So this is a more small sized one day project I did in the winter of 2016/17. Having moved into an apartment with large rooms and brick walls, heating the place took a while and a pretty penny. I always liked the idea of the Kotatsu tables from Japan but with retail versions costing an extraordinary amount for a tiny table, assembling one was the only option.
Kotatsu tables, for those who don't know are heated tables with blankets designed to keep the heat in. Users sit on the floor (which I prefer anyway) and can warm up while doing normal table bound activities. The version I made was done by placing a 9mm MDF sheet on top of four cinder blocks. I could have used cut down fencing posts or some other form of table legs but aiming to keep the price down as low as possible, four cinder blocks did the job as I could forgo the tools and the fasteners needed for legs. On top of the MDF I layered a thick blanket to serve as the primary mode of isolation. This would keep the heat contained under the table and reduce the amount of energy needed for heating by focusing on heating a specific area. For my heating element I used a small underdesk heater with an automatic cut-off. This is different than the heating elements traditionally used but in terms of flexibility and usability(I could use it to focus heat onto my feet or use it as a normal underdesk heater on my other tables), it was perfect.
But of course, with a blanket table top, the usability of the table would drop as one could not write on it or use a laptop (overheating by blocking vents, never use your laptop on your bed!). My solution was to add another layer of hardwood, in this case a sheet of 3mm whiteboard/markerboard. This gave the top of the table a smooth surface, and a handy dandy erasable sketching and writing surface for markers. The friction of the blanket kept the board in place and everything else worked out surprisingly well.
Of course, rare is the case where a project is perfect first time out. My choice of using cinder blocks as legs came with a drawback. When moving in or out of the table, or simply moving around to reposition yourself, if you knocked your foot agaist the blocks then you would likely come away with a light scratch. Not particularly a homey feature for a table focused on comfort. Ideas I had to remedy this included coating them in resin to eliminate their sharp textures, wall filler, sanding, and rubber guards. These would have all worked to a degree and some would have worked well, but bearing in mind the budget focused approach, I left them as they were and enjoyed the table regardless(it's surprising how easy it is to fall asleep under these things).
In the end, the total table costed me $30, using blankets that I already owned. The bulk of the cost came from the MDF panels used for the table top. I could have gone cheaper by going and buying used tables and cutting them down but whether or not I could have found the right table is anyones guess.
If someone else were to reproduce this, I would say words of warnings about the cinder blocks for their texture and actual table height, as well as the stability of the table as a whole. Although the table never moved while I used it, the nature of it being completely put together using friction and gravity means that it is not actually fastened together. There is also a word of caution towards using mini heaters for this purpose as this is not their intended use case. There can be risk of fire depending on what you use and I would be selective in choosing a heater for this project.