Disc or drum...?

[Ty Korrigan]

Hello,

 On this dull wet January day, fettling in the garage, I got to thinking about the differences between drum and disc machines.

Having used  several GM CS100 and a Chinesium copy plus a surprisingly good Bugnot fitted with fixed sharp cutting tools, I've often thought that the drum configeration must be the more efficient as it cuts along the grain.

Disc machines requiring more force because of cutting across?

More force, more energy, more stress on parts.

So why are there so few drum machines out there from British manufacturers? 

The French makes of Bugnot, Saelen and Rabaud are all mostly drum offering combinations of flails for shredding or knives for chipping or even both.

I''m not comparing shredders with chippers here but drum with disc chippers.

Any thoughts?

  Stuart

[PeteB]

A disc cuts the same as a drum, except those machines which have an angled disc like some Bandits and Farmi units. Discs are, by and large, more efficient at blowing or throwing the chips out while drums struggle to produce the same level of 'puff'. Drums however, can be very effective at getting a bigger capacity while a disc can only gets less than half the rotor disc as capacity.

[Ty Korrigan]

11 minutes ago, Scottish Cleaning Service said:

I'm a joiner to trade. Take a saw and cut down the grain and then cut across the grain and tell me what way is harder?

I was thinking that the drum cut more by a shaving, paring action than sawing, rather like a plane. 

You can't easily plane across the grain only with it.

Happy to be corrected though, was only musing on a wet day.

There is make of shredder, Elite, who use cutting along the grain as a selling point.

The machines do have very little throw and that only because the larger ones have a fast turning helicoil like turbine after the shredding blades which must cost some energy.

  Stuart

 

[Dan Maynard]

Are the really big chippers drum for this reason?

Other thing PeteB could have pointed out, straight blade drum chipper is taking it in one bite, the round blades in a GM disc chipper spread the cut around and so lessen the shock.

[Watercourse management]

Drum chippers are more efficient as they do cut with the grain rather than against it, the drum also allows bigger capacities but they are a lot heavier to cope with the bigger forces imparted by and on the drum.

The bandit system of feeding at an angle onto a disk allows a bigger surface area of cut.

[aspenarb]

A disc normally incorporates the blowing system and has a lot flywheel inertia, downside is to chip 18" you need 36"+ diameter flywheel. Drum is more compact, in theory just over an 18" drum will do the job of a 36" disc, downside is there is less flywheel effect so a tad harsher on the drive system so they tend to spin them up faster, also needs the added complication of a separate blowing system.

 

Bob

[PeteB]

Stuart is right to a degree in that as the drum blade bites,  it is straight across the grain but aspects deeper, it is changing its angle to ultimately be cutting down the grain. The bigger drum machines end up using a number of small blades so that each one is getting the benefit of more horse power and are cheap to buy and thus more efficient than a full width flat blade. Big biomass units can have a screen as the outer casing so that the chips are of a regular  size. They are often fed to a disc which blows/throws the chips out. Lots of weight, cost and moving parts which would not suit the bog standard Arb chipper.

[dig-dug-dan]

9 hours ago, Ty Korrigan said:

I was thinking that the drum cut more by a shaving, paring action than sawing, rather like a plane. 

You can't easily plane across the grain only with it.

Happy to be corrected though, was only musing on a wet day.

There is make of shredder, Elite, who use cutting along the grain as a selling point.

The machines do have very little throw and that only because the larger ones have a fast turning helicoil like turbine after the shredding blades which must cost some energy.

  Stuart

 

I have an eliet, super prof 2000. Yes, it works on the axe principle, cutting along the grain.  It's a fantastic machine, until that very last piece of wood goes in the rollers sideways, then it jams!

Mine discharges onto a hydraulic conveyor, so it will wither load the truck or make a neat pile of chips. Less mess than a blower style discharge.

New ones have an axeleron discharge, it's like a blower without the power required.

[PeteB]

From memory, the Eliot is a shredder which uses a three sided star blade? The point of the star slashes at the material rather slices through it? This shredding action going up the grain is okay but across the grain, as you say,  slows the feed down and is inefficient. 

[PeteB]

4 hours ago, Scottish Cleaning Service said:

You have got to look at how wood is made up. Its like a pack of straws. So you would expect the drum method to be good but it may not remove much per stroke like a planning machine. I would like my 13/75 flywheel to have two blades in it rather than one which would be more efficient. 

Not necessarily. TW would have done a lot of testing to get the best performance within a few parameters. If you have two blades, it is having two impacts per rotation, and the rotor would slow down quicker given the HP available. With regards to the pack of straws in a big bundle, a disc slices through the bundle at the same angle. With a drum, as it rotates, the blades would/could start to strike pushing up the grain, then transition through the vertical and end up towards the horizontal again, which is trying to pull the material further in - ready for the next blade to do it's job.