LumberJocks

Looking for clarity around spiral router bits

  • Advertise with us

« back to Power Tools, Hardware and Accessories forum

Forum topic by rubber_ducky posted 03-08-2016 07:40 PM 512 views 1 time favorited 8 replies Add to Favorites Watch
View rubber_ducky's profile

rubber_ducky

35 posts in 344 days


03-08-2016 07:40 PM

Hi all, I’m hoping to glean from the collective knowledge-base here to get a better understanding as to what router bit to use for a project of mine.

I’d like to route circles in 3/4” BB ply. I own (but have never used) both up-cut and down-cut spiral bits. From everything I’ve been able to read on the topic, down-cut bits leave a clean cut on the top of the work-piece while up-cut bits leave a clean cut on the bottom of the work-piece. Easy-peasy so far.

There also exist compression bits that are down-cut near the shank and up-cut near the tip, resulting in through-cuts with a clean cut on both the top and bottom. As the up-cut/down-cut transition is in the middle of the cutting length, the transition area needs to be centered in the work-piece. Makes sense.

Questions though… I’ve been taught to limit the cutting depth and make multiple passes when using a straight router bit. It seems that through-cuts using a compression bit should be done in a single pass (so that the up-cut/down-cut transition is centered in the cut). Is this correct?

And in my case, where I don’t have access to a compression bit, can I cut make two (or more) passes, first with a down-cut bit for a clean top and then do my final pass(es) with an up-cut bit for a clean bottom?

http://www.woodcraft.com/articles/445/spiral-router-bits-vs-straight-router-bits.aspx


8 replies so far

View Fred Hargis's profile

Fred Hargis

3949 posts in 1960 days


#1 posted 03-08-2016 07:53 PM

Generally, if you use the compression bit, you would cut the circle out first with a bandsaw, jigsaw or such close to line (+1/16” or so) and then clean it up with the bit. I would suggest you do that even with an up cut (or down cut) bit. Uou may be overestimating just how much clean up there is with either bit. Try a test cut first and see if the “fuzz” ( which is about all you will get with a good, sharp bit) is excessive. I’ve always been able to clean it up with a swipe or two of sandpaper. You could do the bit-swap routine I suppose, but it sounds like a hard way to solve what may be a non-problem.

-- Our village hasn't lost it's idiot, he was elected to congress.

View rubber_ducky's profile

rubber_ducky

35 posts in 344 days


#2 posted 03-08-2016 08:36 PM

Ahh… makes sense. In that case, I suppose that I’d be putting away my circle cutting jig and instead use a template with either a bearing equipped compression bit or a guide bushing & non-bearing bit.

Good to know about the level of uncleanliness the bits leave. Truth be told, I don’t need the edges super clean as I’ll be rounding them over, it was more a matter of curiosity.

Thank you for the response.

View Kazooman's profile

Kazooman

628 posts in 1419 days


#3 posted 03-08-2016 08:49 PM

Have you tried rounding over the edges of a piece of the plywood to see how it comes out? I know it is BB, but with the angle of the curve you end up with some very thin edges on some of the plies.

View splintergroup's profile

splintergroup

829 posts in 689 days


#4 posted 03-08-2016 08:51 PM

I cut a lot of circles for glass displays (basically cut out wood rings).

I do this on a router table with a jig. The jig consists of a simple centering pin.

I have no trouble with ‘fuzz’ and use a spiral upcut bit exclusively. As Fred says, trim close to the final surface with a bandsaw.

Typically I’ll place my wood on the jigs pin, then raise the bit into the wood as I slowly rotate the wood on the jig. After the bit has risen enough to completely cover the edge, I’lll give the wood a few more turns to clean up and then retract the bit. Note that I have the wood trimmed so that the router is removing maybe 1/16” (1/2” shank, 1/2” spiral up cut bit).

Those compression bits look like they would be great for template routing, but they are $$$$!

View rubber_ducky's profile

rubber_ducky

35 posts in 344 days


#5 posted 03-08-2016 10:47 PM


Have you tried rounding over the edges of a piece of the plywood to see how it comes out? I know it is BB, but with the angle of the curve you end up with some very thin edges on some of the plies.

- Kazooman

I haven’t tested the bit on the ply yet. This whole project is a bit experimental. Im making a simple router table fence and the circle is the cutout for dust extraction. The roundover (or chamfer) is simply to smooth out the airflow. I have a Holesaw that I could use for the port. I could also use a jigsaw. I’m just trying to test out the circle jig for my router and use the spiral bits that were gifted to me.

I appreciate the heads up though.

View rubber_ducky's profile

rubber_ducky

35 posts in 344 days


#6 posted 03-08-2016 10:52 PM



I cut a lot of circles for glass displays (basically cut out wood rings).

I do this on a router table with a jig. The jig consists of a simple centering pin.

I have no trouble with fuzz and use a spiral upcut bit exclusively. As Fred says, trim close to the final surface with a bandsaw.

Typically I ll place my wood on the jigs pin, then raise the bit into the wood as I slowly rotate the wood on the jig. After the bit has risen enough to completely cover the edge, I lll give the wood a few more turns to clean up and then retract the bit. Note that I have the wood trimmed so that the router is removing maybe 1/16” (1/2” shank, 1/2” spiral up cut bit).

Those compression bits look like they would be great for template routing, but they are $$$$!

- splintergroup

Seems very efficient.

Curious how the circle then becomes a ring (assuming that the circle then gets hollowed out)? Same jig with the centering pin placed closer to the bit or another method?

View splintergroup's profile

splintergroup

829 posts in 689 days


#7 posted 03-09-2016 03:53 PM

Seems very efficient.

Curious how the circle then becomes a ring (assuming that the circle then gets hollowed out)? Same jig with the centering pin placed closer to the bit or another method?

- rubber_ducky

I start with a ring (segmented, like one would do for turning on a lathe), but that isn’t critical.
The ‘secret’ is to use double sided tape to affix a masonite board with a centered hole onto the wood ring, the hole allows the wood ring to pivot on the jigs pin producing a prefect circle both on the outside diameter and inside diameter. I only raise the bit enough to cut through the wood, but barely nick the masonite. In general, yes the centering pin is placed closer to the bit. This provides an easy way to cut various depth/diameter rabbets. The display below is basically like a circular picture frame with a rabbet for the glass. Hidden inside is also a circular channel that contains LED side lighting, all cut on the router table with a spiral up cut bit.

What diameter are your circles? If you can have a guide pin hole in the center (1/4” – 1/2”), doing this on a router table is rather easy. I’d try a different method if the circles are smaller than 8” diameter however since a good grip is necessary to prevent the bit from trying to spin the wood. Your idea of using a down cut bit and doing 1/2 the thickness would get you the optimal cutting action to prevent edge fuzzies, but chances are, especially with BB plywood, you will get similar results cutting from just one side with a up cut bit.
Your application doesn’t need perfection obviously but doing some test cuts with tooling you already have will teach a lot on what to expect.

View rubber_ducky's profile

rubber_ducky

35 posts in 344 days


#8 posted 03-10-2016 06:44 PM


I start with a ring (segmented, like one would do for turning on a lathe), but that isn t critical.
The secret is to use double sided tape to affix a masonite board with a centered hole onto the wood ring, the hole allows the wood ring to pivot on the jigs pin producing a prefect circle both on the outside diameter and inside diameter. I only raise the bit enough to cut through the wood, but barely nick the masonite. In general, yes the centering pin is placed closer to the bit. This provides an easy way to cut various depth/diameter rabbets. The display below is basically like a circular picture frame with a rabbet for the glass. Hidden inside is also a circular channel that contains LED side lighting, all cut on the router table with a spiral up cut bit.

What diameter are your circles? If you can have a guide pin hole in the center (1/4” – 1/2”), doing this on a router table is rather easy. I d try a different method if the circles are smaller than 8” diameter however since a good grip is necessary to prevent the bit from trying to spin the wood. Your idea of using a down cut bit and doing 1/2 the thickness would get you the optimal cutting action to prevent edge fuzzies, but chances are, especially with BB plywood, you will get similar results cutting from just one side with a up cut bit.
Your application doesn t need perfection obviously but doing some test cuts with tooling you already have will teach a lot on what to expect.

- splintergroup

That’s a good looking piece. I made my cut yesterday, using the same method you described (center piece taped to the backer board). It was a 3.5” circle and I made it in three passes. Perhaps I should’ve made shallower passes, but I was being lazy and using the stop turret on my router’s plunge base which as 1/4” steps. It came out great. The required clean-up was minimal.

Thanks for all of the advise.

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com