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  1. #1
    Join Date
    May 2008
    Location
    Troy, MI
    Posts
    343

    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
    Bridgeport

  2. #2
    Join Date
    May 2008
    Location
    Troy, MI
    Posts
    343

    Default

    6. Picture 6 shows a drawing of the cross section of the bushing, casting and locking pin. In addition to the thread, I also used Loctite 680 on the entire OD of the bushing to retain it in the casting.

    7. Picture 7 shows the setup on my milling machine to bore out the casting to accept the bushing.

    8. Picture 8 shows the bored casting.

    9. Picture 9 shows inside view of the casting with the bushing assembly installed.

    10. Picture 10 shows outside view of the casting with the bushing assembly installed.

    This grinder has also worked fine after the repair.
    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
    Bridgeport

  3. #3
    Join Date
    Mar 2011
    Location
    st-eustache qc.canada
    Posts
    226

    Default

    Wow, a 100$ + job on a 20$ tool is bad investment but such a stubbornness releif....priceless...

    We're on the same page money isn't the object the thing will have to work again.

    good job. thank's for sharing.

  4. #4
    Join Date
    Aug 2004
    Location
    Milan Michigan
    Posts
    1,730

    Default

    Lowes carries a very nice Porter cable grinder for $ 39.00 ea. They are very user friendly, I prefer them over all of the high dollar grinders.

  5. #5
    Join Date
    Nov 2006
    Location
    Lake of the Ozarks MO
    Posts
    3,593

    Default

    Quote Originally Posted by Portable Welder View Post
    Lowes carries a very nice Porter cable grinder for $ 39.00 ea. They are very user friendly, I prefer them over all of the high dollar grinders.
    I have a couple of those

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  6. #6
    Join Date
    May 2008
    Location
    Troy, MI
    Posts
    343

    Default

    Quote Originally Posted by Portable Welder View Post
    Lowes carries a very nice Porter cable grinder for $ 39.00 ea. They are very user friendly, I prefer them over all of the high dollar grinders.
    Quote Originally Posted by FusionKing View Post
    I have a couple of those
    I think I will pick up a few.
    I like to mount different type grinding wheels on different grinders and change grinders as opposed to changing wheels, because it is quicker.
    Thanks for the tip and the endorsement.

    I will most likely still use my 11 amp variable speed Milwaukee for the heavy grinding.

    Don

    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
    Bridgeport

  7. #7
    Join Date
    Aug 2004
    Location
    Milan Michigan
    Posts
    1,730

    Default

    Don 52, That's what I do.
    One for grinding
    another for sanding
    the 3rd one has a cut off wheel and the fourth one has a wire wheel.

  8. #8

    Default

    Quote Originally Posted by Don52 View Post
    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.
    My kind of guy; you and I could surely swap stories for hours!

    I started buying HF 4 1/2" side grinders some years back when the American brand I had used for years off-shored their manufacturing to China and their quality went down. The local rep for that company heatedly denied that there was any difference, and that they had inspectors in China and that their quality was as good as ever. Well it d@mned-well was not!! When the "American" made-in-China grinder costs $95 and lasts only seven-eight months, and the openly-Chinese HF grinder costs $20 and lasts three months, I'm willing to buy HF, even though all HF stuff sounds like the bearings are bad right out of the box. Like you, I also have good grinders, and just use the HF ones for skut-work. The one good aspect, for guys like you and me, is that pretty soon you have a box with two or three dead HF grinders for parts. Well, the other good aspect is that if the HF stuff get stolen, you haven't lost much, and the thief hasn't gained much.

    If anybody else here is willing to lower his standards far enough to buy HF 4" or 4 1/2" sidegrinders, get the $20-25 version with the yellow or wine-colored housing. There is a cheaper grinder with a black housing (called "Workmaster," I think), and when they were on sale for ten bucks each I bought three of them, but the best one only lasted a couple of weeks, and one smoked its motor in the first half-hour. It's not always true that you get what you pay for (see that faux-American $95 grinder), but this time $30 for three sidegrinders was a lousy deal.

  9. #9
    Join Date
    Jun 2014
    Location
    Whittier, CA
    Posts
    97

    Default

    I haven't migrated to the electric grinders yet, I've always used air! I have numerous Dotco and Sioux air grinders/sanders and they don't leave my garage! They do like LOTS of air!
    Glen
    Miller Dynasty 200DX - Millermatic 350P - Hypertherm Powermax 45
    For Sale! - Hobart Handler 150 - Miller EconoTwin HF

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