Circle saw Blade Warms Up

[Babylon519]

 

 
My 1960 circle sawmill has been brought back to life! In November, I put a dozen logs through it to see what kinks have to be worked out. The only thing at issue is that the blade warms up, and that leads to tapered boards. It's a 42-inch blade with 32 teeth (inserted teeth). The fellow I bought it from (Ray) said it likes to run at about 450 rpm. I've experimented with slightly higher and lower rpm's, but the 450 seems smoothest. Ray also told me that it's a tempered blade (not hammered), and that it will "dish" if it overheats. That will change the lead in the saw, and result in boards tapering from front to back. Here's three things I've done about the blade warming up:
1/ When I got the saw, it had been derelict in a field for years. The blade was rusty, but I didn't do any cleaning before using it for the first time. Ray noticed by the third cut that our boards were getting thinner at the end, and suggested I sand the blade smooth to reduce friction - and heat. This seemed to make a difference. After that, I cut 7 pine logs and got fairly true boards.
2/ When I was cutting 12-foot logs of freshly-cut ash, the log would bounce at first entry and on the way out of the log, obviously because those ends weren't supported by the 6' carriage. I noticed the blade was warming again - and dishing - and the boards were tapering. Thinking that the bouncing was causing friction and heat, I decided to cut the ash down to 8' logs. I was still noticing some warming on the blade in an area about 10 inches from the centre hub.
3/ Last Saturday, I was finishing off the ash in a snowstorm!  I decided to put all new teeth in the blade to see if that would help (I had decided to run a few logs through with the original teeth, since they were in decent shape, and this would show me the saw's behaviour before I went messing around!). So I put new teeth in - one at a time. It wasn't a drastic improvement in cutting performance, and I was still getting some warming on the blade, dishing, and tapered cuts.
So, to make a short story long, that's where I'm at. The blade was outside all last week and I didn't sand it again, so there may have been some surface rust causing friction heat. The best improvement I noticed was after polishing the blade - maybe I should be concentrating on that? Right now, I'm out of ideas, so any expertise you guys can offer is sure appreciated. I should mention that I never let the blade get more than warm to the touch - never hot. After cooling, it always "un-dishes" and spins smooth and even. But it's gonna be hard to be productive if I have to let the saw cool down for a half-hour every four or five boards! Help!! - Jason

[sealark37]

Have you checked the lead in the saw?  The cutting edge should be slightly closer to the log than the trailing edge.  This is adjusted by moving the mandrel or husk frame.  I have never heard of a "tempered" saw.    Regards, Clark

[Jeff]

Never heard of a tempered blade either. Most every circle blade mill runs on the same principle. The blade needs to be tensioned for the correct rpm and direction of cut, it needs to have the correct lead, and it needs to be sharp and sharpened correctly. These are all basics. There are many more things that can be happening, but you can't get past these first things I've listed unless they are established.

[Ron Wenrich]

I've never heard of a tempered saw.  Warm to the touch shouldn't be much of a problem. 

Along with the hammering, sharpening, and the lead, your saw guides have to be set so they're not pushing or pulling the saw.  Another thing that comes into play is how you feed a log.  You're not supposed to hit the saw with a log.  You should almost stop before you enter a log.  The ash doesn't saw as quickly as the pine.  If you force it, you could be pulling your RPMs down.  If your shanks aren't up to snuff, you could be having spillage out of the gullets, and that will heat up a saw.

6' is a mighty short carriage.  The bounce sounds like the log isn't supported, and that can cause the log to bounce, especially if it isn't a very big log.  You have to enter and exit the log slower than when you're sawing supported wood.

[Babylon519]

Thanks for the comments so far....
Previous owner cut semi-commercially for 45 years with the saw, and I didn't alter his basic setup during the restoration. The mandrel is adjustable, and the lead-in on the blade (using a method I got from FF) is 6 mm, just shy of 1/4". The saw guides are adjusted to about 1/8" on either side. When the blade heats and dishes, it will start to rub on the outside guide pin.
When I inserted the new teeth, I used them the way they came out of the box - didn't dress them at all - they seemed factory-perfect to me.
Ron, I moved the log into and out of the saw just as you described - come almost to a complete stop before going in, and back off the feed on the way out. Cutting the ash, I was definitely losing rpm's in the bigger wood, and I slowed down to let the tractor catch up. I wondered if I'm allowing more heat to build up when I slow the feed as opposed to "keeping the pace up"? When I was sawing pine last weekend, it was a big difference to the ash - it went quickly and smoothly and produced boards that were straight and true. Maybe this rig isn't up to cutting my hard ash. I'd like to hear more about the shanks; previous owner never changed them, and didn't keep any on-hand...
Last thing: I've heard of lots of applications for 'tempered steel' where strength and some flexibility is required, so I've never questioned this. But Ray insists this blade is tempered, and that it therefore cannot and should not be hammered. He thinks he bought it in 1965, and it worked for him ever since. Not sure what else to say about that. I completely agree that the 6' carriage is a shorty - I've been scheming about making a longer one. The main sawmill frame is 16 feet long, and the infeed and outfeed sections are each 7 feet for a total rig of 30'.
Appreciate all your input and suggestions... -Jason 

[Possum Creek]

Was the sun warming the blade? I am asking because last week I was trying to saw some ash on a sunny day with my belsaw and had no luck. I thought it might be too hard but later when the sun went down it sawed fine. Then I tried a sycamore in the sun and the blade dished toward the sunny side too. So now I am a cloudy day sawyer. Hope that helps, I guess that old saying about sun on a blade is true in my case.             PC     

[JSNH]

The pine sawed true. The Ash did not and you had new teeth. It sounds like the lead and alignment are ok. Could it be you just don't have enough horse power for the hard wood and slowing the feed speed down too much is causing another issue? When you cut the pine was the saw dust pretty big bits like 2mm thick? It should be. I have had issues with very hard wood and slowing the feed down I wind up cutting too slow and the saw dust gets too small and I think it spills past the shanks and heats the blade causing it to dish away from the log. I now run with a blade with fewer teeth for hard wood.
A few years ago my blade was misbehaving and a hammering fixed it right up. It could be your blade is at that point.
I run a blade with 52 bits for soft wood and a blade with 36 for hard wood and I am running with 100 HP.

[Ron Wenrich]

I thought about the sunlight issue.  But, he finished the ash in a snowstorm.  Sunlight will heat a saw, whether its running or not.

I'm not a metals guy, but isn't all steel tempered?  I know one guy who did a little apprentice work with a saw maker.  Seems they put the blades in a kiln to temper them.  The saws still needed to be hammered.  We might have to call in one of our saw docs to give us their expertise.

The shanks should be flat across.  They should be the same width as your saw teeth.  If not, you'll get spillage down the side of the saw.  The ash will produce a finer sawdust than pine.  Its the nature of the wood.  It has more fines with it, because its a harder wood.  Saw black locust or hickory, and you'll have finer dust.  Ash also cakes around the saw teeth.  That's from all the fine dust it produces.  You'll get the same thing with white oak, and to a lesser extent, red oak.  Shanks can be sharpened with a file.  But, if they've been on there since '65, its hard to believe that they aren't loose in the socket.  I used to change shanks in the fall.  Frozen dust is finer, and you would have more of a spillage problem with worn shanks.  Hard to believe shanks lasted that long.  Hard to believe that there is tension in the blade.

If you're losing RPM, then you might have a hp issue or a belt slippage issue.  But, losing RPM means you're asking your saw to do the same amount of work with fewer RPM.  The gullets fill fuller with dust.  You get them too full, and you'll hang the saw.  450 RPM is pretty low to begin with.  I ran one mill that was lower.  When I had the blades worked on, the saw doc said the RPM was so low that it didn't really matter too much about the hammering.  It could be part of the answer to why there wasn't any need for hammering, especially with a smaller blade.

[bandmiller2]

Lon 519,if your running the mill with a tractor PTO I would have the saw hammered for 540 rpm.All mill saws need to be tensioned, slower saws it doesn't show up as bad. After you know the saw is tensioned right I would recheck the lead. Frank C.

[Babylon519]

I'm guessing at the very least I should be replacing the shanks. The existing ones are the same thickness as the blade itself, whereas the new teeth stick out a bit proud of the shanks on the sides. I can certainly feel a ridge between the shank and bit - enough that fine sawdust could get past.
Regarding saw speed, 540 RPM is the standard for all my other equipment, and it seems odd to run a power saw at a slower-than-standard speed. Based on what the previous owner said, I've played with the speed in the 400 to 500 range, but not at 540; I should try that to see what happens. What behaviour should I expect from an un-hammered blade running at 540? Wobble? Blade shape flattening out and touching the inside guide?  ???

[GeneWengert-WoodDoc]

I have not heard of a tempered blade either.  I wonder if he actually meant "tensioned."

By hammering a blade (also called tensioning), we dish it when it is cold and the when spinning and maybe a little heat, the saw will dish enough that it actually straightens and runs true.  Each blade is dished for a specific rpm and that rpm is often stamped on the blade near the eye.

I suggest that you swage the teeth.  There is a special tool to do this by hand using a hammer.  This creates a wider tooth (and wider kerf) that will minimize rubbing.

If you change all the shanks, it is common to find that the saw needs to be re tensioned (hammered, although today a saw this size would be roll tensioned) by a commercial saw shop.  So, try swaging before changing shanks.

One other thought is that the collars used are critical as well.  One should be perfectly flat and the other tapered so that the outside edge contacts the blade.  If the collars are NOT correct, you will move the saw when you tighten the nut on the mandrel (shaft) and make rubbing more likely.  Check the dish before and after tightening...should be no change.  I am guessing that your basic problem is with the collars and not the tensioning.

If you do not have this book, get it...Circular Sawmills and Their Efficient Operation by Stan Lundstrum.  Download from the internet.

[jimparamedic]

Blade need shade. The sun will heat the blade enough to make it change shape and not cut right. Also when sawing you should make chips not dust. Make sure that bits and shanks match the the saw plate. Some older plates are thicker then normal for cutting hard woods. Then there is the fact that the more teeth the more power you need. I only cut with half the teeth in my saw do to low power. The other half of the teeth are old teeth sharpened done to. The very last . More pic. We love pics.