How to accurately drill through wooden posts when using stirrups?

[finnyAB]

I’m install a new fence and using Pryda post stirrups. But can get the drilled holes to line up with hole in stirrups on other side. 
finding I then have to drill through from other side and try to match up. Then make lots of extra drills until I get a clear line between both sides.

just looking for any tips to improve my process and accuracy. As at the end I want the posts vertical and aligned with the other posts.

[MitchellMc]

Welcome to the Bunnings Workshop community @finnyAB. It's brilliant to have you join us, and many thanks for your question about drilling holes.

If you find an effective way to drill holes through a thick piece of timber and have them come out the other side in the exact same position, please let me know! 😃 That's a skill I'm yet to master. I always measure and mark off the hole on both sides and drill halfway through on each side. It splits the difference of how far off you are. Even then, you need to ensure the drill bit is at right angles to the timber. 

Apart from manufacturing a jig to keep your drill perfectly straight, I'm not aware of any special tricks that will ensure a perfect result. Let me mention a couple of our knowledgeable members @TedBear and @woodenwookie, to see if they have any advice.

Please let me know if you have any questions.

Mitchell

[TedBear]

Hi @finnyAB as @MitchellMc  says, the task is best done with a jig... but one way to help align the holes is to get a scrap piece of wood, (such as common pine 40X20) and insert it between the post and stirrup - after you have started the holes in the right place. This will then let the stirrup holes act as your guide (a rough jig) to keep the drill bit going straight as you continue through. When you run out of bit length, just remove the spacer strip and continue. By then you should be in deep enough for the hole to guide you  (or go in from the other side to get a perfect alignment).

[woodenwookie]

If what I saw is the same thing I found online (Full Stirrup Post Anchors - Pryda) then I would screw the posts in with Tekscrews on the bottom to hold them in place. I would then put two 4x2s at right angles to each other, then line them up with the hole. This will create a straight drill path which should hopefully help with the alignment process.

Obviously, this would require the drilling being done prior to mounting the stirrups to the foundation post as the Tekscrews will be on the bottom and hard to get to without a right-angle driver.

[TedBear]

Hi again, @finnyAB 

I can see a flaw in my original suggestion.... there is no room within a U shaped stirrup for the block of wood that would guide the bit through once the post is in there too.

I have attached a sketch of how to make an external jig from a piece of wood (the thicker the better for making a longer guide hole - but limited of course by the length of drill bit that has to go through it and the post).  You would drill both upper and lower guide holes. I have only indicated one of them.

Attach a block of wood, notched as indicated (or use 2 screw heads instead of a notch), to the outside of one stirrup and clamp it there.

Then drill through it from the far side, so that the holes in each side of the stirrup then guide the bit straight through.

I suggest putting a bolt through the first hole, so the jig can't move out of place while you drill the second guide hole.

Then when a post is inserted in the stirrup, you can just hold the "Jig" in place and use it to guide the bit straight through the holes.

You can do this when the stirrups are set in place, or before - your choice.

I hope the diagram makes sense...