Three cornered thumb-wheels

March 16, 2015

To clamp my magnifier lamp in place I’ve bought some nice stainless steel bolts with half thickness nuts. This means that the nuts are roughly the same size as the heads giving it symmetry. I’ve also made some thumb-wheels / thumb-screws that means you can use these without tools.

Design

As before I’ve used OpenSCAD. I initially thought I was going to have to base this on an extruded polygon but after spotting a simple hexagon example I worked out how to create it from primitives.

The design is built up as follows:
Take a rectangle where the width is length/1.75 and add a small circle to one end that is the same diameter as the width. Then subtract a large circle from the opposite end of the rectangle. Position the larger circle so that the perimeter of the circle intersects the corners of the rectangle. You can work out the position using Pythagoras as the lengths are three sides of a right angled triangle.

The repeat this 3 times each rotated 120°.

To complete the thumbwheel, add a cylinder for the collar, subtract a hexagon for the nut (I’ve allowed 0.5mm tolerance on the hole) and subtract another cylinder for bolt hole.

Files

Magnifier Light files on Github

Printing

I printed a test example at normal size and stopped after I printed a couple of layers. I then checked the bolt head size against the hole. It was a bit loose so I dropped from 10.5 to 10.25mm. I then printed a full sample using the standard settings for the printer. There is an issue with the design in that the middle of the part prints in mid air but because of the hole it does not span very well. This resulted in some straggly bits in the middle but after a few layers it corrected itself and was easily cleaned up when finished.

I then printed out 7 more using slightly different settings. These had a better surface finish on the bottom but because I’d dialed down some of the settings to make for a faster print the top surface was not brilliant. I realised after that I actually need two more so I’ve another chance to print with slightly different settings.

Here’s the wheels in use, I’ve a bit more to do on the woodwork side before I can fit the body together and I’ve still the larger print for the head to complete.

Reference

Hexagon Calculator
Catarina Mota’s Shape Library

By Andy from Workshopshed One Comment

  Posted in: 3dPrinting, Magnifier Lamp