I was milling 1/4" wide 3/8" deep mortises in 1-1/4" legs in a router
table with a 1/4" Whiteside solid carbide spiral upcut bit in a PC 7518
router -- nothing I haven't done a number of times before. I milled the
first mortise and was in the middle of the second when the piece
started vibrating and hopping. I turned the router off and found that
the bit had raised out of the router by a good 1/4". Not good. The
collet certainly wasn't easy to get off, and when I did I couldn't seen
any buildup inside or on the threads. The bid was exactly the same
diameter as all my other 1/4" bits to a few thousanths.
OK, next suspect was the collet. I had another identical one from a PC
690 router, so I installed it and gingerly started cutting mortises.
Same thing. Probably not the collet alone.
The last suspect was the router chuck. It appeared normal except that
the threads were rough rather than smooth. Maybe the threads on the
collet are binding against the rough threads of the chuck. I washed the
collet in mineral spirits, and put a drop of light oil on the chuck
threads, thinking that maybe a bit of lubrication would make the
problem disappear. Which it did. I milled the rest of the mortises
without the bit rising out of the collet.
A quick search through the wreck showed that this has happened a number
of times in the past. Always with a spiral upcut bit, which is not a
big surprise since the force on the bit wants to pull it out, unlike
most other bits.
Bay Area Dave and Swingman both had this happen to them, and both with
PC 7518 routers. If your interested search the wreck for a thread
titled "climbing bit" in Feb '04. Others have mentioned other PC
routers, and a few had the same problem with Craftsman routers.
My conclusion is that there is probably no single cause (unless
somebody doesn't tighten the collet enough. :-)
The causes mentioned include
- 1/4 in. spiral upcut bit
- a gunked-up collet.
- rough threads on the router chuck. I wonder if there was a bad batch
of chucks during a production run on 7518s.
- and no lubrication.
As Michael Conrad used to say on Hill Street, Let's be careful out
Vince Heuring To email, remove the Vince.