Advice for cutting circles with router!? - AVS Forum
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post #1 of 15 Old 11-29-2011, 02:56 AM - Thread Starter
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What is the best way to get the hole started for the bit? This is causing a lot of trouble for me. Do the spiral bits self-drill? I mean if the router bit is sitting flat against the wood and it spins up, how can it possibly drill the hole? Wouldn't it just stop up the bit? As far as I can tell, it seems you need a pre-drilled hole for the bit to freely spin up before you can begin the cut.

If the circle guide is laying flat against the board, and the bit is raising the router end up a little, wouldn't this slightly throw off the diameter of the cut?

These picture demonstrates what I'm talking about:




Cheesy, i know, don't hate lol. You see how the guide angles upward from the center point towards the router due to the bit's depth? I understand the depth is adjustable but I just don't know how to get the initial cut going :/.

Thanks for your expertise.

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post #2 of 15 Old 11-29-2011, 03:31 AM
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Upspiral bits will self drill into the wood, but its not the safest way to do it. Circle jigs are usually used with plunge base routers.
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post #3 of 15 Old 11-29-2011, 04:38 AM
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Not sure what kind of jig your using , but there is usually enough flex with the plastic or self made plywood ones to lift slightly above material and then drop.
Practice on scrap to get a feel for it.
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post #4 of 15 Old 11-29-2011, 05:40 AM
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Quote:
Originally Posted by rocko1290 View Post

wouldn't this slightly throw off the diameter of the cut?

If you are doing multiple passes and are starting with a 1/4 inch cut the answer is not enough to ever tell.
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post #5 of 15 Old 11-29-2011, 05:56 AM
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You draw your circle with a pencil... set up your plunge router with the proper bit... make sure the router is unplugged and turn the bit with your hand where it's most outer edge is just touching the pencil mark on the wood tighten your circle jig.. set your plunge for at least 1/4" depth.On MDF you might need to vacuum out the groove to continue..

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post #6 of 15 Old 11-29-2011, 06:25 AM
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The cut can't exceed the outer diameter of the set-up when it's completely flat, raising it a little would only reduce the diameter, so if it was off it would be to the inside.

Wanted to clarify, start with small cut as BIGmouthinDC has said. the flex should be enough to hold the base level with material (will require a moderate amount of force). Homemade ply jigs 1/4" work great (lots of flex).
Don't have bit set to 1" and angle base into cut.
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post #7 of 15 Old 11-29-2011, 08:34 AM
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A plunge router is the way to go and all my straight cut bits will drill their own starting hole. I can't imagine adjusting the bit depth in the collet several times on a standard base to do a multi-pass circle cut. Must be a pain. And i've learned it's not a good idea to cut 3/4" MDF in one pass.. killed my bits pretty quick.

I had some foresight and got a dual-base craftsman router a few years back. I figured it would be good to be able to switch. I don't think i've used the fixed-base a single time since i got it.


If you're cutting a lot of driver holes, the Jasper Jig is definitely worth the money in my opinion.
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post #8 of 15 Old 11-29-2011, 09:56 AM - Thread Starter
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Quote:
Originally Posted by jackbuzz View Post

The cut can't exceed the outer diameter of the set-up when it's completely flat, raising it a little would only reduce the diameter, so if it was off it would be to the inside.

Which is a problem when the project requires the use of the circle, and not just the hole, such as when cutting the end caps for a sonosub.

Quote:


Wanted to clarify, start with small cut as BIGmouthinDC has said. the flex should be enough to hold the base level with material (will require a moderate amount of force). Homemade ply jigs 1/4" work great (lots of flex).
Don't have bit set to 1" and angle base into cut.

I've got to say I'm having trouble following this. Not sure what the "flex" is that you guys are referring to.

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post #9 of 15 Old 11-29-2011, 09:57 AM - Thread Starter
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Quote:
Originally Posted by BigJim_inFLA View Post

Upspiral bits will self drill into the wood, but its not the safest way to do it. Circle jigs are usually used with plunge base routers.

I will probably run to home depot and grab and upspiral bit today. Why is this not the safest way to do it? Whats the alternative? And I am indeed using a plunge router.

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post #10 of 15 Old 11-29-2011, 09:58 AM - Thread Starter
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Quote:
Originally Posted by jackbuzz View Post

Not sure what kind of jig your using , but there is usually enough flex with the plastic or self made plywood ones to lift slightly above material and then drop.
Practice on scrap to get a feel for it.

You're saying lift and drop so that the bit can drill the hole?

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post #11 of 15 Old 11-29-2011, 10:16 AM
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I use an up spiral and it starts the hole fine.
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post #12 of 15 Old 11-29-2011, 10:48 AM
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Quote:
Originally Posted by rocko1290 View Post

I will probably run to home depot and grab and upspiral bit today. Why is this not the safest way to do it? Whats the alternative? And I am indeed using a plunge router.

If you are using a plunge router then anything I have said need not apply. Simply set-up for cut and drop into material depending, upon how thick or how deep the cut (if thick make multiple passes say 1/4"-3/8" at a time). Set stop on router so you can't go to deep.
If you are not experienced with a router make some practice cuts to get the feel of it.
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post #13 of 15 Old 11-29-2011, 12:10 PM
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He may also need to fully understand how to use the plunge function for a cut like this. It's ok Rocko, I learned alot from my first router as well.

Basically, set the depth of cut, raise the bit, start the router, then plunge into the workpiece until you reach the 'stop'. Make your circle, then increase your depth and go through again. Do this as many times as it takes till you cut through. Hopefully your plunge router has the ability to work using this procedure.

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post #14 of 15 Old 11-29-2011, 03:02 PM
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A mortise-type bit also works. It has cutting edges on the sides and on the bottom. Some "straight" bits don't have cutting edges on the bottom.
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post #15 of 15 Old 11-29-2011, 03:32 PM - Thread Starter
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Quote:
Originally Posted by mobeer4don View Post

A mortise-type bit also works. It has cutting edges on the sides and on the bottom. Some "straight" bits don't have cutting edges on the bottom.

I think this was my main issue at first. I was cutting with a rather large straight bit with no sharp edge on the bottom.

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