Router bit heat, surface finish
![](https://secure.gravatar.com/avatar/06032900814cecfabbd3bc0edfed4beb?s=52&d=https%3A%2F%2Fimages.finewoodworking.com%2Fapp%2Favatars%2F200x200%2Fj.png&r=g)
Awkward title, sorry! I took a look at my Amana 1/2″ straight plunge bit today, after having used it in some alder and white oak to clear 1/4″ deep spaces about 3.5″ square. I was gentle and kind in the routing process. What I see is that the body of the bit, in the area of the cutters, appears heat-damaged, darkened. But the cutters seem to be OK.
First of all, is this possible?
Second of all, should I switch to a bit that has a smooth or coated body? Amana bits actually have a rough surface to the body of the bit. The Freuds, CMTs and Jesada bits I have are either coated or smooth (I think they’re all coated).
Won’t the rough body develop more heat, and more importantly transfer it to the carbide cutter?
forestgirl — you can take the girl out of the forest, but you can’t take the forest out of the girl 😉
Another proud member of the “I Rocked With ToolDoc Club” …. :>)
Replies
Don't assume from the discoloration that the steel bit body is getting hotter than the carbide. Steel oxidizes and discolors at a much lower temperature than carbide. In fact, the cutting edges and rake faces of the carbide tips are probably a lot hotter than the body while you're cutting.
I'm not sure you _can_ damage the carbide with the temperatures generated by cutting wood. The carbide tips got pretty dang hot with no damage when they were brazed to the tool body. Of course the carbide wasn't under any cutting stress when it was being brazed on, either. IMO, if you don't have direct evidence, like rapid dulling of the cutting edges, you're not generating anywhere near enough heat to damage the carbide.
I'm pretty much assuming that as long as the bit cuts OK and the carbide hasn't darkened, it's OK. I've always had reservations about the "finish" on the Amana bit bodies, though.
If I get to where I need to produce a few hundred of these items, do ya think it's be a good idea to go to solid carbide? (refresher: 1/4" deep, 3+" square recess).forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the "I Rocked With ToolDoc Club" .... :>)
>> ... do ya think it's be a good idea to go to solid carbide?If you're happy with the results you're getting from your brazed bits, I don't see what it would gain you. From a brief Google survey, it looks like solid carbide bits are mostly really small things like laminate trimmer bits where there just isn't room for brazed on cutters, or helical fluted bits, which would be a real pain to manufacture with brazed on cutters.Have you tried one of the down cut or down shear bits? They're not cheap, but I've heard they will cut a really nice edge, and that might be reason enough to buy solid carbide.One other thing you might consider, since you're cutting a shallow recess, is getting a short bit, with flutes just long enough to clear the chips. The less bit you have hanging out of the collet, the less likely you are to break it off. I don't know if any router bit manufacturers make such a thing. You might have to buy a regular one and have it truncated by your friendly local tool and cutter grinder.
FG,I wouldn't worry about carbide getting hot.I've run them in metal where they turn blue(turning and boring).But you wouldn't want that heat to transfer to your router bearings,etc.
I have some Freuds that have colored as you describe,no detriment.
Just my opinion,whether carbide or HSS,routers like shallow cuts.
Forest,
Do you get burn marks on the wood as well, or is it just the bit?
Nope, no marks on the wood :-) Looks pretty darned good, if I do say so myself.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the "I Rocked With ToolDoc Club" .... :>)
Jamie,My guess is that what you are seeing is buildup of the burnt resin of the chips that aren't clearing from the groove. Not likely to be a cause for concern. Soak them in kerosene overnight and scrub with a nylon bristle brush and they should look nearly as good as new. The coating on our bits definitely helps the cleanup in these cases but if it is the resin from the chips it can happen to anyone's bits.Charles M
Freud America, Inc.
It may also just be gum and crud from the routing that sticking to the surface of the core. Once some gets there it seems to attract more. Generally for my mixed bits (steel core - carbice cutting surface) I clean them in a solvent mixture / bit cleaner at the end of the day. I may just be anal but it seemed to extend the life of the bit.
Tim
Soon-to-be furniture maker
Port Townsend, WA
This forum post is now archived. Commenting has been disabled