# 5/16" or 8mm?



## Midtone (Aug 14, 2012)

I have a 1/2" collet in my router that I want to reduce to take 5/16" bits. Is it better to get a reduce it down with a 5/16" or 8mm? Seems that the 8mm once tightened by the collet would be better because it wouldn't be as tight as a 5/16" reducer bushing but would still grab the bit fine. Haven't bought the reducer bushing yet and was wondering what would be better. I don't know if my logic is off here. Guess it is just the experience of things like this not fitting like they should. Erring on the wiggle room factor.


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## Mike (Nov 22, 2004)

First off nobody makes 5/16" router bits. If you are trying to adapt an end mill please do yourself a big favor and forget about it. Router bits are designed for the speeds they run at which is much faster than a mill. Bits are available in 6 mm, 8 mm, 1/4", 3/8" and 1/2" shanks in the US but the supply of metric is very limited. Your collet must match the bit's shank. Don't risk injury by trying to out guess the engineers.


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## Midtone (Aug 14, 2012)

But why Mike? I have had great success using 2 fl end mills plunging many a mortise. Never had one break. Set to the lowest speed. Slow and easy. They are sharp and work clean and great. And those are 1/4". Seems a 5/16" would be even more stable.
I do appreciate your Sherlock intuition that the end mill was my intention


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## jw2170 (Jan 24, 2008)

What do you want to cut with the 5/16th bit?

If for a groove of some sort, can't you use a 1/4" bit and move the fence back 1/16th for a second pass? Use a shim or spacer?


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## bobj3 (Jan 17, 2006)

Hi

I have one and use it all the time for 1/4" slots.

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## giradman (Jul 23, 2012)

Midtone said:


> I have a 1/2" collet in my router that I want to reduce to take 5/16" bits. Is it better to get a reduce it down with a 5/16" or 8mm? Seems that the 8mm once tightened by the collet would be better because it wouldn't be as tight as a 5/16" reducer bushing but would still grab the bit fine. Haven't bought the reducer bushing yet and was wondering what would be better. I don't know if my logic is off here. Guess it is just the experience of things like this not fitting like they should. Erring on the wiggle room factor.


Hi *Midtone* (no first name given?) - you might want to mention your router brand/model and whether you want to use an inch division bit or an 8 mm one? Collets made specifically for the shank bit diameter are the best option rather than putting bushings w/i a 1/2" collet, just a better design.

Now if you want to use an 8 mm shank bit w/ this router, does the manufacturer (or OEM) offer a collet to fit that size - your best solution? 

Below is a table showing 5/16 and the mm equivalent (i.e. 7.9375 mm); going up to 8 mm is a 0.0025 decimal difference - in Lonnie Bird's book (free PDF file from another thread here), he states (pg. 31) that 'for a secure grip in the collet, a bit shank should be w/i 0.002 in. of the collet diameter...Better manufacturers...of their bits w/i 0.0005 in.' - SO, you're basically 'on the fence' w/ a bushing - would still see if there is a 'dedicated' collet for an 8 mm bit? Good luck and please let us know your solution. Dave

5/16 0.3125 7.9375
. 0.3150 8.0000


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## Mike (Nov 22, 2004)

This discussion comes up from time to time... "Why not?"

End mills are designed to work at a low speed, perhaps 3,000 rpm. The design is for removing metal not wood. Will it cut wood? Yes. Is it safe to run the bit at 10,000 rpm? Maybe. Is it worth taking a chance on? Not in my book. No router manufacturer suggests that you use end mills in your router. Router bits are designed to cut wood at high speed and will do a great job. A solid carbide 5/16" spiral up cut bit with a 1/2" shank can be had for about $18. Better safe than sorry. But hey, there are ER's everywhere so who am I to talk about safety?


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## Midtone (Aug 14, 2012)

I get scared operating most of my machinery. I am extremely cautious. When I use the end mill I go really slow as in 1/16 to 1/8" depth at a time. Mike you are making me reconsider using end mills again. I know they are not the safest, but I can not seem to stop myself from using them. I do have a couple of upcuts too.

I have 2 routers. The Dewalt compact that has 1/4" and a Hitachi with 1/2" collet. I guess the reason I was wondering about the 8mm/5/16" is because Lee Valley sells a 8mm reducer and in () it says 5/16". So I was wondering why they would do that instead of selling a straight 5/16" reducer.

I can just make adjustments with my 1/4" but one pass would be faster and easier than 2.

Now I am scared to go use my end mill at all...


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## Dmeadows (Jun 28, 2011)

Midtone said:


> So I was wondering why they would do that instead of selling a straight 5/16" reducer.


Probably because no one makes 5/16 shank router bits and no manufacturer would accept the liability of enabling the use of end mills in a router. With good reason. I agree with Mike completely!


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## Phil P (Jul 25, 2010)

Mike said:


> This discussion comes up from time to time... "Why not?"
> 
> End mills are designed to work at a low speed, perhaps 3,000 rpm. The design is for removing metal not wood. Will it cut wood? Yes. Is it safe to run the bit at 10,000 rpm? Maybe. Is it worth taking a chance on? Not in my book. No router manufacturer suggests that you use end mills in your router. Router bits are designed to cut wood at high speed and will do a great job. A solid carbide 5/16" spiral up cut bit with a 1/2" shank can be had for about $18. Better safe than sorry. But hey, there are ER's everywhere so who am I to talk about safety?


Hear! Hear! Well said, Mike. Spiral router cutters are specifically engineered for the spindle speeds routers work at - engineering end mills aren't

Regards

Phil


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## bobj3 (Jan 17, 2006)

2 Flute Downcut Bit, 5/16 Dia, 1" Cut Length, 5/16 Shank, Whiteside RD3100

Amazon.com: Amico 5/16" Cutting Diameter Straight Router Bit w Bearing: Home Improvement

Onsrud Spiral Router Bits - Lee Valley Tools


Amazon.com: 5/16 router bit: Tools & Home Improvement
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Dmeadows said:


> Probably because no one makes 5/16 shank router bits and no manufacturer would accept the liability of enabling the use of end mills in a router. With good reason. I agree with Mike completely!


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## Mike (Nov 22, 2004)

BJ, thanks for researching the links! All of these are router bits, not end mills. These are designed for the routers speed range.


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## bobj3 (Jan 17, 2006)

Hi Mike

True but I would bet they are end mills in the HSS type but they don't say that in the listing..(note the Lee Valley items)

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Mike said:


> BJ, thanks for researching the links! All of these are router bits, not end mills. These are designed for the routers speed range.


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## Midtone (Aug 14, 2012)

I do agree with the safety issue, however I can not seem to find an upcut with a 1/2" shank, 5/16" dia. cutter that is longer than 1" that doesn't cost $60 or more. Maybe you could direct me to one. I want to make some deep cuts and I just can't give an arm and leg for a bit at the moment.


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## Midtone (Aug 14, 2012)

I take that back. I do see a Lee Valley that has 1 1/8" cutter on it for $40. Is that as deep as i am going to get with a 5/16"?


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## Mike (Nov 22, 2004)

BJ, all the links you provided specified that they are router bits, hence the speed rating.

MLCS #7466 = 1-3/16" cutting length. $39.95, free shipping.

Your depth of cut does not depend on the cutting length of the bit. It depends on the bit length and the amount of plunge in your router. Since you are only removing about 1/4" of depth per cut a 1" cutting length is way more than enough.


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## Midtone (Aug 14, 2012)

Thanks Mike. Your the boss.


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