Workholding for micromachining?

mhajicek · Jan 17, 2022

I'm getting orders for smaller and smaller mill parts. I have some in the queue with features from .020" down to .005", and that are 3mm OAL. Are there good solutions off the shelf for gingerly holding such parts for second ops? I can't quite drop them complete. Ten each of three such part numbers for now.

Thanks

Hebrewhammer8 · Jan 18, 2022

Would UV cured Adhesive work?

Powerful workholding with a light touch - Blue Photon

RJT · Jan 18, 2022

Mill, lathe, grind, EDM? Prints or a sketch would help.

gregormarwick · Jan 18, 2022

Idk about off the shelf...

Are they shapes that (if "normal" sized) could be held in soft jaws in a vice?

Split a 1/4" round bar with a slitting saw and a cross hole for a clamp screw, then machine the profile in the end of the bar.

Conrad Hoffman · Jan 18, 2022

I've been known to use a grinding vise with very sharp edges, held in the big vise. You'll make a lot of custom parallels of just the right thickness and height.

mhajicek · Jan 18, 2022

Mill parts, as I mentioned. Yes, if "normal" sized I would use soft jaws.

I'm thinking of maybe a rectangular block with a slit and a clamping screw, to be a one-piece machinable vise. Hold it in a normal vise, face it off, and mill the pocket. Dispose after use because I'll never get it located as well again.

Conrad Hoffman · Jan 18, 2022

Nothing wrong with that at all. Remember, if you want the thing to hold up for more than a few, or if clamping tiny steel parts where the forces are high, machinable jaws will be too soft. I use the grinding vise because it's hardened, or will sometimes harden and grind something custom.

mhajicek · Jan 18, 2022

I'm thinking 4140 prehard. Parts are Ti grade 2 and 90/10 Platinum Iridium.

Garwood · Jan 18, 2022

Conrad Hoffman said:
Nothing wrong with that at all. Remember, if you want the thing to hold up for more than a few, or if clamping tiny steel parts where the forces are high, machinable jaws will be too soft. I use the grinding vise because it's hardened, or will sometimes harden and grind something custom.

Just curious, but why would the forces be so high with tiny parts?

I make lots of jaws and press tools from mild steel. I have wiper style forming tools that run in high speed presses that are mild steel and have run thousands of steel parts just fine.

I get the whole "might as well make a tool from good steel" mentality, but I don't really see why using whatever steel happens to be laying around wouldn't be fine for this application.

Conrad Hoffman · Jan 18, 2022

IMO, the problem is more one of force control. It just doesn't take much torque on the vise to create crazy high psi on a tiny part. Whatever steel is laying around will certainly be better than aluminum soft jaws!

mhajicek · Jan 18, 2022

So yesterday I made some parts from 17-4 H900 that were mostly a cone with a .015" thru hole and a .047" dia. x .062" long shank. I managed to hold the shank in soft jaws made from 4140 prehard, in a 4" vise. I cut the pocket slightly undersized, with a .015" shim between the jaws. I left the shim in while holding the part, to make sure I wouldn't overtighten, closed until I felt contact, then about three degrees past. Didn't throw the parts, and the shanks still measured good (+/- .001") after.

Next parts are smaller and more sensitive.

mhajicek · Jan 18, 2022

Found a baby centering vise:
Workholding for micro-machining

Booze Daily · Jan 18, 2022

I’ve made a master set of soft jaws with a pocket milled in it. Then make inserts out of whatever , that is custom machined for each application.

Just an idea.

TKassoc · Jan 18, 2022

I have the pneumatic version of this vise on my Willemin for back work. https://schunk.com/us_en/clamping-technology/series/ksa-plus/ No problems getting tiny parts off. I use a set of cut down Schunk serrated jaws as a master and bolt my own disposable 12L14 soft jaws on top. You just need the stiffness of steel for a soft jaw not the hardness so there's no benefit to using 4140 prehard unless there's enough volume to wear them.

TeachMePlease · Jan 18, 2022

I just had some real bad nostalgia for these. I blame you.

TKassoc · Jan 18, 2022

In the mill.

Schunk master jaw with a Willemin aluminum soft jaw.

This shows the serrated Schunk interface. The big steel jaw nests over the top of the master jaw and gets me 4 usable corners per jaw set depending on the part shape.

mhajicek · Jan 18, 2022

TKassoc said:
You just need the stiffness of steel for a soft jaw not the hardness so there's no benefit to using 4140 prehard unless there's enough volume to wear them.

This is true. It's easy to forget, and I've had a hard time convincing senior engineers of this, but all steel is the same stiffness within a very small margin, regardless of the hardness.

mhajicek · Jan 18, 2022

barbter said:
Same as aloooominum!

Metals and Alloys - Young's Modulus of Elasticity

implmex · Jan 18, 2022

Hi mhajicek:
I have been using a home made grinding vise for decades to do this kind of work.
The vise is built with a long sliding jaw running on super accurate box ways and using a fine pitch screw that allow me to really control how hard I squeeze a part in a way I can't do with a normal milling vise.
I built it like a brick shithouse out of A-2 so it can take the abuse of milling and I lapped the moving jaw until it runs really freely but still has only 2 tenths of clearance.
That way I can tighten it by feel with just my fingers, or with a small torque wrench

I also built a matched pair of super accurate mini toolmaker's vises with dovetailed bases I can quick mount on to a square block in various orthogonal orientations repeatably within a tenth or two.

I also like to use Crystal Bond and my laser welder on occasion to temporarily stick a part to a handle.

One of my favourite techniques is to make the part from a larger piece of stock and cut the part free as my last operation using the wire EDM as my super precise bandsaw.
Not having to mill the second side makes some difficult parts very easy...especially those that are too fragile to hold in soft jaws.
I've never felt the need to have a self centering vise like the one you linked to in post #12...I've found they're never really accurate enough to be worthwhile for me.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

implmex · Jan 19, 2022

Hi again mhajicek:
While I'm at it, there is another workholding device I use an awful lot and that is small vee blocks...small enough that I can get to the workpiece without having to hang my cutters out a mile.

I wire cut them from a hardened lump of A-2 (I like A-2...it's nice and stable and gets really hard but is still decently easy to grind), and I make them so the clamp does not protrude over the sides of the block.
That way I can clamp them in the mill, I can drop them on the mag chuck and I can lay them over on the surface plate without that stupid strap getting in the way all the time.
Here's one of my bigger ones...it's an inch square and 1.25" long.
The smallest wire I can clamp accurately in this one is half a millimeter, but I have blocks that will go smaller.

I have long ones and short ones and big ones (for me) and small ones...it was a bit of a pain to make so many, but they've really paid off over the long term.

I know you were looking for "off-the -shelf" but sadly, in our domain, there's not all that much around, so I bit the bitter pill and had some fun rolling my own.
I don't know how motivated you are to do the same.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

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