Workbench Construction Reinforcing Dog Holes.

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pollys13

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My workbench materials, I have a solid Beech worktop and had B&Q cut two 19mm MDF sheets to size to be laminated together and screwed into the Beech top.

In the plans after he had made it, in the comments section, he added,
" if I was to do this again, I'd not use MDF for the under layer. The original plans called for two layers of MDF, and I decided to use a layer of Ikea oak countertop over it. I thought, at the time, that MDF wouldn't be tough enough to hold up, over the long term, and it turned out I was right. The problem I encountered was with the holdfasts. These work with a "cantilever pinch", which depends for its holding strength on the pressure of the holdfast against opposite sides of the top and bottom of the hole.What happened, over time, is that the bottom of the hole crushed the MDF, resulting in a holdfast that wouldn't hold. See the first picture. So, I flipped the bench upside down (using the same block-and-tackle rig I'd used in building it, and then screwed some strips of hardboard into the bottom, covering the holes. After flipping it back on its feet, and redrilling the holes
through the hardboard, I had dog holes that would work with a holdfast. Hardboard is tougher than MDF, so this should last longer. And when it crushes, it'll be easy enough to replace.
Lesson learned? If you're going to use MDF for a workbench top, design it so that it has a sacrificial hardboard layer both on top and on bottom. "

I'm thinking I could screw and glue some suitable timber to the underside of the bench to avoid this problem? Perhaps complete boards, side to side or to reduce cost, squares places over the dog holes.
What species of timber would be suitable for this job?
As ever any help and advice, much appreciated.
 
Not exactly a species, but on the evidence of your reading, I guess hardboard would work!

However, and to be a bit more helpful, I've used holdfasts for years on my bench, and the current top is made of ordinary studding grade softwood. The holdfasts work just fine.

So overall, I don't think it matters - just use whatever you have to hand. I'd use a single strip, fix it, then deepen the existing holes through it from above, so the new holes line up perfectly.
 
Not all users of MDF worktops have had the same issue with excessive wear using holdfasts. The specific holdfast, the amount of play in the holes and not least the quality of the MDF must all play a part. I'm sure you can take it for granted your MDF is at the low end of the quality scale given it's from B&Q though!

pollys13":337t4mqp said:
What species of timber would be suitable for this job?
Something tougher than MDF. So presumably that would mean anything :mrgreen:
 
I had 18mm birch ply on top of 3" redwood on my first bench. I removed after few years and it was a big improvement - basically anything involving hammering such as chopping mortices felt more dead solid. Laminations can make a top springy, which is the last thing you want.
Dogs and holes are best square as there is a larger surface area resisting pressure, as compared to round ones. Square ones don't seem to come loose and last forever. Mine about 1" square with a hardwood dog. I've only got one. Making a square hole is harder than drilling but we are woodworkers, aren't we!
 
Having had several other peoples views. I think the best course of action is forget about the MDF and get another Beech worktop to join to the other one. What would be the best method to secure two solid Beech worktops together?
 
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