[abfa9358]

After upgrading from my minimill to an Optimum BF30 mill and doing the cnc conversion, I have been debating what to do with the minimill. Sell it? keep it as a mill? Hmmm. I have also been looking around at designs for a 4th axis and it struck me that the head of the minimill might make a pretty good basis for a 4th axis for the BF30.

So the other night I set too and got the head off the minimill and from first inspection it looks like it will work quite well. The plan is to use a harmonic drive and stepper motor coupled to the minimill spindle for the motive power and attach an adaptor plate to the front of the spindle. In this way I retain the MT3 tapered bore plus I have mount point for lathe chucks and tooling plates if required.

Attached is the first bit of CAD, more to follow.....

[abfa9358]

So things have moved on a bit. I now have a working design that connects a Harmonic drive FB type pancake drive to the spindle of the minimill. Motive power will come from a small NEMA34 stepper motor - the harmonic drive is 160:1 ratio so no need for masses of input torque.

Attachment 258136
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[hiep]

like

[asuratman]

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

[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

[Fastest1]

Did you click on the highlighted "Harmonic Drive" in his post? It takes you straight to the ad on Amazon.

[rowbare]

Did you click on the highlighted "Harmonic Drive" in his post? It takes you straight to the ad on Amazon.

You can't be sure of any link on this site anymore. Most are just some autolink advertising/redirction crap. Like harmonic drive for instance... I didn't add a link there btw so if one shows up...

bob

[asuratman]

Hi,
Yes, I clicked on the highlighted "Harmonic Drive" . I found it not clear explanation. Then I tried to find on alibaba, Many type of "Harmonic Drive", I do not know which one the best suite for 4th axis. Maybe in the future, I plan to make 4th axis, It is low backlash as said in the ads.

[mcfatburger]

Hi, Yes, I clicked on the highlighted "Harmonic Drive" . I found it not clear explanation. Then I tried to find on alibaba, Many type of "Harmonic Drive", I do not know which one the best suite for 4th axis. Maybe in the future, I plan to make 4th axis, It is low backlash as said in the ads.

you can order things from alibaba? Isnt' that site just a listing? its not like ebay with buyer protection and a very removed payment process like paypal to protect customers or anything like that. You deal direct with the manufacturer right?

[hoss2006]

Right, you can disable Skimlinks in your profile under general settings, I see no highlighted text for harmonic drive in any of the posts here.
Hoss

[Fastest1]

I see a highlight AND it took me to a harmonic drive for 400 bucks. Weird you didnt link it. In fact I just clicked on every phrase "harmonic drive" in this thread (all have highlighting from my side, will have to check into settings) and they all take me to the same Amazon ad.

[abfa9358]

Links added by site not by me. Harmonic drive came off ebay after a bit of waiting. Reference is here for the FB series drives.

Products | Component Sets | FB Series Pancake Component Sets :: Harmonic Drive LLC.

[asuratman]

It is clear enough I learned from catalog. Thanks.

[abfa9358]

Well after a bit of a break, I've started to make parts for the 4th axis. Tonight, I just about completed the connection between the minimill spindle and the harmonic drive (red part in 3d views above). I still need to cut the slot for the key but that shouldn't take much time - I have a CNC script for cutting slots. I've added a few images of the machined part plus the assembly with one half of the harmonic drive and the minimill spindle.

I managed to remove the spindle from the minimill housing - I had to drift the spindle out from the bearings, not a task for the faint hearted. When I re-build the spindle, I will replace the 6206ZZ bearings with 6206RS versions to protect from swarf.
Attachment 263922

[Potatohead908]

The torques specs for that drive have me a little curious. Are they listing the input or the output torque? If its output are you not going to be way over that with the gear reduction?

[abfa9358]

A bit more progress. I made a jig plate to hold the housing and motor plate whilst I finished machining them. The motor plate and housing are now complete and the next thing I will do is make a custom nut to hold the rotating part of the harmonic drive on to the spindle.
Attachment 271628

[abfa9358]

Over the last night or two I've been making the clamp nut that retains the spindle and preloads the bearings. First off, I measured the spindle thread as M27 x 1.5. Not exactly standard but no problem I thought I have a 127/100 change wheel for the lathe. Looking at the Boxford tables it appeared that I needed a 24t driver gear and a gear box setting of 16tpi. First problem - I couldn't find a 24t change wheel at a reasonable price.

Hmmm, what wheels have I got? In the box I found a 30t gear, hmmm.... if I use that and set the gear box to 20tpi that should cut a 1.5mm pitch thread. Sure enough, it did. Project back on track at no extra cost

I machined the steel nut from a piece of 2" steel bar and cut the thread, as I started to fit the spindle to the new nut I realised that the spindle thread was M27x1.5 LEFT hand - DooooH! (Age old advice - measure twice, cut once).

So tonight I reversed the tumbler wheels and cut a thread from the chuck outwards. This resulted in a nice fitting M27x1.5 left hand thread in the new nut - happy days!

[abfa9358]

Torque specs are output and yes a 1Nm stepper theoretically can deliver 160Nm at the output and probably destroy the drive in the process! I plan to use the axis for light cuts / engraving rather than taking really heavy cuts with big endmills. Its up to me to program the machine within its limits.

[Potatohead908]

I am not to be trusted with "self limiting". I will be watching you progress.

[photomankc]

I was thinking the same thing a few years back. The headstock on the X2 is pretty much the same as the 7" lathe so it would make sense. I would unfortunately be saddled with an R8 spindle instead of an MT so not ideal but should be useful for engraving, indexing, and light milling.