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Discussion Starter · #1 ·
I recently purchased some 8mm dovetail bits and it came with an 8mm collet adapter. My question is should I purchase a dedicated 8mm collet or will the adapter suffice as these are the only 8mm bits I own. My concern is can the adapter damage my 1/2 collet?
 

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Hi Todd,

If the adapter is made by a reputable manufacturer for a 1/2" collet, there should be no problems.

I know a number of members use 8mm and 1/4" adapters in their 1/2" collets.
 

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Hi Todd

The adapter will Not damage the 1/2" collet... (8mm = 5/16" shank router bits)

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I recently purchased some 8mm dovetail bits and it came with an 8mm collet adapter. My question is should I purchase a dedicated 8mm collet or will the adapter suffice as these are the only 8mm bits I own. My concern is can the adapter damage my 1/2 collet?
 

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Hi Todd

The adaptor is unlikely to damage anything, but bear in mind that the grip will be slightly less than that of a dedicated collet, so avoid heavy cuts.

Cheers

Peter
 

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Personally I'd only use a collet adaptor as a last resort. As Peter says they grip quite a bit less strongly than a correctly sized collet which means that on medium to heavy cuts you can experience bit slippage, so sometimes the bit will move up or down in the collet. As I'm generally routing as part of my living that's obviously a complete no-no.
 

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Discussion Starter · #6 ·
Thank you everyone for your expertise. I think based upon the feedback I will purchase the additional collet due to potential slippage.
 

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Just my 2 cents

Some of the funny routers are setup to use the 8mm shank router bits, the ones over the pond the norm..some of the router bit sets are made just for the 8mm bits ,like the one below, I'm sure if they would damage your router they would not sale the adaptors.

As far as "slippage" I don't think so, they make many types of "adaptors" the best ones are the ones with the 3 or 4 slots in them and they do hold the router bits in tight..

This dovetail set below includes all the router bits needed to use for Leigh D4, D4R and D1600 Jig to make drawers, chests, or any other project.

16 pc 8mm Shank Dovetail Router Bit Set For Leigh Jig - eBay (item 140474120341 end time Nov-10-10 22:19:26 PST)

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

http://www.leighjigs.com/cutters-d4.php

Just a bottom note,,,Out of many,many routers I have not one of them is setup to take on the 8mm (5/16") shank router bits..and I would be hard press to find them for sale in the states..

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Bob is right. A decent adapter won't slip. Besides, you could just tighten it a little more than usual and it will be fine.
 

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Hi Todd - If it really bothers you, you probably get collets for your Freud's fairly easily, possibly for the Bosch and Ryobi.
 

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I have the same 8mm set from George, with the adaptors, although being this side of the pond, I'm using 8mm collets and not the adaptors.

A dedicated collet has either 3 or 4 independent fingers depending on the make, which enable maximum gripping power.

The adaptor has three slits, only one of which goes all the way through. (If they all went right through, the thing would fall apart). It therefore fits only where it touches and when tightened, is limited in its movement by two of the slits being only partial and thus attached to their neighbour and moving in tandem, not independently. It relies on the inner circumference reducing as it tightens. However, the inner circumference of the individual segments remains constant and any change is a bend at the point of the partial slits, which is not optimal. The grip will even vary depending on where on the adaptor the collet fingers are pressing.
Mostly it will work, until the day the cut is a bit heavier, or the feed rate a bit faster, when the reduced grip will allow the bit to move when a dedicated collet would have held it.

I must admit that I don't know why this particular 8mm set is being offered by George for a primarily US market, although I was glad to get mine. I only wish he'd offer more 8mm shank stuff ,as he is far cheaper than anything otherwise available over here. There are times when something more rigid than 1/4" but not as big as 1/2" is handy, particularly if I don't want to use the bigger routers.

Cheers

Peter
 

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Hi Peter

You can find more of the 8mm stuff on the site below.
Router Bits, Router Bit Accessories by Whiteside Machine

I think George sales the bit set because it's a default size for Leigh jig and they are a bit longer than the norm . in the 8mm size...

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I have the same 8mm set from George, with the adaptors, although being this side of the pond, I'm using 8mm collets and not the adaptors.

A dedicated collet has either 3 or 4 independent fingers depending on the make, which enable maximum gripping power.

The adaptor has three slits, only one of which goes all the way through. (If they all went right through, the thing would fall apart). It therefore fits only where it touches and when tightened, is limited in its movement by two of the slits being only partial and thus attached to their neighbour and moving in tandem, not independently. It relies on the inner circumference reducing as it tightens. However, the inner circumference of the individual segments remains constant and any change is a bend at the point of the partial slits, which is not optimal. The grip will even vary depending on where on the adaptor the collet fingers are pressing.
Mostly it will work, until the day the cut is a bit heavier, or the feed rate a bit faster, when the reduced grip will allow the bit to move when a dedicated collet would have held it.

I must admit that I don't know why this particular 8mm set is being offered by George for a primarily US market, although I was glad to get mine. I only wish he'd offer more 8mm shank stuff ,as he is far cheaper than anything otherwise available over here. There are times when something more rigid than 1/4" but not as big as 1/2" is handy, particularly if I don't want to use the bigger routers.

Cheers

Peter
 

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I use an 8mm adapter all the time for some English made bits. Lee Valley Tools sells them for about $5. Never had problems with slippage or in removing a bit.
 

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There is another difference, which may or may not matter to you.

All routers (all rotary mechanisms) have "run out" = deviation from circular motion.

An adapter adds it's runout to the collet's runout, which is added to the runout of the shaft in the motor. If you replace the collet with a different collet, it may have a different runout, but you don't add the runout of the adapter.

Most collets for routers don't consider runout a critical dimension, but some do.
 

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Thank you everyone for your expertise. I think based upon the feedback I will purchase the additional collet due to potential slippage.
Hi Tod, I purchased the 8mm collet and 3/8 for my Bosch routers.
I had one slip in the 8mm collet adaptor, likely my fault for not tightening
enough. When you use the adaptor (I used the one that came with
Leigh sets) you are really tightening 2 collets.

I feel safer with the dedicated collet nut.

Picked them up at Plumbers surplus in US. They are Bosch collet nuts.
Mind you I have a US shipping address available, which was convenient,
and the price was low. Don't know the best price for Freud routers, if
that is what you have.
 

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I experienced some dangerous slippage about 5 years back on a Hitachi MV12 12mm to 8mm reducer, I'll never use one again, and I'll never need to with the collection of collets I now have.
 

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Discussion Starter · #16 ·
I need it for My Bosh 1617, I am going to pick one up along with a 3/8. I live in Niagara Falls and go over the border weekly. I take my kids to see my mother every Saturday. I am going to order from a local supplier, Phillips Brothers. I figure better safe than sorry. Thanks again everyone for your expertise
 

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Hi,
Collet or adaptor are not the most important. Both will work if the collet and conic recess are clean,the thread oiled and the tightening correct. Now a specific collet certainly will grip your bits safer. Living in Europe, I mostly use 8 mm bits, but I bought specific collets for each of my routers, for the few 1/4 bits I have.

Brume
 

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I would not recommend to use adapters with The Hitachi M12, its collet is not the best ever ! The one-piece design with short cone and important conic angle provides poor shank tightening, I'm afraid. Small angle two piece collets such as the DeWalt are far better. Pity, I appreciate the rest of the hitachi.

Brume
 

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The only adaptor I have used is one that came with the Rockler dovetail jig. I had nothing but problems removing the bit and adaptor. When I asked the store for suggestion they said some JB Weld the adaptor to the bit. I guess that could work but being somewhat skeptial I purchased an 8mm collet and haven’t had any more problems.
 

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The only adaptor I have used is one that came with the Rockler dovetail jig. I had nothing but problems removing the bit and adaptor. When I asked the store for suggestion they said some JB Weld the adaptor to the bit. I guess that could work but being somewhat skeptial I purchased an 8mm collet and haven’t had any more problems.
Hi Michael - adaptor that comes with that jig is a POS, at least it was for me. I don't think I like the idea of epoxying the thing to the bit either. My problem was keeping the thing at the top of the collet, kept wanting to slide in. I just ended up buying the right profiles in 1/4" shank.
 
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