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KyMike
02-18-2013, 11:36 PM
Greetings Folks,

Was wondering if anyone here might remember an article in one of the home shop magazines from around 15 years ago about an unorthodox method for leveling a lathe bed that didn't require the use of an expensive precision level. As near as I can remember it involved a bar several feet long pivoted from an overhead support with a lead weight attached to the free end and a simple dial readout of some sort attached to the upper end of the bar. I thought it was in Live Steam but a search of my back issues didn't turn up anything. Maybe it was in Modeltec. I would like to locate a copy of the article if possible.

Mike

Tony Ennis
02-18-2013, 11:47 PM
"Rollie's Dad's method" ?

gcude
02-18-2013, 11:54 PM
"Rollie's Dad's method" ?


Oh boy, here we go again ...

JoeLee
02-19-2013, 12:10 AM
I can't remember what I had for lunch!!!

JL............

J Tiers
02-19-2013, 12:35 AM
I believe it was in either HSM or MW, and it was indeed a pendulum method.

I can't understand it being really very sensitive, not without such large supports etc as to possibly affect the result. But I don't remember enough of it to discuss it in an informed way.


I can't remember what I had for lunch!!!

JL............

If we get into another session of RDM, we may all get another look at what we had for lunch.......or dinner.....

darryl
02-19-2013, 12:52 AM
If we're talking about some kind of sensitive mechanical level, then it would be a base and column, with the pendulum hanging from the top and the pointer hovering over a bit of a scale. The base is set on the ways- if built properly it's not too long to fit between the lathe and the ceiling- and the relative position of the pointer is noted. You repeat the test at each end of the bed, and you shim the mounting bolts until you get the same reading at either end.

In a variation on this, there's a mechanical amplification added to spread out the small deviations that may exist into a wider reading.

Machtool
02-19-2013, 12:55 AM
Theres a Utube video of a guy trying it.

http://www.youtube.com/watch?v=wANmXuwowqw

Forrest Addy
02-19-2013, 01:04 AM
Not enough info: What make lathe, swing, etc? How old? What condition? What class of work?

I looked at the link above. It appears to be based on the pendulum levels used by the Pharoh's stone masons. The YouTube guy demonstrates a very sensible adaption. However his apparatus is subject to error from drafts purturbing the pendulum, it loses sensitivity in proportion to height limitation and the riser tube is sensative to heat input. A hand on one side will warm it leaning the tube sligtly dragging the bob with it. However the aluminum tube conducts heat well and if allowed to settle will soon reach thermal equalibium. If you wish to shorten thermal recovery time wear thick fluffy mittens or barbecue mitts when handling the instrument.

The bob's decaying oscillation may be more quickly damped if an aluminum fin is attached that sweeps a magnetic field however the sensitive parts of the apparatus in proximity to the field will need to be made of non-magnetic materials.

The pendulum level's performance could be enhanced if a more sophisticate pointer and scale is fitted to the bob, maybe with magnification or perhaps some form of inductive sensor could be used. It should be noted that electronic pendulum levels capable of sensing 1 arc second are on the market.

The idea bears merit if the pendulum length could be shortened and enclosed in a draft and chip- proof enclosure, magnifed optical display: a spherical lens (a clear glass marble) in a cheap pointer laser's light path, mirror the deflected light up the height of the enclosure and fan the magnified travel on an adjustable scale. Pointer lasers, glass marbles and tiny mirrors are cheap, the pendulum apparatus made of shop surplus. Hm, could be made cheap at that but expensive in time. The mind boggles at the possibilities.

My advice is to spend a little wise money and purchase a precision level you can use in the future because, believe me, a precision level has many uses in a small shop besides leveling machine tools

Here's a place to start.

http://www.ebay.com/sch/Manufacturing-Metalworking-/11804/i.html?_udlo=22&_sop=15&_from=R40&_mPrRngCbx=1&_udhi=176&_nkw=precision+level.

You do not need a used $350 Starrett #199 from eBay or a $750 Starrett #199 purchased new, or $1200 Wyler. Import quality is fine for a precision level for the low-use home or small commercial shop. Their graduations may not be spot-on but their sensitivity is adequate and, if adjusted or used with treverse checking technique, can be easily and consistantly read to 0.001" per foot or better; planty good enough for all but the most persnickity lathes.

luthor
02-19-2013, 02:45 AM
Just get a precision level and save yourself a lot of effort trying to use other methods.

The Artful Bodger
02-19-2013, 02:57 AM
I have seen a couple of the Pharoh's pyramids and they seem to be standing up quite well, considering the few thousand years they have been there and the centuries of having bits pilfered off them. Good enough for those guys probably good enough for my lathe.

Machtool
02-19-2013, 05:56 AM
I have seen a couple of the Pharoh's pyramids and they seem to be standing up quite well, considering the few thousand years they have been there and the centuries of having bits pilfered off them. Good enough for those guys probably good enough for my lathe.

What does that mean? The pendulum was accurate enough, or the ancient Egyptians had Starrett master levels?

SGW
02-19-2013, 06:23 AM
Here's the link to Rollie's Dad's Method: http://www.neme-s.org/Rollie%27s_Dad%27s_Method.pdf

Rosco-P
02-19-2013, 08:43 AM
Here's the link to Rollie's Dad's Method: http://www.neme-s.org/Rollie%27s_Dad%27s_Method.pdf

Waste of time. Don't give sh!t if he's you're personal friend. Over a hundred year of work by Millwrights in setting up and aligning machines says use a precision level, known accurate straightedge, taut wire,etc. If you can't afford to buy a Starrett, Mitutoyo, etc., borrow one, offer to pay shipping and insurance if the lender is far away. Until that time use the most accurate level you own to align the bed, swapping it end for end until the readings are the same.

Mcgyver
02-19-2013, 09:02 AM
Waste of time. .

Why? you don't think it will work?


Over a hundred year of work by Millwrights in setting up and aligning machines says use a precision level, known accurate straightedge, taut wire,etc.

The conclusion you might draw from that is that if you frequently do this work a 199 Starrett is the quickest way to get the job done, not that this won't work

The method, at least the first part checking with the bar, is basically how you scrape a headstock into alignment. It's also not dissimilar from doing a test cut and tweaking the levelling. I can see Rollie's method being of value from someone without a level, or when the lathe is worn to point of not having much confidence on the surface you're placing the level on.

firbikrhd1
02-19-2013, 09:27 AM
There has to be an accurate way to do this without a level. Ships have lathes and they roll around in the ocean negating the ability of a level to help at all. During WW II warships took all kinds of punishment from everything from enemy shells to plane crashes and typhoons. Certainly the lathes aboard had to be readjusted after such incidents. Maybe an old veteran navy machinist here can chime in with a method.

Peter.
02-19-2013, 09:37 AM
Could be that if you were making wartime running repairs to a ship you didn't give as much thought to how 'level' the lathe was as you did to how many sharks would be circling you in the water should you not get that bilge cock repaired :)

dian
02-19-2013, 01:12 PM
i dont believe this! why dont you turn some stock and adjust the lathe until its true?

Rosco-P
02-19-2013, 02:06 PM
No, I don't have a Starrett 199, but I do own and use a Mitutoyo level with the necessary sensitivity.


Does everyone need one? Debatable. Can you get by with a "precision" level from Poland? They are supposed to be of excellant quality and a good value for the money.


For those that seem to be confused, a lathe isn't "leveled", a level is used to take the twist out of the bed so it turn true (within limits) from one end of a piece of stock to the other. A lathe on board ship isn't leveled, but it is bolted firmly to the deck after being adjust to turn true.

RDM has been discussed to death before. It will tell you about the lathe, but as I recall from the thread(s), the two collar test will only tell you so much.

KyMike
02-19-2013, 03:51 PM
Thanks for the replies. My situation is that I recently relocated my 60+ year old 9" SB to another part of the basement and I'm fairly sure the bed has a slight twist in it due to the uneveness of the floor. I'm getting a taper on work over about 5 inches long even with the tailstock aligned about as well as I can do it and before trying to set the tailstock more accurately I wanted to be sure the bed is not twisted. I will keep an eye on ebay for the next few days and see if a good buy on a level turns up.

Mike

loply
02-19-2013, 05:25 PM
Just buy a second hand level?

I picked up an excellent Hilger & Watts one for 30 here. Not only useful for levelling/twisting the lathe, but also for leveling other machines.

oxford
02-19-2013, 06:52 PM
Are the starrett 98 levels good enough to "level" a lathe with? I am in the market for a level.

darryl
02-19-2013, 10:21 PM
Pick up some glass tubing from a lab or somewhere. 1/4 OD might be about right. Heat and seal one end, let cool, fill with acetone and plug the end. There should be about a bubble's worth of air left in it.

You will be able to bend the tube by a few microseconds of arc- just enough so the bubble will seek the high spot. Damn sensitive level that will be- of course you have to make a base to mount it in, etc.

What the hay- nothing wrong with experimenting!

tdmidget
02-19-2013, 11:05 PM
Thanks for the replies. My situation is that I recently relocated my 60+ year old 9" SB to another part of the basement and I'm fairly sure the bed has a slight twist in it due to the uneveness of the floor. I'm getting a taper on work over about 5 inches long even with the tailstock aligned about as well as I can do it and before trying to set the tailstock more accurately I wanted to be sure the bed is not twisted. I will keep an eye on ebay for the next few days and see if a good buy on a level turns up.

Mike

So you expected a 60 year old POS to turn a perfect cylinder? The people who built it certainly didn't. South Bend was after all the Harbor Freight of it's time. A half step above Atlas on a good day. It turns a taper? How much? Between centers or from the chuck?
As noted lathes do not need to be level. They need to be aligned and no level is required for that.

J Tiers
02-19-2013, 11:17 PM
A starrett 98 does a fine job...... it's gonna beat the daylights out of not leveling, using a carpenter's level, trying to fiddle with a pendulum, etc, etc, etc.

Remember....

It's not the listed sensitivity of the level, that's "per line'...... it's what you can SEE as far as the bubble having moved. And that is going to be around 0.0005" to 0.001 per 10".... which is plenty fine.

Once you have it that close, you can start with a piece of stock in the chuck, and set up to not have it taper.... check again after, with the level, to be sure you didn't turn the lathe into a pretzel getting the wear compensated out.

darryl
02-19-2013, 11:33 PM
That's true of course- once you have it close, you still test and tweak anyway. You don't 'need' the ultimate in sensitivity in a level.

Jaakko Fagerlund
02-19-2013, 11:46 PM
Maybe only the old timers will remember this:

http://pitstopusa.com/images/F14604806.jpg


Absolute percision!

:D

KyMike
02-20-2013, 02:40 AM
>>> So you expected a 60 year old POS to turn a perfect cylinder? The people who built it certainly didn't. South Bend was after all the Harbor Freight of it's time. A half step above Atlas on a good day. It turns a taper? How much? Between centers or from the chuck? <<<


No not expecting perfection, just interested in getting it back to what it was before it was moved. The taper is about .008-.009 over 6 1/2 inches between centers. I realize the tailstock needs readjusting but want to be sure the bed is straight first.

Mike

darryl
02-20-2013, 04:41 AM
Rollies dad had a way of doing it- :) Sorry, couldn't resist-

J Tiers
02-20-2013, 08:26 AM
The taper is about .008-.009 over 6 1/2 inches between centers. I realize the tailstock needs readjusting but want to be sure the bed is straight first.

Mike

Well, chuck up a fat piece of pipe and try on that.... as you have figured out, between centers tells much less about the bed than "free turning" with only the spindle aligning the part.

Rosco-P
02-20-2013, 09:06 AM
Are the starrett 98 levels good enough to "level" a lathe with? I am in the market for a level.

A Starrett 98 level? For leveling your milling machine so parts don't roll off, yes. For taking the twist out of your lathe bed a Starrett 99 or other make: Scherr-Tumico; Mitutoyo; Lufkin?, etc., with equivalent sensitivity.

Carld
02-20-2013, 02:23 PM
The Starrett 98 level does an excellent job of leveling almost any machine. Many times you will need a wide long accurate parallel under the level to span a distance and two accurate wide parallel's to support the long parallel for some lathes and machines. The marks on the bubble vial will let you easily get the machine as level as you want it by comparing the location of the bubble relative to the marks.

I don't believe there is a better way to adjust the twist out of a bed than with a level. That will take care of the bed twist and turning a long piece of pipe will tell you if the head is out of alignment with the bed. First you have to remove the twist from the bed then test the headstock alignment.

J Tiers
02-20-2013, 08:48 PM
A Starrett 98 level? For leveling your milling machine so parts don't roll off, yes. For taking the twist out of your lathe bed a Starrett 99 or other make: Scherr-Tumico; Mitutoyo; Lufkin?, etc., with equivalent sensitivity.

I suspect you are a perfectionist..... perhaps of the type who won't even attempt anything that he cannot do at least as well as the best expert...........

But in fact you are headed the wrong direction there.....

A precision Starrett might make a difference on a new unworn lathe. But as soon as it has wear, the level actually will lie to you. The level and the bed may not agree, particularly if your lathe does not have flat ways only, and especially if it has V-ways. The indicated reading often may not correspond to how it would actually turn a part, since the level reading is a "once-removed abstraction".

You can get "close" with a good level (the 98 IS a good level), then finish up with actual turning tests such as the "two collars" test. (sometimes done with 3 collars). That tells you what really happens.

Mostly the turning test finds misalignments with a new lathe, but with a used lathe, they are conflated with wear issues.

darryl
02-20-2013, 09:22 PM
Can somebody re-enlighten me- assuming the ways are not worn, under what conditions can a lathe turn either a bulge or a concave when it should be turning a straight section- even if tapered? I ask because I think it's important to know when an 'untwist' of the bed is appropriate, and when a headstock re-alignment is appropriate. It would seem that if the headstock alignment is out slightly, it would still be possible to correct from turning a taper by twisting the bed. It would be more appropriate in this case to align the bed first, then correct the head secondly. It would seem that aligning the bed would have no test that's valid unless the headstock was already true- but how do you know that? These are interdependent things.

A headstock out of alignment will make you turn a taper, even if the bed is right on the button. With the headstock aligned, a twist in the bed will have you turning a taper. With both out of whack, there's no frame of reference to use to correct either. This is a case where you would have to use a sensitive level and get the bed straightened out first, then accept that as good with no testing. The headstock alignment would follow, with a two collar test.

My main question would be whether a twist in the bed alone would cause a turning to be football-shaped or hourglass shaped, regardless of whether it's tapered or not.

As soon as you get into worn ways, it becomes much more complicated.

gcude
02-20-2013, 09:40 PM
Can somebody re-enlighten me- assuming the ways are not worn, under what conditions can a lathe turn either a bulge or a concave when it should be turning a straight section- even if tapered?

I would think this would happen if the bed were bowed up or sagged down. The owners manual on my larger lathe recommends moving the carriage out to the far end with the tailstock when not in use.

darryl
02-20-2013, 10:15 PM
There are some effects from the cutter moving up or down from center- these effects would be greater the smaller the diameter of the test piece. I would think though that the effects would be very small if not unmeasurable due to bed sag. Any error of consequence would have to be moving the cutter in or out- bed twist is going to enhance this effect the further the cutter gets from the headstock. But is twist going to cause an hourglass effect, or it's opposite? Or will it cause only taper, straight sided taper-

I'd like to first look at the lathe alignment issue from the standpoint of the lathe being new. This should mean that the ways are not worn and the saddle has been machined to sit in full contact with the ways- provided that the bed is in alignment. It might be more important in a new machine that the bed be tweaked such that the saddle does not rock. Tweaking to remove evidence of taper turning would then be done by aligning the headstock. If a proper alignment has been done at the factory, then when the lathe is in it's final position in your shop, a tweaking of the bed should bring everything back into alignment. The moment the bed reaches a point where the saddle does not rock would be the same point where taper turning is eliminated.

But that's for a new machine. What you do to bring an old machine back to the best it can be alignment-wise- well it seems the first thing is to level the bed, then make test cuts. Stop when the type of work you do normally can be done to something within your criteria for error. I would presume that you would be looking at it as if the headstock has not gone out of alignment, and all that's realistically doable is to level the bed and make test cuts. Beyond this it's re-grind time, and then a precision level would be needed so you can first level the bed most accurately without testing, then use that level bedway as a reference when you go about scraping the saddle to fit. In this case again, the final adjustment to null out taper turning would be to adjust the headstock.

uncle pete
02-21-2013, 12:10 AM
I can't comment on what the very large and very heavy duty industrial lathes are like since I've never leveled or tested one after leveling. I can say that on at least my lighter weight equipment that even getting a lathe bed as perfect as possible with a pretty pricy Mit. machinists level, that it's still only a static condition. I've always had to do some minor tweaks after testing under cutting conditions to get really accurate and parallel shafts. Level is just a faster and easier way to get to that mostly unstressed and with luck straight lathe bed and initial starting point of those minor adjustments.

It's certainly not impossible for any lathes headstock to be out of alignment with the bed. But I'd be willing to bet far more hobbiest lathe headstocks have been realigned to compensate for other alignment problems.

Darryl,
They make what are called lathe test bars that can be used to double check a lathes headstock to make sure it's looking straight down the bed. They usually have a Morse taper on one end and then a fairly long parallel shaft. Good accurate hardened and precision ground ones are fairly expensive. The same can be used to check tailstocks also.

To correctly narrow down say a slightly barrel shaped shaft, you would need to turn a pretty large diameter shaft to make sure there's no real flex in it under cutting pressures.

Pete

Mcgyver
02-21-2013, 08:04 AM
I would think this would happen if the bed were bowed up or sagged down. The owners manual on my larger lathe recommends moving the carriage out to the far end with the tailstock when not in use.

interesting, I wonder if there is merit to this or just some 'doin' what me pappy did' thinking? Is the cast iron subject to some sort of plastic flow like a liquid? I've always thought like other metals it deflects under load and unless the point of plastic deformation is reached consistently returns to the original shape when the force is removed.

Rosco-P
02-21-2013, 08:49 AM
I suspect you are a perfectionist..... perhaps of the type who won't even attempt anything that he cannot do at least as well as the best expert...........

But in fact you are headed the wrong direction there.....

A precision Starrett might make a difference on a new unworn lathe. But as soon as it has wear, the level actually will lie to you. The level and the bed may not agree, particularly if your lathe does not have flat ways only, and especially if it has V-ways. The indicated reading often may not correspond to how it would actually turn a part, since the level reading is a "once-removed abstraction".

You can get "close" with a good level (the 98 IS a good level), then finish up with actual turning tests such as the "two collars" test. (sometimes done with 3 collars). That tells you what really happens.

Mostly the turning test finds misalignments with a new lathe, but with a used lathe, they are conflated with wear issues.

Ummm.....no. Sometimes my work is to a very loose tollerance. I follow, try to follow tried and true practices set out by those more experienced then myself. As a matter of fact, I begin my Millright's training this fall. As far as setting the level on un-worn sections of the bed, right under the chuck and the very end of the bed see very little, if any wear.

I didn't say the 98 was useless. I did say, according to what I've read in texts about lathe and machine setup, that a Starrett 98 doesn't possess the requiste sensitivity. Those that want to hide behind excuses: don't have...; can't borrow...; can't afford....; don't need ('cause I'm a HSM)....; read on an Internet board that...., .......carry on a usual.

Doozer
02-21-2013, 10:16 AM
Ok, let me join the circuis.
I have never leveled a machine with an anytihng more than a carpenter's level.
(never needed to)
For a lathe, make sure it either sits on 3 even points,
or if 4 points (or more) make sure it does not have a soft foot.
If the lathe is 10 feet long, and has 6 or 8 points on the ground,
then you need to use a level as a reference tool to adjust any
sag out of the bed. The bed does not have to be level, only straight.
If you know your bed is twisted (with a properly adjusted tailstock,
the taper of a part turned between centers varies with tailstock
position along the bed) then a level is useful as a reference to
adjust out twist. Again, crosswise the lathe also does not have
to be level. It is just a useful reference. As to say, if the level is
half a bouble off everywhere you take a reading (extreame example),
then the bed is straight. Stop thinking that level is a necessary thing.
If you are setting up a pool table or air hockey table, that is a different matter.
...But I bet that pool table in the bar is not level, and you never noticed.

--Doozer

dian
02-21-2013, 10:53 AM
exactly. and why make life difficult? go and chuck up something (the bigger, the better) and see how it is. adjust the bed. i believe on most leathes the headstock cannot be adjusted without a major effort anyway. then turn something between centers and adjust the tailstock. it will be right for a certain extention of the quill only. take measurements what happens to the taper as you move the quill in and out. thats very usefull information.

bob_s
02-21-2013, 10:58 AM
interesting, I wonder if there is merit to this or just some 'doin' what me pappy did' thinking? Is the cast iron subject to some sort of plastic flow like a liquid? I've always thought like other metals it deflects under load and unless the point of plastic deformation is reached consistently returns to the original shape when the force is removed.

Cast iron is a brittle material, which displays almost no plastic strain before failure, because the tensile strength is about one half of the compressive strength, if you are lucky.

There are elasto-plastic models for analyzing failure of cast components subjected to impact loading, turbo-charger housings for example.

Most machine tools are designed to utilize cast iron in a compressive fashion. If tensile stresses are anticipated machinery rapidly becomes massive.

dian
02-21-2013, 12:36 PM
i dont know what "plastic strain" is, but my acording to my experience you can permanently deform cast iron (a lathe bed). will not work with concrete.

Mcgyver
02-21-2013, 01:26 PM
Cast iron is a brittle material, which displays almost no plastic strain before failure, because the tensile strength is about one half of the compressive strength, if you are lucky.

There are elasto-plastic models for analyzing failure of cast components subjected to impact loading, turbo-charger housings for example.

Most machine tools are designed to utilize cast iron in a compressive fashion. If tensile stresses are anticipated machinery rapidly becomes massive.

agreed, this was why I thought a manual suggesting move the carriage seemed like BS, but I'm still quite far away from knowing everything :)

There are seemingly lots of old wives tales out there, my suspicion is those manual writers bought one. As another example, Lazlo's written many times that current research and engineering suggests cast iron does not move; once the forces reach equilibrium it stays put. Yet Standard Modern and others used to age castings and many still believe these ideas of wandering cast iron. Point is guess just because pappy or industry did such and such doesn't always make it valid or correct.



i dont know what "plastic strain" is, but my according to my experience you can permanently deform cast iron (a lathe bed). will not work with concrete.

coming out of the plant warped, wear, heat, machining that changes the stress equilibrium, twist due to gravity or being bolted down etc can all change the shape....but you're claiming you've experienced lathe beds being permanently bent? From what? Can you give specifics and how you came to this conclusion?

J Tiers
02-21-2013, 08:02 PM
There are seemingly lots of old wives tales out there, my suspicion is those manual writers bought one. As another example, Lazlo's written many times that current research and engineering suggests cast iron does not move; once the forces reach equilibrium it stays put. Yet Standard Modern and others used to age castings and many still believe these ideas of wandering cast iron. Point is guess just because pappy or industry did such and such doesn't always make it valid or correct.


There isn't any mystery in the temperature change driven warpage..... and there is NO QUESTION that CI DOES warp after it is poured.... and cooled. It's the first time it has ever been that cold, and no surprise if small compositional variations through the mass cause "movement".

You don't suppose that the old guys were so tricky that they said "let's all do something that costs money and slows production for no reason, just to mystify this guy named Michael who will come along in 50 or 80 years and wonder why we did it" do you?

Nope, they found that if you DO "age" CI, it "moves" less. So that's what they did. I have seen evidence that if you do that all at one time,. by a cryogenic treatment, you get nearly all of the movement "over with" in one step.

The key seems to be letting the item get to the largest temperature change it will ever see, after which everything else is less, and does not cause the same stresses.

As for bending...... it's easy to give a first cut estimate of what can happen. See the relation of the yield point to the ultimate tensile strength. Some materials have no observable yield point because if they have one (presumably in theory), it is past the tensile strength and so has no practical application.

oldtiffie
02-21-2013, 08:46 PM
Maybe only the old timers will remember this:

http://pitstopusa.com/images/F14604806.jpg

:D


I wouldn't call it much of a precision level - accurate to 0.10 degrees - which is normal for many digital levels.

0.10 degrees is 1 in 573 or 0.0017" per inch

Which is way out of "precision level" territory.
http://www.google.com.au/#hl=en&rlz=1R2IRFC_enAU360&sclient=psy-ab&q=acculevel+digital+level&oq=acculevel&gs_l=hp.1.1.0l4.1746.4588.0.11108.9.9.0.0.0.0.608. 2486.2-4j1j1j1.7.0.les%3B..0.0...1c.1.4.psy-ab.2-o9Us3yPa0&pbx=1&rlz=1R2IRFC_enAU360&bav=on.2,or.r_gc.r_pw.r_qf.&bvm=bv.42768644,d.dGI&fp=a6b372b0509e79be&biw=1920&bih=846

jep24601
02-23-2013, 09:32 AM
i dont know what "plastic strain" is, but my acording to my experience you can permanently deform cast iron (a lathe bed). will not work with concrete.
Actaully you can plastically deform concrete. High rise concrete frame buildings experience creep shortening. Concrete basement walls will sometimes twist instead of cracking when undergoing differential settlement

It's all relative

dian
02-23-2013, 01:05 PM
o.k., but thats because of rebar, right. concrete itself is full of cracks, althought they might be tiny.