Tuesday, September 23, 2014

Building my own 3D printer based upon Prusa and Mendel90 designs

I have been trying to build my own 3D printer.  I am trying to use "off the shelf" parts as much as possible. I did end up buying X axis ends on eBay.  I designed and made my own stepper motor mounts.

Here is a picture of the frame as I first assembled it.  The blue tape is so I can write on it for my hole markings.

Right now I am stuck on the lead screws for the Z axis.  The holes for the nuts are .55 inches across and they are supposed to be for 8mm nuts.  But 8mm nuts are .51 inches and 5/16 nuts are .5 inches. Both nuts rotate freely in the hole as the hole is for a nut that is .55 inches across.  The nuts that are found on hollow electrical threaded pipe commonly used in table lamps fit perfectly.  One of these is seen on the right side below.  However that would be hard to adapt that to the 5mm stepper motor shafts!


Some of the other problems I have faced so far include:

The stepper motors came with gears on them.  I used a gear puller to remove the gears.  When I connected the motors up to the lead screws I discovered that their shafts were bent so much that the top of the lead screws rotated in about a one inch circle.  I had to get new stepper motors.  When I installed the new stepper motors I discovered that the problem was actually the 5mm to 8mm shaft coupler!  It was drilled so crooked that it causes the lead screw to rotate.

As I said above the holes for the nuts in the X axis ends are .55 inches across and both 8mm and 5/16 nuts spin freely in them.  I might have to make my own "nuts" out of aluminum using a 5/16 tap.   Wow was I really off on that one.  It turns out that the nut holes on the top are .55 inches but the nut holes on the bottom are .51 inches!  So I was just looking at the wrong nut holes.

When I assembled the Y axis carriage and slid it towards the back it returns back to the front on its own!  That is because the rod spacing varies by 1/8 of an inch causing the bearings to bind.  I enlarged the holes on the back side and adjusted it so the platform moves smoothly now.

The 8mm bearings are terrible.  They do not move smoothly and they loose some of their balls every time I remove them from the rods.  I might have to replace them with better ones from another vendor?

Some of the 8mm rods are from printers and scanners.  The one on the right side is a tiny bit bigger than 8mm.  I used emery cloth to take it down a little bit so that the bearings move smoothly.

I used 10mm rods (from scanners) and bearing for the Y axis.  They work so much better than the 8 mm bearings.  However their outside diameter does not fit either 1/2 or 3/4 pipe holders.

The spacing of the z axis guide rods varies by 1/8 of an inch from the top to bottom.  That is a tricky measurement since there are rod holders at the top and a home made motor mount at the bottom.  I will have to move the rod holders in about 1/16 of an inch on each side to fix the problem.

While testing the Y axis I realized that the gantry is at the wrong position.  When I move the Y carriage back the print head will not reach the front edge.  I had to unbolt the gantry and move it forward one inch to resolve the problem.  It was six inches from the back edge but it is now 7 inches from the back edge.

The Y axis bearing holders hits the stepper motor that is mounted under it.  That is because I mounted the stepper motor all the way to the right.  It needs to be moved at least an inch to the left. It also needs to be moved so that the wires to the Y platform can be run in the center, the drive belt is there currently.

I cannot put nuts on the Y axis hot plate screws.  The bearing holders are too close to the front and back edge of the Y platform so there is not enough room to put the nuts on the hot plate screws.  I will have to move the Y axis bearing holders 1/4 inch further from the front and back edges.

I tried to mount the Arduino Mega, but like all Arduino's the mounting holes are an afterthought.  I wanted to have screws come through the plastic, then a nut, an insulator then through the Arduino then a last nut.  However the nuts cannot be on that side.  I am trying to rework it to use the standoff's that are used for ports on a PC.

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