stress strain of roller chain

Rack and pinion drive is the most common / popular for most plasma tables. Plenty of sources out there for the components and plenty of info on CNCZONE.

Yea, I spend more time over there than here. rack pinion is best but I'm refitting an existing machine with a clever cable drive. Won't be a big deal to replace pulleys with sprockets and cable with chain. lots of machines have been built with roller cahin drive over there also. But, no sign of mechanical design for chain size.

Karl

The chain mfrs list the maximum allowable tension for low speed drives, but I don't recall ever seeing tabulated values for the "stretchiness" of chain. It'd be easy enough to estimate by treating the sideplates as a solid strip.

For example, the sideplates of #40 chain are .059 x .472. .059 x .472 x 2 = .05 in^2

Young's modulus, stress over strain = 30E6 (lb/in2)/(in/in) for steel

.05 in^2 x 30E6 (lb/in2)/(in/in)) = 1.5E6 lb (in/in)

In other words, if you had an imaginary chain made of steel with infinite yield strength, 1.5 million pounds would stretch a length of #40 chain to twice its original length. In other, other words, a 100 inch length of real #40 chain will stretch about .007" under a 100# load.

I was moving an heavy injection head between 2 presses over 22 ft via belt drive using their product. You can get a timing belt any length you desire. Give it a look.

As far as chain, about anything will do, plasma isn't that fast, head is not that heavy.

Wes

BTW, you can find this data on steel corded timing belts, if you want to compare. The metric AT profile belts are generally stiffer and stronger than the trapezoidal toothed belts. I know Breco, for one, has this data in their catalogs.

Karl, There are many, many different chain types for any given size and each have their own use parameters. I use

for my chain solutions. Here is a tip, never use keyed sprockets for bi-directional loads, as the keyways will eventually loosen. Tsubaki markets sprockets with compression (friction) drive hubs and they are brilliant. Another tip, metric and US standard chain sizes are practically interchangable and that fact is never stated anywhere. Steve

Karl,

Machinerys Handbook is your friend for this information... I use this info, with appropriate safety factor, for certifying assembly line lifts in automotive plants.

Just be aware that chains introduce some pulsing into the linear motion.

As was pointed out above you can get wire reinforced timing belting in straight and practically unlimited lengths. You might want to compare costs between chain and belt.

Wolfgang

I wonder if this is a valid model

Specifically, I would expect that play in the plain bearing between the links would add up to more than .007

Why wouldn't it be adequate for an estimate? I'd be surprised if you couldn't get within 20% of the real value with a little care.

That's a different issue than the elastic behavior of the chain. Presumably the chain would be pre-tensioned to eliminate the play.

I would expect the elongation due to bearing play to be at least somewhat load dependent. I would not be surprised if this overshadows what you calculate from the solid elasticity model. But I could well be wrong.

I can see how pin clearance in the sideplates would cause some bending of the plate around the hole, which would not be accounted for by my approximation, but it would be an elastic effect. An extreme example would be regular lifting chain. In that case there's clearly a significant bending component in the curved segment of the loop. I guess the question is, how big is this effect with a close fitting pin? My gut sense is that it'll be pretty small, but I'll wait 'til someone runs an FEA on it before I dig my heels in.

ciditad had written this in response to

: Hi Karl,

Roller chains do not "stretch" under load - the "elongation" is called wear. What happens to the chain is the pins inside each of the chain link's bushing gets worn as time go on with each revolution of the chain around the sprockets and loses material, and that's why you see "stretching" or "elongation". Chains are not supposed to stretch like rubber, and if your chain stretched then it's not made with the proper material.

As for chain sizes, I suggest going to Diamond Chain's website:

Under the "Product Support" tab, you can choose to download a very useful program that will help you identify the proper size chain for your application.

------------------------------------- Karl Townsend wrote:

##-----------------------------------------------## Delivered via

Forums Web and RSS access to your favorite newsgroup - rec.crafts.metalworking - 162279 messages and counting! ##-----------------------------------------------##

But the OP will be pretensioning the chain to eliminate backlash, surely?

*Everything* stretches under load

A friend who is a serious bicycle commuter told me that not only did I need to replace my "stretched" chain, but also the sprocket sets that had been worn-in to its out-of-spec pitch.

Just call up the nearest chain supplier and ask them the question. They will have a set of specifications as long as your arm. Some of the details will be of no value to you but a simple stress vs strain would be somewhere near the top of the sheet

Apperent stretch in roller chain is usually NOT stretch in the sideplates, but wear in the roller/pin assembly.