Lini Mod

[OCNC]

I made a mechanical modification to the Linistepper by installing 3-position
female headers (digikey S7036-ND) where the TIP 122's go. I then took
the heatsink from a Masscool CPU Cooling Fan (tigerdirect item #S457-1111) and drilled
and tapped four holes into it at 1/2" centers and 9/16" up from the edge. I also
drilled and tapped two holes on the fin surface of the heatsink (lies coplanar with the
circuit board). These holes line up with the two outer TIP holes and are 19/32" from the
heatsink edge (same edge that the TIP holes are referenced from). They also are drilled
and tapped to a depth to penetrate two fins. The stand off's were
cut from 1/4" aluminum tubing to a finish length of 9/16". The screws used are all #4-40.
The ones holding the TIP's down are 3/8" long and the two for the stand off's are 1" long.
Following the best mechanical practise I used a lock washer and flat washer under the head of each
screw. Belleville washers are recommended for the TIP's but they seem too expensive at $.50 each
so I used split ring. I rubbed the backs of the TIP's on a sharp file to get the
best contact surface possible. I also filed the mating heatsink surface and then
polished it with some steel wool. In place of mica and paste I used Berquist silicone
heat pads (digikey BER220-ND). With 1A steppers at 24V I'm unable to detect by touch any
heat rise in the TIP's.

I feel that this is a better solution than the bracket that the kit suggests because it eliminates
a heat transfer junction and it allows for very easy replacement of the TIP's. Also if you have to
drill and prepare a piece of angle for a bracket why not just do the same right on a fan
cooled heatsink? The small cost of the additional parts seems insignificant compared to the
utility of the final product.

Chris