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I would like to cut a hole that is wider on the bottom of the sheet than at the top. So for example using a 60mm holesaw gets me the same diameter on both sides of a 21mm thick sheet. How can I get 60mm on the one side and 70mm or so on the other side, with a flush straight angled surface between the two sides (around 45 degrees).

Doing some googling, I came across beveling but I cant seem to find any large enough bevel or countersink bits. The purpose will be for a spherical object to sit nearly flush on the cut section and slightly protrude on the visible top/front side of the sheet (I have attached a basic image trying to show what I am trying to accomplish).

Any advise appreciated but ideally using the machinery I currently have (drill, table and circular saw, jig saw and grinder).

Please also forgive my lack of terminology here as I am new to this.

enter image description here

  • I think a router fitted with a suitable bit is THE way to do this today, but if you don't have a router you don't have a router. But, all the other methods by which this could be done involve tools you don't list Traditionally this sort of shaping would be done by reaming, and you could still do it this way if necessary but you'd need to make the reamer. Because the conical surface is a non-show surface you could do it just by drilling a hole and then enlarging the back of it by carefully paring with a gouge. It's also doable with a suitable rasp or file, although trickier to do neatly. – Graphus Jun 17 '18 at 13:24
  • @Graphus, thanks for your answer. If anything I learnt a new word in reaming, so will research that a bit more for possible solutions. For now, the unclean way will be a jig saw at 45 degree's and file or chisel as I have those on hand. – David Jun 17 '18 at 13:40
  • Do practice on a scrap piece when you first try the jigsaw for this! Very tricky cut to do well. – Graphus Jun 18 '18 at 11:49
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I'm not sure it's doable with the tools you list.

For really clean and accurate results my choice would be to use a router:

  1. Make a hole template in a bit of scrap plywood by drilling a hole with your 60mm holesaw.
  2. Make the 60mm hole in your workpiece. You could leave it slightly undersize (1mm or so).
  3. Use your template with a 45 degree chamfer router bit with a bottom bearing to cut the bevel. Don't try to hog it all off in one go - take small bites.

If you don't have access to a router you could use a half-round file or rasp if you have a good eye.

  • Thank you for your effort in answering. A router is on my to buy list, but for now I have to try work it out with what I have (jig saw at 45 degrees as well as the file might be my only option for now but as you say, the result will not be as clean). – David Jun 17 '18 at 13:30

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