Original Prusa MK4S: The Open-Source Bedslinger, Assessed
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The MK4S is a 250 × 210 × 220 mm open bedslinger with the Nextruder (290 °C, load-cell probing where the nozzle is the sensor), a 120 °C bed, 360-degree part cooling and the MMU3 five-material option. It is open-source hardware and firmware, repairable for a decade, with the best support in the hobby. You pay a premium over a Bambu A1 for that, not for speed or size.
Where to buy
Specifications
| Item | Value | Note |
|---|---|---|
| Build volume | 250 × 210 × 220 mm | |
| Max nozzle temperature | 290 °C | Nextruder, swappable 0.25 to 0.8 mm |
| Max bed temperature | 120 °C | Magnetic spring-steel sheets |
| Levelling | Load cell; the nozzle is the probe | No offset calibration needed |
| Cooling | 360-degree fan duct | MK4S upgrade over MK4 |
| Multi-material | MMU3, 5 spools | Optional |
| Enclosure | Optional, 45 °C | Separate purchase |
| Camera | Optional Buddy3D | Prusa Connect remote |
| Firmware and hardware | Open source | Printed parts on Printables |
| Sold as | Kit or assembled | Kit takes a day |
What you pay for
- Repairability. Every part is documented, most plastic parts are printable, and Prusa ships spares for machines a decade old.
- Support. Live chat with people who own the printer.
- Load-cell probing. The nozzle touches the sheet; there is no Z-offset to tune and first-layer problems are rare.
- Upgrade path. MK3 owners upgraded to MK4 and MK4S; Prusa has kept that promise for years.
What you do not get
- An enclosure. The 120 °C bed helps ABS, but the frame is open; the Prusa Enclosure is a separate purchase.
- Bambu-level automation. Input shaping is there; flow calibration is manual.
- A price competitive with Chinese bedslingers. See Bambu vs Prusa.
MK4S or CORE One
The CORE One+ is the enclosed CoreXY built from the same electronics and Nextruder, with a 55 °C chamber and a 250 × 220 × 270 mm bed. If ABS or engineering filaments are in your plans, it is the better buy; see MK4S vs CORE One.
The units in the box
The listings are the MK4S kit, the MK4S assembled and the Bambu A1 as the mainstream comparison.
FAQ
Kit or assembled? The kit saves money and teaches you the machine; assembled arrives tested.
Does the MK4S support Klipper? It runs Prusa’s Buddy firmware with input shaping; community Klipper ports exist but are unofficial.
LayerWalker
Print defect diagnosis, calibration procedures and parts that actually fit. Corrections welcome through the contact page.
