Do you have anything that is highly polished, but needs to be handled rather forcefully? One tool that might be useful to you is a rubber mallet. Another option is to wrap vice grips in a towel, or put a hand towel over a metal hammer. If none of these will work, you need a custom scratch-free press tool, and this instructable is about how I made mine.
I needed a tool that would let me pop small tapered pins out of their matching tapered holes, or push them into place, without making the slightest scratch. You'd think a rubber mallet might be perfect, but my lab-mate found that it caused too much vibration, and that putting one pin in would make another bounce out.
That's how the scratch-free press tool was born. It is really just a custom plastic clamp, with a plastic tipped pusher that can pop pins in or out without scratching my parts. By the way, the parts are high voltage electrodes that will be installed in a high vacuum chamber.
Better still, the clamping tool is made out of PEEK, a vacuum compatible plastic, so the rods and pins don't even need to be re-cleaned after the clamping tool is used on them.
Follow along to see how I made this, in case you want to make something similar or see some of the subtleties involved, also check out the newly attached video which hopefully clarifies the operation of this tool!
Step 1: Tools and Materials Needed
- Peek Bar: 1.25x1x5". Follow the link to order from McMaster. It's expensive! But not on a lab budget.
- Peek Rod: 1/4" OD
- 1/4-20, 1" setscrew
- 8-32, 1/2" setscrew
- 0-80, 1/8" setscrew
- 1/2" Aluminum Rod
- Measurement Calipers
- Tap & Die Accessories
- Various Drill bits and end-mills
- (lathe and mill required)
- 48 inch-ounce hand torque driver
Step 2: Prepare Clamp Body
First we turn the PEEK bar into a clamp body.
Begin by milling a 1/2" slot, about 2.5" long in one side. Keeping your Y-position in the mill, turn the bar tall-ways in the mill and drill a 1/2" hole perpendicular to the slot. Go all the way through the top, but NOT all the way through to the other side, just go in a 1/4" or so. We're going to make an aluminum insert that pushes in, and it needs to have some material to push against.
Mark the X-position of the PEEK in the clamp somehow, then loosen it, flip it upside-down, and drill a 7/16" hole from the bottom, parallel to the 1/2" hole you just drilled.
Finally, turn to the unadultered slide. Drill a 13mm hole and mill a 3/16" slot intersecting it. The 13mm hole should intersect the slot, and be close to the side of the bar with the 7/16" hole, not the 1/2" hole. 13mm is just a conveniently available bit just bigger than 1/2".
Step 3: Make Threaded Insert
Put your 1/2" Aluminum on the lathe. Drill an inch or so with a #11 and then tap with a 1/4-20 tap.
Turn it down to 7/16" OD for 3/4", then cut it off to 1" overall length.
Slide it into the PEEK part as shown, then put the PEEK back on the mill and drill into the aluminum part, but only a 1/16" after you hit the aluminum. It should be sufficient to hold the aluminum insert into the PEEK clamp with your hand, since it is well ensconced in the PEEK. You should be drilling so as to then tap with 8-32. Make sure you choose your drill bit for tapping aluminum, not steel. Plastic is soft, so you want deep threads (smaller tap drill).
Step 4: Prepare the Pushing Setscrew
We need to be able to put a plastic sleeve over the setscrew. We also need the pusher to fit into a small hole on the back of the 1/2" electrode rod to push pins out. What we will do is turn down a 1/4-20 setscrew on the lathe so that it has an OD small enough to push pins out, and then just make a plastic sleeve sized to that OD.
Mount the 1/4-20 setscrew in the lathe and turn it down to 0.11" for the bottom 3/8". Smooth the bottom of the 0.11" stub so that it doesn't cut through the plastic sleeve when pressure is applied. Do this either on the lathe or save time and use a scotch bright wheel or belt sander.
Run the setscrew through a die to repair the threads close to the stub.
Step 5: Make the Plastic Sleeve
Take your PEEK rod, drill it to 0.111", 3/8" deep. Cut it off 1/2" long, then mount it backwards and make a small dimple with a centering drill so it locates on the top of pins. Take it to the drill press and make a crossing hole with #56 I think, the tap drill for 0-80 threads. Don't try to clamp this small, delicate plastic piece. Just hold it firmly with your hand while you drill. Yes I just said to drill something and hold it by hand, but it is a soft plastic piece that will drill easily, and the tiny bit is not very dangerous.
Drill all the way through, and then tap all the way through, again just by hand. This way you can use the setscrew on the other side if it strips on the first side.
Step 6: Practice Using Your Press Tool!
In the photos you can see me pushing pins in and also pushing them back out. I found that 48 in-oz was a good amount of tightness for the pins. With this torque, it was completely impossible to tug the pins out by hand or rattle them out with a mallet. 80 in-oz was sufficient to push them back out. These torques seem small, but keep in mind the mechanical advantage the threads provide. Quite a bit of force is being applied to the pins.
I found that if I tightened the pin as hard as I could with my hand (50 in-lb maybe?) they were physically deformed so that they sat 1mm lower than before, and took nearly as much to drive back out.
I'll try and remember to write an update after I use this to push ~700 pins into four different rods.
I thoroughly cleaned all my parts, first in an alconex ultrasonic bath, then with rinses of DI water, acetone, isopropanol, and lastly methanol.