Sleeve bearings for CNC router?

[jeffmorris]

I know that 3D printers and CNC routers have beds, gantries, motors, and electronics. The difference is the tool in the machine. I have a large CNC router in the woodworking shop at the program for mentally-handicapped people where I work. I found out that I need new plastic sleeve bearings. I asked for help at CNC Zone forum and someone referred me to a company that makes sleeve bearings. They have so many different kinds of plastic sleeve bearings! The sleeve bearings have shaft diameter of 25mm, outer diameter of about 35mm, and I don't know the exact length.

Website: https://www.igus.com/iglidur/plain-b...presetsurpre=1

Someone at CNC Zone told me that sleeve bearings with ball bearings don't work on shafts where plain plastic sleeve bearings are used.

Any suggestions?

[awerby]

Does this large CNC router really run entirely on unsupported shafts? That's not recommended over long spans. Do you have a way to press out the old bushings and press in new ones? If it were me trying to fix this thing, I'd call the manufacturer of the machine as well as the people making the bearings you want to use, and make sure everyone's on the same page.

[jeffmorris]

The company that made the CNC router went out of business. It has 25mm linear shafts and bearings. I don't know the exact size of the bearings that I need because the machine is inside an enclosure and it would be very hard to take the machine out of the enclosure. The machine is shown at: https://www.bing.com/images/search?v...113&ajaxhist=0

[Trakyan]

Most machines that use plastic bushings can't be converted to linear ball bearings. The reason for this is that when using plastic bushings, the rods usually aren't hardened and ball bearings will wear them out very, very quickly. The lengths are usually pretty standardized, and one size smaller or longer wont hurt much, so measure approximately how long they are and get the closest size, that will probably be right.

[awerby]

You're going to have to take it apart anyway to replace the bearings, so wait until you do that before ordering the new ones. A different length won't matter much, as Traykan says, but a different OD would be another matter entirely.

[S550Stang]

https://www.mcmaster.com/#standard-s...rings/=1arol73

better than plastic...

[Trakyan]

Metal sintered and oil impregnated bushings tend to have higher friction than polymer bushings and potentially higher wear on the shaft since these likely aren't hardened. That and their lubricant can run out, whereas the polymer bushings keep lubricating as long as the bushing is there, they just get sloppier in terms of their tolerances.
Honestly I think either will work, one is less maintenance (polymer) one has more constant tolerances over time (metal).

[awerby]

I agree with Trakyan; those bronze bushings are meant for shafts to spin in, not for sliding along shafts.

[S550Stang]

I disagree. The shaft is of a harder material. These bushings are great for rotary motion, but have been used for years in linear motion applications even up to 4 m/s speeds....

These bushings will also lubricate as long as the bushing is there...

These bushings, unlike polymer, will hold there tolerances longer.

These bushings can often be found at local hardware stores (real ones, not orange box stores)

If It were me, I would upgrade the shafts to hardened and go with a sealed linear bearing...

[Trakyan]

I never said the shaft was softer, just that it might not be hardened steel (i.e. unsuitable for linear ball bearings), and any metal on metal contact will wear out both parts. It just so happens that the brass/bronze gets worn down more than the steel. As for the lubrication, not quite. Polymer bushings will lubricate as long as the bushing is there, because the plastic itself is the lubricant. Bronze/brass bushings (the sintered kind) are impregneated, basically soak in and absorb oil like a sponge through all the pores left by the sintering process. This does run out, and while the plain brass/bronze will slide relatively well on steel once the oil has left the bushing, I think most people would recommend adding oil. I totally agree on the tolerances, and I mentioned the same thing in my earlier post.

I simply recommended polymer bushings because they are (slightly) lower maintenance. The original poster (at least from what I've gathered) is just looking for advice to get the machine back up and running to do its job as quickly and easily as possible. For much the same reason I wouldn't recommend replacing the shafts and going for linear ball bearings.