MendelMax

MendelMax

MendelMax is a new Open Source RepRap 3d printer designed by Maxbots and based on the Prusa Mendel. It is a true reprap, using printed brackets, but instead of using threaded rod for the structural elements it uses inexpensive aluminum extrusions. This gives a huge increase in rigidity for a minimal extra cost (Self sourcing will cost about $80 more than a standard Prusa when purchased from the recommended suppliers). The required extrusions are available world wide from a variety of suppliers.



In addition to the increased rigidity, the printer is much easier to assemble than a standard Prusa. Even an inexperienced builder should have no trouble building the whole frame in an evening, two at most. And along with the easy assembly comes easy hackability. Almost any part on the bot can be removed with just a few screws, so swapping out literally any part on the bot is now a trivial operation.

All that said, MendelMax keeps the best parts of the Prusa Mendel. The Prusa Mendel kept the frame of the Sells Mendel, but fixed the problems in the X,Y and Z axes. MendelMax builds on that by largely keeping the current XYZ axes, but completely redesigning the frame.

The X axis is taken stock from the Prusa Mendel, in fact we don't even specify a specific X axis design, there are several good ones available, including the various vertically-orineted X axis designs that many people are exploring lately. As long as it sticks to the defined standard spacing between the Z rod and the Z leadscrew, it will work fine with MendelMax. We also use the standard Prusa Y design, though we simplify it just a bit by making it easier to get everything aligned right. Z adds optional thrust bearings to support the weight of the axis (greatly reducing the problems with printed couplers), but this is a purely optional upgrade, and you can easily use the old design if you prefer.

Because MendelMax is primarily defining a new frame design, it is linear-bearing agnostic. I have used both LM8UU's and PTFE bushings and both work just fine. Brass or even printed bushings could be used, though I recommend avoiding the latter for highest reliability.

We also plan on offering a design for MakerSlide in the very near future. As soon as I can lay my hands on the parts I will provide updated parts to use MakerSlide instead of smooth rods on at least the X & Y (Z will be converted after testing to see if there is a benefit).

Links

• Lots of pictures, including of the assembled printer and several finished prints here.
• 3D PDF (View with Adobe Acrobat, most 3rd party viewers do not support 3d PDFs. Click on the image to view in full 3D, pan, zoom, rotate, etc.)

Community

• For more information, visit our FreeNode IRC Channel at #MendelMax (or ask in #reprap).
• Please join our Google Group.

MendelMax Store

Full MendelMax kits, MendelMax hardware kits and a variety of other parts are available now in the MendelMax Store. This store is run by Maxbots and your purchase help assure the continued improvement of the MendelMax.

Bill of Materials

These are the parts needed by the frame, as well as the linear rods for the XYZ axes and the leadscrews for the Z and the belts for the X & Y. You will also need the parts for your X and Y axes, which are not included here.

• The BoM listed on this page is for the frame only, and is suitable if you are upgrading from a Prusa. If you are building a new bot, see the Full BoM, with recommended part numbers, prices and recommended suppliers. Some suppliers only ship to the US (McMaster), but these should help you find suitable parts. This is for a high-end build, you can easily shave probably $100 off this total by shopping around a bit and cutting some reasonable corners. If you are concerned about whether a particular ocrner is reasonable to cut or not, ask in #mendelmax

Misumi is my preferred supplier for Aluminum extrusions. They have excellent prices, and have offices around the world. Below are the required parts from Misumi. A list of alternate extrusion suppliers is listed at the bottom of the parts list.

Misumi Parts

The following parts are for a "standard" sized MendelMax with a print area of roughly 215x235x190mm. The design is very scalable, so see scaling if you would like to build a larger or smaller bot.

Part Number	Quantity	Price Ea. (USD/Euro*)	Extended Price(USD/Euro)
HFS5-2020-420*	6	$2.39	$14.34	420mm extrusions
HFS5-2020-340*	4	$1.93	$7.72	340mm Extrusions
HFS5-2020-300*	4	$1.71	$6.84	300mm Extrusions
HNKK5-5	1	$19.32	$19.32	T-Slot nuts for 5mm screws, bag of 100
HTJ5**	4	$.62	$2.48	Self-tapping screws for blind joints
Total			$50.70

* You can substitute part number HFSB5-2020-NNN if you prefer black annodized extrusions instead of clear (silver) anodized. Black anodized extrusions are $8.80/meter instead or $5.20/meter.

** You can subsitute a M5 10-20mm button head screw such as McMaster # 92095A214. It must be a screw EXACTLY like that (other than length possibly). Other screw types suchs as a Phillips head or other screws will almost certainly not work. The screw head needs to fit into the extrusion slot, and anything bigger than those will not work. You MUST use a washer or you risk breaking your extrusion. If you go with this option, you do not need the Torx 25 screw driver. Unless you already have these screws on hand or don't mind buying a box of them, you are probably better off just buying the Misumi screws.



Misumi's website sucks, for the easiest time, I recommend calling in your order to your local Misumi office.

Optional Misumi Parts

You can get these parts cheaper from Stock Drive Products (SDP-SI). See my Choosing Belts and Pulleys guide for some suggested parts. If you prefer, you can order these parts from Misumi instead.

Part Number	Qty.	Price Ea.	Price Extended	Description
GBN 994 2GT-60	2	6.60	13.20	Timing Belt
GPA32GT2060-A-P5	2	14.90	29.80	Anti-backlash Pulleys

You can use standard printed pulleys or other types of pulleys, but GT2 or GT3 pulleys/belts are recommended for the best print quality.
*Misumi charges the same price in either USD or Euros

Additional parts

Part	Qty	Comments
M5 10mm screws	100	You need about 84, but it is far better to buy them in packages of 100
M5 or #10 Washers	100	Whichever is cheaper
M8 or 5/16" Smooth rod	3 meters/yards	Drill Rod or Stainless is recommended, do not use Zinc coated
M8 or 5/16" threaded rod	1 meter/Yard	Stainless or plain steel recommended, do not use Zinc coated
M8 or 5/16" Nuts	6	Stainless or plain steel recommended, do not use Zinc coated
M8 or 5/16" Screws/bolts, 25mm/1" long	2	Idler bearing Mounts
608ZZ bearings	4	Idler Bearings, 2 per axis for best results

Additional Tools

In addition to normal screwdrivers and such, you will need the following tools to build your MendelMax:

• A hand drill or preferably a drill press and a 6mm or 1/4" drill bit.
• An M5 tap and tap handle. I strongly recommend this tap, even if you already have an M5 tap. You have to tap 16 holes, and it takes a fair amount of effort to get them all done. This tap is designed to minimize the force required. I have used both this tap and a normal one and trust me, it is worth the couple extra dollars.
• A Torx T-25 screwdriver. You need a driver that is less than 6mm diameter for at least the last 20mm.

Alternate suppliers

A list of recommended alternate suppliers is available at Alternate Suppliers. Please add any favorite suppliers to the list.

Printed Parts

You can download the STLs to from Thingiverse.

Assembly Instructions

There are a few things that need to be done in the correct order, so it is best not to just try to put everything together randomly.

If you want to build your bot before I post the instructions, please post to the Google Group or ask in the #mendelmax IRC channel on Freenode.net.

In the meantime, here is a rough draft of the instructions, that should be enough to get the basic frame assembly complete.

• Important: Any place where you use a screw through the plastic, be sure to use a washer on the screw to spread the load.

• Tap both ends of the four 300mm extrusions and two of the 420mm extrusions, and one end of each of the 340mm extrusions.
• Use the Top Rod Jig to drill holes to drill holes through one side of the two 420mm extrusions with the tapped ends. You want to drill from the same side on both ends. You will drill through the center of the extrusion, so later you can reach a screw head behind the extrusion (see the pic in the lower left corner here: http://us.misumi-ec.com/pdf/fa/PDFViewer.html?catalog=Metric2010&page=2389 (also available here)).
• Partially screw the self-tapping blind joint screws into the non-tapped end of each of the 340mm extrusions. Leave them about 4-5mm from fully seated.
• Find the four Lower Vertex Middle pieces, and attach each one to the opposite end of the 340mm extrusions. You will use 1 M5-10 screw and T-slot nut in one of the slots, and one screw through the hidden hole in the printed part into the tapped end of the extrusion.

• On two of the four 300mm extrusions, insert 2 T-nuts into one side of each extrusion, and one nut into the opposite slot. These will later be used to attach the motor or belt idler and the Y rods
• Use t-nuts to attach the two 300mm extrusions to the two diagonals. Be sure that the side with one inserts T nut is on the outside.
• Attach the two Lower Vertex pieces. Use two T nuts to attach to the diagonal extrusion first, then screw into the ends of the 300mm extrusions
• Repeat the previous three steps with the other end.

• Insert two t-slot nuts in one slot each of two of the untapped 420mm extrusions.
• Loosely attach the two ends together using the two Top Vertex Y pieces. These should be right at the top of the extrusions.
• Attach the two ends together using the untapped 420mm extrusions. The two inserted T nuts should be on the lower outsides of the bot.

• Insert the four Top Vertex X pieces into the diagonal extrusions. Insert the screws and nuts in the other end, but leave them loose.
• Insert the two remaining 420mm extrusions (these should be tapped and have holes drilled though them). These will slide over the blind-jopint screws and the nuts already inserted in the Top Vertex X pieces above.
• Line up the holes drilled in the extrusions and the blind joint screws, and tighten the screws, as well as those on the Top Vertex X Pieces.

• Insert two T slot nuts into the top slot of the top extrusions. These are not needed for the included parts, but will be used to mount a filament spool (I have not posted this parts yet, but will do so soon).
• Attach the Z motor mounts, with two T-nuts and two screws into the ends of the extrusions.

Smooth and threaded rods

X ~445mm depending on your X ends.
Y 420mm
Z 405mm

In all cases, it is ok to use longer smooth rods, not shorter.

If your smooth rods are 1 meter long, you can just cut them however you want. If you have 36" smooth rods, you will need to cut one 445mm rod and one 405mm rod from each of two rods

If you use the thrust bearing, the Z leadscrew will be about 365-370mm. Place your Z motor in the motor mount and measure from the bottom of the motor shaft to the bottom of the lower Z rod mount, and make the threaded rods about 5mm shorter than that. If you do not use the thrust bearing, approximately 300mm should be fine.

Frequently Asked Questions

Q: Can I use 80/20 brand extrusions?
A: Absolutely. I recommend Misumi because of their outstanding prices (typically 1/2 the cost of most other suppliers) and the fact that they cut to length for free. If you prefer, 80/20 or another supplier's extrusions will work fine. See alternate suppliers for several suggested alternatives.

Q: But I can get 80/20 cheap off ebay, it must be a better deal, right?
A: No, not really. Even with their discounted "scratch and dent" extrusions, Misumi is a better deal. 80/20's "discounted" price is basically the same as Misumi's regular price, but instead of extrusions cut to the precise lengths you need, you will get 6 foot long stick that you will need to cut to length yourself. One of the main benefits of the MendelMax design is that it basically needs no adjustment after assembling. The accurate cuts assure that everything is square from the beginning, so later adjustments are simple. If you cut it yourself you risk losing that benefit.

Still, for our purposes, ANY 20 mm extrusions will work. If for some reason you prefer 80/20, Bosch-Rexroth, or any other supplier's extrusions over those from Misumi, they will work fine.

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