MIMF

Until recently, this Makita RT0700C was one of my favorite routers—a good combination of size, weight and features. I use it to cut truss rod slots and saddle slots (with a plunge base). Last year, it destroyed one if my neck blanks when the bit slipped in the chuck, pulling itself longer as I cut. I discarded the bit and replaced the collet. I got a few successful cuts after that. It just destroyed another blank. I was cutting 1/8” depth at a pass with a 1/4” bit. What gives? Is the conical hole in the armature end worn out (a new router fixes this)? Or, is it just a bad design? I cannot tighten the chuck enough that I can’t turn the router bit with less force than it took to tighten it.

Probably not pertinent, but I have a different brand/type router that I have the same problem with, and I've discovered the chuck nut (or whatever it's called) threads are bottoming out on the spindle shaft, before it's tight enough to squeeze the collet tightly on the bit.

check the shank of the bit you were using. I had same problem with same router and it was the shank on the cutter that was damaged.

I may have fixed the problem. I checked the threads as suggested by Peter—plenty of threads left. The shank of the bit that slipped matched all of my other bits (.2485”). So using the test in the picture below with the big wrench, I noticed the collet turned with the bit. I took it apart and cleaned all of the mating surfaces in the collet and armature with alcohol. It was very difficult to make it slip after that. So, it may have been dirt or grease in the collet that caused the problem. I hope to not wreck another neck.

Make sure that the bit is not bottomed out.
I put the bit in, then pull it out a tad before tightening.

One of the neat things about the router is that the end of the bit can be seen through shaft where the stop button hits (the stop button is only a convenience; it can’t hold enough to fully tighten the collet). So, I can tell that the bit isn’t bottomed out.

I had the same problem but different brand router. I had to replace my rather expensive Stew-Mac rabbit bit that only had small scratches on the shank with a new one. After that, no problem. The collet had slipped on the one with the scratches, so I replaced it first and it happened again so I replaced the bit. good luck

Trend Routers sell a set of small brass brushes specifically for cleaning collets. Well worth the purchase.
https://www.ebay.co.uk/itm/Trend-Cb-Kit ... QgEALw_wcB

I have found this stuff to work very, very well:
https://www.precisebits.com/products/ch ... etcare.asp

Thank you. I will go after this product if the cleaning I have done hasn’t solved the problem.

Have the same Makita at home (which I love to use).
Do you tighten the router bit by pressing the red button? I always tighten the bit using two wrenches.
When you lay the machine flat, with the wrench on the shaft resting on the workbench, you can tighten the locking nut very well.
Never had a loose bit until now.

I find the red button useful for only hand tightening. I always tighten as you describe. That’s why I was so surprised when the bit slipped.