Open Hybrid Mendel

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Open Hybrid Mendel (OHM)

Release status: Working

A hybrid between Prusa and Mendel models using several improved pieces from the community
CAD Models
External Link


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. This, and the OpenY

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.


Download Zip: File:OpenHybridMendel

Frame and Z Axis Parts

Quantity File-Name Comments Diagram
6 camiel_frame_vertex_6off Alternative part by Camiel Camiel frame vertex 7off.JPG
2 z-prusa-motor-mount_2off Pm-z-motor.jpg
2 z-bar-top-clamp_2off Z-bar-top-clamp 2off.JPG
4 prusa_bar-clamp_2off Pm-bar-clamp.jpg
8 y-bar-clamp_8off Y-bar-clamp 4off.JPG
1 y-idler-bracket_1off Y-idler-bracket 1off.JPG
1 y-motor-bracket_1off_mod3-15 Modified by PSU Reprap Collective Y-motor-bracket 1off mod3-15.JPG

Y Carriage Parts

Quantity File-Name Comments Diagram
4 bed-spring_4off Bed-spring 4off.JPG
1 8mm_Belt_Harness_1off Open Y by Buback, modified by PSU Reprap Collective 8mm Belt Harness 1off.JPG
2 8mm_Crossbar_Mount_2off Open Y by Buback 8mm Crossbar Mount 2off.JPG
2 Arm_90-180_2off Open Y by Buback Arm 90 - 180.JPG
1 Arm_210_1off Open Y by Buback Arm 210.JPG
1 OpenY_Undercarriage_Bracket_1off Open Y by Buback OpenY Undercarriage Bracket.JPG

X Axis Parts

Quantity File-Name Comments Diagram
4 pla_coupling_nophead-1piece_4off.STL Alternative part by Nophead Pla coupling nophead.JPG
2 x-180-z-bearing-plate_2off X-180-z-bearing-plate 2off.JPG
2 x-360-z-bearing-plate_2off X-360-z-bearing-plate 2off.JPG
2 x-360-z-bearing-plate-mirror_2off X-360-z-bearing-plate-mirror 2off.JPG
1 xaxis-motor-bracket_1off Alternative part by Rhys-jones Xaxis-motor-bracket 1off.JPG
6 x-bar-clamp-m3_6off X-bar-clamp-m3 6off.JPG
4 x-bar-clamp-m4_4off X-bar-clamp-m4 4off.JPG
1 x-end-bracket_1off X-end-bracket 1off.JPG
4 x-vert-drive-nut-trap_4off X-vert-drive-nut-trap 4off.JPG
2 x-vert-drive-side-plate-180-end_2off X-vert-drive-side-plate-180-end 2off.JPG
2 x-vert-drive-side-plate-360-end_2off_rebuild X-vert-drive-side-plate-360-end 2off rebuild.JPG
2 x-axis-side-plate-nut-jig_2off X-axis-side-plate-nut-jig 2off.JPG

X Carriage

Quantity File-Name Comments Diagram
1 OpenX_Carriage_1off Open X by Buback OpenX Carriage.JPG
1 OpenX_Undercarriage_Bracket_1off Open X by Buback OpenX Undercarriage Bracket.JPG
1 OpenX_Arm_1off Open X by Buback OpenX Arm.JPG


Currently not included in STL zipfile

Quantity File-Name Comments Diagram
1 HerringboneDrivenGear Alternative part by Rhys-jones HerringboneDrivenGear.JPG
1 HerringboneDriveGear Alternative part by Rhys-jones HerringboneDriveGear.JPG
1 Gregs_accessible_wades_v6 Alternative extruder by Greg-Frost Gregs accessible wades v6.JPG
1 Gregs_accessible_wades_idler Gregs accessible wades idler.JPG

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 Electronics board mount.JPG

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 - 13 2 - 24
M3 Nut - - - - - - -
M3 Nylok 1 8 - 13 2 - 24
M3 Washer 6 16 - 34 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 22 - 2 44
M4 Dome Screw 30 mm - - - - - 3 3
M4 Nut - - 2 8 - 2 12
M4 Nylok 8 1 10 23 14 1 57
M4 Washer 28 6 38 82 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

State College RepRap Users Group
S.C.R.U.G. Main · The Make Space · Intercollegiate Future Society · Wiki Help
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