Is one layer of 3/4 ply sufficient or should I add a 2nd layer of 3/4 MDF
How thick a table top to use dogs.
- Thread starter tomcoleman
- Start date
To your specific ?--one layer of 3/4 ply is sufficient until you put 300#+ of pressure on the dog. FYI one layer of 3/4 MDF is not enough. The holes will hog out over time because MDF is not as strong as plywood.
In general, only 3/4" thick of any material is not enough. The top will flex with normal use pressure. Try to figure out how to screw the MDF to the plywood from the underside. You don't want the metal screw heads anywhere close to the working surface. This way you can replace the MDF working surface when it gets gouged and scratched up or it gets wet. If you glue it you can't replace it.
All of that leads to this: better workbench tops are made of solid wood for a reason. Solid wood can be resurfaced and made like new; man made materials can't. This includes plywood. The primary reason plywood and MDF are used in production and manufacturing of products is cost savings. Look at Black & Decker workmate benches, then get the top wet and try to fix it.
In general, only 3/4" thick of any material is not enough. The top will flex with normal use pressure. Try to figure out how to screw the MDF to the plywood from the underside. You don't want the metal screw heads anywhere close to the working surface. This way you can replace the MDF working surface when it gets gouged and scratched up or it gets wet. If you glue it you can't replace it.
All of that leads to this: better workbench tops are made of solid wood for a reason. Solid wood can be resurfaced and made like new; man made materials can't. This includes plywood. The primary reason plywood and MDF are used in production and manufacturing of products is cost savings. Look at Black & Decker workmate benches, then get the top wet and try to fix it.
Depends on the dog. The clamp dogs can use 3/4 plywood but they won’t hold much. The plastic planing dogs can be used in 3/4 plywood because there is not much pressure on them. Steel or cast iron bench hook dogs need solid wood 2.5 to 3.5 inches thick.
My top is made of 30mm Valchromat (HDF). It seems plenty strong.
Just dogs, a single 5/8 is fine. My old Workmate has 5/8 ply as tops and plastic dogs. Works fine for 25+ years. OK, it is an old one with birch ply, not MDF. I guess it depends on the style of dog. I have cylinders about 3 inches long with no flange so their height is adjustable. They need a thicker top for them to work so the spring contacts the side. I have some aluminum ones with a 3/8 top button so they would work fine in a 5/8 top. Then a pile of various plastic ones, all would work in a 5/8th.
How stable depends on the hole size. As I have discovered, 3/4, 19, 20, 21, 22mm depending on brand. And then there are various DIY round and square dogs which are up to your imagination.
Hold-fasts and other clamp down devices are another story. My outfeed had double 5/8 MDF and works fine with the lever and screw hold-downs, but a hold-fast would tear it apart. My heavy bench is 5 inches SYP and holdfasts work quite well. Yea, overkill but it does not wiggle.
How stable depends on the hole size. As I have discovered, 3/4, 19, 20, 21, 22mm depending on brand. And then there are various DIY round and square dogs which are up to your imagination.
Hold-fasts and other clamp down devices are another story. My outfeed had double 5/8 MDF and works fine with the lever and screw hold-downs, but a hold-fast would tear it apart. My heavy bench is 5 inches SYP and holdfasts work quite well. Yea, overkill but it does not wiggle.
Just glue up some hardwood strips about 1" thick by 3" wide under the dog hole rows and bore them out with a Forstner bit. If the dog holes start to wobble, use a hole saw to cut them out larger and do a hardwood insert, unless you are able to jut replace the entire top.
I used a bench with a top composed of 3 layers of 3/4" cabinet-grade birch plywood for at least 15 years. I regularly used cast iron holdfasts and self-made bench dogs and never noticed any issues with gripping power or chipping.
3/4" MDF will work just fine for dogs. I have two bench tops I've used for at least 15 years and the only thing I have to do is ream the holes out every now and then. It's not any thing special just Lowes garden variety MDF. I use 20 mm dogs and one top has poly on it. If you intend to use a holdfast you'll probably need something thicker.
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