Thread: Cutting a 90mm diam circle

I have one of these, use it to cut large holes in my nest boxes for Kookaburras and ducks

Wouldn't use it in a handheld drill though, I use it on slowest speed in my drill press.

Adjustable Circle Hole Cutter for Electric Drills 30mm to 200mm | eBay

Crikey Fred, does that look scary ! - imagine it whizzing around at 300rpm

I imagine that it would be difficult to get the two cutting blades at the exact same cutting distance from the centre ?

Yeah, you don't want to stick your nose too close

I run mine at the slowest drill press speed, can't remember what that is but wouldn't be slower than 300rpm.

It isn't too bad, I usually do batches of about 40 nest boxes and have never had a "scary" moment.

I have made some template holes and use those to set the cutters, but to start with I drew some circles with a compass and lined the cutters up with that. The cutters are quite sharp and cut quite a clean hole, no burning.

Edit:

Just checked, minimum speed is 450rpm. I have a 3phase motor and am planning to install that with a VFD to get more control over my drill press speeds, but my metal mill needs to be done first.
Too many projects, not enough time

Originally Posted by Dengue

Crikey Fred, does that look scary ! - imagine it whizzing around at 300rpm

I imagine that it would be difficult to get the two cutting blades at the exact same cutting distance from the centre ?

I have a one sided version and have used it in my drill press at 160 RPM and it works OK.

If you have access to a router a circle cutting jig in a router will cut a very tidy circle.
These are relatively easy to make and come in hole and no-hole versions.

Hi Dengy,

90mm is the exact size of hole that a lot of downlights are mounted in. You can buy a 90mm hole cutter from your hardware quite easily. They are sold for this purpose. Fine in a hand drill, but I think for accuracy, I'd use a Press.

Regards,

Rob

Originally Posted by Big Shed

Just checked, minimum speed is 450rpm. I have a 3phase motor and am planning to install that with a VFD to get more control over my drill press speeds, but my metal mill needs to be done first.

Just started working on mine yesterday - hopefully will finish today. Upgraded from a 1 kw to 1.125 kW motor. I have left the original motor pulley on so lowest practical RPM is 64 rpm

Originally Posted by BobL

Just started working on mine yesterday - hopefully will finish today. Upgraded from a 1 kw to 1.125 kW motor. I have left the original motor pulley on so lowest practical RPM is 64 rpm

These things need a bit of torque at their bigger settings, do you expect to get good torque with that VFD/3pahse setup?

BTW I tried the one sided one and found it very unbalanced at the sort of sizes I use it for.

Originally Posted by Big Shed

These things need a bit of torque at their bigger settings, do you expect to get good torque with that VFD/3pahse setup?

They sure do. I guess I'll find out this morning.

BTW I tried the one sided one and found it very unbalanced at the sort of sizes I use it for.

I agree they are unbalanced at the larger sizes.

If you have a router make one of these very easy to make.



Regards
Harold







router circle jig (1).pdf

Originally Posted by pal

If you have a router make one of these very easy to make.
Regards
Harold
router circle jig (1).pdf

Great tutorial Harry, looks like a handy piece of kit. For the complete novice (me), would you happen to have a video on how to use the jig?

I think I understand the concept but not sure how you anchor the centre point. Also, what happens when you make the final plunge and break through, doesn't the disc come free and ruin your alignment? I must be missing something.

Very nice, Harold, just what I was looking for. I like the construction guide, warts and all

Looking forward to your answers to the points cray- raised, and yes, a video of it in operation would be great.

PS Would kill for a drill press table like you have

Hi Dengy,
sorry I don't have a video of it, The pin in picture 15 anchors the router to the centre point, don't rout right through with your last plunge leave a mil or two then remove the disc with a sharp knife.

Regards
Harold

Got it.

What about if you had a longer centre pin that went through your work piece and into a sacrificial piece below? That way you could route all the way through but it'd still be anchored? Maybe that's over complicating things, knife will certainly work. Cheers.

I must point out that this PDF is not my work although I have made one of the jigs. It was posted on another forum by a member (Harry Sinclair). So all thanks for the design and credit must go to Harry.

Regards
Harold