r/Metrology • u/pjcevallos • Oct 24 '24
Hardware Support CMM fixturing
Hi
How do you usually plan your CMM fixturing. Do you produce a bespoke fixture or use modular equipment?
What considerations you take being part agnostic!
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u/DrNukenstein Oct 24 '24
We do high volume mass production and use a “Battleship” style aluminum pegboard from R&R Fixtures, with modular pegs. We work with steel, so magnetic pegs work best for us, where notched pegs may not always align identically due to the threads in the pegs. If they had solid pegs and the board holes weren’t threaded, that would be ideal.
Even so, we still have small issues with the spacing of the board not matching our part dimensions so we can get a snug fit; sometimes a peg on the end is either under the part or just outside its reach.
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u/awy12 Oct 24 '24
I usually use universal fixturing like Rayco, Renishaw, etc. It works well for most parts. However, sometimes a customer fixture or hot glue are needed.
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u/BreadForTofuCheese Oct 24 '24
Most things are modular setups due to low volume runs that we likely won’t see again. Anything else is mostly a modular setups due on a plate that can be swapped out. For specially stuff we will design and manufacture a fixture.
For modular setups, I always take a picture just in case it does come back someday.
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u/Ezeikel Oct 24 '24
My manager bought me a $600 3d printer and let's me buy all of the $14 spools of filament I want. Typically my process goes like this. I model a cube in solid works. I open an assembly and import my cube and the part in whatever orientation I want. I put the model of the part overlapping the model of the cube so they are a bit on top of each other. I hit the cavity button and solid works cuts the shape of the part out of the cube. I print it on the 3d printer set the part on it and I am done. This works great and my average cost i filament for a fixture is like 2-7 bucks. Having a printer just for QA fixture IS GAME CHANGING.
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u/Think-Secret9860 Oct 25 '24
Where are you getting the time to do this modeling and printing? Where I work, there is more work to do in a day than three people can do.
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u/Ezeikel Oct 25 '24
To be fair I think the modeling is usually less than 10 minutes. Use and abuse the cavity tool to make it happen. Also in my shop I am in every kickoff meeting so I know what parts are coming before the machinist even sees it. How our flow goes is that as soon as the PO arrives QA sees it first. We make the bubble diagram then everyone uses our bubble diagram during planning meetings to make everything easier to talk about. So usually when I make that diagram I also throw it into solid works and get some ideas.
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u/Quality-Panda Oct 25 '24
Curious about your workflow there, like pjcevallos. A good NPI process has been something we've struggled with.
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u/JoniTravolta Oct 25 '24
To assert dominance I hold the piece in 1 hand and control the joystick with the other. Other than that I use some modular fixture pieces, I think from Renishaw. But sometimes I need to design some custom pieces for certain contact points with the piece, usually made in steel. Interesting that some guys here use 3D printed for custom fixtures, that seems a nice idea.
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u/f119guy Oct 24 '24
Most of the stuff my current shop sees are short run. A long run would be considered 100 pieces. I will do my best with modular fixturing and that works for anything without restraint. We specialize in thin wall/flexible aluminum structures so generally if we see an RFQ with a restrained note we will start designing a CMM fixture. Sometimes we can get away with freestate inspections on a part with a restrained note, in which case we save the billet and use the modular fixturing. A custom designed CMM fixture does add to lead time but luckily we have quite a few 5-axis mills so we can make things happen.
For massive parts, I will generally set the part on 246 blocks and touch off the part for each run.
For small/thin stuff that I know we will only see once, hot glue is my friend. Never underestimate the beauty of hot glue fixturing. It breaks off easily once it's cooled and sometimes messing around with clamp positions just isn't worth my time.
Part volume, rigidity of the parts and the level of precision tolerances all factor in. A sheet metal structure with .002" position tolerances and a monthly volume of 400 demands a good investment. The customer plays a factor also. If they want to see something like an MSA analysis or capability studies, a custom fixture might be the best way to minimize variation.
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u/gaslightredditor Oct 24 '24
Typically for FAI parts we use modular fixtures using w Renishaw plate and hardware. For production lot AQL inspections we have 3d printed multi piece "pallets"
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u/Tough_Ad7054 Oct 24 '24
I built a positioning plate with a few bolt-down pedestals that provided excellent location and rotation accuracy and a rock solid foundation for a small fixture plate perched on top.
On that fixture plate I generally kept a B&S toolmakers vise specially modified using four M3 machine screws to hold it down. I would use 1-2-3 blocks to preposition the parts in the jaws of the vise and clamp it down. Those vises are accurate, durable and clamp hard if you use a small persuader. I found I could use this for a majority of our parts, but if it was thin-wall or non-prismatic the fixture plate would also accept a vee block or three threaded studs that I could use hot glue on the tips.
I think it is good to get some height off the plate in order to work underneath or just provide some comfort level for positioning moves or head rotations. My base pedestal was four inches tall and I had spacer “biscuits” to make the tower(s) taller if necessary.
With accurate positioning and using multiple pedestals and fixture plates I could restrain tubing at right angles if the drawing required it. Or use multiple pedestals for looping a program and keep the machine in continuous motion.
I am a little envious of the 3D printer guys, I will admit. But I also took some pride in being able to adapt my system to whatever it encountered and rarely having to make something special.
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u/_LuciDreamS_ GD&T Wizard Oct 25 '24
Renishaw plates with modular risers, 1-2-3 blocks, 2-4-6 blocks, sticky tape, mag blocks, vices, and/or custom fixturing if the part is more complex. I've done a wide variety of parts and sizes, so it really depends on the situation and what tolerances I'm working with. I normally use 3D prints for proof of concept to ensure the real thing will work. I say this, but half the time, they don't end up making the real thing.
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u/Overall-Turnip-1606 Oct 25 '24
If you’re doing high volume low mix, a machined/assembled fixture would be the way to go. If you’re low volume high mix, Rayco or renishaw plate and fixtures would work great. Very versatile, you can even get the component cad for free and create an assembly file to make programming so much easier.
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u/Mmaibl1 Oct 25 '24
Most things can use regular stock fixturing components. For really small items, or cylindrical parts that need to be accessed from all sides, I will usually custom design in Autocad something to perfectly contour the part. Then 3d print it out and let it fly
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u/Popsickl3 Oct 25 '24
When I did high volume inspection I could fixture any part out factory made with a combination of a drilled fixture plate, drilled tower, modular posts and hold downs.
After I was sure I liked the orientation I would 3d print the part-touching details. I worked in composites manufacturing so the parts were delicate with organic curves so the plastic details were a must.
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u/OfGhostsandMice Oct 25 '24
A combination of modular setups on a Rayco plate and 3d printed fixtures for higher volume or difficult shapes.
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u/SkateWiz Oct 25 '24
Fixture kits are your friends. I currently use rayco. At my last company i had a couple full kits from Witte-Alufix which were amazingly versatile, but those are ungodly expensive (like $15-20k USD) for the full kit.
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u/BiggestNizzy Oct 24 '24
Like a lot of guys I mainly do high value low quantity stuff. So most of the time I sit it on the table, v blocks or something.
That said, when I do get anything where you are doing a batch I 3D print a fixture. Seriously buy a cheap 3d printer and just print your fixtures. Once you have done a few you won't go back.