Open Source Cold Saw – First Prototype Test

Posted in 2012. We have developed an open-source Cold Saw – a cutting machine that produces  rapid, precise, dust-free, burr-free cuts that leave the material cool to the touch.

Cold Saw Intro:

The Cold Saw’s CAD (computer-aided design) model displayed here:

And the first test results of cutting 2″ diameter cold-rolled steel round bar here (note: noisy from the Powercube and slow for safe testing):

The Cold Saw development was motivated in part by the need for precision cuts for
the fabrication of the CNC Circuit Mill version 2. The Cold Saw will also improve the speed and quality of cutting operations for our CEB Press production runs.

Alternative cutting technologies include the bandsaw, abrasive saw,
and oxyacetylene torch, each with varying tradeoffs.

The Cold Saw uses a hydraulic motor to rotate a teethed circular blade at high torque and low speeds (typically 30-90 rpm for ferrous materials such as steel) to chip away at the material being cut; much of the thermal energy generated is transferred to the chips.

During the cut process, a submersible pump sprays a continuously recycled stream of cooling/lubricating liquid (mostly water and a bit of water-soluble oil) from the collection reservoir into the blade so as to prevent the blade metal from overheating (higher temperatures cause the blade teeth to expand). When the blade teeth expand, they become wider than the width of the cut from before, hence the sides of the teeth grind through the narrow cut slit, generating even more thermal energy. Without sufficient cooling, the blade teeth will wear out much faster and can even break during the cutting operation.

An autocentering vise allows material to be always clamped in the center of the blade’s descent. Autocentering allows the operator to quickly clamp a variety of material sizes in the optimal cutting position without the use of spacers.

The Cold Saw can accommodate angled cuts of up to 45 degrees in both directions; angled cuts are achieved by loosening a nut at the bottom that holds the swivel assembly in place. The acme threaded rod (blue) is welded to the swivel plate and the nut applies clamping force from the bottom.

The complete Cold Saw bill of materials/component index can be found here (made with Libreoffice Suite). The total so far is approximately 1500USD, expected to rise to 1600 with the automated coolant system. Simple cost breakdown:

Innovation: Fabrication Diagram

We are proud to report an innovation for optimizing fabrication in our open product development process. We have used the Fabrication Diagram technique for the first time. The Fabrication Diagram is essentially a diagram of all parts and their order of fabrication, coded by number as actual fabrication drawings. By visually placing fabrication steps horizontally on a page, we know that several steps can be taken in parallel. Items going down the page, or vertically down – are subsequent steps that have dependencies on prior parts being fabricated. This technique is useful when a team of fabricators is involved in production, such that fabrication can be done in parallel. We will be testing this method to build a CEB Press in one day with 8 people.

I explain the Fabrication Diagram framework here:

The Cold Saw documentation and Fabrication Diagram can be found at its github repository here. The build diagram was made using Inkscape, an open-source vector graphics editor. Download the Fabrication Diagram here.

Specifications

Next Steps

• Further cutting tests with improved base mounting.
• Automated coolant dispenser and collection system
• Install variable flow control valve for adjustable blade speed
• Dedicated Cold Saw Table
• Attain <1-2 thousandths off-perpendicular deviation for every inch of cut.

Summary

Design-for-fabrication and minimum unique part count was excellent. Materials cost can be reduced by reducing the number of specialized parts. Overallall prototype took 1 month to design, and a week to build.