The parts ordered from Ebay kept arriving and the only bits still outstanding are the 8mm steel rod which unfortunately is needed quite early on.
I cut an old sheet of 15mm Medium Density Fibreboard (MDF) to make the frame and a large base sheet and used wood glue, screws, clamps and Gripfill to joint it all together. As MDF has very little strength to resist splitting when screws are driven into the sheet side on I made sure all were drilled with a suitable pilot drill. I also used very coarse thread screws – they were plasterboard/drywall screws. I also added some 4″x2″ sawn timber to add weight and stiffness to the frame. To add further stiffness I added some triangular fillets to the back of the frame (as seen below).
I had planned to use simple aluminium angles to hold the 8mm smooth bars at the correct height but soon realised that fixing them directly to the baseboard would give me little allowance for fine adjustments. I realised that the original Prusa i3 with its threaded rod was the way to go…but I didn’t have access to a printer to make the corners. Instead I decided to use some old scrap 25mm box section steel (bit rusty) to make the corners. These looked like this:
I ensured the bottom face was filed perfectly flat. Then I measured from the bottom face to centre punch and drill the holes. As the steel is about 2.5mm thick I drilled each face rather than drill through both faces (as this can cause the drill to wander). The final holes are 10mm diameter to accommodate the 10mm threaded rod. The shorter bars are 250mm and the longer ones are 500mm. I bought the threaded rod from a UK shop called Toolstation
I still need to slot the tops to accept the 8mm smooth bar – which still hasn’t arrived.
The whole frame for the Y-axis, loosely assembled, looks like this:
I’ve also started to look at the print bed – I’ve used a square of 15mm MDF for a start and mounted the 15mm pipe clips on all four corners.
I had a 8mm rod from an old scanner and chamfered the end and lightly oiled it before putting it into one of the LM8UU linear bearings. I was upset to find they didn’t run anything like as smoothly as I would have hope or though they should. After a few passes they became easier to move but I then noticed the rod was getting badly grooved. Searching the internet it would appear this is a common problem – I wish I had bought some bronze bushes instead. Therefore, trying to keep the costs down I tried to improvise a linear bearing. I made one from hot melt glue and it seemed to work fairly well (centre/right below).
I also tried wrapping some glass fibre skrim around the rod and them adding hot melt glue. This also had a lower friction than the LM8UU bearings. Finally I tried potting hot melt glue into a short length of copper pipe. These were accurate and at first appeared to move freely. However after being left for a hour the friction increased vastly and they were difficult to move at first until the friction was broken. I wonder if the hot melt glue absorbs the oil off the rod and expands slightly ?
Also see Part 1 of this build