Introduction: How to Make a Round Thing Without a Lathe (plus Model Making Tips)

By dadcando
About: Eldest of five, son of two doctors, 10 years in Graphic Design and marketing, then retrained as a Biomedical Materials Engineer, don't ask me why, I think it was because I had always wanted to design artificia…

You want to make a model of something that you've seen in a film, but it's round and has lovely compound curves and you don't have a lathe. Don't worry, this instructable will show you how you can use a simple profile and some car resin filler to get a lovely round shape with out using any machines at all.

For me I used it to make this alethiometer from the book Northern Lights (aka the Golden Compass in the US) and shortly to be released as this Christmas's big hit, the Golden Compass. Which looking at the trailers is a mixture of Riven (the game for those that know), Steam Punk and a bit of Round the World in 80 Days thrown in for good measure.

Full instructions on how to use this instructable to make a Golden Compass can be found on my website dadcandohere, including free printable templates for all the graphics and an accurate profile template guide.

But then you can make loads of round things using this method... I'm sure you'll think of them. Post pictures here if you do, we'd love to see them.

Step 1: Make the Basic Shape

In this case I wanted a flat disc a little bit like a large ice hocky puck or in fact a pocket watch, to match the shape of the device drawn on the front of the book. I made my basic shape out of cardboard, but really you can make it out of anything.

Model Maker's TIP #1

If you model is of something that has weight, i.e. it is made out of metal, plan to fill it with some ballast. This will make the final model much more realistic and fool people into thinking that it has been made out of metal, or has more of a quality feel to it. But be careful not to stick anything over the centre hole area, you are going to need to be able to poke something through the card right there in the next step.

In this case I cut two discs and then used up right spacers to make sure they were at a constant space apart and then wrapped a piece of card round the assembly to give me the disc shape.

Step 2: Make and Insert a Spindle

Using a piece of straight coat hanger wire push it through the cardboard disc so that it is on the axis of the shape you want to "turn", i.e. it is as close as possible to being at right angles with the top and bottom surfaces. If you have trouble pushing it through, make a (very) small nick in the surface with a craft knife first (just to break the surface) and to get started.

It should be a nice snug fit, but be able to turn. This is what you are going to stick you profile on to.

Step 3: Stick a Rough Handle on the Bottom

Model Maker's tip #2 Think how you are going to hold the project while you make it!

Model makers often run into into the problem of how to hold something small or fiddly or awkward shaped when making, finishing or painting a model. The way they get round it is they stick a handle on to the model that they are going to remove later in a place that no one will look, or in a place where the mark left when the handle is removed can be covered up later.

For small things this might mean super gluing (cyano-acrylate) a cocktail stick to the edge of something small, right up to resin gluing a piece of doweling or a metal bracket to something big.

In this case you are going to need some way of turning the disc when it is covered in wet filler, so this handle will do nicely. later in the model we will remove it and cover the mark with some flat filler.

Obviously don't put the handle over the centre hole area. It needs to be central but not over the place where the hole is going to be and clearly not overhanging the edges, because we are going to be making a profile there.

Step 4: Cut Your Profile

Measure the crucial dimensions of your basic form (you should already know them from making it to the right shape. But if you are anything like me and make it up as you go along... now is the time to get measuring. Draw up your profile on a piece of paper. and cut out and offer up to the basic form. if it fits and can rotate around the axis without fouling any where (being stopped turning), then the profile is right and you can stick the paper to a piece of plastic and cut it out.

I always like to use what I have lying around, and the plastic I used for this model profile was from an old detergent bottle that had reasonably straight sides from which I could cut a big enough shape to hold.

Glue your profile to the wire coat hanger making sure that it is nice and square to the rotation axis of the basic form. I used glue gun glue and then sticky tape to make sure that it stayed put. You don't want it coming off half way through the exercise.

NOTE: I tried cardboard for the profile, but it could not keep a clean edge.

Step 5: Mix Up Some Filler and Start Spreading It Round With the Profile

It's magic, you shape starts to appear immediately. try to make the shape as clear as possible, but you don't need to do all the shape at once. In fact this is almost impossible so don't try it. You are going to be building your shape up over a few goes. ( I have pictures of each step). Given the resin only takes about 10 minutes to go off, this process won't take that long, even if you have to do 6 layers!

Between each layer trim off any wayward prongs or bulges that impede the easy rotation of your profile, i.e. stick up in the way of the profile, If you are using car filler resin (see below) then the best time to do this is when the resin is in the gelling phase as it is going off. Be quick, the gelling phase is only about 30 seconds to 1 minute long. This type of resin is called a "snap cure" and once the setting reaction gets going it is a driven by what is called an avalanche effect at the molecular level. Once it is set the only real way to remove lumps and bumps is by rasping, filing or sanding. (note always wear a mask when doing this to avoid inhaling the dust). In the gelling phase the resin is hard enough to keep it's shape but cuts like rubber, so quick gross modeling is possible then. However, be careful, before it is set it is not stuck that well so you can also dislodge what you have just made, if you cut to aggressively.

As for the filler I used... My favourite is two part auto body repair filler (resin car bodywork filler). You mix it up from a big pot of resin and a tiny bit of hardener.

Model makers like two part fillers because they set very hard very quickly and can be sanded very smooth and take paint well.

Model Maker's Tip #3 Use two part car filler to make nice fillets round you models, and even cast the odd detail (if you have a suitable mould pattern).

TIPS...
Don't put the mixed up resin covered spatula back in the pot to get more, the hardener on the tip will set off a reaction that hardens the whole tin.

Be ready with your profile before you mix up, once mixed up, the resin is going off and will become very hard so you don't have much time to get things right

If you want it to go off quicker mix a tiny bit more hardener, but be careful too much and it will set as you are mixing it.

CAUTION
It sticks to anything and once hard is impossible to remove, either wipe it off straight away when it is semi liquid or wait till it is in the gelling pahse and chip off quickly (very quickly) before it is stuck.
It gives off fumes so open a window when using resin filler

Step 6: Put More Filler on and Shape With Profile

In total I did about 6 applications of filler. I have shown pictures taken at stages 2-3-4, here. Looking good. I took the profile out after each application so that I could chip the filler off it between each application so that I got a neat shape.

At step 4 the handle fell off the back. I just glue gunned it back on, it was only cardboard after all, and I still need it for a couple more goes.

Step 7: Put Filler on Shape With Profile and Sandpaper

Stages 5 - 6
Maybe you already had a quick go at sanding down between each application. if not now is the time to start doing that. Start with coarse paper P80 or P100 go with the curve and don't worry too much as you know that the next application will fill all the scratches left by the grit on the paper. After the final application you will want to move first to about a P200 and then finally to a really fine paper. I used P600, but that was only because that was the finest I could get in my hardware / DIY store.

You might note the slight colour change from the photos as we go along, this is just my digital camera and the fact that the sun was going in and out. These pictures were taken at each stage so that you can see how much filler went on and how much the shape evolved at each stage.

Looks nearly done now (shape wise that is).

Step 8: Finish Off the Back

If you want a curved back then really you have to do the same again, on the back. For me, I was happy having a flat back, so I just pulled off the handle (carefully), filled in the hole with filler, sanded, filled, sanded and that was that.

It looks soo cool now I could almost each it.

Step 9: Spray or Paint the Project

What you do now depends on how eager you are to finish it off, or whether you are prepared to do a perfect job. If it's the latter you want to go for then you should spray with undercoat first and sand down with very fine paper, say P800 or finer, between each coat.

For me I just wanted to get on and I had no primer anyway.

As you can see here I sprayed and then sanded off, because I sprayed too much and it started to run. If that happens to you. bite the bullet and remove at once using thinners and a rag. make sure you don't get a load of lint fibres and dust stuck to the surface. Rub down with sandpaper till fine and start again.

Model Maker's Tip #2 (yes I know I have already had a tip #2) But this is the same one.

Remember the tip? find someway of holding the model so that you can spray it and then leave it to dry without it getting stuck to something or getting marks on it. I guess the tip here is THINK of this before you start to spray and not half way through when it is wet! In this case I gently rested the disc on a coat hanger wire poked into the hole that was left in the top, as the hole in the base was filled.

You could use any bit of spare real estate. In real models, witness marks (the marks left when where something that was holding the original moudling is removed) are usually covered by a label or another component.

Step 10: Spray or Paint the Final Top Coat

Oops sprayed my thumb, but oh joy... it's finished, and boy doesn't it look trick. Don't get impatient now. All this hard work will go to waste it you handle the finished thing before it is dry. Find some way of propping you work piece up while it is drying. In this case i used a small desk top vice to grip the coat hanger wire, but a hole in the top of a scrap of wood would work just as well. Make the stand or place to rest the piece BEFORE you start spraying. Don't make it anywhere it will get disturbed, and leave it for as long as possible to make sure the paint is really hard and dry. over night should help, somewhere warm would be good... you get the picture.

Woo Hoo, but... this is just the basic shape of my Alethiometer. Theres a whole lot more to be done to make it in to that model... but that is another story and for the full instructions of how to make the Alethiometer and all the templates needed, you can get them at dadcando right here. But then this is only one of the 100s of things you could make using this simple technique.

NOTE: for the glorious paint i just used a can of BRILLIANT metallic paint which in my hardware / DIY store come in both gold and chrome and gives the most outrageous finish, if the surface is nice perfectly smooth, perfect for showing off all those lovely complex curves.

If you make something don't forget to post a picture of it.