Changing between PLA and ABS and back again

Is there a best practice when you're changing materials on a printer (other than using a completely separate extruder and hotend for each!)?

How to get rid of all previous material (and what temperature to do this at)?

When to introduce new material?

Do you need to check bed height etc again as you're working at different heater and bed temps?

etc etc

i think its generally a bad idea to change between PLA and ABS

i found that ABS gets stuck inside the J-head Nozzel and causes jamming while printing PLA again

what i had to do was run my hotend at around 250C for 10 mins then just push a load of PLA to try get rid of the ABS

iv sticking with PLA for now as ABS was lifting a lot.

but iv also switched to richraps quick change carriage and are going to have an ABS extuder to try and play in the future

I've done some thinking about that problem and I think I found a solution.

I constructed a full metal hotend where you change the barrel together with the nozzle. Virtually they are one part, called the 'pipe'. It takes you some 10 minutes to change the pipe.

Basically you have one pipe for PLA and another for ABS. As everything is well documented, you can build it yourself.
A pipe will cost you less than 1€. I guess, a second extruder will cost a little bit more.

I am still testing it, but up to now I am very happy with it.

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Detlef

Excalibur Hotend

reprapclean32.png

reprapzone.blogspot.de

Nice design Detlef, it's given me a lot to think about. I've come to the conclusion that the faff of trying to clean a hot end out between plastics is too great and probably won't help extend the life of the hotend either.

Going back to the extruder itself I find that my wade's works much better with PLA with a tapped hobbed bolt (rather than a dremelled hobbed bolt) but the tapped bolt seems to fill with ABS almost immediately and the dremelled bolt doesn't last much longer before shredding the filament - anyone got any suggestions of best bolts to use for each material (or anything else that helps)?