How to Patch a Rusted Lawn Mower Deck





Introduction: How to Patch a Rusted Lawn Mower Deck

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Tutorial on how to repair a rusted lawn mower deck. This lawn mower deck was removed from a lawn tractor, but this same procedure can be applied to any form of rust repair on sheet metal. I wasn’t able to find a used replacement deck and this was also a great way to save some money. For this I used a fluxcore mig welder, but a gas shielded mig welder can also be used.

Tools/Supplies Needed:

  • concrete blocks
  • wood blocks
  • welding gloves
  • welding coat
  • file
  • sheet metal welder
  • grinder
  • grinder cutting disc
  • grinder flap wheel
  • safety glasses
  • welding shield
  • fluxcore mig welder
  • adjustable wrench
  • ball-peen hammer
  • locking pliers
  • paint marker/caulk/marker
  • primer
  • paint
  • wire brush
  • chipping hammer

Step 1:

Unfortunately I do not have photos going back to what I started with. I originally roughed out the area by cleaning off the existing paint and rust to determine the extend of the rust. For that I used the grinder with a flap wheel which removes the paint fast and efficiently, while minimizing damage to the existing surface. The belt cover was removed to get full access of the damaged area.

Next I picked the correct gage of metal required for the repair. This can be purchased at a metal supplier, automotive parts supplier, or hardware store. I took rough measurements of the material that was required, then began to cut it to size. For now it was just a rough layout, the exact size can be finalized after. Using a mix of concrete blocks for weight, wood blocks to help achieve a smooth bend, a hammer, and adjustable wrench I formed the main bent from the horizontal to vertical portion. During the bending process I made sure the metal I was bending matched the contour.

Once satisfied with the main bend, the sheet metal was cut into two sections which I found was the easiest to match the multiple angles of the deck. I started with the more complicated piece first, using the grinder with a cutting disc to make shallow “V” cuts on the horizontal portion. This will allow for a smooth curve while keeping one solid piece of metal.

The piece was then slowly formed using the block of wood and a hammer, matching the curvature of the deck. Some material was required to be removed from the “V” cuts to help achieve a tighter curve.

Step 2:

Once the curved piece was done, I finalized it’s size. Then draw an outline using a marker on the deck and cut out the damaged area using the grinder and a cutting disc. Cut the hole slightly smaller so you do not remove too much material as it’s harder to add it back afterwards. Slowly grind the edges to fit and make any minor bending adjustments as needed.

For the next piece, it was cut to shape, again making an outline and cutting the damaged sheet metal from the deck. This too was fitted by hand, making any minor adjustments to the size and curvature. For small adjustments, use a file.

After the pieces have been fitted, use the flap wheel on the grinder to clean up the metal for welding. Any rust, paint, or oil must be removed to prevent impurities in the weld and allow for a strong bond.

Step 3:

Wear proper safety equipment when welding such as welding gloves, welding coat, and a welding shield. For this I am using a fluxcore mig welder which does not require a gas shield, can be easily operated from a 120v receptacle, and isn’t overly expensive to purchase. Set the welder’s heat range and wire feed, you may need to experiment on a scrap piece of metal to determine the best settings. Welders also have a quick reference guide for heat range settings based on the gage of steel you are working with.

Clamp the pieces into place using locking pliers, c-clamps, or magnets. This will prevent the pieces from jumping or falling out of place.

Tack weld the pieces into place, I started with the corners first and then eventually placed the tacks closer together. The tacks will hold the pieces into place and minimize warpage as it’s only short bursts of heat. Even when the short welding beads are ran, these tacks will keep everything aligned.

Step 4:

Run short one inch beads to keep the heat down and prevent warpage, this is especially a problem with thinner gage steel. Warpage is the metal expanding and contracting from the heat, in the end causing waves in the surface. Run one bead, then start another bead at least a couple inches away so the other area can cool down. Considering we are working with a fluxcore mig welder, there will be slag so it needs to be removed by using a chipping hammer and wire brush. If the slag isn’t removed, it can push impurities into the welds.

Step 5:

When all the welding has been finished, you can either leave the beads as is or for a cleaner finish, grind them smooth using a flap wheel on a grinder. Remove all the high spots and smoothen out the surface. If you find a pocket or seam, run a small bead and grind again smooth.

Step 6:

Drill any mounting holes as required. To apply a final finish, give the freshly repaired area a sand, along with the rest of the deck removing flaking paint or surface rust. Apply a primer, then a paint of your choice. I used a brush on farm implement paint, with a low gloss black finish. Farm implement paint can be purchase at a heavy equipment or farm supplier, it’s easy to apply and very durable compared to some other paints.

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    37 Discussions


    5 months ago

    This is noteworthy in my view because of the craftsmanship you demonstrated in this instructable and the justifiable pride you have in the end result. No hot glue duct tape or tie wraps that seem so prevalent in some areas.

    Nicely done. I've always made the mistake of running a bead on thin metal and having it blow through. Next time I am going with your approach of several tack welds before running short beads.

    Nice instructable.

    6 replies

    Thank you :) Are you using a fluxcore as well? You may also be able to use a thinner wire, if I remember correctly fluxcore wire comes in 0.030" and 0.035". The thinner wire will burn up quicker, whereas the thicker wire will concentrate more heat on the area you're welding. Also when welding, work from top to bottom as heat rises.

    I've never used flux core.
    I use .035 and C25 Mix.
    Yes definitely will give that a go.

    You can go with even thinner wire yet if you want, but you may need to change the drive wheels in the welder. The flux core wire, needs room for the flux which is why it's thicker.

    Sometimes you can still blow thru; in that case, just continue to make essentially small welds - like a tack weld, but with a bit more penetration.

    Jump them around, again to keep the heat from building up in any one area.

    Keep doing this all over the seam, as "randomly" and spaced as possible, until the entire seam is filled in. Then go back and grind with the flap wheel. Fill in any voids or valleys as needed and re-grind.

    Doing this is a test of patience, it is not fast, and very tedious. But for very thin sheet metal (thinner than a mower deck, for instance), it is almost the only way you can do it short of a TIG.

    Awesome to hear and thank you so much for the support :) I really appreciate it!

    Wow! That's an incredible difference! ( a whole lot better than duct tape and some diet coke cans! :)

    1 reply

    Wow. That's some *really* impressive work!! I wanted to do this to my riding mower deck to eliminate the 'grass chute' that sticks out and convert it into a nice mulching mower. However, I do not seem to possess your excellent metal bending and welding skills. Haha. Mine did not turn out quite so hot. So, while this is a great Instructable, I would say there is a certain level of skill required to do this. =)

    1 reply

    Thank you for the kind words and feedback :) Yep, I've definitely worked with metal forming in the past. By no means a professional, just a hobbyist.

    I have to say that's an impressive job you did with a small 120V flux-core welder; your beads are about as perfect as one can get with such a machine. And your skill at forming the metal was spot-on.

    This was a great instructable that shows what can be done with a bit of prep and a lot of patience.

    I know from experience that what you did here wasn't something that took 30 minutes - this kind of job requires planning, thought, trial, error, fitment, grinding, pounding, sometimes a bit of cussing, a few beer breaks in the shade - but when done (likely more than a few hours later) - it's all worth it; that deck looks excellent.

    2 replies

    Thank you so much for the kind words and feedback! I would have to say this probably took me about 6hrs. I didn't really keep track unfortunately, it was just something I did in my spare time.

    Total agree. Grat to the lawnmover healer.


    7 months ago

    I did this sort of repairs for 40+ years and have amassed a fair amount of tooling but had forgotten how daunting these problems are for some. You did a very nice job in the easiest way hopefully inspiring others to 'have a go'.

    Thumbs up!