Switching from PLA to ABS

Hi all,

My extruder was made with ABS, it has been working perfectly for the last few months. I always print in PLA, and I tried printing a wade accessible extuder with it. Sadly... probably my hotend was too hot, the heat from the PEEK deformed the joint where it touched the extruder... so now.. I am thinking of switching to ABS for printing extruder.

I have a few questions...

My heated bed can only go up to 70C with a piece of glass on top, will this be hot enough?
Do I need to cover my glass with Kepton tape? When removing the prints, do the parts stick too well that I might break the glass?
I have cooling fan for printing PLA, mainly because I am printing at high speed.. Do I need to use fan for ABS too?

Thanks everyone

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My heated bed can only go up to 70C with a piece of glass on top, will this be hot enough?

Not in my experience. I run my heated bed at 100C and get pretty good adhesion.

What design of bed are you using? 70C seems pretty low.

How do you have your bed mounted? Do you have the bed mounted flat against another surface? I have tried a couple of things that allowed me to get to higher temperatures. Initially I used a sheet of cardboard as an insulator between the wooden structure and the HPB. I now use just fresh air as I find that if I go over 100C then I get warping of my models anyhow.

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Do I need to cover my glass with Kepton tape? When removing the prints, do the parts stick too well that I might break the glass?

The answer to this one is probably yes. While some people have been successful at getting ABS to stick to Glass directly, It's easier if you use tape.

I find that I get best results when I use Tape t 100C with a light coating of ABS juice on the tape. ABS juice is made from acetone with some ABS plastic diluted into it. It preps the Kapton tape very nicely.

Will you break the glass? I use 3mm Glass and sometimes larger prints stick pretty well. I remove the HPB, stick it in the fridge for 10 minutes and then gently chip the parts off with a small hammer. I have yet to damage the glass.

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I have cooling fan for printing PLA, mainly because I am printing at high speed.. Do I need to use fan for ABS too?

I see plenty of people who say that you dont use a cooling fan with ABS, apparently they find that it causes layer separation. But I find that I get a bit of slump on my parts when I dont use fan on my ABS parts. I suspect the answer will differ between different brands of ABS, so "suck it and see" is probably the best answer to this one.

I second Justblair suggestion of ABS juice. I have had great results using just ABS juice and glass (no tape). If you are going to go with that low of temperature I would HIGH suggest really coating the glass with the juice. I have found that taking a paper towel and dabbing a few layers on causes the surface to become rough. This really helps keep the ABS stuck to the glass (NOTE you may have to re zero your Z axis due to build up)

Also add some skirts to your print. I use Slic3r and found that by adding 4-6 skirt passes 0mm from the part helps keep the corners from curling.

Get a heat lamp or some kind of high watt bulb and shine that on the print as it is running. It is not much but it will help reduce the temperature difference between the warm/cold ABS. I have seen some people even cover their printer with a blanket just to keep as much heat in as possible.

As for a fan and ABS I would suggest using one. I currently have two on my Prusa. One blows right on the PEEK to keep that cool, and one is ducted right to the tip of the hot end. I have found having small air movement helps keep corners crisp, and allows me to print smaller detailed parts faster.

thanks guys for your useful info.

I made my own heated bed using nichrome wires.. 50ohms/m and I have 10-11 wires running in parallel. With the underside, I am using tin foil in oven bag and a piece of thin wood at the bottom. As far as temp difference, the top is about 70C and bottom about 50C... i am thinking of making another parallel circuit of nichrome wires which is connected in series to the existing one.. and hope it can double the output..

This is my first time hearing ABS juice! how interesting! I have 2 pieces of glass, so maybe I do one for ABS and one for PLA.

Its interesting using heat lamp to heat the print.. i thought the print has to be cold and hotend has to be hot.. as far as I know.. from my experience in printing PLA.. I get much better result to have fan to cool the printed plastic as much as possible while keeping the hotend at a stable temp, didnt know that ABS is almost the opposite!

Do you think ABS is trickier to print compared to PLA?

With my current setup, I have a Prusa printing PLA, Parcan hotend insulated with kapton tape, heated bed, and 2x 70mm fan mounted on the frame. I am printing at 60mm/s for edges and been getting perfect corners and straight lines.. I just dont know how long I need to spend again on learning how to print ABS to the quality I can achieve now...

Another question, what happens when I want to change PLA filament to ABS and vice versa. Do I need to ooze out all existing PLA or just pull out the filament? What happens when PLA and ABS got mixed together inside the hotend??

cheers

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With the underside, I am using tin foil in oven bag and a piece of thin wood at the bottom.

Do you have an air gap between the base and your heated print bed?

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Do you think ABS is trickier to print compared to PLA?

A bit, though once you get a working setup, not a huge difference. I get better looking prints from PLA, but more durable from ABS

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Another question, what happens when I want to change PLA filament to ABS and vice versa. Do I need to ooze out all existing PLA or just pull out the filament? What happens when PLA and ABS got mixed together inside the hotend??

To change from one to another, you heat the nozzle to ABS temps (240C in my case) and run through some filament to flush out the nozzle. When the plastic runs out smooth you have done enough.

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i am thinking of making another parallel circuit of nichrome wires which is connected in series to the existing one.. and hope it can double the output.. confused smiley

If you connect another circuit in parallel to the first, the R will go up in value and the current will go down so the power output will be less. If iyour bed is pwered by 12V you will need a final R of about 1 ohm

Here is the link for the ABS juice thread
[forums.reprap.org]

For me I actually use the same sheet of glass (one side ABS one side PLA). just make sure the ABS side does not have any bumps.

ABS and PLA print differently. Think of it like this. ABS extrudes like one of them playdough spaghetti presses, uniform and holds its shape. PLA prints like pressing on the end of a toothpaste tube. It comes out as a circle but will not hold its shape. So for PLA it is important that it cools ASAP in order to keep its shape

The trick with ABS is that it goes through a large dimensional change. This is what causes ABS to warp so much and why a heated bed is necessarily for large prints. As the print goes on the lower layers cool and begin to shrink causing the print to pull away from the surface. The more you can keep your whole print relatively the same temp the less chance you may have warping.

The reason I want to print ABS is only because of my extruder heating problem.. to be honest, I don't want to spend so much time again by trial and error since I can achieve decent PLA printing quality now..

guys, what other convincing reasons that I should be printing ABS, apart from being able to withstand heat??

thanks.