Choosing your first 3D printer: FDM or resin, bed-slinger or CoreXY

The first question everyone asks is “which printer should I buy?” The better question is “what will I print?” This lesson names no winning brand. It walks through the four big choices instead: FDM or resin, which frame, whether you need an enclosure, and how much build volume is enough. It ends with five questions that, once answered, let you pick a printer yourself.

This is lesson 1 of a 20-lesson path. The next one takes an FDM printer apart, part by part, with the vocabulary you need.

FDM or resin

FDM (Fused Deposition Modeling) melts a plastic strand (filament) and lays it down layer by layer. Resin printers (SLA/MSLA) cure liquid resin with UV light, one layer at a time. Neither is better; they suit different jobs.

Topic	FDM	Resin
Common layer heights	0.1–0.3 mm	0.025–0.1 mm
Surface	Visible layer lines	Smooth, close to injection moulding
Strength	Tough, takes loads well (PLA, PETG, ABS)	Standard resin is brittle; tough resins cost more
Post-processing	Pull supports, light sanding, about 5 minutes	IPA wash, UV cure, supports, about 20–30 minutes
Liquids and chemicals	None	Uncured resin is a skin irritant and toxic: nitrile gloves, glasses, ventilated room
Typical build volume	220–300 mm	150–220 mm
Best for	Board cases, brackets, household parts, larger toys	Miniatures, game models, jewellery, fine detail

For maker work (a case for a board, a sensor bracket, a gear, a toy a child will actually play with) FDM covers nearly everything. Resin makes sense when the main output is figures that need 0.1 mm detail and you accept the wash-and-cure routine and the smell.

Uncured resin must not touch skin and must not go down the drain; leftovers are UV-cured solid before disposal. If your bench is in a bedroom or a room with children, choose FDM.

Bed-slinger or CoreXY

Home FDM printers come in two main frame types.

• Bed-slinger (i3 style): the bed slides front to back (Y), the print head moves left to right (X) and up (Z). Simple structure, few parts, and for years the cheapest way in.
• CoreXY: the bed moves only on Z. Two motors fixed to the frame drive the head in X and Y through one shared belt system. The head is light and the bed never moves, so tall parts do not sway.

Topic	Bed-slinger	CoreXY
What moves	Bed + part (mass grows as the print gets taller)	Only the print head
Speed and acceleration	Moderate; must drop for tall or heavy parts	Higher; some vendors advertise up to 30,000 mm/s²
Tall, narrow parts	Can sway or break loose	Steadier
Desk space	Needs front and rear clearance for bed travel	More compact for the same build size
Repairs and tuning	One belt per axis, easy to diagnose	Complex belt routing, harder to tension
Enclosure	Usually bought or built separately	Many models come enclosed

What we see on our bench: palm-sized PLA parts come out equally well on both. The difference shows above about 150 mm of height or when you push speed. If the budget is tight and you start with small things, a bed-slinger is not the losing choice.

Do you need an enclosure?

An enclosure does two things: it blocks drafts and keeps warm air around the part. Whether you need one depends on the material.

Material	Nozzle (Prusa KB)	Bed	Enclosure
PLA	185–235 °C	50–60 °C	Not needed
PETG	230–240 °C	85–90 °C	Not needed
ABS	about 255 °C	80–110 °C	Recommended; required for large parts
ASA	about 260 °C	105–110 °C	Recommended; required for large parts

ABS and ASA shrink about 1–2% as they cool. Without an enclosure the corners lift off the bed (warping). Both give off fumes (ABS includes styrene), so the room must be ventilated, but without a draft blowing on the print.

PLA is the opposite case: it dislikes trapped heat. A tightly closed enclosure during a long PLA print stops the hotend from shedding heat, the filament softens before it reaches the nozzle and jams (heat creep). Most enclosed printers therefore tell you to open the door or the top lid for PLA.

In short: if year one is mostly PLA and PETG, an enclosure is not a condition. If you already know you will print parts that must survive heat or sunlight (ABS/ASA), buy an enclosed printer or plan space to build an enclosure from day one.

Build volume: size it from a real part, not the brochure

Common bed sizes are around 180 mm (small machines), 220 × 220 mm and 256 × 256 mm. Do not pick from the number alone. Measure the largest thing you intend to print in the first six months.

Worked example. You want a cable tray 250 mm long, 30 mm wide, 20 mm tall on a 220 × 220 mm bed.

1. Straight: you need 250 mm but the bed is 220 mm. It does not fit.
2. Diagonal at 45°: the length taken along one axis = (length + width) × cos 45° = (250 + 30) × 0.707 = 198 mm
3. Add a 5 mm margin per side for the brim and the edge the nozzle cannot reach: 198 + 10 = 208 mm ≤ 220 mm. It prints.

For a 300 mm part: (300 + 30) × 0.707 + 10 = 243 mm, over the 220 mm bed. Split it into two pieces with a tongue joint, or move up to a 256 mm bed.

Height (Z) is rarely the limit. Tall prints take long and are the ones most likely to fail halfway; laying a part down flatter beats buying a taller machine.

Five questions before you pay

1. What will you print in the first six months? Name three real parts with sizes. If small figures dominate, think about resin. If it is cases, brackets and toys, choose FDM.
2. Which materials? PLA/PETG only, or also ABS/ASA/TPU? TPU wants a direct-drive extruder (explained in the next lesson). ABS/ASA want an enclosure.
3. Where will it live? A bedroom or a shared living room is a poor fit for ABS/ASA and for resin. Measure the desk, and remember a bed-slinger needs extra depth for the bed to travel.
4. Do you want to tinker or to press print? Kit-style machines with manual bed leveling teach a lot but cost time. A printer with auto bed leveling and ready material profiles prints on day one.
5. Spares and community. Nozzles, belts, PTFE tubes and bed sheets are consumables. A machine with locally available spares and enough users to answer questions saves more time than a small spec difference.

Safety to know before the box arrives

• The nozzle runs at 190–260 °C and the bed at 60–110 °C. Never touch them while printing, and keep the machine out of children’s reach.
• Do not leave the printer alone during the first layers, and keep flammable things away from it. Modern printers have thermal runaway protection that cuts the heaters when the temperature sensor misbehaves; never disable it.
• ABS/ASA give off fumes and need ventilation. Resin needs nitrile gloves, eye protection and a well-aired room.

Common mistakes

• Buying resin for the finish, then discovering there is nowhere to wash, nowhere to cure, and the smell lives in the bedroom.
• Choosing by the advertised top speed. Real speed is capped by how fast the hotend can melt plastic, not by the motors. Lesson 18 covers this.
• Buying the biggest machine the budget allows and then printing palm-sized parts. A big bed heats slowly and eats desk space.
• Forgetting the surrounding costs: filament, a dry box, spare nozzles, calipers, bed glue. They add up.
• Printing PLA with the enclosure fully closed and wondering why the nozzle keeps clogging.

Sources

• FDM vs. SLA: Compare Filament and Resin 3D Printers — Formlabs
• FDM vs Resin 3D Printing — 3DPrinting.com
• CoreXY vs Bed Slinger — Flashforge
• PLA, PETG, ABS, ASA — Prusa Knowledge Base
• Thermal runaway — Prusa Knowledge Base