Adjustable reamers are really scraping devices. They scrape out small quantities of metal from holes. They are not as rigid as solid reamers and should only be used to take small cuts.

There are usually two types.  The 5 bladed reamer and the 6 bladed reamer. The 6 bladed can be measured to determine the hole size, 5s cannot.

To set the reamer up for he first cut, put the reamer into the hole and adjust it until it just begins to grip the hole. Then increase its size by ¼ of a turn of the collars. Always make sure that the top collar is tightened down. Make your first cut. Repeat this by increasing the size of the reamer by no more than ¼ of a turn of thee collars. Measure the hole frequently. Measuring the 6 bladed reamer gives you an idea and only an idea of the hole size.

GOLDEN RULES

1. NEVER turn the reamer BACKWARDS – can You break/chip a blade.
2. Never put more than ¼ turn on the collars, reamers are greedy beasts and can easily seize up. (Not nice)
3. If you get a jam loosen the blades and pull the reamer out and start again. Remember a jam will leave a number of ridges and these have to be cut away or you will get another jam.
4. Make certain that the collars are tight.
5. Clean the reamer after each pass.
6. If the reamers grips, STOP and ease/reduce the cut.
7. Do not push down on the reamer too hard or it will gripe or jam. Take it slow and easy
8. Measure the hole‘s diameter frequently.
9. On each turn try to stop in a different place.
10. Use oodles of cutting oil.

As I have very few metric reamers I use expanding reamers quite frequently.

Regards

Dick