For my delta printer – I started with the design of the frame. It needs to be sturdy and stiff. Resist the bending of vertical members and torsion at the top. If your frame is not rigid enough, you will have problems in calibration which is a PITA. Since the frame is an equilateral triangle, you have to make sure the corners meet at 60 degrees. The joints should not have relative movement to deviate from this 60 degree.

As a wild idea, I liked the HotBot printer frame from a google group:

https://groups.google.com/forum/#!topic/deltabot/xsK_v-7lE9I%5B1-25%5D

Here are the pictures:

Hotbot-1Hotbot-2Hotbot-3

The 6 vertical extrusions make the frame costly. Moreover, if you are using linear rails this frame may not be suitable. It may be OK when you use wide carriages like below:

Carriage-Hotbot

I dropped this HotBot idea because of linear rails but nevertheless, it is an interesting concept for sturdy frame

Based on various blogs, I was planning to use robotdigg’s metal corners.

Metal Corners

I also wanted to use 4040 aluminium extrusions to make the printer rigid (from the datasheet, 4040 is almost 4 times as rigid as 3030 extrusions). There are no robotdigg metal corners for 4040 extrusions so once again have to back from this idea.

I contemplated about using Kossel 25000 metal brackets (picture below)

Kossel 25000 bracketKossel bracket frame

I was a bit sceptical about relative movement between the members and bending of the sheet. Thought it has worked for many people but I am not convinced. I wanted to have as minimal joints as possible to avoid loosening or have play between them.

I came across an extrusion with a cross section that seemed very interesting for my purpose:

The main selling point for me was the 3 faces: I can mount the horizontal rails on two of these faces to ensure 60 degrees for an equilateral triangle and linear rails on the other face. It also reduces the number of fastening points, makes the construction easier, ensures 60 degrees and not so expensive, so I decided on using this concept of my frame.

Idea-Extrusion

I bought these extrusions from this vendor in Germany:

http://www.smt-montagetechnik.de/produkte/1120n.htm

In the next post, I will describe my design for the frame and construction.