Mini mill fine tune mechanism

[redvan22]

Hi,
While using my MM fine adjustment, the head suddenly dropped enough to cause the cuter to jam into the work. There's a ton of play in this knob but I do not see any way to remove it. I took it all apart and everything looks OK to me except the worm gear. The teeth look flattened and are very shiny.
I have the Micro Mark mini mill.

 

[tghsmith]

I have had mine apart(LMS 3990) lubed it all and checked for smoothness,, I keep the gibbs well adjusted and lubed,, but I do engage the fine feed well up from the work with the locking screw loose,, bring it down some and then add some resistance with the screw.. if I need to raise the head the process is repeated

 

[Dhal22]

That helps pushes me further into a higher quality mill decision. There is a CF mill on CL right now that I've been watching. Will probably hold out for a PM25.

 

[tech610]

The vibration, even the small one will cause the millhead to creep down and the fine feed alone will not prevent this kreep. Keep the locking screw really tight. I even tighten up one more screw on the mill head gibs. When done milling loosen it up for drilling and other milling tasks.

 

[tghsmith]

I shortened the locking screw and added a section of brass rod that is angle cut to match the gib angle,, no changes up or down when the locking screw is tightened.. also did a major mod to the fine feed handle,, much better feel..

 

[tech610]

Nice looking handle wheel. I just screwed a piece of a steel strip to the existing wheel and added the knob. Helps a lot when gibs screw is tightened.

 

[homebrewed]

The head-drop issue with this class of machines is a well known problem. I own a micro-mark mill as well, and did some modifications to mitigate it. The first was to replace the torsion spring lift mechanism with the LMS air spring upgrade. This also gives you a bit more Z because the kit includes a longer rack.

The core problem(s) with this machine are the worm gear and and fine/coarse feed mechanism, which is a pair of castle nuts that are either engaged (for fine feed) or disengaged for coarse feed. On my machine most (but not all) of the "slop" is associated with the castle nuts. It might be possible to find or make some that have tapered teeth and eliminate that source of backlash, but I'm not sure how you would maintain full engagement of the teeth -- the stock arrangement just has the castle nuts on a slip shaft. I had thought of some sort of tapered wedge thingie to drive between the teeth but didn't get very far with that. I did try locking the nuts together using a hose clamp and that worked, but it was a pain to switch between fine and coarse feed.

Making sure to lock the Z axis when face or side milling is good for preventing damage to your piece, and a DRO on the Z axis will keep track of where your head is. Adding a single DRO of the igaging type will cost less than $100, and it's easy to make the mounts you need.

Like @tghsmith I also put a crank handle on my fine feed knob to make it easier to use the fine feed. With its increased mechanical advantage, I can tighten the Z axis gib screws up a bit more without making it too difficult to move the head, and that also helps with the head drop problem.