Ronthomp Mendel
Think, Draw, Print. 3D printers ROCK!

Under Construction

Written and maintained by Ron Thompson.
December 15, 2011


Read this entire step before you start.

This is what you are making, above. Most photos can be clicked to see a much larger version.

The triangle is held together with  pan head machine screws, flat washers and nuts. Phillips heads are recommended. Use flat washers under the heads of the screws. Make sure the nuts align in the nut trap recesses, so they will pull in easily. Tighten enough to pull in the nuts, then back off. The triangle parts will need to slide for adjustment.

*DO NOT OVER TIGHTEN. If you hear cracking noises, you went too far. If a nut just won't go in, you can carefully heat it with a soldering iron and push it in. This is a last resort and shouldn't be needed.

3D printed parts usually need some clean up to be their best. Use a razor knife or a hobby knife to trim any stray strings. Holes may need to have a drill run through them.

Make sure not to drill any holes that are expected to self tap when you run the screw in.

An example of this is on the Z motor mount. The vertical smooth rod is held by a captive clamp. The 6-32 screw should self tap. There is a nut trap (a recess for a nut) in case you strip it, but you shouldn't need it. More on this later.


There are also 2 nut plates not shown in the image above. There is a visual part list here:

The nut plates go under the nuts that hold on the Z Motor Mount so you don't have to fumble with a wrench.

Start by laying out the plastic parts for one triangle as shown above. The side plates should go on the outside to prevent any possible interference with a large print. Assemble all 12 screws loosely. The parts should be able to move at this point.

Parts needed for this step:
Crown vertex, 1
Side plate, 2
Footed vertex, 2
Z motor mount, 1
Nut plate, 2
6-32 x 1 1/4" Pan head machine screws, 12
6-32 Nuts, 12
#6 Flat washers, 12

Tools needed for this step:
Phillips screwdriver

Once you have everything you need, assemble the triangle.

When you have one triangle assembled, go ahead and make the second one.

You should now have two loose triangles.

Step 2, Assemble the frame.

Parts needed for this step:
Triangle assembly, 2
Y axis motor mount, 1
Bar clamp, 4
Threaded rod, lower, 5/16 -18x 12", 4      
Threaded rod, top, 5/16-18 x 16", 1      
Nut    5/16-18    30      
Flat washer    5/16"    30      
608 skate bearing, 2            
Tools needed for this step:
Open end wrenches, 1/2", 2

There are five threaded rod assemblies that tie the two triangle assemblies together. Each is shown below. Don't worry about exact dimensions at this point, but assemble the rods to look like the diagrams.

Upper idler rod assembly.

Lower idler rod assembly.

Motor rod assembly. Added the Y motor mount.

Top rod assembly

Once you have the rods assembled as shown, it's time to add the triangles.

Add the washers and nuts as shown. Leave them loose to aid further assembly.

Do the same for these rods.

Add the other triangle and washers and nuts.

Adjust the end nuts so there is about an inch of thread sticking out past the nuts. tighten the nuts on each side of the triangle finger tight. You want them snug in the triangles, but you will be readjusting them, later. Do this for all the threaded rods.

Step 3, Adjust and tighten the triangles.

*DO NOT OVER TIGHTEN. If you hear cracking noises, you went too far.

Start by making a couple of spacer jigs. Use whatever you have on hand.

I suggest a piece of wood. 1/2" plywood or a furring strip will work.
They will each need two holes to fit over your threaded rod. Space the holes on one at 15" and the other at 13 1/2". Mark them with the length and a center mark. A thinner center mark than is shown would be better.

*These measurements were taken off my Prusa Mendel. It is possible to increase the Ronthomp Mendel frame to its maximum extension, but it's untested. Some parts, like the smooth rods, will need to be increased in size. This may upset the part economy as more full length rods may be required. (it may increase the left over scrap.)

This is my handy jig made from parts I had on hand. My garbage can makes the perfect work platform. Maybe yours will, too.

Using the 15" jig, put the holes over the upper pair of threaded rods as shown above. (The threaded rod should be sticking out about an inch and the nuts should be finger tight.)
The Z axis motor mount needs to be centered between the holes in the jig. I put tape on it and marked a center line. Future parts will have a center line in the part.
Line up the center marks, hold the parts level with each other and snug the screws. Recheck the alignment and adjust as needed. When the Z motor mount is centered and even with the mating parts, tighten the screws.

Next, use the 13 1/2" jig on one side as shown above.
Roughly center the side plate and hold the parts level with each other and snug the screws.  When the side plate is even with the mating parts, tighten the screws. No need to measure for center, an eyeball estimate is good enough.
Repeat for the remaining side of this triangle.
This side should now be completely tightened and aligned.
Repeat this for the other triangle.
We will verify the squareness after the smooth rods are installed.
Step 4, Adjust the Width.

You can make a wooden jig (stick) cut to length, but I find it is just as easy to use a tape measure.
I am following the dimensions of my Prusa Mendel, and it's about 9 1/4" inside to inside on the footed vertexes and the same at the top.

Start with the Y motor end, upper rod, as above, and keep the threaded rod pretty much centered. Adjust the nuts until the footed vertexes are 9 1/4" apart and the nuts on either side of the footed vertexes are tight (firm, but do not crush the plastic).
 Then do the same for the lower rod.

Go to the opposite end (where the Y idler bearing is) and do the same thing again.

When all the bottom rods are tight, then tighten to top rod using the same procedure.

Continue to page 2, The Y axis.

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