Replacement Armrest Pad for AKRacing Gaming Chair

The armrest for an AKRacing gaming chair.  The armrests appear to be used across multiple models.

The foam on mine broke apart and disintegrated within a few years.  The armrest is reinforced with a metal plate inside the foam.  However, this plate is obviously stamp pressed sheet metal, and was not post processed after.  It had a lot of sharp burrs that had apparently destroyed the foam around all the edges.  I also found that the screws that went in from the bottom were far too long, and also contributed to destroying the foam inside.  One of the screw induced cavities coincided with my preferred elbow position.

I modelled up a new pad to encase the metal plate extracted from the old foam one.  It is not really the same shape as the foam original, and mostly follows the contours of the plate itself.  The overall dimensions are similar to the original.

The plate is also about 2.5mm thick, and the space within the model is about 2.8-3mm to give some room, but not enough to wiggle.

Before starting, it is highly recommened that you preprocess the metal plate.  File or grind down any burrs or sharp edges on the plate, as well as the screw holes.  Flatten the plate as much as possible, but don't remove the screw hole bump entirely.  Either bending or sanding flat to remove as much warp as possible.  There is some clearance in the model, but due to manufacturing defects, and wear and tear, you may need to do a little bending, or a lot.  I was able to bend the plates by hand into mostly straight, but one plate I had to sand down further to get it flatish.  TPU can give a little while while printing, but it may need a little help.  Also, be sure remove any stuck leftover foam, wash the plate with a degreaser and rinse well.

The other thing would be to cut down the screws.  They are too long and I had to cut mine down by 8mm.  Be sure to deburr them as well.

For printing, I used 95A TPU, but I expect that any TPU will do.  The firmness of the pad can be tweaked with wall counts and infill density, depending on your preference and TPU choice.  Four walls, five top/bottom layers and 15% infill may be sufficient.  I recommend that moves do not cross perimeters.  This is important later when the plate is inserted.  Perimeter order shouldn't matter, but Inner-Outer is what I used to good effect.  After slicing the model, enter a pause at the layer for the first bridge.  For a .2mm layer height, that ended up being layer 100 for me.

If you have a textured PEI sheet, this will also add an appealing texture to the top surface of the pad.  I recommend printing top down, as I designed the bridging with this orientation in mind.  Printing upright should be possible, but it is not optimised.

I also highly recommend gluestick along the bottom side of the metal plate (the side that will face upward) so that the bridges will adhear to the plate.  This greatly helps keep them in place for the next layer.  It can also help with the first bridges underextruding due to parts of the plate being warped.  The top face is the side with the screw hole protrusions.  There are divets in the cavity to accomodate these protrusions.

Once the print pauses, insert the plate into the cavity and resume.  When the print starts running bridges, be sure that the nozzle is not striking the edge of the plate.  Observe closely for all bridges for any sign of underextrusions or the nozzle knocking into the plate.  You may need to use a long utensile to put pressure on the plate to give it that little bit of clearance.  The bridges run in two phases; first the short ones on either end, and the next layer will do the narrow long ones up either side.

One of my plates was fine, and had no collision, but my second one was a bit more warped, and I had to press down the plate where it was actively printing with a chopstick.  Once secured with the first layer of bridging on either end of the plate, the bridges seemed to hold down the plate in place.  Your milage will vary based on your plate flatness. So, I still recommend observing closely for the next few layers.