{"id":713,"date":"2010-11-30T22:47:45","date_gmt":"2010-12-01T04:47:45","guid":{"rendered":"http:\/\/haveblue.org\/?p=713"},"modified":"2010-11-30T22:47:45","modified_gmt":"2010-12-01T04:47:45","slug":"adding-a-build-platform-to-the-stratasys","status":"publish","type":"post","link":"https:\/\/haveblue.org\/?p=713","title":{"rendered":"Adding a build platform to the Stratasys"},"content":{"rendered":"

\t\t\t\tWith the support nozzle on the Stratasys still acting up (it likes to stick in the ‘down’ position once the head gets up to temperature), I thought I’d try running without support material for a time so I can at least be back to making parts. While I could technically deposit ABS right onto the foam base (as I did with one of my very early prints when I first struggled with feeding support filament), this doesn’t make for nice part bottoms, as the ABS fuses vigorously to the glass foam, embedding the foam into the base of the part. Starts making a mess of the foam itself, too. So, I needed to make a regular build platform just like all modern FDM machines use, RepRap included (Stratasys stopped using foam bases years ago and now uses plastic build platforms instead – I should really find out what polymer they’re now using).<\/p>\n

I decided to make a modular platform that I could swap into one of the carriers in place of a piece of foam. A piece of 10.125″x10.125″x0.5″ polycarbonate sheet serves as the ‘base’, into which I drilled holes to accept the pins that normally secure the foam. I drilled and tapped the 4 corners of the polycarbonate for 10-32 screws, and then drilled and counterbored matching holes in a 12″x12″ plate of Garolite from McMaster-Carr<\/a>. Using plastic tubing as standoffs, 4 button head screws then secured the Garolite plate to the polycarbonate base plate. I wanted a good solid platform, as I knew that the Garolite itself would probably be a poor surface to print onto, and my intent was to clamp other surfaces to the plate with binder clips just as nophead does<\/a> with his heated build platform.<\/p>\n

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The cap screw heads stick past the upper surface of the Garolite by just a tiny amount - I sure hope the nozzles will always clear. I still need to make some clearance cutouts in the Garolite so that the platform won't hit the nozzles during the Z homing portion of the cycle.<\/figcaption><\/figure>\n

After trying to level the platform as best I could by tightening down the screws for adjustment (using a feeler gauge between the platform and ABS nozzle), I found that the Garolite is bowed downward slightly in the center. Hopefully this shouldn’t cause any major issues, though – I haven’t measured the amount, but I’m sure it’s less than 10 thou, which is the default layer thickness. This does raise a commonly overlooked use of support material, which is that the support raft helps to ensure that the bottom of the part is flat. Without a support layer, you’re at the mercy of the platform flatness itself. When a raft can be laid down, the first few raft layers can droop or smear to conform to the platform, as the flatness improves with each subsequent layer. Of course, this flatness can be destroyed by part warping, but that’s a separate issue.<\/p>\n

With the platform reasonably level, I thought I’d heat up the machine and see if the generic ABS would adhere to it in some manner. I used an alcohol wipe to clean off the platform, knowing that my fingerprints and other gunk would make adhesion much harder. I let the chamber get up to around 55\u00b0 C before I got too anxious and started extruding (I don’t think the extra 15\u00b0 C to hit normal temperature would have done much). The generic ABS appeared to have zero affinity for the surface of the Garolite when dropped from perhaps 2mm above, so I brought the nozzle down far enough that it would extrude right onto the surface. With the filament feeding through the nozzle at a 20% feedrate, I jogged the head around. The ABS actually appeared to stick to the surface, but when I opened the door to see how much adhesion there was, I found that there was hardly any. Note that I’m using the Garolite surface as it came – I wonder if sanding\/blasting\/grinding the gloss layer would improve adhesion any.<\/p>\n

For the next test, I placed a silicone sheet (McMaster-Carr part number 8632K62<\/a>) on the platform to see if that would have any adhesion. None at all, it turns out – the ABS practically bounces off the sheet (which made a lot of sense in hindsight, as silicone sprays are commonly used for release agents). A pity, as the high heat resistance and flexibility would have made for a great surface.<\/p>\n

Finally, I thought I’d try what has become quite popular among RepRap users and even UP! printer users – masking tape (specifically blue 3M painter’s tape). I thought this was an entirely ridiculous idea when I first read about it some time ago, but so many people were using it that it wasn’t likely to be a running joke. I applied a few strips of tape to the platform, let the chamber heat up once more, and gave a small Mendel part a shot. I was amazed at the results – the ABS sticks to the tape beautifully, yet separates cleanly once cooled. I still had significant corner lifting, however.<\/p>\n

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First layer of a Mendel x-vert-drive-nut-trap_4off<\/figcaption><\/figure>\n

With a decent platform, I thought I’d try my luck once more with running a plate of parts over the Thanksgiving break.\u00a0 I dialed the extruder temperature down to 245\u00b0 C and let the machine hammer away.\u00a0 I stuck around for a layer and a half, and things were looking okay, so I figured I’d check back in 50 hours when the print should be done.\u00a0 Unfortunately, the print started failing at some point within the next 24 hours, as a coworker who had stopped in at the office noticed that the machine “appeared to be dispensing low-grade dental floss” rather than doing anything productive.\u00a0 Sure enough, I had another chamber full of ABS vomit.\u00a0 The post-mortem points towards massive warping and corner lifting as a likely culprit – one of the parts looked like the hot nozzle had rammed into a lifted side, halting further movement of the head (and causing lost steps as a result).\u00a0 There were also various small tears in the blue tape, so obviously a struggle had ensued.<\/p>\n

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Annoyingly, this sight is becoming increasingly common.<\/figcaption><\/figure>\n

During all of this, I also thought I’d check to see what sort of die swell I’m getting with the NIP ABS versus the Stratasys ABS.\u00a0 Quite surprisingly, the NIP ABS only swells to 0.013″ (out of a 0.012″ nozzle), while the Stratasys ABS swells up to a whopping 0.017″.\u00a0 The significance of this finally dawned on me a week later – no wonder I was seeing drooping filaments on crosshatch infill, and a ‘bunched up’ looking filament on the first layer.\u00a0 The same volume applied to a smaller diameter filament means that the filament will have to have a longer length!\u00a0 It wasn’t a matter of too much temperature after all (though the generic ABS remains much more finicky than the OEM ABS).<\/p>\n

The only way to make the generic ABS work in any tolerable manner will be to modify parameters in Quickslice to account for the significantly reduced die swell when compared to the OEM ABS.\u00a0 However, since properties of the OEM material are very tightly controlled, there is no way in the software to adjust such settings – the only thing that can be modified is the ‘road width’, which may not help me much.\u00a0 Tinkering with the definition file<\/a> may be the ultimate method of customization. Unfortunately, the file’s format (though sprinkled with some comments) isn’t documented anywhere that I’ve found.\u00a0 This definition file is for a specific machine (FDM 1600), running a specific material (P400 ABS), with a specific nozzle (T12, which has a 0.012″ orifice), at a specific slice height (0.010″).\u00a0 In all, Quickslice 6.4 has has 24 different definition files just for the FDM 1600:<\/p>\n