How to repair damaged lawnmower drive

[Andrew DockeryParticipant @andrewdockery72578]

Hello all, I am hoping you clever engineers can help me with the right method and tooling for repairing the drive for my lawnmower blade. The bolt holding it together came loose allowing the two parts to logger and wear. The drive shaft has two flats machined on it and the driven part is a rectangle to match, see photos.

I will attempt to weld replacement metal on to both parts, my question concerns how to machine the parts and in what order with which grade of tooling. I have not got a surface grinder so I am thinking mill the flats on the shaft first but I do not know if my carbide cutters will tackle the weld material or not. As for trying to make a nice accurate rectangle in the driven part I can only think of using a die grinder very carefully with a small cutter.

I look forward to your suggestions, thanks Andy.

[Andrew DockeryParticipant @andrewdockery72578]

[john halfpennyParticipant @johnhalfpenny52803]

Mig and file. Once it is a tight fit your problem is solved.

[Simon Williams 3Participant @simonwilliams3]

Blade shouldn't be hard. Tough as old boots, yes, but not hard as it mustn't shatter. So – as John says – butter a bit of mig in the hole, and file to shape. Nice variation on the apprentice exercise of filing an internal and external hexagon.

The drive piece with two flats is likely mild steel anyway. Butter and file. Don't make the flats too wide. If you can machine them and get them symmetrical and central so much the better. Carbide tooling is probably overkill.

Do let us know how you get on.

[Andrew DockeryParticipant @andrewdockery72578]

Thanks for the replies. I have mig welded a lot of car bodies and always thought the weld would be to hard and damage the file. I will give it a go.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Andrew Dockery on 04/07/2021 18:46:48:

Thanks for the replies. I have mig welded a lot of car bodies and always thought the weld would be to hard and damage the file. I will give it a go.

.

The local car mechanic closed some drilled holes in heavy gauge steel tube for me, by MiG welding … it was no problem at all to dress them down smooth with a file.

MichaelG.

[noel shelleyParticipant @noelshelley55608]

As all above have said, MIG and File ! Noel

[JohnFParticipant @johnf59703]

Its unlikely any local hardening would occur on car bodywork but it is possible it may happen on the mower blade – higher carbon content ! If this should happen you can resolve it by local heating with a propane torch, best to clean the area so its bright and heat until blue, cool as slow as possible. Not a full anneal or normalise but sufficient to allow filing etc.

John

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