[cds333]

I am upgrading my LMS 3960 Hi-Torque minimill to CNC and I dont know which ballscrews I should get.

The two options are:

1) .625" X .2" with a tolerance of +/- 0.004" over 12"
2) 16mm X 5mm with a tolerance of +/- 0.0012" over 12"

I would surmise that this means for option 1, a workpiece of 1.2 inches would have a tolerance of +/- 0.0004", and option 2 would give me 0.00012"

Now if that is in fact how those numbers translate, I know for a fact that my spindle runout (when measured with an indicator on the end mill shaft) is greater than 0.0004", (in fact it is about 0.0005" for the 3/8 collet)

Mostly I will be machining small parts for robotics, 3d printing and maybe a lower receiver, but nothing that requires crazy tight tolerances afaik.

So is there any point to getting the upgraded ballscrews? Or would they be wasted on this entry-level mill?

Under what circumstances or with what type of work would they be necessary for this mill?

Again, I am not a machinist and I have no training in the field, so feel free to elaborate if you like.

Thanks!

[109jb]

That isn't how ballscrew specs work. Take your first option with 0.004" in 12". Even if that whole 0.004" happened in just one revolution the ballscrew would still be within specifications. Basically, anywhere the nut is positioned in a 12" length can't be off of ideal more than +- 0.004", but it can be off +0.004 in one spot and -0.004 in another and still be OK according to the specs.

That said, In actuality it is nowhere near that bad even on a rolled screw. The 5/8" screw you are looking at is probably a Roton, or Thomson or similar. Many fine machines have been built using those screws. My G0704 has Thomson rolled ballscrews I bought from McMaster Carr with the square nuts and works great with not much error, at least as measured using a temporarily mounted cheapo DRO. Has certainly been good enough for me.

I will point out something though. The typical 1605 ballscrews and nuts come with wipers installed in the nuts, so getting chips into the ballnut is less likely. I would probably go with the 1605 ballscrews now, but they arent so much better that I'm about to change them out.

I am currently starting conversion on an RF45 size mill and am using 2005, which I have already picked up and they look fantastic.

[dazp1976]

I'd be happy with 0.004".
I didn't need that much tolerance over 12" so I used the cheap Chinese 1605 in mine. Most of my stuff is 50mmx80mm sized.
I get 0.0012" backlash from those and haven't checked them over the full travel tbf. Near enough for me.
Getting those nuts cut down to fit under the X table was a pain though.

If you have access to another mill then I'd extend the Y slot to give more travel while it's in bits. I have the basic 350w version, belt drive kit and I upgraded to the solid column. spec said 130mm on Y axis, I extended the slot which gave me a Y of 160mm in the end.

[cncuser1]

@cds333, if you are not sure. go with the .004".

If you needed better...you would be sure due to your experience and knowledge.
If you are entry level, which X2 is, then go with .004".