Thread: Cutting groove into pergola post

Originally Posted by yoboseyo

I need to cut a 10*300mm groove into the end of a 200mm blackbutt post to fit a T blade stirrup. What's the best way to do this?

The best method I can think of is to come from opposites sides with a 235mm circular saw that will go past half way, but I'll either have to go half a saw blade further into the post, or somehow get rid of the excess in the middle somehow.

Any ideas?

Do what you suggest up to the line, finish bottoming out the cut with a handsaw or recipro saw, chisel out the waste

Originally Posted by mic-d

Do what you suggest up to the line, finish bottoming out the cut with a handsaw or recipro saw, chisel out the waste

yoboseyo

As mic-d suggested. I would add that drilling a hole at the bottom of the cut full width will assist removing the waste. It might be easiest to drill the hole before using the combination of saws. I would use a suitably sized spade bit or a brad point bit.

Regards
Paul

Thanks for your thoughts!

I don't have a reciprocating saw, but I concur that it would be better to manually remove the waste. I just didn't know how much work it would add, working with blackbutt. I will look to use a hand saw. I have the option of drilling a row of holes and chiselling the walls, like doing a mortise. Depends on how much work it is to hand saw.

Originally Posted by yoboseyo

Thanks for your thoughts!

I don't have a reciprocating saw, but I concur that it would be better to manually remove the waste. I just didn't know how much work it would add, working with blackbutt. I will look to use a hand saw. I have the option of drilling a row of holes and chiselling the walls, like doing a mortise. Depends on how much work it is to hand saw.

Paul's got the best idea, drill down at the bottom of the slot with a 10mm drill, come from both sides, cut the sides to the hole with your 235mm saw, cut down remaining cheeks with a handsaw, if you don't have one, good excuse to get one. Waste should fall out, probably no need to finish up with a chisel... Blackbutt is pretty easy going

Small Chainsaw

So imagine my infinite disappointment when I realised that my 235mm circular saw (Hitachi C9) only goes a max of ~80mm deep. Looks like a recipro saw is mandatory.

Also ran into a bunch of other issues.

Cutting the end sufficiently square such that the post will be able to stand upright without support requires a reference face. Not only did I not have a reference face, but I need to cut both sides as the saw doesn't go deep enough, which would require 2 reference faces. The end ended up being out of square by the width of a saw blade.

The cut depth of the saw was also out of square, such that I'm at 0 on the angle adjuster and it's still not square. I anticipated this but was hoping it would not be the case.

Alas. Lessons learnt

Originally Posted by yoboseyo

So imagine my infinite disappointment when I realised that my 235mm circular saw (Hitachi C9) only goes a max of ~80mm deep. Looks like a recipro saw is mandatory.

Also ran into a bunch of other issues.

Cutting the end sufficiently square such that the post will be able to stand upright without support requires a reference face. Not only did I not have a reference face, but I need to cut both sides as the saw doesn't go deep enough, which would require 2 reference faces. The end ended up being out of square by the width of a saw blade.

The cut depth of the saw was also out of square, such that I'm at 0 on the angle adjuster and it's still not square. I anticipated this but was hoping it would not be the case.

Alas. Lessons learnt

You got there in the end. Sorry I mentioned the recipro saw, I just thought if you had one it would do, but they're mainly good for demo work (I haven't used mine for years) You'd be better served with a good rip saw and crosscut saw just in my opinion . A sharp rip saw would have cut the rest of the waste pretty quickly. I don't really understand the problem you had with the docking. I would do it this way with limited tools. I'd square around with my biggest square (I have a builders square with stair gauges) and see if the lines meet, if they do I'd use that square as a fence for the circ and cut all way around and finish off with a handsaw. I might even clamp a longer straight edge to the square to make it more accurate. You can also make a collar out of ply that slips over the post and acts as the fence, if you make it up out of sqaure ply parts it can't help but make the cuts meet up. I do this for smaller posts where I'm putting on details such as grooves and pyramid tops...

Thanks everyone!

I eventually got it done. Ended up buying a used recipro saw from the Facebook marketplace, and it came in mildly useful to chop out the middle after both sides were ripped using a circular saw.

The challenge was to get the cuts to meet in the middle, which was very difficult because the posts were nowhere near square. I had to use a lot of guesswork and shims to align the cuts.

post-groove.jpg

I started the job during the New Years break before the stirrups shipped. After the stirrups arrived, I realised I had a massive problem - the stirrups were so far out of square that if they were to sit on their base and the post being put on it, it would borderline tip over because of how far off vertical it is.
stirrup-out-of-centre.jpg
I'd ask for a refund but it's too late - this was the only spare time that I had to do concreting, so I set the stirrups in the concrete and made sure the blade was upright, and just allow the base to be crooked.

The problem with the stirrups being so far out of square was they won't sit all the way into the grooves that I cut, which made it very challenging to cut the bolt holes from either side and make sure they meet in the middle through the holes in the stirrups. I ended up doing a barely adequate job - M12 bolts and M16 holes, so there's quite a big margin for error. They don't line up perfectly, but enough for the bolt to go through.

I regret the effort I went to to ensure exactness - it was obsolete with the stirrups. I had no idea how rudimentary outdoor stuff is. I know I'm not making fine furniture but this is ridiculous imo.

The next step is to get some mates and push the posts up, and then somehow align the base of the posts on the stirrups to get the bolts through. No idea how to do that, but cross the bridge when I get there.

Those stirrups are woeful, but I think you could have straightened them by levering once the post was on. To align the post holes use a big hammer and a block of wood for left/right and a crowbar for up. Once you partly align you can use a long punch to bring it into final alignment.

How did you attach the stirrups to the concrete? Not just concreted in surely? They won't have any tie down capacity, unless you put in anchors?



Cheers
M

Originally Posted by mic-d

Those stirrups are woeful, but I think you could have straightened them by levering once the post was on. To align the post holes use a big hammer and a block of wood for left/right and a crowbar for up. Once you partly align you can use a long punch to bring it into final alignment.

I didn't think of that, and I'm not sure how much 10mm steel will bend. Thanks for the tip on aligning the bolt holes. I dry fit the stirrups before setting them so I shouldn't have to adjust them up.

Originally Posted by mic-d

How did you attach the stirrups to the concrete? Not just concreted in surely? They won't have any tie down capacity, unless you put in anchors?

I used 100mm concrete bolts

I managed to put the posts up without much trouble.

It turns out that there is a fair amount of lateral movement from side to side of the T blade, which I had expected to be perfectly rigid, as it is 10mm steel.

As it is, there is a racking force on the pergola that I now need to address. I'm hoping that closely fitted half lap joints fit the rafters to the joists (more like quarter lap) will progressively add rigidity. If not, I'll add knee braces in the direction of the rafters.

I still prefer keeping the posts out of the ground for longevity

20240311_191351.jpg

IMG_20240316_133825-1.jpg

All done, except for the corner braces. The notched joinery improved the stability so that it is not a concern but it still racks with a firm shake. I'll add the corner bracing in the future