picclock's modified i3 3d printer attempt

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picclock:
Just an update on drilling granite worktop. Bought some cheapo diamond core bits (9mm, 5 for £4-50) and some 25mm m5 threaded spacers. Marked up granite top to layout I had worked out earlier using sticky labels. Made a dam with plasticene and filled with water, then using and ancient pillar drill I had got busy with the boring. I slipped some neoprene rubber sheeting under the drill to stop movement, and it all went fairly well. On one hole I managed to break right through but the rest were ok. I found it quite hard to get the remains of the core out of the blind hole.

I tried various epoxys for fixing the spacers on the non critical stuff and found permabond steel offered the best characteristics, although the setting time proved unpredictable, so I could only do one at a time. Tried two and ended up drilling it out :wack:. The spacers were fitted with a nylon screw fully inserted. Under the head of the screw was an M5 type c washer and another washer I had made out of ptfe gasket material. Once the epoxy was mixed a suitable 'dollop' was put into the hole followed by the spacer/screw assembly. This was pushed down until the washer was resting on the surface of the granite. I used the pillar drill as a weight while it set. After 10-12 mins, the epoxy had hardened but not fully. At this point I removed the nylon screw and the washers, and used a sharp blade to clean up all the excess epoxy which had squeezed out of the hole. This seems to be an easy way to get the spacers flush to the granite top.

Once completed I mounted the smooth rods and brackets for the y axis and printer bed. It seems to work very well, with nice smooth travel. The rod heights were set with a spacer block I machined to 36mm, giving a rod center of 40mm. The spacer was placed under the rod next to the support bracket, and the adjustment screws tightened whilst applying pressure on the rod. This technique enables easy, accurate setting height of all 4 ends, within quite tight tolerances ~1thou difference measured.

Gantry and X axis next time. Thanks for your interest.

Best Regards

picclock

picclock:
Interesting 3d printed digital sundial http://i.imgur.com/z0N3dFY.gif . I wish I had been clever enough to think of this. OTOH we don't get much sun in the UK :palm:.

The gantry is mounted at the base with angle iron and supported at the top by two pieces of M10 studding. This allows fine tuning of the vertical and horizontal axis with respect to the Y axis rails. I had originally planned to use triangular braces to set the vertical right angle but in the end I decided on this method as simpler to implement and adjust. Even so, I threaded the base mounts at the wrong angle (both 3.5 degrees out :scratch:), still don't know how that came about but easily resolved. As drilling the granite is a bit of a job I made the decision to get the rest of the holes done in one go.

This led me to constructing the carrier for the Aruino/Ramps/buck convertor boards. I then needed to find out if I would need stepper driver heatsinks and a cooling fan. This led me to setting up the system and setting the driver current. The drv8825 driver chips, with 0.1 ohm current sensing resistors have a reference voltage gain of 5. So 1 amp of winding current will need a reference voltage of 0.5V. This can be set using the small trimpot and measuring the wiper voltage using a metal screwdriver and a crocodile clip lead. The reference voltage range is up to 3v or so, even though the useful maximum is 1.25V, making the setting more difficult. I intend to run the motors at 1.5A so X,Y,and Extruder setting will be 0.75V. As the Z axis requires two motors and as the driver current is limited, 2.5A or 1.25A per motor, requiring a reference voltage of 1.25V. This assumes that the motors are connected in parallel (the normal configuration), although there would be minimal downside to running them in series, just slower movement speed. The chips have a thermal trip which operates if the junction temperature exceeds 150C. Temperature measurements indicate that a fan is essential but that the heatsinks only reduced the junction temperature 10C or so. Measurements were made with an infrared thermometer, and via a thermocouple to the underside base pad. For the Z axis driver with its much higher current, the small heatsink would not be adequate so I have decided to machine one up from some aluminium scrap. If this works well I may make heatsinks for the other 3 drivers, just to be kind to them :wave: .

Y Axis testing and X axis assembly up next.

Thanks for looking

Best Regards

picclock

PeterE:
Looking good so far picclock! :thumbup:

Any advancements lately??

/Peter

picclock:
Hi Peter
Am currently in Cairo on holiday, hence no updates. Am flying back today. Very poor internet here, though quite good at this hotel. Am looking forward to seeing your build progress and latest achievements - plastic parts soon I hope :-)
Will update build log in due course, mistakes and all.
Best Regards
Picclock

PeterE:
Hi picclock,

I see, hope you have had a nice vacation without too much rain and wind.

Will be interesting to see how far you have come.

BR

/Peter

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