Motorizing my Adjustable Angle CNC Clamping Fixture

Using my adjustable angle clamping fixture is relatively easy.  One nagging "flaw" it has is the ease or perhaps unease of setting the angle on it.  Projects often expect a precise setting. The action of lifting the jig and holding it in position while setting the clamps is usually an awkward ballet.  If only I could motorize it. 

Setting the Angle

The desire to motorized my clamping fixture is an old one. I've looked into stepper motors with Arduino control, drive screws and rack and pinion gear drives, long counter-balanced lever arms, magnetic repulsion, etc.. Magic had only a fleeting consideration as I found it an unreliable force.  😉

This project strives to motorize the lifting of the fixture with a linear actuator.  It is also a test to see how fine of control I can achieve with momentary toggle switch up/down button presses to control the actuator.  I hope the actuator movement can be slowed down with a variable speed controller for more precise positioning of the fixture angle.  

Actuator Placement

The tough challenge was finding an actuator that could work with the geometry of my fixture and how it is mounted on the CNC relative to the base the CNC sits on. Position of one end of the actuator needed to be "exactly" where the end limits of a specific actuator would line up in both horizontal and vertical positions of the fixture.  An actuator with eight inches of travel would only work if mounted in a very specific position.

As the fixture rotates from vertical to horizontal, the actuator had to be entirely behind the vertical position.  Geometry dictates exactly where it could be mounted. Ideally the push of the actuator would be 90 degrees from the fixture plate, but that is impossible given the arcing transition from vertical to horizontal.

The actuator I ordered has 8" of travel.  It has built in limits to not go past 8" or under 0" when closed. In the diagram above I had to find a position under the bed of the fixture where when mounted the actuator moves exactly 8" from vertical to horizontal positions.  You can see that I've come very very close.  Within a few 1/1000ths from 8" .

Mounting brackets that came with the actuator are represented in the drawing.   

I took the fixture off the front rail and clamped the bed of it to my CNC so I could cut pockets and holes for the nuts and bolts needed to mount the actuator end brackets

I've now got one end bracket bolted to the underside of the fixture bed.  I've at least momentarily mounted the other end bracket on the CNC base.  I'm waiting for a variable speed control to arrive before wiring up the actuator to see if where it is mounted works.

Wiring the speed control took some contemplation.  The control box is a simple toggle relay that switches the current depending on which control button is hit.  It suggested the speed control should be between the power supply and the control relay box.

The speed controller arrived.

Speed Controller

The lead from the power supply needed to be cut off and wires stripped to attach to the speed controller. Done. The wires from the control box to the actuator need to be soldered together.   

I'd hoped the speed controller came with a way to bolt/screw it down, but that appears to be another puzzle to solve. I want to affixed it to CNC frame so it is secure and won't move when I raise or lower the actuator speed.  It appears to be an aluminum extrusion, capped with plastic ends and a front frame for a metal plate that has the speed dial and markings on it. There are a couple of screws on one end, but not the other end although there are holes for screws there. There are also two screws on one side of the extrusion. In line but not equally spaced from the ends.  I suspect I'll need to open it up to see if I can drill a couple holes in the bottom to put screws through for attaching to the CNC frame.

Soldering the actuator cable to the control box cable is done.  A system check verified that the speed control and remote control all work as expected.  Installed on my CNC it looks like it will do the job.  There is a bit of flex in the fixture, but with the speed control and a magnetic digital angle gauge attached to the metal blade of a tri-square it only took a few second to set the angle on the fixture.  Tightening the cam levers momentarily wiggles the CNC and make the angle on the gauge vary, but once done and settled down the angle returns to what the actuator set it to. 

Actuator in Place

The controller came with a wireless switch.  That is nice as finding a place to mount a wired switch would be a challenge.  I can keep the wireless control in the drawer of the work station. 

In practice I'll never need to bring the fixture to a horizontal position as I have a better setup on the bed for horizontal work.   For now though this linear actuator should do fine handling any or of he future angled or compound angle CNC jobs. 

One small shortcoming is that when beginning at the vertical position and actuator retracted, starting out the actuator force applied is at a shallow angle relative to the fixture bed. Due to play in the connection points precise setting of angles from 80 to 89 are best done manually.   The ideal angle between fixture and actuator would have been 45 degrees at both starting (vertical) and ending (horizontal) positions of the fixture. Unfortunately no such mounting point for the actuator exists. If I could mount the base of the actuator 45 degrees from the bracket when vertical I'd need a bit more than 8.5" of travel to push it to horizontal position. 

A revision to make it work at 45 degrees would require a new mounting platform for the bottom of the actuator, and new positions for both end brackets. The bottom end would extend much farther away from the CNC base. I'm looking for an indirect mechanical approach/solution, but complicating the mechanism is contrary to my personal design philosophy. A better strategy might be to start from scratch and design a new fixture that includes motorized control from the beginning.  

Questions? Suggestions?  Leave a comment.

4D