Drilling Dog Holes

[Mike Burke]

I am building a Rob Cosman bench with a 3" thick MDF top. I am getting closer to drilling Bench Dog Holes in it. I am going with 3/4" dog holes and will treat the top and hole openings with sealer of some kind to stiffen the MDF. I am going to make some kind of guide to get them straight. My question is :

What kind of bit would be good with MDF ?

My experience with MDF is it dulls tools and bits pretty quickly. Like cutting cardboard.

Any suggestions on a 3/4" bit for MDF ?

Thanks

[Paul F Franklin]

I used the Lee Valley HSS brad point bit and it worked well for me. Others use router bits in a plunge router, but that won't be easy in a 3" top.

One tip if you go with drilling. A bit that size is pretty aggressive and it's easy to get some tearout on the top surface. I found that rotating the bit slowly *in reverse* for a few revolutions with moderate pressure allows the knickers on the bit to score the top layer and that seemed to reduce tearout on the top.

[Jim Becker]

Start the holes with a Forstner bit or a router, but only go in up to about an inch. That gets you a clean hole that can also be a guide. Then use something more aggressive, such as a spade bit with wings (sharpen often) to complete the cuts.

[Ronald Blue]

Nothing to add except a CNC router would be perfect for it. What's the dimensions of it?

[Mike Burke]

Thanks for the suggestions
I am going to try a couple ways before I commit to the final process.
Top is 22x64 x 3" (4 layers of 3/4" mdf)

[Brian Holcombe]

I think it will wear out quickly, dogs are pretty hard on the material they are installed into.

[Mike Monroe]

Pretty sure Rob used a plain twist drill bit, albeit a large one, and guide block to get the holes just right. He also rounded over the openings and coated the inside of the holes with super glue. - This is all from my memory of watching one of his videos some time ago.

[Dave Sabo]

This
https://www.leevalley.com/en-us/shop/tools/workshop/workbenches/benchtop-accessories/72602-dog-hole-bushings


with these
https://www.leevalley.com/en-us/shop/tools/power-tool-accessories/drill-bits/42247-hss-lipped-imperial-brad-point-drills?item=07J0248

[Carl Beckett]

I have a router table top that is MDF that I shellac'd. Quite surprised how well it has held up over the years. So if you were not making inserts around the holes, you might consider coating the inside with shellac. It soaks in and hardens the top surface of the MDF and provides some durability. In general though, I might try to sleeve it. Make hollow tubes of a hardwood - say 1" dia with 3/4"holes (on the lathe?). Then drill/glue those into place. (could probably buy aluminum or delrin already to size)
Having said that if Rob Cosman endorses it in MDF then it is likely quite adequate.

[Ronald Blue]

This
https://www.leevalley.com/en-us/shop/tools/workshop/workbenches/benchtop-accessories/72602-dog-hole-bushings


with these
https://www.leevalley.com/en-us/shop/tools/power-tool-accessories/drill-bits/42247-hss-lipped-imperial-brad-point-drills?item=07J0248

No question it would add immensely to the durability but it would get expensive fast. I guess buy once and cry once because it is something you want to last for a long time.

[Mike Burke]

I am going with 3/4" dog holes and will treat the top and hole openings with sealer of some kind to stiffen the MDF


I have a router table top that is MDF that I shellac'd. Quite surprised how well it has held up over the years. So if you were not making inserts around the holes, you might consider coating the inside with shellac. It soaks in and hardens the top surface of the MDF and provides some durability. In general though, I might try to sleeve it. Make hollow tubes of a hardwood - say 1" dia with 3/4"holes (on the lathe?). Then drill/glue those into place. (could probably buy aluminum or delrin already to size)
Having said that if Rob Cosman endorses it in MDF then it is likely quite adequate.

I plane on putting a sealer on the entire top and putting a 3/4 edge on it. I have used MDF on several speaker box's and am surprised how hard it can be after a coupe coats of sanding sealer or other type of sealer. Soaks it up and get pretty hard. I thought I would try MDF for the top because of the seasonal movement of Hardwood tops. I have a large maple top that's 2 1/2" thick and it gets out of flat with season changes. I'm wanting something that will stay flat.

Thanks

[Jack Frederick]

Perhaps consider going to a 20mm dog hole. I’ve done this recently drilling out my MFT. The UJK drill bit has been excellent. I also bought the 20mm reamer and chamfer bit. So far I am very pleased with the result.
https://tsoproducts.com/brands/UJK-Technologies.html

[Cliff Polubinsky]

No question it would add immensely to the durability but it would get expensive fast. I guess buy once and cry once because it is something you want to last for a long time.

Ronald,

The bushing is used to guide the drill bit, not to be placed in the dog hole. You only need one.

Cliff

[Bill McNiel]

This
https://www.leevalley.com/en-us/shop/tools/workshop/workbenches/benchtop-accessories/72602-dog-hole-bushings


with these
https://www.leevalley.com/en-us/shop/tools/power-tool-accessories/drill-bits/42247-hss-lipped-imperial-brad-point-drills?item=07J0248

this is what I used as well. Worked beautifully, no complaints.

[Ronald Blue]

Ronald,

The bushing is used to guide the drill bit, not to be placed in the dog hole. You only need one.

Cliff

My error. I didn't read the description. I'd read the comment by Dave saying the durability might not be good and I made the quantum leap to that being a solution. This is how I stay in shape. I conclusion jump. If it only worked......