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Screws VS nut inserts

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Woodypk

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Hi guys,

I was going to make a simple oak top (30mm thick) coffee table on a steel frame. I was thinking for attaching the top, I would have some metal "tabs" approx 30mmx30mm that will be slotted to allow wood movement in the correct orientation.

My question is, could anyone offer any information with regards to using the drill and screw in threaded nut inserts with bolts rather than using regular wood screws?

Has anyone used these for this type of application and had any good/bad results that they can report?

Thanks guys
 

marcros

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I have used the threaded inserts a couple of times for table tops to frames. It works fine and is my current preferred method (although I dont make many items, so dont read much into this). I haven't managed to find anywhere selling the tabs from anywhere though and they strike me as being a useful item. I have done it with a slotted hole in the lower piece. If I were sourcing the tabs, I would use a circular piece so that I could use a forester bit to inset them.
 

marcros

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thinking further, on your steel frame...

what does the base look like? can you drill and expand the holes directly in the steel or is it tubular? Can you make the top of the base a plate and then drill/slot that? I was thinking more about wooden tops and wooden bases when I answered.
 

Phil Russell

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I have recently made some smallish (c 45 x 15cm x 15cm high) oak tables for our cat to feed from (don't ask). I used insert nuts fitted (screwed) into the underside of the oak (18mm thick) to fasten legs. The legs, 30mm diam had more insert nuts in the ends; table top and legs being connected by 6mm studs. Using insert nuts into the end grain of the legs worked well except when I tried a soft wood when the insert nut would not grip enough. Using beech legs was fine.
As an experiment I did try using pronged T nuts which you hammer in: I did not think they were strong enough.
Cheers, Phil
 

Droogs

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If you are envisioning that the table will be disassembled fairly often then inserting Helicoils (other brands are available) and using machine screws through the metal frame with a washer would be the better way to go. But if it wont be done often then decent wood screws will suffice.
 

Rorschach

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If you are envisioning that the table will be disassembled fairly often then inserting Helicoils (other brands are available) and using machine screws through the metal frame with a washer would be the better way to go. But if it wont be done often then decent wood screws will suffice.
Helicoils in wood? I think you are thinking something else. Helicoils are fitted into thread holes in metal to repair damaged threads, not to provide a threaded hole in another substrate such as wood.
 

Woodypk

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thinking further, on your steel frame...

what does the base look like? can you drill and expand the holes directly in the steel or is it tubular? Can you make the top of the base a plate and then drill/slot that? I was thinking more about wooden tops and wooden bases when I answered.
Marcros, the base design is if you can imagine, a wireframe cuboid. I'll probably use 25mm or maybe 30mm steel box section. I'm not sure about screwing direct to the frame. 1/ I want to hide the fixings as best as possible and 2/ I think it would be much easier to slot some thin steel plates and weld them on in maybe, 2 pieces per side of the frame so 8 in total.

The Tabs will be made from 2/3mm plate steel, welded flush to the top of the frame, pointing inwards ( imagine the way the small black picture frame tabs look on the back of a photo frame) with slots in the correct direction to allow movement.

I don't actually envisage it ever coming off, I was just wondering if there is any strength advantages of using say, M8 nut inserts drilled and glued with a dab of Araldite vs regular wood screws.

As Rorschach has mentioned, I've used helicoils in metallic threads but don't know how they'd fare in timber.

Thanks for the input guys
 

Droogs

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Helicoils in wood? I think you are thinking something else. Helicoils are fitted into thread holes in metal to repair damaged threads, not to provide a threaded hole in another substrate such as wood.
Helicoil is the name of the Brand- See below @Rorschach (you really should, stop engage brain and then mouth), might be less embarasssing

 

Woodypk

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Droogs,

Have you use the helicoil wire type inserts vs the regular screw in nut type inserts? Have you found one to be better than the other?
 

Droogs

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I actually prefer the Helicoils to the "normal" brassy coloured thread inserts, i just feel the are stronger and in wood go in quicker. They must cut in easier. I found that with MDF that it is best to screw in and then screw out and give the hole a quick bit of thin CA and put the insert back in, seems to strengthen the area around the insert a bit better.
That though may just be in my head :dunno:
 

Rorschach

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Helicoil is the name of the Brand- See below @Rorschach (you really should, stop engage brain and then mouth), might be less embarasssing

Well there was no need for that. As you can see above, I am not the only one to question you.

I am well aware of the helicoil brand, I have never seen those wood inserts for sale though, where do you buy them?
 

Droogs

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@Cooper The army only taught me to assemble, they had gone metric by the time I joined up, so trade training never covered how to mantle
 

Rorschach

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UK distributor is Rivetwise, i apologise for being a bit shirty - not a good day
Thank you.

Looking at Google it seems they are not as common as the normal threaded inserts or t-nuts that you see. I couldn't find them for general sale but I did see the website you mention so maybe they are more of an industrial rather than retail item? Are they any good? Do you know what makes them different to their inserts designed for metal?
 

Droogs

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They seem to be steel to me and have a sort of more flattened diamond /rhomboid cross-section and are at a true 60 degree V to give wood the best amount of material in the thread for strength. I get them from Rivetwise after being given some a few years ago, can't remember how much they were. But as I mentioned they seem to need a bit of help re the thread inside of MDF, they have a tendency to just pull the mdf apart rather than just pull out if the panel is yanked . I think the brass coloured ones are designed more for MDF whereas these are defo for use in solid wood. I use them for removable veneered solid edged panels that need to be taken off of internal steel frames in custom PC/Printer integrated desk builds for servicing, component replacement etc.
 

Rorschach

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They seem to be steel to me and have a sort of more flattened diamond /rhomboid cross-section and are at a true 60 degree V to give wood the best amount of material in the thread for strength. I get them from Rivetwise after being given some a few years ago, can't remember how much they were. But as I mentioned they seem to need a bit of help re the thread inside of MDF, they have a tendency to just pull the mdf apart rather than just pull out if the panel is yanked . I think the brass coloured ones are designed more for MDF whereas these are defo for use in solid wood. I use them for removable veneered solid edged panels that need to be taken off of internal steel frames in custom PC/Printer integrated desk builds for servicing, component replacement etc.
Good to know for the future. Cheers.
 

Cabinetman

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The oak that I was fastening into was about an inch and a quarter thick but this was a seriously heavy piece of furniture, more on here, search under the word Behomoth. Ian
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Jos7000

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Woodypk, I'm intrigued as to why you want to use metal tabs fastened to the underside of the top and then fasten these to the frame. Would it not be just as strong and easier to drill the box metal in a size suitable for the bolts and then widen the lower side to facilitate the head of the bolt to pass through (and a socket to tighten it) thus hiding the bolt?


Disassemble = to take apart with a view to being able to reassemble.

Dismantle = take apart often by brute force without a requirement to put back together.
 

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