The 58 has a 28mm hollow bore and keyway. I turned a shaft with a flange to mount the chuck. The 28mm shaft to flange is the most compliant (opposite of stiff) of the whole thing, but nothing I can do about it.
The 59 had a 28mm hollow bore with extension that was compression clamped to the shaft of the load. I cut the extensions off and cut a keyway. The Fifth axis platter has a 28mm shaft and 150mm diameter
platter. Again the 28mm shaft to platter is the most compliant part of the design, but it is what it is. To date I have been happy with its stiffness.

Craig