So first off I'd like to give credit to Mikey77 and his original Ooogoo tutorial as well as The King of Random for his "Proto-Putty" tutorial for the inspiration for this project!
So one issue I had when experimenting with using silicone caulk for different projects is that the material is so thick and sticky that it's very hard to form it into clean shapes, so if you want to get a cleaner look on a project using this you'll need to spend a lot of time shaping and cleaning it up.
Another project I also wanted to try was 3D printing grips or additional pieces for pre-existing objects. The difficulty I've had with this is how tight the tolerances need to be, otherwise you've got a lot of sanding and gap filling to do.
This project was my attempt to solve both of those problems. It has several benefits over hand-shaping or fully printing as you can re-use your CNC'ed or 3D Printed (Or even handworked) mold multiple times. You only need to have tight tolerances on select parts of the object you're covering, as the silicone is fluid and fills the gaps perfectly. Making a mold around a straight PVC pipe is pretty simple, but it might get complicated with differently shaped objects so you'll need to do some more intricate modelling, otherwise I've got the STL file available for my grip if you want to make a 1/2" PVC pipe grip, or get inspiration for your own project.
Here are some good resources to design your own grips and molds:
"A Check-List for Handle Design" A good PDF with info on ergonomics
"How to generate a 3D printable mold for an object!" A very in-depth tutorial that I wish I found before I started designing my project. I used Autodesk Inventor and had a friend 3D print the part for me, so I won't give much of an in-depth tutorial on printing or designing, as every piece of software and every printer is different.
Step 1: Materials Needed
-Clear Silicone caulking, MUST BE PURE SILICONE, usually labelled "Silicone 1". It can be white caulking but it will not take dye very well.
-3D Printer or CNC and material
-Nuts and screws or some other way to apply pressure to your mold.
-Object to apply grip to, in my case I used 1/2" PVC pipe.
-3D Modelling software
-3D Model (Link to my grip for 1/2" PVC)
Step 2: Design a Grip
First off you need to decide what object you want to make a grip for, for me I wanted to make a grip for a friend's PVC blowgun, or some PVC walking sticks. PVC pipe is relatively easy to make grips for since it's a uniform diameter cylinder, so I just made a 2D sketch of a rectangle with a length slightly larger than my hand and the width equal to the diameter of a PVC pipe, and revolved it to make a solid model. This technique would work pretty well for simple tool handles, bike grips, etc.
If you want to make a grip for something more complex than a pipe the best thing to do would be to get some calipers and measure a few cross-sections of the object at the edge of each area you want to cover. Of course, if your modeling skills are lacking you can always hand-mold the silicone around them.
Step 3: Make the Handle Model Into a Mold
The specifics of how to create a mold of your grip varies depending on what software you're using, so I won't go too in-depth for it (Youtube is your friend!) but I'm using a limited student version of Autodesk Inventor and had a hard time figuring out how to make a mold with it, so I just took the 2D profile I sketched for my grip and did the same revolving extrusion of it, except set to "cut" and placed on the surface of a rectangular block.
You'll need to make some alignment nubs for your mold, so what I did was mark 6 points on half of the mold, make a hole on each point for some bolts to go through (to tighten and apply pressure to the mold), then made a mirrored 3D model of it. On one side I made a hole on each of the 6 points that went down around 3/8" and then the other side got some tapered cylinders sticking out to fit into the aforementioned holes.
When you're designing the mold you need to consider how the mold will close and squeeze out the excess material. To do both of these things you will need to apply pressure to the mold, which can be done in a vice, with clamps, or in my case, with screws. Screws have the benefit of being cheap and easy to apply even pressure with.
Step 4: Make the Mold
Once you have the 3D models of the molds finished you can 3D print or CNC them for use. I recommend printing at very high resolutions and low infill as there will be little stress on this part, and you'll want them to look clean. Of course, if you print at lower resolutions the ridges and layers will be more pronounced, which will actually add additional texture and grip to your finished rubber part.
You can also sandblast, (or acetone finish for 3D printed ABS parts) molds for an improved surface finish of the final part.
.STL files for my 3D Printed Mold: Thingiverse
Hardware used in my mold:
x6 3.5" long #10-24 screws
x6 #10-24 wing nuts
x12 #10 washers
Step 5: Prepare Your Object for Molding
Silicone will not stick to anything other than itself, so unless the object you're covering is made of silicone you'll want to add some texture to your object to be covered. I did this by sanding the PVC pipe rough, and adding spirals of hot glue to the surface, but you could always sand or cut grooves into your object's surface if it is smooth enough that you need to worry about the silicone sliding off.
The second picture shows a cross-section of the silicone grip cut in half, showing the indentations left by the hot glue that made the grip harder to slide off of the object.
Step 6: Make Your Silicone and Fill the Mold
For making your silicone material simply follow the original Oogoo tutorial or The King of Random's Proto-Putty video. In a very short version, you can just squirt a few drops of food dye into a cup or bowl, and then squeeze out some silicone caulking on top of it, then mix it together until the silicone is a uniform color. From there it'll be very sticky, so you can roll it and knead it in corn starch until it's less sticky and easy to work, but for our purposes of just globbing it into a mold it's not necessary.
WARNING: This stuff smells bad and releases fumes that burn your nostrils and other areas, so mix it in a well-ventilated area, and leave your finished product to vent once it's fully cured if it still smells. Also wear gloves since it may damage your skin or stain your hands with dye.
Pro-tip: Seal your caulk tube nozzle with a rubber-banded ziploc bag/glove finger / etc. or tape so it doesn't dry out.
Use a Popsicle stick to scoop the silicone out of the cup into both sides of the mold. You'll want to make sure to push the caulking into all the corners and fine details of the mold to prevent bubbles from forming. It's better to make too much silicone than too little, as even if you over-fill your mold, any excess will just squeeze out the sides, but too little will cause voids and bubbles.
Step 7: Insert Your Object and Close the Mold
Simply place your object into one half of the mold, squishing it into the silicone, then press the second half of the mold on, making sure to align the nubs. If there is squeeze out, that's a good thing, as it shows you have more than enough silicone to fill the mold. Press the mold together by hand to the best of your ability, then apply whatever clamping method to the mold for additional pressure, in my case this was inserting the 6 screws, with washers to distribute the pressure, and tightening the wing nuts to press the mold shut. Any excess squeeze out can be wiped away or left alone for removal once it is cured.
Step 8: Pull Object From Mold
Leave your silicone to cure for several hours, depending on the size of your object and the amount of silicone the cure time will vary, so to be safe I left mine alone for 24 hours to make sure it cured all the way through.
When you pull the grip from the mold there will be a thin layer of flashing covering the seams along with any squeeze-out along the edges, which can be cut away with a razor blade or x-acto knife, or just plucked off by hand if it's thin enough to not leave much material behind.
Step 9: Gap-filling Mistakes or Bubbles
So say you pull your grip from the mold and there is a bubble or void, fear not! You can make up another small batch of silicone, and apply it to the gaps in your grip, and press it into the mold again. I did so with a different color to clearly show it filling gaps. I also didn't have any large gaps so I just cut chunks off of the handle for illustration purposes. In the 3rd picture the bubbles at the top are a result of inadequate pressure as I didn't have a pipe through the while grip, and I only pressed it into one half of the mold, but if you do it properly the results should turn out perfect.
Step 10: End Results
After pulling out the finished product and cleaning it up you should be left with something like this! Depending on how big your grip is it will usually only cost about a dollar or two, with a regular tube of caulk costing ~$6 and the food dye costing a few dollars for a pack of 4, which you only use a small amount of in each grip.
The silicone will smell for a while, so it's recommended to leave it in a well-ventilated area as even once it cures it will off-gas some fumes.
Step 11: Using Oogoo/Proto-putty for Mold Making
Using Oogoo/Proto-putty for molds:
It's a great material for casting resin and other materials as nothing sticks to it easily, but make sure you use mold release when necessary, and realize that it'll be hard to get results comparable to liquid silicone products specifically for this type of application. I have a picture of a rough keyboard key casting from an Oogoo mold, which has pretty good results (other than the dust on it due to the resin still being tacky) so it's definitely viable for simple parts casting, and I believe you could even produce 2 part molds with it, so long as you use the proper technique.
Thinning Silicone for mold pouring:
Many people have tried to turn silicone caulking into something thin enough that you can pour it like a liquid over objects and make molds. This is likely not possible for silicone caulk, and you're better off buying the supplies from a craft store, Tap Plastics or another plastic supply store, or online from a supplier like Smooth-on or Alumilite. Your best bet for thinning silicone is either adding a solvent such as paint thinner, which thins it slightly but still not to a liquid, or adding silicone oil. I have only experimented with paint thinner slightly, with limited results, but some claim that the mold will dry out and shrink over time which is sub-optimal.I have yet to try silicone oil, but it seems like a more logical additive, and if I get good results with it if I ever experiment with it, I will be sure to report on them in another Instructable.
3D Printing inverse molds/ Silicone external molds for resin casting:
If you like you could make a positive mold instead of the negative mold I did earlier in this instructable. The second picture is an example of such a mold. You could press the Oogoo over this positive part to get a negative mold made of silicone, and you could follow a roughly similar process to instead make an external grip from resin instead of silicone rubber, so long as you seal it tight and add proper vents. Clamping would be different as it's softer and would require a different mechanism, plus the resin will be much more fluid and prone to leakage than the silicone, so modifications would need to be made but it's definitely viable.
Step 12: Additional Notes and Experiments
So while doing research for this project I came upon a lot of other processes for different mixes and uses of silicone:
Making Silicone softer or tougher:
One easy way to make silicone tougher is to roll it in cornstarch, I found that The King of Random's recipe for proto-putty tends to be somewhat harder and less stretchy than just silicone with food dye in it, so if you want a more firm grip roll it in cornstarch, just make sure you don't try to stir it into the mixture, as it tends to clump up and give you poor, non-uniform results.
I haven't done any empirical testing but I felt as though the silicone I mixed paint-thinner into was softer than any of my other mixtures, so take that into consideration. Be warned though, that paint-thinner also smells bad, so you'll get a noxious mix of vinegar smells and chemical smells from the caulk and solvent.
Mikey77 experimented more in his original Oogoo, and Ooogoo II instructables so check those out
Re-using scrap silicone:
I failed to acquire a blender in time so I have yet to experiment with this, but I believe that you can save the scraps from your failed experiments or excess leakouts from the molds, and blend them into fine pieces to add to your rubber. I know it's common for recycled rubber particles to be added to tires or other products, since you use less new rubber. The colors might not all be the same, which can be good or bad depending on your effect, which leads me to my next idea/experiment
There is nothing saying you have to use a single color in your project! You can mix several different colors of silicone, and apply them in different patterns or designs for neat looking effects. You can also experiment with adding different particles like sand or glitter to your project, which can have interesting results, although when I tried adding sand for a 'gritty' effect I added too much and it was chunky and fragile, so add small amounts.
Step 13: Final Note
Thank you all for reading! This was my first instructable and I apologize if it got a bit rambly at some points, let me know if there are any points I need to clarify, or if you have any questions.