How to fix cracked pot metal?
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  1. #1
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    Default How to fix cracked pot metal?

    Restoring an old Hammond Dustless grinder that had been damaged in the past. One of the light housings is cracked and I'm looking for suggestions for the repair. Its functional, but I would like to fix if possible.

    I have a TIG machine. Not sure if this is best or not, especially since the metal is thin and I'm still learning the art of TIG welding. Thought about JB weld or brazing...

    Any suggestions?

    gm.

    Click image for larger version.

    light.jpg

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    I would leave it damaged without trying to bring it back into shape. Make a support from 6061 that matches each side of the break as close as possible. Clamp into position and run tap drill though both the support and the part damaged. Tap through both the support and the part while still clamped. Clean the tapped areas with a cleaning solution that will remove all traces of contamination. Snug the machine screws in place while still clamped. Use JB Weld (not JB Kwik) and cover the intersecting seams of the part and support. Warm the JB Weld with a heat gun and let the JB Weld flow. Leave it alone for 24 hours and then remove clamps.

    You can place the support on whichever side is convenient. If on the outside and you have no interference, use a big support to gain surface area.

    If this part shown is the base, Attach it to a new base and gain support from it.

    If the device is an important tool, I would replicate the entire piece using CAD and exacting measurements to design a machinable replacement, then you can always make another. It will also fit like a glove to the device.

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    grinder.jpgboth-light-hoods.jpg

    Thanks for the reply.

    Here two more pictures showing an undamaged light hood as well as the complete grinder.

    I had thought of designing a complete hood, but I think the original can be repaired.

    Sounds like the JB will be the best option.

    gm

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    You should have posted last week I scraped 2 last week... cleaning out the shop...Phil

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    I've had success soldering zinc alloy castings with TIX solder. Works quite well if you use the proper flux.

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    I just picked it up last week. Just my luck lol!

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    I'd make a sheet of aluminum that closely fits on the inside, clean everything up and use some J.B.Weld to epoxy it. If the appearance bugs you, clean up the outside and follow with Bondo and paint.

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    Quote Originally Posted by Conrad Hoffman View Post
    I'd make a sheet of aluminum that closely fits on the inside, clean everything up and use some J.B.Weld to epoxy it. If the appearance bugs you, clean up the outside and follow with Bondo and paint.
    Yeah...I do get a little anal about the appearance. The John Deere green had to go.

    The cover on the left was missing also so I plan to make that side into a tool cutter/grinder. Going to fab an adjustable table with a miter for that side and use a flat diamond wheel. Should be a fun project and I need a tool grinder.

    Which leads to another question: I don't understand why commercial grinders, (like Baldors), have the table going around the back of the wheel as well as the front. Why would you ever want to grind on the back of the wheel where the rotation is moving up away from the table?

    gm

    grinder-diamond-wheel.jpg

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    Quote Originally Posted by gmoushon View Post
    Why would you ever want to grind on the back of the wheel where the rotation is moving up away from the table?
    Most of those grinders also run in both directions. It allows you to grind both sides of the tool at the same setting of the tilting table.

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    Quote Originally Posted by trevj View Post
    Most of those grinders also run in both directions. It allows you to grind both sides of the tool at the same setting of the tilting table.
    Thank you. That makes perfect sense.
    gm

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    Muggy Weld makes a good solder for this. I used it on some pot metal parts for an old wind-up Victrola record player with great success. Be very careful to bring the heat up slowly. TIG may or may not work, depends on the metal and composition. Most of the pot metal I've tried to TIG just falls out in a puddle. Sometimes it's fine. Thin pot metal stuff is about impossible to TIG. Might be able to get it with a pulsed TIG and a little higher amperage.

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    One thing that 'can' work with die cast parts, is to pack the part in casting sand and essentially re-cast the part, while welding it.

    The sand formed tight to the part supports the material and keeps it from falling out in a puddle while welding. Probably want to use greensand rather than petrobond.

    Seems like a lot to go through for the sake of a 'original' looking shield.

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    It may sound odd, but my go-to for repairing pot metal is dental acrylic. Powder + catalyst, I guess. It adheres very well to a porous surface like pot metal. You can paint it on or mix up a batch and pour it in place. Harder than a landlord's heart. You can thread it, grind it. I probably use the stuff every other day for small tasks where epoxy is too slow.

    You can find it at dental supply stores on ePay. Probably about $100 for two pounds of the powder and enough catalyst.

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    Instead of calling any white metal you haven't identified "pot" metal why not ID it and work from there? That piece has been around the block a few times. I would not blame the material. I would say it is as likely to be aluminum as zinc based die cast alloy.

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    muggy weld

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    Quote Originally Posted by gmoushon View Post
    both-light-hoods.jpg

    Sounds like the JB will be the best option.

    gm
    First choice:
    What MichaelP wrote. Don't trust JB Weld for strength. Trust it for filling and blending.
    Run a file on some scrap aluminium and mix the filings with some non-5min epoxy. Fill and sand to make shield 2 look like shield 1.

    Second choice:
    I would buy some aluminium and mill two new shields. My experience with JB Weld has not been good for holding parts together.
    Last edited by rons; 03-28-2020 at 01:00 AM.

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    A couple of tacks with MIG using aluminum wire should work just fine.
    I'd do it on the back surface. The front can be filled and painted if you desire a good look.

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    finished-grinder.jpg

    Finally got the grinder finished. Ended up simply soldering the crack then bondo and paint. Not sure what material the hood was made from but it melted almost as fast as the solder! Could literally melt through it with the soldering iron.

    Now I need to build the table.

    Question: Since its main use will be to sharpen carbide lathe tools, do you think its necessary that I put a water drip system on it?

    Thanks again for all the responses.
    gm


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