In the past I've used the third hands/helping hands available at chain electronics shops and have been frustrated with their usability. I could never get the clips exactly where I wanted them or it took more time than it really should to get setup right. I also wanted the ability to hold small circuit boards and alligator clips just don't do a very good job.
I was familiar with the adjustable coolant hose systems used to spray coolant at cutting tools in the machining industry and thought that would be a great place to start. I ordered various nozzles and hose segments from my favorite online machine tool supply company and started experimenting. This is what I came up with. While it still has plenty of room for improvement it has served me well over the last 3-4 years.
These arms can be placed into pretty much any position and they will stay there.
Another nice feature is that you can make all sorts of attachments for holding whatever you need to work on. So far I've made a circuit board holder, a clamp, a mount for an LCD, and an extraction fan for keeping fumes out of your face.
All you really need are some simple hand tools, a couple taps, a drill bit and a drill to make the basic version. If you have all the tools you need, it can be made for $20 or less.
Step 1: Getting Started
The first step is to gather everything you'll need.
- Drill (A hand drill will work but a drill press would be better.)
- 3/8" drill bit
- 1/8-27 NPT tap
- 6-32 Tap
- A tap handle
- Center punch
Don't forget safety glasses!
- The Base:
I used a block of 1/2" thick aluminum (5.75"x2.5"x0.5"). Aluminum is heavy enough to be stable and is easily tapped. You can use whatever you want as long as it is at least a 1/2" thick and can be tapped. (Plastic, wood, MDF, steel, etc...) The lighter the material, the larger the base needs to be in order to remain stable. If the material is too soft the threads will wear out and the arms won't stay in. If you don't have a local source for the aluminum you can order it from an online metal sales company cut to length for about $6 plus shipping. I have used www.onlinemetals.com for other projects in the past.
- The arms:
The arms are made from coolant hoses and nozzles used in the machining industry to keep cutting tools cool and lubricated. I used the Snap Flow brand coolant hose system which I bought from www.use-enco.com. They sell a "Male NPT Hose Kit" that has 13" of hose and an assortment of nozzles and connectors. That gets you most of what you need to make a two handed Third Hand. I'd recommend buying two kits and a few extra nozzles and connectors. For around $12 you will have more than enough parts to make 4 arms.
For each arm you will need:
- One 1/8 NPT connector
- 4-5" of hose
- One 1/8" 90 degree nozzle.
You may want to consider buying the hose assembly pliers for $23. They are a little difficult to snap together by hand. I didn't buy the pliers but I kind of wish I had.
- The Hands:
Each hand is made out of a banana plug threaded into the 90 degree nozzle and an alligator clip. I chose the "Flexible Banana plugs (2-Pack)" from radio shack because it has 6-32 threads that will thread into the nozzle. The alligator clips are the standard 2" size.
Step 2: Building the Base - Layout
Once you have chosen your base material you will need to cut it to size, if it has not been done already. I used a block of 1/2" thick aluminum (5.75"x2.5"x0.5").
Next you need to layout the location of the hole for each arm. In this case I'm using three arms. The arm locations are not critical, they just need to be close enough that the hands will be able to reach each other and symmetrical so they look nice. It will also depend on the shape and size of your base material. A triangular base might also be a good way to go if you plan on using 3 arms.
Use a center punch to mark the center of each hole for drilling.
Step 3: Building the Base - Drilling the Holes
I usually start with a smaller drill bit to get it started and then finish it with the 3/8" bit. Make sure you drill all the way through the material so it can be tapped. You want the hole to be perpendicular to the base so the hose connector will be flat on the surface when threaded in. This can be done with a hand drill but a drill press would be easier.
Step 4: Building the Base - Tapping the Holes
Tap the holes for the arms using the 1/8-27 NPT tap. Remember that pipe thread is tapered so you will need to tap it deep enough that the hose connector screws all the way in. But tapping it too deep will cause it to be loose and potentially strip the threads on the hose connector. Also remember to keep the tap perpendicular to the base.
I don't have a tap handle large enough for the 1/8-27 NPT tap so I used one of my sockets designed to hold taps.
If your base is metal, I recommend using thread cutting oil or any lubricant like WD-40 that you may have on hand. I use Tap-Magic thread cutting oil.
Step 5: Building the Base - Surface Finish
Now that the holes are drilled and tapped you can smooth the surfaces and round the corners using sand paper. I started with 80 grit, then used 220 grit and finished it off with coarse Scotch Brite. The Scotch Brite gives it a nice satin finish.
Step 6: Building the Hands
Remove the red and black covers from the banana plugs and discard. We only need the metal parts. Using the 6-32 tap start threading the 90 degree nozzle. The banana plug threads aren't actually 6-32 but are close enough and provide a nice tight fit. Once the banana plugs are installed you can just slide the alligator clips onto the banana plugs.
The alligator clips work pretty well as is, but they do have a tendency to rotate when holding longer or heavier items. In the next step I'll show you how to improve them.
Step 7: Improving the Hands - Optional
As I said in the previous step, the hands have a tendency to rotate on the banana plugs. While this is a feature I wanted, the ease at which they rotated was a problem in some situations. This is in part due to the alligator clips expanding when installed. You can see the gap in the picture below. To fix this I came up with a couple solutions. You can certainly skip this step and be happy with the results but doing this will make it a lot easier to use.
I had some stainless steel tubing sitting around that was the perfect size. OD:1/4" ID ~3/16" (0.192"). I cut a 3/8" long section of tubing and using a hammer, lightly tapped the alligator clip into the sleeve. This is the best fix in my opinion.
Wrapping with wire.
I found some thin solid core wire, wrapped it around the clip and soldered it in place. This is the easiest and cheapest solution to the problem.
Step 8: Assembling the Arms
Unless you bought the assembly pliers($23) when you ordered the coolant hose parts, assembling the arms can be a little tricky. I didn't buy it, but here is how I figured out how to put them together with ease. Slide the parts you want to join onto a #2 Phillips screwdriver. This will keep everything aligned and all it takes is a sharp tap to get the parts to snap together. Just hold onto the hose and tap it on the work surface in the direction of the part you want to attach.
Although theses pictures show 10, I found that about 7 hose segments per arm to be about the right length. Of course that is my preference and you can use as many as you want.
Step 9: Finishing It Up.
Now all you need to do is thread the arm assemblies into the base and you're done!
Next I'll show you some of the attachments I've made.
Step 10: Attachments - Circuit Board Holder
The circuit board holder has been one of the best attachments I've made for the third hand. I've used it to hold boards as small as an inch wide all the way up to ~8 inches wide.
Making these might be beyond the capabilities of most people because of the tools needed.
I used two pieces of 1/2 x 1/4" aluminum** each about 2.5" long. In the end of each I drilled a 5/32" hole around 3/4" deep. You could do that with a hand drill and a vice but there isn't a lot of room for error. A drill press or a mill would be best.
To make the slot I used a slitting saw in my mill. The slot is a little over 1/16" wide and 1/8" deep running the entire length of the rail. I suppose you could do this with a hack saw or dremel, but it would be difficult and I suspect the results would be pretty rough.
** - Next time I would make them out of Delrin or other plastic since many circuit boards have components and traces right up to the edge of the board and could be shorted by the aluminum.
Update - Below is a picture of the circuit board holder made out of black Delrin plastic. These were a bit easier to make since I was able to use a 1/16" end mill instead of the slitting saw.
Step 11: Attachments - Fume Extraction Fan
I made an extraction fan using an old CPU cooling fan, a bit of filter material, another 1/8" 90 degree nozzle and a couple screws. All stuff I had lying around the house.
For the filter I cut a piece of white scotch bright to the shape of the fan and attached one corner with a screw. The opposite corner I used a long screw to go through the fan and filter into the nozzle. Connect it to a twelve volt source and solder without having fumes in your face.
In my next version I plan to add white LEDs to provide extra light in addition to the extraction functionality.
Step 12: Attachments - LCD Mount
I made this mount to hold a graphics LCD a while back when I was playing with a BASIC STAMP II.
I used a mill to build this, but I'm sure it can be done with hand tools.
I milled the black bracket out of delrin plastic, drilled and tapped the appropriate holes and screwed it to a large straight nozzle. I'm not going to get into the details as it is fairly self explanatory and not everyone is going to have the same LCD. I mostly wanted to show you the variety of attachments that can be made for the helping hands.
Step 13: Attachments - Clamp
This clamp can be used to hold larger items than what will fit in the alligator clips.
All I did to make this was to remove the bolt at the end of the clamp and replaced it with one twice as long. Then I screwed it into a straight nozzle that I had drilled and tapped to a M3-0.5 thread.
This version can hold about 10oz. before it starts to pivot. However if you drilled a couple holes in the bar near the stationary end of the clamp and attached it to a 90 degree spray bar nozzle with two screws it could probably hold a few pounds.
UPDATE: I've made the improved clamp arm and it holds about 2.2lbs. I used a right angle adapter to make positioning the clamp easier. #4-40 screws thread right into the spray bar nozzle without having to tap them. However, drilling through the hardened metal bar of the clamp took some effort.
Step 14: Other Attachments and Ideas
When I made the first version, which I've used for years, I was concerned with ESD and so I soldered a wire to the banana plug which ran inside the arm and was grounded to the base. I also drilled holes in the front and back so I could plug in a static wrist strap in the front and in the back, connect it to the static ground at the workbench. I probably should have soldered in a 1M ohm resistor to the wire going to each hand for more protection.
I've also thought about adding binding posts to the base and wires going up to the banana plugs so that voltage can be applied to the hands for powering circuits or loads being held by the alligator clips.
The down side to the above ideas is that the left and right hands are wired to the base so changing attachments, that requires a nozzle change, means you have to disconnect the wire. However, most of the attachments I made that require a nozzle change are primarily used on the center arm. The alligator clip hands and the circuit board holder just slide onto the banana plugs so no nozzle change is required.
I am also working on an attachment to hold voltmeter leads or an O-scope probe. I always seem to run out of hands when measuring signals on a circuit board.
Although I never used the magnifying glass on the old helping hands I had, I'm sure many people would use one. It would be easy to adapt one to use on the center arm.
A little extra light would be helpful as well. I plan to combine the extraction fan and an LED light.
Small Parts Tray
Below is a picture of a base that I made for a friend that has a pair of parts trays milled into the aluminum. Also below is a picture of a 4 armed version that I made for an instructables member with 3 pockets milled into the base.
There are a ton of different nozzles and connectors available for the coolant hose systems. I'm sure there is no end of attachments and accessories that can be made for this third hand.