What is happening here ?

This is a replica of a pushbutton that protrudes through the front of an instrument cluster. It so you can change the clock or check mileage among other things. The original broken in half so I was reproducing one with my Rep2.

its only about 2" long and about 3/16" in dia. As you can see the printer starts off fine but the last 1/2"'or so and it just goes wonky. I'm confused as to why it does most of it just fine but the near the top something changes and ruins the print.

i hope the pic is big enough so you can see what's happening. Settings on printer are just default but with the temp set at 220. I think that pla is from colorfabb. Funny thing is that I printed one of these a couple of weeks ago with no problem but now something's wrong but I haven't made any changes.

the printer is having problems printing cylinder shapes for some reason. I use a lint filter that's moistened with canola oil so the pla is cleaned and lubed before going into the extruder. Extruder was cleaned about 2 weeks ago just for preventive maintenance but I've printed things since then, just not cylinders though.

Attachment 3691

Are you printing just one of these at a time? Assuming that you are as well as that (due to your description) the long piece is being printed upright then the issue is likely that the print is just not being allowed to cool enough before the next layer is layed down. I have seen these problems before on some of my own prints. The part isn’t getting proper cooling throughout the print, but the problem is exacerbated at the top.

The easiest recommendation is to print 2 or maybe even 3 at a time, even if you only need 1. By printing a couple of them, you will give each layer sufficient time to cool a bit before laying down another layer of molten plastic.

Give that a try and see if it helps.

It's not a problem with the printer, it's a design problem. Having small width and big height cause trouble. At some point your prints will break in half should you print something taller with the same diameter.

3/16th diameter is just way too small for an object of 2" length.

I am more surprised that you could pull something last week. Because this is the kind of parts that I tend to avoid printing, because I know it's a lost cause.

However, you might do some magic. Drop the temperature down to 200 and start blowing a fan directly on the printed parts. You have to force the PLA to solidify before it has time to warp itself and fall under the pressure from the nozzle. You have then to play with the printing speed.

Wpilgrim is most likely correct. Since Rep 2s already have an awesome fan that blows like crazy right onto the build, it's just a matter of making some prime pillars in the same build. We make smaller, taller objects all the time at the standard Rep 2 Temp of 230°C. You just need to throw a couple prime pillers on there.

For those not familiar, a prime pillar is a sacrificial object, normally a cylinder a couple cm in diameter that is the same height as the object to be built. KISSlicer can make them automatically, but for other slicing software (like Makerware for example) just make one with your favorite CAD program and drop it into the build. Some builds require multiple prime pillars.

What the prime pillar does is make the nozzle go somewhere else on each layer, allowing time for the last layer of the build itself to cool and harden before the nozzle returns for the next layer.

There is another possibility too though. The way the Rep 2 wiring is designed, the X axis wires get flexed a LOT from Y movements, and they do wear out and break eventually. You'll start getting intermittent X skips when this starts to happen. Makerbot redesigned that section of harness partway through the production of Rep 2s so that just that section of harness can be replaced, rather than the entire X,Y and Z harness, which is a true PITA procedure.

Well, I printed 3 at the same time, as suggested, and they came out fine !

now that you guys mentioned it, it does seem like a cooling problem. Maybe I need to check the operation of my cooling fan, maybe it was only working intermittently ??

thanks for taking the time to respond