tweetyduck Posted September 11, 2015 Share Posted September 11, 2015 I'm building something from 20mm x 20mm Square section and it has a 2mm wall. I want to screw something through the box from one side to the other. The far side can be spot welded and then ground flush to stop anything backing out. What thread pitch is good for 2mm material. I want something like an M8 bolt so will M8 x 0.75 be good enough to have enough threads in the material? Thanks Neill Quote Link to comment Share on other sites More sharing options...
ejparrott Posted September 11, 2015 Share Posted September 11, 2015 2mm isn't very much at all, how much load are you looking to apply? You'd probably be better off welding on a pad if you need any kind of strength. M8 x 0.75 will be a very fine thread with not much load carrying capacity. Quote Link to comment Share on other sites More sharing options...
tweetyduck Posted September 11, 2015 Author Share Posted September 11, 2015 Its hard to explain but consider two lengths of the material side by side. 40mm wide looking end on and joined together by a piano hinge. 1500mm long. Its part of a flip up bed split in 3 parts. The bed supports 2 people. Its a standard size king. 1500mm x 2000mm. The middle 1/3 board cannot be supported and is in hinged on 1500mm each end. The hinge cannot support the load and if the 20x20 bends in the middle this will damage the hinge. So the idea is to use hinge bolts to support the middle board directly to its adjoining board. I need to make some hinge bolts. They need to be flush to the frame and almost push fit into the adjoining frame. So the load on them is sheer not longitudinal. I think we will be OK as long as its sheer. Is that as clear as mud ? Quote Link to comment Share on other sites More sharing options...
Blanco Posted September 11, 2015 Share Posted September 11, 2015 What about a length of flat bar material inside which can have all the threading, and clearance holes in the tube, simple and strong?? Quote Link to comment Share on other sites More sharing options...
Gazzar Posted September 11, 2015 Share Posted September 11, 2015 Weld the hinges to the 40mm? Puddle weld? Otherwise use a steel tek screw, like the roofers use to attach tin to rafters, and use lots. Quote Link to comment Share on other sites More sharing options...
ejparrott Posted September 11, 2015 Share Posted September 11, 2015 Clear as mud!!! I think I understand what you're doing yes, something similar to what I need to do as well to be honest. I'd ask the same question as Gaz, why not weld the hinge to the box? Quote Link to comment Share on other sites More sharing options...
tweetyduck Posted September 11, 2015 Author Share Posted September 11, 2015 Fixing the hinge to the steel is no problem as yes they can be welded on. Its the load on the bed that's the issue and supporting the middle board. The middle board is effectively hanging off the hinges. So to put 5 hinge bolts along the length of each steel will "join" it mechanically to the adjoining fully supported 1/3's. Making the hinge bolts is the problem. http://images.sdslondon.co.uk/img/upload/products/2/l_75174.jpg need to make the above work on two pieces of 20x20....push fit. Must be flush for the pin of course. How do i make the pin? Quote Link to comment Share on other sites More sharing options...
Cynic-al Posted September 11, 2015 Share Posted September 11, 2015 Not entirely sure I understand the question but what about getting an M8 nut and welding it flush in the box section. Ie sink it in. You have a good quality thread, a good peripheral area to weld and theres no tapping required. Alternatively, depending on the length of box you can get special rectangular nuts (like you use on the ali profile that machine builders use) that you can slide inside with a rod and just pickup with your bolt. They're fine so long as you never fully remove the bolt. Quote Link to comment Share on other sites More sharing options...
tweetyduck Posted September 11, 2015 Author Share Posted September 11, 2015 an idea but its 1500mm long and the pin would then need a diameter change. I've got no lathe to make that. Good idea though. Considering..... Quote Link to comment Share on other sites More sharing options...
tweetyduck Posted September 11, 2015 Author Share Posted September 11, 2015 i wonder if I just put something like this all the way though and welded it on the far side. If it were push fit and then welded it wouldn't move and would be strong enough. http://www.amazon.co.uk/Yale-Locks-P125SC-Hinge-Bolts/dp/B004J340VY need cheaper and need them made....... Quote Link to comment Share on other sites More sharing options...
vulcan bomber Posted September 11, 2015 Share Posted September 11, 2015 If I understand it then either a threaded bush welded in or a crush tube through the box and a nut underneath. Quote Link to comment Share on other sites More sharing options...
ejparrott Posted September 11, 2015 Share Posted September 11, 2015 Right...think I'm getting with you now! As you say, drill through and weld in those type of pins. Make sure you clamp the two bit's together when you drill them, then open out individually as required. When do you need them? Quote Link to comment Share on other sites More sharing options...
Tanuki Posted September 11, 2015 Share Posted September 11, 2015 An 8mm fastener needs **at least 4mm** of thread to engage - assuming the material you're threading-into has the same hardness/ductility as the bolt you're screwing into it. If in doubt aim for the same depth of engaged-thread as the fastener-diameter. In your case 8mm. In your circumstance given that you seemingly have no data on the characteristics of the material you propose to thread into, I'd drill oversize and fit a "clinch-nut" or "Rivnut" or similar. Then you know you've got a good depth of thread to torque into. [Tapped-direct-into-thinwall-tube-without-reinforcement is an instant fail in any of my vehicle/aviation inspections] 1 Quote Link to comment Share on other sites More sharing options...
tweetyduck Posted September 11, 2015 Author Share Posted September 11, 2015 Right...think I'm getting with you now! As you say, drill through and weld in those type of pins. Make sure you clamp the two bit's together when you drill them, then open out individually as required. When do you need them? Yes thats it. Not sure those are short enough though the bit that protrudes into the other side will need to "cam" and then sit in the hole quite tightly. If its too long on the part that sticks out then it will catch. I'm not sure that something off the shelf will work perfectly but it only need to really sit flush on top so i might be able to oval the hole a bit to allow the "swing in". I'll sketch something. need em next week for sure. Need the bed finished for the show on the 25th and i've not even started. 75meters of 20x20 delivered this afternoon so i'm rocking and rolling tomorrow AM building the bases. The technical stuff will wait as i need to order Phenolic Ply and Piano Hinges. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted September 11, 2015 Share Posted September 11, 2015 Rivnuts. Quote Link to comment Share on other sites More sharing options...
tweetyduck Posted September 11, 2015 Author Share Posted September 11, 2015 Bit rubbish but then again i'm an Engineer.... correction thinking about load directions the pin needs to be on the left section board 1 and then the load is the top of the hole so the cam action can still be accommodated. Quote Link to comment Share on other sites More sharing options...
tweetyduck Posted September 11, 2015 Author Share Posted September 11, 2015 Rivnuts. not flush. needs to be perfectly flush correction.....they make countersunk ones.....so flush. but i hate the damn things,,,, is my main reason....LOL Quote Link to comment Share on other sites More sharing options...
tweetyduck Posted September 11, 2015 Author Share Posted September 11, 2015 just so you can get an idea what i'm trying to do....... Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted September 11, 2015 Share Posted September 11, 2015 Was about to say, countersunk rivnuts, but meh why hate them, do you use the tool or just a spanner? for M8 they are easy to put in... Quote Link to comment Share on other sites More sharing options...
Gazzar Posted September 11, 2015 Share Posted September 11, 2015 The tool works better. Where are you? If you're local (and I can find it) you could borrow mine). G. Quote Link to comment Share on other sites More sharing options...
Gazzar Posted September 11, 2015 Share Posted September 11, 2015 The hinge bolts I understand, but is it over-engineered? Instead of piano hinge (weak) use door hinges, 6 per length, and just puddle weld them to the box. Hinges for fire doors would be strong enough, wouldn't they? No need for the hinge bolts then. And instead of having the box below the timber on the leftmost fold, have the timber butt to the box and weld an attachment strip so the timber rests on the strip, rather than the box, eliminating the need for the lower hinge bolts there. Quote Link to comment Share on other sites More sharing options...
tweetyduck Posted September 11, 2015 Author Share Posted September 11, 2015 You know. The hinge thing might be a point. If i can find stronger hinges that fit flush and open and close the 180 then we might be on a winner. i've looked at hinges and they all fell short but looking further i can see a SOSS Hinge might be strong enough and work. More investigations needed. be right back....... Quote Link to comment Share on other sites More sharing options...
Gazzar Posted September 12, 2015 Share Posted September 12, 2015 Is this for a sleeping surface? I'm thinking you may be suffering from princess and the pea syndrome (laugh, only joking emoticon). The depth of the hinge would only be 8 - 10 mm, not enough to be felt through a mattress. And, of course, if you butt the timber to the box, you can take the hinge depth into account and put a shim on top of the box to make flush. G. I'll try draw out what I mean, as I've finally found the pen tablet graphics thing! Quote Link to comment Share on other sites More sharing options...
tweetyduck Posted September 12, 2015 Author Share Posted September 12, 2015 I'm not overly bothered about the hinges and they will be sticking up in the join between the mattress sections as this is also on thirds so it will be fine. Good idea though. The mattress thirds also form the cushions for the seats, Well at least two of them do..... I still like the SOSS hinge as long as i can fit them in 18mm ply. The problem now is they stick out quite a way when open so i need to consider the width of each section as when folded up it needs to stack. Quote Link to comment Share on other sites More sharing options...
tweetyduck Posted October 9, 2015 Author Share Posted October 9, 2015 This is how it ended up. It stacks and the first hinge has them on top the second on the bottom so it folds correctly. They are counter flap hinges the same as i used last time and i used all 10. Its been slept on for 4 nights now and doesn't move. Quote Link to comment Share on other sites More sharing options...
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