Chinese 3040 CNC With Loose Z-Axis Linear Bearing

I'm a newbie to hobby CNC but I've been using an ebay Chinese 3040 CNC for a few months now. Up until today I haven't had any problems. Today I noticed one of the Z axis linear bearings has somehow become pretty loose and slides up and down within the z-axis spindle mount.. This machine has a pair of LM12UU linear bearings on the Z axis that are basically press fit into a hole in the aluminum spindle clamp mount. It appears nothing holds the bearings in place except friction.

One of the linear bearings is so loose it actually slides up and down in the spindle mount with a little finger pressure. It also falls down due to gravity and vibration when the machine is cutting. When the loose bearing slides down it creates binding when the z axis goes to lower. The left bearing stays in place but the right bearing slides down. When the z-axis lowers and attempts cutting it binds, the Z-axis stalls out and blows the spindle fuse.

Has anyone experienced this issue? Since these bearings have a groove for a snap ring I was thinking I could remedy the bearing dropping down by installing a snap ring at the top of the bearing. Would this be a suitable solution or is the bearing loose because it is bad? The bearing sounds/feels fine when it slides along the shaft, the issue seems to be it slides too freely within the z-axis itself. Any input is greatly appreciated.

I would try some red Loctite 262 to ''glue'' the bearing into the housing. Should last forever.

Thanks Jim. I had thought of red loctite myself but I'm a bit leery. If and when it comes time to replace these bearings I imagine it may be a nightmare to get out? I'm not sure it would press out easily? I know from using it in the past in aircraft and automotive applications that it will soften and let go if you heat it up enough. I just worry how that chinese aluminum would withstand a few minutes of heat from a propane torch. With my luck it will probably warp like a vinyl record in the sun.

Quote:

---

Originally Posted by Jim Dawson

I would try some red Loctite 262 to ''glue'' the bearing into the housing. Should last forever.

---

Quote:

---

Originally Posted by JayBee44

Thanks Jim. I had thought of red loctite myself but I'm a bit leery. If and when it comes time to replace these bearings I imagine it may be a nightmare to get out? I'm not sure it would press out easily? I know from using it in the past in aircraft and automotive applications that it will soften and let go if you heat it up enough. I just worry how that chinese aluminum would withstand a few minutes of heat from a propane torch. With my luck it will probably warp like a vinyl record in the sun.

---

If this machine is used in normal hobby use, that bearing is probably good for 20 years or better. You could just put the Loctite on one end only, maybe a 1/4 inch or so. You could also use blue Loctite, pretty sure that would hold it also. I don't think it really would take much to hold the bearing.

You're probably right. I'll give it a go. In the event these cheap chinese bearings fail I'll worry about it then. Thanks again!

Don't like to bring threads back from the dead but I felt this was one of the rare cases where it is appropriate. I ended up simply installing the snap ring in the groove on the bearing and it worked fine. About 2 1/2 years later and I've had no more issues with the bearing moving or the z-axis binding.

I have no doubt red loctite as suggested by Jim,one of the loctite retaining compounds specifically designed for press fit bearings, epoxy or something similar would have worked fine too. Thought I'd try the snap ring first and follow up with loctite or something if it didn't work long term. Turns out the retaining ring was I needed. I added a snap ring to the other (non problematic) side too as a precaution. I've had no further issues with the bearing.

If I do have issues again I'll loctite the bearings and reinstall the snap rings. Just thought I'd share in case anyone wonders whether the repair worked!

I have the same problem and was considering Loctite, but like the snap ring solution.
However, you mention THE snap ring as though it is part of the kit - which I don't see in mine.
Are you referring to a purchased part, and if so can you provide a link, please?
Thanks

If you're gonna use Loctite, the stuff you want to use is NOT the threadlocker, but rather "Sleeve Retainer". It's green. Here:

https://www.amazon.com/Loctite-37424.../dp/B0002KKTIG

Quote:

---

Originally Posted by Donjohnson24

I have the same problem and was considering Loctite, but like the snap ring solution.
However, you mention THE snap ring as though it is part of the kit - which I don't see in mine.
Are you referring to a purchased part, and if so can you provide a link, please?
Thanks

---

No. They aren't included with the machine. I had to purchase them. In my case it almost looks like they should have been installed but the manufacturer doesn't due to the press fit and the fact that they can save a few cents. I'm not sure on a part number but you should just be able to measure the bearing/groove diameter or google the bearing number and get the spec. Then most of the the time a suitable e-ring, snap ring or retaining ring should be available at the local hardware store.

Hope that helps!
-James

Agreed that the loctite specifically for press fit bearings, pins and sleeves is probably a better choice than the basic threadlocker. Although I have worked with the red loctite around cars and aircraft. I have no doubt the red liquid loctite thread locker, something like 271, would be a permanent fix as well. I went the cheap and easily reversible route. At most hardware stores 4 snap/retaining rings shouldn't be more than a few bucks. Likely many ways to skin this cat. . .

I was mainly worried about getting things apart in the future. I know red loctite usually requires some heat to break easily. Generous heat is not something I'd be thrilled with on a cheap chinese aluminum machine. Not sure how easily the green sleeve retainer stuff would come apart. You'd likely never need to worry about it anyway, but I'm a bit paranoid and plan for the worst. I chose to leave myself the option of easily getting things back apart. The fact that the snap/retaining rings were cheaper than the red or green sleeve loctite just made it even better.

Quote:

---

Originally Posted by JayBee44

No. They aren't included with the machine. I had to purchase them. In my case it almost looks like they should have been installed but the manufacturer doesn't due to the press fit and the fact that they can save a few cents. I'm not sure on a part number but you should just be able to measure the bearing/groove diameter or google the bearing number and get the spec. Then most of the the time a suitable e-ring, snap ring or retaining ring should be available at the local hardware store.

Hope that helps!
-James

---

Thanks for the response - I would expect that there should be a groove in the plastic mount for the bearing that would be exposed when the bearing is pushed further into the block, but if the manufacturer would not bother to fit a snap ring, it is unlikely that he would have cut the groove. I should add that I have a CNC3 3018 Pro machine rather than a 3040 so there may be a difference in this version.
It seems that some green Loctite should do the job for me.
I have to smile, though, at your and other posters references to finding snap rings in the local hardware shop. That may be the case in the US, but hardware shops in the UK have largely disappeared, being - partially - replaced by what you call big box stores. They carry only a range of packets of standards screws, nails and other general hardware items - nothing specific such as snap rings. I could probably find a box of assorted snap rings at Amazon.uk, but would certainly have to find what is specifically needed by an intensive search online. As I am 80 years old, I do remember the old hardware shops of my youth, which were usually known as 'The Oil Shop', as that was where you went for the paraffin for one's Valor heater - and possibly to get accumulators charged for the supply to the valve heaters in your wireless set !

Quote:

---

Originally Posted by Donjohnson24

Thanks for the response - I would expect that there should be a groove in the plastic mount for the bearing that would be exposed when the bearing is pushed further into the block, but if the manufacturer would not bother to fit a snap ring, it is unlikely that he would have cut the groove. I should add that I have a CNC3 3018 Pro machine rather than a 3040 so there may be a difference in this version.
It seems that some green Loctite should do the job for me.
I have to smile, though, at your and other posters references to finding snap rings in the local hardware shop. That may be the case in the US, but hardware shops in the UK have largely disappeared, being - partially - replaced by what you call big box stores.

---

It definitely sounds like there's a difference in construction between your machine and mine. If I recall correctly for the z axis on my machine the linear bearings extend slightly past the aluminum housing on top and bottom. The pre-manufactured linear bearings have a retaining ring groove machined on both ends. It was just a matter of sliding the bearing back where it went and installing the retaining rings in the grooves.

I'm sure the suggested loctite solution should work out fine for you and sounds like the logical approach in your situation.

Believe me the local mom and pop hardware stores are nearing extinction here in the US as well. Most of the them around me have closed or converted to one of two main hardware store franchises. They're essentially just a step above the big box stores. They've got a slightly better selection for some items but they usually can't compete with the big box stores on pricing. The good news is some of our big box home improvement and hardware stores in the US really do have a decent selection. IF you know what you're looking for and where its at that is. Asking for help beyond basic screws, lumber and paint will typically draw blank stares in the big stores!

What you need is a Threadlocker (https://www.albanycountyfasteners.co...ions-s/966.htm)
Threadlocker is an adhesive used to prevent the leakage, loosening, and corrosion of fasteners such as screws and bolts. These chemical threadlockers provide better torque retention than mechanical methods.
The most common formulas used in threadlockers are methacrylate-based. The threading-locking fluid is thixotropic i.e. it can flow well over time and resist shocks and vibrations at the same time. It can either be permanent or removed using heat etc. Many brands color code to show strength, and method to remove if it is removable.
Chemical threadlockers work differently than washers. They fill the spaces in between the female and male threads and lock the fastener in place after hardening into a tough plastic. It prevents the loosening of fasteners due to vibrations. This also seals out dirt moisture and all sorts of contaminants that cause corrosion and damage the assembled joints.
You should check your environment before use to prevent contact with harsh chemicals and high temperatures as it will affect the performance.
You can also check the strength of threadlocker on the website of Albany County Fasteners before buying the fluid. They provide top quality products. Intense vibrations can also loosen the fastener assemblies even with the solution on them if you do not select the right hold strength.

Just thought I'd update this thread. The snap ring solution on the top side of the bearing is still working fine for me since my main issue was the bearing sliding/dropping down. I also wanted to share another possible solution.

I recently saw a newer version of my machine. It appears some of the Chinese manufacturers are now addressing the issue of loose fitting Z-Axis bearings by simply drilling and tapping a hole and installing a small set screw through the aluminum bearing housing near the center of the two linear bearings on the Z axis. The small hex head set screw pinches against the bearing's outer race just enough that it should help hold the bearing in place.

I just thought I'd share because that should be another relatively easy solution to implement for others coming across this issue. Of course, keep in mind drilling and tapping for a bearing set screw with the bearings in the machine would be more difficult. You'd have to take care to avoid damaging them. Ideally you would do it with the bearings removed.

Just another update for anyone finding this thread through Google searches etc.. The snap ring solution is finally failing me after about 6 years. I almost ruined a 40 minute cut yesterday when things started binding. Took a minute to discover there's now a little more slop in the press fit. With enough vibration from the spindle, the z axis bearing can now spin in the spindle mount and will actually start to walk up the shaft. I'm sure some movement and rotation of the bearing over the years probably enlarged the aluminum sleeve where the bearing sits a little more.

I'm going to Loctite it and/or drill and tap for a set screw like I (and the manufacturer) should have done originally. I was in the middle of a project when the original problem came up and didn't have time to wait 24 hours or more for Loctite cure time. (No primer or accelerator to speed cure times available locally either.) The snap ring worked well enough I forgot about the issue for years. Moral of the story: if there's enough slop in the press fit for the bearing to slide up and down, it'll probably eventually rotate too.

I'll likely try the green Loctite 640 retaining compound or Permatex's 64000 sleeve retainer since that's more readily available locally.