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2009-10-02 18:09

CNC Abene




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CNC - Abene VHF-3 - Motormounts


As you probably can see in one of the first photos the mounting brackets for the servomotors as well as the pulleys had seen better days. I'm sure they would've worked but I just couldn't stand the way they looked so I decided to make new ones.


I started by looking up the various belts and pullies available. Originally the machine was equipped with T10 belts but I settled for AT5 instead. The AT-profile is supposed to be a little better than the T-profile when it comes to positioning applications and although it can't transfer just as much torque per tooth as the T-profile there will be more teeth in contact with the pulley so I'm pretty sure it will suffice.


I wanted a 2:1 ratio between the motor and screw so I went for 30 teeth on the motor and 60 on the screws. The Z-axis is a little special, it has a 90 deg bevel gear with a 2:1 ratio but fitting the 60 teeth pulley to the gear-shaft won't work because it would interfere with the Y-axis sadle of the machine. So for the Z-axis there's first a 2:1 belt-transmission, then there's a 1:1 belt and then there's the 90 deg 2:1 gear reduction for a total reduction of 4:1.

Here's a screenshot of the CAD drawing for the three axes. (Sorry for the Swedish notations in the drawing...)


With the CAD done it was just a matter of ordering the belts, pulleys and mounting hardware. The original pulleys were fitted with a key but I don't have access to tooling for that so I went for the type that clamps to the motor-shaft. Besides, I've had bad experience with using keys in applications like this where the axis of rotation changes direction on a regular basis. If it's not absolutely 100% tight it will develop a lash and once that happens i going downhill, fast.



For the X- and Y-axis I got some 12mm aluminum sheet watercut at a local shop. I then mounted them on my small machine in order to bore out the hole for the boss on the servo-motor as well as drill and countersink the holes for mounting the motor.


I generated a helical toolpath and let the machine bore out the hole to final dimension.


It turned out pretty good...


And here's the more or less finished motor-mount for the Y-axis. The two remaining holes are for dovel pins that will be fitted once I know it all works out as it's supposed to.


For the X-axis I went about the same way. Unfortunately I made a mistake while measuring the bearing-plate on the machine to which the motor mount will be mounted so I ended up with an extra slot in the wrong place. It doesn't matter much but even so I hate it when that happens.

This is the "original" but it turned out that the four small slots shouldn't be evenly spaced as I had drawn them...oh well.


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