Hybrid Rotary Cutter Proof of Concept

[jmc]

I'd bet Deere was sorry to see you retire!

 

[350c]

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.

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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.

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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.

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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!

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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 work and great idea; good luck with future progress in marketing. On a related matter, I question why trail- or pull-type rotary cutters are not readily available, if at all, for SCUTs and CUTs -- in my experience, the vibration from a rotary cutter is not transferred to the tractor nearly as much through a drawbar as through a 3-point hitch. That vibration cannot be good on a tractor, especially on smaller tractors. The flex hitches help some, but the vibration is still transferred more. Since you worked for JD, is there a reason for not having more, or at least SOME, choices in pull-type mowers for smaller tractors?

 

[Runner]

I would think tow-behind mowers would be much harder on the U-joints than three point mounted models. For that reason alone, I would stick with the three point model, unless I really needed tow-behind because of the size.

 

[dieselscout80]

Thx so much!

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.

It’s 3 spindles (114” cut) and the stripe is from the left tire to the far left side.

 

[dieselscout80]

I would think tow-behind mowers would be much harder on the U-joints than three point mounted models. For that reason alone, I would stick with the three point model, unless I really needed tow-behind because of the size.

I love my pull behind mower it doesn’t bounce around like a three point does with a cutting height of 6” to 8”, so the ride is better. I do wish it was a batwing so the deck followed the terrain better.

Backing into fence corners it not as easy and lifting a 9.5’ mower would be difficult for my tractor. I outline my pastures with my flail mower and a fence trimmer.

 

[shooterdon]

Very impressed with your skill and execution.

I cannot fabricate so must buy whatever I need to get the job done.

I would buy a fail mower and not wait for the grass to get 24" high. I doubt you need more than 20 PTO HP for cutting grass at a 48" mow width. The flail will not leave those windrows either.

Sorry, but those windrows are not acceptable.

 

[5030]

Very nice but not marketable because the cost to make it commercially would be prohibitive. Not many people would pay the added cost when much cheaper alternatives are available and if that ground was mine, I'd be cutting, raling and bailing it....lol

 

[dadohead]

It’s 3 spindles (114” cut) and the stripe is from the left tire to the far left side.

Ok, looked up Woods C114-1: 3 spindle, CW conventional rotation, staggered spindles.

From videos I see on YT, the LH tire track hits the left spindle at about 10:00-11:00.... that's the forward sweep on this CW blade. Anytime a tire track aligns with forward sweep it spells trouble!

So, what to do... sharp blades, WOT (wide open throttle), slower ground speed, lower HOC, and most effective: shift mower left to put tire track 12:00 or more on LH spindle (BACK SWEEP IT!). Hopefully won't screw up RH spindle cut.

A ring baffle may help... exactly like radiator fans: close to the blade helps (3/8- 1/2" radially) and just into the wing region axially. In Experimental, I'd have the guys weld more wing on a blade too (welder needs to KNOW what they're doing! Pre-heat 5150 etc). Wing: 30 deg for better lift / 45 deg wings = less lift and THROWS grass further. Welcome to the club!

 

[dadohead]

Very nice but not marketable because the cost to make it commercially would be prohibitive. Not many people would pay the added cost when much cheaper alternatives are available and if that ground was mine, I'd be cutting, raling and bailing it....lol

Lol... you always have an opinion Flip!

Disagree... similar build costs as 3pt finish mower. One less spindle / blade set, less 4 gauge wheels / mounting. Add: more steel / weld time. Had this discussion with Woods.

Target BIG volume 1000/BX tractor owners.... sell mowers. You know what they say about opinions though... ;>)

 

[dadohead]

I would buy a fail mower and not wait for the grass to get 24" high. I doubt you need more than 20 PTO HP for cutting grass at a 48" mow width. The flail will not leave those windrows either.

Sorry, but those windrows are not acceptable.

Smart. But I'm an old rotary guy who's not smart! Would not trade the 72" WOC with 1 foot right side trim for 48" flail.

Yes, the windrows after cutting 24" are there... after a week or so they are not. I can live with it. Remember, this is a first shot. If I was at Deere, I would have started with a carrier rig that held the mounting and drive. Fiberglass deck shells would be made to insert in. After the cut was behaving, ALL KINDS of work would go into the discharge (deck shapes, baffles, etc) to spread it out better. I don't have those resources anymore. That's why I want somebody to make it... they'll do it better!

Implement companies are small. They cant spend resources then just "get on base".... they need "home runs". This might not go anywhere.... I tried. Sure love reading all your comments!