Optimum MH 50V mods and accessories

[Futterama]

Unlogic, thanks for the very elaborate reply.

I'm in a situation in my life where I start to have the funds to buy bigger machines. If I had the room for it, I would get a SYIL X7. But currently I need the machine to fit through a regular 80cm doorway. In 10 years or so, I will move to a house with a real garage/workshop and then I will have the room for a real CNC like the SYIL. Until then, I want something sturdy that I can convert to CNC down the line. The MH 50V seems like a good candidate and I have local distributors in my country.
I had a quick look at the Mobasi build, and I feel like I could accept the price tag of around €17k for a complete build including the machine. I'm comparing to the €43k for the SYIL since to me it makes sense there is a good price gap between the two.
I don't have any experience with a CNC build so I should probably start smaller than the MH 50V. I have an Optimum BF16 Vario, basically the smallest machine I could get many years ago, and I could start with that machine and Chinese components when I get the MH 50V.

This is purely hobby for me. So I don't NEED the precision of a real CNC. Maybe even the BF16 as a CNC will be fine for me for a long time.

Enough about me. Now that you have the MH 50V converted to CNC, do you miss the manual machine? I don't have a drill press so I use my BF16 even for drilling simple holes. If you need 1 hole in a piece of steel, the location is marked with a punch or a pen, would it be just as easy to drill the hole on the CNC as it would cranking the hand wheels of a manual machine?

 

[Unlogic]

I used this machine in manual mode for over two years and I was actually a bit worried that I'd miss the manual milling when I did the CNC conversion.

For small quick things like a single hole or a simple facing operation a manual mill is hard to beat.

Drilling in CNC mode was really scary in the beginning but now that I have a bit more experience it's actually quite nice. Especially the ability to do automatic pecking and very precise patterns.

By the way if you listen to the noise in the video above I think you'll understand why I wanted to get rid of the gearbox and go with belt drive instead.

Before I would make a template then mark and punch holes before drilling. Now days I usually start FreeCAD, make sketch, select the correct tools from the tool library and generate the tool path. Then I let the machine do it's thing.

 

[Unlogic]

I did the first proper test of the new spindle servo motor today milling some 7050 aluminium.

The test was done using a 80 mm face mill at 100% width of cut, 0,5 mm depth of cut, 2000 rpm and a feedrate of 600 mm/minute. This worked splendid.

Not only is the machine much quieter but the finish at high feed rates is noticable improved which was unexpected. I suspect that this is the result of removing all the gears and shafts from the transmission as there are much less vibrations from the head now.

 

[gschora]

Thanks, I'm actually surprised by the quality of parts that an amateur built machine like this can produce.

Right now I feel that the limiting factor is my CAM software skills. Currently I'm using FreeCAD which I really like but it has a few limitations when it comes to certain 3D tool paths. However all the proprietary CAM software suites have rather expensive license/monthly fees which feel way too steep for a hobby machinist like me.

I'm using fusion and have the subscription but I'm paying because of the different file formats that are supported (for working with other companies). Even if you pay you wont get access to the really nice toolpaths but the standard paths are fine.
Designing things in fusion is great and easy but I'm used to Autodesk Inventor. I made complex designes with over a hundred parts and moving parts and had no problems. But the best thing is the simulation of toolpaths which saved me from lots of crashes.
I would try out the free version and for most this will be enough.

 

[gschora]

I'm following this thread with great interest. It seems like you know what you are doing

I'm curious about 2 things:
Why use a servo motor instead of rigging up a belt drive for the existing motor? Is it due to max RPM or low RPM torque?
What is the cost of these parts? I have no idea about what a CNC conversion like this would cost compared to just buy the Mobasi converted version of the mill so I would like to know

I have a Mobasi MH50 with servos bought in 2022. If you have any questions, I'm happy to answer so drop me a pm...
I don't want to hijack this nice thread

 

[Unlogic]

The direct drive servo motor I installed has really been working great. Milling 7050 aluminum with this 20 mm roughing end mill is like cutting butter.

I got a little bit carried away with the good results and started milling a large piece of aluminum with G-code generated with Fusion instead of FreeCAD. Big thanks to @gschora for convincing me to take a look at Fusion as it's 3D toolpaths are much better than those of FreeCAD at the moment.





However my already noisy spindle bearing didn't like this and the noise from them went from bad to horrendous forcing me to stop the milling. Here is what bearings sounded like when I decided it was time to stop milling and replace them.

At high rpm's the noise was so loud that I could hear it through the hearing protection I was wearing.
As I would have to take apart a lot of stuff on the head of the machine to replace the spindle bearings I decided to install a pneumatic tool release cylinder while I was at it.
So I ordered a pneumatic cylinder, a solenoid and some fittings from Festo along with another Eaton M22 button. I then milled an aluminum plate to hold the cylinder in place.
Here are all the parts laid out.



What's missing from the picture above is the extension for the piston in the pneumatic cylinder. I made the extension by partially cutting the head off a 12.9 cup head hex bolt.





In order to cushion the impact on tool release bar a bit I added a small piece of high density rubber foam.



To prevent the bolt from rotating too easily I added some teflon tape to the threads.

Here is how the cylinder sits when mounted to the plate I machined for it.



In order to reduce the amount of stiff air lines on the machine I decided to mount the solenoid right next to the cylinder itself using a small aluminum bracket.



Here is a quick test before bolting everything in place.

With everything bolted in place it quickly became obvious that I had overlooked one thing, the damping when releasing the pressure on the tool release bar. I could hear the spring inside the spindle ringing when the pneumatic cylinder retracted.

So to solve that I ghetto rigged a small air restrictor that I installed in one of the outlets on the solenoid. The restrictor is just a piece of pneumatic line partially melted and pressed together with a 1 mm hole drilled in it.



Here is a how a tool change sounds with the restrictor in place and everything bolted in place.

And this is how the whole assembly looks on top of the head of the machine.

 

[Unlogic]

With the pneumatic tool release in place I turned my attention to the spindle bearings.









I quickly noticed a few things.

The larger bottom bearing was in much better condition than the top bearing which had clearly been vibrating a lot on the shaft. This was a bit unexpected as the bottom bearing should see much higher forces.

The oil which used to leak from the transmission made it's way into the spindle dissolving any grease they used to contain and also contaminated the bearings.

There is a step inside of the spindle tube for some reason and the step was not deburred at all. Here is how it looks after I did my best to deburr it (I later cleaned it properly).



This is the burrs I removed.



Next it was time to remove the old bearings and press in the new ones.





The spindle assembled with new bearings and expensive Klüber NBU 15 grease applied in precise amounts.



Next began the black magic of setting bearing preload on conical roller bearings... this took quite a few hours.

I'm used to setting preload with schims inside manual transmissions but this spindle used a primitive nut on a rather coarse thread. So making precis changes was a challenge.

My aim was to aim for as little noise and heat as possbile. The first attempt turned out to be too much preload cause the spindle got very hot even at 1500 rpm. So I took out the spindle and reduced the preload. That turned out to be too little preload as the bottom bearing now rattled instead.

On my third attempt I tried a preload just between the amounts I had previously used and it seemed to work very well so after a few hours of test runs I assembled the whole machine with quill spring etc. Only to be greeted by a rattle from the bottom bearing when the machine had cooled down. So I had to take everyting apart again...

The fourth time I added a bit more preload, almost as much as I had initially started with before running in the bearings. I then ran the machine to make sure that it sounded good and the let it cool overnight before checking again.

It still sounded good so I assembled everything again and this is how it sounds now at 2500 rpm. Surprisingly quiet actually. No ear protection is needed anymore.

On another note however the spindle as it's designed at the moment will not be suitable for high rpm's over any prelonged period of time. The tall splined shaft sticking out on the top of the spindle is largely unsopperted and starts to vibrate as speeds increase. I order to be able to run higher RPM's the spindle will need to be modified or replaced.

The quill on my machine has always tended to bind and not move really smoothly. As I rarely use the quill any more I haven't looked anything further into it. However I unintentionally found the cause when I tore everything apart. The cause is flimsy spring used to retract the quill, it binds on itself making movement jerky.




It seems that everyting I do work on this machine I remove more and more stock parts. There are the parts which I removed this time...



Here is how the machine looks after these latest modifications.

 

[Unlogic]

By the way when I had the spindle apart I added a small 3 mm spacer underneath the spring for the tool clamping mechanism to increase the clamping pressure a bit (this was the result of another great tip from @gschora).

As I don't have lathe I purchased a washer with the right thickness and outerdimensions. I then ghetto rigged a setup the washer at the bottom of the chuck for my rotary table which I then mounted in one of the vices.



Then I generated a shallow helix toolpath in FreeCAD and used a 20 mm indexed end mill with 3 APKT 1003 inserts to enlarge the center hole.

The results was surprisingly good and the hole ended up being 4-5 microns undersize which allowed me the manually remove the final amount of material.



My initial thought was "how much difference can 3mm make on that beefy spring" but with the washer in place I had to increase the pressure to pneumatic tool release cylinder from the previous 4 bar to 5 bar else it wouldn't be strong enough to release the tool.

 

[Unlogic]

I've had time to do some milling with the new spindle bearings now and I have to say I'm pleasantly surprised with how big of an improvement it was. Not only is the noise reduced but I can also take deeper cuts without getting chatter.

The surface finish has also improved compared to how it was previously was, especially when using large face mills.

I milled a narrow and very deep pocket in 7050 aluminum and finished it off with a 12mm DLC coated ball end mill using a step over of 0.5 mm.

This is the results which is the best I've managed so far:

However I've noticed that the servo motor for the spindle still gets a bit hot after a few hours of milling so I decided to improve the cooling by adding aluminum heat sinks to it using thermal conductive tape.






I've also ordered two slightly more powerful fans which should be here sometime next week. I'll report back on how it works.

 

[Unlogic]

I did some milling this weekend and the aluminum heat sinks worked better than I had expected. The spindle servo stays much colder now so I'm not sure that I'll need the more powerful fans. I'll test it for a few more days before I make a decision.

With everything working so good I took the brave pill and decided to test rigid in LinuxCNC. I threaded M10x1.25 threads on aluminum using a spiral tap.

Threading that by hand takes a fair amount of force due to the toughness of the 7050 aluminum but the mill went through it like butter so I think that my hand tapping days are numbered

However an hour or so into a heavy milling session I started hearing the telltale sounds of bearing rattle followed by slight chatter and a reduced quality of the surface finish. Removed the spindle and clearly the bearings or grease had been broken in a bit because there was less preload than what I had previously set even though the adjustment nut had not moved. Added a bit more preload and assembled everything again which cured the problem. I have never worked with spindle bearings before but it seems to be a bit of black magic to get the perfectly set, especially given the course thread used for the preload nut on this machine.