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?
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.
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.
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...
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.
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.
I ran a 30" cordwood saw years back. Nasty beast. Used a sliding table rather than moving the arbor. I'm guessing it ran in the 900 rpm range (hard to know exactly since the drive mechanism was NON STANDARD!!) The
30" saw was used on huge piles of green birch running up to about 8", would slice it like butter. Saw teeth were on the order of an inch high,
1-1/2" tooth to tooth. (As in .6 teeth per inch?)
Found these pics:
For your 18", 3hp would be a good start, 5hp would be better. You would want double 'V' belts, notched belts would be better. I'd try for around
1800 rpm which means finding an 1800 rpm motor so you could get a 1:1 pulley setup.
I don't think you will like the 18" blade, too small once you deal with the arbor, bearings, and pulley. Hard to get more that 6" to 7" of actual cut diameter. Keep in mind that logs have curves and knots. You really need some guards that both work to keep hands out and work with logs that are not anywhere near as straight as cheap 2x4's
I'm pretty sure a chain saw is a safer, faster and cheaper way to cut fire wood. I also question the motor sizes others have indicated since a chain saw with an 18" bar does just fine with about a 3 hp gas engine. If you really want a "chop saw" style setup I think you could do just fine building a unit with a quality electric chain saw.
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 :)
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.
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.