circular saw blade cup or dish

handhewn · October 01, 2020, 07:46:54 PM

Given a 60" circular saw, which way should the saw blade cup, towards the log or away from the log?

moodnacreek · October 01, 2020, 08:41:05 PM

The saw when standing vertical should straight edge flat on the log side or have just a trifle cup [teeth ] to the log. A perfectly hammered saw is flat except that the taper is on the board side. This is because most saws are 1 or2 gages thinner on the rim.

handhewn · October 03, 2020, 07:25:05 PM

If I understand you correctly, RPMs up means saw is near or at flat. as RPMs drop, saw should cup towards log (slightly)? I own one of each and need to be sure which I use. For some reason I can't download the U.S. Govt docs. on this.

moodnacreek · October 03, 2020, 08:25:49 PM

I tend to disagree that saws are cupped and straighten up with centrifugal force. Saws are hammered to make them flat and tensioned at the same time so that there is pre stretched steel in the center of the saw plate to compensate for the centrifugal stretch that comes with rpm. Saws run flat when turning slow then flop side to side at half speed and go flat at the hammered speed. When this doesn't work they must be hammered by a real expert. Very few men can hammer saws and even less can do an excellent job.

dgdrls · October 03, 2020, 11:00:15 PM

Quote from: handhewn on October 03, 2020, 07:25:05 PM
If I understand you correctly, RPMs up means saw is near or at flat. as RPMs drop, saw should cup towards log (slightly)? I own one of each and need to be sure which I use. For some reason I can't download the U.S. Govt docs. on this.

Handhewn,
Try this link
https://www.fpl.fs.fed.us/documnts/misc/circsaw.pdf
D

kantuckid · October 04, 2020, 06:43:35 AM

Quote from: moodnacreek on October 03, 2020, 08:25:49 PM
I tend to disagree that saws are cupped and straighten up with centrifugal force. Saws are hammered to make them flat and tensioned at the same time so that there is pre stretched steel in the center of the saw plate to compensate for the centrifugal stretch that comes with rpm. Saws run flat when turning slow then flop side to side at half speed and go flat at the hammered speed. When this doesn't work they must be hammered by a real expert. Very few men can hammer saws and even less can do an excellent job.

First off, I'll readily admit that I've never hammered a circle saw. What I am is a wood freak, if there ever was one who lived down the road from a man who was considered the guru of circle saws in a wide area. His name was Opel Smallwood and he's dead now, maybe 15 years or so, having lived into his nineties and had quit sawing after a lifetime of logging and sawing in WI and his native KY to only hammer saws for people who brought them directly or shipped them from out of the area.
His nephew whom he mentored is now the largest sawmill operation in my county.
Since he sawed my logs & lumber for me (prior to my own WM LT15 in ~ 2003) I'd come to know Opel well and being a skilled tradesman and tech teacher myself I watched him hammer them, asked questions etc.. As it were he often got blades that others had found problematic or had given up on to cut properly. He'd sit there and hammer away with pure seat of the pants judgement (as I could tell) other than a steel straight edge for reference and a piece of chalk.
Funny looking hammer he used!
My main point is to agree with the last two sentences above from moodnacreek based on the blades sent to Opel Smallwood

Don P · October 04, 2020, 07:39:29 AM

A dog head hammer

.

moodnacreek · October 04, 2020, 09:15:39 AM

Well I can't hammer a saw but I can use a straight edge. You always hear that these saws are cupped when still. I have had saws that touched the log side guide when stopped but the 4 saws I have don't. A straight edge long enough to go from the eye to the teeth will tell the story.

handhewn · October 04, 2020, 01:16:21 PM

I have been asking a question in various places on this forum. I expected to "literally " get a one word easy answer "Towards" or " Away". I'm getting much great info that I desperately need but I'm not getting or understanding the problem so I'm asking the wrong questions. Problem: I have two 60" circular saw blades. Right and Left. Which to use. My blades are cupped. The one on the mill leans (or cups) away from the log as RPMs drop. Other blade would lean into the log if RPMs dropped. WHICH IS CORRECT? Note: for some reason I can not download the Govt. cirsaw info I have been given by a few nice people on this site.

handhewn · October 04, 2020, 01:53:02 PM

when it is at rest it is cupped (away from log). My spare saw is cupped opposite. As I do have a cupped saw, which way does saw go?

JoshNZ · October 04, 2020, 03:36:51 PM

I was looking at an old flat top saw a guy here in NZ runs. For what it's worth, his blade cupped towards his fence, teeth 'pointing' at the board he was cutting off. He didn't dwell on which direction it was dished though. He did say he runs it up and while spinning, hits the face with the butt of his hand. He could tell by the sound and any wobble, if it was tensioned correctly and running at optimal RPM.

From my understanding the centrifugal force on a perfectly flat circular blade would cause the rim to expand more than the centre (or material just below the rim at least). The circumference of the rim being greater than the circumference of the metal supporting it below, causes it to become wavey as this is the only way to fit a longer piece of material on a shorter piece of material and have it be the same length.

Pretension offsets this difference so that when under centrifugal force at RPM, the rim and material below are at equal lengths and everything is running straight. Therefore I bet it doesn't matter which way it's dished.

Try both? See what works better.

Don P · October 04, 2020, 04:54:52 PM

What appears as the convex face is the board side.

moodnacreek · October 04, 2020, 04:55:12 PM

The saw can only be used one way unless you have 2 mills, l/h and r/h. Often saws after long use are pushed away from the log and require to much lead if they will run at all. The other way the saw will tend to run in unless off filed to compensate.

handhewn · October 04, 2020, 05:05:01 PM

I finally got the Gov. cirsaw info downloaded and I learned much. Thank you guys for that info. I had not realized that whether the saw is going or stopped, one side of the blade is flatter than the other. The straight edge (that you guys suggested) showed me the truth of the matter. While I was there I measured lead distance (as you guys described) and found that I am 1/4" closer at the leading edge. After I left saw years ago another guy ran the saw and got cracks in the saw blade just inside the arbor clamp (don't know proper term). I suspect he did not get things back together correctly when he put new blade in.

Jeff · October 04, 2020, 05:23:32 PM

Please do not start multiple topics about the same thing. I've merged these topics. Please read rules on posting. Thankyou

Don P · October 04, 2020, 05:26:22 PM

Running too much lead and crowding the saw wedges the saw over the collars and will crack the saw if you don't end up sawing the carriage, that sounds like it might be what has happened.

moodnacreek · October 04, 2020, 05:30:01 PM

Jeff, I really don't understand what I am doing wrong.

Jeff · October 04, 2020, 05:34:59 PM

well, since you did not start these two topics that i merged, odds are its not you i was referring to, so, probably nothin.

moodnacreek · October 04, 2020, 05:43:14 PM

Quote from: Jeff on October 04, 2020, 05:34:59 PM
well, since you did not start these two topics that i merged, odds are its not you i was referring to, so, probably nothin.

Ok, thanks for the quick answer. I just realized what's up, actually the other day.

moodnacreek · October 05, 2020, 08:16:09 AM

Quote from: handhewn on October 04, 2020, 05:05:01 PM
I finally got the Gov. cirsaw info downloaded and I learned much. Thank you guys for that info. I had not realized that whether the saw is going or stopped, one side of the blade is flatter than the other. The straight edge (that you guys suggested) showed me the truth of the matter. While I was there I measured lead distance (as you guys described) and found that I am 1/4" closer at the leading edge. After I left saw years ago another guy ran the saw and got cracks in the saw blade just inside the arbor clamp (don't know proper term). I suspect he did not get things back together correctly when he put new blade in.

Sounds like someone kept sawing with a hot saw. Saws must be run cold or not at all.