Sorry for coming to the party so late!
A lightweight hammer is better than a heavy one. 6-10 oz ballpein hammers work just fine. Make sure to polish the main face of the hammer. It's mostly a one time deal--unless one's child uses it for hammering nails...
The face of the hammer just needs a slight curve--very slight. Too much causes too big a dimple. Too little and one has a larger risk of creasing the saw plate from the edge of the face of the hammer.
Remove the handle from the saw. That way you can ensure you get all the way back under where the handle is bolted and that the plate isn't the cause of any wonky wave in the steel. There's another reason...below.
Mark the saw plate down the center on both sides every 2" or 3". 2" for a really loose blade. 3" for uniformity. I use what we call lumber crayons, some use chalk. Make sure the marks are in the "same" location on each side. They need to be reasonably close, not engineer close.
I begin at the heel. I start at the heel to get a feel for the steel--some are softer than others. 2-3 lightish taps per mark, do one mark, flip the saw and same number of taps at the corresponding mark.
You can always go over the saw once or twice more. So don't over do it.
An anvil is very handy. A piece of long railroad track even better. Mine is about 24" in length. I also have a piece of milder steel 1.25" thick I use sometimes. Point is the density is very good. You can--and I have--use a log section of a very dense species of wood. Don't ask me why, but at that point I use a light brass hammer. I have used a caulking mallet on the wood block as well. The technique to strike the saw plate is a little different depending on whether a steel or wood "anvil" is used. But the "strength" of the blow is roughly equal (a bit lighter on the wood block). Using wood takes 2-3 more passes, but there's also a greater risk of damaging the saw plate if you use too heavy a hammer or hit too hard.
As a general note. There's a difference between a "loose" blade and a blade which has a slight arc along its length. With a slight arc, you can actually bend the saw back on itself towards the convex side (if the blade curves left, bend to the opposite side). Take a bit of getting use to. Once the saw is fairly even along its length, retensioning is easier as you are not simultaneously removing bend and making the saw plate stiffer.
General note two...you can also over do the tensioning. A couple things will or may happen. The saw plate will have little "natural" flex to it--to stiff. Another possibility is you will introduce twist over the saw plate. Check the "flex" of the saw before tensioning several times to see and feel the present state. A loose saw will bend quite easily. One with tension takes more effort. It's good to have a benchmark around. A saw which you know is "proper."
So test cut after the first pass (assuming the blade is straight at that point). If the saw rattles in the cut during the back stroke, make sure there is sufficient set to the saw for the species being cut. Some woods are grabby, some shear more cleanly. If the saw goes down and back in the cut smoothly, can be held flat out in front of you and "droops" fairly equally (nice arc) as each side of the saw is flipped, a single finger through the hand hold with the blade hanging down and appears straight, you are probably good to go.
Well off to the shop.
Take care, Mike
