Broke Bosch Router Bit

[Dean Maiorano]

> I know this discussion is over but...you might want to research feed and speed rates for your bits and routers. Here's a sample table from Onsrud Cutter (IMHO one of the best bits out there - IMHO better than Whiteside - my experience includes running a CNC router for almost five years so I've used a few router bits in my lifetime):

http://www.onsrud.com/xdoc/ChipHardwood

(note the 'hardwood' on the end of the URL, they have soft wood, plastic and metal charts as well)

> Also, I've had great luck using routers with rpm modulators in both home and production settings (you plug the router into the variable speed unit which plugs into the wall). Just make sure you read the manual, etc.

http://www.woodcraft.com/Product/2003957/9183/Router-Speed-Control.aspx

> FYI, if you weren't aware, up cut spirals can leave a jagged top edge (especially on softer woods). That's why they make down cut and compression spirals. As you know, heat is the bit's enemy - using an up cut spiral bit IS a great idea as it helps get the chips (which hold the heat) out of the channel. Using a good vacuum or dust removal system attached to your router will help in that same way with any shape bit.

 

[jimsto2]

Thanks for the good info Dean. According to the hardwood chart, and assuming the Whiteside bit is comparable, I should have been able to move at a feedrate of 240 IPM taking a 1/4" deep cut. I'm certain I never covered the 24 inch pass in less than 10 seconds and I was taking 1/8" cuts.

That said, I think it is very likely I over heated the two straight cut Bosch bits I started with. I don't know why the Whiteside solid carbide spiral up cut broke so easily. My only thought is the slight side load from not being perfectly centered in the groove that was started by the Bosch bit.

Probably a case of inexperience combined with poor technique. I'm new at this woodworking hobby. i can see that it's going to be a patient builder & budget drain!

Thank for the good source of info. I'll give Onsrud bit a try sometime.

jIM

 

[Dean Maiorano]

Jim,

You're welcome. The times are really for CNC tooling but I figured it could give you 'frame of reference'. Obviously there are any number of possible reasons for the breakage...could also have been REALLY HARD maple (kidding) or a problem with the collet/router (not kidding).

Here's some FYI of which you may already be aware:

The proper use of the collet requires that the end of the bit should be down approx. 1/8" from the top of the collet. The collet and its seat are conical in cross section, the deeper you screw in the more you compress the collet around the bit, grasping/pinching it in place. Many people I've had work for me thought the right way to install a bit was with the bit end even with the collet's top or with it pushed THROUGH with the bit shaft sticking out the top end. Obviously this gives the collet no compressibility and therefor no real hold on the bit.

Then there was the issue of their tightening techniques, all of which involved over tightening using one method or another. We even had a guy that liked to bang the wrench at the end 'just to make sure'. One does not have to 'crank down' on the collet, tight is good enough. The point here is that even when you think the collet is holding the bit properly it may not be IF one has used the equipment wrong. Even if a bit is even a little loose it can spin and if it spins even ever so briefly it snaps when you push against it. Make sure you use collet adapters properly as well, using an adapter to step down a 1/2" to a 1/4" or a 1/4" to an 1/8" can create spin risk as well, if not properly used.

Last point - always make sure the router bit shafts are smooth and clear of dinging/dents. Using the 'push the shaft all the way through the collet' technique is a good way to put damage/crimp marks on even the hardest bit.

If that spiel was all old news my apologies. If it was a lesson then thank you for the chance to help.

Buona Fortuna,

Dino

 

[mkepke]

<snip> I don't know why the Whiteside solid carbide spiral up cut broke so easily. My only thought is the slight side load from not being perfectly centered in the groove that was started by the Bosch bit.
<snip>

Solid carbide bits are prone to snapping under impact loads ('bumping' them into the work)...your bit may have encountered an excessive impact load when it ran into the walls of the mortise.

-Mark

 

[Dean Maiorano]

Solid carbide bits are prone to snapping under impact loads ('bumping' them into the work)...your bit may have encountered an excessive impact load when it ran into the walls of the mortise.

-Mark

> Mark is absolutely correct, that is another huge concern with certain bits, especially one with the thin cross section of a spiral cutter. Solid carbide has a fine 'grain'/crystalline structure and that makes it great for sharpening but poor for impact (as opposed to HSS, etc.).

> BTW, Onsrud bits can be found on Ebay if you're interested. When I was buying bits for the shop I ran I procured through several NC suppliers where you can order small quantities. Onsrud's been in the router business for years and is a leader in bit technologies. They not only make bits they also make industrial routers of various types, including CNC. It is claimed that CR Onsrud invented the router ( https://www.onsrud.com/xdoc/Onsrud-Cutter-History ).

> I certainly do hope all this information is useful Jim. It is a pleasure to share experience and insight with you, it helps offset my indebtedness to oh so many online legal and professional advisors I've been helped by through the forums they frequent!

Dino

 

[McRabbet]

One factor that will lead to bit failure is cutting too slowly! At 24,000 RPM, a 2-blade cutter is cutting wood at 800 cuts per second and if the bit is left touching the wood without cutting, it will overheat rapidly. The chips actually cool the bit and allow smoother cutting. If you have any evidence of burning, then the bit will overheat and that could lead to failure. At 1/4" diameter and shallow passes, you should be able to move your router fairly quickly without placing too much stress on the bit axis.

All that said, I did once break a 3/8" spiral bit with a 1/2" shaft -- it was a CMT bit and the manufacturer replaced it without question. I was hogging out a 1-1/2" x 3-1/2" x 1" deep mortise in SYP and I hit a knot.