Question
I have a small circular mill (Foley-Belsaw m-14). In sawing some hardwood, I've found that the mill is a little under-powered. I'm using a slant 6 dodge motor for power. My saw size is 48". Does anyone know what the equation is to find out the horsepower needed to run this size of saw? How can I find out if I'm running the saw fast enough?
Forum Responses
Here is a standard HP formula:
Gullet area x teeth per minute x .003
Use .003 for a kerf of 11/32. For thinner or thicker kerf, use the percent it is of 11/32.
A lot of mills have saws hammered for 550 RPM. You need to know what RPM your saw is hammered for. That is what you need to run it at. Also, an F pattern tooth has a gullet area of 2 square inches. A B style is 2.5 square inches.
I would say that a slant 6 with a good governor should have enough power unless you are cutting deep cuts all the time. I would highly recommend finding a diesel powerplant of some type. Your fuel costs will go way down.
Also make sure you have enough hook in your teeth. If you don't, it will take a lot of power to feed the log through the saw. You will push like heck on the feed lever and she just won't go.
As for the fuel consumption, all I can tell you is look for a diesel engine. Problem is, if your mill is set up for PTO you can not direct drive the saw. It will turn the wrong way. I have seen fellows run a tire up against a pulley to change direction of rotation, but never tried it myself. I have taken a 3/4-ton pickup with a 6.2 in it and welded the rear end solid, put a PTO stub on the right axle and had more power than I would ever need.
The way I see it, a gas engine with a carb on it at a given RPM will mix a fixed amount of fuel with the fixed amount of air the engine sucks through it at that RPM. It just gets worse under load. A diesel will only feed enough fuel to keep you at governed RPM with no load. Makes a hell of a difference at the end of the day. I have sawed for 10 hours on 5 gallons of off road diesel. My brother has a Chevy 6 and could burn 25 to 30 gallons a day.
If you look around you can find the older Rockwell PTO units on some of the old gas powerplants. Back around WWII and later with step down unit that also changed direction of rotation. Every time I find one I pick it up and I always find someone who wants it. Last one was on a LeRoi 4 cyl. for 25 bucks.
Here are some things I learned:
1) HP of car/truck engines: take the advertised brake HP and cut it in half (this will equal PTO or electric motor HP).
2) You really need to know at what RPM is maximum torque (very important). This is the RPM the engine must not go below. The saw must not fall below hammered RPM so the speed reduction, pulleys must be right.
To run the saw with too small an engine: You must have the saw hammered for very slow RPM (say 350). Keep the engine running just over maximum torque and change the drive (pulleys) to lower saw speed. This increases the power.
I once changed the diameter of a drive pulley by 1/2" and dropped the engine 200 RPM and hit maximum torque and started sawing much better.
From contributor A:
I have sawmilled quite a lot and would have to say that of all the power units I've used, GM has to be the best. Here in NC that's about all you see pulling mills. I've used the 3 and 4 cly. units and have had good luck with both. The 3 would be plenty of power for a farm mill or even for production. I could keep an edger man and two offbearers busy with the 3 - you can saw hard all day on 7-8 gallons of fuel.
My advice is if electric is available then use it. It is expensive, but in the long run you are better off if you want to get serious. If you stay with a fuel engine then you would be better off using a smaller saw with higher mandrel rpm. Smaller saw equals thinner plate and kerf which in turn increases hp.
