Hi Brent, The eBay 624UU are the wrong size.
1 Like
I finally got replacement linear modules which are a treat - no play or bed wobble anymore.
Thanks @Brent113 and Support for your help.
Will definitely research this further.
2 Likes
I am even more convinced now that I am probably going to have to replace my rails.
Does anyone know if you can just replace say the Z pair, or have to replace all 5 (A350)?
A few months ago I would have said to ask the support for individual rails, but now I think it’s more worth it to replace all 5 with the new rails, which are much quieter
With the new rails you have to replace all 5. They aren’t compatible. (Although technically the Z should still be able to be used if they bothered to write the firmware correctly)
You can buy the old rails still from support for $150 each. So by the time you use the 50% off you might as well just buy a set of the new. Unfortunately though I don’t think they’re shipping yet. Although someone just said they received theirs. Don’t know how much of a backlog there is if you ordered now.
Other option is to buy some used from someone who bought new rails. But haven’t seen many of those show up yet either.
-S
I’ve done a Facebook post asking if anyone was willing to sell his or her old modules and had them after two weeks 
There are people willing to sell.
Wanted to add my experiences when performing this “maintenance” procedure.
Having played around with milling brass and aluminum and possibly 
crashing a facing tool and endmill:person_facepalming:t2:… I found the x-axis to have excessive play. It was around 1-2 mm of vertical play when measured at the ends of the tool head.
I was able to measure the distances between the rollers and found them to be way out of tolerance in respect to what the machine is capable of. When I measured what they were at after taking the carriage out of the housing I found they were between 0.30mm-0.50mm put of the recommended distance of 34.29mm. You can see in the attached pictures of the distances prior to adjustment.
I was able to get the rollers dialed within spec +/- 0.15mm. The eccentric bearings that move the rollers are not very precise, but with a little finesse you can get them dialed into the prescribed 34.29mm. for me the trick was to move the rollers out a little past where you want to be then backing it off just a bit.
The set screws also had an impact on the spread distance by about 0.10mm-0.30mm. I figure this had to do with the manufacture difference between the set screws and where on the thread the set screw was touching the eccentric bolts.
I had fairly good success by dialing in the distance to about 34.32mm and then tightening down the set screw which would bring the distance down by ~0.15mm. This effectively got my roller distances to 34.29mm and 34.31mm, respectively.
When I installed the carriage back into the linear rails, I did notice that the side with the larger 34.31mm thread did require a push and a following “pop” sound when it seated into the rails. The trailing edge with 34.29mm, at least in my installation, went in smooth without incident. I can only assume the nominal tolerance between the guide rails are 34.30mm and having a 0.02mm delta between the rollers and guide rails is just enough clearance to not cause any binding and allow the stepper motor to freely move. Unfortunately, I did not document the final distance measurements of my rollers after adjustment.
Now that I’ve done this, I’m looking to readjust the y-axis to make sure they are within factory spec and then possibly building a minimally intrusive support system to aid in lessening the known the y-axis bed flex when moving back and forth.
1 Like
I haven’t done a measurement, but I’ve been wondering just how straight and parallel the rails are. The extra clearance might be necessary to compensate for variation in rail distance. Any such variation is likely to be on a per-part basis.
@eh9 I could definitely see there being a tolerance range for the rails as they are inset into the aluminum extrusion, which in themselves could also have tolerance ranges.
Of you really wanted to test the tolerances throughout the entire travel of the rails by manually moving the bracket 1cm and jiggling for tolerance to see if up/down and side to side shake is different along it’s travel.
You could also go about it with a dial indicator, but I think that’s maybe too extreme for this type of machine…that being said, I remember the promo vids showing the machine continually hitting 50 microns as it traveled back and forth along the y-axis. In my experience the machine is unable to do that as I once paused a milling cycle after it’s first pass and when it went for the same 0.05mm step down it crashed the endmill as it went too low on the z-height.
I want to thank everyone that has posted to this thread. I have been fighting my machine for over a month now. I have had my machine since Oct. 2020 and got stuck with the 3d printing of it :)! About a month ago I wanted to finally get to the cnc module which is what I actually bought the machine for. I was trying to do some inlays and kept having issues because the bits wobbled so much I couldn’t get a good cut and I was only cutting like .1mm at a time! Now that I have followed this thread and made the necessary changes and fixed the rollers I am able to flycut my table using my 5 flute 1/4 inch bit at 1100mm/min at .3mm deep and the motor isn’t bogging at all and the table is absolutely flat. No ridges, bumps, or barely lines where the bit is running. I am hoping to start doing some 3d carving today for the first time and I feel like it will be successful. And it will all be thanks to those that have posted here with their experiences. Thanks again! Happy cutting!!!
2 Likes
I wrote my own adjustment procedure that is, IMHO, even more complete, My procedure. Using my method, it only takes a few minutes (once you’ve removed the assembly from the linear module) to adjust the cam and, once adjusted, doesn’t change while you are (final) tightening the screws. My expertise comes from being a calibration tech in the aerospace industry for 50+ years.
There was lots of useful info in this forum post but even with tightened rollers I didn’t like the lack of rigidity in the system for CNC use so I have had to “think outside the rail” as you might say… Enough with the bad puns I just came back here because another factor that increases play of the X-Axis is its connection points to the vertical rails. I found that play at this connection point causes the whole X linear module to essentially rotate when applying downward force with the tool head. I have been working on a mod to fix this for awhile to essentially override the need for overtightening my Z-Axis rails to get the slop out of the system, so hopefully this helps someone else too.