I will show here few ideas I did on my machine. Maybe, it is already somewhere - but maybe not yet.
first of all - Z axis
I used ballscrew 20 / 05
the body for the nut is from 2 parts - look at the one piece imbus M12 screw on the bottom. It is in hole -diameter 12mm, with plastic washer to hold it in place for assembly
imbus set screw ? (is that right ?)
the idea is to tighten this screw to M12 in centre through the M12 hole
by the way, if the three nuts are M12 - their head fits exactly to the round slot
BF20 uses MT2 for tool fixing (I do not plan toolchanger)
the tool is fixed in place by M10 x 1,5mm thread - part (114)
to release tool from MT2 - part (114) leans against part (112) - one turn moves about 1,5mm and it is sometimes difficult to release MT2 - often you must hit the screw on top.
I did replace part (114) and (112) as you can see in the picture (botom is the original (114))
When I tighten new part 114a by one turn, it pulls MT2 tool 1,5mm up and at the same time part 114a moves in nut M20x1,0mm - 1,0mm down. That is - I tighten MT2 tool by 0,5mm on one turn - now, just by hand I have enough power to tighten tool and mainly to release the tool - sometimes I use key to release - but never need to hit anything.
(M20 x 1,0 is the origin thread on part 112 - no need any other changes to machine)
I decided to change to 3f motor + VFD -
get rid of noisy gear
get more reliable motor
get easier control by VFD
my choice was power motor (650W / 2,3Nm in size of 550W motor)
1. elektromotor 1LA9070-2LA12
SIMOTICS GP LOW-VOLTG. SQUIRREL-CAGE MOTOR IP55,
WITH INCREASED RATING 2-POLE,THERM.CL.155(F)*
SIZE 71M ALUMINUM ENCL.
3 AC 50HZ 230VD/400VY * 0,65 KW 2750 ot.
3 AC 60HZ 460VY * 0,75 KW
220-240/380-420 (50HZ)
belt - HTD5M x 15mm x 450 mm
pulley motor - 64 / spindle - 36 center distance - 97,5 mm max speed 9778 at 100Hz
pulley motor - 30 / spindle - 68 center distance - 97,9 mm max speed 2426 at 100Hz
in practice - over 6000 the big ball-bearing on top gets hot
and top speed is about 8000 - I have 750W VFD and it has no more power
sometimes I run motor around 15Hz (speed 350) and motor does not need external cooling
for me - I am satisfied with my belt conversion
chart - Nm / speed
Pulleys and shield are made by 3D print / ABS - it is in use for about 30 hours of work without any wear (it is hobby machine :-) )
on top of part "206" I had ring with 4 magnets for measuring spindle speed - I did remove it (maybe you have another detail for measuring spindle speed)
(I measure speed on top of the cover - little blue dot on picture not ideal, must redo it)
and the left side of this - I put inside part 206
(on the right side there is thread M40 x 1,5 for nut)
(the dimension 19,50 is for the collet
take it as princip - if you need details ask for them
my new probe - after problems with clasic probe, where using collet to hold the probe gave me error up to 0,05mm + error of the probe
I decided to make the probe fixed to the mill body. Now repeatable accuracy mesuring position is < 0,015 mm. Mach3 macro calculates the exact position of "zero" from measured position by probe. The probe can mesure only X - Y direction, not Z
Second picture is cover, when the probe is not used.