Tuesday, December 3, 2013

Building the 3DR “Simple” Delta Printer, Part II

This is the fifth part in my series on a delta printer that I designed, which started life as just a few changes from RichRap’s similarly named 3DR RepRap Delta Printer. Here are the previous posts:

3DR “Simple” Delta Printer, Part I
3DR “Simple” Delta Printer, Part II
3DR “Simple” Delta Printer, Part III
Building the 3DR “Simple” Delta Printer, Part I
Building the 3DR “Simple” Delta Printer, Part II
Building the 3DR “Simple” Delta Printer, Part III

In my last blog post, I covered printing all the parts and assembling the top and bottom frames. The next step is to disassemble your Printrbot Simple as you’ll need the various vitamins to continue this build.

Finishing the Top Assembly

In this step you’ll mount the Printrboard and end-stop switches. Use two M2.5 x 10 screws and nuts for each micro switch. You’ll want to ensure the free end of the lever is towards the center, as shown here.

Next use two M3 x 10 screws to attach the Printboard to two of the posts. The board will need to be attached next to the wing with the extension for the power connector, as shown at the top-right of the photo above. Plug the end stops into the correct slot of the Printboard as shown above. The center socket is attached to the micro switch in the upper-right corner.

The power connector is designed to be held in place with the nut on the back. Unscrew the nut and slide the wires through the slot, with the nut on the inside. Place the nut into the slot and then turn the power connector to screw it into the nut. Once this is tight you can plug the square power connector into the Printrboard.

Next, each smooth rod is held in place with an M4 x 10 screw and nut. Place one M4 nut into each of the six slots next to the smooth bar holes. Then screw in an M4 x 10 screw so it’s all the way into the nut, but not projecting into the smooth rod hole.

Adding the Carriages

Add one LM8UU bearing to each smooth rod. Then use four zip ties to attach one carriage to each pair of smooth rods. The carriage should be oriented so the rod connections are on the top, like this:

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Make sure the zip ties are very tight.

Installing the Top

Now install the top, with the Printrboard facing down. Carefully slide the parts over the extrusions, and then over the smooth rods. Work it down until 20 mm of extrusion is extending out of the top of each corner. Then lock in place with an M5 x 8 screw and washer that attaches to a T nut in the extrusion. Finally, tighten the six M4 screws on the top corners that hold the rods in place.

Installing the Stepper Motors

The cords on the stepper motors are much shorter than you’ll need. Obtain some 26 gauge stranded wire. You should use the same four colors as on the original motors: red, green, blue, and black. I chose to use new wire and connectors, and also to install connectors on the bottom between the stepper motor and where the wire enters the extrusions. This will make it easy to change stepper motors if I need, but I’m not sure it was that important. In any case, you’ll need to cut the wires on the stepper motors and either splice in new wires, or use a connector like the one shown below.

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The connectors I used are Molex 1625-4PRT .062” 4-pin connectors, although you can use other connectors. These have both a male and female part, and the pins crimp to the wires. To ensure a secure connection, I also soldered the wires to the pins after crimping. Ensure you have the colors matching as shown before you push the pins all the way into the body:

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For the wires that will be attached to the Printrboard, cut wires more than long enough to go through the extrusions and to the Printrboard (you can cut them to length later when you know exactly how long you’ll want them).

Once you have the connector attached to the long wires, fish the cut ends of the wires through the rectangular hole on the bottom part and into the hole in the extrusion. Keep feeding them until they come out the top.

Mounting the Stepper Motors

Cut three lengths of Spectra fishing line. RichRap recommends two meters each. It’s better to have them too long than too short. Thread one end through the holes in the spool so it looks like this:

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The two lengths of string coming out of the spool should be about the same length. Next wrap the string around the  spool in opposite directions. Each one should be wrapped eight times around. Secure in place with a piece of tape. Make sure you wind all spools the same way.

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The nuts and screws can be a little tricky to install on the spools. Using a round object inserted in the hole can help hold the nut while you place the screw, as shown here:

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Now attach the spool to the stepper motor shaft. There should be a small gap of about 1 mm between the spool and the stepper motor. Tighten each of the three set screws in turn so you keep the spool aligned with the shaft. Make sure the set screws are all quite tight. You might wish to place some thread lock on the screws to keep them from coming loose.

Finally, attach the stepper motors to the lower mount and connect the cables. It will look like the following picture once you’ve finished string the fishing line. Remember to install the bottom end cap on each extrusion so you don’t scratch your work surface.

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For now, tape the fishing line to the top surface of the base:

Running the Fishing Line

First create the idler assemblies. Each one consists of an M5 x 20 button head screw, two 625ZZ bearings, one M5 nut, one M5 washer (a wider penny washer would be better, but I didn’t have any handy), and finally an M5 T nut:

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You’ll need three of these assemblies, with one for each extrusion. Insert these into the slot closest to the center, at the top of the extrusion. You can either leave the T nuts loose or tighten them ever so slightly to keep them in place. Make sure the regular M5 nut is very tight against the back of the bearings. If it’s not, the fishing line could work it’s way down between the two bearings and get stuck.

Now tape each carriage so it’s towards the top of the tower, but with enough distance so you can get in there to tie the fishing line to the carriages. You’ll want it to look like this when you’re finished:

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Note: Although this photo shows the rods attached to the carriage, it’s easier to tie the fishing line to the carriages before attaching the rods.

The fishing line shown on the right loops over the top of the idler bearing you installed and then down to tie onto the top hole of the carriage. While the other side of the line coming from the spool ties to the bottom hole in the carriage. Try to make these somewhat tight when you tie them on.

Then push up on the idler bearing as much as you can and tighten them in place. The strings should be fairly tight, but will loosen a little after some movement, so you’ll need to re-tighten every now and then.

At this point you can remove the tape holding the fishing line to the spools and move the carriage up and down to ensure they work smoothly without any binding.

Making the Rods

I found a really nice jig on Thingiverse by ichibey: http://www.thingiverse.com/thing:166605. Print out two of these and add two M3 x 20 screws from the back. Then use two M5 x 10 screws to attach them to one of the extrusions (using two T nuts, of course):

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As you can see, these two printed parts make it really easy to set the length exactly the same for all six rods. If you’re using 200 mm rods, like I am, the carbon fiber tube needs to be cut into six lengths of 160 mm each (the printed adapters and joints add 40 mm to the total length). I used 5-minute epoxy to glue the tubes into the printed adapters (shown in yellow above), and the Traxxas joints into the other end. Do one rod at a time, and before the epoxy sets, fit the assembly onto the jig as shown above and adjust so it’s a loose fit. Also make sure the flat parts of the Traxxas joints line up with each other.

Take your time on this step. It’s very important to have all six rods exactly the same length for the best performance of your printer.

Attaching the Effector

Once you’ve finished all six rods, you can move on to attaching them to the carriages and to the effector platform. First attach them to the platform, as shown here, using M3 x 16 screws and nuts (this is looking at the bottom of the platform):

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Next attach the other ends of the rod to the carriages with M3 x 16 screws and nuts, as shown here (make sure the attachment points on the platform are at the bottom, as shown here):

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I used a tape roll on the print bed to help hold it in place, which made the work a little easier.

Print Bed

To make things a little easier, I designed clips that allow leveling the bed and slight adjustments between the bed and the nozzle, shown in the previous photo. These clamps use three of the bed leveling springs from the Printbot Simple, along with M3 x 20 screws and nuts. The nut slot under the frame is tapered, which allows you to trap the nut firmly in place. Before installing the clip, add the nut to the bottom side of the frame and then screw an M3 screw all the way in, pulling the nut firmly in place. Then remove the M3 screw.

Attach the clips to the print bed and then use an M3 x 20 screw through the clip, and then through the spring, to hold the bed in place.

Next Up, Extruder

There are two more parts I expect to publish. Next up will be building the extruder and hot-end mounts, and finishing up the wiring. The final part (I think), will be on installing new firmware onto the Printrboard and getting the printer running.

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