How much do holes in metal shrink when it is galvanized

You can make watertight trays from flat sheet metal without soldering or riviting.

Take a sheet of metal whose

• length is the length of the finished tray plus two time the height of the sides;
• width is the width of the finished tray plus two time the height of the sides.

Fold the sheet so it ends up looking like this:

You can fold up one side at a time using a piece of wood (maybe 1x2), a bit shorter than the length of the side you are working on, as a bending edge.

Work around the piece, clockwise or counterclockwise.

You will have to work the angle fold in the corners as you move to each successive side. The angle corners will point outward initially. Then you bend them inward toward the short end.

All edges will end up at the height of the sides with no seams. The easiest kind of waterproof.

Normally gym equipment is powder-coated. in your picture, they have used an electrostatic powder coating process and finished with a sort of hammertone finish..

IMO- your options are as follows:

• Stainless steel is the best metal in terms of durability. it will never rust, however, its more expensive and is slightly harder to drill/bend. I would recommend pricing the bench with Stainless, then you can assess the viability. In terms of stainless, the most common stainless is 304, which is industry grade.. This grade is perfect... but will turn slightly yellow over time, if you are concerned with tarnished stainless you can go for the more expensive 316 stainless.

• Mild Steel is your other option, and obviously this will rust, so your rust prevention options are

  • Metal Oxide primer with enamel coating (paint)... which will not look as clean and will rust after a short time
  • Powder coating - you can imagine this as a sort of plastic coating which is baked onto the metal. in terms of finishes. this looks really neat, however the impact of the power bar on the bench will chip away the coating and it will show signs of rust after a while. not to mention that the coating is only on the outside of the tubing and the tubing will rust on the inside.

  • Chrome is another option, in which the metal is coated in chrome, this is also on the exterior of the metal, but I am not too certain if you will find a person who can chrome such a large item

  • Your last option (and most cost effective) is to galvanize the metal. this results in a zinc layer being coated on all surfaces of the metal (inside and outside) your second photo looks like it has been hot-dipped galvanized. the galvanizing will look really shiny at first, but will form a dulled coating and will last for many years.. Galvanizing comes in two types

    • Hot dipped , where your bench will be dropped into molten zinc and will come out with a thick layer of zinc covering all surfaces. with this your bench will last for 20+ years without rusting.
    • electrogalvanized, where the bench is dipped into a solution and a current creates a charge which attracts the zinc coating (this coating is a lot thinner so will not last as long), however the finish is a lot prettier. I would not recommend this in your case.

So to summarize, I would say your options are stainless steel, or hot-dipped galvanized steel. Both will be extremely durable but I like the look of stainless more

If you decide on Galvanized, I would also place some rubber strips in the areas where the power-bar lands on the bench, since the zinc coating will wear away there over time.