picclock's modified i3 3d printer attempt

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picclock:
Just an interim update on progress so far. Z Axis driver overtemperature could rise to over 120C above ambient (see piccy with std heatsink and fan blowing directly onto it). Tests were done using a mobile phone and octopi over the local wifi network. Seems to work very well. Max temperature is achieved when one winding only is driven, a condition which occurs at full step positions. I think max t occurs because localised heating causes the fet resistance to increase, and power is I2R.

Three possible solutions occur. Use a separate driver for each z motor. Marlin will allow the second extruder motor to do this, but I want to keep this option for feeding carbon fiber loaded filament at strategic locations. Second option is to connect the motors in series. This will keep the driving current the same as a single motor but halve the maximum running speed/acceleration. Quite a good solution, but I opted for better chip heatsinking with a homemade heatsink, see piccys. This reduced the max temperature change by 40C allowing good margins for normal operation.

Bed heater preparation was made by fixing cork sheet to the back of the pcb using a high temp silicon glue. The board connections were made with flexible silicon wire, soldered in place, ensuring the top surface remained flat. The thermal sensor was also affixed using high temp silicon. I have little faith that the glass temperature will accurately reflect the sensor temp, as only the top of the sensor is in contact with the glass, the rest being pulled toward the temp of the surrounding pcb. Depending on performance I may opt to change this for a clip on thermocouple attached directly to the glass surface.

In my final y axis preparation I made a new idler pulley with a slightly smaller diameter. In order to ensure concentricity between the outer and inner parts of the pulley I bored the inner to take the bearings. I always find small hole boring tricky because I never have the correct boring bar size. So I used a two flute endmill, axially offset by one or two degrees to ensure that just the tip cuts, a neat dodge I have used before.

Thanks for looking

Best Regards

picclock.

PeterE:
Hi picclock,

Coming together nicely :thumbup:

Your "extended" heatsink for the drivers are quite a lot larger than the standard small ones. They will definately do good work. Reworked pats from a larger heatsink or your own design?

/Peter

picclock:
Hi PeterE

I think design is too strong a word :dremel:. Measured available space on ramps board and dug around scrap box for something close. Ended up with piece 27.5x23.6.x13.6mm. cut 3mm wide grooves to suit with stack of slitting saws. Only hidden detail is that contact pad (10.5x7mm) connecting to chip is raised 0.8mm to ensure hs did not touch connections on board.

Original hs surface area around 200 mm2. New hs area around 3400mm2. Original hs only affects chip temp by around 10C even when blown.

Best Regards

picclock

picclock:
Hi. Just a few pictures of the X Axis belt tensioner and idler. This uses the two horizontal smooth rods to generate force against to maintain belt tension. It is effectively decoupled from the z axis rod as the plastic support allows the horizontal rods to slide smoothly. The X axis smooth rods were drilled at the end and an extension piece of 5mm dia bar were inserted. The original plastic part was altered as shown. The adjuster arrangement slightly increases the available x carriage movement.

Spring is 11T of 1.2mm piano wire wound at 2.5mm pitch on a 6mm rod to allow tension adjustment up to 4Kgs. Max motor rating is 2.8Kgs at 20mm from motor flange.

Best Regards

picclock

picclock:
A little more progress. Pictures of installed X tensioner and belt, with extruder mounted. As soon as I get acceptable prints I will replace the extruder, and at a later date install a bowden type version as this will reduce the load on the X axis. Made a neat bracket for mounting the X limit uswitch. Also made a mess of the cooling fan shroud as it hits the X carriage as it descends. Its about 17mm too high so I think a redesign is likely the best approach.

Best Regards

picclock

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