Friday, November 28, 2014

First Prints in ABS

ABS print

Summary: Printing in ABS is easy. Lower default nozzle temperature for best print quality.

I have a number of parts to make for my custom hexacopter. I needed to print them in something tougher than PLA that can hold up to some hard landings and withstand high temperatures like in a car. So I ordered some Pro Series ABS filament from MatterHackers. If you read up on printing with ABS you can easily psyche yourself out. So much advice on getting successful prints with ABS. I chose to ignore all of it and just print the Ultimaker Robot with the default ABS settings at normal quality.

normal quality print at 260 C

The default ABS settings are 260°C nozzle, 90°C bed, 50% fan, 2.85 mm filament diameter and 107% flow. I used glue on the bed to help the part stick. The part printed without any problem and stuck to the platform firmly. Print quality was pretty good but it looked like it printed a little hot. The color also looked to go a little light and matte compared to the bright gloss red of the filament. The first few layers printed a little messy with nubs of material, same for some of the infill. The small details like the antennae and ears looked melted and the bridges looked bad. The Pro Series ABS is rated for 230°C - 240°C so I decided to print again at 240°C. This time I adjusted the filament diameter to 2.90 mm.

260C print (L) vs 240C print (R)

This 240°C print turned out a little better. The initial layers printed clean as did the infill. The color of the part also got brighter. The fine details printed much better and the bridges improved slightly. On another note, many people complain about the smell of ABS during printing. While it does have a faint smell of melting plastic, I found it underwhelming. It was only really noticeable when close to the printer; not a problem. Let's try one more print at 230°C.

240C print (L) vs 230C print (R)

At 230°C the small details and bridges improved a little more. Most noticeable, the sides of the print were smoother. At this point, the ABS prints nearly as well as PLA. Larger prints may not be so easy, bed adhesion and warping may become an issue, we'll see. But for now I'm ready to make some parts in ABS.

ABS (L) vs PLA (R) prints

Tuesday, November 25, 2014

Separating Parts in Cura

all parts are one object

Summary: Separate multi-object files into separate parts for easier printing.

I am working on a multi-part model. One of the stl files contains several parts. When the file is imported into Cura, they are seen as a single object. This was a problem because some of the pieces needed to be rotated. Luckily this is easy to fix in Cura. Simply right click on the model and select "split object into parts".

model split into 11 objects

In a matter of seconds, Cura splits the model into multiple parts. Each part can now be repositioned and rotated as needed. Or, you can save each of the parts as a separate stl file by copying the file and deleting the unwanted parts. This is just one of those handy options in Cura that is easy to miss.

A Note About Gluing Print Bed

warped corner

Summary: Use glue to prevent warping. Smooth glue out with water to thin the glue layer.

I just finished a marathon 11 hour print for the MakerBot tractor. (I will write up the whole build when it is finished.) I was printing two pieces of the grille. The quality of the prints was perfect, but the corner of one of the pieces warped. I didn't expect this since I was using a heated bed with PLA. I guess using some glue to help with adhesion on large prints is a good idea.

When I used the glue stick on past prints, occasionally I could see some of the layers of glue on the bottom of the print. Usually it is not a big deal because you don't see the bottom of the print. But I came across some good advice on 3D Verkstan regarding gluing. After you apply the glue stick to the build platform, use a damp lint-free cloth to smooth the glue out. As the bed heats up, the water evaporates. The glue layer left behind is very thin and will not leave any trace on your print.

no warping

I reprinted the part with the glue and no more warping. So while the heated print bed helps to prevent warping, gluing down that bottom layer gives you just a little more insurance.

Finishing PLA

stock surface finish of a high quality print

Summary: Sand and polish your parts to remove any hint that it came from a 3D printer.

I have been extremely impressed by the surface finish of the high quality prints from my UM2. On many of the things I have printed, I have come to appreciate the very fine layers and lines of the print. They prove that the object is printed and that just makes the object that much more amazing when showing it off to friends. However there are times when you want to hide the printed quality of the print. There are many different finishing techniques for printed parts. I decided to try a few techniques on a scrap PLA part that warped during printing.


First, I tried sanding the part. I started by sanding the surface with 220 grit sandpaper. This removed any trace of the layers but left visible sanding marks.

220 grit sandpaper
I followed that up by wet sanding with 600 grit waterproof sandpaper. The water really makes the sanding easier as the part does not stick to the paper and the PLA does not heat up and clog the paper if you apply too much pressure. As a bonus, the water keeps the sanding dust from getting everywhere. The 600 grit left a matte surface that was smooth to the touch. The sanding marks were visible up close in the right light but disappeared if you moved the model away by just a few inches.

600 grit wet sand
Lastly, I tried #0000 steel wool. This removed all sanding marks. After this step there was no trace of the layers or sanding marks. The surface had a nice even semi-gloss finish that looked like a molded part.

600 grit (L) vs. #0000 steel wool (R)


With the sanding marks removed, I wanted to see if I could get the PLA to shine. Starting with the #0000 steel wool surface finish, I used Novus platic polish. Normally, you start with #3 and work your way to #1. I skipped #3 as it is designed to remove heavy scratches. The #2 Fine Scratch Remover definitely brought some shine to the part. But the polish gets into all the nooks and crannies and made any fine scratches more noticeable. The #1 Clean and Shine just seems to be a cleaner, it didn't add any polish to the part. If you need more shine on your part, like for a clear piece, I would just purchase the #2 formula. But it's a lot of extra work for a finish that isn't much better than the #0000 steel wool.

it's hard to make out in the photo, but the polished side (R)
has a little more shine


Just for the heck of it, I hit the piece with 80 grit silicone carbide in my sandblasting cabinet. It didn't seem to do much in the way of smoothing and it made the surface very dirty. I don't recommend it. Maybe blasting with baking soda would work better as anything caught in the part would dissolve in water leaving a clean surface?

sandblasted area on right

Acetone Vapor

This technique involves melting the surface of the part with acetone vapors to smooth out the print lines. I personally don't care for the look, it destroys a lot of the detail and the part often looks like it melted. But I can see some instances where that look might be appropriate. I definitely would not use it on parts that need to be glued together as I think the parts would distort too much to get an invisible glue joint. If you had to, I would do it after I glued the parts together.

First I just tried sealing the part in a Ball jar with some acetone in it. Over two hours later I still could not see any effect on the part so I removed it. I tried again, this time leaving the lid of the Ball jar on loose. I also put the jar on a mug warming plate to heat the acetone and speed up the process. Five hours like that and still no appreciable effect!

5 hours of acetone

The print lines are still visible, not even close to the glossy melted look I have seen on other prints. Maybe the MatterHacker PRO Series PLA is resistant to acetone? The part softened and distorted, especially where the corners touched the jar. But the surface did not smooth out. I'm done with acetone for now. Apparently it's not as easy as it looks. I'll try again if I ever have a part that I want that look on.

Printing with Supports

Long bridge will likely need support

Summary: Print support structures for clean bridges.

Yesterday I printed out a very large part that took 19 hours to complete. The part has a long bridge that probably would not have printed well without a support structure. I was not going to risk a print this large so I selected the "print support structure" option in Cura.

waffle pattern of the support structure

The support structure is designed to print just enough surface to support the layer above. It is also designed so that it will separate easily from the rest of the print.

finished print with support
close up of support

The support did a great job of keeping the layers above nice and flat. I tried to peel the support off by hand but I couldn't. So I started by carefully pushing a razor blade in along the edge of the support line. Then I tried to remove the layer by hand again. Not quite. Finally I used a chisel blade on my x-acto knife and slipped it in between the support and print along both sides. That popped the support off.

The bottom surface is a little hairy looking where the support was but that's ok as it is the bottom of the piece. I used a file to knock down some of the high spots. More importantly, the sides of the piece are nice and clean.

support removed
nice clean bridge

Saturday, November 22, 2014

Raven Skull

Summary: 3D Kitbash models are amazing!  UM2 print quality is unbelievable on the high quality defaults.

While browsing Thingiverse one day I came across this amazing raven skull model. It is from the Boneheads collection by 3D Kitbash. The Kitbash models are really well designed. First, the surface detail in the model is impressive. Where most models have smooth surfaces, the Boneheads seem to have a subtle surface texture in the model which breaks up the print lines and makes the final print look like bone and not plastic. Also, the models are designed in multiple parts to avoid bad overhangs, odd flat spots from the print bed, or the need for supports. The parts assemble with pins that are printed from a separate file, no glue is needed.

2 part model

I have wanted to print this model ever since I got the UM2 set up. But I wanted to wait until I was sure the machine was up to the task. My prints have been turning out really nice so I decided to give it a try. I was pretty sure it would print fine, I just didn't know how good the print quality would be. I loaded up the model in Cura and selected the high quality print setting at 215°C. A little over 6 hours later, the print was done. I realized after the fact I probably could have gotten away with a lower infill and saved some time.

hot off the printer

The print was nearly flawless. I never expected the UM2 to print this well; the layers are almost invisible. The tip of the beak was a little melted and there were a few blobs on some of the worst overhangs. But everything else was perfect. Both issues were easily fixed with an x-acto knife and a small file.

slight melting at beak tip

small blobs on the overhangs

Next I printed the pins and assembled the skull. The pins held the skull together tight, but there was a little play in the parts and the joint was too visible for my liking. So I added some cyanoacrylate glue and held the parts together to close the gap. My printer leaves about a 0.5 mm lip around the base of any prints. I needed to remove the lip around the seam of the skull. I used a new blade on my x-acto knife and carefully cut away the bulk of the lip. Then using the edge of the blade, I scraped the remaining seam down to the surface of the skull. By following the grain of the layers, the scraped area blended nicely with the rest of the print. It is more obvious in the pictures; in person it is hardly noticeable.

top seam

right seam

left seam

The raven skull is one of the few free models from 3D Kitbash. There are several other equally awesome models available for sale on their website. With all of the free 3D models available I never thought I would pay for a model. But I am so happy with this one, I just may have to drop a few bucks for some of the other models. This print will likely be the flagship of my collection. But first, you just know I am going to print the wall mount.

Thursday, November 20, 2014

Replacement Nuts

cracked nut

Summary: Using 3D printing to fix things around the house.

Today I noticed one of the nuts was missing from our floor mop. Upon closer inspection it became apparent that the other nut was broken. I could easily have grabbed a pair nuts from my shop and used those as replacements, but where's the fun in that?

I quickly designed a replacement in 123D Design. I changed a few measurements to try and make the new nuts stronger. Then I printed out a pair on the UM2 at normal quality.

What do you know, they fit! There were a few design challenges. I tried to size the hole so the screws would cut threads into the nuts. The size of the screw hole was critical. Too small and the nut would crack. Too large and the threads wouldn't catch. I also added a chamfer at the bottom of the hole to make it easy to start. I guess I got it right because the screw is on nice and tight without cracking. I needed pliers to screw it on the first time, but after that I could do it by hand. I also needed to make the nut strong. I meant to print it solid but I forgot. But luckily it looks like the 20% infill was sufficient.

problem solved

The new nuts work perfectly. And as a bonus, the print lines give the nuts a no-slip texture! Maybe this wasn't the most practical solution but the blue plastic knobs look much nicer than a pair of steel hex nuts. And who wants to use a wrench on their mop anyway? I wonder what else needs fixing around the house?...

The files are available on YouMagine and Thingiverse.

Printing Multiple Files at Once

5 files printed at same time

Summary: Print multiple files at once for ease and better quality.

I have always wanted to get an old Spirograph set for my kids. But then I discovered this 41 piece Spirograph set on Thingiverse. Why buy when you can print? Looks like a nice Christmas present I can make for the kids. There are a lot of parts to this set, so I decided to print several gears at once. Printing multiple parts at once is not only easier, it can also result in nicer prints because each layer has plenty of time to cool before the next layer is printed.

To print multiple parts you just keep loading model files. Cura will automatically space the parts out for you. Select the "print all at once" option under the tools tab to for better print quality. Otherwise you will just be printing one model at a time and you won't get the benefit of letting each layer cool. Then just save the file to the SD card and print as you normally would.

I printed these at 220°C with the normal quality defaults and they came out great. The teeth mesh perfectly. The one downside to printing multiple parts is you can get stringing between the parts. There was no stringing on this print. I'm going to wait until I have some more colors of PLA before I finish the set to make it a little more colorful. Six parts of the Spirograph done, 35 more to go!

Wednesday, November 19, 2014

Steam Train Whistle

Summary: My first print with custom settings. Use the pause function to correct minor errors during a print.

Since before I got my 3D printer, I have wanted to print this steam train whistle from Thingiverse. I thought it would be cool to print something functional, even if its only function is making noise!

first try

My first attempt didn't turn out so well because the filament feeder was skipping.

second try

I tried again after "fixing" the problem only to have the feeder start skipping again and ruin another print. I was feeling cocky after a successful print so I had upped the printer speed to 80 mm/s. That's still a conservative speed for the UM2 but maybe that was the reason for the skipping?  Rather than repeat the print at 50 mm/s, I ended up disassembling the filament feeder and performing an Atomic Clean on the print head. While feeding the filament back into the bowden tube I noticed that unless the curve of the filament matched the curve of the tube, the filament would bind firmly in the tube. The deep pits in the filament from the feeder probably didn't help either. So I cut off any filament that had been through the feeder already, made sure the filament was uncoiling cleanly and following the curve of the bowden tube, and fed it back into the filament feeder.

stray filament

Bingo, that did the trick. The PLA seemed to be flowing smoothly so I set up the whistle print again, this time at 50 mm/s. About a third of the way through the print I noticed a piece of PLA had been pulled out of place and was sticking up in the middle of the whistle chamber. I was worried that this might affect the sound of the whistle so I paused the print. To pause a print, just go to tune < pause printing with the navigation button on the printer. A pause also moves the print head out of the way. With the print paused I was able to cut off the piece of stray filament. Hit "unpause" and the print picks up where it left off with no visible sign of the interruption.

third time's a charm

About an hour later the print finished. I didn't hear or see the feeder skip once during the entire print. The whistle looks great and sounds just as good. And it is loud. The kids should love wife will hate it.

I used the full settings and made some adjustments as recommended by the whistle designer. The final print settings were as follows.

0.25 mm layer height
0.75 mm bottom/top layer
25% infill
0.8 shell
0.3 mm initial layer
50 mm/s print speed
all other settings were default

Don't Over-tighten the Material Feeder!!!

this is what happens when feeder tension is too high

Summary: Over-tightening the material feeder will cause the filament to slip and will lead to under extrusion.

Yesterday morning I made the nice print pictured above with the normal quality settings. That evening I tried to make some more prints. They did not look good.

Multirotor helicopter foot.  WTF!

The picture above was the result of a normal quality print. Looks like under extrusion again. I was already printing at 220°C so I didn't think temperature was the issue. It was a model that I designed from scratch so I thought maybe the problem was with my model. I downloaded a popular whistle model from Thingiverse and tried again. This time I used the full settings so I could change the layer height, number of layers, and infill as directed.

not even close

As it was printing I could hear some clicking coming from the material feeder as the knurled wheel slipped on the filament. I thought the tension on the material feeder might not be high enough so I tightened it until the indicator was on the center line. No improvement. I canceled the print after about 30 minutes; the layers were a mess.

reducing resistance on spool

I thought the nozzle might be clogged but before I tore it down I decided to check the UM forum again and search the under extrusion posts. I noticed that under extrusion can occur when the coils on the filament spool have trouble unwinding. This seemed particularly common with Ultimate-Blue PLA as it seems stiffer than some other brands. So I removed the spool, unwound a bunch of coils, and tried to straighten the filament as best I could. Then I tried printing the multirotor foot again.

proper tension setting on the feeder

With the machine back facing me, I noticed the material feeder slipping about every 5 seconds. With the better view I could see how too much tension (rather than not enough) could lead to the slipping I was seeing. So I backed off the tension until the slipping stopped. The material started feeding just fine, no more slipping.

that's better

The foot printed perfectly. Thinking back, I believe the first thing I did to combat under extrusion was increase the tension on the material feeder when I should have been increasing the temperature. Keep in mind there are two different versions of the material feeder for the UM2. There is an older version which apparently had some problems and needs to be adjusted to about the middle setting. And there is the new version which I have which likes to be set towards the top. This setting is much more critical than I expected and I wonder how many under extrusion problems are a result of improper tension on the material feeder. Check this first as it can save you the trouble of cleaning your print head!