# Straight vs Plunge Bits



## kolias (Dec 26, 2008)

I’m practicing with my hand held router by cutting slots, rabbets and dados on MDF & Plywood and need some extra bits. I’m looking at the Lee Valley catalogue to get some bits and I don’t understand this:

One section has the *Straight Plunge Bits – Double Flute*, and another section has the *Straight Cutters – Double Flute*. What is the difference between them two?

Perhaps the straight cutters are no good for plunge routing?

Thank you,


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## TWheels (May 26, 2006)

Nicolas, this topic has been discussed extensivley; a quick search revealed some 16 pages of threads. In sum, it seems that many router bit companies have a "dirty little secret". The straight bits are designed for edging but without some "trickery" cannot plunge straight down. One exception may be the spiral solid carbide bits. The bits labeled as "plunge cut" often have an extra cutter on the bottom of the bit that crosses the center. "Normal" straight bits do not have this extra cutter My experience is limitted primarlly to MLCS/Katana and Freud bits so I have no direct knowledge of other company products. 

The "normal" nonplunge cutting bits basically burn their way way down when used to plunge cut. A plunge cut can be made by angling the bit to start the cut, then cutting small depths at a time. Otherwise the wood and the bit will be burned, and a burned bit is dulled and due to the increased chance of breaking, a dangerous bit.

The MLCS and Katana plunge bits have this extra cutter and do plunge nicely. The Freud bits do not have the extra cutter but Charles M. informed me that the design allowed them to clear the material and so could plunge cut. Indeed they do but they leave a slightly raiseed, I would guess less than 1 mm height elevated area in the bottom of the plunged hole. This raised area has never interfered with anything I have tried to do that required plunge cutting to a specific depth. The MLCS/Katana plunge bits leave perfectly smooth bottoms. 

While many advocate the use of the solid carbide spiral bits for plunging, the MLCS/Katana information specifically states they do not plunge cut. I am still confused by this point, but have not pursued the point because I have straight bits designed to plunge cut.

The plunge cut bits do cost slightly more than "normal" straight bits but to me at least the extra capability make them worth extra small amount. 

I hope this post is helpful.


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## Ghidrah (Oct 21, 2008)

All the plunge bit I own have a cutter that runs across the top of the bit, all the non plunge bit have a void. If you try plunging with the non plunge bit you'll likely smell smoke from the wood that jambs between the carbide knife edges, creating mini char dowels.


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## dovetail_65 (Jan 22, 2008)

The Katana solid carbide are for mortising which by definition is plunge cutting. Mlcs also sells the solid carbide spiral as inlay bits which also is plunging.

The entire point of down cut bits is to hold the work down which again has to refer to plunge cutting.

I do not know which carbide spiral bits you are referring to that do not plunge, but I would say most do and any advertising being used saying to hold down stock or to mortise most definitely do plunge.

And if upcut bits help remove materiel(which they do) they definitely do not do it on the edge very much, so again are designed for plunge operations. I use MLCS all the time and never burned anything plunging using their bits and the new Katana solid carbide are really nice and advertise plunging.

So I would say no worries on the solid bits plunging. I think you may have misread the info on the Katana solid carbide spiral page: KATANA Solid Carbide Spiral Router Bits 

KATANA Solid Carbide Spiral Router Bits - "flute flat bottom cutters. Premium grade and superior quality micrograin solid carbide cuts faster and smoother and stays sharper longer. Upcut spiral helps remove material. Ideal for making mortise and tenon joints. Downcut spiral helps hold the material in place while using handheld routers. *Will plunge cut *and plane edges. Eliminates chipping at the top of the cut. Ideal for soft & hard woods, plywoods and composites, laminates, plastics and some non-ferrous metals. 1/4" and 1/2" shank".


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## kolias (Dec 26, 2008)

Sorry Tom, never thought to do a search before...

I guess a plunge bit is the way to go

Thank you


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## bobj3 (Jan 17, 2006)

MLCS plunge cutting straight router bits

=========


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## dovetail_65 (Jan 22, 2008)

And those are a darn good price!


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## kolias (Dec 26, 2008)

bobj you are a life saver


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## harrysin (Jan 15, 2007)

When I read the question I intended to give a detailed answer, but you have all beaten me to it. I'll simply confirm that for all my plunge routing I use plunge cutters with the extra blade at the bottom and for dowelling and the occasional mortising I use spiral cutters.


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## kolias (Dec 26, 2008)

All the bits I have came with my router and of course are the cheap ones including the 50 pc set I bought for about $40.00. 

As a beginner, I didn’t know the difference between a plunge and straight bit. I thought that since the carbide tips extend a little on the bottom of each bit I have, that they were plunge bits. Of course they do a good job but only because on each pass I take off about 1/8” MDF or plywood stock which is easy on bits. 

Now and thanks to the advice of all of you, I know that a plunge bit should have the carbide center bottom cutting tip. Perhaps all beginners should take a note of this.

Well, still learning and still have a long way to go, but is very interesting


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## TWheels (May 26, 2006)

Nicolas, what I meant to convey is that there is so much related to the topic that sorting through it all would require a substantial amount of time, so posing the question afresh is probably a good thing. Besides, things change and there could be new information.


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## TWheels (May 26, 2006)

Bob, the URL you cite leads to solid carbide bits that plunge cut. I was referring to the straight that on the web site are on the Katana straight bit page,

MLCS Router Bits and Woodworking Products
pages/katana_bits4.htm

They describe bits numbers #15450, #17740 and #17750 as Solid
Carbide	and in the description above state "2 flute, carbide tipped with bottom cutter insert for plunge cutting, (except for solid carbide router bits #15450, #17740 and #17750, which do not plunge cut).

The solid carbide bits you refer to have this discription "2 flute flat bottom cutters. Premium grade and superior quality micrograin solid carbide cuts faster and smoother and stays sharper longer. Upcut spiral helps remove material. Ideal for making mortise and tenon joints. Downcut spiral helps hold the material in place while using handheld routers. Will plunge cut and plane edges" The bit part numbers are #15141, #15161, #15146, #15145, #17467, #17487, #17468, #17488.

Can you explain the difference?



bobj3 said:


> MLCS plunge cutting straight router bits
> 
> =========


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## dovetail_65 (Jan 22, 2008)

Well those number are not spiral bits. #15450, #17740 and #17750. They seem to be straight bits that are solid carbide. 

I believe I have a few solid carbide bits that have two cutting edges and are not spiral. I will try to get one and take a pic. And they do not plunge well at all. The ones I have are also 1/4" or smaller.


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## bobj3 (Jan 17, 2006)

Hi mftha

" Can you explain the difference? " = Price for one thing.. all spiral bits will plunge ...but they are not cheap ..  and the biggest ones that I know about is the 1/2" diam.one.


"2 flute, carbide tipped with bottom cutter insert for plunge cutting, (except for solid carbide router bits #15450, #17740 and #17750, which do not plunge cut). 
Items #17740, #17742 and #17744 are designed for European metric size plywoods. 
See chart below for undersize equivalency. 
Straight router bits are the workhorse of any router bit collection and will plane, cut grooves, rabbets, slots and dadoes. 
Also used for mortising and carving, as well as other applications where a flat bottom is required. 1/4" and 1/2" shank. "

http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/katana_bits4.htm

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mftha said:


> Bob, the URL you cite leads to solid carbide bits that plunge cut. I was referring to the straight that on the web site are on the Katana straight bit page,
> 
> MLCS Router Bits and Woodworking Products
> pages/katana_bits4.htm
> ...


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## kolias (Dec 26, 2008)

Those darn bits are very confusing and probably will take forever to learn

I bet that at least 50% of mastering the router techniques is related to knowing your bits.


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## TWheels (May 26, 2006)

Nicolas, you are absolutely correct.
Nick, thanks for the explanation. I had assumed that a solid carbide bit would be spiral but apparently not.
BobJ, I am certainly sleep deprived and very stressed but aside from the price difference and the size limitations you pointed out, I am not sure I understand the rest of your post.


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## hcim (Sep 13, 2009)

I have two similar straight bits with different diameter. One of them 'burned' most of the time when cutting a mortise. 
After reading this discussion... now i know why :dirol:

Thanks everyone !!


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