Advise on driving an 18" circular saw blade

Am contemplating constructing a wood cutting chop saw for cutting up fireplace logs. 18" circular blades are readily available here and would
seem about the right size for the size of logs I'd be working with. Question is, what HP electric motor would be required (about 3?) and, what would be best RPM for the blade?
All suggestions appreciated.....
Laurie Forbes
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On Mon, 20 Feb 2006 23:01:17 GMT, "Laurie Forbes"

I find it reprehensible, and perhaps even illegal, to cut down habitat that squirrels need to have in order to survive. You cut down that habitat, baby squirrels fall to the ground, which enables people to make pets out of them. And we all know that's just cruel.

Save the whales, collect the whole set?
Snarl
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Laurie Forbes wrote:

7.5hp MINIMUM motor, and that's electric. If gas, make it 18hp.
Blade speed 3000 sfm. 1.5' diameter, 4.7' circumference, rpm = 636.
Figure 1760 rpm / 3 = 586 rpm, close enough, gear a 1760 motor down 3:1-ish.
This sounds *extremely* unsafe. Better type all your questions now while you still have hands.
GWE
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I have a wood cutting saw that I mostly use to cut up scrap lumber for my wood stoves. Mine is just a 10 inch blade and powered by a 1.5 hp motor. The blade turns at about 4000 rpm. Works good, but not really safe.
I would definately drive an 18 inch blade much slower. The 4000 rpm is somewhat dictated by wanting a small pulley on the saw blade mandrel so I can cut 4 by 4's. The saw blade that I have has a fairly thin kerf. An 18 inch blade would probably have a kerf two or three times as wide, and therefore would require two or three times the hp for the same cutting speed. My intuitive guess is that hp required is proportional to the surface area of the sawdust created per minute. I think you would be happy with a three hp motor. I would rather stall the motor when the blade binds that have so much hp that it never stalls. And instead throws wood at the operator.
Dan

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I think you are right - if a 10" blade normally operates at a given cutting speed at say, 3600 RPM, an 18" for a similar cutting speed would be about 2000 RPM. This seems quite reasonable as I have noted that *max* speed advertised for the particular 18" blade I was looking at is 3600 RPM. The HP being proportional to the rate of chip production also seems reasonable so, particularly if the saw is not forced too hard, 3 HP seems like it would do it alright. As well, the logs I will be cutting are all aspen & balsam poplar which, as woods go, are quite soft (and, it's all cross cutting, no ripping).
As far as throwing wood, I am thinking of devising a long actuator "handle" which would be operated from the side of the saw rather than in front of it. I think that would be safer but would appreciate any comments otherwise. It also seems to me that operating the saw as a "chop" saw (pivoting feed as opposed to sliding) would also tend to make it safer as the blade would not tend to pull itself into the wood.
Laurie Forbes
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I've run a 36" circular saw blade on a 7.5HP 3 phase motor. There's enough power to get the job done. That was for ripping, not cross cutting.
PDW
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Seems a bit large but I would be interested in how those values are calculated. Keep in mind I won't be ripping with it and don't require particularly fast cutting speed.

I'm not sure where the 3000 ft/min derrives from - my 10" radial saw turns about 3600 RPM which gives a surface speed of about 9500 ft/min. Is there some inherant reason why larger blades should be a lot lower?

I realize such a saw would have to be built solidly, with proper shielding etc. and operated with caution but I would be interested in specific reasons why it would be necessarily unsafe (18" is certainly not by a long ways the largest saw blade in use).
I appreciate your response but would be interested in more detail if you could provide it...
Laurie Forbes
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3000 sfm is what is used on bandsaws when cutting wood I believe.
The horsepower I was gaging based on abrasive metal cutting. After all, this *is* a metalworking NG. The electric/gas hp equivalency I was told by an industrial air compressor company (Quincy) when I called to inquire about repowering an 18hp trailer-mounted compressor with electric.
The issue with safety is probably just my own fear. I have an incredible fear of large saw blades, or maybe I should rephrase that as respect.
GWE
Laurie Forbes wrote:

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I agree on the respect issue.

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I hear your concerns re large blades and am now not completely sanguine about it either (that's one reason I'm asking for advice). In regard to metalworking NG, the connection is that I plan to cut wood with this thing, not construct it using wood :)
Laurie Forbes
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On Tue, 21 Feb 2006 17:23:51 GMT, "Laurie Forbes"

Interesting choice of words, sanguine. You want to avoid exsanguination with this saw.
Pete Keillor
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wrote:

It is appropriate alright ("sanguine" - also defined as 'Colour. Of the colour of blood; red.').
I have accidentally deleted recent posts to this thread but thanks anyhow to the poster who seemed to agree that 3 HP and 1800 RPM would be appropriate. Someone else also posted that much higher HPs would be needed (can't remember exactly what numbers were given) - called the manufacturer of the blades (Dimar) I've been looking at and, while they did not have published HP data, he suggested looking at commercial saws to see what HP motors they come with for the same (18") blade diameter. I found a range of 5 to 7.5 HP for that blade size but no corresponding current draw figures were given for the motors so I wonder if they are quoting "Sears" HP units or similar. Anyhow, the guy at the manufacturer guessed that 3 HP might work but would be a minimum. Seeing I am only going to crosscut softwoods and don't need a whole lot of speed, hopefully 3 HP will be adequate (I suppose I could always add a bigger motor afterward if need be).
As to the suggestion that 18" might not be large enough, there is a 20"er also available but I'm thinking the 18 would be good enough as it would handle 90% of the logs I will be cutting and the large logs can always be cut from both sides.
As to using an electric chain saw, I asked here about that a few months ago and the consensus was that they would be unsuitable as they are generally used mainly for light pruning type of work. The local vendors I spoke to pretty much confirmed that. Chain saws electric or gas also need chain sharpening which I would like to avoid.
Thanks again for everyone's help!
Laurie Forbes
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Chain saws electric or gas also need chain sharpening which I would like to avoid.
Not trying to be a jerk here. But, you're going to have to sharpen that 18" saw blade too, unless you just intend to run it dull and then burn it up. I'm with the rest of the folks here, get yourself a small chain saw, unless you are after doing it the way Great Granpappy did it, belted up to a small gas engine.
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On 21 Feb 2006 18:07:28 -0800, snipped-for-privacy@sbcglobal.net wrote:

And that must be a Fairbanks-Morse single cylinder, hit and miss; or alternately, mount the blade in place of a rear wheel on a Model "T" drive line. Gerry :-)} London, Canada
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Yes, but the 18" (carbide) saw blade would last *much* longer than a chain saw between sharpenings (hundreds of times??). It would be great if you could buy carbide chain saw blades, AFAIK you can't.

I have one but am tired of the smoke, noise, stink and blade sharpening - just looking for an easier way and besides, I need a new metal fab project :)
Laurie Forbes
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Laurie Forbes wrote:

You can buy carbide chain, but be prepared for sticker shock http://onlinestore.forestindustry.com/cgi-bin/baileys/scan/se &2/mp=p_search.html?id=5mAQnXeG Joe
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Laurie Forbes wrote:

So get a decent electric chain saw and build a chop saw style mount for it. An 18" circular saw isn't going to be any quieter than an electric chain saw and both will need sharpening periodically. I expect sharpening for a length of chain will be cheaper than an 18" blade as well.
Pete C.
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Rapco in Vacouver, WA has been making carbide tipped chain saw chain for a lot of years. They make a lot of it for fire departments, etc. Good quality and nice folks.
Ron Blehm Rapco 6000 NE 88th Street, #D-104 Vancouever, WA 98665 360-573-0090 snipped-for-privacy@rapcoindustries.com
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An 18" saw blade is a lot of saw blade. At that size you start to get into serious issues about steel tension. The outer rim runs so much faster than the inner rim that it wants to dish over on you. If you hit the wrong freguency it can wobble uncontrollably.
Circumference = pi x diameter 3" diameter = 9.4" circumference 18" diameter = 56.5" circumference
9.4" at 600 rpm = 5.3 mph 56.5" at 600 rpm = 32 mph
Things found in logs (from Internet list)
a side-harrow tooth.
an old lead musket ball counted rings and it was about 100 yrs old.
I hit a small metal box. as it had a small quantity of gold dust and flakes in it. One of the benefits of sawing in California!
a Coca-Cola bottle
two 6-inch diameter by 8-inch long rocks, sitting vertically.
I cut into a nylon rope
an automotive-type water pump
a piece of a steel T-post one day. The sawhand who cut the tree felled it toward the old fencerow, not knowing it was there. The tree fell directly on top of one of the posts, driving a piece about 6" long into the tree and driving the rest of the post completely into the ground out of sight!! When the log hit the ground it apparently rolled enough to break off the imbedded piece and no one saw it until the sawyer cut into it at the mill.
four railroad spikes on one side of the log, three railroad spikes and an 8-inch lag screw on the other.
including animals (raccoons, squirrels, mice, cats, snakes and of course bee's honeycombs)
disk blade with the 12-inch bolt holding it into the tree. A
1/2-inch rebar
a metal-jacketed 50 caliber round. T
an anvil,
horseshoes
railroad spikes and one time I pulled 18 electrical staples out of one place in a walnut log.
sap spiles (to drain the sap for Maple sytup)
a deer stand
an ants' nest
a 3/4" wire rope
Shrapnel in a teak plank form ex-Rhodesia, now Zimbabwe. Apparently, finding bullets or shrapnel in trees from that area of the world is very common.
an old wrought iron fence straight through the middle.
a mushroomed ball of lead about an inch in diameter
nails
insulators
a metal roofing cap several feet long.
a live 50 caliber shell.
a spoon made from lead.
a training grenade from WW1.
a three inch hollow with an old five cent coke
My helper was cutting up the branches of a felled Virginia pine when a section of about 8 inches burst into flames, producing a bright white light like magnesium burning. There was a water hose nearby, and he instinctively tried to flood the flames with water. It continued to burn - this was not pine resin. Finally, after repeated attempts to put it out, he decided to just pile the rest of the freshly cut, very green pine tree on top of the fire. Even with all the water from the hose, the flames ignited the whole tree into a blaze. I have a degree in biochem, and all I can figure is that some sort of explosives or fireworks, or a form of magnseium, etc. had been in a hollow, and the tree's new growth calloused over it.
We also found an old 1940(?) generator in a tree, old bullet slugs, rocks many feet up... The most unusual was in a healthy, sound red oak. It was huge, so we took it down from the top. It was between two houses, and over one of them, about 55 feet up, I discovered that the fork I had been depending on was, to my horror, hollow. I can not believe it did not break from my weight and the ropes and pulleys, plus the shock loads and leverage/distance over the house. So I am cutting off sections about one foot at a time, 56 feet, then 55 from the ground, and a small hollow appears - packed with dirt. It was about 9 inches, with no opening to the outside air. I cut it off, drop the section, and dirt sprays the homes like a huge dog with diarrhea. When I make another cut, many little skinny red worms pop up squirming. I suppose it was an old squirrel nest in a hollow which eventually calloused over.
a live monkey from the local zoo
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When I was cutting wood for sale (8-10 hrs a day, 6 days a week) I managed to wear out about a chain and bar every month. If you don't hit dirt or a piece of steel or stone while cutting that chain will stay sharp for a long time and even then it would take about 5 minutes to hand file the teeth and repair any damage, normal touch up to the teeth takes about 2 minutes. Also used a 40" buzz saw for limbs and smaller wood that was powered for the OLD F-20 I used as a power source for the saw and an elevator to stack split wood. Neat to use but VERY dangerous as well. That saw has 18" of exposed blade spinning in front of you on top of the bed. One misstep and folks will be calling you Lefty or Cap'n Hook for the rest of your life.
Your idea on carbide is also wrong it will dull just like a chain if it hits steel or stone tried a carbide chain myself due to mud on the logs. They worked OK but not well enough to justify the price.
Carbide chain is easy to get but not really worth the bother unless you have a real need like concrete or fire service demolition work. You can also get diamond bonded chain if you cutting into mixed material like reinforced concrete. We have a demo saw in one of the engines at the station just for difficult work like cutting cars apart or cutting through roofs to provide ventilation that came with carbide.
--
Steve Williams


"Laurie Forbes" < snipped-for-privacy@nospam.nospam> wrote in message
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