Curious Chain and Bar temps while milling

[BobL]

Found this infra red temperature scanning gizmo at work and decided to see what it might tell me about chain and bar temps while milling.

I started by measuring the temperature of the chain exiting the cut kerf - like this - it has a little red laser dot to tell you where it's measuring. it has to be no more than about 6" away from the chain to measure the temp of the chain.

The typical chain temp reached in very hard Aussie wood is 160F. By pushing the mill harder till it was almost bogging down I was able to hit 170 - 175F.

Next the bar like this. It was around 140-150F pretty much across the whole bar.

Then the chain on the other side of the bar.

Now, here is the curious bit. The temp of the chain entering the kerf was only 90F? So in the fraction of a second that it took for the chain to go around the sprocket and pick up a skerrick of oil it went from 160F down to 90F?

I also measured the temperature immediately after stopping the chain.
The chain on the cutting side dropped rapidly - below 100F on the cutting side in about 10 seconds - this suggests the 160F is a skin temperature.

The chain on the non cutting side also dropped but not as rapidly.

Both sides of the chain reached within 10F of ambient temp (65F) in a couple of minutes after stopping. The bar took about 10 minutes to reach close to ambient.

The outboard aux oiler made no noticeable difference in chain or bar temperature but I did not turn it off for very long.

Anyone have any explanation for this?

 

[slabmaster]

Interesting post! I have always wandered about milling temps.AS for the non oil temp vs oil temp. It probably takes awhile for the oil to delute enough to raise the temp.But it should.It also takes awhile for the metal to heat up.Try waiting longer before the test next time and see if that makes a difference.I bet it will.If it dosen't ,that means the oil is lubebracating but not cooling

 

[BobL]

Interesting post! I have always wandered about milling temps.AS for the non oil temp vs oil temp. It probably takes awhile for the oil to delute enough to raise the temp.But it should.It also takes awhile for the metal to heat up.Try waiting longer before the test next time and see if that makes a difference.I bet it will.If it dosen't ,that means the oil is lubebracating but not cooling

Thanks slabmaster, I guess I turned off the aux oiler for only about a minute - I will try for a bit longer.

 

[TedChristiansen]

Bob,

Interesting...you must be an engineer.

The heat transfer path is likely from the chain through the oil and into the bar where it is dissipated into the wood on both sides. I think your suspicion is correct - the high temperature is a skin temperature. The temperature gradient must be quite steep if the assembly cooled off that quickly.

Ted

 

[woodshop]

...Now, here is the curious bit. The temp of the chain entering the kerf was only 90F? So in the fraction of a second that it took for the chain to go around the sprocket and pick up a skerrick of oil it went from 160F down to 90F?...Anyone have any explanation for this?

Very very interesting post Bob. Sheeesh... from 160 down to 90 in the time it takes to go around the sprocket? If I didn't see it in your pics I almost wouldn't have believed it. First thing that comes to my mind is, as you alluded to in your post, much of that high temp is surface temp that (apparently) dissipates pretty quick... as in milliseconds. Well... if your aiming that red bead at the side of the cutter on the chain, that would probably be the hottest spot. I mean that's the business end of the chain that severs the bundles and does most of the work. Of course when you're milling you aren't exactly severing bundles since you're cutting with the grain, but it's still the part of the chain that I guess gets most of the direct contact with the wood, and thus would get the hottest. The top flat part of the chain, being at an angle, doesn't fully contact the wood, but that side plate does. Still hard to believe it drops that temp that quickly though. Seeing is believing but of course now I have to go out and try and replicate your little experiment. I have one of those cheapie Chinese versions of what you have there, but it does seem to work at grabbing a temp. I bought it to check router bearing temps and bit temperatures while routing on the CNC and the thing will differentiate between the bit, the collet and the router bearings only 1/2 inch above it, so it should be able to pick up the temp of my milling chain like you are doing. I'm backed up in the shop for a few weeks so won't be milling any time soon, but next time I do I'm going to try and do what you did. Also might be interesting to check Ripsaw bandsaw blade temps as the band goes into the wood and then when it exits. I know from past experience that that band gets pretty hot when it gets dull.

btw, what's a "skerrick "... is that an Aussie expression?

 

[BobL]

Bob,

Interesting...you must be an engineer.

Experimental Physicist.

The heat transfer path is likely from the chain through the oil and into the bar where it is dissipated into the wood on both sides. I think your suspicion is correct - the high temperature is a skin temperature. The temperature gradient must be quite steep if the assembly cooled off that quickly.

There are three main frictional sources,
1) Chain on log
2) Chain on Chain
3) Chain on bar
(and chain on sprockets)

Because the wood was so hard I had heaps of lube going - the oil from the aux oiler was even pooling on the bar - I don't think sources 2) or 3) were as much as 1) ie chain on log.

WS - it would be good if you could check with your setup - the other fella's here reckon the difference could be due to a hot sawdust film on the chain that get's blown off by the chain going around drive sprocket - I will check that on saturday.

Skerrick - is a british term meaning "small portion"

BTW the photo's I put up were staged. I didn't try to to get action photos of CS on WOT plus camera plus Temp Scanner - I'll try again next saturday.

 

[carvinmark]

Very interesting thread. Wonder how much ,if any diff, B&C length and size (3/8-.404) would make or how sharp the chain is. Even diff types of wood, hard and soft.:monkey:

 

[John Henry]

Interesting thread!

Great post and comments! I admit to not having worried about temperatures, but find it interesting anyway.

As a reformed thermodynamicist (sort of, reformed that is...), I think the comments are spot on. The major source of heat generation is friction, and that depends on the relative coefficients mentioned above by BobL. I think if you have enough oil flowing, you've reduced what friction you can, and the oil has little cooling effect other than reducing frictional heating. (the heat capacity contribution is pretty small).

I would discount the effect of any sawdust, since there's just not much there in terms of heat contribution. The mass is small, the conductivity is small.

The skin temp thing is certainly possible, though I wouldn't have guessed that. It's a good observation. The thermal conductivity of the steel is pretty high, so you would think that the temp will equilibrate pretty quickly, maybe too quickly to see the spike unless you're right on it with the thermometer.

I too would agree with the chain metal serving as a heat sink and making the temp drop that quickly, though the difference seems higher than I would have guessed.

 

[slabmaster]

Bobl,A chain that is sharp will create less heat than a dull one will as a dull chain has more friction as it's going through the wood.You might want to try this test at the start and at the end of the sharpening cycle of the chain to see the difference in temp there as well.That will give you difference on heat to the bar from start to finish on a sharpening cycle.Just another idea for you while testing. Mark

 

[woodshop]

...BTW the photo's I put up were staged. I didn't try to to get action photos of CS on WOT plus camera plus Temp Scanner...

Now THAT would be a feat... I'm thinking I could actually get a true instant action shot/temp if I talked the wife into taking the pics/ holding and reading the temp sensor while I'm actually milling. After 30 years of marriage it's amazing how much she puts up with me performing milling/woodshop shenanigans like this.

 

[ckthorp]

You should also remember that the emissivity coefficient of shiny metal is /way/ less than the 0.90 or 0.95 that the IR thermometer is expecting. They really won't work on shiny metal. The painted bar is ok. In your first shot of the "chain" temp, you're actually reading the bar temp because there is a parallax issue between the laser and the IR window. In the second "chain" temp, you're likely reading off the ground. I also suspect that the reading diameter is too large to accurately read off a chain.

I suggest reading up on the theory behind IR thermometry as it really is enlightening on how to best use them, their limitations, and workarounds.

 

[BobL]

You should also remember that the emissivity coefficient of shiny metal is /way/ less than the 0.90 or 0.95 that the IR thermometer is expecting. They really won't work on shiny metal. The painted bar is ok. In your first shot of the "chain" temp, you're actually reading the bar temp because there is a parallax issue between the laser and the IR window. In the second "chain" temp, you're likely reading off the ground. I also suspect that the reading diameter is too large to accurately read off a chain.

I suggest reading up on the theory behind IR thermometry as it really is enlightening on how to best use them, their limitations, and workarounds.

Parallax - - I just tested the unit (and read the instructions - ha! there has to be a first)- it has vertical parallax from the laser of about half an inch at 6" which would be enough to explain what is going on. It has minimal sideways parallax so that is the preferred way to measure.

Reading diameter is 1/2" at 3" which should be enough to read the chain

In terms of emissivity it doesn't really matter as I'm comparing chain with chain. Apart from cutter chrome the chain is also a blue black colour.

 

[BobL]

OK tried it again today and sure enough the parallax thing turned out to be the problem. Today I was cutting this and the chain temps only reached 115F and were the same temps when both exiting and entering the kerf. The timber I was milling was much softer than last weeks log which was lemon scented gum. I still have two more lemon scented gums to do so can recheck in a couple of weeks time. Didn't have time to do any other experiments - took too long groveling around in the sawdust looking for my clutch nut!