Z-Axis
Transport
Design
& Suppliers
The Z-Axis transport is the set of linear bearings and rods that carry the build platform down/up during the build process.
While
conceptually simple, there are some non trivial issues in the design.
Most center around alignment issues and my limited experience with the
A1 build/alignment process. Two points determine a line but you need to
line up a stepper motor, a coupling (motor to feedscrew), and both ends
of the feedscrew so that they are in line. At the same time you need to
line up the two rods and their linear bearings so that all 3 are in the
same plane. The trick is to design an assembly that is, more or less,
self aligning.
Figuring out the size of the various components it also not as easy as it looks.
We'll
start with the length of travel for the Z-axis, called Z.length, that
and the length of the Z-axis feed screw nut, called Z.nut, determines
the length of the threaded portion of the Z-axis feedscrew, called
Z.threaded:
Z.threaded = Z.length + Z.nut
The Z-axis feedscrew
has stepped (turned down) sections on both ends to enable mounting
bearings and coupling to the stepper motor.
At the top (bearing only end) the step down should be the thickness of the bearing, called Z.top.bearing
At
the bottom you have both a bearing, called Z.bot.bearing, to take the
load of the build plate and the Z drive as well as the end of the
coupler between the threaded shaft and the Z-axis stepper motor, called
Z.coupler. Given all the definitions, the overall length of the Z-axis
feedscrew, called Z.feedscrew is
Z.feedscrew = Z.top.bearing + Z.threaded + Z.bot.bearing + Z.coupler
We're thinking of using Misumi's parts:
Lead Screws - Both Ends Stepped 12mm - MTSRW12 (actual part number requires more specifications which we'll develop).
Resin Lead Screw Nuts - MTSFJR12 which is 30mm long.
608zz bearings - 8mm ID, 22mm OD and 7mm thick.
that gives us Z.top.bearing and Z.bot.bearing at 8mm each (7 + 1 for clearance)
the Coupler shaft clamp should also be about 8mm (assumption - we have not picked a part yet)
Length of travel for this design is ~12 inches - let's use 300mm.
so:
Z.threaded = 300 + 30 = 330
Z.feedscrew = 8 + 330 + 8 + 8 = 354
Supplier Information (Note: some information duplicated from Belt Drive section)
Stepper Motors
http://reprap.org/wiki/NEMA_17_Stepper_motor
The Kysan 1124090 seems to be the stepper motor of choice.
- Step angle: 1.8° (200 Steps per Revolution) - Number of phase: 2
- 21 mm long, 5 mm Shaft - D Cut
- Rated voltage: 4.2 V - Current / phase: 1.5 A
- Holding torque: 5.5 Kg-cm (54 N-cm, 76.4 Oz/in, 4.77 lb-in)
- Resistance / phase: 2.8 O ± 10% - Inductance / phase: 4.8 Mh ± 20%
- Insulation resistance: 100 MO (500VDC)
- Kysan Electronics SKU: 1124090 - Mfg: 42BYGH4803-DC
- Operation temperature: -20°C ~ +40°C [is this a concern? steppers usually run hotter than this!]
sources
3dmakerworld - http://www.ebay.com/usr/3dmakerworld?_trksid=p2047675.l2559
$14.50 each + 13.85 ship (tot $86.35/5 motors)
biowavescom - http://www.ebay.com/usr/biowavescom?_trksid=p2047675.l2559
$80 + $15 ship (tot $95/5 motors )
Other Motors
NEMA 17 BIPOLAR STEPPER MOTOR 76 oz-in, KL17H248-15-4A
Shaft: 5mm diameter with flat, shaft length: 24mm
Current Per Phase 1.5A - Inductance: 4.8 mH - Rated Voltage: 4.2V
Holding Torque: 5.5Kg.cm (76 oz-in)
automationtechsinc - http://www.ebay.com/usr/automationtechsinc?_trksid=p2047675.l2559
12.99 each + 17.85 shipping (82.80)
http://www.alltronics.com - OSM - NEMA17 Single Shaft 2A/83oz - $18.25
http://www.phidgets.com/
Shaft Couplers
WWX Electronics - wangwx2013 - http://stores.ebay.com/WWX-Electronics
4/5/6/8mm Aluminum Shaft Coupling Flexible Coupler Motor connector D20L25 - $7.98 + $1.98 ship
Contact
Information
Contact me using: fpirz (at) media (dash) conversions (dot)
net