Left And Right Threads On A Minimill?

unioncreek

unioncreek

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I have a Harbor Freight mini mill, it does what I want. But, was wondering why the X axis is right hand thread and the Y axis is left hand. I plan on putting new lead screws in, so I can get .001/revolution. I would like to just put right hand threads on both axis, but was curious why it has both left and right.

Bob
 
The y axis has a left hand thread so the movement is more intuitive.
Not sure about going to 0.001/rev. That mill is not that precise unless you have scrapped the ways and put some very very expensive bearings in it.
A thread that fine will also not be very robust, it would probably have to be a v-thread. V-threads have more friction, are weaker, and clog more easily than trapezoidal threads.
If you put a 20TPI screw in, you will get 0.050"/rev and you can easily eyeball 5/10th's or go finer with a DTI or DRO. Precision ground Acme screw will outperform ball screws in many applications, and they can be taken down to a very low lash and still have good movement and very positive feedback to the user.
 
The only difference would be that the dial would read backwards. There would be no difference in anything else. It would take a little getting use to, but you would adapt quickly. It would just be non-standard compared to other mills.
 
Don't forget you can get some more precission in your dial markings by adding larger hand wheels for more sensitive movements.

Did you meen a 0.001 per rev or per devision ?

Stuart
 
Going to be a might difficult to find a 1000 TPI leadscrew. Gear it down some if you want smaller grads, or easier, as Stuart says, put a larger handwheel on. Or go with a DRO.
 
The reason for wanting to change the lead screws is backlash. I may try some Delrin nuts first to see if I can get rid of most of it. I have iGaging DRO on it right now and it works for what I do. The mill doesn't have to be super precise, though I try to be as accurate as I can. The mill comes with 16 TPI, and the dials have a larger space just before the zero. I may also make some new dials if I decide to keep the original lead screws.

Bob
 
unioncreek said:
The reason for wanting to change the lead screws is backlash. I may try some Delrin nuts first to see if I can get rid of most of it. I have iGaging DRO on it right now and it works for what I do. The mill doesn't have to be super precise, though I try to be as accurate as I can. The mill comes with 16 TPI, and the dials have a larger space just before the zero. I may also make some new dials if I decide to keep the original lead screws.

Bob
Click to expand...
Don't worry about backlash on a mill unless you going to CNC it, then you want ball screws.
People get all wadded up over mill backlash. Mill backlash means almost nothing, it would only be a concern for conventional milling if you climb mill, which you should not do on a mini-mill.
Your DRO will tell the truth regardless of lash. iGaging scales are pretty low end, if you want to be more precise, buy better scales. If you want to climb mill, get a bigger mill.
Ignore backlash unless it is like 2/3 of a turn on the hand wheel, then just adjust the nut.

Backlash is much more important on the lathe, on the mill it is nothing to worry about (almost)
 
You can use an edge finder a dial indicator and a piece of metal in a vice to practice dealing with the backlash whilst counting on the dials.

Or even a spike in the chuck and a steel ruler to look at where the point relates to.

The reading is ok with one direction, if you change direction you need to go one extea handwheel turn and then back up one, this will remove all the backlash.

Umm did that make any sense, please somone jump in and explain it better for me :)

Stuart
 
If you overshoot your mark, simply back up enough to get rid of the lash and do it again. That's why backlash isn't really such a big deal. You really seldom make bilateral moves to and from a fixed origin.
 
When milling pockets, backlash can give problems especially when the cutter sits in a corner. You are trying to change direction and the cutter can chatter/squeal from lack of movement.
 
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