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Optimum MH 50V mods and accessories
- Thread starter Unlogic
- Start date
- Joined
- Nov 7, 2019
- Messages
- 491
That's some beautifully machined parts!
With all the parts manufactured it was time for the scary bit, taking apart the gearbox and removing all the parts that will no longer be needed.
First thing to be removed was the huge 2kw induction motor.
Next up was the top cover for the gearbox which to to my great delightment had two threaded holes where long bolts could be inserted to gently lift the cover.
Getting the cover off and removing all the gears however was a bit tricky as the gears and gear change mechanism had to be removed in a particular way in order to not get all tangled up.
Here is a test fit of the servo mount on the top cover of the gearbox.
After verifying that the mount actually fit I removed two of the three shaft in the gearbox. On the final shaft I pressed off all the gears that could be removed from it and installed new steel caged SKF bearing rated for 12k+ RPM
Here is how the shaft looks with the pulley adapter on top (just loosely installed at this time).
With the gearbox emptied of unnecessary parts I installed the new servo and turned my attention to the electrical stuff.
Last time I soldered the cables myself for the DB-44 connectors on the Delta B3 servo drives. This was very tedious as the DB-44 connectors are very densely packed and a small mistake where two cables had their insulation melt slightly during soldering caused a short circuit on humid day which partially fried one of the stepper outputs on the 7i96S board.
To avoid similar problems this time I bought a DB-44 cable from AliExpress for 39$ including shipping. It took a while to get the cable but when it finally arrived it looked okay and seems fairly well made.
First thing to be removed was the huge 2kw induction motor.
Next up was the top cover for the gearbox which to to my great delightment had two threaded holes where long bolts could be inserted to gently lift the cover.
Getting the cover off and removing all the gears however was a bit tricky as the gears and gear change mechanism had to be removed in a particular way in order to not get all tangled up.
Here is a test fit of the servo mount on the top cover of the gearbox.
After verifying that the mount actually fit I removed two of the three shaft in the gearbox. On the final shaft I pressed off all the gears that could be removed from it and installed new steel caged SKF bearing rated for 12k+ RPM
Here is how the shaft looks with the pulley adapter on top (just loosely installed at this time).
With the gearbox emptied of unnecessary parts I installed the new servo and turned my attention to the electrical stuff.
Last time I soldered the cables myself for the DB-44 connectors on the Delta B3 servo drives. This was very tedious as the DB-44 connectors are very densely packed and a small mistake where two cables had their insulation melt slightly during soldering caused a short circuit on humid day which partially fried one of the stepper outputs on the 7i96S board.
To avoid similar problems this time I bought a DB-44 cable from AliExpress for 39$ including shipping. It took a while to get the cable but when it finally arrived it looked okay and seems fairly well made.
This is how the cabinet looks now with the 4th servo driver installed.
As always when modifying the cabinet with expensive electrical components the first power on was a bit scary. However there was no magic smoke but instead I was greeted with the most horrible fan noise I've ever come across.
I promptly removed the new servo driver and popped off the side cover to find two small 40x40x15mm 24v fans rated at no less than 11 000 rpm!
I made a short term fix for now and soldered in a 80ohm 3w resistor for each fan to bring them down to 15v.
However they are is still far from quiet so I'll be monitoring the temperature of the spindle servo drive and see if I can get away with installing quieter fans.
Before I turned my attention to the configuration and HAL changes required for the new servo driver to work I replaced the keyboard attached to my control panel.
I had previously been using a full size keyboard but some functions in Probe Basic like selection of multiple lines in the editor (normally done with shift + arrow up/down) doesn't work without a mouse so I opted for a new old stock Microsoft All-on-One Media keyboard instead.
This keyboard is slightly vintage in IT terms but it has some features which I liked such as a dedicated left mouse button on the left side of the keyboard and touchpad which actually moves down when you click on in. This simplifies the use of the touchpad with gloves on.
To make sure that the keyboard stays in place while in use while at the same time be simple to remove when necessary I attached it with magnetic tape this time.
As always when modifying the cabinet with expensive electrical components the first power on was a bit scary. However there was no magic smoke but instead I was greeted with the most horrible fan noise I've ever come across.
I promptly removed the new servo driver and popped off the side cover to find two small 40x40x15mm 24v fans rated at no less than 11 000 rpm!
I made a short term fix for now and soldered in a 80ohm 3w resistor for each fan to bring them down to 15v.
However they are is still far from quiet so I'll be monitoring the temperature of the spindle servo drive and see if I can get away with installing quieter fans.
Before I turned my attention to the configuration and HAL changes required for the new servo driver to work I replaced the keyboard attached to my control panel.
I had previously been using a full size keyboard but some functions in Probe Basic like selection of multiple lines in the editor (normally done with shift + arrow up/down) doesn't work without a mouse so I opted for a new old stock Microsoft All-on-One Media keyboard instead.
This keyboard is slightly vintage in IT terms but it has some features which I liked such as a dedicated left mouse button on the left side of the keyboard and touchpad which actually moves down when you click on in. This simplifies the use of the touchpad with gloves on.
To make sure that the keyboard stays in place while in use while at the same time be simple to remove when necessary I attached it with magnetic tape this time.
The configuration and HAL changes in LinuxCNC ended up taking over a day to figure out but in the end I managed to get spindle soft ramp up and ramp down in place along with encoder based RPM and actual spindle load displayed in the Probe Basic user interface.
In order to test the new spindle motor I decided to mill a new polycarbonate shelf for my parallel blocks.
With the gearbox on the machine 1500 rpm was the max sustainable spindle speed, anything above that made the gearbox sound like it was going into orbit.
I milled the polycarbonate at 2500 rpm with very little noise however another issue crept up which I had overlooked, heat!
The old induction motor had a big fan on the back which not only cooled the motor but also indirectly cooled the head of the machine. Without any airflow the new spindle servo got pretty hot after running for an hour straight. The head of the machine was also uncomfortably hot.
In order to be able to finish milling the polycarbonate I ghetto rigged a small USB powered fan on top of the machine which did the trick.
Here is how the polycarbonate shelf came out.
With the gearbox on the machine 1500 rpm was the max sustainable spindle speed, anything above that made the gearbox sound like it was going into orbit.
I milled the polycarbonate at 2500 rpm with very little noise however another issue crept up which I had overlooked, heat!
The old induction motor had a big fan on the back which not only cooled the motor but also indirectly cooled the head of the machine. Without any airflow the new spindle servo got pretty hot after running for an hour straight. The head of the machine was also uncomfortably hot.
In order to be able to finish milling the polycarbonate I ghetto rigged a small USB powered fan on top of the machine which did the trick.
Here is how the polycarbonate shelf came out.
In order to tackle the cooling of the servo motor and head of the machine I ordered two 80mm Ncotua branded fans.
I installed the fans in the top cover so they blow across the head of the machine including the toothed belt and then onto the spindle servo motor.
I wired the two 12v fans in series and power them with 24v from one of the outputs of the Mesa 7i84 expansion card in the control cabinet.
In order to have the operation of the fans automatically controlled I added a line of HAL code to my LinuxCNC configuration which slaves them to the spindle-enable signal. So they turn on and off with the spindle for now.
Next up is the replacement of the spindle bearings which have been making bad noises for quite some time. I just have to figure out how to remove the quill, hopefully @gschora here on the forum can give me some hints
I installed the fans in the top cover so they blow across the head of the machine including the toothed belt and then onto the spindle servo motor.
I wired the two 12v fans in series and power them with 24v from one of the outputs of the Mesa 7i84 expansion card in the control cabinet.
In order to have the operation of the fans automatically controlled I added a line of HAL code to my LinuxCNC configuration which slaves them to the spindle-enable signal. So they turn on and off with the spindle for now.
Next up is the replacement of the spindle bearings which have been making bad noises for quite some time. I just have to figure out how to remove the quill, hopefully @gschora here on the forum can give me some hints
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 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'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
Hi Futterama, thanks for the kind words.
A normal induction motor like the one that came with the machine has very little torque at low RPM henche the need for a gearbox.
On the other hand most modern servo motors have very high torque at low rpm.
So the main benefits for me were three fold, getting rid of the noisy gearbox, higher spindle speed (6000 instead of 3000) and a built in encoder which enables rigid tapping and precise monitoring of spindle speed in closed loop mode (done by the servo drive in my case).
When doing a CNC conversion like this I'd say that there are two main things which dictate the cost and ultimately the precision of the parts made on the machine. That is first and foremost ball screws and then servos.
You can buy ball screws in the range from very cheap to crazy expensive. The precision and backlash of the ball screws will be the foundation for the precision of the machine.
Servos and their associated drivers are very important for closed loop positioning, speed, torque etc.
The rest such as controller boards and associated electronics are a much smaller investment and I don't think the difference in precision between the established brands and models for hobby CNC's is that great in that area.
The quality of pre converted machines varies greatly depending on which components they use. So prices can be hard to compare without knowing what parts that are actually used.
I tried contacting Mobasi when I was planning this build to see if I could buy some parts from them but they never replied to my email.
For my build I decided to go with fairly expensive but also high grade C5 Bosch-Rexroth ball screws for the X and Y axis. However they cost more than all the other parts of the build combined
If I had gone with Chinese ball screws the price would have been a fraction of what I payed but most likely the precision of the machine would have been somewhat reduced. However in some cases that might fine, it depends on your requirements.
Same thing with servos there are cheaper/simpler models and more expensive/sophisticated ones. They all work but it depends on what you're requirements are.
I think a conversion like this could be done for around 3 000€ if you buy cheap parts and manufacture all the ball screw mounts etc yourself.
However I'm probably past 10 000€ when it comes to my conversion as I wanted a solid build that would allow me to make batches of parts with good precision and repeatability.
However when compared to buying "a real CNC" macine I haven't spent much money at all.
A normal induction motor like the one that came with the machine has very little torque at low RPM henche the need for a gearbox.
On the other hand most modern servo motors have very high torque at low rpm.
So the main benefits for me were three fold, getting rid of the noisy gearbox, higher spindle speed (6000 instead of 3000) and a built in encoder which enables rigid tapping and precise monitoring of spindle speed in closed loop mode (done by the servo drive in my case).
When doing a CNC conversion like this I'd say that there are two main things which dictate the cost and ultimately the precision of the parts made on the machine. That is first and foremost ball screws and then servos.
You can buy ball screws in the range from very cheap to crazy expensive. The precision and backlash of the ball screws will be the foundation for the precision of the machine.
Servos and their associated drivers are very important for closed loop positioning, speed, torque etc.
The rest such as controller boards and associated electronics are a much smaller investment and I don't think the difference in precision between the established brands and models for hobby CNC's is that great in that area.
The quality of pre converted machines varies greatly depending on which components they use. So prices can be hard to compare without knowing what parts that are actually used.
I tried contacting Mobasi when I was planning this build to see if I could buy some parts from them but they never replied to my email.
For my build I decided to go with fairly expensive but also high grade C5 Bosch-Rexroth ball screws for the X and Y axis. However they cost more than all the other parts of the build combined
If I had gone with Chinese ball screws the price would have been a fraction of what I payed but most likely the precision of the machine would have been somewhat reduced. However in some cases that might fine, it depends on your requirements.
Same thing with servos there are cheaper/simpler models and more expensive/sophisticated ones. They all work but it depends on what you're requirements are.
I think a conversion like this could be done for around 3 000€ if you buy cheap parts and manufacture all the ball screw mounts etc yourself.
However I'm probably past 10 000€ when it comes to my conversion as I wanted a solid build that would allow me to make batches of parts with good precision and repeatability.
However when compared to buying "a real CNC" macine I haven't spent much money at all.
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