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Fan assembly fouls on foldback clips

Posted by dc42 
Fan assembly fouls on foldback clips
December 21, 2013 03:26PM
I'm finding that the bottom of the fan assembly is fouling on the foldback clips that hold the glass plate on the heated bed. So I dare not try printing anything, or testing the automatic bed compensation, because any attempt to home the head or move it between the compensation points when it is lowered will result in a crash.

It looks to me that the problem stems from two causes:

1. The X-idler bearing is too small in diameter, so the whole extruder head assembly droops towards the extrusion head. There is enough play to increase the X-idler bearing diameter by well over 2mm. Is it possible to get a larger bearing? Or perhaps I should attach a shim along the X-plate where the bearing runs?

2. The cap head screws used to hold the extruder head to the nozzle mount appear to have been forced a little off-centre by the weight of the fan/heatsink assembly. I'm wondering whether countersink screws (which the nozzle mount was evidently designed for) would be better - or was the change to cap head screws made because they are better in this respect than countersunk?

Any suggestions gratefully received. btw this is using a replacement x-rib and x-plate to the new design.
Re: Fan assembly fouls on foldback clips
December 21, 2013 04:16PM
Further to my earlier message:

- When I said "X idler bearing" in my previous post, I should have said "X runner bearing".

- Looking at it closely, I can see that only the very top of the runner bearing makes contact with the X-plate, confirming my suspicion that the main problem is that the runner bearing is mounted too far away from the X-plate.

- If I insert a 1mm thick steel rule between the runner bearing and the X-plate, then this takes up about 2/3 of the play, and the bearing contacts the ruler all the way along its length.

- I tried loosening the screw holding the runner bearing, squeezing the bearing closer to the X-plate and tightening it again, but this made no difference.

So I think I need to take up 1mm of play, using one of the following solutions (unless anyone has another suggestion):

1. Get someone to print me a new Z-runner with the hole for the bearing screw 1mm in from where it is now. [Maybe I should ask RepRapPro to send me a new X-runner when they re-open, in case I just have a bad one.]

2. Replace the 9mm MR93ZZ bearing by a 13mm bearing. I found just one UK supplier that has a small number of MR113ZZ bearings in stock - would MR113ZZ have the same hole size (3mm) and thickness as MR93ZZ?

3. Find a way of modifying both ends of the X-plate support so that the X-plate is shifted 1mm with respect to the X-rod from where it is now

4. Find something 1mm thick and about 200mm long that I can use as a shim attached to the X-plate.

Has anyone else had this problem?

Edited 4 time(s). Last edit at 12/21/2013 04:48PM by dc42.
Re: Fan assembly fouls on foldback clips
December 21, 2013 04:51PM
@dc42, probably not helpful, but I do not have this problem. The bearing runs nicely along arm and the printed parts all look square and correct.
I'm sure you have done this, but check the assembly again and that the bearing used was the correct type.
In the instructions it states

Fit the runner bearing using the M3x12mm cap head screw. The washer should be positioned between the bearing and the x-carriage. Check that the screw can move in the slot; this allow you to adjust the angle of the hot end.
I don't recall adjusting mine so guess I was lucky, but perhaps you should check the slot clearance or enlarge?

Just for reference the printed part that holds the bearing is in-line or flush with the black acrlic rear surface on mine.

Also check the shaft printed mount at the end where the black acrylic are clamped, here the relationship between the bearing running surface and the linear head bearing are defined, so any error here will be presented along the travel.

Regarding the clips, yes, I removed the one by the home position for this reason. Also doing plate levelling I had to remove another clip. So currently doing my normal testing with one clip removed, but it does not affect the performance from my tests.

In another post it was suggested that clips are not used and the kapton tape is used for clamping, but I haven't got that far....
Re: Fan assembly fouls on foldback clips
December 21, 2013 04:58PM
Thanks, Treth! Either I missed the bit about the slot, or it wasn't in the documentation a week ago when I assembled the runner. I'll take it apart and elongate the slot if necessary.
Re: Fan assembly fouls on foldback clips
December 21, 2013 05:04PM
@dc42, good luck. the documentation is changing regularly, Ian is doing a great job. I have missed some important steps/info, so regularly revisit now.
Re: Fan assembly fouls on foldback clips
December 21, 2013 06:56PM
I've now managed to stop the print head sagging. The main problem was that the nut trap in the X runner wasn't flat, so when the bearing screw was tightened, the screw tended to move towards the outside of the runner. In the end I had to use a 3mm drill to elongate the slot, and a 2.5mm drill and knife to rework the nut trap. With the screw up against the end of the newly-elongated slot, and after fettling the slot for the Bowden tube in the nozzle mount, I think the print head is just about vertical.

However, there still isn't enough clearance between the fan housing and the foldback clips. Worse than that, because the print nozzle can reach all four corners of the print bed, there will always be a risk of the print head crashing against the clips. In particular, the clip near the origin will get in the way when the head is homed.

A solution would be to lengthen the aluminium heat spreader and the glass plate by 30mm, so that there is a 15mm margin outside the printable area at each end in the Y direction. The foldback clips could then be used to clip the glass plate to the heat spreader using this margin. Ideally, the heated PCB would also be lengthened to avoid the extra aluminium reducing the temperature at the edge of the printable area; but with any luck, the temperature reduction would be small enough not to need this.

Ian, what do you think? Am I missing something, or is there another solution?

Edited 1 time(s). Last edit at 12/21/2013 06:58PM by dc42.
Re: Fan assembly fouls on foldback clips
December 21, 2013 08:14PM
The heated bed PCB is as big as it can be, without incurring ridiculous cost.

I'm not sure why we haven't had a problem with this; perhaps something we do when we put the hot ends together causes us to have a tiny bit more clearance. I need to update the hot end instructions anyway, to match the rest of the documentation - Adrian wrote the hot end instructions, and I and Jean Marc tend to build hot ends in a slightly different order. But I do know that Adrian has been playing around with different, low profile, ways to clamp/clip the glass to the bed.

I'll take a look in the morning, as I'm back in work... last day at work this year! Don't worry, I'll be keeping an eye on you lot... and answering emails, between Xmas and New Year.

RepRapPro tech support
Re: Fan assembly fouls on foldback clips
December 21, 2013 08:35PM
Ah, just remembered. On a couple of our Ormerods, we just tape the glass to the bed on the short side (which butts up to the edge of the bed), or over the corners, with Kapton tape. You could leave the clips on the Y idler side, if you don't trust the Kapton tape Generally on these ones, we've put 5 x longer cap screws through the corners and centre of the PCB/Aluminium/MDF sandwich, so we can put a nut on the other side to hold it together. I must create an 'improvements' page...

RepRapPro tech support
Re: Fan assembly fouls on foldback clips
December 22, 2013 02:44AM
Ian, thanks for your feedback. I've ordered some 250x250x1.5mm alu sheet from eBay, and I'll visit my local glazier tomorrow. In the meantime I'll commission my printer by taping the print surface down as you suggest.

Edited 1 time(s). Last edit at 12/22/2013 02:44AM by dc42.
Re: Fan assembly fouls on foldback clips
December 22, 2013 06:08AM
I've abandoned the clips altogether and tape the glass down to the mdf- this has the advantage that there's no snagging and no slippage, with the clips alone, the heater, heat spreader and glass hold together firmly, but can slip relative to the mdf /carriage . Using the tape I get much better vertical surfaces.

For the nozzle height, I screw I n the brass end of the guide tube as far as it will go before screwing in the nozzle, treth, I think, added a washer for the same effect. It's also worth making sure the fan housing is parallel to the bed so one corner doesn't hang lower

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