From RepRapWiki

Contents 1 Overview 2 Parts 2.1 Frame and Z Axis Parts 2.2 Y Carriage Parts 2.3 X Axis Parts 2.3.1 X Carriage 2.4 Extruder 2.5 Electronics Mounting 2.6 Quantity of Materials Needed by Subsystem 3 See Also

Overview

The Open Hybrid Mendel (or OHM) is a project of the State College Reprap Users Group. It is a Mendel design, which uses both standard Sells Mendel parts, a Prusa Z drive, various redesigns from the community at large, and a number of small design improvements developed in our PSU Reprap class. It is so named due to this hybridization of designs, and obtains the 'Open' designation from the OpenX and OpenY axes it uses. The prototype for the OHM design was Etherdais_Unit_One

Expanding into the realm of the biological, the OHM is the basis for a Mendel-based PCR system, currently designated the RepRap Mullis.

Any Mendel can be broken down into 6 sub-systems, which are somewhat interchangeable between designs:

Frame - The OHM uses Camiel's thin shelled Vertex design, maintaining vertices similar to the Sells design, but using less filament

Y-axis - The OHM uses a modified OpenY, with an optoless belt harness, and a second 90/180 arm in place of the 90/270 arm. This demands two additional bearings, but we find the result is more stable, while retaining the benefits of the OpenY. A modified Sells y-motor bracket is used, which avoids printing an unused endstop holder from the original Sells design. The original Sells y-bar clamps seem well suited for mounting y-axis opto-endstops.

Z-drive system - The OHM uses a Prusa, double motor design for driving the Z axis, avoiding the large prints and continuous belt of the Sells Z-drive design. We still use Sells bar clamps to clamp the smooth rod to the Z-motor mounts, as they are compatable, and look sharp together.

X-Z assembly - Currently, the OHM build uses a standard Sells X-Z assembly, as described here in Mendel_X-axis.

Carriage - The OpenX carriage is the design of choice currently, with modifications to the Undercarriage Bracket and Arm that have been found to reduce side to side wobble and skew. For a list of changes, see the X Carriage section.

Extruder - We are in the process of finding a design which is more compatable with the TechZone steel hot tips we've been using recently, though the current design is a hack of herringbone extruder gears, and GregFrost's hinged wades extruder.

Spool Arm - The OHM uses an "in-house" design to support the PLA spools. See Spool Arm Design.

Parts

Download Zip: File:OpenHybridMendel 0.1.zip

Frame and Z Axis Parts

Quantity	File-Name	Comments	Diagram
6	camiel_frame_vertex_6off	Alternative part by Camiel
2	z-prusa-motor-mount_2off
2	z-bar-top-clamp_2off
4	prusa_bar-clamp_2off
8	y-bar-clamp_8off
1	y-idler-bracket_1off
1	y-motor-bracket_1off_mod3-15	Modified by PSU Reprap Collective

Y Carriage Parts

Quantity	File-Name	Comments	Diagram
4	bed-spring_4off
1	8mm_Belt_Harness_1off	Open Y by Buback, modified by PSU Reprap Collective
2	8mm_Crossbar_Mount_2off	Open Y by Buback
2	Arm_90-180_2off	Open Y by Buback
1	Arm_210_1off	Open Y by Buback
1	OpenY_Undercarriage_Bracket_1off	Open Y by Buback

X Axis Parts

Quantity	File-Name	Comments	Diagram
4	pla_coupling_nophead-1piece_4off.STL	Alternative part by Nophead
2	x-180-z-bearing-plate_2off
2	x-360-z-bearing-plate_2off
2	x-360-z-bearing-plate-mirror_2off
1	xaxis-motor-bracket_1off	Alternative part by Rhys-jones
6	x-bar-clamp-m3_6off
4	x-bar-clamp-m4_4off
1	x-end-bracket_1off
4	x-vert-drive-nut-trap_4off
2	x-vert-drive-side-plate-180-end_2off
2	x-vert-drive-side-plate-360-end_2off_rebuild
2	x-axis-side-plate-nut-jig_2off

X Carriage

Two major issues affected the Open-X carriage: carriages occasionally "walk" up off the tracks, and inconsistent spacing of the undercarriage bracket occasionally allowed the extruder to move/twist laterally. Both of these issues were minimized through modifications by user Joe Bartolai. The OpenX Arm was shortened and an offset was added so that the bearing attached to it is centered on the rail. The OpenX undercarriage bracket was also modified by making the angle steeper where the lower bearings contact the rail and by increasing the spacing where the undercarriage bracket attaches to the carriage. Part models will be added soon.

Quantity	File-Name	Comments	Diagram
1	OpenX_Carriage_1off	Open X by Buback
1	OpenX_Undercarriage_Bracket_1off	Open X by Buback
1	OpenX_Arm_1off	Open X by Buback

Extruder

Currently not included in STL zipfile

Quantity	File-Name	Comments	Diagram
1	HerringboneDrivenGear	Alternative part by Rhys-jones
1	HerringboneDriveGear	Alternative part by Rhys-jones
1	Gregs_accessible_wades_v6	Alternative extruder by Greg-Frost
1	Gregs_accessible_wades_idler

Electronics Mounting

Quantity	File-Name	Comments	Diagram
2-5	prusa_modified_endstop_holder_2-5off	Prusa opto holder modified to have a thicker end	No picture yet
3	electronics_board_mount_opt	Created by RUG member SethG. Optional

Quantity of Materials Needed by Subsystem

Part Name	Frame	Z-Axis	Open Y-Axis	Open X-Axis	X-Carriage	Extruder	Total
M3 Cap Screw 20mm	4	-	-	8	-	4	16
M3 Cap Screw 25mm	1	8	-	9	2	-	24
M3 Nut	-	-	-	-	-	-	-
M3 Nylok	1	8	-	9	2	-	24
M3 Washer	6	16	-	26	3	4	63
M4 Cap Screw 16mm	-	4	-	4	-	-	8
M4 Cap Screw 20mm	-	1	12	9	14	-	36
M4 Cap Screw 40 mm	12	-	8	28	-	2	44
M4 Dome Screw 30 mm	-	-	-	-	-	3	3
M4 Nut	-	-	2	12	-	2	12
M4 Nylok	8	1	10	31	14	1	57
M4 Washer	28	6	38	102	34	14	202
M8 Nut	72	8	4	4	-	-	88
M8 Washer	72	8	4	-	-	4	88
3/16" Fender Washer	8	-	-	8	-	-	16
Bearing 8x22x7 mm	-	-	-	-	-	3	3
Bearing 4x13x5 mm	4	-	12	4	10	-	30

See Also

• Open Hybrid Model Build Guide
• State College User's Group

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