Hollowing out oak beam.

[Bogart]

re the fire rating, I would try a layer of fireproof plasterboard between the steel and the beam - get that signed off and then add the beam as a decorative coating. Have you got a hollowed out beam approved as 30 minute fire break? I know that in practice it will be fine but interesting experiment if a BCO will put his signature to it as I doubt that it has a certification stamp on it, so it's his neck on the line rather than buck passing to some 3rd party agency*.

We have granite worktops that have mitred edges then chamfered. it looks very good and you can't tell that it's two pieces of granite glued together



*I had a great BCO who let me use hand-made oak ledge and braced doors with a clear intumescent coating as equivalent to fire doors but I have the suspicion that lots of BCOs wouldn't do that

The BCO is fine with my proposal ie 50mm thick all round offering nearly 100 minutes of charring resistance. Oak has clearly defined fire resistance, approx 0.5mm/min, so if thickness is sufficient no need for any certification and nobodys
neck on any line.
Granite worktops are laser cut not with a saw blade.

 

[Bogart]

re the fire rating, I would try a layer of fireproof plasterboard between the steel and the beam - get that signed off and then add the beam as a decorative coating. Have you got a hollowed out beam approved as 30 minute fire break? I know that in practice it will be fine but interesting experiment if a BCO will put his signature to it as I doubt that it has a certification stamp on it, so it's his neck on the line rather than buck passing to some 3rd party agency*.

One wall of our kitchen extension is the original outside wall of our C16 timber-frame house - a jettied wall of close-studded oak. When the BCO came along for the final inspection, he refused to sign-off because of the exposed studs and said they would have to be covered with plasterboard due to fire regulations. I pointed out that the rest of the house had abundant exposed woodwork, to no avail. I pointed out that 450+ year old 6x4 inch oak studs would almost certainly provide 30 minutes of structural integrity in case of a fire and that we also have multiple exterior doors and more than one staircase, so we have many fire escape options, all to no avail. I then pointed out that the house is G2* listed and that I couldn't cover everything in plasterboard without CO approval and suggested that he should discuss this with our CO when he returned to his office.

I didn't hear anything more but a few days later the fully signed-off paperwork arrived by post. :roll:

Sounds like one of the jobsworth BCOs who do exist. Most tend to be of a younger generation and basically are deluded. Probably went back to the office and had a word with somebody more sensible and experienced.

 

[Bogart]

Cutting oak with a circular or table saw takes some effort. I cut a plank off my piece 65mm thick, which started out with a 250mm x 250mm cross section. I used a big old Metabo circular saw with a cutting depth of 90mm. To cut 90mm into the oak needed 3 passes each doing 30mm. Same from other side finishing off with the chainsaw so my cross section was then about 250mm x 180mm the size required to cover the RSJ. Depending on the weight of your beam will determine how easy it is to push the oak against the blade and will definitely not be a one man job. My oak before the start weighed over 300kg.

Mine are only 4x4 inch so a lot lighter. Does the blade struggle to cut oak or is the weight of the oak the problem? I've never tried cutting oak before.

Oak is considerably harder to cut than most woods, fairly obvious being a hardwood for starters. That is why I did three cuts of 30mm each to not strain the saw. It would have done it on one hit at 90mm but would have been very very slow progress.

 

[LadyArowana]

Easier yes but not as nice looking. You will never get three planks to blend or join exactly. Also if it is a structural item, as in my case, it is covering it will have to have a 30 min minimum fire rating and the joints have to be filled in with an
intumescent seal between the planks, again rendering a nice perfect finish nearly impossible.

Too late now, but as you had the original large piece of timber couldn’t you have taken that to the sawmill, had them cut it into the 3 pieces and then reassembled?

 

[Bogart]

Again we have the problem in getting the 3 pieces to match. A sawmill blade is about 5mm thick and will rip a bigger gap than that. Plus weighing over 300kg, 6 man lift no easy transportation job.

 

[Zebra]

Well it looks like you're doing very well with it. Almost there! Whenever I've had to do something like this -remove material from a timber face-on - I've used a flat drill bit or auger bit and just drilled as many holes as I can as close together as I can, then chiselled in between. You blunt them fairly quickly in oak but flat bits at least are cheap.
It'd be safer than your chainsaw method, if perhaps slower. The only downside is that in order to go deep enough with the flat part of the drill bit, the tip goes further, so you can be left with lots of little holes. This might not matter in your case, as you don't need a perfect finished surface.

 

[Bogart]

Finally got there using chainsaw, chisel and mallet and one of these.

https://www.amazon.co.uk/Original-Graff-SpeedCutter-Woodworking-grinder/dp/B07KFKWF7F/ref=sr_1_2_sspa?dchild=1&keywords=Grinder+Wood+Carving+Disc+GRAFF&qid=1586363722&s=diy&sr=1-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzVTQ1ME9GT09DSUxCJmVuY3J5cHRlZElkPUEwNjA3MTU2M1YyVERBNkdITzhYNiZlbmNyeXB0ZWRBZElkPUEwODkwNzAxMVYwUElaMDU0T01JTyZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=


Need to get a hamster now to make use of all the wood chippings and sawdust.

 

[Flyfisher]

Excellent! You’ll be well practiced to make a traditional canoe now :wink:

 

[Bogart]

Now where is that adze? :mrgreen:

 

[Zebra]

Excellent. Well done. You'll have to start a hamster bedding online shop.

 

[Bogart]

Could make a fortune. My first time hollowing a beam and will be my LAST. If I ever need one again I will get it done for me.

 

[a twig]

Beautiful, lovely bit of work, well done for persevering!