Dog Holes in MDF

[Dan Case LR]

I'm about to build a bench. It needs to be economical and practical, and to the degree possible use materials I already have on hand--like that stack of 3/4 MDF (sheets ripped in half the long way left over from a big countertop job).

I'm thinking about an MDF bench top, but the one thing that makes me hesitate is dog holes. It doesn't take much imagination to see round holes turning oblong and crumbling. I need to do something beyond just holes in MDF.

One thought is to inset a couple of strips of hardwood in the top, where the dog holes go. That seems like a good idea, but the only hardwood I have on hand is a little cherry that I'm NOT using on a benchtop. :)

I was thinking about the possibility of lining the dogholes with something like PVC pipe or EMT conduit to reinforce them. Has anyone seen that done? Any other ideas?

Thanks!

D.

[Van Huskey]

No need to be paranoid, MDF is fine without anything else. Get FWW's latest "Tools and Shops" Bob Van Dyke has his plans for the bench he uses in his school, the top is actually a sheet of MDF with two sheets of PARTICLE BOARD under it and they have stood up to student abuse for over 10 years.

PS if you line the holes items that require friction like hold fasts probably won't hold properly.

[Prashun Patel]

Instead of lining them with a tube, I would drill 1 1/4" holes in the MDF, and glue or epoxy in a hardwood dowel. Oak ones from HD are < $10 for a 36" piece. Then drill yr dog holes in these.

My mdf top has dog holes right in the MDF. They held ok for a couple years. However, the clamping load eventually has caused the holes to elongate a little. It still holds fine, but causes the dogs to lean a little away from the vice under some clamping loads. This has caused some pieces to slip up and off the dog. It's slight, so it only happens on things that are awkwardly shaped to begin with. I keep wanting to do the dowel thing, but it's just a big pain now...

I imagine holdfasts would not hold very well in my or most mdf tops.

[Jerome Hanby]

Instead of lining them with a tube, I would drill 1 1/4" holes in the MDF, and glue or epoxy in a hardwood dowel. Oak ones from HD are < $10 for a 36" piece. Then drill yr dog holes in these.

My mdf top has dog holes right in the MDF. They held ok for a couple years. However, the clamping load eventually has caused the holes to elongate a little. It still holds fine, but causes the dogs to lean a little away from the vice under some clamping loads. This has caused some pieces to slip up and off the dog. It's slight, so it only happens on things that are awkwardly shaped to begin with. I keep wanting to do the dowel thing, but it's just a big pain now...

I imagine holdfasts would not hold very well in my or most mdf tops.

Variation on the same theme, you could glue in a strip of hardwood (or several if you want multiple rows of dog holes) and drill the holes in that. I haven't tried it, but I think Prashun is right about the holes in MDF. If you do go that route, I'd forgo the use of holdfasts and get some of those plastic dogs like a workmate uses.

[glenn bradley]

The dogs on this MDF bench have been in service almost daily since May of 2007. Just MDF and BLO.

[Larry Frank]

One thing that you could try is to coat/soak the holes with super glue or thinned down polyurethane. This will be absorbed and make the material very hard.

I did this with my bench top but I do not use the bench dogs that you hammer in. I use the holes as stops. Many of my holes have a hardwood bottom that is threaded for a 3/4" wood thread and put wood threaded rods in them.

[Tim Janssen]

I built my bench in 2000, 3 layers of 3/4" MDF plus a sacrificial layer of 1/4" hardboard. Never had any problems with the dogholes.
The picture shows some of my homemade dogs
http://i129.photobucket.com/albums/p209/timwillift/Pic1166.jpg
Cheers,

Tim

[Thomas Canfield]

The suggestion about using super glue / CA to harden the holes should help a lot. I have used CA to harden the threads in some internal threaded jam chucks that I make for my lathe and it really helps. I do run the threader a second time after applying the CA to the original threads, but do not use the CA prior to threading. I have also used thin shellac. A second drilling will likely be needed since there can be some swelling of the MDF or fibers.

[Jerome Hanby]

Those look like exactly what you would need for MDF dogholes. I think metal ones would be a lot harder on them.


I built my bench in 2000, 3 layers of 3/4" MDF plus a sacrificial layer of 1/4" hardboard. Never had any problems with the dogholes.
The picture shows some of my homemade dogs
http://i129.photobucket.com/albums/p209/timwillift/Pic1166.jpg
Cheers,

Tim

[Larry Edgerton]

I use a lot of MDF for templates, and it is the subbases in my benches. I use holdfasts on my benches so I need the holes to be a bit tougher.

My solution is West System. I tape the bottom of the hole, pour in some epoxy and let it soak in a bit working it in with a brush, and when it starts to get warm I pull the tape and let the excess drain into a pan. It has been twenty years of beating on the holdfasts and the holes are still fine. I hardsurface my MDF templates with West, and the router bearings never make a mark and never swell.

Larry

[Marc Burt]

I built my bench in 2003 with 3 layers of MDF. My dog holes are still perfectly fine. I use the brass dogs from Lee Valley.

[Dan Case LR]

I use a lot of MDF for templates, and it is the subbases in my benches. I use holdfasts on my benches so I need the holes to be a bit tougher.

My solution is West System. I tape the bottom of the hole, pour in some epoxy and let it soak in a bit working it in with a brush, and when it starts to get warm I pull the tape and let the excess drain into a pan. It has been twenty years of beating on the holdfasts and the holes are still fine. I hardsurface my MDF templates with West, and the router bearings never make a mark and never swell.

Larry

Great idea, Larry. Which hardener did you use?

D.

[Larry Edgerton]

Usually 205 Dan, but for this purpose it really doesn't matter, run what you brung....

When you soak mdf in this manner and then cut it apart you will find that the West has sunk in about .25 inch and turned it into reinforced plastic. I have signs outside [MDF Letters]that I did this way and then painted that have been out there 20 years or so and are still going strong.

Larry

[Terry Hatfield]

I built my top with 3 layers of mdf and have never had an issue with the dog holes in 8 years. I edge banded with 1 1/2" white oak and covered the mdf with 1/4" white oak plain sawn ply to get that "traditional" look.

220225

[John Petsche]

like the ideas for homemade dogs.