How to Make a Wooden Dome | Fire Pit Cover

We’ve got this lovely fire pit for our patio,

but what about when it rains?! Since we already have a pond,

we’re going to make a cover. Which is a great excuse for us to experiment with router jigs.

Our plan is to make this cover a Convex Dome so it sheds the rain. Let’s get to it…

Thinking about it, it sounds like we need a Lazy Susan and a Router Jig. First up let's glue up a

panel we used leftover Scots Pine from the Patio Table we made in the last video. This should match

nicely with the table, although sitting here with the benefit of hindsight. I can tell you

the reduced stability of softwood is not ideal. The leftover stock we had, wasn’t in the best

condition. We’re talking knots, damaged edges, and visible heart wood. So not a huge problem

on an experimental project like this, but we were still careful how we ordered the boards.

As we’re making a dome, we’ll be removing more material from the perimeter than the

centre. That means the best sections go in the centre and we put our defects to the outside,

to where we’ll be cutting it away. We also won’t be using any biscuits

or dominos in the glue up. Don’t want to run the risk of accidently exposing them when we cut the

dome. Some waterproof Titebond 3 wood glue and an edge to edge bond should be perfectly strong.

With a little YouTube magic the glue is dry and we’re ready to turn this panel into a circle.

To make the circle we’ll be using the 6-in- 1 Router Jig from Tamar at 3x3 Custom. Thank

you Tamar. The jig is pretty smart and can be configured to work without a hole in the

centre. But seeing as it was the first time we’re using the jig and we thought we might

reference the centre later on. We decided it was easier and safer to drill the hole.

The jig is a bit of a transformer and in this configuration, we cut the outside perimeter.

As the material was thick we only cut about halfway through. We haven’t cut many circles

like this before and we were pleasantly surprised just how easy and accurate

it was. It was fun as well… so we need to find more excuses to make circular things!

We then moved on to cut a groove with a Round Nose cutter. The rim of the firepit will seat

in this groove as well as serve as a drip stop to stop any water finding it’s way into the firepit.

The moment of truth, did we cut the groove the right diameter? Yes we did!

Now using a jigsaw we trim the remaining material around the perimeter.

And tidy up the edge with a flush trim router bit. It looked so good here, we were actually really

tempted to stop. But a plan is a plan, and if we’re anything… we are sticklers to a plan.

Okay, so, let me try and explain our idea! Our concept for the jig is to have two

curved rails above the firepit cover. The router will move along these rails to cut

an arc. We’ll mount the cover on a bearing from a Lazy Susan, so that it can rotate.

We can then create the dome by setting the router at a point on the arc and

spinning the cover one revolution. Then we’ll move the router up the rail a small

amount and repeat. By doing this enough times, we will create a dome shape.

Now there are a few challenges we need to overcome. This is where CAD modelling really

comes into its own. We can throw all our critical dimensions at a drawing, and the geometry will

dictate to us how we need to make the jig. First challenge… What radius should the dome

be? This is governed a little by aesthetics, but largely by how thick the starting material is,

and how much we want left at the perimeters. Second challenge… How will we guide the router

to move in the required arc? We’ve already said rails, but the router

can’t move forwards or backwards, nor can it rock. It also needs to sit as low as possible.

And that ties into the final challenge… the router and router bit will only be able to cut to a

certain depth. That depth will need to be equal or greater than the maximum cut depth on the dome,

plus the height of the jig itself. Given we want the jig to be sturdy, it will need to have

as much material as we can give it, without making it too tall to work. So easy right!

After a little back and forth we decided the best way to guide the router was using the guide rods

that it came with. These will keep the router as low as possible and the base of it can also sit

between rails to restrict any forward backward movement. Also, being two cylinders mean that

the router will stay stable on the arc. By mocking up both the cover and the

router in CAD, we can see how tall and at what arc we need to make the rails.

To draw the correct radius onto the rails, I left Michael to it and he came up with this

hair brained scheme. First, he measured out the radius using a laser and tape measure. Then put

a screw in our desk at the measured point and using the old string technique drew an arc.

We then cut out the arc at the bandsaw,

sanded smooth and copied and pasted at the Router Table.

Using centre marks on the base of the cover, we secured the Lazy Susan with a few short screws.

Then we marked a cross on the top surface of the cover.

Now we can bring in the magically assembled router jig and align it to the cover using that

cross to keep things centred. The important part of this jig is that the Lazy Susan,

cover and jig must all have the same centre point. We then screw the jig down to stop any movement.

Hands up if you can spot a problem!

It quickly became abundantly clear that this wasn’t going to work.

These bearings are designed to be secured to both sides, but access holes need to be drilled

through one part. Given we didn’t much feel like drilling four big holes in either the cover,

nor our workbench, we had to get creative. Thankfully the solution was a simple one.

We cut a circular puck the same size as the hole in the centre of the bearing. Then at

the same centre point as everything else, screwed it to the workbench.

We then dropped the cover on top of it and all was right in the world again.

Well... not everything. The cover still had a little uppy downy play where the

router would be cutting. To stop this, we placed a little finger underneath to remove the wobble.

For the router bit, we used this 1” surfacing bit. We shopped around a bit for the right cutter.

It was important that it was able to cut when plunging, as well as in horizontal movement. Our

thinking was that a 1” cutter was probably safer than anything larger. And given we were unsure

how much abuse the cutter might experience, we thought it important get something higher

quality. Speaking with the benefit of hindsight now, I can thoroughly recommend this cutter.

And with the rails in the router we are almost ready. Just need to add

these spacers that keep the router centred between the rails. And we’re good to go….

So I was all set to start there, Router in hand when Dora popped in and quite rightly pointed out

that my curve is pretty rubbish. There's a high point or a low point here, I'm not sure which,

which I think when duplicated around the circumference is going to become pretty

obvious and pretty ugly. This is probably a consequence of my string technique.

Although it's a reasonable technique, over a 3 meter length the string is very stretchy and

it that led to a very wobbly line, and so I cut a very wiggly line as a result.

Thankfully I've cut the curve on this side, but this side's still square. So I'm going to

try a different technique and hopefully get the right curve this time. As is so often the case,

the best solution is also the easiest solution. Lofting is a drafting technique used to generate

a perfect curve from a few key reference points. It’s used a lot in traditional boat building and

one we’ve seen used many times by Leo on his channel Sampson Boat Co. Frustrating we didn’t

think of it sooner, but, glad to have a solution. All we needed to do, was mark the depth of the

arc onto the jig. A measurement we got from the CAD model. Then we secured a thin strip

of MDF at these marks. The MDF naturally forms a curve, giving us the perfect arc.

Again another bit of YouTube magic and we have our jig, this time with a perfect arc.

With everything good to go, we put the router on the rails and moved it into position. We

thought starting at the outside with a shallow pass was the best place to start.

It was slightly nerve racking to start with. Although we’d tried to cover all bases,

we had concerns that the router might move, or could potentially grab the cover and spin it out

of control. We covered these concerns by clamping the router to the rails and working together.

Michael was in charge of the Router, while I rotated the cover, being sure to rotate clockwise

against the cutting force. We also started out with a shallow pass to get a feel for things.

With one rotation done, we could plunge the router further and do another pass. We thought the best

approach would be to remove the bulk of the material first, leaving just 1mm or so that

we could remove at the end. The thinking being, that this would give us the best surface finish.

Setting the right depth was easy, off camera we moved the Router to the centre of the cover

and moved the cutter down to 1mm above the surface. We then locked in the depth stop so

we could repeatedly return to that depth. It was then just a case of incrementally

moving the router along and repeating. Each time we move along was just a little less

than the radius of the cutter. This worked very well, and we were soon moving quickly.

We were really pleased to find the jig worked perfectly. It was effortless to

remove material and it left a really good surface finish. As we went on,

we became more relaxed about removing greater amounts of material in one pass. Every time the

router just kept cutting like a hot knife through butter. In hindsight we could have

potentially used a larger diameter cutter to speed things up. But it really didn’t

take that long and we are yet to test this with hardwood so perhaps the smaller cutter was best.

So that was going fantastically... until it wasn't! Our plan there was to

Router all the way up the surface and then just do one final 1mm pass to to get a really

nice surface finish at the end. But what happened is when we went

for a coffee break and when there wasn't the material to support it anymore the the whole

circle has warped a little bit. So when we did our 1mm past around here

in places it's perfectly at 1mm, in other places we've got like almost 6mm of removal.

That's because here, it's nice and tight against our peg, whereas over here there's a blatant

wobble to it all. So we looked at different solutions, we were trying to run a caster

maybe to hold this down, and that would solve it. The problem is is there wouldn't be enough space

to get the caster and the router in, we could run the caster here, but then that doesn't

really solve the wobble issue. So what we're going to do instead is cut our losses and we're

going to put a round over on this edge here. And we're just going to sand this off because

our surface finish at the moment is pretty good. What a pain eh? In hindsight we should have just

gone to final depth on that first pass and we’d have avoided all these problems. It

always amazes us how much wood can move and how much internal stress it can be under.

If this piece really mattered to us, we’d... well remake it, or maybe look at inlaying a

piece of wood in the worst affected areas, then re-machining the round and dome shape.

But seeing as this is just an experiment we’re happy to slap some wood filler in and

call it a day. Our hope being that none, or very little will be visible once we add a roundover.

And there you have it, you’d never know. It now just needs a final sand and boom,

we have a perfect dome shape. We’re really pleased

and wondering now how we might apply it to other projects, any ideas folks?

Unfortunately, the cover is still warped. But we can fix that with this brace on the

underside. We glued and screwed this. Which… yes is not the best plan for future movement…

but we ran out of time and this will do for now. To do it properly, we wouldn’t use glue and we’d

either drill the outside holes as slots. Or, better yet, create a sliding dovetail for the

brace. We might have even added this stabilising brace before we’d started cutting the dome.

We’re going to chalk up this experiment as a success! The jig work perfectly… very accurate,

great surface finish and was much faster than we had anticipated. Also,

it could easily be modified to create any flowing curve. Maybe a wave shape, or any of these…

One big learning moment was how important it is to appreciate the

stability of the material you’re working with. When we do this again in the future,

we’ll certainly keep this in mind. The good news, is there are plenty of ways to deal with it.

Let us know if you found this video useful, there are so many applications that it can be used for,

we’re keen to know what you guys are making! Ta-da it fits perfectly and it sheds the rain

so job done gold star. As always if you enjoyed the video or learned something new a Thumbs Up

and a Subscribe go a long way for us. We're still trying to navigate to this YouTube algorithm and

get ourselves known so any support is much appreciated. Until next time folks.... cheerio.