[TravisR100]

I have a part I'm working on that I'm just not sure how to fixture. One of them could easily be held in a vise but that just won't do it. Here's the problem. We're talking about a small part. By small I'm talking about a 5/16" cube. On the faces of the cube there will be some small half spheres that protrude 1/32" from the face. There will also be some small half spherical dimples or pockets which are 1/32" deep. So my question becomes how to machine a large volume of them.

My first thought was something like Geof had suggested to me previously on another part. Simply take a length of 3/8" bar, mill all the faces of the little parts in each of the 4 lengthwise sides of the bar, then cut them into the smaller pieces and machine the remaining two faces.

Any thoughts?

[Geof]

My first response was: You are nuts, give the job to somebody else to worry about.

My second response was: Are you making dice?

But then I realised a 5/16" dice is very small.

What sort of precision do you need and what is a 'large volume'. If the volume is large enough maybe a stamping/forging operation is the way to go.

[Donkey Hotey]

[TravisR100]

Of course I'm nuts. Nah, wouldn't give it to someone else. Remember, for me half the fun is making it myself and learning. I'd say the cubes need to be +- .002 maybe. And there I go forgetting to define something. By large volume I'm thinking maybe 500 or 1000 pieces initially. This single cube is a basic building block. There will be other rectangular shapes in multiples of this cube's volume. For instance, there might be a 2x4 block of these cubes which would have 28 of these little "things" on each face where a cube would fit. Not sure I'm making myself clear. But just imagine a 4x2x1 of these little cubes. This particular one is just the smallest size piece I'll make so I decided to start with it. I was actually amazed the machine could do something that small with much precision. I cut the pattern into a piece of test stock. The pictures attached are a piece of 3/8" stock. Those little half spheres sticking up stick up 1/32". THey are 1/16" diameter spheres. The pictures aren't the sharpest in the world but it's hard to focus that close.

[Delw]

real easy,
get the 4th axis that donkey posted. I am sure they will hold 6" long bars, then fabricate a sping loaded collet. and you have a small bar feed for a mill your cut off tool would be a jewl saw.

all automatic till the bars run out of stock, they you load more 6" bars into the collet and hit the button.

if your think about how to make each bar come out seperatly and accuratly, simple you have a 4th axis, you rotate it xx degrees were you have a small plate for a bar stop. hit the collet open code ,spring pushes the bars out of all collets, close collet code, flip up and start machine all over again.


we hooked up a 6 foot lathe air feed bar feed to one of my mills for cutting 4th axis brass parts, it worked out well and it freed one of my operators up for a long time.

Delw

[Delw]

Of course I'm nuts. Nah, wouldn't give it to someone else. Remember, for me half the fun is making it myself and learning. I'd say the cubes need to be +- .002 maybe. And there I go forgetting to define something. By large volume I'm thinking maybe 500 or 1000 pieces initially. This single cube is a basic building block. There will be other rectangular shapes in multiples of this cube's volume. For instance, there might be a 2x4 block of these cubes which would have 28 of these little "things" on each face where a cube would fit. Not sure I'm making myself clear. But just imagine a 4x2x1 of these little cubes. This particular one is just the smallest size piece I'll make so I decided to start with it. I was actually amazed the machine could do something that small with much precision. I cut the pattern into a piece of test stock. The pictures attached are a piece of 3/8" stock. Those little half spheres sticking up stick up 1/32". THey are 1/16" diameter spheres. The pictures aren't the sharpest in the world but it's hard to focus that close.

oh forgot to ask, did you use a hollow endmil on those or single point them?
Now you go me thinking I wonder how small someone can single point a sphere. would be interesting to see how small something can run.

single point meaning running a ball endmill to make them.

smallest I ever ran was a 1/64 endmil along a piece of .082 aluminum sheet metal to put a part number and serial number in it.

[Runner4404spd]

this job cries out for using a live tooled lathe. you can do 5 sides all at once and then part off and finish the last side in the mill. omniturn makes a machine for stuff like this.

[Geof]

Its called Lego, Travis, made out of plastic and dirt cheap.

For your half sphere use a tiny radius cutter, much faster than single pointing.

[TravisR100]

Thanks for all the suggestions! Yes, a live tooled lathe would be the best option. And the 4th axis seems like a great idea too. But at the moment I'm working with what I've got to get at least a small batch done. That means no live tooled lathe and no 4th axis. And don't forget no that with either of those suggestions there is still the 6th face to be cut.

Geof, you're right, a tiny radius cutter would be MUCH faster. The test cut I posted pictures of took 5 minutes to run which is way too long. More than anything I made the test cut to see if it could be done and to see if the parts would work for what I wanted them to do.

Delw, a hollow end mill??? Not familiar with that. Yes, I suppose I single pointed them. I used a 1/32" ball end mill to cut the protruding sphere and a 1/16" ball end mill as a drill to cut the dimples.

So while both suggestions (live tool lathe, 4th axis) are great I don't have either of them. In addition I've still got to hold them to cut the 6th face. Also keep in mind that some of them will be 2 units (5/8") wide x 1 unit (5/16") wide. Even still I guess this could be done by machining an emergency collet.

Now that I've seen the end result and how tiny those little spheres are in real life I'm thinking I might just have it be "studs" or round bosses that protrude as opposed to spheres. I just thought the spheres were more elegant looking.

Geof, have you ever seen a radius cutter that tiny? If I had one of those the machining time would be less than a minute as opposed to five minutes.

[Delw]

omniturn makes a machine for stuff like this.

They sure do, I got 2 omnis and love them, one I had since they first came out. both are built off old ahc.
were rebuilding one of them to a live spindle machine with a c axis.

[Delw]

you can buy or get made a hollow end mill,its basically a ball nose endmill i reverse.
you move down in the Z axis only and it forms the sphere.

for interpulating those spheres like that you did a pretty nice job, what was your step over .0005?

[TravisR100]

Hmm... I'll have to look for one of those. I've never seen one before.

Stepover was .001. I did one planar finishing pass then another 45 degrees to the first.

[Delw]

with a hollow endmill you would run it with a spot drill canned cycle, so basically one line for each sphere

[TravisR100]

Sounds perfect but I can't locate one that small by doing searches on the Internet. A corner rounding end mill like Geof suggested might be easier but those that I've located seen to have a cutter diameter that's too large.

[TravisR100]

The question is still how to best fixture them when cutting the 6th face.

[Runner4404spd]

why can't you use a collet chuck and machine an emergency collet to hold them? usually you can setup multiple fixtures in on op and run a bunch of these. either that or make a fixture plate for yourself that holds a ton of them.

[TravisR100]

I assume you mean a spin index like this?
http://www.use-enco.com/CGI/INSRIT?P...PMAKA=505-2280

[behindpropeller]

Find somebody to make them out of plastic....

Have them design the mold and you can build the mold....I'm sure it would give you plenty of "challenge"

[Delw]

the 6th face meaning the cut off face?
like others said a 5c collet fixture and a emergency collet and face them in the mill.

you can locate on as little as .015 and not have problems.

or you buy a surface grinder and use a mag chuck providing your part is magnetic.

[Delw]

Also a tool house can make you a corner rounding endmil for those, harvey tool may have those in stock, they have some pretty small corner rounding endmills

Delw