Router bits: 1/4" vs 8mm

[Packard]

[member=74278]Packard[/member] Jeff spelled it out above, “On cuts that are at the upper limit of what 1/4" shank should do, the 8mm shank provides additional stability. Case in point is dovetail bits. A half-inch dovetail bit with 1/4" shank is a screamer in a dovetail jig. You can't overcome that by making multiple cuts...you have to cut to full depth in one pass or your dovetail is a Christmas tree. The same bit in 8mm is much stiffer, and vibrates far less, which means the dovetail cut is much more consistent.”

I think we are looking at this all wrong.

I have both a 1/4” and a 1/2” diameter pattern bit with a bearing on the end.

The 1/4” is handier.  It gets into tighter corners and rides in a compact router.  But the 1/2” has a longer shaft and can handle thicker material.

So, was Whiteside worrying that I would bend or break the shaft if they made the longer one out of 1/4” also?  I don’t think the relatively short height of a router would provide the leverage needed to damage the shaft.

I think the issue is the bearings in the router itself.  I think the issue is that with a machine designed for 1/4” bits will not have sufficient space to incorporate the larger bearings needed for the larger bits.

It is not the shaft strength of the bit that is at issue, it is the machine’s’ spindle bearings capacity to handle lateral stresses.  The larger shaft diameter simply prevents users from overloading the bearings in undersized machines.

In any case, try and bend a 1/4” diameter heat treated drill rod with the equivalent leverage that a router provides. I’m pretty sure that the approximately 10” height being pushed laterally on a flat base is not capable of bending or breaking the shaft.  It is capable of damaging the machine’s bearings however.

ADDENDUM:  I have written to Whiteside asking for their thoughts on this discussion.  If they respond, it will likely not be before Monday, the beginning of the work week. 

I don’t think the members here have sufficient experience to drive this conversation to a consensus.

This is likely not the typical question that they [Whiteside] typically fields, so they may take extra time, decide that they don’t want to comment on a forum thread, or that I blindsided them with the question and they need extra time. 

I linked this thread.  Whiteside might find this interesting reading regardless.

Packard

 

[Crazyraceguy]

Yeah, [member=74278]Packard[/member] diameter does make a difference. If you "need" smaller to get into a specific shape, it's unavoidable. In general though, larger diameter shanks are stiffer, meaning less flex. This is exacerbated in longer length of cut. This leads to grabbing and pulling into interior corners.
If you ever cut a rectangular shape, using a bushing/template and had the corners over-cut/bulge it is from the bit flexing. That bit is running along, taking a certain percentage of its diameter (as the chip load) then it hits the corner and that contact increases dramatically.
This even happens with solid carbide bits, where the shank is inherently stiffer.
You can demonstrate this by doing the same type of cut with a flush trim bit. Because of the extra support of the bearing on the end of the bit, the flex is reduced.
Personally, I have always preferred to use the larger diameter flush-trim or pattern bits. They don't seem to tear-out as much, because of the contact angle of the cut. The Amana insert type have a cut diameter of 3/4". Those are my choice, whenever they will fit, unless I feel the need for a spiral flute.
I think the one I use for that is 1"? IIRC

I'm not particularly a fan of collet adaptors. Some have worry about holding power, but my concern is concentricity. The smaller the diameter of the cutter, the worse this gets. The chip-load gets shifted more to one flute than the other, this matters, especially with tiny cutters.
I started using 1/8" shank bits with an adaptor and saw a significant difference swapping to a legitimate 1/8" collect. Better/smoother cuts

 

[Cheese]

I think we are looking at this all wrong.

So, was Whiteside worrying that I would bend or break the shaft if they made the longer one out of 1/4” also?  I don’t think the relatively short height of a router would provide the leverage needed to damage the shaft.

I'd argue the first point and for the 2nd point ...yes.

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[luvmytoolz]

I have a multitude like that yellow one with the step down shank from overly aggressive toolpaths on the CNC! Never actually worn one out, but have broken many! That's why I buy cutters by the kilo! ;-)

 

[Packard]

I must be out of touch—I never bent or broke a single router bit.  I cannot even imagine how to go about it (while using a router; I’m pretty sure one of my hammers could make short work of it).

I am, however, pretty adept at wrecking cars.  But that is an entirely different skill-set.

 

[jeffinsgf]

Just to add another direction to the thread...

Anyone with a router that used ER-20 collets, we now have 8mm ER-20 collets available. They're pretty well hidden on our site, and searching for an ER-20 collet won't produce any results  [crying], but they're on the SpinRite page:https://www.woodpeck.com/spinrite-router-motor.html

 

[Packard]

I would be absolutely shocked if I were to bend a router bit shank or break off the cutter. 

I let the sound and feel dictate the cutting speed.  I’m apparently working on the conservative side on cutting speed (and giving away some productivity), but avoiding the kinds of failures pictured above. 

I do see at the home centers (Lowes and Home Depot) the staff using the panel saw and pushing the saw well above what I would consider appropriate. I can hear the motor straining and the operator pushing hard against the cut.  Their cuts almost always are heavily splintered and rough, but then they seem to use the blades well past the time when they should be sharpened.  So I don’t know the real cause of the rough cuts. 

But I cannot imagine my cuts with the router causing that kind of damage unless I hit a metal bolt that was hidden from sight. 

 

[Crazyraceguy]

I would be absolutely shocked if I were to bend a router bit shank or break off the cutter. 

I would too, though I have seen it happen when the router was not running, by banging the bit into something. I would have thought that a steel shank would bend, rather than breaking, but I see the pics.
I have also seen guys run flush trim bits to the point of exploding the bearing. That never works oout well.
I have seen CNC machines snap them off, even the bigger 8mm ones are not immune there.
I saw a 2" pattern bit come out of the collet at speed one time too. I'm pretty sure that the collet was worn out on that one.

 

[woodferret]

Spirals and complicated geometry are typically solid milled carbide straight through, and are brittle.  The bent shafts you see are either brazen carbide only at the cutting edge or even sometimes just HSS.

Giveaway tends to be the shank size vs the head geometry, as milling a giant 1" blank would be wasteful vs just brazing on carbide.  If the cutting dia is the same as shank or vary slightly, it's more economical to just mill it down.

 

[Packard]

I would be absolutely shocked if I were to bend a router bit shank or break off the cutter. 

I would too, though I have seen it happen when the router was not running, by banging the bit into something. I would have thought that a steel shank would bend, rather than breaking, but I see the pics.
I have also seen guys run flush trim bits to the point of exploding the bearing. That never works oout well.
I have seen CNC machines snap them off, even the bigger 8mm ones are not immune there.
I saw a 2" pattern bit come out of the collet at speed one time too. I'm pretty sure that the collet was worn out on that one.

I knocked a router off of a workbench once.  The anticipated damage did not show up however.  I counted that as good luck.  I fully expected a cracked casting on the router or a damaged bit.  Nothing but a few scratches.

In the 1970s I bought a new IBM Selectric.  When I left the house, I would place it up on a shelf so my cat would not sleep on it.

When I got home, my 6 month old Doberman puppy had pulled it off the shelf.  But it looked fine.  When I went to use it next, I found that the primary casting was cracked and it was not salvageable.

Just over $500.00 back then, just under $4,000.00 in today’s dollars.

I was sure I had cracked the main casting on my router.  But just scratches.

But other than an accident, I still can’t imagine damaging the bits like those in the photos.

 

[luvmytoolz]

But other than an accident, I still can’t imagine damaging the bits like those in the photos.

I'm guessing you don't own a CNC? ;-)

My ability to destroy things much more efficiently definitely improved when I got a CNC.

 

[mino]

I would be absolutely shocked if I were to bend a router bit shank or break off the cutter. 
...
But I cannot imagine my cuts with the router causing that kind of damage unless I hit a metal bolt that was hidden from sight.

Sorry to be blunt, but by same logic there is no need for 1/2" bits .. 1/4" should handle it all ..

On a more serious note, three bits that are very much beyond the 1/4 capability but allowing usage of a nimble router like the 1010 instead of the bigger babies:https://www.festool.de/zubehoer/fraesen/fraeser/buendigfraeser/491028---hw-s8-d19nl25https://www.festool.de/zubehoer/fraesen/fraeser/beschlags-duebelbohrer/491077---hw-s8-d35https://www.festool.de/zubehoer/fraesen/fraeser/profilfraeser/491130---hw-s8-d4321-akl

I cannot find the huge 50 mm compound bit FT made for 8 mm.

Again, the point is that 8 mm is small-enough for practically making small bits in it, including trimming bits. 1/2" is just too big for that which *necessitates* everyone having a 1/4" small router to go along their bigger one. That same 8 mm is big-enough for most of the "casual" jobs one would need 1/2" for was there no 8 mm available. This makes it the optimal "go-to" shank size for handheld routers. My view.

And I am not speculating. I see how it works over here - most (90% in the hobby market) get by with 8 mm while 12 mm and 1/2" are "reserved" for the minority of the heavier jobs.

The corresponding 6 mm is in turn almost non-existent. Outside specialty trimmers it just does not make sense when 8 mm is small-enough so that even the trimmers, like the now-legendary Makitas, are built to take it.

 

[Cheese]

In the 1970s I bought a new IBM Selectric.

Maybe that's the reason IBM jettisoned the typewriter business. That letter ball rotating around at 20,000 rpm probably gave them food for thought.  [smile]

I wonder what the shaft diameter was?  [poke]

 

[Woody Knotsensplintahs]

...The 8mm has four times the surface area of a 1/4", and the advantage of greater stiffness and less flexing...

I did not get far down the thread because I like to use 1/2" shanks for 1/2" routers and think of my 1/4" miniature routers as miniature devices, which are super handy when a miniature device will do the job. Personally, I don't see a need for a nuanced comparison of what might be available between 1/4" and 1/2", but if you did it is easy to get a 3/8" (9.525mm) collet for a Bosch 1618 and easy to get 3/8" shank bits. I mention the 1618 because I have a few of them.

If I absolutely needed an 8mm shank bit for some special job. It also seems easy to get an 8mm collet for the Bosch 1618.

Having said that, I was surprised the stated premise quoted above was left without comment.

The circumference of an 8mm shank is 0.99 inch
The circumference of a 1/4" shank is 0.79 inch

For any given length of insertion, an 8mm shank provides approximately 20% more surface area for the collet to grip than a 1/4" shank.

 

[luvmytoolz]

...The 8mm has four times the surface area of a 1/4", and the advantage of greater stiffness and less flexing...

Having said that, I was surprised the stated premise quoted above was left without comment.

The circumference of an 8mm shank is 0.99 inch
The circumference of a 1/4" shank is 0.79 inch

For any given length of insertion, an 8mm shank provides approximately 20% more surface area for the collet to grip than a 1/4" shank.

As a fellow Aussie I admit we sometimes get accused of exaggeration, by next week it would have become 8 times the surface area if it was my post!

 

[derekcohen]

...The 8mm has four times the surface area of a 1/4", and the advantage of greater stiffness and less flexing...

Having said that, I was surprised the stated premise quoted above was left without comment.

The circumference of an 8mm shank is 0.99 inch
The circumference of a 1/4" shank is 0.79 inch

For any given length of insertion, an 8mm shank provides approximately 20% more surface area for the collet to grip than a 1/4" shank.

As a fellow Aussie I admit we sometimes get accused of exaggeration, by next week it would have become 8 times the surface area if it was my post!

Aahh, but that extra 20% surface area has the equivalence of 10x the strength! Any Australian knows this.

Regards from Perth

Derek

 

[mino]

...The 8mm has four times the surface area of a 1/4", and the advantage of greater stiffness and less flexing...

...
Having said that, I was surprised the stated premise quoted above was left without comment.

The circumference of an 8mm shank is 0.99 inch
The circumference of a 1/4" shank is 0.79 inch

For any given length of insertion, an 8mm shank provides approximately 20% more surface area for the collet to grip than a 1/4" shank.

Pretty sure derekcohen meant the cross section area (aka "surface area" in a bad translation), not the "outer" contact surface. But still messed it up ... it is 4x the section and 8x the strength between 1/2" to 1/4" ... but only 1.59x section area and 2x strength between 8 mm to 1/4".

 

[Michael Kellough]

...The 8mm has four times the surface area of a 1/4", and the advantage of greater stiffness and less flexing...

...
Having said that, I was surprised the stated premise quoted above was left without comment.

The circumference of an 8mm shank is 0.99 inch
The circumference of a 1/4" shank is 0.79 inch

For any given length of insertion, an 8mm shank provides approximately 20% more surface area for the collet to grip than a 1/4" shank.

Pretty sure derekcohen meant the cross section area (aka "surface area" in a bad translation), not the "outer" contact surface. But still messed it up ... it is 4x the section and 8x the strength between 1/2" to 1/4" ... but only 1.59x section area and 2x strength between 8 mm to 1/4".

Not really sure Mino but I suspect “10x the strength!” is the culturally appropriate level of competitive exaggeration for an Australian.

 

[mino]

Not really sure Mino but I suspect “10x the strength!” is the culturally appropriate level of competitive exaggeration for an Australian.

Guilty as charged .. cannot get rid of the habit of coming with facts into an impressions fight. The ladies keep telling me that all the time.

.. goes hide in the corner​

 

[tsmi243]

Not really sure Mino but I suspect “10x the strength!” is the culturally appropriate level of competitive exaggeration for an Australian.

I'd never stoop to such a thing, speaking as an American...

We're a million times better than that