Cracked X-axis idler part B7 during assembly: try to continue?  

RE: Cracked X-axis idler part B7 during assembly: try to continue?

Do you have a temperature controlled soldering iron? If so, you can use that at 240C and some filament to weld a temporary repair. For that rod pocket, the load is cantilevered so top of the pocket IS stressed.

Plastic weld it and you will be good enough to get the printer running and print a replacement part.

When next you are going to insert rods, pre-drill the holes with an 8mm bit.

Yes, you should obtain a metric drill bit set. You're going to do a fair amount of metric hole drilling for screw holes in the future anyways.

RE: Cracked X-axis idler part B7 during assembly: try to continue?

I do not have a termperature controlled soldering iron, so that's out.

I don't understand where those rods are cantilevered; they are supported at both ends, so I would expect the load to be pretty much straight down.

I don't think waiting for a replacement will slow me down; I'll hold off on doing the Z-axis until I have a good X-axis done, but the extruder appears to be very time intensive, so I can work on that while waiting....

*so* close...

RE: Cracked X-axis idler part B7 during assembly: try to continue?

I got my kit today and I also cracked the same part. I have a temperature controlled soldering iron but don't really like the idea of touching a hot iron to filament and and trying to get it to melt into place. Does the welded filament have to be the same material (PETG) or is PLA ok?

The holes are super tight so I wished I had read about drilling them out with a 8mm bit. I am pretty frustrated with myself.

RE: Cracked X-axis idler part B7 during assembly: try to continue?

Same material is best, but most likely you won't even need to add more plastic. This is a temporary weld to hold things together until you can print a replacement part.

Set the iron to 230 C. You can go hotter to 240C, but at 230, you will have very good control. Clean off the tip.

Don't worry too much about making it pretty. Also, the soldering iron won't be like a light saber suddenly slicing the part in half. You will have plenty of control. 

Touch the crack and let the tip melt plastic on both side of crack. Stir molten plastic across the crack and gradually advance along entire length of crack. Make the depth of melt about 1.5 mm. 

You will do fine.

RE: Cracked X-axis idler part B7 during assembly: try to continue?

I tried melting the idler piece near the crack at 240C and melting new filament in there at the same time but it was a big failure. The new plastic didn't fuse to the part and instead I just started making a larger channel in the crack. I also went to half a dozen printing on demand sites and the prices for the part were super high, surprisingly ($50-95 USD). I found a place that was reasonable at $18 but there was a surcharge since the order was under a threshold - which then brought it back up to $50 🙁

I will print a replacement piece when the printer is done. Does the new part need to be PETG?

RE: Cracked X-axis idler part B7 during assembly: try to continue?

Turn down the soldering iron to 220C. It sounds like it is running hotter than indicated. Gradually increase temp if needed to achieve melt. You just need to bridge it well enough to hold together for a day of printing. Another repair method is to bend a piece paper clip into a flat zig zag. Put zig zag across break and melt the wire into the plastic surface. Use tip of iron to move some of the plastic over the wire. Repair will hold long enough to get the job done.

PETG is the recommended material. It is easy to print and has enough long term resistance against stress fracturing. PLA would be OK for a short term part, but I would not recommend it.

RE: Cracked X-axis idler part B7 during assembly: try to continue?

I made the assumption that you have the rods already seated all the way in but the part is cracked. 

If it isn't already fully seated, wiggle the rods out. One end of each will probably still be stuck in an x-end. To remove (and reinsert) rod most easily...

Chuck variable speed drill onto free end of rod. Hold x-end in other hand. Spin rod at low RPM. It is a lot easier and gentler than push/pull or hammering. 

Also, keep your plastic repair away from top rear edge of x-end. That edge where it hits top z-mount bolt heads must remain level with top surface of x-end. Otherwise, z won't level when printer pushes z up against top during auto leveling.

RE: Cracked X-axis idler part B7 during assembly: try to continue?

Posted by: guy.k2

I made the assumption that you have the rods already seated all the way in but the part is cracked. 

Hi, yes, this is accurate. The x-idler cracked while I was inserting the two rods on. Both ends are so tight so it took some force/pressure to get them to fit. I have a friend printing a replacement parts in PETG. Thanks for your tip on removing the rods. I expect I will probably end up breaking both sides when trying to remove the rods but now I have your drill rod spinning trick to use. Do you still suggest using a 8mm bit to clear up the holes, in the new part when installing the replacement pieces? 

Hopefully this doesn't delay my build too much 🙁

RE: Cracked X-axis idler part B7 during assembly: try to continue?

Yes, the 8mm drill makes a huge difference in how easily the rods slip into place. You will also be glad of having done it when you need to service the x-axis in future.

Just spin the drill at low RPM. You only want to enlarge the rod pocket diameters, but not increase depth.

I used to recommend just doing it with one of the rods instead of a 8 mm bit, but after comparing both techniques, I now recommend using an actual 8 mm bit. Using the rod to do the enlarging could give variable results depending on spin time and speed.

That said, using the drill to move a rod in or out of the pocket is still a great technique. Just don't spin in one place a long time.

RE: Cracked X-axis idler part B7 during assembly: try to continue?

I heard back from prusa.

In my case, the crack is pretty small, and Prusa customer support was pretty confident it would hold up long enough to print a replacement (if it ever failed at all!), and that due to the location of the idler, replacing it later after assembly would not be a big hairy deal. They also recommended doing an acetone weld on the crack if I was worried about it.

RE: Cracked X-axis idler part B7 during assembly: try to continue?

As for a temporary repair - personally - I'd use a thin cyanoacrylic glue, one that can penetrate into the crack.  A surface weld won't penetrate deep enough and risks separating the crack even further.  The next best choice is like real welding, removing material so a V is present, then using a filament pen to refill the void repair and having depth to add strength.  

RE: Cracked X-axis idler part B7 during assembly: try to continue?

Hi, thanks to both of you for the fits. I will spin the rod to remove them from the PETG ends and will use a 8mm bit in the new parts for easier install. Good idea about the crazy glue. I will keep that in mind in the future. Unfortunately I don't have a filament pen, I've never had a use for one until now so it might be worth picking up a cheap one. Any recommendations?

RE: Cracked X-axis idler part B7 during assembly: try to continue?

Don't use it much, but has come in handy a few times. Works fairly well for what I've done with it (touch up and support repair / strengthening on complex parts).

https://www.amazon.com/gp/product/B01BLQ24IW

RE: Cracked X-axis idler part B7 during assembly: try to continue?

I use one of those pens when I need to attach items to an existing plastic housing. If you first stipple the native plastic with the tip of a soldering iron, extruded plastic will stick quite well. Things like creating loops for adding twist ties to the back of LCD screen are super simple with a 3d pen. It's also WAY faster than our 3d printer.

RE: Cracked X-axis idler part B7 during assembly: try to continue?

Thank you both!