Looking for tiny U-channel

[beanflying]

Take a glance at the Mitee-Bite assortment for low profile clamping solutions. Very different level of workholding (Mill and Lathe workholding) but the jaw designs and clamp mechanics are worth a look and read about https://www.miteebite.com/products/ The point to take away from this is maybe your jaw might be better not entirely straight and if you are making these on a CNC mill then it is fairly trivial to do over a straight solution.

Those when used with a SMW low profile vice which effectively used the taper on a countersunk screw for the clamp are really effective. https://saundersmachineworks.com/products/modular-vise

More of a point contact will likely solve any sliding issues which is a little counterintuitive but the jaw will tend to softly bite into the upper surface if machined like this.

LINK to the Fusion Model 3D viewer and downloadable model if you want to play or make https://a360.co/3w7nXv3

[ataradov]

Yes, I've seen YT machinists (and John specifically) use them, but I was afraid that sharp edges would damage the PCB. But may be sharp rare points would work better indeed without causing too much damage.

I'll have to experiment.

In case if the sharp biting jaws, they would need to bite into the side of the PCB. I doubt simply wavy surface would do much to increase friction.

[Nominal Animal]

I have another idea: take four quick connect cross dowels or tall barrel nuts (cylindrical pieces of metal with a threaded cross hole), and use high temperature gasket silicone (like Permatex Supra Blue/Black or Copper) to cast it a wider, cylindrical or mushroom-shaped head.  It'll take several days for it to cure, and it'll stink, but when it's cured, you can make a very shallow horizontal cut (in the plane of the axis of the threaded cross hole) for the edge of the PCB to slip into.

Permatex Supra Blue can handle 260°C/500°F, and Permatex Supra Copper 370°C/700°F, and they're very rubbery, so should grip nice.  Here, one can find them in all hardware stores, but car part stores definitely have them too.

I was also thinking of seeing if I could modify some alligator clips by trimming out the tips off the teeth, and coating/casting them in the same stuff.  Stubby muzzles with rubber dentures.  I got some of the adjustable hose I can attach three or four to, for work holding.

[ataradov]

I'm not sure how that high temp gasket silicon behaves, but regular silicon in soldering mats deforms like crazy under the temperature. It withstands it, no problem and returns to the original shape after cooling, but it definitely does not hold its shape.

This is not an issue for gaskets, as they are clamped between two solid chunks of metal.

[thm_w]

I like the side knobs idea. Although you wouldn't get the same bending action as the vertical knobs.
To get that, can place knob at an angle, forcing the two jaws together, but then you'd have to have a complex shape shim to apply even pressure to your sliding rod..

I tried a few edges in 2020 aluminum, as mentioned earlier, the dovetail or wavy edges doesn't seem necessary for my PCB. It might be necessary if board has really bad mouse bite stickouts though.

The first was 1mm depth with a countersink bit, I think it needs to be just a bit deeper, 1.5mm or so.
Second is the plain square edge, 2mm cut depth, 1.6mm inset. Depth is good, inset can be 1-2mm depending on how close you put parts to the edge of your boards.

[ataradov]

It looks like you don't even need the groove. The design from #74 works really well if instead of screw heads I use the threaded part of the bolt. I have 10 mm set screws on a way to remove the bolt heads, so they are not in a way. Other than this, moving to 5 mm rods made them match the holes much better. You still don't get that feeling of clamping pressure control as with the screw design, but it holds the board pretty well. I'll test drive this with real boards once I have any. And if This lets me get away with standard components like this, it is great.

The screw threads act similar to Mitee-Bite, so the clamping pressure for reliable holding is reduced a lot.

So generally yes, it looks like the undercut is not necessary and just straight jaws are sufficient for this.

[Nominal Animal]

Maybe it's just me, but I don't like the idea of small hard metal contact area at the edge of the PCB: I want a wider, more positive contact, and would prefer something pliable instead of metal, for easier control of the clamping force. (I might get that in your reply #74 design, by using clamping rings and some stiff springs between the moving jaw and the clamping rings.  I'm currently using the cheap Pro'sKit SN-390 PCB holder, and it is "good enough" for a ham-fingered hobbyist like me, but definitely not ideal.  That uses a spring in one jaw to help control the pressure.)

McMaster-Carr has high-temperature silicone rubber strips in 1/2" by 1/2" that they claim can be used in -100°F/-73°C to +500°F/260°C: 1462N18.  If you punch a hole through that (or 1/2" by 1/4", 1462N16) that is a bit smaller than the screw heads you use, it might make suitable soft square gripper heads for your screw heads in reply #74.

If you want the threads to grip the board, then use long grub screws instead; then there is no head to interfere with the board contact.  I might consider dremeling a suitable horizontal groove in the bolt head, though.  Looks very interesting, though.  Please do keep us informed of your tests and what worked or not for you!

[ataradov]

As I said, I ordered long set screws. The head just gets in a way. I see no visible damage on the side of the board from the contact with the threads. I'm sure there is a microscopic contact point, but there is no visible damage cosmetically, much less functionally. I don't see it as an issue. Rolled threads are not that sharp, but they grip well.

I experimented with silicon from the soldering mats. While it can absolutely withstand soldering  temperatures, it still expands and warps while hot. Solid teflon would probably work better here if soft jaws are needed.

[Nominal Animal]

Solid teflon would probably work better here if soft jaws are needed.

Now that is an excellent suggestion for me to try, thanks! 

PTFE rod in 1/2" or 3/4" diameter should not be expensive at all, and if I make say 1/2" tall heads, I can make a counterbore at the other end so the bolt head sits inside the PTFE, and still have various edge grooves on the cylindrical PTFE head –– even add them as needed.

In particular, a shape that has a small ledge below, a groove, and relief above (for components near the edge) seems perfect for my needs, and is easy to do with a fret saw and a scalpel or knife.  This way, the groove and the ledge are responsible for holding the board level, even with zero force on the edge of the board, and the clamping force just ensures the board does not slide in the horizontal plane.

(And, I guess, I could do the same from aluminium round or hex rod later, if I find a hat shape that works well for me.)

[ataradov]

Here is the last "complete" iteration. I don't have anything real to assemble at the moment, but I tested this with random low value components on a scrap board, and it works like a charm.

So far I noted a couple issues. First of all, the corners of the brass parts are a bit sharp. This is trivially solvable, of course.

The second issue is with a grip. For soldering I used minimal amount of clamping pressure. This worked without any issues, even pretty aggressive solder wick action did not cause the board to move. But when I went to clean the board with alcohol, the pressure required was a bit much and the board started to slide. Slightly increased, but still very reasonable clamping pressure solved that.

Another good thing I noticed is very good heat handling. I used a heat gun on a board for much longer than I normally would to see how hot the vice would get. The parts between the bars where the board is got hot, which is expected. But the hanging parts outside of the vice, which you naturally use fo handling only got slightly warm and could still be handled without burning the fingers.

I'll keep it as it is right now and I will use it with real boards to see if any other issues come up. And obviously the set screws can be positioned to accommodate the board size.

[beanflying]

Nice lash up 

Also have this small vice saved on an ideas list with a view to it doing small parts or even PCB fixturing on the bench. The standard jaw width would be 'ok' for smaller PCB's on the screws but it is a neat swivel base that a larger frame could be fitted to. eBay auction: #224778809118

[ataradov]

Also have this small vice saved on an ideas list with a view to it doing small parts or even PCB fixturing on the bench.

This is awesome. I was looking for a replacement for this piece of junk https://www.ebay.com/itm/302164028130 I currently use for quick work holding.

I'm not too interested in the swivel part, but the base cube is exactly what I wanted for a long time. This does not look like a wide spread product, so I ordered one while they are still available.

[beanflying]

Not that common but I did find them on AliX too https://www.aliexpress.com/item/32838702283.html?spm=a2g0s.8937460.0.0.46922e0efV1YDR