Flywheel on a circle saw?

[Jesper Jepsen]

Hi

I'm in the very beginning of designing my home made circle saw and in that I have a couple of ideas that I like your input on.

The drive power to saw will be from a PTO and I had the idea to put a flywheel on the drive shaft to even out the load from the saw blade hitting the log and when I engaging the carriage. My thought is to have a axel coming from the PTO with the flywheel parallel with the mandrel and connected with a flat belt. That make it possible to have some kind of clutch and to have a gearing if needed to get the right blade speed. 
But what is your take of putting a 200 pound flywheel into the driveline of a head saw? The blade I'm thinking of using is a 52-56" ITW.
Another idea is to put a drum brake on the end of the mandrel so if needed I kan bring it to a stop very quickly.

The other question I can't find a answer to is, how do I find the kerf width for a ITW blade? 

Is there a formula to get an idea on how many horsepower I need for a saw blade? I know i depends on the wood, the feed speed and many other things but is there a rule of thumb on how many horsepower pr. tooth or anything other way to get close to the power need?

Jesper

The power to win lies in the courage to fail

[Gary_C]

A parallel shaft should only be used if you cannot align the power supply with the saw mandrel. Otherwise it only adds complications and expense. You can also add a flywheel and clutch to an inline shaft if you deem it necessary.

The complications I mention are much larger shaft bearings near the belt for the higher side loading from the belt plus belt slippage, wear, and belt tension requirements.

[Kbeitz]

I was also wanting to do this on my swing saw.
I was going to use friction plates on both sides of
The clutch and keep the flywheel on the same shaft.

[ozarkgem]

I don't own a circle saw but I would think if the fly wheel would be an advantage they would have them on the mills. Yes you will get  the effect when you hit a knot but it will also take more time to recover back to full speed. Then all the bearings you have to add will complicate your build. Keep it simple. The key is the proper hp for the blade.

[longtime lurker]

Around here the rule of thumb is 5HP per inch of saw in the cut. So for a one inch deep cut you need 5HP, for a 20 inch deep cut you need 100HP etc etc. Thats just the saw spindle, ancillary hydraulics, carriage drives, turners and all the fruit arent in that HP calculation.  Thats probably overpowered for most species, particularly softwoods, but be aware that too much HP only costs fuel, too little HP can cost you your life. Underpowered circle saws are dangerous.

Rather then play around with a flywheel the best bet would be to use an engine with an electronic governor... I got a play with one a while back and it was sooooooooooo good, no bogging down in the cut, as soon as she came under load the power came through pretty much instantaneously and if the load got heavier it just opened her out more. Far better then the mechanical setups I've used, it was as good as electric drive: add one more thing to the wishlist.

[bandmiller2]

Jep, the width of your kerf depends on the width of the bits, if you figured from 5/16 to 3/8" you wouldn't be far off. Say you had  5/16" bits your kerf would be a little more due to saw run out, it should be small but its there. Flywheels are helpful for an underpowered power supply as the regain energy between cuts and deliver it during the cut. If you have decent power flywheels will just add expense and complication. Frank C.

[longtime lurker]

Jep, the width of your kerf depends on the width of the bits, if you figured from 5/16 to 3/8" you wouldn't be far off. Say you had  5/16" bits your kerf would be a little more due to saw run out, it should be small but its there. Flywheels are helpful for an underpowered power supply as the regain energy between cuts and deliver it during the cut. If you have decent power flywheels will just add expense and complication. Frank C.

The problem you run into Frank is that if you're depending on the momentum from a flywheel and you've got more log/ bigger knot/ larger lump of metal then you have momentum then you're back to an underpowered circle saw.

When big circles run out of power and go into a stall they stop slicing fibre and bite... and when they bite then things get interesting. Dogs torn out, log leaving the carriage at great speed interesting. Sawplate wrecked, husk bent interesting. Interesting is expensive and dangerous: I've only ever had to pay a repair bill, but one of my mothers uncles was killed when a big cant was thrown back and stove his chest in while he was working the knees on an old handset mill.

The other thing is that there's no "save" on the horsepower requirement anyway. You might have less HP, but the motor is still under heavy load after you've finished cutting because its got to rebuild flywheel momentum again. So your overall power requirement/fuel burn isnt going to change a lot I should imagine.

I'm not saying a flywheel wouldnt work, or is a bad idea. But I am saying that I would be very reluctant to be depending on it as a substitute for an adequate power plant.

[Gearbox]

I don't see a advantage on a circle mill . Time in the cut will negate the advantage of the flywheel . They worked on cut off saw's but they had a short time in the cut . With a PTO drive all you need is a shear pin . You will learn to live with what ever HP you have . I have ran mill's with every thing from a 300 farmall to a 6 71 Detroit . HP is fun but not a requirement .

[Don P]

I agree, unless the flywheel is too massive. Diameter is part of the hp requirement, feed and # of teeth in cut plays a big role as well.
There is some good info in here;
http://www.simondsint.com/circularsaws/circle%20sawing%20publications/ld%20publications/the%20efficient%20saw%20mill_10-09.pdf

[Darrel]

I'm thinking that if you have a 52-56" saw blade spinning at 300+ rpm you already have one heck of a flywheel.

[Gearbox]

Darrel 500 to 700 and even up from that .

[Darrel]

Darrel 500 to 700 and even up from that .

Even more flywheel action then.  I know the big 72" one at the stud mill I worked at wouldn't even come to a complete stop when we took our coffee break.

[Jesper Jepsen]

Well if a flywheel had been such a great idea surely it would have been on saws,my take on it was not to compensate for too little power plant but to even out the load so the engine would have a smoother run.

I have been reading the link you gave me and wonder why a diesel engine needs so much more horsepower than electric or steam, to me the only reason is that both electric and steam engine have much more torque so that the power question is not only about horsepower but also about the torque in that power or am I wrong on this?

My main issue is that ITW blades are not to find in Europe so I have to import one and all the parts and tools to maintain it.

Jesper

[Kbeitz]

Smokstak talks about flywheels on a saw...

https://www.smokstak.com/forum/showthread.php?t=140800

[bandmiller2]

I'am not promoting flywheels on circular mills, years ago when large single cylinder engines (gas, diesel, steam) were used to run mills they were a necessity. As someone mentioned, in an application with a short duration cut they help. My old shingle mill made good use of a flywheel and an added large "V" sheave. To mill with too light a power unit is not a good situation for the saw, sawyer, and production. Just because it can be done doesn't mean it should be done. Frank C.

[dblair]

I've got one with a 700 lb flywheel . go to Appomattox sawmill on youtube if you want to see it . the drive is a moline 403 about 74 hp.

[Dleavitt]

Larger tooth space, I run a 40 on 4ft with a pto (56 hp diesel) and it seems to run great, or at least my limited experience says it does..... smooth and steady

[ozarkgem]

Dave B
  That is one smooth running sawmill.

[jeep534]

there is a HP to blade size chart in the frick sawmill manual I have.  I will try to get it uploaded sometime soon

archie 

[jeep534]

Here you go



Happy Hunting
archie