Wednesday, June 3, 2015

Enlarge Your Holes With Cheap Tools


Two reason you may need to enlarge existing holes in your workbench.

1. You're upgrading to forged holdfasts (like our's, or those by Peter Ross or other smiths) that require a 1" hole.

2. You're benchtop is too thick for standard (e.g. Gramercy) holdfasts to get a grip, and you need to open up the bottom portion of the hole.

There are  piloted counterbores designed for metalworking that will get the job done, but they are expensive (close to $100) and you'll likely only need them once. We've had customers chuck up a 1" twist bit only to chew up their bench, ruin the hole entirely, and twist their wrist off in the process. Using twist bits to enlarge holes in a handheld drill is very dangerous. These bits are designed for drilling metal in a vise or other movement-restricted scenario. One can use a Forstner or Owl bit guided by an auxiliary board with a hole drilled in it to help the bit get started, but the process is a bit fussy, although it works well, especially with the Owl bit (the long shaft helps it run straight.) Routers can also be used, but, well, routers.

So here's a cheap and easy way to enlarge holes with tools you can get at even the worst hardware store. You probably already have 3/4" dowel and a 1" spade bit already kicking around your shop.

Here's the process for making the piloted spade bit.

First, drill a 3/4 hole dead center in a scrap block, stick the dowel in the hole, then run the block over the table saw to kerf the end of the dowel. If you don't have a table saw, cut two kerfs by hand, and pop out the web in between.



My blade was a tad wider than my spade bit, so I shimmed the kerf with (what else) masking tape. I also ground the spur point down on the bit so it would fit deeply in the kerf.


Chuck the bit into a drill, put a little epoxy in the kerf, and slide the dowel onto the bit. Center it up by eye, then turn the drill on slow and watch the dowel to make sure its spinning on center. Once you get it centered up and straight on the bit's axis, walk away. After the epoxy cures, the tool is finished.


You can use the bit to enlarge the front portion of a hole (counterbore) then if you want to make the entire hole larger, finish up with a 1" drill bit. I like the Owl bits for this. Forstners work too, but it's difficult to keep the hole straight with their short profile. Use the piloted spade bit to get as deep as you can. When using the spade bit, back out frequently to clear chips since the paddles won't pull chips out of the cut.

3 comments:

  1. Amazing. I try not to use the word genius if I can, but in this case I'll make an exception! It shows it good to have a background in multiple areas, because other group may have a solution to a problem you haven't seen.

    Mike

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  2. Absolutely brilliant!!! For more precise centering (my eyeballs suck), I would clamp a four squared 1-1/2" piece of scrap to the drill press fence....drill a 3/4" completely through the block and the drill press table's clearance hole....insert the dowel...chuck up the 1" spade bit.....epoxy the dowel slot....and presssssss-toe!

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  3. I totally need one of these. All my holes are 25mm and all the dowels I get are 1" (exact). This is a fantastic idea.

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