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Drilling a 120mm dia hole

PostPosted: 11 Feb 2020, 22:50
by RogerS
A friend of mine is the manager at one of the Roman forts up here. They've got a larch that's been felled, very straight and about 400mm dia. They want to cut it into 1m lengths and then make a hole 120mm down the middle and about 300mm + deep. He asked me how to do it and I've not got much of an idea. Huge lathe ? Some machinery a shipwright would have ?

Any ideas, chaps ?

Re: Drilling a 120mm dia hole

PostPosted: 11 Feb 2020, 23:21
by Woodbloke
No idea but the Romans apparently used to bore out elm logs to carry water, which were then laid alongside their roads; hence the origin of the term 'trunk' road - Rob

Re: Drilling a 120mm dia hole

PostPosted: 12 Feb 2020, 08:54
by 9fingers
How about laser or water jet specialists for high tech approaches?

Bob

Re: Drilling a 120mm dia hole

PostPosted: 12 Feb 2020, 11:10
by Rod
Burn out with hot rods.

Rod

Re: Drilling a 120mm dia hole

PostPosted: 12 Feb 2020, 12:19
by StevieB
I may be missing something here, but you can get core bits at 120mm diameter and extension bars for them to easily cope with 300mm depth - sure they are not designed to cut wood particularly, but as the timber will be wet and the 'teeth' on some of these things are large, I would definitely be giving this a go as a cheap and low tech solution.... or have I misunderstood what is required?

Re: Drilling a 120mm dia hole

PostPosted: 12 Feb 2020, 12:21
by Andyp
Drill lots of smaller holes then chisel them out/together. Smoothing with a drum sander.

Re: Drilling a 120mm dia hole

PostPosted: 12 Feb 2020, 12:22
by Andyp
StevieB wrote:I may be missing something here, but you can get core bits at 120mm diameter and extension bars for them to easily cope with 300mm depth - sure they are not designed to cut wood particularly, but as the timber will be wet and the 'teeth' on some of these things are large, I would definitely be giving this a go as a cheap and low tech solution.... or have I misunderstood what is required?


How would you snap off the core when it reaches the max depth of the bit?

Re: Drilling a 120mm dia hole

PostPosted: 12 Feb 2020, 13:31
by MY63
What you need is a man with a chainsaw sorry I don't know how to make the video work.

https://www.youtube.com/watch?v=w4356Um ... e=youtu.be

[youtube]w4356UmM_KM[/youtube]

MOD EDIT : I've put the video into the post for you - Trim

Re: Drilling a 120mm dia hole

PostPosted: 13 Feb 2020, 11:20
by StevieB
Andyp wrote:
StevieB wrote:I may be missing something here, but you can get core bits at 120mm diameter and extension bars for them to easily cope with 300mm depth - sure they are not designed to cut wood particularly, but as the timber will be wet and the 'teeth' on some of these things are large, I would definitely be giving this a go as a cheap and low tech solution.... or have I misunderstood what is required?


How would you snap off the core when it reaches the max depth of the bit?


Chisel / spade bit / smaller drill etc - once you have the outer limit of the hole bored it should be relatively painless to remove the centre surely? It depends how flat you want the base of the hole I guess - what is the purpose of boring the hole in the first place Roger?

Re: Drilling a 120mm dia hole

PostPosted: 13 Feb 2020, 11:42
by Andyp
StevieB wrote:
Andyp wrote:
StevieB wrote:I may be missing something here, but you can get core bits at 120mm diameter and extension bars for them to easily cope with 300mm depth - sure they are not designed to cut wood particularly, but as the timber will be wet and the 'teeth' on some of these things are large, I would definitely be giving this a go as a cheap and low tech solution.... or have I misunderstood what is required?


How would you snap off the core when it reaches the max depth of the bit?


Chisel / spade bit / smaller drill etc - once you have the outer limit of the hole bored it should be relatively painless to remove the centre surely? It depends how flat you want the base of the hole I guess - what is the purpose of boring the hole in the first place Roger?


Seems like a plan.

When are you going to start Roger?

Re: Drilling a 120mm dia hole

PostPosted: 13 Feb 2020, 16:39
by RogerS
Andyp wrote:
StevieB wrote:
Andyp wrote:
How would you snap off the core when it reaches the max depth of the bit?


Chisel / spade bit / smaller drill etc - once you have the outer limit of the hole bored it should be relatively painless to remove the centre surely? It depends how flat you want the base of the hole I guess - what is the purpose of boring the hole in the first place Roger?


Seems like a plan.

When are you going to start Roger?


Not me, sunshine :lol:

The general consensus is to bandsaw it in half then use one of those grunty wood carving bits that go on a angle grinder. Hollow out as necessary. Maybe use a template to approximate to the required shape. Then glue and dowel back together with polyurethane. If I had a bigger bandsaw then I might have had a go.

Re: Drilling a 120mm dia hole

PostPosted: 13 Feb 2020, 16:45
by Andyp
Shame you don't feel brave enough to upend a chainsaw as per the vid. :)

So whats it for?

Re: Drilling a 120mm dia hole

PostPosted: 13 Feb 2020, 16:49
by RogerS
Andyp wrote:Shame you don't feel brave enough to upend a chainsaw as per the vid. :)

So whats it for?


I forgot to look at that video. Superb...especially the guarding.

It's to replicate the position of the uprights used in the medieval hall. They've got some concrete pads with vertical steels where they found the original (but rotten) uprights. Just wanted to improve the aesthetics .

Re: Drilling a 120mm dia hole

PostPosted: 15 Feb 2020, 23:57
by PitchPine
I’m interested to find out how you do this. I have two ideas -

- Make / find someone to make an enormous Forster bit...

- Ask a machine shop with an oil country lathe to do it for you, they might laugh at first but it would be a quick job. Lots in my area.

Re: Drilling a 120mm dia hole

PostPosted: 16 Feb 2020, 00:54
by PitchPine
PitchPine wrote:
- Make / find someone to make an enormous Forster bit...



Maybe a spade bit, easier than a forstner. I’d have a go at making one if your friend is interested.

Re: Drilling a 120mm dia hole

PostPosted: 14 Mar 2020, 13:44
by PitchPine
About 10 minutes in...

https://youtu.be/Z2ZhHR1IDF0

These smugglers know how to do it (to a considerable depth!)

Re: Drilling a 120mm dia hole

PostPosted: 14 Mar 2020, 15:04
by RogerS
Thanks for the suggestions. favourite seems to be the chainsaw but think the project might be on hold.

Small world...the guy that does our stone walls used to live in or near Wark and knows the area well. The farmer you mentioned going via the forest to Haltwhistle ? Well, my mate knows him and has done work for him.