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Minimill to 4th Axis....
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.....
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Re: Minimill to 4th Axis....
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
Attachment 258138.
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Re: Minimill to 4th Axis....
Hello,
What kind of harmonic drive? Can you show me? Where is the source of cheap harmonic drive?
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Re: Minimill to 4th Axis....
Did you click on the highlighted "Harmonic Drive" in his post? It takes you straight to the ad on Amazon.
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Re: Minimill to 4th Axis....
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.
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Re: Minimill to 4th Axis....
Quote:
Originally Posted by
Fastest1
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
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Re: Minimill to 4th Axis....
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
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Re: Minimill to 4th Axis....
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.
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Re: Minimill to 4th Axis....
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.
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Re: Minimill to 4th Axis....
It is clear enough I learned from catalog. Thanks.
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Re: Minimill to 4th Axis....
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
Attachment 263926
Attachment 263928
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Re: Minimill to 4th Axis....
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?
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Re: Minimill to 4th Axis....
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.
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Re: Minimill to 4th Axis....
I am not to be trusted with "self limiting". I will be watching you progress.
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Re: Minimill to 4th Axis....
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.
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Re: Minimill to 4th Axis....
Well a bit more progress. The part I made the other night now fits nicely on the spindle. I cut the keyway using a purpose made tool mounted in the CNC miller, and then wrote a simple loop to shave off 0.001" per pass.
I then made a start on the housing which involved cutting a 100mm dia steel bar - a job for the new bandsaw!. I got it at Xmas during a Machine Mart vat free day, after changing the blade to a bi-metal M42 blade from Tuff Saws - Tuff Saws, Quality Bandsaw Blades the saw cuts an absolute treat - I advise anyone getting one of these saws to change the blade to a quality part prior to performing complex "tune-ups". I did extend the vice and added a screw jack at the far end, I also junked the "stand" and built a wooden wheeled trolley out of an old kitchen work surface.
I mounted the steel bar in the lathe and started to rough machine the outer body. As this proceeded it struck me that a NEMA23 motor rather than the size 34 motor would result in a much neater design solution and would allow me to create all the flanges / mountings from the 100mm dia steel stock.
Back to TurboCAD...and here are the results, much better than the first attempt.
Attachment 265440 Attachment 265442 Attachment 265450
Attachment 265446 Attachment 265448
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Re: Minimill to 4th Axis....
Quote:
Originally Posted by
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.
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?
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Re: Minimill to 4th Axis....
Aliexpress is the business to customer site. Alibaba is business to business really, aimed at large quantities.
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Re: Minimill to 4th Axis....
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.
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Anywhooooo...
I've been machining the outer housing from the 4" bar stock and made a start on the jig plate for machining the reverse side of the outer housing and motor plate.
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Re: Minimill to 4th Axis....
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.
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Re: Minimill to 4th Axis....
Quote:
Originally Posted by
mcfatburger
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.
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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
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Re: Minimill to 4th Axis....
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 Attachment 271630 Attachment 271632
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Re: Minimill to 4th Axis....
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!
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Re: Minimill to 4th Axis....
following with great interest ...looks great
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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.
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Re: Minimill to 4th Axis....
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 274046Attachment 274048
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Re: Minimill to 4th Axis....
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
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Re: Minimill to 4th Axis....
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
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Re: Minimill to 4th Axis....
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
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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.
https://youtu.be/x9MdNyrYQ54
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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.
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Re: Minimill to 4th Axis....
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 300734Attachment 300736
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Re: Minimill to 4th Axis....
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?
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Re: Minimill to 4th Axis....
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
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Re: Minimill to 4th Axis....
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!!
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Re: Minimill to 4th Axis....
Many thanks.
Here's a link to a video of a repeatability test of the axis.....
https://youtu.be/Khy2YQ3gYmY
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Re: Minimill to 4th Axis....
That's fabulous!!!
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Re: Minimill to 4th Axis....
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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