Re: (ET) In Search Of... Again

[Dick Dunn <rcd talisman com>]

Let me add some detail on two-blade ICE mowers and correct a point from
David Roden, then on to electric and back:

ICE mowers in the usual situation, driving multiple blades with one
serpentine belt, do -not- need to have the blades at right angles, and in
fact they wouldn't stay that way because of belt slippage.  You couldn't
depend on the blades staying at right angles, and you couldn't risk the
blade paths possibly overlapping:  Hit a rock and the blades would collide;
the result would be catastrophic.

The -paths- of the blades, as the mower moves forward, -do- overlap.  The
circles of the blades' rotation do -not- overlap, because one blade is set
slightly in front of the other, (yes, even with 2-blade mowers; of course
you've seen it with 3-blade).

In the usual situation, the blades rotate clockwise as seen from above.
The mower discharges to the right, and it is the left blade which is
slightly ahead of the right.  This allows the leading edge (cutting edge)
of the left blade's circle to throw clippings in front of the right blade
and be able to push them out the right discharge.

This also explains the phenomenon noted by Tim Maxwell--that you can get an
un-mowed strip when turning sharply:  If you make a right turn, the blade
circles overlap more than usual.  If you make a left turn, it's more like
having the blades exactly side-by-side so there's a gap between them.
(Unfortunately, that has an awkward interaction with mowing a rectangular
area:  You want to start clockwise so as to mow as close to the border with
the non-discharge side of the mower. Then you turn around and mow
counterclockwise on the rest of the area so that you windrow into the
already-mowed area and don't end up bogging down in piled-up clippings.
But that means most of your turns are left, which is the turn that leaves
a gap in a sharp turn.  We live in an imperfect world.)

If you look at electric instead of ICE, again the blades don't have to be
synchronized (nothing to keep the motors in sync) but for example with a
3-blade deck, the center blade is well in front of the left and right
blades, so that the forward-moving paths of the blades overlap even though
the blade circles don't.

ALL that said (sorry for the length!), there are multiple sins which can
cause an unmowed stripe in the center of a two-blade mower path...I should
know; I've committed some.
Someone mentioned installing blades upside-down, which means the blade
doesn't have lift.  That seems unlikely to me since that also puts the
blunt trailing edge of the blade in the lead and it would make quite a 
mess.
If you wait way too long to replace blades (done that), they get shorter at
the ends where they're moving the fastest, to where you get a gap.
If you don't keep the underside of the deck and the discharge decently 
clean
the blades can't produce the lift which pulls the grass into the blades.

On Wed, May 22, 2019 at 09:22:31PM -0400, David Roden wrote:
> On 22 May 2019 at 16:08, Dean Stuckmann via Elec-trak wrote:
> 
> > The only reason I can think of for an un-mowed strip would be blades 
> > that are
> > too short. I think that would be true for any deck - regardless of the 
> > number
> > of blades it has.
> 
> I may not know what I'm talking about, but the few ICE riders / tractors 
> I've had (limited) experience with had blades whose paths overlapped a 
> bit.  
> However, the blade drives were belted together.  The belt was set so 
> that 
> the blades were always at right angles to one another.  That is, they 
> were 
> timed so they'd never strike each other when rotating.  (I guess you 
> hope 
> that the belt doesn't slip.)
> 
> When you have 2 independent motors driving the blades, as in the R36 / 
> ER8-
> 36 and E8 / E10, you can't time them that way.  You have to find some 
> other 
> way to ensure that the blades will never strike each other.  The ways I 
> can 
> think of to do that are by allowing clearance between the blades, or by 
> setting one blade slightly higher than the other. 
> 
> If you offset them in height, the cut will be uneven.  Not so good.
> 
> If you allow clearance between the blades, you'll have some amount of 
> grass 
> that's missed.  That's not great either.  Maybe it should only be a few 
> mm, 
> but there has to be some. 
> 
> If you have an E15 or E20 with a 3-motor deck, the center blade is 
> farther 
> forward.  It can (and IIRC does) overlap the others' cuts horizontally.  
> That eliminates any gap.  
> 
> You don't have this on a 2-blade deck such as the ones on the riders and 
> the 
> small-frame tractors.
> 
> Now, it may be that my R36's blades are indeed too short.  They're what 
> the 
> mower came with when I got it  I've been assuming that they were 
> standard 
> factory issue, but I bought the mower used, so who knows for sure?  
> Maybe 
> they're aftermarket blades.  But they always leave an unmowed stripe an 
> inch 
> or so wide in the middle of the deck.  So I overlap cuts about 55-60% 
> when I 
> mow.
> 
> Really?  Nobody else with an R36, ER8-36, or E8/E10 has this problem 
> with 
> the mower leaving an unmowed stripe down the middle of the deck?
> 
> 
> David Roden - Akron, Ohio, USA

-- 
Dick Dunn          rcd talisman com          Hygiene, Colorado  USA