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backlapping a rotary lawn mower

How to Set a Reel Lawn Mower Blade

This is going to be centered around sharpening my reel or cylinder mower blades.

If I was to say what is my number one thing with regards to the quality that I can see on my lawn it’s going to be a sharp blade and properly set bed knife.

This concept also applies to Rotary Motors having a sharp blade will produce a better cut on the grass blades, will help prevent bleeding and overall much improved visual appearance on the lawn.

If in any doubt follow at your own risk or use a professional sharpening service

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Setting Cassette Lawnmowers

So for this type of mower from Allett it comes with a cassette type system it acts like a chopping action against the bed knife as the real spins.

I’ve got quite a bit of debris built up over the mowing season and overall I think it is probably been at least 4 or 5 years without any maintenance work done on these blades.

There’s a lot of debris along the edge of the blade, it looks mostly like dry grass but it could also be some small burrs on there as well as on the bed knife there is a few chips perhaps from stone strikes or other material has been hit.

The blade and the cut quality has degraded from where it needs to be.

How to Set a Reel Lawn Mower Blade

Set a Lawn Mower Blade using the Paper Test

So how do we check the lawn mower real is cutting properly?

First of all I’m going to turn off the mower take out the spark plug that way there is no danger of the mower starting up when I maintaining it.

Now as the blade is spinning it’s acting as a chopping mechanism as it makes contact with the bed knife, so to adjust the height of the cylinder you can turn the 2 screws on the top and this will lower or raise the cylinder and in relation to the bed knife.

You need to be careful that the noise of the blade is not too loud as noise during operation will result in excessive wear, unpleasant use and a reduced quality cut.

The next step to test how close the blade is cutting is using the paper test to check this you can prepare some paper that is folded in half.

I made some samples from regular drawing paper cut into strips and used to test the effectiveness of the cut on the mower.

When using the paper test you want to check the blade is cutting along the full face of the cylinder which means on the left hand side the right hand side and across the middle.

On my mower it doesn’t quite cut on the right hand side without making excessive noise so I will try to make some adjustments and see if I can correct this problem by adjusting the screws on the mower cylinder.

On this unit you will need to remove the grass catcher box which you can do by pinching in the sides and pulling it out of the mower.

This will reveal the 2 settings screws which are both on almost ratchet mechanism and you can audibly here when you make a turn on the screw that it clicks as you change the height of the cylinder.

The ideal scenario is that blade is making a whispering noise but is also able to cut the paper across the left, the right hand and the centre of the blade.

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Sharpening the cylinder blade

If you are unable to achieve this your blade may need further maintenance and adjustments which leaves 2 further options.

Option number one is self maintenance using a lapping compound or grinding paste, I’ve linked this in the article above and you can apply the paste by spreading it on the blade using a paintbrush and a power tool to drive the real in reverse.

As the blade spins this will reproduce the edges as the blade rubs against the bed knife and the lapping paste will sharpen things up

Take care for your safety and wear the right PPE near the rotating blade.

Alternatively, you can send your mower off for professional maintenance to be re ground and re set up a grinding shop, I will leave a link to one of the shops I have used in the past to get your blades and cassettes serviced.

Using the self maintenance techniques called back lapping can be good for intermittent maintenance between the seasons and then sending the blade off to be professionally sharpened can be done more periodically in order to reset it back to the desired standard.

I have recently just produced a video on full lawn mower maintenance which you may enjoy to watch next see below for my YouTube channel and please leave me a comment if you have any questions

How to Service a Petrol Lawn Mower (Allett Cylinder)

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