Lack of Adjustment on Flail Mower Cutting Height?

[morrisond]

I'm about to purchase a JD 390 with 26" offset.

This is the table of cutting heights:

Setting/Position Cutting Height
1 13 mm (0.5")
2 51 mm (2.0")
3 89 mm (3.5")
4 127 mm (5.0")


What Happens if you want the cutting height to be say 1-1.5"? Can you just adjust the top arm of the 3Pt hitch so you get any height you want?

I'm getting Top-and Tilt on the Tractor as well, so would that give me Hydraulic Control of Cutting height?

How much damage will I do to Smooth Cut knives if they hit some gravel?

Thanks

 

[greg_g]

The 4 positions listed reflect nominal cutting height of a level mower with the rear roller in each of the 4 sets of mounting holes. Consider that the gross cutting height adjustment. After installing the rear roller in the desired hole set, you can then change cutting height to either side of that nominal height by varying the length of the tractor toplink. And yes, a hydraulic toplink makes this process much easier. But hydraulic sidel cylinders have no value in this application.

About the gravel question. Compare the "smooth cut" knives to the blade on a rotary push mower. If you've ever hit gravel with a push mower, you already have your answer. The HD side cut knives are stouter, and the T-type (or scoop) knives are - in my opinion - best in terms of durability.

//greg//

 

[morrisond]

Thanks for the answer.

So If I want 1", I mount in the .5" spot and adjust the top link - makes sense.

The two options I have for baldes are "Heat-treated Reversible Side-slice or Optional Smooth-cut Cupped Knives"

I mainly using it for mowing large areas, and along the driveway. Will the side slice Knives produce a good enough cut?

There are 84 pairs on the 390.

Thanks

 

[greg_g]

"84 pairs" suggests 3 rows of 28 hangers. I think you mean 42 pair, which is consistent with the number of hanger stations; 3 rows of 14 staggered hangers, each holding two knives. One pair of knives is typically responsible for about 1.5 inches of cut. The optional smooth cut (cupped) knives require a different rotor. It's got 3 rows of 11 staggered hangers, each holding one cupped knife. Typically the "slice" knives are considered fine cut, and the "cupped" knives are considered either general duty or rough cut (depending upon manufacturer). The cupped knives by the way are T-shaped, each with two edges. They're individually responsible for about 2.5" of cut. Other than the rotor/hangers/knives, the two JD390 variants are the same. Mechanically. Can't speak for price though.

The fine cut knives are really most effective in grass. Cupped knives work fine in grass, but fewer cutting edges means not a true finish cut. The advantage is that they can also be used for rough stuff up to 1.5 inches or so. So the decision will be whether you want an 84 knife finish mower (84 knife edges), or a 33 knife general duty mower (66 knife edges).

About the rear roller position. I'd be afraid of scalping in the 0.5" spot. If a 1" cut is your target, I'd be more inclined to recommend the 2.0" spot. That would give you a more reasonable adjustment range with the toplink. From there you adjust the toplink to cut either side of 2", while still keeping the mower reasonably level.

//greg//