Plastic for filling FDM objects

I can make HDPE objects that stay flat until they are removed from the base board. I can also make them with 50% criss cross fills and I suspect a lot more sparse that that. Can anybody suggest a plastic I could inject with a syringe afterwards that is thin before it sets and rock hard when it cures.

I want to try filling an object before removing it to see if it will cure the warping.

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[www.hydraraptor.blogspot.com]

PU resin fast cast see [www.tomps.com] is like milk when mixed and goes de-mould hard in about 15 minutes and full hardness in about 24 hours it only has a 3 minute pot life so syringe is out of the question unless you're really quick! but a direct pour would likely work due to its viscosity.

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Ian
[www.bitsfrombytes.com]

I've used Alumilite [www.alumilite.com] before. It's a two-part urethane that's low-viscosity and fast-setting. Might be interesting to create a two-chamber toolhead that mixes them as it dispenses. Something like this: [underbid.com]

I've used this [www.freemansupply.com] before for a school project. The project didn't require much structural integrity, but this stuff seems to harden pretty well, and it has a 10 minutes work time, so that should allow for you to use it in a syringe.

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Jay

holy cow thats a great idea. i've been thinking about it before just to make it easier/faster to print an object (print the outline + sparse infill, then fill with resin) if it fixes the curling problem as well, that would really rock.

the stuff i use to do casting is smoothcast 300. 5 minute pot life. ~10 minute hardening time. an added bonus is that it releases a bit of heat as it cures, so it might heat up the HDPE a bit and release some of the stress.

i'm very interested in how this pans out for you. please post about it!

another cool thing is that we could *definitely* make a RepRap head that automatically injects the resin. i'm thinking something like this:

1. print object, except last layer
2. fill with casting resin
3. wait 15 minutes
4. print last layer to cap it off.

good luck!

... one problem with complete infilling after fabbing could be bubbles between the criss-crossed filament-meshes inside the object.

Maybe its better to output the contour-outlines of some layers (3 to 6 layers, so you didn't need criss-crossing filaments and it's faster too), then fill the inner volume with the filler-medium, wait the hardening time, and so on?

With a 2K-head this should be the best method to avoid air-bubbles and warping ...

Viktor

Thanks guys for the suggestions, looks like some form of PU is the first thing to try.

My reasoning for the criss cross is so that you can put a top surface of HDPE on. I don't know if you can lay HDPE on top of PU. Even if you can you would have to fill it to just the right level.

I can see surface tension being a problem getting anything to flow through a mesh though. That is why I thought injecting it with a syringe might help. I probably don't need to fill the object completely if the plastic is very hard. 5-10mm in the bottom might be enough.

It will be a while before I have my machine working again but I will definitely post my findings.

The other thing I aim to try is to heat the table to about 100C. I estimate that will take about 50W but I might be completely wrong. I will use a zigzag track on a PCB to make heater the size of the table and put it under the PP chopping board with a sheet of PTFE below it. I got the idea from a youtube video showing water boiled with a PCB but for some reason the author has removed it.

[www.raphnet.net]

Edited 1 time(s). Last edit at 01/02/2008 07:13PM by nophead.

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[www.hydraraptor.blogspot.com]

this stuff is very viscous, especially if you go with the smoothcast stuff. seriously viscous. think consistency of milk. it is used for fine-detail casting, and the details it can replicate are very good... the parts coming out of the RRRF molds you could see the individual lines from the printed part that was the master.

i doubt it'll have any problem getting around the infill =)

I have some Smoothcast 300 on the way, mainly because the others were on holiday or out of stock and the 5 min pot life seems good.

I don't think you mean very viscous (thick and sticky) but the opposite?

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[www.hydraraptor.blogspot.com]

ha, crap... you're right. its very fluid.

Sorry, I tried to post something in this thread before but somehow my firefox shunted and all my post was lost!

I see now that most of what I wanted to say has peen already said, so yes. PU is great if you manage to dispense it fast enough. Polyester hardens slower and epoxy is also an alternative. Maybe using some sort of helicoidal mixer head would solve the problem of syringe clogging. you can buy cheap helicoidal HDPE mixer nozzles in hardware stores. This will keep your syringes operational and only require nozzle replacement when clogged.

Also, you may consider pouring the stuff Zach talks about when the HDPE is still kinda hot. i don't know if this is makable at all, but considering that PE doesn't glue to anything once hardened, it's worth trying... just a hunch of mine...

The Smoothcast 300 says it has a limited shelf life:

"Shelf life of product is drastically reduced after opening. Remaining product should be used as soon as possible. Immediately replacing the lids on both containers after dispensing product will help prolong the shelf life of the unused product. XTEND-IT Dry Gas Blanket (available from Smooth-On) will significantly prolong the shelf life (up to 4 times longer) of unused liquid urethane products."

I can't find any figures. Are we talking days, weeks, months? As I have a pint and only want to use about 10ml in my first experiment I don't want to waste it all as it is expensive.

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[www.hydraraptor.blogspot.com]

i'm not sure. i did a google search for more info, and it appears related to water moisture. not sure though.

its definitely not days. i went through about 5 gallons doing casts for the extruder housings, and i used the same 5 gallon container for about a 2 week long period. my guess would be months.

i did the last casts about 2-3 weeks ago, so when i get to the lab tonight, i'll get out the smoothcast and give it a shot. if it still works right, then i'd say we're looking at months. if you get the smallest size available, you wont have to worry about losing too much.