SAE Prusa Mendel

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Prusa Mendel

Release status: working

SAE Prusa Mendel is an offshoot of Prusa Mendel.
CAD Models
External Link

SAE Prusa mendel is an offshoot of the Prusa Mendel, only difference currently is it only uses 1 screw size (SAE #6 instead of metric M3 and M4), and only uses 608 bearings. Spacexula did the conversion, and is currently trying to maintain this branch.



The Prusa Mendel is on hosted github:

You can follow the changes on Changelog

You can sign up for github for free and fork the project to begin working on it.


Bill of Materials

The SAE Prusa Mendel BOM is slightly different than Metric Prusa Mendel, but as close as possible.

(in works, not complete yet)

Printed Parts

Quantity Description Type Comments Diagram
2 coupling RP Pm-coupler.jpg
3 endstop-holder RP
1 x-carriage RP Pm-x-cariage.jpg
1 x-end-idler RP Pm-x-idler.jpg
1 x-end-motor RP Pm-x-motor.jpg
1 y-motor-bracket RP Pm-y-motor-bracket.jpg
2 z-motor-mount RP Pm-z-motor.jpg
4 belt-clamp RP Pm-belt-clamp.jpg
8 bar-clamp RP Pm-bar-clamp.jpg
2 rod-clamp RP Pm-rod-clamp.jpg
2 pulley RP Pm-pulley.jpg
4 frame-vertex with foot RP Pm-frame-vertex-foot.jpg
2 frame-vertex RP Pm-frame-vertex-footless.jpg
12 pla-bushing RP-PLA check your build file, the file makes either 4 or 12 Pm-bushings.jpg

Non-Printed Parts ("vitamins")

Quantity Description Type Comments Part Numbers
1 box (100) 5/16" nuts Fastener 95462A030 (1 box)
1 box (100) 5/16" washers Fastener 90126A030 (1 box)
1 box (100) #6 washers Fastener 90126A509 (1 box)
1 box (100) #6 1" screws Fastener 90272A153 (1 box)
1 box (100) #6 nylock nuts Fastener 90631A007 (1 box)
1 box (100) 5/16" Fender Washers Fastener 91090A111 (1 box)
3 608 Bearing Sets Bearings 5972K91 (?)
1 box (100) M3x10 bolt Fastener Motor Mounting 92005A120 (?)
2280 mm ~90"/7.5' Neoprene Belting .200" Pitch, 1/4" Drive Belt This is not compatible with the T5 pulley in the git repo (see below) 7959K24 (?)
1 9 foot smooth rod (NOT GALVANIZED) X,Y,Z bars 8893K41 (3 foot sections, $4.30, no straightness spec, one arrived bent)

8888K41 (3 foot sections, $8.53, 0.005"/foot straight)

both are +/-0.0005" and may bind on bronze bushings if oversize

1 21 foot threaded rod Frame 98841A030 (3 foot sections)
4 7/16" x ~1" springs optional, or from a spring loaded pen
1 Wade's Geared Extruder (or any other compatible extruder)
5 Nema 17 Stepper Motors
1 Standard Mendel electronics + endstops This can be RAMPS, Pololu Electronics, Gen6, Gen3, or anything else compatible

Aquiring Drive Belts

(No need to split belts, no continuous Z axis belt)

  Belt 1- 870mm ~34.25"/ 2.8'
  Belt 2- 1410mm ~55.5"/ 4.7'

The 0.2" pitch XL belts are very close in pitch to the T5 metric belt (5mm = 0.197") so the XL belt will run on a T5 pulley. The ratio of tooth to gap size is different and the T5 pulley (such as the one in the Prusa git repo) will have backlash as each time the pulley reverses the small XL tooth will slide in the larger T5 gap of the pulley before it starts moving. If you use XL belts print an XL pulley such as the one on Thingiverse.

You will need to adjust the X/Y_STEPS_PER_MM in your firmware to match XL pitch.

Acquiring Smooth Rod

Do not get Galvanized Rods, they are much rougher. Drill rod (also called tool steel or silver rod) is smoother and made to tighter tolerances. Look for a straightness tolerance if mail-ordering (e.g. 0.005"/foot) or order extra and be prepared to cut around bent sections.

If you want to use bronze (also called brass or oilite) bushings in holders note that even drill rod spec is +/-0.005 while bushings are +0.0010/-0, so an oversized rod will not work smoothly with a bushing. Precision ground rods are +0/-0.0003 and work much better with bushings. 8mm precision ground rod is cheaper than 5/16" so going with an 8mm smooth-rod system makes sense with bronze bushings. VXB Bearings has 8mm rods in 495mm, 406mm and 330mm which are suitable.

Use Standard Mendel lengths for cutting 420x2 406x2 and 330x2.

The smooth rod is cut into varying lengths, therefore, its common to acquire in 3 foot sections.

If you have 3x 3ft smooth rod 8893K41

Rod1: 420mm,330mm                 16.5",13"
Rod2: 420mm,330mm                 16.5",13"
Rod3: 406mm,406mm                 16",16"

Aquiring Threaded Rod

The rods should be cut (by you) to the following sizes, in mm (the original sizes) or in inches for the SAE purist who wants to avoid little bits at the end.

To the right are "close enough" lengths in inches that will minimize number of cuts. (Note: Cut one of the threaded rod sets listed below, not all!)

If you have 3 ft lengths,

3' Rod1: 440mm,440mm              18",18"
3' Rod2: 440mm,370mm,50mm         18",15",2"
3' Rod3: 370mm,370mm              15",15"
3' Rod4: 370mm,294mm,210mm        15",12",9"
3' Rod5: 370mm,294mm,210mm        15",12",9"
3' Rod6: 294mm,294mm              12",12"
3' Rod7: 370mm                    15"

At Lowes in some towns you can get 4 ft length allowing you to combine Rod7 and 3 into 1, 4 foot rod, or you could use 3 four foot lengths and 2 three foot lengths for a less wasteful (and probably cheaper) set as follows:

3' Rod1: 440mm,440mm              18",18"
3' Rod2: 440mm,370mm,50mm         18",15",2"
4' Rod3: 370mm,370mm              15",15",15"
4' Rod4: 370mm,294mm,210mm        15",12",9",12"
4' Rod5: 370mm,294mm,210mm        15",12",9",12"

At Menards or Ace Hardware you can get 6 ft rods. You can use three of them as follows:

6' Rod1: 440mm,440mm,440mm,370mm,50mm         18",18",18",15",2+"
6' Rod2: 370mm,370mm,370mm,370mm,294mm        15",15",15",15",12"
6' Rod3: 370mm,294mm,294mm,294mm,210mm,210mm  15",12",12",12",9",9" + extra

About the Electronics

The Prusa Mendel uses the 4 drivers in the standard Mendel electronics package to drive 5 motors by using "two steppers wired in parallel to one driver" [1].

Where To Purchase

See the Mendel Buyers Guide for information on where to purchase all of the parts needed.

Printed Parts

A printed set of Prusa Mendel parts

Printing a Prusa on a Mendel

An easier option then individually printing each part if you are printing Prusa on a RepRap Mendel is the pre-assembled build file containing the Prusa parts. With this option you only need to print the Mendel plate and the PLA bushings to get a complete Prusa Mendel:

Printing a Prusa on a CupCake CNC

There are also pre-assembled build files available to fit your CupCake CNC's build area (download using right click => save as)


  • These plates are 85x95mm in size.

Plates for the MakerBot (The plates have changed, these print times are no longer accurate):

Printing a Prusa on anything else

Last but not least, if you have a machine that doesn't fit into any of the previous options all the .stl files necessary to print a Prusa Mendel are available on the PrusaMendel Github where you can download them and print them individually.

Buy the printed parts



Assembly of an SAE Prusa Mendel should proceed in exactly the same order as the original Prusa Mendel. Consult the Prusa Mendel Assembly Guide for more information.


See Also

External Links