Tutorials: Simple Clamps

Introduction

My old handmade clamps needed a replacement, even though they served me quite well. They were made as a rectangular block of MDF 30x100mm, with a "rounded" piece of MDF glued on one side. The main difficulty was to clamp thin pieces of material (e.g. MDF of 3mm). Since the height of the clamp was fixed it forced the clamp to bend too much and the work piece slipped away.

The idea was to make a new set of clamps using T-nuts and an inverse screw to adjust for the height of the material

Design

I sketched something very quickly with librecad. A rectangle of 30x100mm, with round edges, containing a slit in the middle of 70mm x 5.2mm and a hole of 6.5mm.The slit is for letting the top screw move freely and adjust it to the right position. I am using M5 screws, so I let some tolerance of 0.2mm that the screw can freely move. After constructing the clamps I would say that maybe a bit more wouldn't hurt; e.g. 0.4mm tolerance.

The hole of 6.5mm is to insert the Tnut for the inverted screw, M5 as well.

Generating the gcode

1. Start the bCNC program and open the dxf file from the menu, or directly from the command line: $ bCNC MyClamps.dxf

2. Click on the Tools tab and select the proper EndMill (Bit) you are going to use. The first time there is nothing there so just click on [+] and add a new one. The most important parameter is the diameter

3. Select the Material and modify it accordingly. For the MDF material with the 1 flute end mill I use 1200mm/min with DOC 1.5mm z step.

4. Select the Stock object and set the thickness in my case it is MDF of 19.5mm thick.

Creating the profiles

• Goto the Tools tab
• Select the Profile tool
• Select the external rectangle
• Set the proper endmill
• Select the outside cut
• Click on Execute on the bottom of the screen

Alternatively you could do from the command line, just typing the command profile out

You will see the new path to be created and the original to be greyed out. Do the same with the two internal Inside paths. Click [Control] to select both and type

prof in

• Select the Cut tool
• Select all profile paths
• Click Execute (or alternatively type the command cut)

Selecting the ISO1 view you should have the cut paths like the following image

Important: Before sending to the machine you need to reorder the paths to cut the inner parts first. To do this go to the Editor tab select from the editor the path to be moved and move it up/down with the Control-Up or Control-Down keys.

Milling

• Place the stock piece in the worksurface.
• Run a homing cycle
• Manually move the gantry to the desired zero location (either with the keys) or with the mouse (Control+Shift+Click) or type gantry key in the canvas and click with the mouse in a desired location. It works only with the X-Y,Y-Z,X-Z plots.
• Set the 0 location on the WCS tab or by typing set 0 0 0 on the command line. You could send one by one the axis by entering set 0 for the X axis or set . 0 for the Y axis etc.
• I typically use a paper to find the 0 on the Z direction and move the gantry with steps of 0.1mm until it touches the paper (you can no longer move the paper). Then I set 0.1mm as the Z coordinate set . . 0.1, since the typical thickness of the paper I am using is 0.1mm.
• Lift the gantry a bit 3-5mm
• Click Run

Final Clamp