Need Bit to drill Wood and 1/4" Steel at same time

[Tom Hyde]

I'm looking for a high quality 1/2" drill bit to simultaneously drill through a 6x6 cedar post and embedded 1/4" carbon steel knife plate. This is for a post to base foundation anchor using 1/2" steel pins. I might end up pre drilling wood and knife plates separately but the matching holes must be perfect. Seems "easier" to do it all at once. It's tough to drill down through all the bit choices out there (sorry for the pun) so any help in narrowing choices would be greatly appreciated.

[Alex Zeller]

I've had many brands of drill indexes over the years, some just plain high speed steel all the way up to a few carbide tipped drills. I'm currently using a set of Irwin M35 Cobalt steel bits. They were expensive but I have a set at work and was impressed enough to buy the same 29 piece set for me personally. I've used them to drill everything from stainless to grade 5 bolts. Do you know if the steel is hardened or just high carbon? I've heard of people taking masonry bits after sharpening the carbide tip when it comes to harden steel. The key is going slow and not heating up the bit.

If possible I would start off with a smaller diameter bit. Maybe drill the post in place and when you reach the steel let the bit make a mark so you know where the center is, remove the post, and then drill out the steel. With the wood masking the steel it'll be much harder to tell if the bit is drilling or if you have overheated it.

[Bill Dufour]

I would drill as deep as possible with a 3/8 jobber length bit then drill with a 12" long 1/2 HSS twist drill. Any big box store will have one. I would use water to keep the tool cool once it hits steel. Oil is better but will stain the wood. Just pull it out every 30 seconds or so and dip it into water. That will also clear the chips. No need to wait for it to stop spinning while cooling.
It would be easier to make a 1/4 pilot hole then step up to 1/2. But that is not worth the extra cost for one or two holes. Another choice is a threaded aircraft drill and a long extension behind it.
Make sure the drill is not carbon steel. Thin the web if possible before drilling. Even if you do not thin the web at least take some of it off.
Bill D.

https://www.yardstore.com/drilling-and-cutting/drill-bit-accessories/drill-extensions/threaded

[Tom Hyde]

Alex, well that makes a whole lot of sense. Excellent. Thank you. I can set the knife plate base in the concrete with threaded anchors and nuts, level and place them perfectly, remove the base from the embedded anchor rods, and then attach the bases to the posts in the shop using the method you suggested. I don’t know if the steel is hardened, never used these European bases before and can’t find “hardened” in specs (double perpendicular knife plate with moment resistance). I might just upgrade to the m42 cobalt bit for extra measure, and buy two. 16 holes to drill. Thanks again.

[Tom Hyde]

Thanks Bill.

[Joe Wood]

Tom, I'd be interested in seeing these knife European plates, got a link for them?

[Tom Hyde]

Tom, I'd be interested in seeing these knife European plates, got a link for them?

I'm never quite sure on what I'm allowed and not allowed to post on sawmillcreek when it comes to direct links to products. But it's the "Rothoblaas Typ X10 Cross-shaped post base (https://www.rothoblaas.com/products/fastening/brackets-and-plates/pillar-bases/x10)" available through "Timberframe Headquarters." Google should take you there.

Funny you should ask since this is for a Japanese Garden Gate entrance. This would seem to be a good, if somewhat expensive, solution to avoid direct burying the posts. I'm still going to include the secondary bracing posts - seems they will also work as good stops for the gates themselves. And wish me luck as I try my hand at traditional Japanese joinery for the first time on this project, particularly the saotsugi joint with the pole tenons!

[Joe Wood]

Man I looked at that saotsugi joint, makes my head swim! Why can't you put the posts in the ground? Wrap the posts at grade with copper and that'll stop all rot / decay. I've heard the Japanese have been doing that for centuries. You're in Wa. state, can you PM your website?? Do you do a of of Jpn style structures??

[Lee Schierer]

I'm looking for a high quality 1/2" drill bit to simultaneously drill through a 6x6 cedar post and embedded 1/4" carbon steel knife plate. This is for a post to base foundation anchor using 1/2" steel pins. I might end up pre drilling wood and knife plates separately but the matching holes must be perfect. Seems "easier" to do it all at once. It's tough to drill down through all the bit choices out there (sorry for the pun) so any help in narrowing choices would be greatly appreciated.

Since you have to cut the slots for these cross knife plates to slip up into your posts, Drill your holes, cut your slots and then slip the plates up into the post. Use a 1/2" drill bit and the holes as a guide to mark the centers for each of your pin holes using the drill bit or a sharpened 1/2" pin. Pull the plate out and drill the holes in the plates on a drill press. Then slip the plates back into the posts and pin them in place. Be sure to mark the orientation of each plate to each post as you mark the centers.

[Wes Grass]

If it's in place, by hand, ouch.

As for drills, a split point is the only way to go. And I'd vote no on a pilot hole. It's gonna make the next drill chatter. If theres no choice, size it to match the web thickness of the larger drill, or a hair less. That will help a lot on getting a round hole.

[Bill Dufour]

I doubt if the iron is hardened. If it was hardened it might snap from stress fractures from wind loads over time. Or snap in two during a quake. Much safer to have it bend from overloads and keep stuff sorta under control.
Bil lD.

[Tom M King]

A good half inch bit will go right through 1/4" plate. It just needs a little help. I'd drill the wood like you want it, then use a 1/2" right angle drill with a lever rigged up behind the angle. I've done this a bunch of times, using a 2x4 for a lever, and clamp a block in place for the pivot. Don't push too hard-just enough to make sure it's going in. It shouldn't take much force, at all, on the lever. If you're having to push hard, the bit is dull.

The hole in the wood will be a plenty good enough guide for the bit. Any good high speed bit will work, but Cobalt will cut quicker. Water will work, but the best thing is to make sure the bit is cutting, and it will go right through.

[Tom Hyde]

Man I looked at that saotsugi joint, makes my head swim! Why can't you put the posts in the ground? Wrap the posts at grade with copper and that'll stop all rot / decay. I've heard the Japanese have been doing that for centuries. You're in Wa. state, can you PM your website?? Do you do a of of Jpn style structures??

A lot of the literature I've seen on traditional Japanese architecture has posts on buried rock foundation with post bottoms above grade, often scribed to the rock. But I'm no expert. A few years ago, I saw the demo at a public garden on a Japanese gate with direct bury posts. Very high quality work. The wood was old growth clear VG Port Orford Cedar. The posts were rotted through even well below grade after 20 years. The bottoms were cut off, spliced and reattached using stainless threaded rod in concrete. If it was a larger 8"x8" post I might skip the special base and use a 1" threaded rod, standoff plate, and nut in the post. I'm investing quite a bit in clear VG Western Red Cedar with as many as 50 growth rings per inch. If the base is strong, it should last many multiples of 20 years. I certainly hope so. The wind is what I worry about.

I don't do a lot of Japanese style structures, mostly custom high-end mortise and tenon cedar gates and some custom furniture. My website, fwiw, is in my profile here on the Creek. There are several incredibly talented outfits in the Seattle area specializing in traditional Japanese architecture. Some people apparently are willing to pay $2,000 a square ft. for an authentic teahouse.

[Tom Hyde]

Since you have to cut the slots for these cross knife plates to slip up into your posts, Drill your holes, cut your slots and then slip the plates up into the post. Use a 1/2" drill bit and the holes as a guide to mark the centers for each of your pin holes using the drill bit or a sharpened 1/2" pin. Pull the plate out and drill the holes in the plates on a drill press. Then slip the plates back into the posts and pin them in place. Be sure to mark the orientation of each plate to each post as you mark the centers.

Thank you Lee, I think that's exactly the plan now. Your last sentence might prove the most valuable. Don't ask me how I know that.

[Tom Hyde]

Again, thanks to all for the great tips and comments. Extremely helpful. And it reminds me I need to re-up my membership with the Creek. Gotta keep this invaluable place going.