Expanding Spade Bit?

I need to make 8 rather large holes, about 3-3.5" in pool steps that have already been installed. They're 2x12 pressure treated boards. The instructions for the solar lights suggest using a hole saw, but I don't have one that big and only need it for this project.
I've seen expandable spade bits for something like $10-15 at Menards. (It's been a while) Has anyone used these things? Will they work without too much trouble?
My other option would be a jigsaw or router, but I don't have a lot of space to manuever.
Puckdropper
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On Thursday, June 7, 2018 at 1:59:29 PM UTC-7, Puckdropper wrote:

Spade bits that big would be TERRIBLE in soft wood - grabby and splinter-producing. Drill a pilot hole for center, and use a deep hole saw with a (waxed?) solid rod as its pilot (it's a nuisance to make the pilot hole at the same time as the hole, you can't see where the center is). If the hole saw won't do the full 1.75" depth, you can chisel out some of the wood and keep on pushing.
Compressed air gun is the quickest way to get sawdust out of the kerf (hole saws need this every few seconds of cut). If the treated wood is toxic, use a vacuum as well.
I've used expandable auger-type bits, but they usually have a fixed screw-feed center, aren't easy to get started, and splinter at finish (unless you have access to both sides of the step... and 'a lot of space to maneuver'. That's probably a no-go.
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wrote:

Hole saws go that big - but you need the bigger mandrel ..
http://www.leevalley.com/en/wood/page.aspx?p2276&cat=1,180,42316
... starts to get pricey < at LV > maybe similar at amazon or HF for cheap ? dunno.
.. or the cheapest way always - borrow one ! :-)
John T.
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I have one of those stuck in a drawer somewhere. If memory serves, I used it a few years back to cut some 4-inch holes in hardwood. Worked fine.
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On 6/7/18 5:12 PM, snipped-for-privacy@ccanoemail.ca wrote:

Yes, hole saw. Easy to use and works amazingly well. A tip is to drill the pilot hole first (so you can accurately locate it, then drill a 1/2" or so just inside the hole cut line. This gives the sawdust a way to escape the kerf so you don't burn up the hole saw.
-BR
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On 6/7/18 3:59 PM, Puckdropper wrote:

You can get one for 15 bucks. What am I missing?
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I'm out of date on my pricing. It seemed like hole saws were either useless garbage or very pricy several years ago.
Looks like $20 for a hole saw will get this done, as much as the expanding spade bit costs. Don't get to test that tool out, but from the sound of it I wouldn't like it anyway.
Puckdropper
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On 6/7/2018 4:59 PM, Puckdropper wrote:

If you are getting into the 3-3.5" then you are not talking a spade bit but a fly cutter and the latter is not something you would use in a hand-held drill. Even in a drill press a fly cutter is scary at that size. Do yourself a favor an invest in a proper hole saw -- they are not all that expensive. As an alternative one might do what is sometimes done with holes through masonry and drill scores of holes inside the perimeter and saw/chisel/rasp/whatever the material inside out to the line but that would be sheer hell for even one hole especially if the location is awkward.
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They would work, not neccessarily the best option. And I expect they may be pricier than you remember.
I know for sure that Irwin made them in at least two sizes. AIR the smaller max diameter was less than you need but the larger would do it with plenty of room left over. They are intended for use with a brace.
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