Medallion nut repair

Discussion in 'Saw Makers Forum' started by Dusty Shed Dweller, Jul 25, 2016.

  1. Dusty Shed Dweller

    Dusty Shed Dweller Most Valued Member

    Messages:
    120
    There are a couple of resources on the net outlining how to make simple split nuts but I thought I'd outline how to repair a medallion nut using basic workshop tools.

    We all know the scenario - you've found a very nice little saw at the flea market and after you get it home for a closer look at the superb medallion you flip it over and there is that sinking feeling when you see a hole on the reverse side where the split nut and shank should be.

    The first task is normally to drift out the remnants of the medallion nut with a small punch. A nail with a similar diameter and ground flat works adequately. If the medallion nut is a sand cast one they often have a small boss on the rear and you can use that to effect repair.

    1. The first thing is to get a scrap block of wood into which you drill a flat-bottomed hole the diameter and depth of the medallion disc. This is so you can hold the medallion without mangling it while you work on it.
    2. Remove the shank above the boss and file it flat. Use a sharp centre punch to mark the centre of the nut - be aware that the boss may not be centred to the head!.
    3. I used 3 mm brass rod and metric taps for this work because I had them at hand, they were similar in diameter to the existing shank and the fine metric thread was a bonus.

    I used a SHARP bit in a drill press to bore the requisite tapping hole in the boss (2.5 mm for M3) being careful not to bore through the face side of the medallion, so use the press' depth stop.

    Then place the tap in the chuck and tap the hole by turning the chuck BY HAND- this helps keep the tap straight. DO NOT turn the press on. Be gentle with the tap as the small ones are fragile. After this you have a medallion nut with an centred, M3 threaded hole in the back.

    4. Cut off about (2") 5 cm of 3 mm brass rod and thread one end with an M3 die. Thread it into the medallion and viola you have a nut with a new shank. I used solder to lock it all in place as it is more traditional but you could use epoxy or CA threadlocker etc.

    5. Work out the length of shank you need and cut the brass off a bit over long. Thread this with the relevant die. I leave the shank over long as the starter threads may get a little damaged during fitting and you will be filing the bolt/shank flush after fitting anyway.

    6. Use some scrap brass to make a replacement split nut. Start by drilling and tapping an M3 hole in the brass, then shape it using a hack saw and files. Don't make a round disc and then try to tap a hole in it.

    Using a drill press as a metal working lathe is extremely poor working practice and I advise against doing this but needless to say I managed to get a nice round nut chamfered nut with a centralised threaded hole. The "split" was cut using a hack saw and a fine file using the aforementioned medallion holder.

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    You now have a refurbished bolt and nut for fitting into the handle. The shank of split nuts are often damaged or cut through where they traverse the plate, especially if there is any movement in the handle so after fitting I insert a discrete little wedge of timber (frequently a piece of veneer is sufficient) between the rear of the blade mortise and the spine to take up any shrinkage and restrict handle movement.
     
    Batman3000 likes this.
  2. Underthedirt

    Underthedirt Most Valued Member

    Messages:
    221
    Hi Dusty,

    That is a very good tutorial & a great way to salvage the medallion once the shaft has broken off- an all to common issue with vintage saws, kudos for figuring out a solid way to fix that awful problem...:)

    Regards

    Mari