This is a printer built on the chassis of an old Durst M900 enlarger.
X is an ld Lexmark dot matrix printer, Y and old Applewriter dot matrix printer. Both feature Nema23 motors.
The enlarger was built to utilise a 6*9cm negative and has a pretty sturdy backbone of a 100mm stainless steel plate 1meter tall strenghtened by a mild steel box 75mm*20mm. The base rests ona 500mmsq by 25mm melamine covered MDF or similar base.
Along the one side there is a nice rack with the pinion enclosed in a rugged cast aluminium block that supports the enlarger head. The enlarger head weighs close to 5Kg including the condenser lenses and other housings. Unfortunately, the rack could not be used immeditely due to backlash when direction is changed. A servo drive will be fitted to correct for the backlash.
Most of the excess weight was immediately stripped and a 10mm bolt was exposed that held the head to the travelling lift arrangement. The lift exposes a 8mm shaft for raising and lowering the head using the rack, a pinion and approx 2:1 gearbox. Apparently sufficient to be usable as a z drive.
The X drive was bolted directly to this bolt, with a spacer of 100mm square aluminium tubing to position the X axis nearer the center of the base.
The X axis was taken directly from a wide carriage Lexmark printer with most of the mechaics intact. The rint head was replaced, and in its place a bracket holding the hotend and extruder. The mass of the extruder and otend is about 500gm – more or less the same as the original print head. As the printer uses nema 23 motors (52mm cubed) it was capable of 450-500cps printing on a 250-300 character per line it was evident that the mechanics and motors should be sufficient for travel speeds up to 500mm/sec (30 meters per minute). Tests have verified this.
The Y axis was salvaged fro an ancient narrow format Applewriter printer with a travel of 220mm. Likewise the printer used Nema 23 motor and was capable of good printing speed.
A ‘normal’ 200mm square PCB bed heater was attached wher the print head had been with a 3mm aluminium plate and 3mm glass mirror which forms the print surface. Despite the mass, it is also capable of nearly 500mm/sec travel.
Travel sppeds, acceleration and step skipping need to be fully investigated, together with vibration and other artifacts. Both axes feature good quality spring tensioned belts. I replaced the HTD belt on the Lexmark with GT2 belts but may revert as the stepping accuracy should be sufficient and the HTD belts may suffer from less stretch.
The printer is often run at 150mm/sec when draft quality, usper fast printing is required. I slow it down to a more pedestrian 70mm/sec when I want better quality. Most of my work is for functional parts where aesthetics are not important.
The Z drive using the rack and pinion needed to be replaced by a 8mm lead screw as the backlash in the first few layers was appaling and could not be tuned to produce consistent results.
A modification to the hotend mount enables fine adjustment in Z while the printer is operational. This is great for taking out minor printing problems withoit restarting the entire print. Such adjustments include fine tuning the first layer as the brim is laid down, and adjusting for thermal expansion, over or under extrusion and backlash inthe first few layers. Thereafter fine adjustments are seldom required as the natural plasticity tends to absorb differences.
The printer uses Arduino Mega 2560 with RAMPS1.4 and either MArlin, Repetier or Klipper firmware.
What I like about the printer
a) Ease of construction
b) Mechanical capabilities
c) Bushings
d) Motors
e) Tremendous height
f) Ability to fine tune the base layer
Things I don’t like
a) Arduino/Ramps
b) Marlin
c) Y drive limited bed slinger
d) Lack of z probe
e) Old motors designed for single step operation
Things I learned
Things I will do to improve it.