Prevent router burn

[steve-norrell]

I am making cutting boards / trivets for Holiday gifts. They will be various combinations of padauk, walnut, cherry, and maple. (See photo of one example.) I prefer to not cut grooves, but the LOML says I should, at least in the larger cutting boards.

The problem I am having is burning of some of the wood, especially around the corners where I slow the rate of cut. I need help on how to avoid the burning on mixed wood projects. Is there some combination of depth of cut, rate of cut and router speed that would minimize burning without causing tearing?

Note: I also need to practice following the template and getting straight-edged grooves.

Thanks for your help. Regards, Steve

[JimD]

making sure the bit is completely clean helps. Using a plunge router might help because if you need to reposition yourself or the work piece you can just let the bit up and then plunge it back down when you are ready to go. Making the groove with a smaller bit and more than one pass might help.

My cutting boards are just plastic store bought pieces but they don't have a groove. I think deleting the groove is the best solution.

[LCHIEN]

I have not dealt in multi-wood glueups but what I find in general helps avoid burning is to make a several partial passes and then make a last fast pass that removes little wood. That way burning on the earlier passes won't show if you don't burn it too badly (deeply) and a thin pass can be done relatively quickly. This expands the range of speed you can use. e.g. any router pass is limited - max speed is goverened by the point at which it chatters and makes a rough cut and minimum speed is goverened by where it burns. Avoiding problems and making a clean rout depends on staying within these two speed limits. Having a wider range makes it easy to control than a narrow range. So open the range towards the high end by taking a thin cut on the last pass and make it quicker. Since you can usually hear where it cuts well or starts to chatter, but you can't see burning until its too late, its easier stay towards the max speed.

This is easiest on bearing- or fence-guided cuts (outside edge) and profiled groove cuts (Vee, round bottom) where each deeper pass removes more wall material. And harder to do on straight dado cuts where you don't remove material from the upper sides on subsequent passes.

with the profiled cuts you have to drop the router bit lower each pass.
with the outside edge cuts you simply don't push all the way into the bearing or fence - just bear down lightly and make multiple passes until you are riding firmly against the bearing or fence.

[cabinetman]

A sharp clean bit makes a big difference. Keeping it simple, my suggestion is to take several passes, and the last pass is just a skim pass. I wouldn't necessarily speed up the last pass. You will have problems in corners or transitional areas, and with those, scraping them clean works good. Use properly shaped carving tools, turning tools, or chisels, depending on the profile. Ultimately, there is always sandpaper.
.

[RAFlorida]

As other's noted.

I always make several shallow, thin passes. Generally that helps eliminate the burn marks.

[herb fellows]

+1 on the final skim pass. I would experiment on scrap until you feel confident with your settings, it may take a little trial and error to get it right. The important passes are your last 2: not to leave too much of a burn on the next to last one, and therefore be able to take a very light cut for the final.

[JR]

+1 on the final "skim" pass.

To give you an idea as to what a skim pass is like, here is what has been suggested when using a router table. Put masking tape on the part of the wood that would ride on a bearing, or put it on the fence. Run the wood through, then remove tape. Run it through one last time for cleanup.

I know your setup is a bit different, but I'm just trying to offer some context for setting up your final pass.

JR

[steve-norrell]

Thanks for the input and advice.

The grooving bit is relative new and I did clean it carefully.

I had used three passes to cut the grooves shown in the picture, which is around 5/16 inches deep. I guess I will have to plan on using more passes, the last two or so being in the range of 1/64 - 1/32 inch. JR's suggestion give a good clue as what a "light pass" really means.

If I read Loren's comments correctly, I might try increasing the speed of the router, rather than decreasing it as I expected.

Again, thanks to every one for all the help. Regards, Steve

[LCHIEN]

Thanks for the input and advice.

The grooving bit is relative new and I did clean it carefully.

I had used three passes to cut the grooves shown in the picture, which is around 5/16 inches deep. I guess I will have to plan on using more passes, the last two or so being in the range of 1/64 - 1/32 inch. JR's suggestion give a good clue as what a "light pass" really means.

If I read Loren's comments correctly, I might try increasing the speed of the router, rather than decreasing it as I expected.

Again, thanks to every one for all the help. Regards, Steve

yes, that is the feed rate of the router, not the RPM Speed.

[steve-norrell]

yes, that is the feed rate of the router, not the RPM Speed.

Thanks, Loren. I had read it the other way.

The places where most of the burn problems occur are at the corners when I slow down so as not to over-shoot. Maybe I need to make a template that fits outside of the groove, rather than on the inside (similar to the templates used to make cutouts for router plates). That seems like a lot of trouble unless I am going to use the template many times.

Regards, Steve