In this article, I am going to show you how I made this very simple CNC plasma cutting fixture.
What does it do?
It started with these small 1” x 1-1/2” coupons. I needed to put five holes in each.
I had 24 of these in total that needed to have the holes added. That’s a total of 120 holes.
This is a perfect job For the plasma CNC, but how do we secure the pieces while we cut them?
The fixture has two movable platforms with a small lip that will support the stock.
The stock is placed between the two platforms
The Fixture Base
The base is the means by which the fixture is mounted to the CNC.
In this case it will be mounted on a CNC Construction Set plasma table.
The 3/8” holes near the edge are used to attach the base to the table slat standoffs.
The two holes in the center are used to attach the fixture bracket. They should be 8.625” apart and tapped with 1/4"-20 threads.
The stock I used was 3/8” thick. It is what I had on hand at the time. For the CNCCS you could probably get by with 1/8” stock for this component. It is not really under any load and the fixture bracket will make it more rigid.
The Fixture Bracket
The fixture bracket attaches to the base and performs the function of supporting the support brackets.
The fixture bracket is made from 2” x 2” x 1/8” steel angle 16” long.
The two 5/16” holes should be 8.625” apart to mate up with the center holes on the fixture base.
While the drawing does shown the holes as 5/16” in diameter, by making them 3/8” you will have more adjustability when squaring the fixture to the torch.
The Support Bracket
The support bracket, along with the support lip are what hold the stock in-place.
The support bracket is made from 2” x 2” x 1/8” steel angle 3” long.
The four holes are used to attach the support lip.
The cutout in the center is used to allow a clap for holding the support bracket against the fixture bracket.
The Support Lip
The support lip is attached to the support bracket. It is what the stock will sit on while it is in the fixture.
The stock is a piece of 3"/4” xx 1-1/2” x 1/8” rectangle bar.
Contains the files needed to build the Simple Plasma CNC Fixture.
You can find the build instructions here:
Contains the following drawing files:
SF Fixture Bracket.pdf
SF main Base.pdf
SF Support Bracket.pdf
SF Support Lip.pdf
SF Support Brackets.ai
SF Support Lips.ai
Simple Bracket Test.ai
SF Support Brackets.dxf
SF Support Lips.dxf
Simple Bracket Test.dxf
SF Support Brackets.eps
SF Support Lips.eps
Simple Bracket Test.eps
SF Support Bracket.job (sheetcam)
SF Support Lips.job (sheetcam)
SF Bracket Test.job (sheetcam)
Hold down.job (sheetcam)
Hold down 2.dxf
Hold down 2.ai
Hold down 2.eps
Hold down 2.job (sheetcam)
While you can build this fixture using the layouts shown in this article, help support this website by purchasing the drawing files.
These files will put you on the fast track to building this project.
You will need the following to assemble your fixture.
2 small clamps
8, #10 washers
4, #10 lock washers
4, #10-32 Hex nuts
4, #10-32 x 1/2” Machine screws
2, 1/4-20 x 1” Hex bolts
2, 1/4” Washers
2, 1/4” Lock Washers
2, 1/4” Knobs or wingnuts
Step 1 - Install Support Lip
Attach the lip to the bracket, as shown here.
You want the lip to stick out about 1/32”
Step 2 - Install Fixture Bracket
Attach the fixture bracket to the fixture base.
Start by adding a 1/4” lock washer to each of the 1/4”-20 x 1” hex bolts.
Thread the bolts into the two threaded holes from the under side and tighten.
If you are using a 1/8” thick base be careful not to strip the threads.
Slip the bracket over the bolts and secure with washers and wingnuts.
Step 3 - Mount the Support Brackets
Place the support brackets against the fixture bracket and secure with small clamps.
The left and support bracket should be flush with the left of the fixture bracket.
The location of the right hand support bracket will be determined by the stock you are trying to cut.
Mounting the Fixture
You will need the following to assemble your fixture.
4, 1/4-20 x 3/4” Hex bolts (1” will probably work as well)
4, 1/4” Washers
4, 1/2” or 5/8” bushing 1” long
Step 1 - Remove Slats
Remove the first seven slats and set them aside.
Step 2 - Add the Bushings
Slip two of the bushing over the fourth and fifth standoffs, as shown here.
Do it on both sides.
Step 3 - Set the Fixture In-place
Set the fixture on the bushings and align the holes with the standoffs.
Step 4 - Add Hardware
Insert a 1/4-20 x 3/4” hex bolt with washer into each hole and snug them up with your fingers.
Step 5 - Index the Fixture
Before tightening the bolts, you want to index the base against the bolts. You can do this by pushing both sides of the base forward until it rests against the bolts. You have a choice indexing each side to the forward or rear. In my case the right side was indexed forward and the left side was indexed to the rear.
As and option you can make a spacer out of MDF or plastic that indexes the fixture base against the front of the machine.
The goal is to create a method of placing the fixture into the correct position each time it is installed. Properly indexing the fixture means you don’t have to do any adjustments when reinstalling the fixture.
Step 6 - Tighten the Bolts
Once the base has been indexed, tighten the four bolts.
First Time Adjustments
With the base indexed, and the bolts tightened, you can now square the fixture bracket to the torch. You will need to remove the support brackets to perform these adjustments.
Place the torch on the right side of the machine just in front of the fixture bracket.
Slightly loosen the right knob.
Move the Z axis down until the right side of the fixture bracket can be pressed up against the torch nozzle, as shown here.
Snug the right knob.
Without changing the Y axis, raise the Z axis to clear the fixture bracket and move the torch along the X axis until you get to the left side.
Loosen the right knob slightly.
Slowly lower the Z axis. Pull the left side of the fixture bracket back so that the nozzle has some clearance.
Slowly lower the nozzle into position as before. Once lowered press the left side of the fixture bracket against the nozzle and tighten the left knob.
Repeat the back and forth procedure a couple of times to make sure everything is aligned.
If you have an alignment camera connected to your torch, you can use it as a very easy way to align the fixture bracket.
Re-install the support brackets.
Your simple plasma fixture is now complete. Go and make some things.
Setting your X and Y references
This is the point you want to set your X zero and Y zero references.
Here I am using s simple alignment camera I setup to do just that.
You can also use the nozzle to set the references by touching off and adding the nozzle radius to the touch off point.
The cutouts in the support brackets will accommodate many types of clamps.
Small C clamps are the most secure, but they stickup and tend to get in the way.
This is a small clamp used to attach things to a table.
The clamps I am using are the weakest but provide the best access to your parts.
You can purchase these here:
It is possible to add additional support brackets to the fixture.
Cutting Steel Angle
The lips have enough clearance to allow you to insert steel angle into the fixture.
Here I am inserting a piece of 1-1/2” x 1/8” steel angle into the fixture.
You should be able to fit up to a 1/4” thick piece of steel angle into the fixture.
Note that you can readjust the lip stick out as needed.
You an also grind the inside edge of the lips down a little to fit other thicknesses.
This is a simple set of holding arms I created to help secure the stock.
The arm extension is attached to the holding arm using a #6-32 x 1/2” machine screw. washers, and lock nut.
The holding arm is attached to the support bracket, by replacing the 10-32 x 1/2” machine screw with a 10-32 x 3/4” machine screw.
It is secured with a washer and lock nut
The holding arms can be used alone or with the arm extensions. IF you are using the holding arm only, you have to add a 6-32 screw and nut, otherwise it is optional.
The drawing files for the holding arm and the arm extension as well as their sheetcam jobs are included in the drawing file bundle.
Making the support bracket and testing the fixture.
Making the holding arms for the support bracket.