Cutting a channel in a larch beam

[Tom at Heartwood]

Hello.

 

I am currently milling some very nice straight and clean grained larch and have an order for a beam with a channel cut in to house an RSJ or steel I-beam. The larch beam is to be 4m in length and obviously not structural

 

I would appreciate any thoughts on what I propose to do particularly regarding the stability of the beam as it dries from fresh cut and settles in an internal centrally heated space.

 

The steel is 158mm x 89mm and the overall larch beam cross-section proposed is 200mm x 200mm.

 

I will probably cut the channel with a portable chain morticer and allow a little clearance for ease of fitting, maybe 6mm. However, I am wondering if there will be enough timber thickness remaining (i.e. only about 36mm on the lower face) or whether to increase the overall dimension.

 

Any thoughts or advice from your experiences would be welcome.

 

Thanks,

 

Tom from Heartwood Enterprises in Cumbria.

[gobbypunk]

Hi I have never done this but from other things I have done if it purely decrotive I would increase so bottom thickness is about 50mm so if any big cracks do appear then I dought very much that you would see the steel thats my thaughts other people may differ hope this is some help

cheers mark

[farmer rod]

building regs may say that the steel needs to be covered in a fire resistant material, sorry if throws a spanner in the works. (If the beam is entirely wood then I think it can be argued that it would take more than 30 mins to burn through)

[Craig Johnson]

wot he said

[muttley9050]

I've done this before with two different methods. First one i did I used an oak beam. Took two inches off each side and two inches off the bottom then rebuilt beam around steal. Joints were almost hidden but still a little visible.

Second one I did as you suggest. Mortise the hole out of beam and pushed up over joist. Definitely keep all faces 2" thick. I fixed this by banging 4x2 into the webbing of the joist, marking where they are on the beam. Hold up beam with acro's then peg/screw plug beam to 4x2.

 

Sent from my GT-I8190N using Arbtalk mobile app

[agg221]

I have a beam which needs to have a plate inserted in it. The beam is box heart. Box heart tends to open up round in a wedge, ie you cut a slot but the top gets wider than the bottom. If you don't let it, splits develop somewhere else (it would be different if it was fully seasoned).

 

I cut the slot as early as possible, as narrow as possible, let the thing open up, which with a deep cut in like this makes seasoning much quicker, and when I am ready to insert the plate I will also add a wedge, and plane the sides up to square again. The beam has developed no splits anywhere else.

 

Alec

[farmerjohn]

if you look on my profile there is one album on it with photos of how i covered some crappy softwood lintels with elm, each with 2 bits of timber, far more stable as it does not matter about cracking etc. you need a bit of width but it works out really well.

Regarding fire regs you can get around it 2 ways, one get a suitably qualified person to calculate the amount of 'sacrificial char wood' needed to give you your fire protection or buy a fireproof varnish, last time we did it you buy and tin, follow instructions and fill in a certificate, its expensive but gets around the problem.

[farmerjohn]

just to add another 2p worth, larch moves a fair bit if green and in central heated room, i fitted a 6X8 larch lintel in a not very warm house just before christmas and theres a 5mm wide X 75mm long shake so think it would easily open up if less than 50mm thick all round

[Tom at Heartwood]

Thank you for the thoughts and advice. I will cut the beam so that I can leave a 50mm thickness all around and try to post some photos when it's done. Tom.