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Prototype "Creation" Theory

B.A.D.Kustoms

Plastic
Joined
Dec 1, 2020
Location
Ft. Collins
I'm a prototype machinist that went to a machining school and then moved into a bio-medical shop and started working as their only machinist. I've never had a apprenticeship or worked for a giant shop (any other machine shop for that matter) and have only had the mentorship of an excellent Mechanical Engineer. He taught me a great deal but from an engineers perspective whose played in the shop. I hope for this thread to be something that spills some knowledge from others onto my limited experience. I've been working as a prototype machinist for 5 years now and have a very nice shop to work in. We have a 4 axis CNC mill, manual mill, manual lathe, waterjet, CNC pressbrake, and a TIG welder. So that means not only machined parts as well as sheet metal parts. But I'd like to focus on the machining aspect of the creation theory.



I've got some curiosities as to how some of you set out to machine. Your "creation theory" if you will. Like what's your go to setup for onsie, twosie, parts. Please share your practices.


I'd be happy to share mine:
8" Talon Jaws from Mitee Bite ( The approach being I machine all but one side of the part leaving a sacrificial "brim" of material to hold onto on the bottom that is removed last. I call this the "top hat method" or decking the part. This is my number one go to means of fixturing prototypes. )

Aluminum Sub-Plates (6061 or MIC-6) ( The approach being the part bolts down to the sacrificial aluminum sub-plate and is machined away. I start with toe clamps to put in tooling holes and face then sometimes bandsaw off the boarders and flip to face again the opposite side to desired width then bolt down and finish machining. This method is used when I'm doing larger plate work and I've used "stripper bolts" I believe they are called for locating positionally when flipping over the part. )

These are the main two ways of my creation theory. Please shares your thoughts, ideas, practices for your creation theory.

Cheers,
Brad
 
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I would add window machining to the methods that you've included above as my go-tos.

If you're not aware, this is the approach where parts are embedded into material leaving stock around the parts to support during clamping and referencing. Usually I tab or leave a thin film supporting the parts. It doesn't work for all parts but when it fits the situation it's great.

Here's a pic of some recent window machining with some tiny parts that would have been a pain in the neck otherwise.
ee480954b04c603a66c1e55d79d9fdb9.jpg
 
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I once saw a show about a retarded sculptor. He was known for producing breathtaking works using just his hands and a few basic tools. As part of the show, they filmed him as he carved a beautiful horse out of a block of granite. When they asked him how he was able to do such incredible work, the goofy bastard simply said, "I just imagine a horse, then cut away anything that doesn't look like the horse." I looked down at the girl who was, at the time, filing my toenails into points, and said, "Gosh! Isn't that amazing? He's technically retarded, but nonetheless he's able to view the world in a way the average non-retarded person is unable to do!"

It's that sort of profundity that I seek and adopt for use when I machine something. I find that machining is 1% work and 99% theory.
 
There is one technique that I use that most machinists probably also use, but I use it in a more deliberate manner than most do or at least than most would admit to. When faced with a complicated part, I often create a written list of the operations needed. Sometimes I even sketch the part at the various stages to help in this process. Since I often do the design as well as the machining, on some occasions I even put this list of operations right on the drawing for the part because I want to be sure I can make it before moving on to the next part for that project.

This has probably saved a lot of work due to trashed parts. And many times where I do not use it, I find that I run into trouble.
 
Perhaps similar to EPAIII if I have a complicated part or even a part with lots of operations I will sketch all the features out on the material complete with hidden lines. This helps me make sure I have all my orientations correct as I am machining so I don't put that slightly off center hole on the wrong side of center. Also if I am working off some napkin sketch or a drawing made in MS paint I can make sure there are no features interfering with each other.
 
Perhaps similar to EPAIII if I have a complicated part or even a part with lots of operations I will sketch all the features out on the material complete with hidden lines. This helps me make sure I have all my orientations correct as I am machining so I don't put that slightly off center hole on the wrong side of center. Also if I am working off some napkin sketch or a drawing made in MS paint I can make sure there are no features interfering with each other.


I'm not the only idiot with rough sharpie marks on a part with compound angles and such, making sure I tilt the sine table the right way?
 
Hi B.A.D.Kustoms:
Two things:

1) If it's little, leave a handle on it until the last possible moment.
Prep your stock so it's accurately square, parallel and of a known size if you're going to work on it from multiple orientations.
Preserve the accuracy of the stock for as long as you can...it's your handle and your reference.

2) Model it in CAD if it's complicated or ambiguous, or use the CAD model the engineer was SUPPOSED to model it in, then hold up your developing part in front of the CAD model and do what TeachMePlease does:
Scribble on it with Sharpie so you don't drill the hole pointing the wrong way from the wrong end.
Model the stock (to the dimensions you ACTUALLY made it) in an assembly together with the part, and put it in the proper relationship to the part model so you can measure off the assembly model.

3) Get a wire EDM to use as your cutoff saw:D.

4) Ask the engineer for clarity if the model or the drawing doesn't give you an unambiguous picture.

5) Demand to see the WHOLE assembly...if you just make parts without understanding how they are supposed to go together, sooner or later (usually sooner) there will be bits that don't fit, and it's usually that tolerance that was overlooked or never stated, so they don't fit by half a thou, and the fuckaround to fix it is often more expensive than making the part.
Prototyping engineers tend to model everything size for size, and we all know how that works out.

6) Never ever EVER give a firm fixed price...sooner or later (usually sooner) you will be working for free to fix something unanticipated that wasn't even your fault.
While you're at it, never ever EVER commit to a delivery date...sooner or later (usually sooner) you will regret it and you'll be working all night or all weekend (for free).

7) Start more than one part even if you only need one.
Run through all the easy operations that the CNC can do.
That way when you fuck up the first one, you don't have to start all over from scratch.
Try to be wise with this...it's things like squaring up a few extra, and milling the first side, or doing the CNC turning on them or whatever.
No point in having ten finished parts on the bench when you'll only get paid for one but it's awfully nice to have two prepped blanks when you fuck up the first one on the last operation.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
It is not really a theory but here is a work holding method that I am using today.

20201202_100015.jpg

It seems pretty obvious but it had never occured to me to block my part away from the vise jaw so I could mill a feature until I saw a coworker doing it.
 
That's genius!!! I've never seen it done before, that's incredibly helpful Kenton. Sometimes it's the most simplest things that are the most illusive.
Thanks
 
Since much of the machining I do is for toolmaking for my line of work, almost everything I make is generally one-off or could be considered a prototype. But I don't have a CNC machine, just manual lathe, mills and TIG welder.

A big part of my "creation theory" is figuring out how to make what I need in the least amount of time possible. I work for myself, so any minute I'm not putting product out the door is a minute I'm not getting paid.

I find that I'm always trying to remember all the tools at my disposal, and how to integrate them together to arrive at my goal by the quickest path. Just a couple days ago, I needed to make a replacement part for one of my machines, and went to the lathe stock drawer to find some raw stock. Found a piece that was an almost perfect blank for the piece I needed, so very little material needed to be removed. But I had no way to hang on to it, so I tig welded it (very firmly) to another piece of bar stock, made the part I needed, then cut the part off and faced the back, and presto it was ready to go. Same goes for things like a rotary table , or whatever else I have in the shop, I just have to remember I have it, and that I can use it for something!
 
Hi All:
Kenton wrote:
It seems pretty obvious but it had never occured to me to block my part away from the vise jaw so I could mill a feature until I saw a coworker doing it.

Yep, and you can do it with soft jaws too.
Just shove a blank SJ into the side you plan to mill into.
Put in your blank, squeeze it in the vise and go to town.
Works great and allows you to get a great grip on your blank.

Notice that with this method, you don't mill a part shaped pocket in the soft jaw first... you just put in a blank jaw, put in your workpiece and have at it, trashing whatever bits of the soft jaw that get in the way of the cutter.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
In the Beginning, there was Nothing. And God said, "Let there be Light." And there was still nothing, but now you could see it.

That is not what I was taught in the RAF.

And God said "let there be light". And there was light, you could see for F'ing miles.
 
I used to do quite a bit of medical work. A lot of the implants were 6AL-4V ELI which only comes in round bar.
One of the first tricks I used was to mill flats on the round to hold on.
junk 006.jpg

I use a tombstone and double vise on my 4th, so I could mill this at A0 and A90.
junk 005.jpg

I also use a lot of custom milled soft jaws to do the 2nd ops.
junk 004.jpg

junk 003.jpg

Machine all the extra stock off the back on the 4th.
junk 002.jpg


If I recall, there were 3 different sizes of these. I think the initial run was 20 pcs of each size.
I was able to do 1 pc complete (minus the tang) per cycle.

My customer never could figure out how I made them. So if you're a member here TJ, this is how.:D
 
If your big plates don't have too many holes get a 1/2 hp vane type vacuum pump, a 1 to 2 gallon coolant collection chamber that goes between the pump and part with a vacuum gauge, and as big of a 1" aluminum plate as will fit on your mill table. Put one port in the middle of the table to pull the air out and get sheets of 50-60 shore a neoprene rubber that you can use to make the gaskets for your parts and lift the part off the fixture plate. This is the best way I have found to do big plate work without too many holes to block off. It will also save you on many other weird parts that are too thin and flimsy to vise without distortion. Just don't helicopter your part when pocketing!!!
 
Hi Booze Daily:
Those are very impressive parts...that's what...5/8" diameter bar stock you're starting with?
I assume those are bone plates of some sort??

So how did you keep from squashing the snot out of them in the soft jaws?
Did you have to make the soft jaws out of titanium too?

When I did dental implant prototypes, I could only handle them with titanium fixtures and collets and tweezers to avoid even the thought of contamination...big PITA because all the collets and vise jaws had to be custom made.

But when I asked about embedding bits of tungsten carbide in the titanium everyone in the meeting looked at me stupidly.
I had to explain that when a cutter gets dull, the carbide that's lost has to go SOMEWHERE.
This was a small startup...they didn't last long!

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
If your big plates don't have too many holes get a 1/2 hp vane type vacuum pump, a 1 to 2 gallon coolant collection chamber that goes between the pump and part with a vacuum gauge, and as big of a 1" aluminum plate as will fit on your mill table. Put one port in the middle of the table to pull the air out and get sheets of 50-60 shore a neoprene rubber that you can use to make the gaskets for your parts and lift the part off the fixture plate. This is the best way I have found to do big plate work without too many holes to block off. It will also save you on many other weird parts that are too thin and flimsy to vise without distortion. Just don't helicopter your part when pocketing!!!


I'd love to see a sketch or picture of this setup. I've been really interested in vacuum plates as a means of fixturing thin parts and plate work. I don't know enough about it though. You still need a sacrificial plate on the vacuum right otherwise you'd cut right into it. Or is it like the "top hat" method where you leave stock material on the bottom of your part to be removed later?

Can anyone explain some basic knowledge/principals on vacuuming fixturing to me?

Brad
 








 
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