Printing Production-Ready Flexible Parts with Vexi-Flexx70

• Printer: Direct-drive extruder (recommended: Bondtech BMG, Creality Sprite, or any geared extruder with a 3:1 or higher gear ratio). Bowden setups require significant modification and are not beginner-friendly.
• Hotend: All-metal (e.g., E3D V6, Slice Engineering Copperhead). PTFE-lined hotends degrade at TPU printing temperatures above 220°C and produce inconsistent flow.
• Build surface: PEI sheet or smooth glass with adhesive (Magigoo Flex or glue stick). Avoid textured PEI flexible parts bond too well and tear off the coating.
• Enclosure: Not strictly required, but draft shields prevent cooling inconsistencies that cause layer delamination. A simple cardboard box works for small prints.
• Filament drying: Forced-air oven or food dehydrator capable of 50 60°C for 6 8 hours. Vexi-Flexx70 is hygroscopic skipping drying invites stringing and bubble voids.
• Slicer: PrusaSlicer 2.6+ or SuperSlicer with custom filament profile; Cura works but requires extra per-model settings for retraction.

1. Understanding Shore Hardness and Vexi-Flexx70

Vexi-Flexx70 sits at **Shore 70A** that's roughly the stiffness of a car tire sidewall or a firm rubber band. It bends without buckling, compresses under load, and returns to shape almost instantly. Compared to softer filaments like NinjaFlex (85A) or Cheetah (95A), 70A is actually the sweet spot for functional parts: soft enough to absorb vibration and seal gaps, but stiff enough to print clean overhangs and resist creep under sustained stress. I've seen engineers try to print gaskets with 95A TPU and wonder why they leak 70A conforms to irregular surfaces without needing compression gaskets.

One key property that rookies ignore: **flexural modulus**. Vexi-Flexx70 has a flex modulus around 10 MPa (depending on printing orientation). That means a 5mm thick wall will deflect noticeably under a 2kg load, which is great for bumpers but terrible for structural brackets. Always test your part's stiffness before committing to a batch. I learned this the hard way when a customer asked for a "flexible mount" the first print sagged under the component weight within an hour. Simple wall thickening from 3mm to 5mm solved it, but that's a discovery you want to make during prototyping, not after 100 units are shipped.

Why 70A? The Physical Trade-Offs

Going softer (e.g., 60A) gives you more compliance but introduces stringing, overhang droop, and bed adhesion nightmares. Harder (85A+) prints like standard PLA but loses the "rubber" feel. Vexi-Flexx70 is the safe middle ground forgiving enough for a first-time flexible user, yet robust enough for production floor parts that survive thousands of cycles. I've had prototype dust boots last 8 months of daily use on a CNC mill, while an 85A equivalent cracked after 2 months due to fatigue. The 70A's lower modulus distributes stress over a larger area, delaying crack initiation.

Pro-tip: If your design requires both flexibility and stiffness in different zones, print with a dual-extruder setup using Vexi-Flexx70 and a rigid filament like PETG. The bond between TPU and PETG with careful cooling is surprisingly strong but you'll need to tweak retraction between materials to avoid ooze.

2. Printer Setup: Direct Drive is Not Optional

I'm going to be blunt: if your printer has a Bowden tube longer than 15cm, selling yourself Vexi-Flexx70 without converting to direct drive is setting up for frustration. The filament is flexible it buckles inside the Bowden tube under extrusion pressure, causing underextrusion, skipped steps, and a part that looks like a string cheese disaster. I've done the conversions: you can retrofit an Ender 3 with the Creality Sprite direct drive kit for about $60, or use a printed bracket to mount a BMG extruder on the hotend carriage. The cost is negligible compared to the time lost fighting failed prints.

All-metal hotend is also mandatory if you print above 220°C (which many do for higher flow rates). PTFE-lined hotends degrade at those temps, releasing toxic fumes and causing inconsistent melt zones. I've seen a PTFE tube shrink over time, pinching the filament and creating a jam that took hours to clear. With an all-metal heatbreak, you get consistent resistance and no thermal creep. One more detail: make sure your heatbreak is hardened steel or titanium copper ones transfer heat too quickly up the filament path and cause early softening.

Hardware Checklist Before First Print

• Extruder tension spring: dial down the gripping force too tight will grind the filament and create dust that clogs the nozzle. I set mine so that I can barely pull the filament out by hand when the idler is closed.
• Nozzle: standard brass works, but if you're doing high-wear applications (e.g., carbon-fiber reinforced flexible), upgrade to hardened steel. Expect ~0.05mm excess flow diameter with steel compensate in slicer.
• Heatbreak fan: must be powerful (>15 CFM) and always on. TPU conducts heat slower than PLA, so the cold zone gets hotter if the fan stalls. Result: heat creep jams.

3. Slicing Parameters That Actually Matter

Most slicer default profiles for flexible filament are conservative (slow, no retraction, high flow) and they work, but they waste time and material. Here's my tuned Vexi-Flexx70 profile that balances speed and quality:

• Nozzle temperature 230°C first layer, 225°C subsequent. Higher temps improve layer adhesion but increase ooze run a temp tower from 220 to 240.
• Bed temperature 40°C (glass transition is ~10°C below, so the first layer stays soft but isn't molten enough to warp).
• Print speed 25 mm/s for perimeters, 40 mm/s for infill. Do not exceed 50 mm/s unless you are running a high-torque extruder the filament will slip.
• Retraction 1.5 mm at 30 mm/s, with "wipe while retracting" enabled. Yes, you read that right TPU doesn't need massive retraction because the stringing comes from ooze, not jump distance. Too much retraction will grind the filament.
• Flow rate Start at 100% of nominal, then calibrate via extrusion multiplier test. In my experience, Vexi-Flexx70 averages 0.98 multiplier slight underextrusion compared to PLA's 1.0, because the material expands slightly after the nozzle.
• Cooling fan Off for first 3 layers, then 50% minimum speed. Full fan causes layer adhesion loss and brittleness; no fan on overhangs causes sagging. I use a 5015 blower fan with PWM control the stock creality fan is too weak.

The biggest trap beginners fall into is setting the flow rate too high to compensate for visible gaps. That just creates overextrusion, which causes bulging layers and dimension inaccuracies. Instead, increase the number of perimeter shells (e.g., from 2 to 4) thicker walls prevent the melted plastic from drooping under its own weight.

Overhang Performance and Support Structures

Vexi-Flexx70 bridges poorly past 45 degrees because the material droops when unsupported. For any overhang steeper than 55°, you need breakaway or dissolvable supports. I've found PVA soluble supports work but cost extra; breakaway supports with a 0.15mm gap (no z-distance) are better because flexible parts snap off without damaging the surface. Never use tree supports they collapse under flex print's low mod height. Stick to line support at 0.25mm interface gap.

4. The Drying Ritual: Ignore at Your Peril

Vexi-Flexx70's polyurethane base is hygroscopic it absorbs moisture at a rate of about 0.3% by weight per hour in 50% relative humidity. Manufacturers vacuum-pack it, but once opened, the clock starts. I swear by drying new spools for 6 hours at 55°C even straight from the sealed bag, because I've had three spools out of twenty that arrived with 0.2% moisture due to transportation humidity changes. Wet filament produces bubbles, stringing, and layer adhesion failures that look exactly like under-extrusion. If your first layer looks fine but the top surface is covered in tiny pits, moisture is the culprit.

Drying method: Use a food dehydrator that holds 50 60°C (higher will soften the spool and cause tangles). I modified a cheap Cosori oven with a PID controller cost me $40. Leave the filament in for 8 hours if it's been sitting for weeks. Do not microwave the metal foil in some spools will arc.

Storage Best Practices

After drying, store the spool in a vacuum-sealed bag with desiccant (silica gel, not rice). I use a 2kg bag of rechargeable silica beads ($15 on Amazon) and swap them monthly. If you don't have vacuum bags, a large Ziploc with as much air removed as possible works for a week. Also, keep the filament in a dark cabinet UV light accelerates degradation of the polyurethane chains, turning the material brittle over time.

5. First-Layer Sorcery

The foundational layer is make-or-break for flexible prints. Why? Because the material is soft, it will deform under the nozzle's weight if your bed level is even 0.1mm too low, the nozzle will push the first line into a ragged smear instead of a clean squared track. Here's my ritual before every Vexi-Flexx70 print:

1. Clean the build surface with isopropyl alcohol (99%) don't use acetone on PEI; it damages the coating.
2. Apply adhesive : Magigoo Flex is my go-to, but a thin layer of glue stick works. Too much adhesive creates a gooey interface that lifts the part you want a uniform coating dry to the touch.
3. Live adjust Z-height during the first-layer skirt. The filament should be compressed into a flat rectangle about 0.2mm wide for a 0.4mm nozzle if it's round, it's too high; if it's transparent, it's too low and will rip off.
4. Use a brim (10 loops, 0.3mm gap from object) to anchor the first layer. In my experience, corner lifting is reduced by 80% with a brim.

What a first-layer failure looks like : The first line squishes out sideways, then the nozzle catches it and drags a wad of plastic across the bed. Stop the print and clean the nozzle with a brass brush never use steel or you'll scratch the heatbreak.

6. Common Failure Modes and Field Fixes

No article is complete without a troubleshooting matrix from real shop disasters. Here are three scenarios I've dealt with personally:

One time I had a mysterious underextrusion that only appeared on the second half of tall prints. Turned out the spool had a tangle that was locked by the weight of the remaining filament the extruder couldn't pull it. Solution: always unspool the filament by hand before loading, and if you hear clicking from the extruder, pause and check for tangles.

7. Post-Processing and Finishing

Flexible parts are forgiving in terms of support removal just twist and pull. But sharp edges from support nubs can weaken the part; I use a pair of electrician's scissors to trim them flush. For functional parts, you might need to sand the surface for a better seal or fit. Vexi-Flexx70 sands poorly it gums up sandpaper instantly. Instead, use a deburring tool or a sharp knife. If you need a smooth surface, apply a thin coat of Rust-Oleum Flex-Dip (rubber coating spray) it adheres well to TPU and hides layer lines.

Annealing flexible parts? I don't recommend it. TPU's polymer chains reorganize under heat, but without jigging, the part will shrink unevenly and warp. If you must anneal for strength, bake at 80°C for 2 hours in a silicone mold but expect 3 5% dimensional change.

8. Scaling Up for Production

Once you've dialed in your setup for a single part, moving to batch production (10 100 units) requires a few adjustments. First, consider using a larger nozzle (0.6mm) it increases flow rate by 80% while sacrificing minimal surface finish for functional parts. I've printed 50 identical cable boots with a 0.6mm nozzle at 0.3mm layer height, cutting print time from 2 hours to 45 minutes each. Second, use a print bed with multiple parts spaced at least 5mm apart TPU parts tend to lean into each other if too close. I set up a grid layout inside the slicer with 7mm separation.

Third, monitor the first layer of every print batch. If you're printing overnight, use a webcam and a "spaghetti detection" plugin (OctoPrint) a single failed first layer can ruin the entire bed. Finally, consider post-curing: expose printed parts to UV light for 2 hours (if using a UV-stabilized version) to toughen the surface this reduced wear mark in our application by 40%.

One more production tip: keep a spare hotend and extruder gear set on hand. Flexible filaments accelerate wear on brass nozzles I change the nozzle every 500 grams of print. The cost is $2 per nozzle; it saves you from mid-print jams that waste $20 worth of material and time.