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  1. #1
    Join Date
    May 2008
    Troy, MI

    Default Spindle Lock Repair for HF 4.5" Grinders

    I own a really nice variable speed Milwaukee 4-1/2" grinder and I love it. I use it for all of my heavy duty 4-1/2" grinding work.

    I have two Harbor Freight grinders and they have worked ok except for the spindle lock. I like to use the Harbor freight grinders for the lighter work such as the cut off disk, the wire brush or the flap wheel. I find it easier to grab a different grinder instead of changing the wheel. You might wonder why I didn't throw them out instead of fixing them:

    • First of all I took it as a challenge to fix them.
    • I also hate to throw something out that still had a lot of life left.
    • Last but not least, like most people that I know with mechanical ability, I can be stubborn.

    Back to my repair project:

    1. On the first grinder the tip of the locking pin broke off, but it was no big deal I turned a replacement pin on my lathe from a M6 socket head cap screw. The old and new pins can be seen on picture 1. My repair has worked fine ever since.

    2. On the second grinder the spindle lock failed by fracturing the casting as shown in picture 2.

    3. Once the spindle lock failed it allowed the pin to rotate which put excessive force on the plastic head of the pin which caused it to shatter.

    • A pin with the plastic head in place is in the bottom of picture 3
    • The pin that had the shattered head is in the middle
    • The top of the picture shows the M6 socket head cap screw that I turned to make a replacement pin

    4. As much as I like welding, I was afraid that the die cast gearbox might be an alloy that contained zinc, which would make it unweldable. Instead of welding I made an aluminum bushing to replace the damaged casting. An exploded view of the pin assembly with the new bushing is shown in picture 4.

    5. Picture 5 shows the same bushing assembly all together.
    Attached Images Attached Images

    Miller Thunderbolt
    Smith Oxyacetylene Torch
    Miller Dynasty 200DX
    Lincoln SP-250 MIG Welder
    Clausing/Coldchester 15" Lathe
    16" DuAll Saw
    15" Drill Press
    7" x 9" Swivel Head Horizontal Band Saw
    20 Ton Arbor Press
    Miller Spectrum 375 Plasma Torch

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