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HTS Bolts

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mgj01/01/2010 13:59:48
1017 forum posts
14 photos
Don't matter if you have mild nuts.You'll strip the thread out of most ordinary nuts long before you get to yield on HT.  Yield on mild is about 12 tons. Yield on hT - depending on the HT, 50-100% more.
 
I always thought the elongation would be about the same before yield, its just the load per unit area (stress) to achieve that elongation is  greater. 
 
ie the elongation (strain) is the same (similar - except in specialist steels) but Poissons Ratio is greater, as is the strain energy? Still I could have it wrong.
 
I think people are confusing distortion after yield with strain before?

Edited By meyrick griffith-jones on 01/01/2010 14:00:35

Nicholas Farr01/01/2010 15:07:55
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3988 forum posts
1799 photos
Hi Meyrick, your theories may be correct (never could get my head round all of the bolt science) but I have been using nuts and bolts of all sorts of sizes tensile strenths materials etc. in industry for over 40 years and in my experience I have found that softer bolts using the same torque settings as higher tensile bolts streach and thin on thier shanks more before they creep, fracture or become useless. The point I was trying to make is that it is better to use softer bolts on T slots rather than HT bolts. As most people have not had the experianceof the damage HT bolts can do when not used properly and a lot of people use tubes etc. on thier spanners to try and get it tighter. Remember a bolt/stud has to streach within its yield limit to work properly. I believe it has already been said that it is better to use as many claps as possible and practical rather than one or two very or overly tight ones. Nick.
KWIL01/01/2010 16:42:28
3681 forum posts
70 photos
Use a CORRECTLY SIZED ring or combination spanner, use your fingers and NOT your hand to tighten, that should be about right. NEVER use a socket and bar, that is staring disaster in the face
mgj01/01/2010 17:08:50
1017 forum posts
14 photos
Agreed Nick - thats what Poissons Ratio says, but once the shank has started to thin etc you are past yield, and springs and elasticity no longer apply.
 
Poissons Ratio  = Stress/strain. 
 
Where stress is load per unit area.
 
Strain is change in dimension by original dimension  (delta L /L)
 
Strain is also Stress/E (Youngs Modulus of elasticity)
 
So yes the HT stuff will be less elastic for a given load, but that is NOT the same as %elongation at yield.
 
I also agree entirely about using softer bolts and fixings for clamps, for the very good reasons you have given. Also cooking mild "slides" before it goes so you get warning when you have loaded all up to near busting and uslessness. HT tends to snap suddenly because % elongation after yield tends to be quite small and yield tends to be closer to UTS, whereas mild is quite long..
 
I have to disagree about clamps. As I have said before  - 3 is the correct number to use, because three will find a level and 3 (depending on exact placing and circumstances) will not distort the work.
Nigel McBurney 101/01/2010 19:34:19
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1101 forum posts
3 photos
hi  I assume that you were attempting to part off a threaded portion of the bolt shank,well a ht bolt will have some heat treatment plus probable work hardening from rolling the thread,best advice is cut it off with a hacksaw,then just face it in the lathe,why ruin a good parting blade or expensive tip and its quicker.the factory where I worked as an apprentice only used tee nuts ,thee eigths and half inch whitworth.and had a large assortment of bolts so the correct length could be selected ,and we were instructed to make sure the bolts  did not bottom out in the tee slot,there were no tee bolts,also studs were only used on special purpose fixtures,I understood that the reason was someone had had an accident caused by long stud projecting well out above a clamp,so the boss preferred bolts and in such matters his workshop practice was good.Too prevent overtightening only short series spanners were allowed in your toolkit.None of our machines or equipment had a damaged slot,but after I left my first job I have seen a lot of damage to tee slots and machine tables,particularly in trade shops.
Tony Pratt 101/01/2010 19:54:58
2319 forum posts
13 photos
Ok, I'm going where angels fear to tread.There is no absolute right number of clamps, 3 could be ok or you might need any number, some long jobs or irregular shapes require large quantities of clamps to prevent movement.
The only time a job will not be distorted by clamping is when the underside is fully supported either by its lying flat on the table or if so required shims or jacks are used to take up any irregularities, therefore when clamping commences the clamps are acting on a fully supported surface. If these precautions are not observed there is always a risk of distortion irrespective of how many clamps are used.
 
Tony
 
John C01/01/2010 21:50:35
273 forum posts
95 photos
Nigel,
I wish I had cut the bolt with a hacksaw!  I have since discovered that I must have chipped the edge of my indexed parting tool, on the threads as you suggested, so this whole escapade has cost far more than a set of tee nuts and studs!  Hey ho - what price experience.......
John
Circlip02/01/2010 12:39:16
1723 forum posts
Bl**dy Carbides AGAIN, why have most forgotten how to use a Hacksaw?? Have turned bits up to 75 (3")mm dia. in the lathe and by cutting a bit and rotating the chuck by hand manage to get through the bar with a straight cut and "Wasting" about a 1/16 0r 3/32 of an inch (1.5 to 2.3mm) of material.
 
 Cover the bed with a piece of wood to stop the saw hitting it and splash a bit of coolant in the slot while cutting.
 
  YES, I have both a bandsaw AND an industrial (Q & S) hacksaw but whats wrong with execising yer arms??
 
  Regards  Ian.
mgj02/01/2010 15:41:40
1017 forum posts
14 photos
Ian  - you can't blame carbides for that. You'll knock the tip off HSS trying to part HT bolts like that. All it has to do is lift at then end of the cut, and thats it. Tip gone. Tailstock suport, and the right grade of carbide is the answer.
 
BTW I love your idea about hacksawing. I think its excellent. Hacksaws are much better - mine is about 350 watts I think, with a rigid industrial blade, . 
 
But I agree - in this case I'd have just hacksawed them off and used the abrasive linisher to square up the cut and bevel the edge.

Edited By meyrick griffith-jones on 02/01/2010 15:42:17

Circlip02/01/2010 19:34:55
1723 forum posts
Not actually blaming the things Meyrick, it's just that it's an automatic thought to use it RATHER than a basic hand tool.
 
  I remember listening to a "Woodworker" explaining that he'd delayed assembling a dolls house cos he was waiting for the electric screwdriver to RE-CHARGE, and sadly he wasn't joking.
 
  Regards  Ian

Edited By Circlip on 02/01/2010 19:35:48

ANDY CAWLEY03/02/2011 18:40:25
190 forum posts
50 photos
Sorry to be pedantic about this but the elastic stretch of steel bolts regardless of their tensile will be the same. Non elastic stretch or permanent deformation will just occur soo ner in a lower tensile bolt.
 
Also every time I use my ancient Bridgeport I curse the chap who, in the past, just used ordinary sized hex bolt heads in the tee slots and made a real dogs breakfast of the said slots.
mgj03/02/2011 20:28:12
1017 forum posts
14 photos
Elastic stretch of all steel bolts will be the same (to yield)
 
Well now there is a thought - that Youngs Modulus is identical for all steels! I agree that it doesn't differ by much, (in the sense of this post anyway, which leaves out the spring steels etc) but for sure, the strain for a given level of stress DOES differ according to the alloy.
 
It can even differ according to the heat treatment given to the same alloy?
 
There are many sorts of bolts- stainless, of varying grades, mild, HT etc, and they all behave slightly differently don't they?
 
Though you can of course always use an approximation if you don't want to be pedantic
 
 

Edited By mgj on 03/02/2011 20:36:02

Edited By mgj on 03/02/2011 20:38:35

Jeff Dayman03/02/2011 21:56:50
2356 forum posts
47 photos
We seem to be getting rather academic and well away from the original poster's enquiry. Surprised no one just said 'give up the HTS, get some off the shelf allthread rod for clamp studs, cut it to length and chamfer the ends, use proper size T nuts ONLY, and have a happy life'.
 
JD
 
(or continue with the metallurgy theory banter and not make anything)
Gray6203/02/2011 23:33:48
1058 forum posts
16 photos
I think we are all getting too bogged down with the theory of metallurgy. I have, for many years, made Tee nuts out of MS and used common all thread rod with off the shelf nuts. I have never had a vice or fixture move or lose registration. I use an ndustrial turret mill (Ajax AJT4) and have never experienced any issues wiith movement.
If registration is an issue, then as I have done with my precision vice, set it up as required, then machine a registration keyway and add an alignment bar to the underside of the vice, that way you will ensure correct and accurate registration each time the vice is fitted to the table. Using this method, my precision vice is within 0001" every time
 
mgj04/02/2011 01:43:59
1017 forum posts
14 photos
Well if I might just defend my self. See posts on 1/1/10 where the issue of stretch against HT or mild was specifically addressed.
 
Metallurgical theory - not really. Its actually very basic strengths of materials, which every engineer has to know about. In the same way that women when discussing lingerie ask what colour it is, when it comes to materials, engineers want to know UTS, yield and Youngs modulus of Elasticity or E.
 
Is it of use to the model engineer, in the conext of this post, and others? Depends on your point of view
 
If you'l pardon the Freudian slip, with my milling hold down tackle I have deliberately used HT kit more recently, but I have sized my nuts in mild so they will strip before studs, tee nuts and table are damaged.
 
Just recently I made the point to ChrisH that that some driving crankpins on a model of Metre Maid were safe as houses. An approximation since I ignored any bending moment, but good enough. Then I did the caclulation for the mild conrod and coupling rod bolts specified in the drawings. You get about 7ton tensile in that, for a yield of about 12 tons. safe - well yes, until you add in in the preload geneated by the nut. and of course its a cycling or reversing load. So those are a scrapbin job - just for insurance.
 
 
Or on my traction engine. Ordering springs for the safety valves. If you can do the maths without taking shoes and socks off , its pretty easy to end up with the right length of spring, at the right rate, so it fits the turret and works first time. (I had other problems, but spring rates which is the common issue, were not amongst them)
 
Or the great front and rear toolpost parting off argument, when its very obvious why parting tools jam, and the cure very simple. (Though I have carbide tipped parting blades, I use Eclipse left and right hand ground blades much more often and since Chris Stevens got me to took at the problem properly, It has simply been solved))
 
So yes, strengths of materials and the associated mechanics or resolution of forces and vectors, affects us as engineers every day of our lives, consciously or otherwise, and sometimes by omission, when something breaks which could easily have been avoided.
 
At the end of the day, materials and mechanics are what engineering is about -, don't knock it till you have tried it, because a calculator saves a hell of a lot of grief.
 

 

 

 

Edited By mgj on 04/02/2011 01:55:11

Jeff Dayman04/02/2011 02:01:28
2356 forum posts
47 photos
OK, you do the math, I'll do the plain mild steel studs and get on making models.
 
note: I tried to use a calculator once on a clamping problem, but it stopped working when I drilled the stud hole through it. Never bothered since.
 
Re strength of materials: You mean people calculate that stuff? I thought jet aircraft designers just got lucky all these years, eyeballing it.....( ie. Hmm, looks strong enough...)
 
JD
Terryd04/02/2011 07:57:44
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1946 forum posts
179 photos
Hi MGJ,
 
I know from your postings that you like precision and theoretical exercises. So I am surprised at your lack of accuracy in the use of language when you mention a 'Freudian slip'.
 
A Freudian Slip or Parapraxis is an error of word thought or deed due to repressed (unconscious) thought or wish or conflict. As it is unconscious it cannot be known by the person to whom it refers. i.e. if you think it is a Freudian slip, it cannot be one as you are conscious of it.
 
What you were describing might be called a Paranormasia (or pun) where two meanings can be attached to a word or phrase or two words sounding the same. For example, "your description of Poissons theory sounded rather fishy to me"
 
However as there is obviously a reference to genitalia in your posting it could also be described as a 'Double Entendre' but not a Freudian Slip,
 
Best regards
 
Terry

Edited By Terryd on 04/02/2011 08:00:31

Jeff Dayman04/02/2011 13:10:46
2356 forum posts
47 photos
Now we are well off the rails. Come on guys, this is a model engineering forum. I'm sure there are theroretical metallurgy forums and English usage forums somewhere else where this stuff can be bandied about, but please not here.
 
The OP just wanted to cut some studs and clamp some stock.
 
JD
chris stephens04/02/2011 16:19:00
1049 forum posts
1 photos
Hi Guys,
Since I got a mention, I thought I would chip in, then thought better of it and decided against.
It's all above my head, I think in Victorian terms, make it look strong enough then add a bit more for luck.
chriStephens
 
PS Terry, when you were using your dictionary to look up the meaning of Freudian Slip, did you miss the page where Pedantry was explained?
Terryd05/02/2011 08:49:12
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1946 forum posts
179 photos
Hi Jeff.
 
I entirely agree I just thought that mgj would like to be as accurate in his speech as he appears to be in his theory.
 
Like you I'm not sure how much we need to know about UTS at this level of model engineering. I just know that you need to use proper tee nuts with ms bolts and studs. The other important factor is to resist the temptation to overtighten the nuts, Like other have said , I've seen gorillas hanging on 12" lengths of tube on the end of a ring spanner, and even on one occasion a miller using a hide mallet to tighten a clamp. I just had to close my eyes and hold my breath. I too use a short series spanner and never had a problem.
 
I know that at least two clamps must be used on any workpiece never less. any more depends on various factors, e.g. shape, size, depth of cut etc
 
I also know that bolts stretch when tightened and if within the elastic limit , the elastic effect combined with friction is what allows the nut to do it's job. I always use studs due to the possibility of the bolt bottoming out , reducing the clamping and possibly damaging the tee slot.When making tee slot nuts, do not tap fully all the way through, Use a second tap and leave the last few threads tapered this helps prevent bottoming out bu the studs.As an alternative you ca bruise the bottom couple of threas with a pin punch to prevent bottoming out.
 
Oh yes, just one more thing, I always use the correct height packing and thick washers under the nut/bolt head. Hope that's On T enough for you Jeff
 
Hi Chris,
 
Of course not, I know the word full well, other useful words I know are 'imperceptive' and 'humourless', also, a relevant phrase from my book of English Quotations and Phrases is 'Tongue in Cheek' . Useful reference to have, you should study it. I like 'blinkered' as well, lovely word to roll around the tongue, relevant too.  Did you miss those?
 
Best regards
 
Terry

Edited By Terryd on 05/02/2011 09:08:08

Edited By Terryd on 05/02/2011 09:14:17

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