Sticky U-Joints

[townsend]

I wonder if anyone else has experienced this problem and can explain what is happening. I am building a RostockMAX (version 1) ... although evidently I've been shipped the v2 effector plate, however that's somewhat irrelevant, since the same rods and U-Joints are used despite that. Anyway. I dressed and polished up the rods and de-burred the holes in the U-joints and was quite pleased with how nicely the U-joints would spin on the rod when flicked. But after assembly, they began to bind, so I took it all apart and tried again to get everything spinning freely. When disassembling, two of the U-joints were bound so tightly that I was afraid I couldn't get them off!

I cleaned the thing up to make sure there was nothing coating the parts, and tried again. It was wonderful - very low friction, freely spinning, so I reasoned that something must have gotten on the rods, since it was perfectly fine after cleaning it up an reassembling. A few moments later, I went to put the delta arms on, and noticed it seemed "sticky" again, so I took it apart again, and none of the joints were that great, and in fact once again I had two that I had to really work at to remove.

So I've got the rods and U-joints all apart, and decided I won't reassemble till I post this to find out what's happening ... how can it be so great, and then for no good reason start binding? I'm in a climate controlled building, and the temperature and humidity are fixed and normal. Has anyone bumped into such a problem, and if so, how did you solve it? I don't want to just keep chopping away at material until I have sloppy joints, so I'm treading carefully right now.
-gt-

[Eaglezsoar]

I wonder if anyone else has experienced this problem and can explain what is happening. I am building a RostockMAX (version 1) ... although evidently I've been shipped the v2 effector plate, however that's somewhat irrelevant, since the same rods and U-Joints are used despite that. Anyway. I dressed and polished up the rods and de-burred the holes in the U-joints and was quite pleased with how nicely the U-joints would spin on the rod when flicked. But after assembly, they began to bind, so I took it all apart and tried again to get everything spinning freely. When disassembling, two of the U-joints were bound so tightly that I was afraid I couldn't get them off!

I cleaned the thing up to make sure there was nothing coating the parts, and tried again. It was wonderful - very low friction, freely spinning, so I reasoned that something must have gotten on the rods, since it was perfectly fine after cleaning it up an reassembling. A few moments later, I went to put the delta arms on, and noticed it seemed "sticky" again, so I took it apart again, and none of the joints were that great, and in fact once again I had two that I had to really work at to remove.

So I've got the rods and U-joints all apart, and decided I won't reassemble till I post this to find out what's happening ... how can it be so great, and then for no good reason start binding? I'm in a climate controlled building, and the temperature and humidity are fixed and normal. Has anyone bumped into such a problem, and if so, how did you solve it? I don't want to just keep chopping away at material until I have sloppy joints, so I'm treading carefully right now.
-gt-

You need to lubricate the axle on which the ujoints turn. A white lithium grease would work or one of the high tech lubricants like SuperLube.
As with virtually all metal to metal contact areas lubrication is essential.

[townsend]

I had asked my lab assistant to order some white lithium grease, so I had planned on using that before putting the thing into operation. I didn't think it mattered at this point, but from your reply it looks like that's the only reason for the trouble. Actually, the reason I ordered the grease was to prevent the thing from wearing out in the long run ... I thought for now it wasn't so critical. I'm still a bit puzzled how it goes from spinning freely to tightly bound over a few minutes of just sitting on the desk. I wonder if there was still residual moisture from my cleaning on the rod acting as a lubricant which dried up perhaps?

Also, the cheapskates are partially assembled, and they have the same u-joints and rods and are not exhibiting this behaviour. In fact, when this happened, I walked over to where I had left the cheapskate assembly, and flicked the u-joints to test and they all spun freely after sitting for two days. *shrug* ... its the same parts!

Anyway, I trust your judgement, so I'll go ahead and put on the grease as soon as it arrives, and hopefully that will put this problem to rest.
-gt-

[Eaglezsoar]

I had asked my lab assistant to order some white lithium grease, so I had planned on using that before putting the thing into operation. I didn't think it mattered at this point, but from your reply it looks like that's the only reason for the trouble. Actually, the reason I ordered the grease was to prevent the thing from wearing out in the long run ... I thought for now it wasn't so critical. I'm still a bit puzzled how it goes from spinning freely to tightly bound over a few minutes of just sitting on the desk. I wonder if there was still residual moisture from my cleaning on the rod acting as a lubricant which dried up perhaps?

Also, the cheapskates are partially assembled, and they have the same u-joints and rods and are not exhibiting this behaviour. In fact, when this happened, I walked over to where I had left the cheapskate assembly, and flicked the u-joints to test and they all spun freely after sitting for two days. *shrug* ... its the same parts!

Anyway, I trust your judgement, so I'll go ahead and put on the grease as soon as it arrives, and hopefully that will put this problem to rest.
-gt-

I can't answer why they freeze up so quickly, lubricate the cheapskate ujoints also.

[Tinyhead]

Definitely lube them. I had mine bind on my build like you did. Needed a vice and drill to get them apart. Lube would be a good idea regardless.

[townsend]

I bought some lithium grease, but the silly thing still binds right now with the grease on it, after turning perfectly freely before. I'm guessing that the issue is that the clearance is just too low and they were still warm when I first put it together and it was fine ... when it cooled the clearance changed. I think the solution is just to dress and finish them a little more, because certainly the ones I prepared on the cheapskates are not giving any trouble at all. In other words, I guess I'm just not done yet. ... and of course, I'll have to lubricate them too.
-gt-

[Eaglezsoar]

I bought some lithium grease, but the silly thing still binds right now with the grease on it, after turning perfectly freely before. I'm guessing that the issue is that the clearance is just too low and they were still warm when I first put it together and it was fine ... when it cooled the clearance changed. I think the solution is just to dress and finish them a little more, because certainly the ones I prepared on the cheapskates are not giving any trouble at all. In other words, I guess I'm just not done yet. ... and of course, I'll have to lubricate them too.
-gt-

Check the axles and make sure they are not bent.

[Tinyhead]

Check the axles and make sure they are not bent.

+1

Tightened the axle to a bending mount which caused the joint to bind in the first place.
With the u-joint binding, I put a thin piece of scotch Brite in a drill and running it through my binding u-joint to clean up the bore.

[townsend]

I'll try that scotch-brite trick ... I checked with the micrometers and found the bore size is 0.126" ... only 1/1000th of an inch larger than an 1/8" ... but despite that, my 1/8th inch drill bit seems very sloppy in it. I checked the size of my bit with the micrometer and found it is a little smaller than the expected 1/8th of an inch. I don't know if drill bits are purposely designed to be a little smaller than their official size, or what, but the bottom line is I can't find a drill bit that I trust to ream out the hole without making it sloppy. In 1/64th of an inch increments, they are either too small or too big, so I think your idea of using a thin cylinder of scotch-brite might address that problem. I'll pop over the laboratory this morning or early this afternoon to try getting this sorted out. Thanks for the tip!
-gt-

[townsend]

Well, 2 out of 3 ain't bad ... Now I've got two rods and four U_joints spinning freely and reliably ... at least for now. Unfortunately, the third (and last) one that I was working on didn't work out so well. For no particular reason, it suddenly bound so tight, I couldn't get it off. Whatever is happening must have something to do with the soft aluminium joint riding against the hard steel rod. I guess when everything is properly cleaned, sized, and dressed, all is well, but somehow, something happens like a microscopic metal filing getting in the crack and grinding things to a halt. I can't explain it. I had trouble with binding while working on the other two, but I was always able to work the parts apart and continue working, sometimes with a lot of effort, but never any damage. This last one, however, I can't get off no matter how aggressive I am. Prior to becoming aggressive, I tried to swell the aluminium up with heat as a last resort, and one side came off finally, but the other side is now wrecked (aluminium is too soft to get aggressive with) and STILL stuck fast, with only a few millimeters of the rod holding it on.

So I'll have to order a replacement, and this time just make sure its sized, dressed, and cleaned perfectly before I put the parts together. Although my background is electronics and computers, I have had a lot of mechanical experience successfully rebuilding over a half dozen engines and transmissions, and I've never encountered a problem like this before.

I wonder what the longer term effects of this are ... I mean from what I've seen, I can't help but wonder what will happen after running the thing for several months, even if it starts off working perfectly. Since I don't understand what's causing this in the first place, I've got no assurance that it won't resurface in the future. I wonder if it would be better if the rod and U-joints were both made out of steel ...

-gt-

[Tinyhead]

Could just go to the trick laser arms. No worries there.

[townsend]

More on this ... I just talked to my father, who owns a $10,000 metal lathe and has a lot of experience with mechanical things. He didn't have a good explanation, but suggested that I NOT reorder the parts, but pop over to his house with a U-joint that he suggested we could copy on the lathe out of brass instead of aluminium. Neither of us have the time to do that over the next few days, but I'll bet using brass will be an improvement as its a little harder. I'll do it sometime this week. If I like the result, I'll get him to re-make all the U-joints on my machine so that I don't have to worry about this in the future.

Anyway, here's a general question for anyone reading this: Have any of you used the printer for say several months, and then discovered that you had a U-joint that was bound up tight after initially being okay?
-gt-

[townsend]

Hey all,

... well, I checked out the advice Tinyhead posted above about the trick-laser arms ... I figure for $85 I can put this all behind me, so I've ordered them. Although it would have been interesting to see what the brass replacements might have done, its just not worth the effort when I have a ready-made solution available for that price. So, I guess that's it.
-gt-

[teoman]

One of my uJoints have seized up completely. I tried heating the aluminum and putting the part i to the freezer but i was not able to remove it.

I shall try to find a small pipe to insert the shaft in to and banging on the pipe to push the ujoint out.

If it fails my printer is offline for 2-3 weeks atleast

[Mac The Knife]

I was surprised that there was no recommendation in the manual to lubricate them before installation. A drop of oil goes a long ways.

[McSlappy]

My V1 had some binding issues, though my V2 seemed to come with the axles already lubed.

The first lubricant I used was not great (Ezy-glide which is designed for zippers and is a 'dry' lubricant) and kept seizing them up.
I switched to INOX which was quite good, although messy, and never had a snag with that.
I most recently switched to Nano-oil which is a nice gun lubricant and it's been great on both machines so far.

[teoman]

I managed to move te Ujoint to the end of the shaft.

would silicone spray work? Or grpahite powder? If not i have to go out and buy something.

[geneb]

I'd recommend that you replace the aluminum u-joints with the new injection molded ones they're shipping. Huge improvement.

g.

[Mac The Knife]

I managed to move te Ujoint to the end of the shaft.

would silicone spray work? Or grpahite powder? If not i have to go out and buy something.

you got any motor oil? drop off the dipstick would work,,,, better if the oil was clean. I'm not to wild about silicone spray in that application.

[teoman]

Yep. Changing motorbike oil tomorrow. Ill steal a ml or two.

[teoman]

I managed to remove the u joint. I used metal polish on the inside of the u-joint and the shaft. Initially with a toothpick. Then with the shaft inside the u-joint. Finally cleaned everything and it is working smoothly again.

[Mac The Knife]

I'd still put a drop of oil on them.