Newbie Build Query: sticky y-carriage

Hi,
Am having some fun building my first 3D Printer....

But have a question: have just assebled the y-carriage and mounted it. All ok. But it feels a bity sticky to me, not very smooth when run back and forth. Is there a lubrication stage to come later, or I have maybe got something not quite lined up right that is making the bearings unhappy?

Thanks for any advice.

Ralph

With the belt disconnected the bed should run back and forth very smoothly and easily with no sticking, though not so smooth that the carriage will coast far on its own (though it should move smoothly on its own if tilted 20 degrees or so). The rods do not need to be lubricated initially, but should be clean and shiny, as should the linear bearings. If it is sticky you should try to identify the reason. You can lift the bed off of the front bearing and check that that bearing runs smoothly. If the rear bearings are sticking, you may have to partially disassemble to find whether it is one or both bearings that are sticking. There have been a few cases of "bad" linear bearings, and it is also possible that a bit of debris has fallen inside a bearing and needs to be cleaned out. Obviously check that no part of the bed is rubbing against anything.

If it only feels sticky when the belt is connected, then it is likely that the idler pulley bearing (at the end of the Y frame opposite the motor) is not assembled correctly, you have forgotten to twist the belt so that the smooth side is running over the bearing, the belt is touching the side of the idler pulley mount or (less likely) that the belt is too tight. The belt will obviously make the movement a lot stiffer because you are turning the motor, but it should feel smooth.

Only the Z lead screw absolutely needs to be lubricated before the first few prints, though a thin coat on the Z and E gears and all ground rods with a light oil such as "3-in-1" could also be done, and repeated every month or so. Careful not to get oil on the glass or filament path.

Dave

Hi Dave,
Ok, thanks for the feedback. I'll do a strip down and check everything is clean. I guess a bit of debris is the most likely culprit (haven't fitted the belt yet).

I used a bit of wood to tap the rods fully home and have a suspicion a few bits might have come off it - lesson learnt; make sure your bit of wood is properly clean!

Ralph

Ok. Have done a bit of a strip down and a careful clean.

With the screws on the y-bearing clamps finger tight, it is not too bad. Still needs maybe a 45deg incline to move. But with the screws tight it gets pretty stiff - and very lumpy, like the rails are ribbed. You can hold it at 90deg and it still wont move.

I assume the clamps are squeezing the bearings too much - did I miss a note somewhere to smooth the insides?

Thanks,
Ralph

As I see it; it is impossible to squeeze the bearing. My guess is that the bearing's get out of line when tightening the screws. Have you tried without the third bearing popped into the plywood?

If you tighten one clamp and check that it still travels freely you can add washers between the other clamp and the plywood to adjust the alignment. A bit of trial and error and I think you will get it to work.

/Tomas

Hi Tomas,
Thanks also for the reply.

I have spent some time 'fiddling'. It's better, but my gut feeling is something is not right. Trouble is, of course, I don't know what it should be like.

All the linear bearings, moved individually, show a tendency to stick when pushed gently along the rail. They run a few centimetres, then stop and need an extra 'shove' to get going again. This repeats along the rail. Is this normal? I was expecting something very smooth.

Thanks,
Ralph

I've been building mine over the previous weekend, and my experience is that those bearings should be silky smooth when moved individually, and once the table is added. Though once you add the belt connection there is some additional resistance from turning the stepper motor, but it never really 'sticks'

I'm inclined to think that maybe something is wrong. But I'll be the first to admit that I don't have a ton of experience with the Ormerod 2 yet.

Maybe you got some bad bearings? I assume when you say the stickiness repeats, that this repetition is at regular intervals? If one side of the balls in the bearings had something wrong with it, it would repeat every time that part of the ball came back into contact with the bar.

Maybe you could try contacting RepRapPro support, and see what they say; if the bearings are bad they should replace them under warranty.

Are you sure it sticks and its not just the fact that stepper motors run notchy
They dont rotate smoothly like a normal motor but go around in a series of small clicks
. You may be mistaking this for a sticking bearing especially when you said it sticks in a regular repeating way

Don

Each bearing should individually run smoothly along the ground rod, though will have a little resistance as is normal with any greased bearing and will not coast appreciably. If you are feeling changes to the resistance at any point as you move a bearing on its own then either the bearing has a problem or the ground rod is not smooth. Maybe compare with how the Z bearing feels when run along the Z rod, or the X bearing along the X rod - they are all the same or very similar. The cause is usually debris or dirt in the bearing or on the rod, and though it is possible that you have some bad bearings or rods it is very unlikely that all your bearings or rods are bad so you should be able to compare and see if any combination feels significantly different. The angle at which the assembled bed will start to move on its own will depend on its mass, and the 20 degrees I mentioned was going from memory of an aluminium bed complete with glass plate with the Y belt completely unattached. (It was an observation I made while fitting the Y clamp when upgrading my bed). The MDF bed without glass plate is no doubt lighter and so will need a greater angle before it moves on its own.

It the carriage becomes stiffer after you tighten the two rear bearing housings, it means that the housings are not in alignment. Unless the bed is badly warped (curved) you can probably correct it by fettling (elongating) the mounting holes of one of the clamps to give some leeway and tightening the bearing clamps with the rod in place to hold the alignment. There should be enough movement in the front support on the bearing to take up any very slight XY misalignment of the front rod (YZ misalignment will not result in stiffness but will cause problems later when you come to bed levelling). It is not possible that the plastic clamps could deform the metal bearings, so that issue will be to do with alignment.

Dave

Thanks for that.

All the bearings, including the z axis were showing the same problem - so not a faulty bearing then.

Took the top bracket off the z axis and worked on these two first. Used switch cleaner (is that ok here?) to give each one a good flush out. Then added some light oil (used on model trains, so very light) to lubricate. Much better after that. I can now drop them on the bar and they run all the way to the bottom with no further assistance. Wasn't possible before.

So did the same with the other three bearings. Certainly a lot better.

I also fettled out the screw holes in the clamps - thanks Dave.

When the screws are loose, it feels fine now. Still not happy though when they are tightened, so will need to fiddle more with that.....

Ralph

Quote
rjmusto
All the bearings, including the z axis were showing the same problem - so not a faulty bearing then.

Took the top bracket off the z axis and worked on these two first. Used switch cleaner (is that ok here?) to give each one a good flush out. Then added some light oil (used on model trains, so very light) to lubricate. Much better after that. I can now drop them on the bar and they run all the way to the bottom with no further assistance. Wasn't possible before.

Hm, these linear bearings are care free pre lubricated. The only issue could be dirt/debrit. If all behave the same it could also be "design intent".
So using switch cleaner to remove the lubrication first and then use lubricant with lower viscosity to make them run easier is working, but on the long run could (will) cause issues with the sealings in the bearings.