[abfa9358]

More progress, outer housing and motor plate have now been part machined. The outer housing needs the bore opening out to take the motor plate locating spigot. I'll do the roughing on the CNC mill and then swap over to a machine jig plate mounted on the lathe - probably in the 4 jaw. I'll machine the jig plate once mounted in the lathe thus ensuring that it is true. The motor plate will be mounted to the outer housing an then machined thus ensuring that the recess for the motor is true to the rest of the assembly.
Attachment 269026 Outer Housing

Attachment 269028 Components so far plus harmonic drive gear rings

Attachment 269030 Jig plate, 100mm x 100mm x 25mm 7075 Al.

[dracozny]

I have never ordered frm them. So how does it work with aliexpress? Is it like Ebay with all the buyers protection and all that stuff? Sometimes I see good deals just random web searches and showing alibaba sites. But since its direct to the business that inquest stops right there. But if they make transactions safer for buyers like ebay, could have more options.

in a nutshell yes.

[abfa9358]

Here's a link to a video of the mill hogging out the inside of the steel housing. I'm roughing it in the mill and will finish once mounted in the lathe.



https://m.youtube.com/watch?list=UUxV8NVN8WKtu1XQxQB7R6zg&v=RPx_r62JgW4

[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!

[1hander]

following with great interest ...looks great

[abfa9358]

Many thanks.
So here is the nut so far. the groove in it will allow the threads to be locked by tightening two grub screws from the front of the nut once installed. I still need to mil some segments in to the nut to allow the grub screws to clamp the threads.

[abfa9358]

I've now finished the nut and installed it on to the spindle. I have made two cuts across the nut to allow the nut to be clamped on to the spindle thread by tightening two M3 grub screws. Once installed the nut sits in a recess behind on half of the harmonic drive to it is not possible to lock it with a side located grub screw. The two clamps seem to work well.
Attachment 274044Attachment 274046

[abfa9358]

Bit more progress... I've finished roughing out the chuck mount adaptor. This piece will be attached to the minimill spindle by press fitting and then
pinning with grub screws. I didn't want to create a screw mount as I have had experience in the past of chucks loosening during milling operations leading to broken tooling and wrecked parts. It will be final machined after mounting with the spindle between centres.

Attachment 275570

I also picked up a 125mm Bison 4 jaw chuck on ebay, this will be mounted to the spindle and I'll machine up a chuck back plate for the lathe so that I can swap between the lathe and 4th axis.

Attachment 275572

I've put a few pics together to show the assembly, I think it is looking pretty good in terms of overall aesthetics.

Attachment 275574Attachment 275576Attachment 275578

[abfa9358]

Bit more progress. I spent last night checking the lathe alignment, in the end I got it to turn parallel to 0.0003" over 6" at this point I decided to stop as I was at the limits of my micrometer. The tail stock alignment over the 8" length of my test bar was bang on. Not bad for a machine bought in 1980.

Tonight I machined the spindle to take the chuck mount adaptor. I used a centre mounted in the spindle bore and located in a centre drilled piece of steel held in a tail stock collet chuck. I used a chuck spindle mounted collet chuck to create the centre drilled hole.

Once this was done, I swapped over to the 4 jaw chuck and then centred the spindle to run true at the chuck end. I got to a TIR of 0.0005" - good enough for me.

I very carefully machined the spindle to take the adaptor plate, this needed around 0.040" machining off. Once installed on the spindle, I couldn't measure any runout in the adaptor plate - happy days.

I cut a 0.001" recess to take Loctite 603 retaining adhesive and then pushed the adaptor plate on to the spindle. Once set, I'll drill and tap 4 M6 holes at the interface of the plate and spindle and then install grub screws to lock the plate to the spindle.

After that, the chuck plate needs to be final machined to take the Bison chuck.

I've attached a few pics of the above processes plus a pic of the swarf monster that is living beside the lathe.
Attachment 276052Attachment 276054Attachment 276056Attachment 276058

[abfa9358]

I mounted the spindle and chuck in the minimill head last night as a trial fitup. The head has new angular contact bearings in it, heres a link to the video
4th Axis spindle trial mount in bearings. - YouTube

[abfa9358]

I've assembled the whole 4th axis along with the motor and chuck. Here are some pictures of the assy.

Here's a link to a YouTube video of it.

[abfa9358]

I put the 4th axis on the mill tonight after fitting it to a 20mm steel base plate. I mounted my test bar in the mt3 spindle and clocked the length. I measured 0.01mm over 3" or so, good enough.
Next job is to machine the backplate for the lathe so I can swap between the spindle and the lathe.

After that its a case of adding a Gecko drive for the motor and updating LinuxCNC.

[abfa9358]

So after a bit of a delay, I've got round to building a brake for the axis. Its designed around a crane brake mechanism and sits between the chuck and the body of the minimill. I still have to add the pneumatic cylinder to actuate it.
Attachment 300734

[Fastest1]

Excellent work however I do feel like because of those last pics of the 4th axis. Your machine is ceiling mounted or am I upside down?

[abfa9358]

Many thanks - LOL good point, I think it is probably easier to rotate the axis rather than the workpiece and the mill

Sorry about some of the pictures, sometimes its difficult to predict which way round they'll end up after up load. Anyway, here's a link to a test of the completed axis with pneumatic brake under control from LinuxCNC. I used the M62 and M63 codes linked vai the HAL to an output pin of my 7i43.

I'll post a video of some backlash tests tomorrow - I managed to record a video of my feet tonight!

https://www.youtube.com/watch?v=hy8t...ature=youtu.be

[lcvette]

What a cool project and build you have done here!! I comments you on taking on the harmonic drive, and would love to know more about it. It is very interesting to me to see how this has co e together. I K ow nothing a out harmonic drives bit have wanted a way to have a really accurate 4th axis without the backlash headaches of a worm gear drive.

Keep up the great work!!

Sent from my XT1080 using Tapatalk

[abfa9358]

Many thanks.

Here's a link to a video of a repeatability test of the axis.....
https://youtu.be/Khy2YQ3gYmY

[lcvette]

That's fabulous!!!

Sent from my XT1080 using Tapatalk

[lcvette]

Do you have plans for this? I have a spare mini Lathe laying around that I bought the upgraded spindle for that mounts a 4" chuck... Being trying to decide what I want to do with it, this could be a really good option.

Thanks,

Chris

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