Zanon ZRF 1000 drum mower

[Jens767]

Hi

Last winter I decided to treat myself with a drum mower for my BCS 740, so I ordered a Zanon ZRF 1000 with a working width of 40’’. I plan to use the mower to mow tall grass on my own meadow, and to help friends and neighbors mow theirs. As this type of rotary mower hasn’t been mentioned much in this forum, it might be helpful with a little presentation first:

https://www.zanon.it/en/p/zrf-falciatrice-rotante/

The PTO-flange and the gearbox housing is similar to other Zanon mowers that I am familiar with, and the driveshaft housing has the Zanon-typical oscillating swivel-joint, that allows the mower to follow the contours of the terrain. The gearbox powers the two vertical drums, that each ends in a spinning horizontal disc with 3 hinged blades. Underneath each rotating disc is another disc on witch the mower glides over the terrain. The two photos below shows the business-end of the mower without the protective cover.



The entire mower makes the Zanon-typical heavy-duty impression, that I am familiar with from my Zanon ZCR lawn mower.

Early March I was trying out the mower for the first time, mowing a bit of my meadow.



The drum mower turned out to be a very power-hungry implement as expected, but I was able to mow in 2nd gear with my 23’’ tall wheels at all times. Compared to my experience with a sickle bar mower, the drum mower throughs more clippings and debris around, as can be seen on the second photo.

As with all rotary-type mowers, it is important to operate at full open throttle - or at least close to full open throttle. There are at least two good reasons for this:

1. Contrary to a sickle bar mower, all rotary-type mowers are very power-hungry, as the engine has to keep the blades rotating at high speed. Zanon recommends app. 3/4 full open throttle, which is 2700 rpm for the Honda GX 390 engine. From this speed and up to the rated speed of 3600 rpm, the engine produces 86-100% of its rated power. Equally important is the fact that the engine operates above its peak torque at 2500 rpm, allowing a curtain torque rise should the mowing conditions get tough.
2. The hinged blades on the mower are kept „straight“ in their working position by centrifugal force, created by the spinning discs. As the magnitude of this force relates to the angular velocity squared, a small reduction in engine speed, will give a large reduction in the mowing capacity. A reduction like the above mentioned from full open to 3/4 throttle is equal to 25%, but the reduction in centrifugal force is almost 44%, leaving only slightly mere than half the centrifugal force to keep the blades straight!

Best regards

Jens

 

[blee03]

That is a wild mower... never seen anything like that before
Thanks for sharing!

 

[Liquidsilver]

That looks like hard work to use!

 

[joecoin]

Is there a wheel kit for it?

 

[Jens767]

Hi joecoin

Thank you for your reply!

No, sadly not - at least not to my knowledge

Due to the way these drum mowers are build, I think it would be very difficult to mount wheels on them. If you look closely on the second photo in my original post, you can see the lower disc that each drum is resting on. This disc is isolated from the rest of the mower with ball bearings, so that it won’t spin with the blades and their disc. Because of this design, one can’t adjust the cutting height either.

The mower simply glides along on these lower discs, whether you are mowing or simply moving between jobs. It works fine on grass and the like, but is a bit rough on gravel roads and tarmac.

Joel Dufour from Earth Tools has a description of the drum mower on his homepage. Perhaps he can better explain what this mower is all about:

Disc Mower - Earth Tools


Best regards

Jens

 

[Raul-02]

y BCS 740,

That's a haying machine. It's meant to cut the grass and leave it long so it can be collected and or baled.

 

[Jens767]

Hi

Recently I stumbled upon this link:

Rotary mowers

In the specification to this rotary mower, the blade tip speed is given to be 75 m/s (14764 fpm). In more everyday terms, this is equal to 270 km/h or almost 168 mph. Being a curious person, I decided to see how fast the blade tip speed of my new drum mower might be. When working with the mower, I can easily see, hear and feel that it is rotating pretty fast, but is it in the same range as the above „full-size“ mower?

When the Honda GX 390 engine is running at its rated speed of 3600 rpm, the PTO of the BCS 740 is running at 990 rpm. I haven’t been able to find any information on the actual gearing on the Zanon ZRF, and I didn’t want to open the gearbox just to have a look and find out. I did the second best thing, and did my best to see how many revolutions the disc would make, when the PTO turned one revolution. I found that the disc turned 2 and 5/12 revolutions per revolution of the PTO. Based on these numbers, the disc will turn: 990 x 29 / 12 = 2392.5 rpm, with the engine running at rated speed.

The radius from the center of the disc to the tip of the blade is around 26.5 cm (10.5’’), which means that the tip will travel: 2 x π x 26.5 = 166.5 cm (65.5’’) per revolution of the disc.

Based on all of the above, the tip of a blade will travel at: 2392.5 / 60 x 166.5 / 100 = 66.4 m/s (13071 fpm), or slightly below the above linked mower. In more everyday terms, this is still equal to 239 km/h or 148.5 mph - or the speed of a fast car on the Autobahn

The blades are hinged to swivel freely, and are kept straight in their working position by centrifugal force. Like the speeds mentioned above, the forces involved are also rather impressive. A new blade to the Zanon ZRF weighs 100 gram (3.5 oz), and is 10.5 cm (4’’) long. This means that its center of gravity is around 22 cm (8.7’’) from the center of the disc. When spinning at rated engine speed, every blade pulls at the spinning disc with a force equal to its mass times its distance from the center of the disc, times the angular velocity squared. In this case: (100/1000) x (22/100) x (2392.5/60x2xπ)squared = 1381 N, or the weight of 140 kg (308 lb.)!


Best regards

Jens

 

[Tinhack]

That is certainly made for young(er) people. Looking at the size of your meadow, I'd be looking for a ride-on.

Putting one or two caster style wheels on that doesn't seem like too much of a deal. Even if it/they had to be mounted to that extended arm behind the blades.

 

[Jens767]

Hi

After my second job with my drum mower, I decided to give it a closer look to get familiar with the details. As I have used a Zanon ZCR lawn mower for almost 10 years, I have a pretty good idea of what to expect.

As I wrote in my original post, the drum mower has an oscillating swivel-joint to allow it to better follow ground contours. The PTO-flange can also be adjusted up and down, allowing the mower to run parallel to the ground with different wheel sizes on the tractor. With my 23’’ wheels the PTO-flange is in the center position, so I would imagine that it can be adjusted to fit wheels between 20-26’’

Zanon has sadly also copied one of the design flaws that I had on my old lawn mower



In order to allow the movement of the PTO-flange up and down, there is a universal joint in the driveshaft housing, as can be seen on the photo above. Sadly you can also see that the bearing closest to the tractor has walked out of the housing, and simply spins with the axes

I had the same problem 10 years ago when I got the lawn mower, so I am disappointed that Zanon hasn’t corrected this flaw

Luckily for me, my neighbor is a skilled mechanic, and he quickly made a fitting shaft collar, as can be seen on the photo below



This way the bearing is kept in place, but why isn’t this so from the factory?

The bearing at the other end facing the mower is probably fixed, as can be seen below.



I have 2 Zanon mowers, and both of them had this design flaw, so it would be interesting to hear if other members with Zanon mowers has experienced something similar


Best regards

Jens

 

[joecoin]

Yes, my Zanon 33” Heavy Duty Lawn Mower had the same issue, I just pushed the bearing back in the housing and it has stayed there for 3 years so far. I don't use it as much as I use my DelMorino rough cut mower.