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Discussion Starter · #1 ·
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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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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Rick
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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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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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Doug
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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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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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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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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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Theo
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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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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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Discussion Starter · #15 ·
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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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
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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Doug
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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
So……… how did it work out? problem solved?
 

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Discussion Starter · #19 ·
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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Rick
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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.
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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