x axis carriage 9mm bearing not free

Hi All

Just completed a further building session and appear to have found an issue.

On the x axis carriage there is a 9mm bearing used instead of the usual 10mm. An m3 washer is used between bearing and printed part to enable the bearing to turn freely as per many of the 10mm bearings. Unfortunately in this case the m3 washer fouls the outer bearing shell when the socket head screw is tightened. This is the same slotted fixing that has recently been mentioned in other posts. I am curious why it was decided to use a 9mm bearing in this position. It looks as if the standard 10mm would have been fine if not an improvement. This would cut down on the number of diffrent parts used.

Rory

Edited 2 time(s). Last edit at 12/22/2013 07:01PM by Rory166.

Hmm.. I haven't had this problem in test builds, though I'll check tomorrow. M3 washers do come in various diameters. Have we supplied you with extra wide ones? I'll have a look to see if a 623 fits - I would have thought it does, but there may be a reason we used a 9mm that I can't think of at the moment.

Ian
RepRapPro tech support

Ian

Im impressed that you seem to be working at his time. Bit confused what time zone is shown on the forum. Now realize I should have set a custom timezone to GMT. Not quite sure why this is not the default setting?

It may not be that obvious when the bearing is not free because the metal glides along the acylic quite smoothly. Longterm it would wear of course. I imagine a bit of paper held between bearing and acrylic would help show if bearing is free or not. I would have thought there must have been some reason why a bearing different from all the others was chosen. I will try to find a smaller 3mm washer or file down one.

Rory

Edited 1 time(s). Last edit at 12/22/2013 04:11AM by Rory166.

I agree, a 10mm bearing would have been better - I wouldn't have had to elongate the slot and the nut trap as much.

Edited 1 time(s). Last edit at 12/22/2013 05:08AM by dc42.

Hmm.. I've checked mine, and the washer does seem to interfere with the MR93ZZ bearing; but I have to over-tighten the screw to do it. Turning the (slightly dished) M3 washer over makes it better, and moves fine at 'normal' tightness (no, I don't have torque settings...). I swapped in a 623 bearing, which seems to rotate fine when tightened hard, but doesn't give you much adjustment for the angle of the hot end.

The inner race of the MR93ZZ is very thin, which may account for the rubbing, especially if the surface that the washer sits on isn't particularly smooth. I'll feedback these observations to 'engineering'!

Ian
RepRapPro tech support

I've done my bearing up tight - I wanted to make sure it wouldn't slip, as I had it right at the end of the slot - and the bearing rotates freely. I did make sure to put the washer the right way round (the side that bulges in the middle towards the bearing), and I also added a shakeproof washer between the plain washer and the printed part, to make sure it didn't slip against the plastic. But I've ordered some 623ZZ bearings via eBay, because a 10mm bearing here would work better in my build.

As I write this, my Ormerond is doing its first print.

Edited 1 time(s). Last edit at 12/22/2013 11:18AM by dc42.

FWIW I replaced the 9mm X-runner bearing by a 10mm (623ZZ) bearing today, and that finally resolved the problem I had with a sagging print head.

Hi All

I am not too clear on this talk of dished washers. The washers I was supplied with are bog standard and indistinguishable from some I purchased from screwfix.
having been tightened against plastic might well cause some dishing.

What is indisputable is that the inside diameter of the outer race of the 9mm bearing is slightly smaller than the o.d. of the washers. Thus the washer can jam the bearing when tightened agaist plastic which has some resilience and will therefore push up the washer outside of the inner race contact.

The simple solution is to turn down the diameter of the washer, ideally to little more than the inner race plus whatever play there is on the screw. I put 5 washers together on a 3mm screw held by a nut and turned them down using an electic drill and file. I only took them down to 6.5mm which worked fine but I would probably go further another time as above.

Rory

Regarding "dished washers": because of the way washers are made (pressed from sheet metal), they are typically not quite flat. So if you lay one against a flat surface, either the inside or the outside will be in contact with the surface, depending on which way up you put it. The ones I received in the Ormerod kit were indeed not flat, but slightly dished in this way.

Had the same proplem, washer interfering bearing, sagging print head, fixed with a 623zz

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ormerod168
Had the same proplem, washer interfering bearing, sagging print head, fixed with a 623zz

My print head also has a terrible sag - so much so that the fan duct clips the edges of the printed part!

Sounds like I could do with fitiing a 623zz bearing as well.

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Radian

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ormerod168
Had the same proplem, washer interfering bearing, sagging print head, fixed with a 623zz

My print head also has a terrible sag - so much so that the fan duct clips the edges of the printed part!

Sounds like I could do with fitiing a 623zz bearing as well.

I am sure you have adjusted the bearing to it's maximum and checked the slot is fully cleaned out.

I had the 'x sagging problem' , even with the bearing pushed right to the end of the slot the head was a fraction too low and the fan touched before the nozzle.

Not having a 10 mm bearing I taped a used hack saw blade to the side of the X beam where the bearing runs.
This allows perfect adjustment and means the bearing is running along the (smooth) side of the hacksaw blade rather than the perspex.

The sensor is also very close to the bed and I needed to move it up to the limit of the play in the screws
and sand a small bit of the bottom of the sensor support part of the X carrage.

Clearances here are very small, I don't see any reason the sensor + fan casing could not be 1mm higher (or the extruder nozzle 1mm longer!) which would make for a more comfortable build and better clearances.


CHris

Chris

You are ahead of me build wise but looking at the data sheet for the sensor 1.5mm is the minimum spacing I would recommend for operation ie when the head touches.

Rory

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Rory166
I am sure you have adjusted the bearing to it's maximum and checked the slot is fully cleaned out.

Yes Rory - it's as far in as it goes without actually re-boring the hole and nut retaining slot. I did manage to straighten it up a little bit by using a longer bolt and a 3mm nylon spacer to raise the bearing contact point. The fan duct *just* clears the printed piece enough to get me started now but it really looks as though a 10mm bearing would be better.