Precise drilling end of oak uprights and chamfered stones

[Iancd]

Another question from this gradual rebuild I'm absorbed in...

I'm now building an oak frame to sit on top of a stone porch base. The porch has steps which lead up to the first floor where we enter the house: https://millhousedays.wordpress.com/2013/12/01/porch-and-steps/

The design, from our architect, has the uprights sitting directly on top of the chamfered part of the capping stones, with a bevel at the same angle as the chamfer so they'll stand upright... provided they're fixed at the correct angle..! They're to be fixed with stainless steel pins glued into holes drilled vertically into both the uprights (about 150-180mm) and the stones (about 85-90mm).

I'm wondering what the best way might be to ensure the holes are drilled as precisely as possible - (a) into the oak pillars, parallel to their length, and (b) vertically into the stones.?
As far as the latter is concerned, I'm not happy with the suggestion someone made of doing it using a hand-held drill and having someone else judging and advising on whether it's vertical or not!

The ideas I've come up with so far:
(a) Clamping each upright precisely vertical into a vise. I think that'll be essential - unless there's a better drilling method involving the uprights laid flat, which I haven't envisaged.
Then using an old small portable DiY drill adapter which I have, screwed to the workbench, to hold an electric drill. This may sound potentially OK in principle, but the adapter isn't very strong so it tends to give a bit when first striking the wood. It does give better results with smaller sections than I get hand-held, but I'm wondering if a bench pillar drill could be adapted to do this and probably give better results..?
(b) Using a heavy board as a temporary bench laid across the flat parts of the capping stones and again holding my drill adapter or a small bench drill vertical, to drill into the chamfered pat of the capping stones. My adapter can have the drill facing away from the base, so would allow this, but I'm not sure a bench drill would.
Another idea would be to make a jig to mount the drill adapter or bench drill to which would match the chamfer's 9 degree slope and hold the drill vertical..?

Thanks for your thoughts, in anticipation..!
Ian

 

[Racers]

You need a block with a hole drilled in it as a guide, an off cut of your post will be ideal, drill the hole with your pillar drill and screw some ply round it so you can slip it over the end of the post.
The same block can be used on the cap stones.

But I think you are over thinking the problem, a bit of clearance in either hole will solve any alignment problems.

Pete

 

[Phil Pascoe]

I assume the frame is in more than one plane? If so, why the necessity for holes so deep? once it's all in place it won't go walkabout.

 

[Woody2Shoes]

I've just done something very similar with some green oak posts (150x150) supporting a lean-to structure, sitting on brick plinths.

I used M16 stainless steel threaded rod/studding cut to appropriate lengths - about 5 inches into the masonry and five into the timber is ample - you just want to stop it slipping sideways off the plinth - wind uplift etc. needs to be counteracted by gravity and/or by other means. I drilled the holes in the ends of the post with an 18mm drill i.e. a little on the large side - this allowed for any shortcomings in the "squareness" of drilling in timber and masonry as well as giving a bit of wiggle room to adjust the posts to absolute plumb, in two dimensions, once in position.

My take on this is: if you're fairly close to square in your drilling and you've got a couple of extra mm in diameter (and length in the timber) you're fine - any errors are manageable over a 5 inch distance.

I used a small cube-shaped offcut of timber cut squarely, and used the edge as a guide to drilling squareness (in two dimensions) by sitting it next to the hole I was drilling and using one vertex as a guide - alternatively I could have drilled a hole in the offcut as has already been suggested, but I found my technique easier to see where you're starting your new hole.

Cheers, W2S

 

[lincs1963]

Drill the holes into the timber while it is still square, then cut the end to the angle you rquire. The offcut can then be used as a guide to drill into the stonework.

 

[Iancd]

Sorry for the tardy response, folks...
Thanks for all the replies - much appreciated
Pete: Brilliant..! You may be right about me over-thinking this, although I do tend to write in a lot of detail...
Anyway, your idea of a block drilled as a template with ply screwed around it was something I hadn't thought of and exactly the tip I needed.
I used an offcut with matching bevel angle and it worked a treat to drill the posts (once I'd found the right sort of bit to use).
Not so useful on the masonry (too much movement and vibration), but it worked as a guide to locate the drill at the correct start point, and as a visual guide in the way W2S suggested.
Phil: Yes, you're right. I've reduced the holes in both timber and stone, as the s/steel rods I'm using are 150mm - so half will go into each.
Lincs: Again, thanks. I'd already drilled most of the uprights, but I have two corner posts to do, with awkward cuts to fit chamfers both ways so it's a good tip to drill them when square, before I cut.

First tests using this method look good... I'll post an update when I've finished the frame

 

[RogerP]

Too late now and maybe not even applicable in your case but these are very handy devices for drilling upright holes in all sorts of things and in places that wont fit under a pillar drill. Cheap too

 

[Iancd]

Well, that went reasonably well.. Thanks again for your help with this, folks

I'll get onto the roof ( !) - with some help - in the next month or so...
Ian

 

[GLFaria]

I'll get onto the roof ( !) - with some help - in the next month or so...
Ian

Pretty step roof, better be careful!

 

[Mcluma]

That looks like a very nice frame, what did you put under the oak?, or is it in direct contact to the cement

 

[Iancd]

Thanks Chris
The posts are lifted about 2mm off the capping stones (Doulting stone) with M16 stainless steel washers - fairly thin ones from Screwfix.
Ian