Workbench Top Question

[cswann]

Hi. I am building a workbench using (more or less) Ian Kirby's design. Assuming it works, I have attached a picture of his workbench. The less part is that I am making the top out of 3 pieces of MDF. The MDF will be 23 X 59 (small space...), and I am planning to use 5/4 hard maple edging around the MDF. The original design does not use long rails along the top so the top is supported by the two top end rails. After deciding on the MDF top, I started wondering whether I need to worry about the MDF sagging. Do you think the hard maple edging will provide enough strength to prevent sagging, or should I be thinking about adding some additional structure? I would probably continue with the basic design and add an additional short rail midway on the long side if that makes sense.

Also, how would you attach the maple edging to the MDF?

Thanks much for any help.

Best,

Chris

[Mike Davis]

Sorry, I can't help. I never use mdf, blame it on allergies or religion or practical experience.

[NCWood]

Hi Chris,

I made my workbench top from two full layers of MDF and two layers around the perimeter about 6" wide. This sits on a frame just inside the edge. I used white oak for my perimeter boards all around. I made it about 12 years ago and to this day I can't find any sag at all. I used the extra perimeter boards since that is where the bench dog holes are and I wanted more support where the holes were. I glued and screwed the oak edging to the MDF and it is still very tight with no apparent gaps.

Hope this helps,

Gary

[NC_Horn]

Perhaps a long rail running between the end rails. I initially thought of adding 2 long rails between the post but with 3 layers of MDF, would think you wouldn't need two rails. The one rail in the center also leaves the area closer to the edges open for bench dog holes if you chose and also leaves plenty of room for clamps when using for glue-ups. On all of the tops I have made, I have just glued the edging to the MDF. If you are trying to get a little extra strength transferred to the MDF, perhaps biscuits to help keep things in alignment? Never used biscuits in mdf in this manner but would think it would help slightly.

My 2 cents.

Duane

[cpw]

Hi. I am building a workbench using (more or less) Ian Kirby's design. Assuming it works, I have attached a picture of his workbench. The less part is that I am making the top out of 3 pieces of MDF. The MDF will be 23 X 59 (small space...), and I am planning to use 5/4 hard maple edging around the MDF. The original design does not use long rails along the top so the top is supported by the two top end rails. After deciding on the MDF top, I started wondering whether I need to worry about the MDF sagging. Do you think the hard maple edging will provide enough strength to prevent sagging, or should I be thinking about adding some additional structure? I would probably continue with the basic design and add an additional short rail midway on the long side if that makes sense.

Sounds like a job for... the sagulator! Man made sheet goods are at the bottom of the dropdown list.

I have seen similar designs described in books where they used a combination of MDF and quality plywood to minimize sag. I cannot remember if it was in Schleining or Landis, but I think one of them covered it.

The two main advantages to MDF are weight (for overall stability) and flatness, but if your shop is prone to humidity you may lose your flatness to sagging or warping rather quickly if you don't do something to stabilize it like mating it to plywood. Price and time and ease are other factors. Using MDF you can built up a pretty thick top very fast with basic shop tools for less than $100. Laminating a top from lumber is a lot more time and work (and usually more $$).

I hope this helps you in your design.

Cheers,
Charles

[cswann]

Thanks for all of the comments. I did not know of the Sagulator, and I am glad to know about that for the future.

MDF was chosen for the cost and time saving as well as weight (and flatness). I had the pieces cut for me so that I wouldn't have to cut it myself, but friends needed some shelves for a TV, DVD player, etc and the scrap MDF was just right so I ended up cutting it to size and adding dados for shelves. Needless to say, lots of dust.

For some reason I had not considered a long rail down the middle of the top. I think that would do the trick and do it more simply than anything I was thinking about. It also leaves the bottom open which is useful since I am thinking about adding storage down the road.

I think I am good though more ideas are always welcome.

[wormil]

Kirby's bench uses the top as structural support but with an MDF top I would add aprons on the long sides to prevent sagging.

[merrill77]

I would add stretchers on each side to support the top. I'd put them 6" in from the edges, rather than an apron, to allow easier clamping along the sides.

[wormil]

What's the difference between an apron and a stretcher?

[merrill77]

Well, now that I've said it, I'm not sure there is technically a difference without looking for a woodworking dictionary. But the way I see the terms used most frequently, an apron is right at the edge of the surface. Stretchers can be anywhere.

[wormil]

I think they are the same thing just the names refer to the location, an apron also supports the top while stretchers do not but I could be entirely wrong.

Back on topic, I may have posted this before but this is a bench I've considered building... it's kinda Ian Kirby with some traditional features added in. I have the original magazine and they have an alternate top made from 3 sheets of 3/4 ply with hardwood edging glued on. I've never tried gluing edging to mdf but it should work although I'd use extra glue since mdf is a sponge.

[RonJ103]

... an apron also supports the top while stretchers do not ...

That is my understanding as well.

[Jeff]

Interesting points about aprons vs. stretchers. Here's my take whether it's "correct" nomenclature or not.

Apron: Runs around the perimeter of a top, beneath it, and it may be near the edge or inset further. Yes, it adds vertical support and ties the corners together.

Stretcher 1: A jack of all trades IMHO. In the original post pic the lower horizontal stretchers connect all 4 legs and prevent racking of the structure. No immediate vertical support provided.

Stretcher 2: This one is topside and framed by the apron. It provides support and prevents vertical sagging of the top in the center.



As drawn it'll provide a 3" overhang all around for the author's 59" x 23" MDF top.

[cswann]

Very interesting conversation.

I'm now confused about definitions. As defined above, I think I am using edging rather than an apron or stretcher. My current plan is to use 5/4 hard maple edging around the perimeter of the top. It will be glued, and it may be screwed as well. (Thoughts on that are welcome.) Was thinking of mitering the corners and reinforcing with splines but I am not sure how to cut the grooves for the spline (haven't thought much about this or googled so I apologize if it is obvious).

My *assumption* is that the 5/4 edging (2 1/4" or 2 1/2" if I add 1/4" hardboard) will keep things flat over the relatively short span (don't have the measurement handy).

In hindsight, I wish I had asked this question before I bought material and started and frankly I kind of wish I had just gone ahead and made the top out of Hard Maple. But, this is a learning experience and I already know more when I started.

Best,

Chris

[Mike Davis]

and frankly I kind of wish I had just gone ahead and made the top out of Hard Maple. But, this is a learning experience and I already know more than when I started.

Best,

Chris

Chris,

You can always go back and make a solid maple top later. After you have used this bench you may find other things you want to change too. Think about that when you attach the top, you may want an easy way to take it off later.