Any tips on drilling a hole please?

[Beanwood]

I'm installing a pair of electric gate rams, but I have the silliest of problems. I need to drill 6 holes of 12mm through a 200mm gate post for the supporting brackets. But I need to do it accurately.

Normally, if I need a hole drilling at perfect 90 degrees to the face, I'd use my drill press. But the gate post is already in the ground, so that isn't an option.
I can drill it approximately right by eye, but this needs to be precise - on the inside of the post, it needs to match the bracket holes. The outside of the post is visible, and I'd prefer symmetrical rather than 'random' holes.

I've seen the use of a block as a guide - drilled on the drill press - but I'm concerned there's still plenty of room for drift.

Beyond making the drill block deeper, any ideas how I can improve my accuracy please?

 

[Doug71]

Can you mark and drill from both sides and hopefully the holes should just about meet in the middle?

 

[Tris]

You could try something like the wolf craft multi angle drill guide, clamps on the drill collar and acts like the plunge mechanism of a router.

 

[Jacob]

Mark it precisely for both ends of the holes, drill as best you can from each side to just past the middle.
If they don't meet exactly drill through again with a long drill but making sure you aren't disturbing the holes at the surface. Any irregularity should then be on the inside only and out of sight.

 

[transatlantic]

Could you use something like this or this? Starting of with small drill bits, and getting increasingly bigger.

I think I would go to the trouble of making a template. So basically a drill guide made on the drill press, but with metal bushings for better accuracy (metal pipe with a 12mm ID). You can then clamp the template in place.

 

[toolsntat]

This thing really need 6@ 9"bolts to keep it in position?
I assume that the gate is already hinged and swinging.
I'd be looking at 100mm max m12 coach screws
Cheers Andy
Ps any link to what you are fitting ?

 

[Phil Pascoe]

If you drill a piece of 4" x 2" or better 4" x 3" through in drill press with a sharp auger or good lip & spur you should have a dead square hole. Make sure if you use an auger that you clamp the piece down that you can run the bit right through in one go - it will be difficult to stop as it will draw too quickly, and a bit of spelch doesn't matter anyway. Clamp the block well to the post. Once the hole is two or three inches deep a good quality sharp auger will stay true without wandering.

 

[woodbloke66]

I had a similar problem, though not on a vertical gate post. What I'd advise is one of these drill guides. Dispense with the rubbishy plastic bit but use the steel 12mm guide on top of a thick block which you've already drilled out at 12mm dead square. The steel guide ensures that the drill doesn't mangle the hole and you'll be able to drill a true hole through the post by clamping the block in the vertical position. The other thing you'll need of course is a very long 12mm power auger bit, but Ax and others can supply such a beast....a similar but enhanced technique to the one posted above - Rob

 

[Roland]

What about a drill stand clamped to the side of the post:

 

[Farm Labourer]

When the blokes come to erect the steel for new farm buildings - they have a magnetic broaching tool. They mark where they want holes for brackets, align the machine (at any angle from horizontal, through vertical to inverted horizontal) switch the magnet on which clamps the weighty bit of kit to the beam, and power it up. The have some form of self feeding arrangement as they leave it running until it drills or broaches the hole.

Perfect holes every time.

Not sure if these are available from hire outlets but there must be a steel erector near you who would do it for you and take away the headache of potentially imperfect holes.....

 

[gog64]

Normally called a mag drill, you can hire them from most local hire places. I just looked at Brandon Tool Hire, £77 for a day’s hire. They are pretty simple to use.

 

[Beanwood]

Some excellent ideas there chaps thank you.
This is to hold the end of the gate rams in place - which will be exerting a LOT of torque, hence the need for bolts rather than coach screws (Which would be MUCH easier!)

I like the idea of the plunge drill guide from Axmister, but I can't see the reviews for some reason, so don't know if it's any good, or not?

I think I'l go for the 4x4 block, drilled on the drill press, then clamped in place. I'll also go for drilling (Just over) half way through from each side.

I'll practice on an offcut first though

 

[Phil Pascoe]

Normally called a mag drill, you can hire them from most local hire places. I just looked at Brandon Tool Hire, £77 for a day’s hire. They are pretty simple to use.

but not on a wooden post ...

 

[novocaine]

hang a washer off the shaft of your drill bit.
if it moves backwards as you drill, you are drilling upwards, lift the back of the drill up. if it moves forwards while you drill, you are drilling downwards, lower the back of the drill.

clamp a block of wood to the side of your drill, clamp a length of straight timber to the fence post at 90 degrees. use it as a fence for your now modified drill. that's the other axis dealt with. get to drilling.


the washer trick is great and I'd use it even if I was using a guide block as you intend to do. with the two of them, there is no reason to drill from one side then the other although a clearance hole to stop blowout or a block of wood clamped to the other side would be a good idea.

 

[transatlantic]

hang a washer off the shaft of your drill bit.
if it moves backwards as you drill, you are drilling upwards, lift the back of the drill up. if it moves forwards while you drill, you are drilling downwards, lower the back of the drill.

Pretty sure it only works with a wedding ring. Something about commitment.

 

[TheTiddles]

Have you thought about the failure mode of the bolts?

At 200mm long, they’re likely going to not break out the wood (unless you put them silly close to the edge), or break on the shaft somewhere in the middle but rip the head off. At which point, you don’t need them any stronger embedded into the wood than the strength of the head. I’d suggest that a coach/lag screw 100mm into decent hardwood is going to have a stronger grip than the strength of the bolt head and therefore you don’t need to bolt through

Unless I’ve missed something

Aidan