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Sizing A Channel Set Mounting

Angela shares her sizing tips

Have you ever experienced the nightmare of sizing down a channel set mounting that has already been set, with the channel running across the shank (see illustration 1)? If so, you may have also experienced the stones falling out or becoming loose. Though this problem does not exist with all channel set mountings, the following tips may help you avoid having to reset or replace a stone.


  1. Cut out the amount needed to size the ring down to required size at the bottom of the shank, leaving the shank open.
  2. Saw completely through the bottom bearing of the head (see illustration 1).
  3. Saw halfway through the top bearing.
  • You may need to bevel the bottom bearing depending on how many sizes the ring has to go down. This allows the shank to bend in from the top.
  • If the ring is solid (see illustration 2 & 3) saw two-thirds of the way through and slightly bevel the saw cut to allow for movement of the ring during the bending process.
  1. Now you can bend the shank in from the shoulders to fit flush. Solder the shank back together at the bottom, then fuse with torch or laser the relief cuts you sawed. The ring will appear slightly egg shaped, so you may not want to round it out completely.
  2. Finish the piece as you normally would. You may need to tighten stones, but the process will keep stones from falling out of their seats/ or breaking.

Another problem you may come across is sizing a ring up that has already been channel set. This creates a completely different problem. Sometimes when sizing up more than one size you may chip or break the stones.

This does not happen with all channel set mountings, but unfortunately it can happen, especially if the stones are close together or if they touch one another. A good example of this is the mounting shown below (see illustration 4). This particular ring needed to be sized from a size 10 to a size 12. All of the stones were touching one another.

Illustration 1

Illustration 2

Illustration 3

Illustration 4


  1. Saw the shank at the bottom, then saw a relief cut on the inside at the top of mounting (see illustration 4). Slide the ring onto a mandrel, pull the ring down the mandrel with your fingers to a size 11 ¼ being careful of stones. It is not a good idea to go up all at once. This can put too much pressure on the stones and cause stress on the mounting (see illustration 5).
  2. Use a piece of flat or square sizing stock twice the thickness of the shank, you will be hammering it up the rest of the way (see illustration 4). Place sizing stock flush against the opening of the shank, and try to get it flush on the inside of the shank.
  3. Solder your stock in place with hard solder. Let ring air cool. If the shank is not flush on the inside, you will need to remove the excess stock until the inside of the shank is flush. If the shank and stock are not close to being flush, the ring can pop open at the solder joint when hammering the ring up.
  4. Slide the ring onto the mandrel. Round it out slowly to avoid breaking stones. It is important you do not try to round out the top of ring flush with mandrel (see illustration 4). Once you have rounded the ring at the bottom, start hammering on sizing stock with a metal hammer until you have reached the size you need. When hammering up you will need to flip the ring on the mandrel to each side so your shank will stretch evenly. You may also want to leave the shank slightly oval if sizing up more than 1 ½ to 2 sizes. It will be much safer for the stones and place less stress on the mounting.
  5. Once you have reached the size you need, file excess metal off the sides and file top of plug even with shank. By now your plug has been hammered close to the thickness of the shank with a little filing on the outside. File evenly, then finish your ring as you normally would.

Illustration 4

Illustration 5

*It is important to note that increasing/decreasing the size will change the circumference and getting the ring completely round may not be an option.

Do you have any sizing tips? Tell us, in the comments section below.


Angela Busby

Former Stone Setting Model Maker Master / Trainer for Manufacturing

I've been with Stuller since 1984 • I studied opera • I know all the lyrics to every Elton John song • I met my husband at Stuller 31 years ago • My husband thinks I'm an alien • I am the 1st JA certified bench jeweler in the state of Louisiana • I love shoes • I love to laugh.