so I have a queen size bed that is very low. i want to raise it by at least 20cm.
it has slanted bed legs on the corners and two wood columns in the middle.
what would be the best way to raise? I'm thinking to make a square frame that the bed sits on but don't know how.
i tried bed raisers but its not very stable and the middle is not supported.
I looked in my local Bunnings for furniture legs but they have screws of 3/8 and my original screw holes are a size smaller
Welcome to the Bunnings Workshop community @sksk. It's wonderful to have you join us, and many thanks for your question about raising your bed frame.
If the 3/8" screw is too large, then I'd suggest you likely have 5/16" threaded holes as they're the two most used sizes for furniture legs. There are also 1/4" threads, but I'd imagine that's a bit small to be used on a bed. I presume your frame has leg plates installed in the corners. If so, you can remove those and re-install ones that have a more common threaded hole like these Adoored 3/8" Vertical Leg Plates. This will open up the range of 3/8" legs for you to use.
If you are going to use longer legs, I'd suggest moving away from the slanted design and sticking with straight legs. The off-centre design of slanted legs puts incredible stress on the mounting points. Slanted legs wouldn't be suitable if you want another 200mm height on top of the current leg height. Because of the threaded connection, which is essentially designed for ease of installation, not rigidity, any leg over 200mm in height, whether it is slanted or not, will be susceptible to failure due to the stresses exerted on them by the bed frames movement.
Have you considered an additional 200mm mattress instead? They can be had on sale for as little as $100, and considering that alternatively, you'd have to purchase new legs with fixings and then deal with the central support, it could be a viable option. Since it will be a spacing mattress in-between the frame and your current mattress, it doesn't need to be of high quality. I'd suggest purchasing something with stiff springs.
Let me mention @r23on to see if he has any suggestions.
Please let me know if you have any questions.
"I'm thinking to make a square frame that the bed sits on but don't know how."
Personally I'd be heading down that pathway of thinking as well. Sort sort of easy box formation. I'm not sure if you want an additional 200mm height on top of what you already have? So maybe 300 mm dressed timber? It wouldn't be hard to bracket it into place. There would be nearly endless number of designs/ways of creating that "square frame" you suggest above and various ways to paint/stain/varnish.
There are a number of thing that can be done. raising the bed 200m / 300m will give you a huge space that could be use for storage.
Using the concept that @Noyade has suggested.
1. remove the legs all together
2. place the bed frame on top of the suggested frame
3. insert draws into the new frame for storage
4. sanding the dressed pine and seal with a natural finish.
or as suggested by @MitchellMc