[mowbot] Cutting technology

Dave Everett (Deverett nospam at vir.idx.com.au)
Thu, 03 Oct 1996 22:20:45 +1000

Dominic Peterson wrote:
>
> Dave wrote:
> >I have put up information about using a hedge trimmer for grass cutting
> >there.
>
> The pictures illustrate the problem with using a cutter of that size. I
> would estimate from the photo that the teeth on the fixed (lower) comb are
> on about 20mm centres.

I just went and measured them, they are spaced 15mm apart.

Seen as a x-section through one pair of teeth
> (upper and lower)(most definitely NOT to scale):
>
> ________________ |<---- 20 mm --->| ________________
> / fixed blade \ [] [] / \
> /__________________\ [] [] /__________________\
> ------------------ [] []
> \ moving ----> / [] []
> \______________/ [] []
> [] [] <-- grass blade 2
> grass blade 1 --> [] []
> [] []
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~""~~~~~~~""~~~~~~~~~~~~~~~~~~~~~~~~~
>
> It's fairly easy (??) to see from this diagram that blade of grass 1 is
> just going to get folded over but blade 2 will almost definitely get cut.
> If the 20mm dimension is reduced to more like 4 to 5 mm then performance on
> grass will be much (much) better. And at those sort of spacings very
> little is going to get in other than grass - a slotted guide/separator in
> front of the cutter would exclude loose twigs leaves etc and make it safer
> again.

Yep that would definitely improve it.

> Go to a store and look at a Phillips beard trimmer - it has an
> adjustable guide over a comb cutter - all we (I?) need is the same thing
> scaled up by about 5:1 . I'm still working on making a cutter out of
> readily available materials with normal tools but other things (like work &
> study) keep cutting into my experimenting time :-). The only readily
> available cutter of that sort of dimension that I can think of is a
> shearing clipper (Dave, you're an Aussie - want to get into a
> wide-comb/narrow-comb battle :-). For the benefit of non-Aussies, I'm
> talking here about sheep shearing.

I think something based on the sheep shear would work very well, I guess
it's just a case of guiding the grass blades into a slot that is not
much wider than the grass blade.
>
> I'll keep at my experiments, as time permits, and report back with progress
> (and some photos for the Experiment web-page).

Good luck, I'm keen to see the results of your experiments and others as
well. Maybe you could make a prototype out of sheet aluminium.

-- 
Dave Everett                                Email: deverett nospam at idx.com.au
(c) 1996 - Copyright remains with the author unless explicitly stated