In my quest for a better surface finish on FDM parts from the Stratasys (especially with a mind towards having Frankie try some more investment casting), I had decided to try the technique noted in this Stratasys application note. Namely, dipping the parts in MEK (methyl ethyl ketone) in order to fuse the individual filaments together and seal the surface. I poured some MEK into a glass jar and hung two of the Mendel parts onto a length of TIG welding rod. I dunked the parts into the MEK for perhaps 10 seconds, then hung them outside to dry. I inspected the parts the next day, and I was immediately reminded of the climactic scene in Raiders of the Lost Ark where Toht’s face is melted off.
While the surfaces were most certainly smoother when compared to untreated parts, the side effect of severe warping and deformation doesn’t make this treatment method a viable option for these small parts. Spraying MEK onto the parts may work much better, as the loose internal fill pattern I’ve been using makes the parts quite porous, so a little bit of solvent goes a long way. I’m guessing part dipping may work much better with as solid a fill as possible.
An alternative solvent may also be something to try. The Stratasys Finishing Touch Smoothing Station uses a vapor bath of a specially formulated solvent, and methylene chloride (the primary component of Weld-On #3) appears to be preferred over MEK in the latest application notes anyhow (earlier versions of the app note recommended MEK and actually mistakenly claimed that Weld-On #3 was MEK – this mix-up had me running in circles for a while).
The treated parts do indeed feel stronger (based on my unscientific method of squeezing them between my fingers to see if they have any discernible ‘give’ compared to the untreated versions), so the treatment certainly has promise beyond just surface smoothing/sealing. So much for the fail – on to the win!
My patience was rewarded on Friday when I had a box from New Image Plastics waiting for me on the doorstep at home – my fresh ABS and HIPS had arrived! Saturday I ran into work to give the ABS a try, as I still had a reasonable amount of support material left on the spool and wasn’t in a rush to try the HIPS. Additionally, modifying two parameters of a working system is inviting disaster. Anyhow, if the HIPS doesn’t work out as a support material, it’s not the end of the world – I suppose I could afford to buy name brand Stratasys support material, but if generic ABS doesn’t work well as a modeling material, I may as well start looking to sell the unit given what the official material costs.
The one thing that I had failed to account for was how to take the coil of ABS filament and get it onto the empty Stratasys spool I had. I initially figured I’d just wind it on by hand, but a little bit of math would have told me that 5 pounds of ABS extruded into a diameter of .070″ yields about a half mile of filament. I did end up winding it onto the spool by hand, with a swivel stool seat helping the process a little bit, but it still took a few hours, and my fingertips had a bit of wear. I’ll certainly need to come up with a better solution in the future (perhaps winding the spool on the lathe, or even better, maybe New Image can simply deposit it right onto the spool for me).
Despite being relatively fresh, the ABS had about the same amount of ooze out of the FDM 1600 nozzle as the ‘lobster red’ Stratasys ABS I had been using. Given the high humidity as of late, I suppose this isn’t surprising – I’ll make sure to use plenty of desiccant tins in the dry box. Things were looking good with feeding the ABS through the system, so I ran a single Mendel part for a test.
The part turned out great, though it was a little trickier to separate from the support layer than the Stratasys ABS had been. The NIP ABS certainly equals the Stratasys ABS in resulting part quality, and I have no more worries about running it through the FDM. In looking closely at the parts I’ve made thus far out of Stratasys ABS, I’ve noticed a bit of variation in build quality, so it will be interesting to see if the NIP ABS provides more consistent results, or if other factors are affecting the created parts.