Rotary blade

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Chris G
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Rotary blade

Hello, I have purchased a new 17" rotary blade "on line"  advertised as a genuine Mountfield.

The original is over 10 years old and although I have sharpened it a fair few times it has quite a few heavy dings in it now so thought I would be better off replacing it.

I cannot recall what the original one was like when I first got this mower but the replacement has a very dull edge, hardly a blade edge at all it's so blunt, using an angle finder gives just over 30 degrees, I have read that 40 is more what it should be and the edge should be a milled finish. This is covered in thick paint.

Seems it would bludgeon the grass rather than cut it. I know it's a rotary, but does the edge finish sound right? 

Many thanks

hortimech
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No, Whilst the angle sounds

No, Whilst the angle sounds about right (40 degrees is a bit steep), it should be a sharp edge, the thickness of the paint is a bit of a red herring, it may or may not be right.

Of course we could have a philosophical discuss here about wether the machine is a genuine Mountfield or not. If it is one of the older 'M' series, then it is, but if it is of more recent manufacture, then is it a Mountfield at all or just a 'badge engineered' product ? 

Also to muddy the waters further, was the 18 inch Ransomes rotary really a Mountfield ?

wristpin
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Thirty degrees is about right

Thirty degrees is about right for a domestic mower. One of my reference books says 30 degrees with a 1mm margin .  If it is a genuine blade it may even have Mountfield stamped into it but should at least have a part number but that may be a Stiga number as both brands ( and several others) are owned by GGP.  I recently bought several parts for a Hayter rotary and they all came in blue and yellow bags or sleeves marked Stiga as was the belt itself. The reason, Hayter didn’t make their smaller rotaries but had Stiga paint some of theirs dark green and badged Hayter.

Going back to the thick paint , I’ve known of cases where blades secured with just a centre bolt and a Belleville washer have worked loose due to the thick paint breaking down in use.  An American manufacturer started coating its blades in a smart “ epoxy like” grey finish; only to issue an urgent service bulletin telling us to remove all traces around the fixing bolt holes.

Chris G
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Interesting, thanks for the

Interesting, thanks for the replies.

The mower itself is an SP474 Mountfield and thinking about it, have had it from new more like 12 years + so not sure if its a genuine Mountfield. It has been very good though.

This is where I got the 40 degrees from -> https://greenstripe.net/blog/post/6/how-to-sharpen-rotary-mower-blades Given what you are saying it does sound steep, the step in an axe is about 35 for splitting logs I believe..

Might be hard to judge from the pics but the painted edge is well over 0.5mm more like 1mm in places. And painted all over in a nice thick grey epoxy like finish!

I am loathed to send it back so I guess I need to strip back the paint from the edges and mounting boss area and see what sort of edge I have?

 

wristpin
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Not sure why you are

Not sure why you are measuring the blade there - it’s only the last couple of inches at each end that do the cutting. 

Rotary mowers, sharp or blunt are a fairly crude way of cutting grass  but a sharp blade will  bruise the grass less and the lawn will look fresh longer.  

Edit  Looks like the part number for a genuine Mountfield blade is 181004365/3

hillsider
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As wristpin suggests it is

As wristpin suggests it is only the ends of the blade that do the cutting, on the subject of the degree of sharpness of the cutting edge I have always understood that tthe finished blade should not be razor sharp but to have a visible flat on the edge of the blade. The reason being that a blade sharpened to a knife edge will become damaged more quickly.

Having made the above statement and just to confuse things even further I also am aware that for a one of job in dificult grass a fully sharpened blade can be helpful. 

Chris G
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Cheers both, reason I was

Cheers both, reason I was measuring there was just for the pic - its indicative of all over edge thickness!

Thanks for the part number also, confirms what is stamped on the blade.

Given it a mild sharp edge at the same angle on the linisher - tricky with all the angles but good to go for a rotary.