So I’ve been toying with the idea of making a fixture plate for my paintball triggers for about a week or so now. I finally got the CAD drawn up and the fixture plate made. Cut the fixture plate 2 days ago and tonight I finally got to make my first test cut(s).
I did 3 tool changes to make the fixture plate. I started with a 1/8" 2flute AlTiN coated stub nose endmill to cut the larger holes (mounting to the bed) and the profile of the plate. I then grabbed a 1/16" 2flute to predrill the precisely located holes using a pecking drill operation. Then I grabbed my 7/8" diameter - 1/4" shank to face the whole thing down from .19" to .18" in 2 passes, both .005" DOC. Afterward I used a .5" vbit to hand chamfer all holes. Grabbed some 220grit sand paper and my best sanding block, to make the top smooth and get rid of any ripples from the facing operation. Then I ran it over the satin buffing wheel to smooth it all over.
Heres some of the CAM work I did before I made any cuts. I even got the dimensions of the screws I was gonna use to model it up.
And the fixture plate itself, and the resulting trigger.
^no filing or sanding. There are some spots that look “rough” but I assure you, the whole thing is extremely smooth. Not perfectly smooth, but my post-cut work will be reduced by an order of magnitude.
These are by far and away, the highest quality triggers I’ve produced. Just from the sound it makes cutting, you can tell fixture plate reduces most if not all vibration in the cut. This reduces chatter, big time. They are also the most accurate parts I’ve ever cut. Usually I’m lucky to come within .01" of the CAD specs. The parts that came off the fixture plate were as close as .0005" but as far as .0035" from CAD. This isn’t a $160,000 VMC, so I’m more than happy with the precision, now that I’m using proper fixturing.
The big take-away I’ve gotten from this experiment (that I’m going to scale up for production) is that fixturing/clamping is extremely important for high quality cuts.
Almost forgot the pics of the precision.
The quality of the finished part looks great! Where did you learn about fixturing (book, certain forum)?
So I was wondering why you have made this fixture for screwing down the trigger when you could just lay the parts out on a large sheet and use the mill to drill the holes in the triggers where you already have to drill the holes for the fixture and just use screw to screw them down to a sacrificial waste board which would also give you a nice level surface for milling and protect your slotted bed? It is how I do my production runs and I cut out 20+ objects per cycle and it saves me the time of making a fixture for each run or worrying about how each large mill run is placed out on the plate aside from clearance for the cutout.
I get the fixture can be useful but I was wondering what the gain was here for doing it this way for you. How easy has it been for you to remove the fixture, then replace it and reuse it? Are you able to remove it to mill something else then replace it and have it line up perfectly once again without leaving something in your slotted bed when interferes with milling other objects?
I am able to layout large plates of objects to be milled and change the layout as needed to work with larger or smaller plates of stock. I program the mill to drill the hold down screw holes, then use screws into the sacrificial waste board to hold everything down just like the fixture. But as this is done for each new plate of stock, I do not have to worry about lining up a fixture for a new run after milling something else on the mill between large production runs.
I think the fixture is a great idea and it looks to have really helped your final product come out with some clean cuts. i am just wondering how easy it is for you to remove a fixture then replace it and mill with it again if you mill something else between trigger production runs.
@BetaPrints I just did a bunch of googling and watched many machining videos of people using/creating fixtures. NYC CNC and Grimsmo Knives are 2 youtube channels that helped me out a lot. Granted, they have Tormach PCNCs which are in a different class compared to the X-Carve; but the principles of good fixturing should hold true on either machine.
@Travelphotog I considered using a sacrificial waste board. Its a good idea for larger parts, but not so much for very fine, slightly fragile parts like triggers (i think). I haven’t tried it with triggers, because I’m worried the vibrations from the wood could get amplified into the part. Using an aluminum plate makes everything significantly stronger, repeatable, and I have a lot more confidence cutting.
As far as taking the plate off for another cut, its very easy. Its so small I can loosen the tslot screws and just slide it to the back of my machine, theres enough room on the bed. There is some wiggle room if the bolts aren’t tightened down, but when I go full scale it should get better. Also the edge of the fixture lines up with the edge of the Tslot bed which makes it easier to line up quickly. This is just a small scale test, though. The plan, now that this has been a success, is to mill a 3"x12" (or maybe a 6"x12") fixture plate, which should hole about 10 or 12 triggers (or 20-24). I will have that fixture plate on, say, the left side of my bed, then while its cutting those out, I will prepare the next sheet of aluminum to have its mounting holes drilled on the other half of the bed. This keeps the machine running as much as possible. Assuming everything goes as planned, I should only have 3-5minutes of downtime between swapping the plates. The way I’m doing it now means I have to re-clamp after every 4 or so triggers, otherwise the material just isn’t solid enough to prevent vibration. So about 5 minutes of fiddling per 4 triggers.
Also, now that I’ve sort of “figured out” fixtures, I can make them to do 2-sided machining accurately and repeatably.
Cutting a huge sheet of very small parts and using tabs creates a ton of vibration and clamps are just not enough. The main goal is to reduce that vibration to a minimal amount. So I decided the fixture needed to be aluminum. Also I figured if I’m machining aluminum, I may as well machine it how real machinists do, which means making fixtures for production parts.
I’m one of the lucky ones to own a Tormach 770. I have a piece of 1/2" alu tooling plate that I clamp down to the table and then drill and tap for clamps and drill and ream for locating dowel pins. In the same Gcode file I drill and tap holes in the field of the plat that will be under holes in the part I am making.
Without moving any thing and using the same X0 and Y0 I can clamp my material down and drill all the holes in them before the outside profile work.
This plate has had so many holes in it looks like swiss cheese.
Here is a photo of the setup for making new wide/tall end plates of my machine.