Destructive testing mechanical hammering machine

Overview

This machine is inspired by a testing rig made by Fireball Tool for this video: 

To see it in action, as well as see step by step assembly instructions, please see my video: 

Source CAD

https://cad.onshape.com/documents/3708cd847bf60e565612c4a5/w/027012700fa9580a16c5e49e/e/858bb56a08d2868deff223db?renderMode=0&uiState=64fa593afbe4a667db18706f

If you have an Onshape account, click to make your own copy and edit as necessary.

If you use another CAD package, you can still access this document, right click on any parts and export in a editable format of your choice. To export the whole assembly in one go, right click on the ‘hammer tester’ tab and click export.

Printed Parts

Names and quantities are in the download section.

The largest frame parts are 280mm long, so you will need a 300x300mm bed or larger.

Parts are already oriented the correct way. Support material is not strictly needed, but is optional on the two frame parts as shown in the video.

I upped infill density and wall thickness to add strength. I used a combination of PETG and PLA for these parts depending on what printers I had available. Either should be fine for any of these parts.

The frame parts will need blanking holes drilled through after printing. This will either be 3, 5, or 8mm.

Other Hardware

Small hammer: https://www.bunnings.com.au/craftright-14mm-cross-pein-hammer-with-fibreglass-handle_p5560151

The machine is designed to suit this hammer. You may use another if you are prepared to modify the source CAD.

Drill press vice: https://www.bunnings.com.au/craftright-75mm-drill-press-vice_p5860161

Critical dimensions of this vise are included in an uploaded image in case you can't source the exact version.

Geared motor: https://www.jaycar.com.au/36rpm-12vdc-reversible-gearhead-motor/p/YG2734

If you can't get this motor, the downloads tab has the dimensions so you can shop for an equivalent. I found this motor to be a little too powerful. My solution was to supply it with 5V instead of 12V to slow it down. In future, I may modify the design to gear the rpm down.

A switch and power wires need to be soldered to the motor.

12V power supply or equivalent for whichever motor you use.

608Z bearings x2: https://amzn.to/44GxfNi

625Z bearings x4: https://amzn.to/44HJwku

Nuts and bolt quantities are listed below in the assembly section.

Assembly

Please refer to the video above for step by step assembly instructions. Hardware quantities are listed below:

Motor to frame: M3 x 6mm bolts x 2

Vise to legs: M8 x 25mm bolts x 4, M8 washers x 4, M8 nuts x 4

Frames to legs: M8 x 40mm x 6 (alternatively, you can use longer bolts and then add nuts)

Hammer clamps: M5 x 35mm bolts x 6, M5 locknuts x 5

Pivot arms: M8 x 100-130mm bolts x 2, M8 nuts x 2, M5 x 35mm bolt x 1 (frame to pivot arm)

Swivel angle dial to swivel base: M5 x 12mm bolts x 2

Swivels arm bearings to swivel base: M5 x 16mm bolts x 2, M5 washers x 2

Swivel base to frame: M5 x 20mm bolts x 4 (minium 4, 6 for max strength)

Modes of Operation

There are two ways this machine can be used to test part strength. Each will allow to you test and compare printing methods, slicing techniques, materials, geometry, etc. For best results, make multiples of your test pieces and average the results.

Impact testing:

Like in the Fireball Tool video, you can position an object in the firing line of the hammer and count the amount of blows needed for it to break.

Rotate the mechanism so that the hammer is at the lowest position and the swivel arms are vertical, then place your object in the vise in line with the head of the hammer. Turn on the motor and count the imacts until failure.

Alternatively, you can have the hammer strike down vertically as shown in the video, however the inbuilt vise cannot be used in this configuration.

Shear force:

You may position an object you know will break from one impact in the vise and measure how much force it takes for the hammer to shear it. The angle dial will measure how far the hammer swings after making contact. The lower the angle indicated, the more energy it took to break the part. This will allow a relative shear strength comparison between parts.

Rotate the mechanism so that the hammer is at the lowest position and the swivel arms are vertical. Then attach the additional sub-assembly. The motor is not used in this configuration and can be unplugged to avoid damage. Place the test object in the vise, lift up the hammer as high as it can go and gently release. As the hammer swings past the vise, it will rotate the swivel bar in the angle dial which will remain at the highest point. To reset this, just flex the bar so that it clears the angle dial teeth and return it to the bottom.

Modification for More Impact

Just like the Fireball Tool version, you can add weights to the neck of the hammer to increase the force delivered for either mode of operation.