|
|
Wondering if there is a rule of thumb which suggests the proper amount of thread inserting into a base material vs thread diameter of a bolt to acheive an "ideal" fastening strength of two items. Trying to word that the best i can.
Reply:There are drill-tap size tables that list different percentage of thread engagement. Or are you referring to the thickness of the metal to z certain size fastener? I try to get at least the thickness of a nut for a given fastener size.
Reply:Should be the diameter of the thread deep.
Reply:I am mounting something to a piece where the bolt cant protrude out the back as there is another piece of steel back there. The mother material is 3/8" threaded, thats certainly not enough to accept a 1/2" bolt. Im thinking possibly welding a nut atop that 3/8" material, so the four 1/2" bolts have more to bite to.
Reply:I don't feel like looking but google threading chart and you can also get information for tapping softer materials or when you only can meet half the bold diameter depth to thread.
Reply:I would think you would be ok to do that but it depends on what it is.
Reply:This seat is getting mounted to this loader mast. Four bolts 1/2". Mounting plate on loader is 3/8" and same on seat side. I wanted to do studs but fear welding them through the back will change hardness of the bolt/stud. If they were to sheer off im sol in the future. Attached Images
Reply:Why don't you use 3/8" bolts?Airco Ac/Dc 300 HeliwelderMillerMatic 200 (stolen)Miller Maxstar 150STLMiller AEAD200LE (welding and generating power) Hobart MIG
Reply:It's a good question. Just felt four 3/8" didnt look sufficient enough to hold 100 ln frame plus up to 180 person. To me 1/2" just "looked" better
Reply:Originally Posted by brendonvIt's a good question. Just felt four 3/8" didnt look sufficient enough to hold 100 ln frame plus up to 180 person. To me 1/2" just "looked" better
Reply:Weld a small doubler plate in each spot, drill and tap through both pieces.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Generally you want the threaded hole depth to be at least 1.5x the diameter of the bolt for maximum strength. I work with a bunch of engineers and that's kind of the rule of thumb when fabricating things that will be proof loaded. While I don't know this for sure, it's always been said that at 1.5x bolt diameter you will break off the head of the bolt before you will strip the hole. These rules are generally applied when crush/bending/breaking large concrete and steel structures and are generally overkill for a vast majority of applications.
Reply:use bolts and nuts. not everything has to be or should be welded. Tapping threads in some crappy a36 steel isn't going to be anywhere near as strong as an actual grade 5 or 8 nut that's actually threaded to a real tolerance.And the answer to your question is as thick as a standard nut is for that diameter of bolt. I would call it the same thickness if the threads are of the correct tolerance and the nut is as high strength as the bolt.Last edited by MikeGyver; 01-12-2015 at 10:20 PM.Welding/Fab Pics: www.UtahWeld.com
Reply:Always used 2x diameter myself, if I remember correctly at 70% thread profile. 1/2" bolt, 1" of thread engagement, 3/8= 3/4, 5/16=5/8, etc.
Reply:I was looking at something yesterday and it said the thread depth should be the diameter of the bolt which is usually the height of a standard nut. To hold even 1000 lbs. four 3/8" bolts would be plenty. Make sure to put a seat belt on there.
Reply:Check out the first post at http://www.practicalmachinist.com/vb...-depth-173689/In that post it refers to the section of Machinerys Handbook dealing with thread length. In general, the first 3 threads hold provide most of the strength. After 6 threads there is no gain since at that point the bolt will snap first. Look at the nut for a 3/8-16 thread and you will find there are only about 4 threads in the 1/4 deep nut.There are tables for how much load a bolt will take. Machinerys HB has one, or you can go to something like http://www.derose.net/steve/resource...les/bolts.html to see what the yield is.For a 400 lb contraption (seat + person) 3 or 4 3/8-16 bolts will do the job when screwed into the 6 threads that you'd get in 3/8 thick plate. Even if you only screw the bolt in 1/4 inch.Dan----------------------------Measure twice. Weld once. Grind to size.MIG: Lincoln SP100 TIG/STICK: AHP Alphatig 200X
Reply:All noted thank you very much.
Reply:Originally Posted by dbstooIn that post it refers to the section of Machinerys Handbook dealing with thread length. In general, the first 3 threads hold provide most of the strength. After 6 threads there is no gain since at that point the bolt will snap first. Look at the nut for a 3/8-16 thread and you will find there are only about 4 threads in the 1/4 deep nut.There are tables for how much load a bolt will take. Machinerys HB has one, or you can go to something like http://www.derose.net/steve/resource...les/bolts.html to see what the yield is.For a 400 lb contraption (seat + person) 3 or 4 3/8-16 bolts will do the job when screwed into the 6 threads that you'd get in 3/8 thick plate. Even if you only screw the bolt in 1/4 inch.Dan
Reply:Assuming that the nut or tapped material is of sufficient strength, you need engagement of 3-5 fully formed threads, as noted by Drooopy. That is why the bolt normally protrudes a couple threads above the nut. A 3/8" x 24 TPI might work.Some good info here: http://www.boltscience.com/pages/info.htm"USMCPOP" First-born son: KIA Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:Originally Posted by DrooopyThis. Had professor in engineering school who would preach the 3 thread rule all the time. He said something like 97% load in the first three threads. I don't know how completely accurate that was, but probably close at least.
Reply:I don't really care much for the whole seat design and attachment to the mast.
Reply:What do you suggest. Design based off many similar. Attached Images
Reply:No suggestions. I just don't like the lever nature of it.
Reply:I see what you mean. Was curious myself, but see the same thing over and over. Not fat boy approved.Thanks for the help. I decided to have randy cut me parts and figured out a way to use bolts and nuts.Edit: Actually thinking about it, will reduce lever quite a bit too.Last edited by brendonv; 01-13-2015 at 10:37 PM.
Reply:90% of the load is held by the first 3 threads.Anything more than 5 or 6 threads is just wishful thinking.old Miller spectrum 625 Lincoln SP-135 T, CO2+0.025 wireMiller model 250 and WP-18V torchCraftsman 100amp AC/DC and WP-17V torchCentury 115-004 HF arc stabilizerHome made 4 transformer spot welderHome made alternator welderLearned a lot thanks guys.
Reply:Originally Posted by MikeGyverSounds a little incomplete. 3 threads from a fine thread bolt isn't going to have as much engagement as the same size bolt in course thread... Plus if you tap a loose threaded hole I'm sure all of that goes out the window; and tapping into a weaker material has go to effect everything too.
Reply:I've heard that fine thread hold more load because of increased surface contact.
Reply:Originally Posted by JoedanI've heard that fine thread hold more load because of increased surface contact.
Reply:Within the SAE standard thread charts, the fine thread generally has a higher yield strength. If you think about it, a 300 tpi thread may just be stronger than it appears. A thread height of 0.029 inches with 85% engagement means your slop is less than .001 inch. By comparison a 24 tpi thread can be much, much looser.How strong is a 1/2 diameter plug weld that is 3/300 deep? It's late and I'm not up to doing the math. Dan----------------------------Measure twice. Weld once. Grind to size.MIG: Lincoln SP100 TIG/STICK: AHP Alphatig 200X
Reply:Originally Posted by dbstooHow strong is a 1/2 diameter plug weld that is 3/300 deep? It's late and I'm not up to doing the math. Dan
Reply:Originally Posted by MikeGyverA 1/2"x300tpi bolt threaded in a nut .010" represents 97% of the ultimate tensile strength? so it's not even worth threading in any more than half the thickness of a credit card? that's obviously complete nonsense. Like I said, the idea you're trying to recall might be sound, but not as you've expressed it, it's obviously missing some factor or restraint.
Reply:If the bolt breaks while tightening, you have enough threads engaged. If the threaded hole or bolt strips, you need(ed) more threads. "The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt
Reply:Originally Posted by MikeGyverA 1/2"x300tpi bolt threaded in a nut .010" represents 97% of the ultimate tensile strength? so it's not even worth threading in any more than half the thickness of a credit card? that's obviously complete nonsense. Like I said, the idea you're trying to recall might be sound, but not as you've expressed it, it's obviously missing some factor or restraint. Originally Posted by DrooopyYou continue to miss the point. Stop comparing coarse theads and fine threads. That was never the question.
Reply:Since it didn't sound right to me, I figured I'd do a bit of research and try to find some more solid data...The "rule" is 6 thread carry ~98% of the load (not 3). The first 3 threads carry just under 3/4 of the total load.(this distribution varies a bit among different standard bolts and thread pitches).Here's the breakdown:This is also all based on the assumption that nuts are of equal strength or are slightly stronger than their bolt counterparts (which they in fact often are, so the bolt breaks before the nut strips). As long as the nut is of higher strength material than the bolt, having many more than 6 threads will literally do absolutely nothing as far as pull-out tensile strength goes.Note: this only appears to apply to bolts and their equally rated nuts, not tapped holes with unknown or poor tolerances or excessive looseness.The whole reason for this exponential loading profile is because of the elastic and plastic deformation of the threads. This is why an over-torqued bolt always shears at the first thread, and never several threads in. The problem with using less than 6 threads is as follows... If you use say 3 threads, then those 3 threads have to now carry 100% of the load and the percentage breakdown changes from the above test. The first thread has to carry even more than 34% and it quickly yields. Once the first thread enters its plastic region the 2nd and 3rd thread now must carry 100% of the load and they of course just subsequently fail in the same manner.If, for example, you were to tap a hole in a block of cheese, the cheese doesn't have high enough strength to allow for the bolt to be torqued enough to get to the point where it stretches elastically. Therefore in this mode the threads are not undergoing exponential loading, they are all basically even. The loading profile in this situation would be all the threads evenly sharing 100% of the load. In this (extreme but still valid) example, a bolt threaded a foot into a block of cheese is obviously going to have a MUCH higher pull out strength than a bolt threaded in 6 turns, because 6 turns worth of cheese is going to yield much easier than 1 foot of cheese threads. If the threaded material was made out of tungsten unobtainium carbide, then there is nothing to gain after 6 threads because the bolt itself begins yielding before that many threads does. The exponential thread loading profile is due only to the elastic stretch of the bolt. You need enough threads of the nut material to allow for this bolt-break failure mode. This number of threads is dependent on the strength of the nut material.The whole 6 thread rule is based on the assumptions that, nut material is stronger or equal to bolt material, and it's a standard/common thread. The 1/2"x300tpi example doesn't work here, even if the nut is infinitely strong because the bolt would still yield.This paper delves mathematically into why that is.http://www.ajaxfast.com.au/downloads...anythreads.pdfAnd its conclusion is:If a bolt and a nut are made of the same material the minimum thread engagement length required isapproximately 65% of the nominal diameter. For example a M10 bolt will need a minimum of 6.5mmof thread engagement. Typically standard nut height is approximately 80-90% of its nominal diameter [to provide a safety margin].So the final conclusion of "how much thread engagement do I need?"If you want full strength, then 65% nominal diameter absolute minimum (assuming ideal fitment and materials of equal strength), 80-90% is probably a better real world figure.If the nut material is not of equal or greater strength than the bolt, then you need to add more engagement to compensate! (or the joint will fail in the nut-stripping mode instead of the stronger bolt-breaking mode)Short answer: You need enough engagement to provide bolt-break failure mode, and this amount of engagement is a function of the strength of the nut material.Last edited by MikeGyver; 01-16-2015 at 01:30 AM.Welding/Fab Pics: www.UtahWeld.com
Reply:A 1/2"-300 is ridiculous because it is nearly impossible to make and would have no practical use in this world. Additionally, the threads would be extremely weak at 1/300" per thread and subject to almost instant plastic deformation just trying to screw it together, not to mention the immense amount of friction that would destroy it during assembly. Now for the original question at hand and my original response which still recommended 5 threads if possible, but we will call it 3. Also assume Grade 2 strength for the bolt which is less than the tensile strength of A36 and 71% of the load carried by the first 3 threads. I will assume decent threads with a decent tap.A Grade 2 3/8-16 has a proof load of 4250 lbs. Multiply that by 4 to get 17000 lbs x 0.71 = 12070.Now you have dynamic loading that occurs with a 400 lb load on a lever, but I am willing to bet my own tail that it would hold just fine.Your argument about the strength of the nut is valid. If you want to try to thread cheese, be my guest and post pictures. I assume a certain level of basic engineering that someone will not use lead or tin as a nut on a stressed joint. So I will rephrase my statement. With the caveat of the nut material being as strong as the bolt, a majority of the strength in a bolted joint is achieved at 3 threads with no advantage to more than 6 threads.Multimatic 200Ellis 1800Haberle S225 9" cold sawMM 300; Spoolmate 30A w/ WC-24TB 302GDynasty 280 DX Tigrunner
Reply:If you're assuming 3 threads in your calculation, then the first 3 threads carry 100% not 71%, and the percentage distribution must change to account for it (the first thread must now be higher than 34%).Cheese is just a silly example of a low yield material, just substitute plastic or low yield metal like A36; it's the exact same difference. Sometimes it's just easier for some people to visualize results when taken to extremes, which is what the 1/2"-300tpi example is.Here's a simple test:Torque a 1/4"-20 grade 5 bolt into a grade 5 nut that's held in a vise, use a deflection torque wrench and watch at what reading the bolt snaps.Now do the same test using a nylon bolt. You won't even be able to break the bolt, the nut will just strip out.Now go get about 10 nylon nuts, thread the bolt into all of them and hold all the nuts in the vise. Now there might be enough thread distribution into the plastic to actually break the bolt, or at least you'll get a much high torque before the nut threads strip. (I say there might be enough because the exponential loading profile will be much flatter than the chart above because it will require more threads to generate any stretch in the bolt in the first place)Bottom line is, lower strength material needs more threads to distribute the load than higher strength material.If the nut and bolt are matched in material, then you want a minimum of 65% of the nominal diameter plus some safety margin of thread engagement, regardless of the thread pitch or material. So, the number of turns is really irrelevant, it's just a (sometimes poor) estimation of the 65%+ figure.Last edited by MikeGyver; 01-16-2015 at 07:40 PM.Welding/Fab Pics: www.UtahWeld.com
Reply:Nuts & Bolts?All I was ever told by OLD Tool & Die Makers is:At least 3 threads sticking out of the Nut, that way you have time to get a wrench to retighten it before the Nut falls off.Fine Threads screwed in to the same depth as Coarse Threads have more holding power. which is why on some machines, critical parts will have Fine thread hardware.Taps & Dies come in 3 grades, (I don't remember the exact numbers anymore) 65% engagement, 77% engagement and one close to 90%. When asked what do they mean, I was told non critical stuff is assembled with 65% for speed of assembly like in automotive assembly. Hardware holding more critical assemblies that are usually hand assembled as the hardware can't be slapped in by a machine uses 77% engagement like nuts holding a head on an engine block. The highest rated engagement is/was used on stuff where it needed to stay no matter what! Usually hand assembled in a fairly clean environment.Why not 100% engagement?He said back then that would never exist as you need clearance between the Threads to overcome Friction to screw them together. Hence there is a 90 something percent engagement.Clear as Mud?As far as the seat deal?Four 3/8 Grade 5's is plenty for that provided they are properly torqued to prevent "plastic" deformation in the threaded areas of the assembly.
Reply:Originally Posted by mikecwikShould be the diameter of the thread deep.
Reply:If the root diameter of the thread is the smallest section, it would seem that there is no need to have thread engagement any deeper than the cross sectional measure of the root diameter.I remember some years ago, Engineering insisting that an equipment manufacturer/installer remove almost all the hardware from a series of conveyors and replace it with hardware that extended at least 1/4" past the nuts so that there would be a visual indication that the hardware was loose.The general rule for tightening hardware where I work seems to be, tighten it till the head snaps off, then back off a quarter turn.
Reply:The first couple threads are poorly formed and therefore will fail much sooner. This is why they should stick through the nut.Welding/Fab Pics: www.UtahWeld.com |
|
发表于 2021-8-31 22:45:13