Monday, May 09, 2011

Solid prints

Printing solid, structural objects is quite an art.  As I mentioned earlier, I am harking back to a very early effort that eD made with A.R.N.I.E, the precursor to Darwin.  eD wanted to use a cabling system for several of the axes not unlike what you used to see for parallel bars on traditional drafting tables.  eD finally gave up the effort when he couldn't get the cable to grip a sprocket wheel properly.  I have another idea about how to do that which I will talk about in the near future.

Securing the cable and pulleys for the z-axis is tricky.  I've spent quite a few days designing a lower corner mounting block for the pulleys.

At 69 cubic centimeters it's quite a large piece.  One thing you learn very quickly is that when you are designing structural pieces you have to remember that you not printing an isotropic material but rather a grained material not unlike wood.  As a result of this, it doesn't do to lay this block on one flat surface.  That gets you a part that is strong in one plane and fatally weak on the other.  Given it's size that's asking for corner curling in any case.

As a result, I decided to put the grain of the print at a 45 degree angle to both major planes.

Several tries at printing it finally got me settings that yielded a very clean, handsome print.  The preparation time for this piece was about 20 seconds after I removed it from the print table.

You can see how clean the bolt holes are.

As are the recessed pockets for the hex head 5/16ths inch bolts.  No warping.  No corner curling.  Pretty much a perfect print.  The longest dimension is 80 mm.

The part mounted properly without problems.


stevec said...

Holy hell, that's cool.

LogbLogb said...

<3 that man.

Sven said...


Kevin said...

Very nice. Am I wrong or is that an unheated build surface?

Forrest Higgs said...

The print surface is unheated. I use a heat lamp to warm it to about 40-45 C before I begin a print to insure good adhesion between the acrylic surface and the ABS raft. For prints like this one I turn the lamp off when the printing actually begins. That's not a hard and fast rule, though.

Jeff said...

i'm amazed you get good adhesion with such a small contact point between the raft and the print. Looks great either way.

I also wanted to thank you for pointing us all towards new image plastics in one of your earlier posts. I just got 10 pounds of abs from them today. they are actually local to me, about 8 miles away, so i completely avoid shipping. Never would have found them if not for your blog :)

Forrest Higgs said...

@Jeff Jim at New Image made up the original PCL filament that got the whole Reprap project started. I've been using him exclusively ever since.

He has had a lot of trouble in the past few years, mostly from a fire which completely destroyed his business a while back. He's bounced back, though, and appears to be doing well.

He was having trouble getting small lots of ABS for Reprappers until just recently when he found a broker that was willing to deal in sales of that size. As well, I'm told he is now using Taiwanese ABS which is very high quality. I bought a full 30 lb spool from him a few months ago but haven't run out of my previous spool, so I can't speak to how well it prints. Knowing Jim, though, who is a terminal perfectionist, I expect that it will perform very well indeed. :-D

Chris said...

impressive! what settings did you find you needed to tweak to get a healthy run?

Forrest Higgs said...

@Chris Printing at 21 mm/sec head speed, 240 C hot end setting, BfB extruder polymer pump set to 27.5 rpm. That last number isn't very helpful. More useful might be that I was printing a print road that was .6 mm wide and .25 mm thick. At the head speed given that's about 11.5-11.75 cm^3/hour.