Hybrid Rotary Cutter Proof of Concept

[dadohead]

Not to steal the OP's thread by any means, but it does exist.

Absolutely! Been done before.

Woods sold the D80 in two offset versions: mounted and pull type too.

None of these versions back-sweep tire tracks though. ;<)

 

[Jaybr]

It is a similar  intent for sure. For the RD990X, they took their finish mower, mounted swing blades, and called it a hybrid. It still has all the finish mower traits though: shallow deck, high tip speed, designed to cut 1/3rd of the plant. I considered one... dont have enough tractor though.

I can assure you they cut much more than 1/3rd of the plant just fine. I use it on my pastures which I only cut every few weeks. The grass is usually 12" to knee high and I cut it to 4". The cut is nice and clean, but it does leave a lot of clippings. I'm using a Yanmar YT359c and the mower puts no significant load on the tractor.

 

[tradosaurus]

A flail mower does alot better job than a rotory cutter on grass. Where they dont and a rotory shines is woody thicker material. I think you just have the wrong mower.

And maybe needs 20-30 hp more tractor?

 

[dieselscout80]

To the original poster that’s some great fabrication work.

I have a Woods C114-1 that is a bigger version of the D80 Woods. It streaks on the left side. I am thinking about adding steel to smooth the air flow out and hopefully increase the lift.

Here are some picture of it. Do you think just sloping the sides and the front/rear would work or would it be better to just put baffles in like you did?

 

[Sportsman762]

My guess is you're asking about the baffle in the upper left? The bottom of the pic is the front of the mower. You can see how the RH spindle (front) would want to hand-off all of its discharge to the rear one... that was expected. Ring baffles were needed to isolate the chambers. In testing, the RH chamber (in the pic) discharged very nicely right out the back. The left chamber did not! It carried the material too long and slung it along the rear of the mower combining both discharges into one big wind-row... very ugly. To change that I inserted a "cut-off" baffle (upper left in pic). It is there in the flow field (about 3/4" from the blade wing) to create a high pressure wall. The material comes along the LH side toward a high pressure wall or veer out the back to "0" pressure.... so it goes out the back. Cut-off baffles work well but create noise.

Thanks for the explanation. Now I want to go to a mower shop and look under all the deck skirts (oops that sounded wrong)

 

[dadohead]

To the original poster that’s some great fabrication work.

Thx so much!

Here are some picture of it. Do you think just sloping the sides and the front/rear would work or would it be better to just put baffles in like you did?

A few questions:

• It appears to be a 2 spindle, CCW rotation?
• Does the LH stripe align with the LH tractor tire?
• Where does the LH mower spindle align with the stripe? Dead center? Right? Left?
• Just curious. Your mower looks symmetrical (not staggered). How do the 2 blade paths cross to assure complete cutting?

The mower appears to be centered with tractor. If your mower can shift, it would be most effective to move the mower to the right some so the LH spindle can back-sweep the tire track.

 

[Davenj4f]

Hi,
Background: Here is a project I started about 2 years ago. Since I retired (2016) I've wanted to build a rotary cutter that addressed the issues I find in the typical single spindle cutter. For years now I mow about 4 acres of field and the ditches to my lane. I mow about 3x year; sometimes cutting 24" grass to 4" hoc. I mow with a JD 2520 (20hp pto) and a Frontier 5' cutter (I've tried others too). I retired from Deere after 25 years of designing tractors and finish mowers.

The problem: The problem with the single spindle cutter is cut quality; it just doesn't pickup tire tracks! The Frontier RC2060 runs CCW. The tractor pushes the grass forward in the tracks and mashes it down. The LH side of the cutter back sweeps the tire track and cuts well. The RH side aligns the forward sweep of the blade to the tire track and cuts very poorly. After several days, the RH tire track stands back up almost uncut. To combat this, minimal overlap is applied when cutting (essentially keeping the RH tires OUT of the high grass). I only cut about 2 1/2' of a 5' cutter to get acceptable cut quality. Drives me crazy!

The concept: twin spindle cutter, conventional CCW rotation, offset spindles, with mower shifted to the right so BOTH blades back-sweep the tire tracks! Given that I only have a 20hp PTO tractor, a priority was given to power reduction as well. With the tire tracks being mechanically swept up, a lower tip speed could be used as well as a medium lift blade. Impact cutting starts at about 12000fpm tip speed (going lower just "combs" the grass). I targeted this mower at 13,500fpm. 1" rake was designed in so the cut material would release and not recirculate saving power.

The build: I started by purchasing a used, beatup KeenKutter 3pt finish mower. It was junk! I did save the gear box and mounting. Trinkets were cut off of the deck and scrapped. Sheet steel was added to the rear of the mower.

View attachment 3717293
You can see the yellow outline of the original 72" mower. What made this concept possible for me was that Fred Cain (small manufacturer in KY) makes a 3' CCW rotary cutter. I bought 2 of his 3' stump jumpers, blade sets, and assorted parts. He threw in 2 stripped out OMNI gear boxes (just like the one from my KeenKutter). I cut the gear box off of these, annealed the spindles, machined the base castings... they became the mower spindles! I used 1/4" plywood templates to guide my plasma cutter to shape the housing. I needed 2 driven sheaves with a specific diameter and offset to make it all work.

View attachment 3717294

In another life, I was a wood patternmaker at Caterpillar. It's been 40 years since I've turned a pattern but i remember how! Two sheaves were cast in nodular iron at a nearby foundry. They were machined in my shop to receive 2- HB kevlar belts.

Just like we used to design finish mowers, I started with no baffles underneath.... and just like every conventional rotation 2 spindle mower I've ever seen: the front spindle wanted to hand off all of its discharge to the back spindle! Baffles were needed. I started adding baffled using cardboard and duct tape and testing until the cutter started to behave. Then the baffles were reproduced in steel.

View attachment 3717984

View attachment 3717985

Bumper guards and chains were added at the end. How does it work???

Testing: Ok... I LOVE this thing! My 20hp tractor handles the 6' cutter just like it was my old 5' but with better cut quality!

View attachment 3717986
One note: with the mower shifted to the right (to back-sweep tire tracks) you gain a 1 foot bonus trim section on the right of the tractor! Huge improvement. Time to cut the field is half of what used to be. I hired the kid across the road (just out of film school) to shoot some video last year. It was the first mow of the season so the field was tall and extra wimpy.(tough to cut well).

Somebody needs to make this design. What do you think?

Great project. On my Ferris mower, the leading edge of the deck is an inch or so higher than the sides or back, causing the blades to attack higher grass better. Of course, the higher the grass, the harder it is to cut. I find having to cut over my left side tire tracks necessary with higher grass at times, but I think the shorter lip height helps a lot.

 

[Fxfymn413]

Great fab and design work! Congrats There is great satisfaction in being able to define a problem, come up with a possible solution, and than build it yourself.

 

[dadohead]

Great project. On my Ferris mower, the leading edge of the deck is an inch or so higher than the sides or back, causing the blades to attack higher grass better. Of course, the higher the grass, the harder it is to cut. I find having to cut over my left side tire tracks necessary with higher grass at times, but I think the shorter lip height helps a lot.

Yes, dead on. Also, the higher you cut, the harder it is to cut well.

Most manufacturers follow the ANSI guidelines for mowers: B71.1 for residential, B71.4 for commercial. The standards allow for a "raised front skirt"; the limits are clearly set in the standard. You're right... it does help alot. The less the grass is bent forward, the easier it is to stand back up and cut.

I can assure you they cut much more than 1/3rd of the plant just fine.

Lol... of course. That's not what they are designed to do though! Woods laughed about it when they brought out their 3pt finish mower and struggled it through a 24"+ field. They are designed for parks, fairways, and turf.... not pastures. EVERYBODY DOES IT THOUGH.

After looking at used finish mowers to buy for this project I'm convinced their isn't one 3pt finish mower that doesnt have bent spindle pockets! The KeenKutter I bought had all 3 pockets badly bent. Bent blades, bent pockets, and smoked belts were the norm on every one lol! "Yeah, she cuts like new". Cracked me up.

 

[dadohead]

And maybe needs 20-30 hp more tractor?

Yes! Would love more tractor AND a flail! If new tractors weren't choked with emissions, I'd probably have one.

Like most here though, you have more and more attachments that do a great job and money invested. Soooo, this is what a retired mower guy does. Also, I have 3 friends with 1000 series sub-compact tractors with the same issue. They do NOT have the power for a flail. Seems like if a solution is out there.... somebody could sell alot of mowers!