Robust Kossel

This project focuses on improving the reliability, print quality and speed of a Revision A Folgertech Kossel. Before reading more it may be useful to make yourself familiar with Delta Robots

Goals

The main goals of this project are:

• Creating an enclosure for the print volume to reduce warping when printing large ABS parts.
• Modifying the effector to allow Z probing using the print nozzle as the probe to reduce the amount of error when measuring the offsets between where the printer thinks the bed is and where the bed actually is.
• Converting the stock direct drive extruder to a geared wades extruder to allow more a consistent feed of the filament into the hot end and shortening the bowden tube to give more precise retracts.

Heated Enclosure

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Render of a The Kossel with doors

The heated enclosure will be made from sheets of perspex, as long as the temperature of the inside the volume is not too high the enclosure be robust enough to keep the hot air inside. The enclosure will be heated by the hot end and heated bed of the 3D printer.

The enclosure will also have to allow the extruder of the printer to be mounted and pass the bowden tube through the sheet.

After I designed the enclosure I created the Kossel with the shopbot using a 60 Degree bit to create the angles required for a equilateral triangle and a 1/8th inch bit to cut the holes for the M3 Screws.

I Assembled the Enclosure using a 3d printed bracket and used clear tape to seal the air into the chamber. I mounted the Enclosure to the Frame using a 3d Printed fixture.

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First assembly of the heated enclosure

After this I mounted a Wades extruder instead of the stock extruder. This gave some very pleasing results.

This part of the build seems to be effective, none of my prints have warped yet but its difficult to distinguish if this chamber is the reason as I have also changed to printing with a raft for most prints.

Probless Effector

The effector is the part that the hot end tool mounts to. Most commonly to measure the distance to the bed automatically, a probe is attached to the effector and the offset between the nozzle and the probe is a known measurement. With these two measurements the printer can calculate where the bed is, without the nozzle touching the bed.

In a probeless setup the hot end nozzle is the probe. This means that the offset between the nozzle and the probe is 0 in every direction and will improve the accuracy of the probing as the offset cannot be inaccurate.

By using an optical switch instead of a mechanical switch the accuracy is further improved. Subjectively, it felt like the mechanical switch previously used reset at a different height than it activated.

The design used can be seen in this thingiverse page .

This design seems to be very effective however it requires that the printer be calibrated very accurately to give the best results

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probeless effector optical switch

Conclusion

After these 3 modifications the printer has created some really nice prints, such as a low poly stanford bunny. It is much more capable than the standard Folgertech kossel kit.

An example print can be seen below.

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Example print after modifications