Plastic printers for prototypeing

i_r_machinist · Apr 30, 2012

I've known about plastic printers but have no experience with them. This weekend I saw a show about these highschool kids that where making robot parts for competition on one. WOW! I have to justify getting one in here, which should be pretty simple.
I have a few questions:
What is the plastic that is used, and how strong is it?
What kind of tolerance will they hold?
Do the parts have smooth sides like something that was molded?
Any info would be helpful.
I'll google it here in a bit.
thanks
i_r_

escott · Apr 30, 2012

A LOT depends on the printer in question. Tolerances are going to be "poor" by machining standards, but it's not just tolerances, it's resolution and minimum feature size. Strength is also going to be variable dependent on material. PLA is popular, biodegradable, and generally inexpensive but not very strong. ABS is going to do better in terms of strength. The parts are nowhere near molded finish. There are also limits to part features in terms of unsupported overhang, minimum thickness per layer and a bunch of other things.
It's a cool toy, and it makes semi functional (depending on application) prototype parts, especially the lower price ones that are out these days. Anything more is pushing it. The allure of these machines is that you can draw it and just press print, and not need to understand much in the way of how to operate a machine tool.

MattRobertson · Apr 30, 2012

I've been eyeing this one that just came out for only $500.

Solidoodle | Affordable, Easy-to-Use 3D Printers

From their FAQ

What is the resolution of the Solidoodle?

The resolution is determined by the height of each layer. The default print resolution is .3mm, which achieves a good balance among part quality and printing speed. It is possible to print hi-res at .1mm resolution

escott · Apr 30, 2012

Be aware that quoted "resolution" on machines in that range is almost certainly simply a quoted spec on how much a single step moves the table (in theory), not minimum feature size, so you aren't making things .003 or anywhere close to that size. Even on higher end machines you won't approach feature size that small, or actual in practice resolution.

ToolPost · Apr 30, 2012

One aspect that you have to understand with most 3D printers is that the solid part file must be converted to a triangulated surface model that will have very different geometry than the finished part. As stated before, the tolerances will not be tight, and the printer resolution in terms of layer height will be noticable by sight and touch on the final part.

If you want to model a cylinder, the model in Solid Works or Pro E will show a cylinder. The printed version of the cylinder will be like a dodecagon (octagon + 4 more sides), plus textured walls where each layer was built up.

The printer should come with software for creating the triangulated part file, and this software should have provision for automatically creating support material for overhangs. The final file that is fed to the machine prints both the part geometry and the support material at the same time, alternating material feed to the nozzle head appropriately. Support material can be water soluble or snapped/cut off for removal.

My experience has been with an expensive Dimension BST printer. The minimum wall thickness that was feasible was about 0.060".

Cheeseland Dan · Apr 30, 2012

We have a Stratasys here on campus and the thing is capable of some amazing work. It extrudes in layers of .010 and while, as others have said, it won't hold a tolerance anything like a machined part, it shines in other areas. One of the examples they show off in that shop is a clock they made on it. Not a bunch of parts they ran and then assembled but an entire clock mechanism that actually operates made all in one shot. Escapement, gears, even the clock's face and hands. It can even make parts that end up enclosed. There's some cheapies out there, even kits where you can build your own but you get what you pay for.
Dan

i_r_machinist · Apr 30, 2012

I ran into the #2 guy for Westinghouse at this plant last week and asked if he could supply me with some drawings of the reactor head assembly. He wanted to know what I needed them for. I said have a "work in process" solidworks model of the reactor cavity and head. He came over and was very impressed and said he could give me everything but the proprietary stuff. He also wants to know if I could make a model for training.
Thanks for the info!
i_r_

swarf_rat · Apr 30, 2012

I have had some parts printed by Stratasys' service bureau, Redeye. I have to say that it is remarkable what they can do. You upload a file and within a minute or so you have a quote. While not machined accuracy and finish, it is pretty darn good. For example I was modeling pilot holes for 1/4-20 threads thinking we would tap them, but discovered that you can print the threads in. I had them do a hollow piece, machined it would have to have been four pieces, but was printed as one. These pieces are being used in a demo of a product and have been mistaken by some reviewing magazines as molded composite. They were printed for far less than I would have wanted to machine them.

The $500 ReRap type of products are interesting because of the low price point, but don't confuse the quality of the part made by one of these with one made by a $30,000 machine.

morb1lee · Apr 30, 2012

used a Stratasys for yrs in college. It was cool ya... but it really depends on what you need it for. Just a basic visual of something is great if you have the $. If you needed to paint something don't bother with this. you will spend hrs with puddy, primer, paint. better off sticking to the CNC mill and have a small step over. I would say though a big pro for any 3d printer, including Z-corp, would be at the end of the day hit print and you will have a showcase of parts in the morning.

escott · Apr 30, 2012

The z corp stuff is a whole different animal (full disclosure, I'm a tech for them in addition to the 50 other hats I wear). With some of the machines you can get a full color print, whatever you want on the outside. Resolution is much better with those as well. The downsides to the Z corp stuff is the post processing needed and the fragility of the model before you infiltrate it. It's also not "plastic" in the sense that I believe the OP meant, so I didn't mention them earlier. Again, for a purpose, it is great, but it doesn't make machined parts.

i_r_machinist · Apr 30, 2012

redeye looks good, I bookmarked it.
Toolpost:
Are you saying that the printers generate geometry like you get out of meshlab? Where you set the size of the little triangles used to form surface geometry?
field job today, not much computer time
i_r_

swarf_rat · Apr 30, 2012

morb1lee said:
used a Stratasys for yrs in college. It was cool ya... but it really depends on what you need it for. Just a basic visual of something is great if you have the $.

How long ago was that? Curious, because it seems like the technology has come a long way in the last couple of years. The parts I received I would characterize as a whole lot better than a "basic visual".

behindpropellers · Apr 30, 2012

swarf_rat said:
How long ago was that? Curious, because it seems like the technology has come a long way in the last couple of years. The parts I received I would characterize as a whole lot better than a "basic visual".

It has come a long way, but plan on paying for the tech.

RoboDriller · Apr 30, 2012

Try putting a 3D printed model of a bowl in a sink full of water. It is porous. Shit if you ask me. When they can actually PRINT SOLIDS, then I will be interested.

swarf_rat · Apr 30, 2012

Actually there are pictures of printed cups full of water, even from the $500 machines.

As far as paying for it, yes a good machine is quite expensive. However the set of parts I had made by the service bureau cost about $600, quotes from machine shops were around $2500 for machined aluminum. Injection molded, the parts would have been a few bucks. I was surprised how cheap it was, really. And I designed them enroute on my sailboat off the coast, uploaded them at Starbucks in the next port, and had them in a few days.

i_r_machinist · Apr 30, 2012

Does everyone agree on the .06" minimum wall thickness?
i_r_

escott · May 1, 2012

i_r_machinist said:
Does everyone agree on the .06" minimum wall thickness?
i_r_

No, it's dependent on individual system.

behindpropellers · May 1, 2012

i_r_machinist said:
Does everyone agree on the .06" minimum wall thickness?
i_r_

Also,
Depends how the model is printed along with desired function.

RoboDriller · May 1, 2012

escott said:
No, it's dependent on individual system.

Ive seen parts (my previous cup example) with a .010" wall. I imagine if you use the binder/water soluble filler, you could go down to the smallest printable size, build a wall with filler on both sides then rinse the filler off afterwards.

Forgive my lack of correct terminology.

behindpropellers · May 1, 2012

RoboDriller said:
Try putting a 3D printed model of a bowl in a sink full of water. It is porous. Shit if you ask me. When they can actually PRINT SOLIDS, then I will be interested.

Ignorance is bliss.

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