How do I cut this hole

[The Bear]

OK, what I want to do is cut a 41mm diameter hole in some 18mm ply. I have some plastic pipe that is 41mm outside diameter that I want to let into the hole with a nice snug fit. So how? I'm not aware of 41mm spade or forstner bits anywhere, plus I'd like not to have to buy something like one of those drill bits with an adjustable beam with a cutter on the end.

I've tried to free hand the hole with the router but result wasn't great. I'm thinking I need to cut a bit of the pipe to use as a template and use either a collar or bearing guided bit to make a wooden template from this. But I'm struggling to think how? If I could cut the 41mm hole in a bit of mdf I could just then use a bearing guided bit to copy it.

Hope that makes sense. Any ideas?

Mark

 

[Paul Chapman]

Make up a small circle cutter jig for your router. Example on Ron Fox's page here http://www.wealdentool.eu/rf_tips/rf_tips_04.html

Cheers :wink:

Paul

 

[Steve Maskery]

Well there are a couple of approaches.

Do you have a rebate router bit? Something like the CMT Master kit, for example? That has a 1/8" bearing capacity.

So you could drill a 35mm hole (standard Euro hinge bit) then run a 1/8" rebate halfway through. Then flush to that.

Result!

Either that or its a circle-cutting jig that will cope with very small radii.
S

 

[petermillard]

How good a finish does it need to be? Would a 41mm holesaw do the job??

 

[Mr Ed]

I would never have though of doing it that way Steve - funny how the mind works, its a good solution.

Ed

 

[The Bear]

Thanks so far

I didn't think I'd get a holesaw that diameter. I don't really want to spend anything if I can as I only need 2 holes, so this will be my last resort option

Ron Foxs jig looks interesting, but fiddly to make and use I bet. It also looks like you really need to use perspex for the base which I dont have otherwise you wont see what you are doing.

Steve, I like your idea best, I'd not thought of anything like that. Guess thats why you are "Mr Jig". I do have a rebate cutter but no idea what size or what size bearings I've got, so will look at them tomorrow.

3 good ideas to try, thanks guys

Mark

 

[big soft moose]

i would have thought that the easiest way would be either a router or a jigsaw on a pivot - just a strip of perspex or hardboard with a pin in one end - pin in the centre of the circle , blade or outside of cutter 20.5mm from the pin - quick circle - et voila job jobbed ( if using a jigsaw you'd need to drill a small access hole first to start the cut)

 

[Paul Chapman]

Ron Foxs jig looks interesting, but fiddly to make and use I bet. It also looks like you really need to use perspex for the base which I dont have otherwise you wont see what you are doing.

Very easy to use and you don't need perspex - MDF is fine. The main point to remember when using it is to stick the workpiece to a sacrificial piece of MDF with double-sided tape so that you can cut right through. Also the pivot point is on the piece you are cutting out, so the double -sided tape stops it moving as you cut through.

Hope this helps.

Cheers :wink:

Paul

 

[Harlequin]

will these do?



http://www.toolstation.com/shop/Power+T ... 400/p72369

http://www.toolstation.com/shop/Power+T ... 400/p47076

 

[Tintin]

If you mess up the hole you could always rough it out to say 44mm and cut 25mm off the end of a push fit straight coupling and use it as a grommet for your pipe to fit through. The flange of the coupling should cover any irregularities in the hole and provide a snug fit for the pipe.

 

[matt]

For such a small hole I think I'd use a coping saw (if you have one).

 

[Lons]

Cheapest option is Toolstation.com (check to see if branch near you to save postage) Screwfix also an option.

Bi metal holesaw 40mm will cut a 41mm hole if sanded At £2.97 / item 71338 plus arbor £4.20 / 50147. You can also buy dewalt a bit dearer. or a couple of holesaw sets very cheaply.

All plumbers have 32 and 40mm holesaws as these are std waste pipe sizes, as do most electricians. If you know anybody you might be able to borrow one.

Pity you're at the other end of the country or you could use one of mine.

You can also buy on most market stalls, a kit consisting if a plastic / metal disk with pilot drill. The disk has a series of grooves into which you can clip any of the various sized blades provided.
The one I bought a few years ago still works and I'm sure it's got a 40mm blade. Ok for occasional light work and cost me around £3

Bob

 

[monkeybiter]

if you've got a lathe you can turn a hole in a template for the router.

 

[Sportique]

i would have thought that the easiest way would be either a router or a jigsaw on a pivot - just a strip of perspex or hardboard with a pin in one end - pin in the centre of the circle , blade or outside of cutter 20.5mm from the pin - quick circle - et voila job jobbed ( if using a jigsaw you'd need to drill a small access hole first to start the cut)

My for 2p worth - bsm has the answer - I often use this method, and, as bsm says, it doesn't need to be see-thru

Dave

 

[Racers]

Hi,

Drill a series of holes and pair back to the line with a gouge, or a sanding drum in a drill press or hand held.


Pete

 

[WellsWood]

If your router has a round base there is a really easy way to do this which is both accurate and repeatable - simply cut a template with a large hole and use the router base as the guide.
The size of the template hole is easily worked out from router base, cutter and required hole diameters, and will be a doddle to cut with a jigsaw or similar to a line marked with a compass then cleaned up with sandpaper.

The really big advantage with this method is you'll be referencing off something with is attached the workpiece rather than the waste.

 

[wobblycogs]

Depends on whether you want it super tidy or just a snug fit but as it's got a pipe coming out of it I'm guessing it's not on show. A very low cost option would be chain drilling (or jigsaw if you have one) and then file it to shape. Won't be as accurate but it avoids template making etc for one hole.

In fact simpler than that Axminister are doing their metric forstner bit set on special http://www.axminster.co.uk/product-15-Piece-Axminster-TiN-Coated-Forstner-Bit-Set-816857.htm. Drill at 40mm tickle with a file to 41mm.

 

[SeanG]

Bear,

I've done this in the past using an MDF base plate screwed to the router, this had a pin in it to turn it into a compass.

Drill a hole the same size as the pin, in the work. Set the router cut depth to just under half the thickness of the work.

Cut a circular groove in the work, turn it over, cut another circular groove from the other side. As the cut depth was under half thickness, the remaining web stops the centre of the cut out falling away whilst routing. The inner piece can then be cut out with a knife.

It sounds longwinded, but you don't need to worry about the cutter hitting your bench, or the cutter nipping off into the bits you don't want to cut.

HTH

 

[The Bear]

Guys

Thanks for all the replies. I've now done this using Steve M's method of drilling a hole and widening it with a rebate cutter, got a nice snug and tidy fit.
I'm sure the mine circle cutting jig suggested by many would have worked just as well, but this ultimately was quicker as I didn't need to make even a simple jig.

Mark

 

[Steve Maskery]

I win, I win!
Very glad (and slightly relieved) that it worked out OK.
What an excellent thread, eh, a thousand ways of achieving the same end
S