I wouldn't trust the Dremel stand, I've tried it with mine and there is movements in it and this could definitely drill the hole slightly off centre.
to drill a hole in a motor block with Large and small disk rotors, this is a complete different saga, first of all you need a ball bearing which is 5mm in diameter, I bought some a while back with a 6 mm diameter and you don't really want to know the outcome. I was lucky I was able to rescue the whole loco (SBB Re 4/4 (3014) but I would have a good think before attempting another one.
most of the Co-Co locos with large disk rotor could be converted but again I wouldn't try it with a 6mm ball bearing, with 5mm you would have a better chance but your need tools or a compact drill stand with no movements. the Drum collector as Juhan mentioned has 1.5 mm shaft whereas the large or small disk rotor has a 2 mm shaft at the rear.
I had an idea and may go down this path later one whereas I will go to a friend of mine and he is an industrial engineer and ask him if he can reduce the 5 pole armature shaft from the conversion set (60943, 60944) from 2mm down to 1.5mm this would be a much easier option to convert or drill a hole into the back of the motor block a 4 mm than to a 5mm or 6mm hole., a.) it would be done professionally and b.) it would eliminate extra problems commencing down the road with a 5 mm or 6 mm hole because the original hole including the oiling access with pad on these motors is mounted or has been located on the outside of the rear motor wall. by drilling a hole this would completely fall off or disappear and you than have to make sure your shaft is not too long because you've lost that extra length and this brings me to another option will the 5 pole rotor with a shaft diameter of 1.5mm (front and rear) fit when drilling a hole for a 4 mm ball bearing ?
the shaft is slightly shorter than a shaft from a 60943, 60944 conversion set I have thought about this before but never actually tried it out, one could measure the length needed and if it seems to fit cut a hole of 4 mm and if it doesn't fit cut a hole to 5mm and use the shaft with its 2mm diameter, so in the end if everything goes well you haven't done any damage or you haven't proceeded with an option with no return.
Glenn, I may have confused members what I was going to explore. the armature shaft for the conversion kits 60943 and 60944 are 2 mm at the rear and 1.5 mm in front whereas the shaft for the the conversion set 60941 and all other drum collectors have a 1.5mm shaft front and rear. so by reducing a 2mm shaft to 1.5 mm shaft shouldn't weaken the shaft as your concern states.
as mentioned I'm not going to this myself and seek the help of a professional engineer and he will tell me if it is possible to have the armature secured in such a manner whereas he can proceed with the operation.
Francisco, please read my post regarding converting locos who originally had a large or small disk armature, the conversion sets for these are 60944 and 60943 respectively, I had great difficulties(without proper tools and a static non movable drillstand) to drill a hole precisely in the centre and finished off centre and had great difficulties to correct the error I've made.
You are going far beyond the average skills one would expect and any failure of getting it right your motor block could be a scrap metal for the rubbish bin.
you also have to remove all the pin from the gear wheels, secure the motor block or the loco in an upright 90° angle and no motor block provides you with an even or flat surface, so the work you're anticipating of doing could be more difficult than you think it is and you may also have to remove the axles either 3 or 2 to obtain a solid base.
Very interesting topic. I have many DCM 5-pole motored locos, so I want to also try this ball bearing thing. Actually I did not know before that no drilling is needed for the motor block itself and only bushing has to be removed. Makes life much easier...
I just thought is there any ceramic ball bearings available in these very small sizes 4 x 2 x 1.5 mm? I have ceramic ball bearings in one of my RC 1:8 4WD Nitro Buggy. I once read an article about these ceramic ball bearings in road cycling (racing) bicycle and it became very sensitive vs. normal ball bearings and the friction was even lower. Maybe this same is not needed with our very small DCM motors in MRR, but if they are available in the correct size I would like to give them a try with one loco. Obviously they are more expensive, but not so much.
MR681XC-ZZ ceramic ball bearings
My understanding is ID - OD - W is the accepted standard for the order.