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How to find mending plates with M8 holes?

Hi all,

I need mending plates with 8mm holes. Something like this https://www.bunnings.com.au/zenith-125mm-zinc-plated-mending-plates-2-pack_p2765973 but I couldn't find information about the diameter of the holes. This has information about the diameter, which is 10mm https://www.bunnings.com.au/dunnings-120-x-35-x-3mm-black-heavy-duty-bracket-plate_p0131620 but not all mending plates have information about the hole size. Please help. Thank you.

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JacobZ

Hi @otnimus1,

I've had a look around and the majority of smaller, less heavy-duty plates do not specify their hole size.

Did you need the mending plates to be a specific size, or for a specific purpose? Were they going to be used outdoors where rust protection needs to be considered?

If there was a specific use, I can help locate something to suit then get in touch with some colleagues in store to check the hole size.

The alternative to this is to just grab a plate in the size you are after and then grab an 8mm drill bit to enlarge the holes with. This would mean you can use whatever mending plate you'd like. It requires a bit more work, but it would open up your options greatly.

Feel free to share those details when you can. I’ll be more than happy to help with the next steps.

Jacob

otnimus1

Hi @JacobZ thank you so much for looking around.

I want to use it to "hack" my office chair by lowering the armrest. So it is for indoor use and not so much heavy-duty. The main goal is like the picture below. The original bolt and where it is screwed to the chair is M8. I have https://www.bunnings.com.au/ozito-pxc-18v-cordless-compact-drill-and-impact-driver-kit-pxcdik-250_p0195859 and wonder if this will do the job? If so, please advise a suitable drill bit. Thank you so much.

JacobZ

Hi @otnimus1,

Ok, so in that application, the hole location is just as important as the size, so I am near certain you would not be able to find something to match up perfectly as is.

So, drilling your own holes is definitely going to be the way to go. I imagine your drill would be fine to increase the size of an existing hole up to 8mm, however you might struggle going from no hole directly up to 8mm, so I'd recommend starting with a smaller pilot hole then increasing the size of it.

I'd suggest you grab a https://www.bunnings.com.au/kincrome-2-5mm-centre-punch_p0444997 to punch a slight indentation in the plate at the location you will be drilling. This helps to stop the drill skating off and putting the hole in the wrong location. Just mark the hole location then strike your punch with a hammer to make the indentation.

You can then use a standard 4mm HSS bit to put a pilot hole, then use an 8mm HSS bit to finish it off.

Specifically, this https://www.bunnings.com.au/kango-4mm-hss-drill-bit_p0354525 and this https://www.bunnings.com.au/kango-8mm-hss-drill-bit_p0354532 would do the job just fine.

Start the drill slowly, then speed up as you feel comfortable with it. Drill bits come sharp, so they won't have any issues once they get going.

Let me know if you have any further questions.

Jacob

Noyade

Just a thought.

Make your own brackets. Head to the steel section @ Bunnnings and for $15.70c buy 2 metres of 25mm X 5mm. Cut the four lengths required and drill 4 holes as per Jacob's instructions. Grind the edges round. And the great part is you don't have to negotiate around the manufacturer's (Mending Plates) pre-drilled and countersunk (unnecessary) holes.

Insert and bolt in place. Still not right? - remember, you have 1.8 metres of steel left to play with.

https://www.bunnings.com.au/australian-handyman-supplies-25-x-5mm-x-2m-steel-flat-bar_p0917590

Note also, there is now no need to 'double up' as seen on Reddit, where your image comes from…

otnimus1

Thank you both.

@JacobZ do I need the centre punch only if I go with plain plate with no hole as Noyade suggested? What's the cons if I go with something with smaller holes already in place so I just need to enlarge them?

@Noyade you are right I am trying to follow what's shared here https://www.reddit.com/r/ikeahacks/comments/17yd8fw/markus_chair_adjustable_armrest_mod I have the same chair with the same problem. Thank you for your suggestion, I am afraid I don't have suitable tool to cut a plate. I wonder if Bunnings provides service to do the cutting and drilling per specs.

JacobZ

Hi @otnimus1,

If you used the mending plate with holes in place, then there'd be no need for the centre punch. I had thought the plate would run horizontally as I had not seen that thread. Now seeing it, I think enlarging the holes on a mending plate is likely the best way to go in which case you'd just grab an 8mm drill bit and enlarge them.

Unfortunately, we do not provide a metal plate cutting and drilling service, so you would have to do it yourself.

Jacob

Noyade

If this continues to be problematic for you @otnimus1 - I'm more than happy to make them, paint jet back and post to you - no cost. Just need dimensions. PM me if interested, otherwise try drilling, as above. Maybe clamp them to wood before drilling. Cheers - keep us posted.

otnimus1

Thanks for clarifying @JacobZ

@Noyade you're very kind … can I raincheck on your offer? I like to challenge myself with a DIY like this and would like to try it first. I will message you if I can't do it. Thank you so much. Will update how I go.

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