Tips/Techniques Bearing questions Y

[slow-poke]

I'm in the process of sorting out the Y-Axis ballscrew for the 8x30 mill. Question(s) are in Bold Italic to standout in my long winded post. At the end of the day this is a hobby mill and I'm not chasing 0.000x, if this thing is repeatable to 1-2 thousands I will be very happy, the CNC conversion is for convienence of making things not to build NASA stuff.

The end block has two bearings and a pressed in ~17.5mm spacer between them. A nut on the outside takes up the slack in the old leadscrew.

Bearings – Original Y-Axis 20 x 42 x 12
NTN 60042
O.D. 42mm
I.D. 20mm (19.93) [0.7846”] -2.7 thousands measured
Width 12mm

Thrust 20 x 35 x 10
NUK 51104
O.D. 35mm
I.D. 20mm (19.93) [0.7846”]
Width 10mm

When I look these up online, they simple show the nominal dimensions (makes sense if your just replacing), but if I need to machine a pocket, I need to know the nitty gritty details to the 0.0001" so will need to find a more detailed datasheet for possible replacement bearings.

Question # 1
Seems like the moment you mention ballscrew, the first thing you hear is need to replace the existing bearings with high cost angular contact bearings. On the page I found the original bearings (dollars a piece) they had a link to angular contacts ranging from $50-200. How bad are the original bearings? Do I really need to upgrade?

Pictures to aid discussion, and a few comments:
a) I made this little threaded *** spacer yesterday, the 20mm ballscrew is temporarily mounted in a 3D printed block that sort of mimics the bronze one for the old leasdcrew, so I can test fit the new ballscrew.
b) The original leadscrew is slightly larger in diameter and the snout dimensions are longer; 50 vs 40mm, 14 vs 12mm, this presents a problem with two obvious solutions. When I mount the end block with the new ballscrew, the shorter by 12mm ballscrew thread is just inside the outer edge, that's why I made the little threaded spacer yesterday for more of a what if solution, the flange is too thin and I would need to have some means to grab it to adjust and to lock it in place so a really poor long term solution but it helped me get a sense for the fit of everything.

Two possible solutions:
1) Make a new thinner end block, there is more wasted space via the spacer than the new ballscrew is too short.
2) Remove or replace the inner spacer and replace the 20mm bearing with a 15mm so that the ballscrew can shift forward 10mm or so exposing the thread on the outside and then adjust it much like the original, this seems like a much easier approach. Assuming this approach I could use some help specifying bearings (I'm an electrical not mechanical guy)

 

[Mcgyver]

Q1, yes, imo, A/C's are the right bearing for a cnc mill feedscrew mount. They take radial and thrust loads so stop axial movement of the screw. Otherwise you end up with backlash, a no-no for cnc which climb cuts all the time. Regular deep groove can take some thrust, but not much and there will be a bit of backlash with them.

Unless you are going for expensive P4's, regular grade quality ones like SKF aren't crazy expensive. Its when you want match pairs of P4's for a spindle that you need to sell off family members or body parts.

 

[slow-poke]

Q1, yes, imo, A/C's are the right bearing for a cnc mill feedscrew mount. They take radial and thrust loads so stop axial movement of the screw. Otherwise you end up with backlash, a no-no for cnc which climb cuts all the time. Regular deep groove can take some thrust, but not much and there will be a bit of backlash with them.

Unless you are going for expensive P4's, regular grade quality ones like SKF aren't crazy expensive. Its when you want match pairs of P4's for a spindle that you need to sell off family members or body parts.

That's helpful, I'm learning as I go.

The original setup uses 60042 bearings for the radial load and the 51104 for the thrust, and I guess what your telling me is that I can replace both of those with one angular contact bearing that accomplishes both tasks, is that correct?