Chain Stretch

[Crofter]

Do you think that so called prestrected chains are put on a machine and pulled to stretch them. Isn't stretch the seating in and wearing together of the rivet hub and drive link surface and not stretching of the tie straps. If you stretch the tie straps, how do you manage to stretch the greater amount of metal in the cutter the same amount as the partnered tie strap? How does overheating or lack of lube stretch a chain in use?

Frank

 

[sedanman]

Part of "stretch" is taking up all the slop in the rivets. If there is .002 clearance at each rivet and you pull on the chain, that's a lot of "stretch".

 

[ricksvar]

Heat causes expansion of metal.Likely the word "stretch"(but it works for me) does not describe exactly what's taking place.This is why you should not tighten a hot chain and then not use/store the saw.As the metal cools it tightens up on the bar and can damage the powerhead.

Then their is wear which results,in general,from a inadequately lubed chain and bar resulting in greater heat,more metal expansion and slop/wear of rivets.The hotter a chain and bar gets the more wear on the components.

At least that's the way I see it,
Rick

 

[Tom Dunlap]

I've always understood that the chain stretches not the steel. When I put on a new chain, I keep a scrench in my pocket for the first half hour of running. After adjusting a couple of times, I'm done with it.

Like was said, its the tolerances in all the links added together.

Machinists know that a one inch peg doesn't go into a one inch hole.

Tom

 

[rb_in_va]

Originally posted by Tom Dunlap
Machinists know that a one inch peg doesn't go into a one inch hole.

Not without a hammer, or some liquid nitrogen for the peg

 

[Lewis Brander]

Spring loaded bar tip:

It's too bad that someone hasn't invented or come up with a spring loaded, floating type bar tip. The chain could be installed, the bar adgusted to a predetermined mark and everything tightened down. Once the chain or mark moved to a predetermined limit or mark, you simply reajust the bar so that all are back to specs again or you simply replaced the chain due to excessive wear. The spring loaded tip would allow for normal stretch due to heating and cooling and for some wear in the chain. Does this sound imposseble? Has it ever been tried? Any comments. Seems like there would be a minimal predetermined load placed on the power head and sprocket, that might prevent destrucktion of the powerhead ( bending of the crank, seal and bearing wear and case problems.) JMO. What do you think? We got any machinist or inventors out there? Lewis.

 

[Crofter]

Lewis I imagine it would be difficult to have a spring soft enough to follow temp changes and normal tension at rest and still able to overcome the much greater tension of full power or chain grab moments without derailing; that might be finniky!.

I was looking at some disassembled chain and feel that the hole in the drive link is merely punched so it sides are tapered and only give a partial seating surface on the rivet hub until it wears in. Just a few thou at each rivet to drive link juction would accumulate to quite a bit. I should compare Oregon, Stihl and Carlton to see if there is any difference in how the holes are finished.

One good overheating from lack of lube will ruin a chain so that it will not hold its tension again. I am assuming that the metal to metal surfaces get galled and no longer smooth and ever after gnash together like a knee with bad cartilage.

Frank

 

[jokers]

Frank,

I believe that you are making a mistaken assumption that the unequal thickness cutters and tie straps would have to stretch together. I believe that in conjunction with a stack up of all the "worn in" tolerances, you can also stretch the tie straps without stretching the cutters.

When I first started cutting, I stretched a few chains to the extent that it was necessary to remove a link(Hmmm..... wonder what that does to pitch?). Now I shorten chains for other nimrods who`ve done the same.

I`ll see if I can find a grossly stretched chain and disassemble it so that I can make some measurements to support my belief. It`s probably going to take me a few days.

Russ

 

[Crofter]

Jokers: If the cutter does not stretch but its partnered tie strap does, the chain would have to assume an alternating zig zag path although the tie straps that are paired with other straps would still be free to stretch in pairs. The yield strength of the chain would be enough to bend the crank before you ever stretched four tie straps. I also feel that the cross section of the rivet , being much less than the cross section of the thinnest part of the drive links would shear first if it were stressed to the yield point. Measure the components of a visibly elongated chain and I feel you will find wear enough at the rivets and drive links to account for so called stretch. I am only quibbling becauses the bottom line is...... its been trashed, I just dont like to have the right answer for the wrong reasons. The difference in my mind is that you can ruin a chain in a minute with no lube without ever having had it tight enough to have stretched if I am correct.

Frank

 

[jokers]

Frank,

If I can find a specimen chain, I fully expect to find the zigzag pattern that you mention.

I think that you are overlooking a few things with your assumptions based on yield and shear strengths. Just as flowing water can erode very hard rock, small tension or impacting forces repeated endlessly can also make the steel in a chain yield. Furthermore, the heat generated from friction between bar and chain and chain and wood softens the steel by annealing. Couple this with the fact that two .025 tie straps don`t have the same yield strength as one .050 drive link unless the tie straps were fastened to one another at several places around their perimeter.

Also remember the torsional forces the tie straps are subjected to as every other tooth in the cut is attempting to pull the chain in an opposite direction.

I think we are seeing more than simple erosion of tolerances in the chain.

Russ

 

[Crofter]

Talking about assumptions;
tension; does not cause permanent elongation unless yield point is surpassed. ( by definition)
impact; repeated endlessly, chain on bar I presume. The point of impact of chain tie strap with bar is in the area of the rivet since centre section is relieved and beyond rivet is outside of possibe influence. If the area of the rivet were being impact stretched the rivet hole would be elongated causing loose rivets. Look for this when you examine your chain.
"Furthermore, the heat generated from friction between bar and chain and chain and wood softens the steel by annealing"
This you state as fact. Not supported; you are making an assumption. Anyways the temperature necessessary to lessen the hardness of chain chassis is approx. 650 deg. F. I do believe that this temperature is however being reached at the juncture of the drive link hole and rivet hub surfaces causing momentary bonding and subsequent metal tearout when run without adequate lube.

Where do you get the .025 tie strap and .050 drive link figures?

I think we are seeing simple erosion of the surfaces of the rivet hub and drive link hole ( four surfaces per drive link remember)

Frank

 

[jokers]

Frank,

If you want argue we can take it off forum, otherwise accept that your assumptions and mine are not supported, equally unless you can provide evidence to the contrary.

Numbers that you have cited, such as 650°F as the threshold temperature for annealing seem to be remarkably high compared to the temp of 400°F where so many people accept annealing of cutting surfaces to take place due to improper grinding. Maybe 650° is necessary for a certain ductilty spec or something, what is the basis of your number?

If the temperature for soft annealing to take place is not attained, what effect does the elevated temperature that we do achieve have on plasticity of the chain. And you assume that the yield strength of the chain would surpass the yield strength of the crank? What is that assumption supported by? What about the angular forces exerted on a rotating crank shaft? Are you saying that there isn`t a negative vector in any phase of that motion?

I can go on and on as you well know, but what is the benefit of this tit for tat if anyone involved is going to have their judgement clouded by anger. I still believe that we are seeing a combined effect of erosion and true stretching. Prove me wrong.

Russ

 

[Crofter]

Ssettle down Russ

Im just starting to have fun. Yes I make some assumptions too. I do try to see the most likley scenario based on the type of load and relative cross sections and where something is likely to yield based on experience with equipment repair. I am very familiar with track chains on dozers and excavators which exhibit this type of stretch and getting out of pitch with the sprockets. Occasionally some really unusual occurranace will distort the links themselves. It is a bit of extrapolation to compare the two chains but I do feel the proportion of pin size to link cross section is similar.

That number I gave relating to annealing depends on the original hardness of the item in question. If it were a cutting edge or bearing , you aare correct in sayin a temperatur of 400 F would start to anneal. If the item is expected to have approximately spring temper by design (which is about where chain chassis parts fall) then a temperatur of approx 650 F is require to further anneal or lessen the temper of that item, so annealin or lessenin of temper is relative. Full annealing requires a temperature of roughly 1080 F. But that yields a softness approaching that of a nail.

I thought I was discussing not arguing but I am not sure what distinguishes on from the other Lol.

I dont want anyone to be wrong. Regarding proving it I guess someone would have to do a controlled experiment. Can you send me one of your stretched chains to do a forensic on?

LOL!

Frank

 

[jokers]

OK Frank,

I apparently misinterpreted what you were saying to me and I apologize for the tone of my response.

If I can find a severly elongated chain, I`d be glad to share it with you so that we can objectively approach it`s disection. I`ll also post photos to the best of my ability, but frankly I`m not expecting to do this anytime within the next couple of weeks with the way my schedule looks now, remember, I didn`t bring this topic up at this time, I merely jumped in.Unfortunately my presence here on the forum does not represent time that I could be doing something more constructive but I have to make a living somehow.

BTW, I don`t entirely agree that chain chassis parts are tempered to a spring state based on the ease with which you can cut them with a file. Either that or I push too darn hard.

Russ

 

[Lawn Masters]

I have a carlton H1 LP chain, it was originally a .370 pitch, now its about a .380-.385 pitch chain, thats all stretching of the tie straps and the DLs as well. I'm amazed it even works at all. I may just keep it and do a teardown of the chassis and then the same on a newer unabused chain. I'll report the results, I may even try to feel the very FINE ridges with a straight razor blade, the edge is so sharp I could feel each and every little thing with it. I'll report my findings asap.

 

[Lawn Masters]

Ok my findings are: new chain, .325 pitch .050 gauge: the drive link holes appear to be drilled not punched, there is no wear on the rivet hub or the link. all is good. Old Carlton H1 .370 pitch .050 gauge: Inside of the rivet hubs are smooth, but well worn, and the hub is not perfectly round as it should be, the drive links are also drilled, not punched, but are perfectly round inside the rivet holes, and dirve links are also smooth as glass. Upon closer inspection the rear hole on the drive links are normal, the front link, is slightly oval shaped.

 

[tony marks]

rocky i didnt even get on this train.
heck i dont understand enuff o what they sayin,, to have an opinion as to whether they know what they talkin about.kinda like some o them algebra problems in high school .. id ask the teach why,and hed just lookat me and say dont ask ,just accept it,, an set over there an be quiet.

 

[jokers]

Frank,

Sorry to jump back on this topic without some new data or evidence, but I`ve been mulling over this statement that you made, "I do try to see the most likley scenario based on the type of load and relative cross sections and where something is likely to yield based on experience with equipment repair. I am very familiar with track chains on dozers and excavators which exhibit this type of stretch and getting out of pitch with the sprockets. Occasionally some really unusual occurranace will distort the links themselves.".

I`m not convinced that I see a correlation. Dozer and excavator tracks operate in extremely abrasive conditions with high shock loads and no lubrication. Because of this, the tracks use a sacrificial pin and some are even bushed aren`t they? The sprockets on tracked equipment are also sacrificial compared to the track chains based on replacement cost. In thinking about the tracks that I`ve got experience on, it seems to me that the track links themselves are very hard and one reason why you don`t want to hardface the gullets of the sprockets. I agree that you rarely see stretching of those links but rather wear on the pins.

Some of the preceding are spud farmer observations and may not have merit, what say ye?

Russ

 

[Crofter]

Jokers

Heres some figures to kick around regarding how wear in the rivets or pins of a chain can accumulate and cause you to think the links themselves have stretched. Given a 20 inch 3/8 chain with 72 drive links it takes only a bit over 2 and a half thou. wear at each mating surface to enable one whole drive link to be removed. This is roughly the thickness of a hair or a sheet of paper. It is deceptive because each drive link has two rivets and there is wear at both the rivet surface and the drive link surface so 4 points of wear per drive link.

Dozer and excavator drive chain is sealed and lubricated internally. this only stays sealed for about the first half of the chains life. The outside is subject to abrasive wear but this does not change the pitch only the rail height. Pins can be pressed out and rotated and the bushings pressed out and also rotted i/2 turn to bring unworn surfaces in contact and restore pitch. Nexte step is new pins and bushings and that will last to wear out the chain rails.

Regarding the temper of chainsaw chain chassis parts. Attributing "spring temper" was so I was not heaping things to support my rationale. A carbon steel spring can just be filed with a sharp file and good pressure. Chassis parts are a bit softer which means that they have probably been tempered to nearer 700 deg. F. ( Which means you have to expose them to temperatures higher than this to soften or retemper to a lower level of hardness.) This point weakens your position that it is friction with the wood that softens the chain links causing possible stretching.

As for spud farmer observations...Lol !..I have not measured the holes and pins in a stretched chain but if there is not enough total wear in the rivets and drive links to add up to the observed elongation in the whole chain, I will apologise most humbly and accept that chain stretch is caused by the lengthning of the tie straps.

Russ were you suggesting cognitive dissonance might be a factor here?

Lol!

Frank

 

[JimL]

My only guess is the rivets wear into the drive links, making a nice smoothe surface to run on. there is probably alot of wear in a chain in the first few cuts as everything seats together nicely.