SCREW THREADS -The Secret Life of Components, a series of guides for makers and designers 12

[Music] [Applause] [Music] [Applause] [Music] my workshop is full of screw threads all these cabinets uh they just have lots of nuts and bolts in all the drawers um and they're more over here it's just like brass nuts and bolts um then uh oh yes the extra extra large ones here a bit of 20 mil studying for instance um that's not all there's a sort of over spill area here um oh more than a lifetime supply of bolts there i think they came from rex's workshop um but it's not just uh nuts and bolts a lot of the tools have uh screw threads on so uh g-clamps just just uh depend on screw threads then the largest screw thread i've got in the workshop i think is on my my metal folder sort of brings down the top to clamp the uh metal in place really for bending so uh screw thread there and of course as an obvious screw thread on my lathe the lead screw [Music] in most of the tools um do have screw threads but they're hidden sort of kind of protect them so like on the mill uh you can see the one for the horizontal travel is under there so there are screw threads all over my workshop lots and lots of them this video is my experience of using screw threads over the years the first part is sort of just the basic ideas about them and the second part there's a series of examples of uh screw threads i've used in my machines and some successes and some disasters the video is quite long so here's the contents list so you can skip forward if you want to so i'm going to start by looking at how threads are made um well when i want to make a thread i almost always use a thing called a a tap or or its companion a die so this is a tap looks a bit like a bolt but it's got these fruits cut out of it and it's made of a very very hard steel that when you drive it through a slightly undersized hole it literally cuts the thread as it goes and a die is the same thing really but looking a bit like a nut but with bits cut out and this will drive its way over a shaft forming thread in the same way so i thought i'd demonstrate this by uh cutting a thread in a bit of um six mil um quarter inch steel uh so first of all you have to drill the undersized hole for a six mil thread it's a five mil hole so uh normally what you would do is to hold the tap in a tap holder this is a traditional tool um and and then form it by hand but i have to admit i don't often use it uh i nearly always use a battery drill or the drill press instead so um i just uh tightened it up as if it was a drill bit uh put it on the screwdriver setting uh and with not too much torque because you don't want to break the tap and then um a little bit of lubrication on the tap right and then you just sort of have to go for it and i often find it off works better actually at the high speed well made a bit of a meal of that but uh but it does fit the bulk very nicely now the one drawback of this it's not completely at right angles to the bit of steel it's hard to judge just doing it with a battery drill um so this is why i often use the pillar drill instead so really it's exactly the same thing except that i mount the um the tap uh in the pillar drill and the pillar drill has belt drive so um that's a bit like the adjustable torque in the battery drill and doesn't have to it'll just stop if there's too much torque a couple of things i've found useful uh i used to find that taps didn't last very long perhaps it's the way i use them but a few years ago i started using slightly more expensive ones they're got yellow rings on they it's a sort of standard the yellow ring um uh they cost about nine pounds each so but they do they do seem extremely sharp and to last a lot longer i sometimes feel they really just cut steel like butter the other thing i found useful about tapping this is really for very tiny holes for two mil and 2.5 i don't know if they're yellow ring but i i just have a by a pack of 10 from china they're so fragile they do break quite often um but what i found helps them to break a bit less frequently is to drill the holes a little bit bigger than you're supposed to so 1.6 mil is the approved size for a 2 mil tap but i drill a 1.7 mil hole which is what i've drilled through here and um it just does slide through um quite a lot more easily and as far as i can see it still has plenty of strength i've never really had any problems with it so a die fits into a die get holder right way around um and uh in a way this is even harder to uh get it at right angles to a bit of bar as you twist it round some die holders have collars on to sort of guide them that's very helpful but mine doesn't so what i end up doing i nearly always if i want to put a thread on the end of a shaft i do it in the lathe so i put the bar in the chuck of the lathe now the thread goes in this die holder um but it's made specially for a lathe um so you can see it goes in there i've tightened up the allen keys and this fits in the tail stock of the lathe like that so now um put a bit of oil on it lubricate it set the speed um don't want to go around too fast it's actually on the right speed about 70 rpm um and it'll literally wind itself on to the end of the bar the sharp teeth of the dice kind of dig in [Music] [Music] and that's all there is to it just gotta unwind it again [Music] and there it is a pretty perfect thread so uh i've got a bit of bar in the lathe and this is my cutting tool and as the bar rotates um the tool post will move slowly down the bed of the lathe creating the the thread with any luck [Applause] so the tool post is moved along the bed of the lathe by this rotating lead screw then in the head of the lathe there's a gear box down the bottom which adjust the speed of the lead screw so you can set it for any different pitch in this case both metric and imperial threads well i don't often make threads like this i find it they tend to turn out all rough and not very good or do some fine cycle threads occasionally today a totally different way of making threads has become widespread the two plates have rows of sharp ridges they also taper a bit towards the front so they trap the bar in the gap and press the thread into it as they roll through every method of cutting a screw thread involves an existing screw thread so obviously with a tap um the tap itself is a screw thread with the lathe the thread is on the lead screw not so obvious with thread rolling machines but they still do involve screw threads so if you take the example of the lathe the lead screw the machine that cut this lead screw almost certainly cut the lead screws for many other cultures delays and then the machine that cut those lead screws cut the lead screws for a lot of other manufacturers lights so there's a sort of family tree of screw threads that uh in a theory ought to go back to one original screw thread of course it's not as neat as that the earliest known screw thread is on an olive press made entirely out of wood and i don't think that originated any other screw threads but at the beginning of the industrial revolution before there were strong metal working lathes there was a vogue for making screw originating machines and the most famous one in britain was made by henry maudsley it's in the science museum i've been to see it but it's completely baffling you have no idea how it works it's all all underneath the working bits i think um but there's a helpful diagram i found um so this is what i've based my own version on but it's much more fiddly and difficult than i was expecting [Music] so to start with um i made uh a curved blade um out of uh tool steel uh well out of spring steel with a sharp edge now that goes in here and i've mounted it at a slight angle and i'll just turn this round it doesn't look very much from there but it is slightly angled outwards at the top i will now put um a bit of aluminium a softer metal into the vise and now tighten up the curved knife against the that's probably about right and now i just have to start turning the bar and with a bit of luck it will start to form a spiral i can see it's doing it quite well now but mortally actually went a bit further than that um so on the other end if i turn this round i've mounted an actual cutting tool in here um so the idea is that as the rod spirals its way um through the tube uh this cutting tool will cut a proper cut unlike the the shallow knife uh um mark on the other side see how that works no i think that needs to be that's looking good i may have gone a bit too far with that i don't know you can see the swarf coming off the cut but you can't see the thread it's cutting because it's disappearing inside the tubes well i think i'll leave it there if i remove the bar you can now see my final rather imperfect thread so there we have it the uh that's the knife blade cut that was pulling the rod through uh and that's the actual cut by the cut it made by the cutting tool that is a lot deeper and will be the beginnings of an actual thread and the clever thing about this is that you can actually make a thread that's more accurate than the one you started off with because um if you clamp something over a number of threads and use that to move the next bar through when you're cutting the next thread it kind of averages out the imperfections uh in the individual threads so by the beginning of the 19th century um people did have accurate threads and nuts and bolts but each manufacturer made their own and none of them were interchangeable then uh one of maude's apprentices uh joseph whitworth took it on himself to standardize everything and uh he bought nuts and bolts from a variety of different manufacturers and he decided his standard was the best and uh here it is it stood the test of time uh extraordinarily well at the time it was used on the very first cameras uh as the thread that fixes them to tripods so uh this is an ancient camera i've got that's the base so it's still being used in the 30s and 40s um but here's my my digital camera um still got the sh the thread on the bottom fixed into a tripod and it's still exactly the same original whitworth thread well although whitworth standard was a brilliant idea um other people quickly brought in other standards so it soon became quite messy and complicated so today there are lots of different standards um the main difference between these threads is that some are very coarse and some are very fine woodworks with a as the course thread more like this um and uh metric is somewhere in in the middle in america uh still today you get a course thread and a fine thread but in europe people generally just use the the metric standard though it is in it's actually called the metric course and there is a finer thread finer threads are supposed to be stronger because they cut into the bolt less i think um but they're um they jam up more easily uh and can be they can rust up and also it's just more fragile the threads so it can get damaged so in a way the metric is quite a good compromise [Music] i used to think that bolts were made by starting off with a bar that was the diameter of the head and then turning the rest of it down until it reached the right diameter to the thread but it's actually much more fun than that so and uh i don't know if it'll come off no it's got a bit jammed which it does turns upside down tap it out [Music] in fact when they make bolt heads they usually stamp them once to get the general shape and then a second time um with a shaped punch to get the hex shape and also the any text you want to have on the bulb so beside the different standards of course all bolts come in different lengths i i always have a few long ones because it's very easy to chop them down which i do with the angle ground when they come out of the angle grinder um the edges are quite sharp you can't always get a nut over them so then i take them to the lineager they come out of the linisher looking like this and then of course it's very easy to get a nut on a quicker method is to put a nut on before grinding [Music] when you take it off it restores the end of the thread but it's not so good because it still leaves it sharp and easily damaged then of course there are all sorts of different head shapes this is the standard hex head which is good and this is you get a good grip on it with a spanner um but it only goes down to a certain size this is the smallest this is a five mil thread with an eight mil head on it and that's about as small as you commonly get them below that um the the bolts tend to have positive heads or flat heads then of course the countersunk versions of all these things um for smaller sizes it's usually posi for larger sizes it's often like a hexagonal key like for an allen key then of course uh there are torx heads um which have become very common on cars and white goods uh good with automatic screwdrivers i guess um the only trouble i have with those is that the drivers don't seem to last very long it's easy to mash them up then of course they're a lot of older uh head designs well just a basic flat head or um i know that's called a roofing bolt uh a coach screw that's got a square underneath that grips the material and then there are a whole a lot of bolts like set screws uh that uh designed for allen keys i use quite a lot of these i find them good for getting them in awkward places and you can get a good grip on them as well so these this is the cap head this is the countersunk version and this one's called a button head they kind of look rather neat the buttonheads and then there's some more specialist ones like a collar bolt so this is a precise 12 mil diameter so you can put a bearing on it which i find very useful i particularly use uh tiny ones like this this is a five mil collar bolt um with a roller bearing um very compact and hard wearing then for every size of bulk there's also a stainless steel version and i keep both i have to use the stainless steel for things outdoors on the pier obviously i used to love the stainless because they're so shiny and uh um and of course never rust uh but i'd rather gone off them um the steel isn't quite as good for nuts and bolts really there's a compromise because they're stainless it's somehow not quite so hard it's a little bit softer and more sticky so uh nuts uh are much more likely to jam up with stainless than they are with the ordinary mild steel so if you've chosen your bolt and got the right head the next thing is how tight to do it up um well i have to admit i don't even possess a torque wrench uh it's essential if you're working on a car engine or something but for my sort of things uh i just tighten them up it sort of feels about right you get to know after a while and what really helps is that big nuts and bolts it comes with a big spanner so you've got much more leverage on a big bolt than you do on a little bolt this is my little five mil thread eight mil spanner and this comes with a dinky little spanner that's that long so the difference is uh quite quite dramatic but it means you can you sort of automatically get a much bigger leverage on the big bolts than you do on the little ones i mean mainly the point is you don't want them to come undone uh and often the problem with coming undone is vibration you can buy special uh washers spring washers uh this is a common this is a common sort uh it kind of digs into the head and into the metal to stop it to stop it working loose for smaller sizes you get these ones with just lots of serrated edges that dig in bicycles have nuts a similar sort of idea these shapes help to stop top it's spinning loose actually just simple washes help um because it just helps you to tighten up uh the nut more evenly um it reduces the friction so you can get a better tension on it another way of preventing vibration uh running things loose is a nylock nut so these are nuts which have a little ring of nylon crimped in and these grip uh the thread to some extent so it gets a lot stiffer when it's gripping the nylon and that makes it less likely to come undone and of course there's loctite which i've mentioned before it comes in different strengths you just drip it on the joint between the bolt and the nut um and i think it works very well now this one's clever you can actually drip it on a nut and bolt that's already uh done up and it uh seeps in to the crack by capillary action well it's easy to make a mistake though um this is a project i did with my friend andy um it's a version of victorian fairground ride called the haunted swing we gutted an old caravan and stuffed the shaft through the middle with bearings on either end we then later cut the shaft and put a long bench seat in which takes seats about nine people or he took it round to fairs for several years without any problems but then it went to banksy's disabled land and was used intensively for a couple of months and we got a call in the middle saying that he was making loud banging noises so i rushed down there and i found that all these bolts uh had worked loose and this is just a sort of scale model i've made to to show you it's a similar sort of bearing well these bearings they're called self-aligning because uh they have this curved outer uh it's very handy um so because i don't think caravan were particularly true but we thought once it was in place it would just stay in the same position which was fortunate because the bearings we had this was very very stiff this this self-aligning mechanism but i think because it was stiff and we probably hadn't managed to realign the shafts at each end absolutely perfectly it was going in jumps because it was stiff and it was this sort of tapping that eventually force the bolts loose so sometimes now where it's really important that nuts don't come undone like on truck wheels you get these indicators or telltales i call them sometimes which are lined up so they point at each other obviously the point of these is that you can instantly see if one of them has changed position i used to be quite casual about it and often just use the drill bit to drill the countersunk but if the angle is not quite right you can get into trouble the bolt is only in contact at the root of the head not over the whole area well a friend of mine did he built this uh sculpture thing with a huge turntable about 20 foot in the air and uh with an overhanging arm and the people who'd fabricated it had fixed it with 18 12 12mm countersunk bolts but they'd use a drill bit to countersang them [Music] it's very tempting because it's so quick to hit it with a drill bit but it's only making contact down the bottom now the problem with this is that it can then very quickly wear i'm now going to tighten this countersink bolt the badly drilled one into a lump of metal get it as tight as i can [Music] this is the test you can see it didn't take long to get it to be quite wobbly so um once it's wobbly then there's a sort of tapping load on the bolts and it will after a while it'll uh break by fatigue failure and of course in that turntable when one breaks puts more load on the rest and so it's like a sort of daisy chain by the time it was noticed 10 of the 18 bolts had already completely sheared off one other thing about counter thinking i used to have great trouble um getting countersunk bolts drilling the countersunk bolts so they were completely flush with the metal uh and only comparatively recently realized that i wasn't making full use of the little sets of countersunk bits the key is to choose the one that's closest to the diameter of the the countersunk head because then when it reaches the parallel bit you can sort of see it as it drills [Music] when you get to this point there's a little bit of flashing just very very slight raised edge that appears when you get to the um parallel bit that's pretty perfect that's satisfying but of course it's important not to over tighten bolts uh because you can strip the thread and they can also strip just by overused [Music] [Music] so with a lot of these machines when they're new particularly um i keep having to take the covers off the frame um to tinker with them um and so i'll just take this one off like this screwed on but i had to unscrew them so many times that they completely stripped the thread because um the the metal is pretty thin uh it's only about um 1.5 mil wall thickness and um so the answer to this are these little things called clinch nuts what they they're sort of almost like a pop rivet so they go into a sort of pop rivet gun i already drilled a hole and you have to push pull really hard oh yeah it's going now but you can sort of see down the um tube maybe how it's pulled the metal of the nut against the tube so it's a really good fit a tight fit and now there's probably four four mil thickness of thread through there and they'll last forever if you do need to restore a thread to its original size there are these ingenious uh sets of thread restorers that i've only actually ever used one twice i think but there were lovely things so i thought i couldn't resist showing you them so there's my stripped thread a stripped eight mil thread the first thing is to drill out the hole a bit in this case it's to 8.5 mill so the next thing uh is that the sets have a special tap in now this has the pitch of uh of an eight mil but it's a bigger diameter so we now run this through the hole um or just get a bit of wd-40 to put in it so that's our oversized uh tapped hole uh now we use uh this tool and really it's these little inserts that are the heart of the system um and you just wind this in get this right i think that's going now get a bit below the surface is what they say yeah there we go and that now the inside of that is a perfect eight mil thread a perfect fit the to wind them in they have this uh flat bit at the end and a wonderfully crude way of removing the flat bit is just a punch and you just smack it with a hammer and then you're left just with a perfectly threaded hole very clever then of course there are wood screws they've actually been around for a surprisingly long time they're actually made by hand filed individually since the 15th century on posh bits of furniture and there's also a rather cruder version made from nails so most nails were had a square section um because they were forged and um they could be twisted uh like that and um uh i've read that it was gunsmiths who found that it was useful to be able to remove the lock the flint lock the metal part from the wooden gun stock for repair and so they put a slot in the top of these nails to give it a twist to start it coming loose but of course it wasn't until the advent of automatic lathe in the 19th century that mass production became a possibility in britain this was started by mr nettlefold and the shape of the screw is the sort of classic wood screw that remained unchanged until comparatively recently nettlefold set up shop just around the corner from novelty automation in 1819 but of course today wood screws are amazing with the modern production machinery the things you can do are extraordinary really i got this bit here which can sort of grip the screw then further down uh you can see the actual thread is serrated and when you get near the tip uh there's this little v cut out i think that's to help it drive its way into the wood without a pot drilling a pilot hole first i have to admit so that most of the time i just use cheap carcass screws they work just fine for fixing plywood to wooden frames and that sort of thing sometimes um to get them started or it's quicker i find to knock them a bit of the way in with a hammer before before actually screwing them and that won't come undone then there are self tapping screws um these are a sort of hybrid a sort of half and half between a wood screw and a bolt if you look at one closely they're very different shape from either they've got this wide flat bottom and then these very small pointy uh threads the angles of the thread is probably only about 30 degrees and then this one's got an ordinary posse head but these can go through much harder material than wood so they're good for fixing thin aluminium and even steel [Music] and that's surprisingly strong joint so this is a latest machine super cycle uh cycling game obviously um but also with includes a bit of doping anyway the screw threads that are interesting here are the self-tapping screws and i find it particularly useful for polycarbonate fixing bits of polycarbonate together like on these chain guards you can see the rows of little self-tappers and polycarbonate's a lot stronger than perspex so it's better for things like that so uh the thing to remember is because the plastic is quite strong you don't want to drill a hole that's too much smaller than the outside diameter of the screw and so i'm going to drill a 2.5 mil hole in the polycarbonate here oops that's one whoops and just two to those little screws that's enormous amount of strength so the threads in my machine tools and also those ones in g-clamps are a different shape they're sometimes called castle threads i guess because they they look a little bit like the battlement and the point of this shape is that it can transmit a lot of force so you can clamp something up hard but i find them very useful for converting rotary motion into linear motion and i've used this on one or two machines particularly on divorce for opening and closing the house in the middle there's quite a lot of play in these nuts so it's not entirely precise precision screw threads are another subject the most precision screw i have in the workshop is in my micrometer extraordinary thing is uh it's accurate to 0.001 millimeters that's 10 times more accurate than my calipers that i use all the time i don't often use this it's more accurate than i can cope with in a way um but it making a precision screw like this is tricky because uh once you cut the screw you have to harden the thread and to do that you have to heat treat it and that distorts the metal so after the heat treatment it has to be finally ground to the final shape in a precision grinding machine and that's how all precision screws are made so the precision version of the acme thread is the ball screw and these are beautiful things i've never used one in one of my machines because they always used to be so expensive but you can now get real bargains from china i just got this and it was one and it was 17 pounds um i'm not quite sure in one of my machines where i would need this precision but i'm tempted now the nut itself is amazing uh inside there are lots of ball bearings that run around in a in a circular track uh this is the biggest clock or biggest clock dial anyway that i've ever made uh another project with my friend andy and uh just fixing it to the building was quite epic but fortunately we had paul who was an experienced offshore rigger and welder uh who took control and he arrived with a bigger version of this it's a round thing that tapered to a point um and we're quite sure what he's going to use it for but once he was up in the air it was obvious if you've got a huge frame um that's suspended by the crane it's very difficult to line up the holes so what you do you stuff your podger through a hole in the frame that's moving about and then you try and get the other end in the bracket in the building and then as the crane slowly lowers you can sort of lever it to make the holes line up and then of course you can drop the bolt in and the rest is quite straightforward so whenever you see somebody high up on a construction site putting steel together they're bound to have a podger a small scale i find it useful to grind the ends of both the points on my literature so if i've now ground the head on the bolt it's much easier to fit this a panel to a metal frame because i just push it over and uh it'll i can feel now that the tip has gone in and then wiggle it a bit and now the thread has started uh much easier than if it's flat on the end of the bolt so my other uh thing that i've learned about making frames like the frames on my machines they're mostly welded but there are some bolted joints to take parts out for maintenance and to get at other parts that are hidden and it may sound counter-intuitive but i always do the bolted joints before the welded ones i think perhaps the best example of this and certainly the biggest is on the clock i made for uh the exploratorium at san francisco which had to fit around a column so when i arrived on site the whole frame had to be split into two halves and then re-bolted together so just as i was saying i started by the bolted joints of the frame so this is half a side piece that i'm bolting to a short joining piece and i'm now welding the other side of the short joining piece to the other half of the side piece if that makes sense so this is our finished horizontal side piece for the cloth we actually made 16 of them um and this is how we started on the frame um and then the next day uh we went outside and welded everything else together so actually i never undid these bolts uh until i got to san francisco just the night before we assembled it uh and i was nervous where they would go back together but they did all fit perfectly it was very very satisfying so yeah do the voltage joints before the welding i think foreign i thought i'd end by talking a bit about extracting rusty old bolts a frustrating business so if you've got a bolt like this the pan posse head and the head is completely mashed it happens very easily uh you're not going to unscrew that well conventional wisdom is a bit of wd-40 or all heat it up but there are lots of situations where you can't heat it up and wd-40 often doesn't do the trick so um a couple of things that i found useful uh first is my mould grips so um just to grip the bolt around the head um you've got to get it exactly right the tension so it's gripping the head really really firmly and then once you've got it right you can snap them shut and then you can i i've got that one to turn i wasn't sure if i would actually um but i'll tighten it up again because i'll show you the other technique that i've i've found useful and that is simply to use an angle grinder to turn the head back into a flat headed screw [Music] and then i then quite often hammer the screwdriver in so it's got good contact and then uh also another thing i quite often then use my mole grips again just to grip round the screwdriver to give myself better leverage well that was a bit loose already i think so it wasn't a good test really but um i have found that very useful for these pan posies but of course things get more difficult on a for larger bolts so then there are these things called screw extractors the idea is that you drill made of hard steel you drill that bit in up to there then turn it over and then you force this one in the spiral going down into what you've drilled this is a new bolt i just tightened it as much as i could seems to need a pilot hole first uh then if it were to drill the thing in backwards um then flip it over uh and the taper screw thing does grip extraordinarily well that part of it's good [Music] not the biggest success maybe other situations it would work the thing that i've found had much more success with unconventional technique is welding to the the head of the bolt or the remains of the stud so a nice blob of weld um not not only uh gives you a good connection to the head but it also provides quite a lot of heat which can sometimes shake the thing loose and then of course you've got a nice big lever arm to try and uh force the the nut loose let's see if i can tap it loose yeah i think that's going to come quite easily now that was easier than sometimes because the thread wasn't in too bad shape well that's the end of this episode turned out to be rather a mammoth one and there's lots more i could have put in um but i hope you found something useful from it um it was fun to make this one [Applause] [Music] you

Channel: tim hunkin

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Id: yGdszxGiB1A

Length: 56min 5sec (3365 seconds)

Published: Thu Apr 21 2022