3D Printer Build - Calculating Wire Gauge

Most 3d printers use either 12V or 24V 

• Hotend 12V heater cartridge can draw up to 4A 

• A heated bed can draw nearly 12A. 

• Cheaper 26-gauge wire are rated at 2 amps

If your wire gauge is not large enough or longer than needed the resistance will be higher This means less watts going through the wire.

Copper wire size uses the American Wire Gauge (AWG). The lower the gauge number, the less resistance the wire has and therefore the higher current it can handle safely.

Stepper Motor Wiring

Rated Current is the maximum current that can pass through both windings at the same time. Set the motor current to no more than about 85% of the rated current. To get maximum torque out of your motors without overheating them, you should choose motors with a current rating no more than 25% higher than the recommended maximum stepper driver current. 

• Nema 17 Stepper Motors: 22 AWG wire with 4 conductors

• NEMA 17 motor wires are 26 AWG

Most motor torque data assumed 24 Volts, at 1.1 amp to 1.5 amp. Roughly 26 to 36 Watts, but remember that's "chopped" or pulsed.

Wire size is based on power transmission requirements and length of wire.

10 gauge wire - 30 amps

12 gauge wire - 20 amps

14 gauge wire - 15 amps

16 gauge wire - 10 amps

18 gauge wire - 7 amps

20 gauge wire - 3 amps (or slightly more)

22 gauge wire - 2 amps

Stranded wire is best for lengthening motor wires, get 9 strands or more. Solder properly and heat shrink. 20 AWG or larger.

Use a shielded 4-core high current wire, so that the wiring creates much less capacitive and induced interference or a twisted pair of twisted pairs.

 Each individual winding should have a twisted pair, and these two pairs should be twisted (in the opposite sense) together. Twisted pair will reduce induced interference to a minimum, and twist-on-twist is a very flexible way to combine 4 wires. Alas the construction will couple capacitively to nearby signal cables, so it pays to keep separate from them, or ensure all signal cables are shielded. (Signal cables are things like limit switch wiring, encoders, etc...).

Using a cordless drill and a bench vice, keep enough tension to prevent kinking, and reverse briefly to lose any torsion before releasing the wires.

Wire Connectors

The Molex 4 pin connector are rated at about 14 Amps (.093 inch / 2.36 mm diameter terminals.

Wire Gauge Chart

AWG gauge	Conductor Diameter Inches	Conductor Diameter mm	Conductor cross section in mm2	Max Amps for wiring	Max amps for power transmission
0000	0.46	11.684	107	380	302
000	0.4096	10.40384	84.9	328	239
00	0.3648	9.26592	67.4	283	190
0	0.3249	8.25246	53.5	245	150
1	0.2893	7.34822	42.4	211	119
2	0.2576	6.54304	33.6	181	94
3	0.2294	5.82676	26.7	158	75
4	0.2043	5.18922	21.1	135	60
5	0.1819	4.62026	16.8	118	47
6	0.162	4.1148	13.3	101	37
7	0.1443	3.66522	10.6	89	30
8	0.1285	3.2639	8.37	73	24
9	0.1144	2.90576	6.63	64	19
10	0.1019	2.58826	5.26	55	15
11	0.0907	2.30378	4.17	47	12
12	0.0808	2.05232	3.31	41	9.3
13	0.072	1.8288	2.63	35	7.4
14	0.0641	1.62814	2.08	32	5.9
15	0.0571	1.45034	1.65	28	4.7
16	0.0508	1.29032	1.31	22	3.7
17	0.0453	1.15062	1.04	19	2.9
18	0.0403	1.02362	0.823	16	2.3
19	0.0359	0.91186	0.653	14	1.8
20	0.032	0.8128	0.519	11	1.5
21	0.0285	0.7239	0.412	9	1.2
22	0.0253	0.64516	0.327	7	0.92
23	0.0226	0.57404	0.259	4.7	0.729
24	0.0201	0.51054	0.205	3.5	0.577
25	0.0179	0.45466	0.162	2.7	0.457
26	0.0159	0.40386	0.128	2.2	0.361

Motor Current

• Maximum motor current 1.5A peak => Stepper motor rated current <= 1.9A

• Maximum motor current 2.5A peak  => Stepper motor rated current <= 3.0A

• Maximum motor current 1.6A peak with good fan cooling  => Stepper motor rated current <= 1.7A. 

Use motors with lower rated current (e.g. 1.0 to 1.2A) and 24V power, then the drivers will run cooler.

Duet 3 Current

Duet 3 Mainboard 6HC and Expansion board 3HC has a recommended maximum motor current 6.3A peak/4.45A RMS) => Stepper motor rated current <= 6A

Duet 3 Toolboard has a recommended maximum motor current 1.4A peak) => Stepper motor rated current <= 1.75A

2B 2A 1A 1B

One solution is twisted pairs of wire to have one wire carrying the current while the other brings the current back.

Calculating the wire size

A higher voltage means a lower current for the same amount of power. This gives you the opportunity to use smaller wires for the same job. Voltage is proportional to the current.  A higher voltage means a lower current. Wire size influences the amount of current that can pass through it.

• A thicker wire will have less resistance per length

• Less resistance means loss

• The less loss means less temperature increase

In terms of wire size, 24V has an advantage over 12V, as the wires can be much smaller.

A power supply of 300 watts running at 12V or 24V, will use less wire.

Voltage	Current	Power
12V	4A	48W
24V	2A	48W

Wire Sizing Chart and Formula

Calculate the Voltage Drop Index (VDI) using the following formula:

1. VDI = AMPS x FEET ÷ (% VOLT DROP x VOLTAGE)

2. Determine the appropriate wire size from the chart above.

To compensate for voltage-drop, heat and current changes it is recommended to use 6 gauge wire and 4 gauge for over 15 feet.

 Kinematic Bed Mounting

The 3-Point Kinematic Bed Mount is still in the design phase, but it will be made to level and compensate for a bent bed plate or dips. The three z-axis lead screws are used as the three points that make up a triangle and define plane of the bed can raise without binding or twisting keeping your work flat. The kinematic bed mounting system allows the bed to heat up without the thermal expansion effecting z-axis motion or bending the bed.

What is a kinematic mount?

A kinematic coupling is designed to constrain the mechanical components with optimal precision and positional accuracy. For example a kinematic coupling uses three radial v-grooves in one part that mate with three hemispheres in another part. A kinematic mount, which is ideal for bed leveling and proper mechanical constraint. A kinematic mount is a mount in which all six degrees of freedom (three translations and three rotations) of a 3D object are restrained from moving without over constraint.

How does a kinematic mount work?

A kinematic mount is a type of mounting mechanism used for positional accuracy. The movable frame that holds the print bed pivots on a ball bearing which is set into a hole in the fixed frame.

Kinematic Constraints

Kinematic constraints are constraints between mechanical components that decrease the degrees of freedom of rigid systems. The degrees of freedom or DOF of a rigid body is defined as the number of independent movements it has. To determine the DOF of this body we must consider how many distinct ways the bar can be moved. On a two dimensional plane such as a 3d printer build plate, there are 3 DOF. The print bed can be translated along the x-axis and y-axis, and rotated about each axis.

Z-Axis Documentation Drive Folder

CoreXY Belt Routing 

Belt Path Crossing

While the SolidCore 3D Printer design had a lot of influence from the Railcore's design, which also has the "x" shape belt path that some say “serves no purpose.” True, but you see the quality prints that the Railcore community is putting out. The print quality of the RailCore is AMAZING! Although the belts don't have to cross if the pulleys are at different z-levels. I originally thought that the difference between the hbot core xy design was that the corexy belts crossing segment. 

We already designed and built the SolidCore with the crossed belt path so we're going to stick with it for now. Later on after many performance tests I'll try out some other design configurations to test out any changes. 

Hbot vs CoreXY

The difference between hbot and corexy is that hbot has a single belt on a single plane, corexy can have either two non-intersecting planes or a single plane with pulley idlers on different levels which keeps the belts from rubbing.

While the Hypercube has the stacked belts on different planes configuration unlike the SolidCore corexy configuration "x" crossed belts. 

Stacked Pulleys

Offsetting the stepper motors with stacked belt path pulleys may give the belts a clean run and simplify belt alignment. A printer's motors can be offset at different heights so that the belt routing runs a straight belt path and don't have to be twisted. But this belt routing path would also mean that on one side of the gantry the belt would have the teeth on the side of the idler wheel which wouldn't run as smooth and could lead to artifacts within printed parts.

SolidCore and RailCore Crossing Belt Segments

While many frown upon the crossed belts configuration found on the Railcore or SolidCore due to the y-axis could possibly bind if the y-axis isn't completely perpendicular to each other.

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