# Spiral vs straight-plunge



## guitarmaker (Feb 8, 2009)

Hi folks-
New guy here.
I am currently using straight bits in a small laminate trimmer motor to cut pickup openings in guitar bodies. I wonder if anyone can speak to the advantages/disadvantages of using spiral bits instead? I am doing low-volume production work (making maybe 10-12 openings a day that are approx 2X3" and .750 deep) in Maple mostly.
I am thinking that the spiral bits might put less strain on my duplicator rig (shop built) and small 1Hp router motor, any thoughts?
TIA.
Stan


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## xplorx4 (Dec 1, 2008)

Greetings Stan and welcome. I am afraid I cannot help you but will study the answer to learn the difference.


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## bobj3 (Jan 17, 2006)

HI Stan

spiral bits will work much better, but you may want to check out the link below..
http://www.precisebits.com/products/carbidebits/taperedcarve250b4f.asp

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guitarmaker said:


> Hi folks-
> New guy here.
> I am currently using straight bits in a small laminate trimmer motor to cut pickup openings in guitar bodies. I wonder if anyone can speak to the advantages/disadvantages of using spiral bits instead? I am doing low-volume production work (making maybe 10-12 openings a day that are approx 2X3" and .750 deep) in Maple mostly.
> I am thinking that the spiral bits might put less strain on my duplicator rig (shop built) and small 1Hp router motor, any thoughts?
> ...


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## Ralph Barker (Dec 15, 2008)

From my perspective, the choice depends on the nature of the cut and the nature of the wood being cut. 

With shallow cuts, such as hinge mortises and such, there's plenty of room for the waste to escape. With deeper cuts, however, waste being trapped in the cut can be a problem, since the waste is being expelled at right angles to the cutting surface.

A spiral bit (with the proper spiral direction) solves that problem by pulling the waste out of the cut. An additional advantage is the cut, being skewed across the cutting surface, is often much smoother. This can be a _huge_ plus in woods having unusual grain.

One downside to spiral bits, however, is that they are made of solid carbide, and are thus more brittle than a high-speed steel core.


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## Skyglider (Nov 2, 2008)

guitarmaker said:


> Hi folks-
> New guy here.
> I am currently using straight bits in a small laminate trimmer motor to cut pickup openings in guitar bodies. I wonder if anyone can speak to the advantages/disadvantages of using spiral bits instead? I am doing low-volume production work (making maybe 10-12 openings a day that are approx 2X3" and .750 deep) in Maple mostly.
> I am thinking that the spiral bits might put less strain on my duplicator rig (shop built) and small 1Hp router motor, any thoughts?
> ...


Hi Stan,

I'm a new guy also and can only comment from what I've read rather than from experience. I wonder if shear angle straight bits would work for your application? Shear angle straight bits are supposed to "slice" the wood similar to spiral bits. Sort of between a straight bit and spiral bit. The advantage of shear angle straight bits is that they can be carbide tipped instead of made out of solid carbide and can therefore be noticeably less expensive than solid carbide spiral bits.

Here's a link to the MLCS shear angle bits:
http://www.mlcswoodworking.com/shop...ml/pages/bit_straight.html#shear_angle_anchor

I haven't used this bit so the link is just provided as a reference, not a recommendation.


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## guitarmaker (Feb 8, 2009)

Skyglider said:


> Hi Stan,
> 
> I'm a new guy also and can only comment from what I've read rather than from experience. I wonder if shear angle straight bits would work for your application? Shear angle straight bits are supposed to "slice" the wood similar to spiral bits. Sort of between a straight bit and spiral bit. The advantage of shear angle straight bits is that they can be carbide tipped instead of made out of solid carbide and can therefore be noticeably less expensive than solid carbide spiral bits.
> 
> ...


Thanks Skyglider-
I have tried these bits and they work well for trimming to a template, especially with wood that likes to tearout. I have only found them in limited sizes though. I guess I need to experiment (always the best way, right?) and report back...Thanks,
Stan


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## dovetail_65 (Jan 22, 2008)

Freud also makes a helical shear router bit where the carbide is not just on an angle, but circlse around the cutter slightly like a DNA strand. I believe these are the best I have used.

The draw back to the solid crbide(which I love by the way) as much as cost is that they are brittle and tend to snap in half right when you need it most. The solid carbide are slightly less safe than a traditional bit also.

Does anyone else make the Helical non solid carbide router bit like Freud?


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## dovetail_65 (Jan 22, 2008)

Freud also makes a helical shear router bit where the carbide is not just on an angle, but circles around the cutter slightly like a DNA strand. I believe these are the best I have used.

The draw back to the solid carbide(which I love by the way) as much as cost is that they are brittle and tend to snap in half right when you need them most. The solid carbide are slightly less safe than a traditional bit also.

Does anyone else make the Helical non solid carbide router bit like Freud?


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## bobj3 (Jan 17, 2006)

Hi Nick

Check out the link below

http://www.toolstoday.com/nsearch.aspx?keywords=helical+shear+router+bit&x=10&y=10


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nickao65 said:


> Freud also makes a helical shear router bit where the carbide is not just on an angle, but circles around the cutter slightly like a DNA strand. I believe these are the best I have used.
> 
> The draw back to the solid carbide(which I love by the way) as much as cost is that they are brittle and tend to snap in half right when you need them most. The solid carbide are slightly less safe than a traditional bit also.
> 
> Does anyone else make the Helical non solid carbide router bit like Freud?


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## dovetail_65 (Jan 22, 2008)

Yes but those do not look helical. On the Freud you can visually see the carbide circling around like on a solid bit, those on that page look like a simple down shear from the pictures. And in the actual description of the bits it does not say Helical, just down shear so I am unsure they are the same. They very well may be, but do not look like it.

Maybe the Freud expert here can comment on these Helical bits are they different . Freud sells down shear and then they sell Helical down shear and they sure seem different and the helical I have sure works well and appears to wrap around more than my other down shear bits.

Plus these bits state:

"Designed primarily for production applications where the router is above the work. *It is not intended for use in a handheld or table-mounted router* or in a shaper".


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## crquack (Oct 10, 2008)

> Does anyone else make the Helical non solid carbide router bit like Freud?


I have used a HSS spiral bit from Lee Valley on limited occasions with success. They are about half the price of carbide.

I understand, however, that HSS has few friends on this forum


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## TWheels (May 26, 2006)

What am I missing here? How are the bits being discussed different from those sold by MLCS at the following URL:

http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/bt_solid.html#spiral_up_anchor

I have most of these bits. I have had problems wih the smaller sizes breaking but I suspect operator error as the primary cause.

I do not know of any similar spiral bits that are not solid carbide, but I do agree that carbide tipped spiral bits would probably be much more tolerant of "operator error"


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## dovetail_65 (Jan 22, 2008)

Well the bits we are discussing are totally different in the respect they are not solid carbide and made like a traditional bit, but the carbide instead of just going straight down comes down on an angle or helical shape like they do on the solid carbide bits. 

One drawback of solid carbide is that they are brittle and a lot of times it is not operator error that breaks them, more the nature of the beast. If you hit a hard knot in the wood or something much harder in the wood it may be enough to break a solid carbide bit. Plus the solid carbide is more expensive.

A down shear bit and a helical down shear try to mimic(in a slight way) the barber shop pole design of the solid spiral bit.. These bits slice or shear the wood like a spiral as opposed to cutting it dead on. Some have more of an angle than others, in this picture you can see how the carbide does not come straight down, it's angle is slight, but enough to slice the wood.


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## Rick500 (Oct 28, 2007)

Hi Stan! I build guitars too. Good to see another luthier here.


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## guitarmaker (Feb 8, 2009)

Rick500 said:


> Hi Stan! I build guitars too. Good to see another luthier here.


Thanks Rick- What do you build?
Stan


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## Rick500 (Oct 28, 2007)

Mostly solid body electrics. I'm brewing up a plan for a semi-hollow, currently. One of these days I'll try my hand at acoustics as well.


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