Close one, Broken bit.

[syntec4]

I had this happen on Saturday Whilst cutting some grooves on the router table. The bit is (was) a 6mm. It's a Trend one. I think it was a new one, although I have had it a while. I was lucky the bit stayed in the box of the router table.

I was only cutting a slot 4mm deep and using a slow feed rate. the bit broke just after I started too, so I don't think it was heat build up.

Could there be something else I'm doing wrong? I was cutting 12mm birch ply at the time.

Cheers

Lee.

 

[Shultzy]

I would suspect thats metal fatigue, rather than something you have done wrong.

 

[Newbie_Neil]

Hi Lee

Glad that you're ok.

Cheers
Neil

 

[JFC]

Ive had a few of the 1/4" shank cutters break on me but never a 1/2" . Normally when they snap they stop dead but i spose there is always that one time when they don't . :shock:

 

[garywayne]

I thought it was a 1/4" shaft. If so, isn't 4mm rather deep for a pass? Also, shouldn't a 6mm cutter be at a faster rather than slower speed?

These are only thoughts.

EDIT:
As Shultzy suggests. It could just be a faulty cutter.

 

[Steve Maskery]

Hi Lee
It's scary when it happens, isn't it? The worst I've has is a 3-wing raised panel cutter hit me square in the belly on startup becasue I'd not tightened the collet... Fortunately there is plenty of defence material before it can reach any vital organs.

Anyway, to your problem.
1 It's possible you were just unlucky.

2 I do think that 4mm is the at the top end of what you can expect for a 6mm cutter in something like birch ply. In anything really. BP is hard and abrasive (it's the glue and endgrain which do the damage) and I'd be happier with 2-3mm.

3 Looking at your photo, what's that chewed-up area just above the break? It lookes like it's been slipping in your collet there. If so, it could be vibration set up, and that is a killer for bits.

HTH

 

[syntec4]

Thanks for the replies everyone. Steve, that chewed up looking bit is a bit of corrosion. I scraped it off with my fingernail before taking the picture. I had the bit in my pocket since saturday. I think it's happened since then. It was previously coated in that waxy stuff some new cutters come in and I didn't notice any corrosion whilst putting it in the collet, although it could have been there. I had safety specs on, not my proper glasses. As for the depth of cut, Gary- we'll possibly that may be the reason. I'm never sure what the depth of cut should be, just going off 'feel' more than anything. As I'm a bit inexperienced maybe thats the issue. I probably should have done it in 2 passes.

Cheers
Lee.

 

[cant-weld-wood]

hi all
i broke two trend 6mm cutters cutting birch ply on my router table
cutting a grove 6mm deep on the first cut witch was a 1/2 shank bit
then broke the second on a 3mm cut on the 1/4 shank bit but that was down to being in a rush on the second feeding to fast.
both cutters broke in exactly the same place.

 

[CYC]

I also broke the same bit from the same manufacturer. I since changed to use a 1/2" router, so time will tell if they are safer like they seem to be.

Steve, you took a raised panel cutter in the belly :shock: :tongue9:
I was scared to use mine, but now I am terrified. I don't have that defensive material you are talking about :wink: :roll:

 

[promhandicam]

hi all . . .

As no one else seems to have said it yet - welcome to the forum! :lol:

Steve (whose home in the UK is down the road from Erith in Slade Green)

 

[Sawdust]

I've snapped several 1/4 inch shank cutters too, usually cheap ones and to be honest I now don't like using anything other than 1/2 inch cutters in a table as I think you tend to apply a lot more force to them than you think when routing on the table.

Cheers
Mike

 

[woodbloke]

I feel as others do that a 4mm pass with a 1/4" cutter is probably a mite on the large side, 'specially in something like birch ply. I would have been inclined to do it in 2 or even 3 passes, with a reasonably highish feed rate - if you pass the cutter through the timber too slowly a heat build up results and the cutter will scorch the timber and which also might affect the steel - Rob

 

[johnnyb]

scary stuff,
always wear your most important safety items..... your safety glaarses!
i have to say i think a router is a bad way to cut grooves. they just cant properly clear the waste especially with a large cut a excessive pressure. most of the cutter is in the wood and the way it spins it is still in the wood. a dado blade or a grooving cutter on a spindle will cut in a much more efficient way. but is of course dangerous in other ways!!(without proper guarding)

 

[Anonymous]

Hi Lee

I have to agree with much of the above. A 1/4" straight bit in a router table is taking a heck of a lot of pressure as you push the wood through - particularly something as tough as birch ply. I would use 1/2" cutters as a matter of course - there is 4 times as much steel to snap.

I would also never from chouce use a straight bit for grooves - as previously stated the wood chips have nowhere to go and build up around the cutter. Invest in a 1/2" bearing guided arbor and a few groovers or slotters in different widths - This way you will have no problem cutting neat grooves in any hardwood in a single pass.

With a bit of ingenuity using two cutters and some spacers and you've got a great tenoner.

You could try Wealden as an alternative to Trend. They are a lot cheaper and I've never had one break!

http://www.wealdentool.com/acatalog/Heavy_Duty_64.html

Cheers
Brad

 

[newt]

You mentioned the waxy stuff that new cutters have I just wonder if some was left on the shaft and it slipped in the collet. The reason I mention this is that I had and annoying experience recently. I noticed that if I left cutters in the router the shaft would start to corrode, so I put a light covering of 3 in 1 on my cutters. I recently used a new dovetail cutter 6mm Trend, and started to cut in some ASH using a dovetail jig. The router kicked back there was smoke where the wood had started to burn. On inspection the cutter had moved at least 5mm out of the collet the additional depth of cut being to much. The collet was tightened to my normal torque I can only assume that there was a deposit of oil in the collet. I cleaned out the collet and tried again in the same wood and all was ok. However I was was very annoyed as the wood had been prepared for a drawer and the incident recked the piece.

 

[les chicken]

Being a semi retired mechanical engineer I am a bit confused on some of the replys to this thread.

How is a 6mm cutter stronger on a 1/2" shaft than on a 1/4" shaft. The strength is only in the cutter diameter not the shaft i.e. the cutter snaps not the shaft.

When using a milling machine the speeds and feeds of cutters can be calculated using charts for different materials, also using different types of coolant to keep both the cutter and work cool.

When using a router the same must apply but there is no automatic feed or coolant on a router table. Therefore the speed must be set to that recommended by the manufacturer and the feed rate and depth of cut is something that has to be considered very carefully.

It is better to take lighter cuts with a faster feed rate than big cuts with a slow feed rate ( less chance of burning ). It is not straightforward but great care must be taken as there is a lot of power in a router.

A router cutter is held by friction in the collet, if you oil the shafts to protect them from rust you must wipe them clean and dry before putting in the collet.

Les

 

[OPJ]

Crikey! I'm also glad to see you're okay after this! :shock:

How long ago did you purchase the cutter - perhaps Trend are liable to replace it if not long ago?

At work, we used a nasty OLD DeWalt Radial Arm Saw. Hit a knot or trying cut anything larger than 3"x1" and it'll have your free hand at any time of the day if you leave it too close (I'm not speaking from experience though)! That's always scared me but I'm now weary of a cutter breaking and flying across the workshop next time I used my router table - I always wear full protection though. :shock:

 

[Losos]

Also glad your OK - Looks like a clear case of metal fatigue, but as people have said the interesting question is "What was the cause"

Why not return it to Trend?

You may not get a refund or replacement but they will be interested to examine the bit carefully and it may help with their 'quality control' so in the long run it'll help everyone.