# Enlarge a completed cut out circle?



## newbie2wood (Apr 22, 2016)

Now that I've finished my circle project, I ran into a gotcha...

Once I cut out the circle, it wasn't large enough by just a hair and I needed to enlarge the circle - about 1/4".

But, since the center was cut out, I couldn't figure out how to enlarge it with the router without doing it free hand.

I tried and almost really messed it up since I could not control the router around the circle, so I switched to my jig saw and did the best I could.

Is there (there must be) some technique or jig for enlarging a hole once it's been cut out?

Thanks as always in advance


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## lowracer (May 22, 2015)

Use a straight bit, with a guide bearing - then swap out the bearing with one where the radius of the bearing is 1/4 inch smaller.

so the first time you cut a rabbet. 

then afterwards you just use a trim bit where the bearing and the bit are the same.


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## RainMan 2.0 (May 6, 2014)

I would cut another circle out of a piece of material that would fit tightly inside the hole you have now ,thus providing a surface to secure to . 

Or you can cut a bigger hole in another piece of material and secure it on top of your hole to act as a guide for a flush mount bit on your router and remove the excess material .

Is this a subwoofer box? I always do a test hole on another piece of material first. Once I get it perfect I save the plug for future woofers


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## mgmine (Jan 16, 2012)

I would place another piece of wood under the hole and use that piece of wood to attach the trammel to. You might not be able to get the new circle in the exact location but as long as the bit was able to cut on all sides the circle would be round.


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## Stick486 (Jan 4, 2013)

newbie2wood said:


> Is there (there must be) some technique or jig for enlarging a hole once it's been cut out?


cut a bearing guided rabbet to desired depth...
switch to a bearing guided straight bit...
follow the inset wall of the rabbet w/ the straight finish to the size you need...


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## kp91 (Sep 10, 2004)

Since you may have boogered up the shape of the original hole, I would agree with tacking your workpiece to a sacrificial board. Then take the center piece you cut out originally and tacking that to the sacrificial board, centered as best as you can. Use your circle cutting jig again.

You'll get a better looking circle, more practice with the jig, and less frustration.


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## harrysin (Jan 15, 2007)

lowracer said:


> Use a straight bit, with a guide bearing - then swap out the bearing with one where the radius of the bearing is 1/4 inch smaller.
> 
> so the first time you cut a rabbet.
> 
> then afterwards you just use a trim bit where the bearing and the bit are the same.


Wont that remove 1/2"? A 1/4" all round.


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## chuckgray (Aug 2, 2015)

harrysin said:


> Wont that remove 1/2"? A 1/4" all round.


True, but we don't know if the OP was referring to 1/4" radius or diameter.


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## Cherryville Chuck (Sep 28, 2010)

If you still have the sacrificial backing board and it has both the center hole in it and the outline of the original circle showing (provided you cut into it slightly when you did the original) you can line the finished hole with that outline and then drill a piece of ply the same size and pin through it into the original center hole and simply cut a slightly larger circle. You'll be set up exactly the same the second time around.


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## The Hobbyist (Apr 25, 2015)

I just use the new Kreg Hole Stretcher. :grin:

Joe


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## PhilBa (Sep 25, 2014)

chuckgray said:


> True, but we don't know if the OP was referring to 1/4" radius or diameter.


Worse than that, we don't know the true difference - OP said "about". The bearing swap or rabbet (basically the same) approach will only work if the difference is a standard size. If it is, that's great. If not then the sacrificial approach is the only way to go.


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## Herb Stoops (Aug 28, 2012)

I would just throw it in the garbage and go take a nap, then come back another day and try it again.
Herb


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## JOAT (Apr 9, 2010)

Depending, I possibly would just sand it larger. But if the edge will be out of sight, might just cut it with a sabre saw, and call it good enough. Look at some antique furniture some time, the parts that are not seen are not as pretty as the parts that 'will' be seen.

Almost forgot. I take out the centers of a lot of my projects, mostly banks. For that I mark exactly the hole size I want. Then drill a hole, so I can use my sabre saw to rough cut as close the the like as reasonable. Then sand down to the line. That is my master. Then tack that down, then use that as a guide to rout exactly the size hole I want. Then can use the master to make as many more holes as I want, all the exact same size. That way I only have to worry about making just one perfect hold, the rest are all clones. Easy peasy.


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## harrysin (Jan 15, 2007)

This is how I overcame the problem. An extra long pin in the circle jig so that it went through the sacrificial table using the original hole. It would be simple enough to mark a hole in the sacrificial table then center the cutout by measuring, then drill a hole to suit the pin in the jig. The work-piece is held to the table with a scrap of wood/MDF against each side.


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## newbie2wood (Apr 22, 2016)

harrysin said:


> This is how I overcame the problem. An extra long pin in the circle jig so that it went through the sacrificial table using the original hole. It would be simple enough to mark a hole in the sacrificial table then center the cutout by measuring, then drill a hole to suit the pin in the jig. The work-piece is held to the table with a scrap of wood/MDF against each side.


Thanks @harrysin

Oh, I like that scrap idea a lot - then clamp the sacrificial to the table?

When you pin into the sacrificial table, is that something you keep on hand or do you use a new piece all the time?

My thought is to keep a sacrificial piece on hand until it has too many cuts then swap it for another.

That would mean yet another lumber piece to keep in the shop as if I don't have enough scraps 

Thanks as always in advance


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## harrysin (Jan 15, 2007)

newbie2wood said:


> Thanks @*harrysin*
> 
> Oh, I like that scrap idea a lot - then clamp the sacrificial to the table?
> 
> ...


I use a sheet of 3/4" chipboard on top of my router table. It has an angle Aluminum strip front and rear which holds it firm. I only replace it when it is too disfigured as you have suggested.


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## cris (Aug 12, 2005)

chuckgray said:


> True, but we don't know if the OP was referring to 1/4" radius or diameter.


Or 1/4" circumference.


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## kp91 (Sep 10, 2004)

newbie2wood said:


> Thanks @harrysin
> 
> Oh, I like that scrap idea a lot - then clamp the sacrificial to the table?
> 
> ...


So……… how did it work out? problem solved?


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## newbie2wood (Apr 22, 2016)

kp91 said:


> So……… how did it work out? problem solved?


I didn't really enlarge it that much - I used a jig saw and cut out a few areas that was missed when I set the router to the diameter and missed the size.

I posted the results in this thread:
https://www.routerforums.com/general-routing/141435-routing-out-circle-jig-need-advice-please-2.html

But with all this help, I know what to do next time.

I have another project coming up now that I know how to cut a circle, I can cut a few.


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## RainMan 2.0 (May 6, 2014)

newbie2wood said:


> I didn't really enlarge it that much - I used a jig saw and cut out a few areas that was missed when I set the router to the diameter and missed the size.
> 
> I posted the results in this thread:
> https://www.routerforums.com/general-routing/141435-routing-out-circle-jig-need-advice-please-2.html
> ...


When I cut holes for subwoofers I was very critical and wanted the hole to be within a rickometer , ( that’s one bizzilionth of a meter) , so I would use another piece of material that was thinner , like 1/4” , and do a test hole . 
Once I had the perfect hole I would save the plug that was cut out and write on it so that I had a template saved for the next time.
It’s so easy in the future to secure your circle jig and router to the plug you saved and set it up for the same cut . Well as long as you turn the router bit till the carbide cutting area is touching the edge of the previous plug you cut out


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## DaninVan (Jan 1, 2012)

You wrote on the plug which bit you used, right, Rick?


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## RainMan 2.0 (May 6, 2014)

DaninVan said:


> You wrote on the plug which bit you used, right, Rick?


Nope ,I got that in my head . But good point . FYI , I always use a 1/4” ,as why would you hog out more material than you need to . Not sure if I’d trust anything smaller ,and don’t actually own anything in a smaller diameter


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## newbie2wood (Apr 22, 2016)

RainMan 2.0 said:


> When I cut holes for subwoofers I was very critical and wanted the hole to be within a rickometer , ( that’s one bizzilionth of a meter) , so I would use another piece of material that was thinner , like 1/4” , and do a test hole .
> Once I had the perfect hole I would save the plug that was cut out and write on it so that I had a template saved for the next time.
> It’s so easy in the future to secure your circle jig and router to the plug you saved and set it up for the same cut . Well as long as you turn the router bit till the carbide cutting area is touching the edge of the previous plug you cut out


So wait a minute... I'm not understanding something...

If you cut out a circle, let's say it's 12" diameter (that's 6" radius correct?) and you use the one you cut out for a template.

Wouldn't using the template make the cutout larger because of the kerf of the bit (not sure if kerf is the correct term for the width of a bit, it would be for a saw blade width).

I ask this because I want to cut out multiple 1/8" sheets of BB plywood for some projects and I need a 12" circle every time.

Thanks in advance


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## RainMan 2.0 (May 6, 2014)

No not at all . You merely put the guide pin back in the 1/8” hole on the plug then set the guide till the carbide edge of the bit is just kissing the plugs edge . 
You replicate the last one exactly ,and it always worked for me .

If your in doubt, use a scrap to test on . I never just measured and assumed it would fit . I always used a piece of 1/2” or 1/4” scrap and did a test . Sometimes a few tests to get it right.
When I dropped a subwoofer in the hole it usually took a few seconds for it to seat . That’s how accurate I could make it


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