Core hole size for 30mm round

[Thrashsmith]

Hi folks, I've got to install some handrails soon. Most of which have 3 posts, but some have 2 + fixing holes against a wall.

The posts are 30mm solid round. What core size would you use to resin these in?

In the past I've cored 52mm holes so I can get the railings in situ, then get a resin nozzle down into the hole alongside the post & get the nozzle all the way to the bottom of the hole (typically 150mm or there abouts), but I think the look of this isn't as neat as it could be & a smaller hole size would look nicer. It will mean pre-filling the hole with resin, then dropping the handrails in.

ScrewFix do 38mm diamond core bits, do you think that's too snug a fit / not leaving enough room for error? Thanks

 

[8ob]

As said would it not be easier to resin the hole and let it squidge out as you install the posts? Anything else seems like hard work.


Bob

 

[Agroshield]

...not leaving enough room for error?

The smaller you can make the margin or error, the smaller the bit can be.

You can go to Hilti's website and see what size bit they recommend for drilling a hole to accommodate 32mm reinforcing bar. That will give you the increment over nominal size.

Look how project Binky made their reverse suspension jig and make something similar (a drilling template). Square plates with a hole in them to act as a guide for the core bit, with the two or three of them fixed together in the correct spatial relationship. Buy two core bits or find some tube of the same diameter as the bit. Drill the first hole and leave the bit in the hole so the template cannot move relative to that hole. Use the template to guide the bit for the second hole.

It is not clear on the three fixing one if all three legs are going into a core drilled hole. If one of the three holes is at 90 degrees to the others (i.e. two are vertical into the floor and one is horizontal into the wall), you need some wiggle room to put the railing in place.

Slip some (in effect) large washers over the legs that can be slid down after the grouting is done and will cover the excess hole. Look at how a shower pole is fitted in your bathroom - you slide the covers onto the pole, fix the two wall brackets, install the pole and then slide the covers back over the joint to make it neat.

The idea is the same as these, but in metal:

Real Wood Pipe Collar

• Easy to fit• Push-together dowel radiator pipe collars• Disguises cuts on real wood or laminate flooring• Hole diameter: 15mm

www.toolstation.com

 

[addjunkie]

I doubt with 38 mm bit youll get a 38 hole, more like 40 or 42 mm.

 

[Mick Annick]

When I resin in railing posts I aim for 4/5mm oversize - as @addjunkie says with an SDS masonry bit you always end up oversize anyway, resin in first, drop the post in, level up and clamp it to something until it cures. I wouldn’t go as large as 38mm - 35 would be fine, as long as you’re confident in drilling the holes perpendicular!

 

[Mick Annick]

I’ve just had a look at your website - you do some beautiful work, you should share more of it with us!

 

[addjunkie]

I’ve just had a look at your website - you do some beautiful work, you should share more of it with us!

I concur!

 

[Agroshield]

I doubt with 38 mm bit you'll get a 38 hole, more like 40 or 42 mm.

Another source of error with freehand drilling is if the drill is not square with the surface. The post will go in plumb, and if the hole is skewed, that will reduce its effective diameter. Hence, the better you can guarantee the squareness of the hole (by, for instance, using a drill on a stand or standing two squares next to the bit as it drills), the smaller you can drill.

 

[Thrashsmith]

Cheers all.
Because these are going off to be galved, I've tacked a bit of light weight bar to the bottoms of the posts to stop the posts from getting distorted in/out.
What I thought of doing when they come back was getting some wood batons & offering them up next to the posts, marking up on them where the posts go, the clamping the batons side by side & drilling 30mm holes down the centre, so when I take them apart I've got half round holes in the batons.
That way when I go to site, I can clamp the batons back on, cut off the welded bar at the bottom, and the batons will hold the legs in their correct spacing. Stand the railings up where they're meant to go, mark around the posts to give me the hole positions, then drill. Do you think that'll be a good system?

 

[Thrashsmith]

I’ve just had a look at your website - you do some beautiful work, you should share more of it with us!

Cheers. I wondered how you found my website, then I realized I left my name on the designs I posted

 

[gordon stephenson]

I did quite a lot of setting railings into sandstone around my sons house, We used lead as per old fashioned method, left about 6mm gap all around the metal posts, Worked a treat, but do it on a dry day, otherwise hot lead and water blow back out of the hole, Made a split ring to place around the posts before leading, made the lead 6mm above the sandstone,