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Ponoko RepRap - Fitting The Bed and Z Chain

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With the outer framework in place, we can now add the Deposition bed. This comes in two pieces; a Bed Frame and the Adjustable Bed. These are held together under tension and can be adjusted so that the actual deposition surface is kept parallel to the Extruder Nozzle. The lasercut Adjustable Bed can be made of MDF, 8mm clear acrylic - which really needs covering with hardboard - or cardboard. Do not deposit on the cardboard bed if you have one; it is intended for use as a template to cut your own Adjustable Bed with.

Apologies to "early adopters," as your Bed Frame may be a tight fit - the jig used to space the frame was a little short initially. You can compensate by using M3 25mm machine screws instead of M5 ones as long as you have big enough washers to cover the mounting holes.

Do not fit the Z Opto Flag yet. It is easily broken and we'll wait until it is necessary.


The deposition Bed is lasercut from 8mm MDF (medium density fiberboard). It's fairly strong, has no wood grain, doesn't warm, and accepts deposition well. The Frame is lasercut from 8mm acrylic and has a hole in the center, which space is used for parts. The bed is mounted on <part>three M8 60mm screw</part>s in three M8 holes arranged in a triangle. Orient the Bed on the Frame such that you can read the laser-etched "RepRap" and "Y-axis" at the same time. There is a notch in the side of the Bed which lines up with captive nut holes in the Bed Frame. The three M8 holes should now be lined up.


Put a <part p="three M8">washer</part> on each screw, insert it through the M8 hole, and fix it with a <part p="three M8">washer</part> and <part p="three M8">nut</part>. We want the deposition bed to have a little bit of "give" so that crashing the extruder into the bed doesn't break either, so the bed is held up with a <part p="three">8mm i/d compression spring approximately 16mm long</part>.


Place the deposition bed on the frame over the bolts. Tie it down with <part p="three M8">washer</part> and <part p="three M8">nut</part>s.


You'll need these parts to anchor the frame to the Z Axis.


Place the bed on the Z axis mounts. <repeat count="4">Put a <part p="three M3">washer</part>s on <part>three M3 25mm screw</part>s and insert them through the bed into the Z axis mounts. Fix with <part p="three M3">washer</part>s and <part p="three M3">nut</part>s. Repeat for the other three corners. </repeat>


The following tools will come in handy for gripping and cutting <part>2200mm of 4.5mm ball chain</part>:


You want to aim for a very snug fit on the chain, but do bear in mind you're going to destroy one link when you join the ends. There will be a tensioning mechanism later, but try to keep it tight now as things loosen off as they wear in.


Make the chain slack by taking it off the pulleys an looping it around the threaded rods. This gives you plenty of room for manoeuvring.


File the faces of the two end balls flat - do not saw them. If you can do so without grinding your fingers, feel free to use a Dremmel tool or similar.

Make sure you pick all pieces of swarf and cut link out of the centre of the ground balls.


Once you have the faces of the end balls filed flat, tin them with a light coating of solder. This makes them much, much easier to join.


Now hold the two tinned faces together and apply a soldering iron. Do not use too much solder or you will solder the link inside the balls solid too. Tidy up after with a file when cool.

One way of holding chain together for soldering:

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Another way of holding the chain together for soldering. Reverse the spring on a clothespin so the handles are pushed shut. Whittle them thinner so they fit between two balls. Cut a slot down the middle so the wire will fit into the slot.

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A similar trick can be achieved by cutting matching slots in the jaws of a metal bulldog clip such as are used on clipboards.


Now take the top off one of the Pulleys by undoing the M8 nut on top, put the chain under the flower-shaped rim, and thread the chain around the other pulleys. Prise the chain into the last pulley and secure the rim back down firmly with the M8 nut. Remember this trick when you need to trim the bed level later.

The finished chain fitted in place:

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