Grinding Down Bits when Only the Tip is Worn

ztp If you're cutting solid hardwood in many shallow passes, you may be able to re-grind bits and use them for longer.January 31, 2012

We've been cutting a lot of 8/4 red oak for a big curved crown project over the past couple weeks. We use down cut spiral HSS bits for a number of reasons. In this particular process we are cutting the 1 7/8" thick material in 4 passes at 1/2" deep per pass. It is going quite well and fairly fast. Although the process is working well, it is toasting the bits on the end 1/2" and not using them at all for the rest of the 2" cutting length. Just for kicks I took one of these used bits to the grinding wheel and carefully removed the bottom 1/2". When we put it back on the router to see how it worked, we were pleasantly surprised. It did a very good job of cutting and we used it for the remainder of that particular phase of the project.

Mind you these are $15 bits vs. $80 bits, so it's debatable as to whether or not it's even worth the time and effort to do this. Again, it was more of an experiment than a cost saving effort. Has anyone else has done anything like this?

Forum Responses
(CNC Forum)
From contributor J:
Yes, we have had this done many a time.

From contributor M:
In solid wood do you find that the bits wear most at the tip or pretty evenly all along the edge?

From the original questioner:
With the 8/4 red oak job we were cutting the 4 passes at about 1/2" deep per pass. Each pass went deeper so only the end 1/2" ever did any cutting. More typically we cut 15/16" and 1 1/8" material in volume. We use 3/8" HSS down cut spiral 2-flute bits cutting in 1 pass down to .1" below the material. These bits wear evenly on the full length of the cutting edge.

From contributor M:
I don't do so much solid wood, more sheet stock, but have noticed my tips, in particular the very point of the flute wearing more when dadoing or multipassing even in solid wood.

All I can say is when I do this sort of cutting, which is not all that often, I use carbide chipbreakers in multiple steps roughing passes about 1/16 from final size, then a HSS steel final pass of 1/16 at full depth for a finishing pass. I am sure you have tried this already. It seems to work well. Wish I had a better suggestion. Maybe I should try your method.

From the original questioner:
Actually we are using your method... just not through programming. Our parts are held on the table with vac pods and there is a slight amount of movement of the parts on the pods. As such we climb cut on initial passes which in effect makes the part about 1/64" over size on both edges as the part shifts away from the bit. We then follow up with the same bit at full depth (or half depth at 2 passes in the case of 8/4) doing a conventional cut to remove the last 1/64" and give a cleaner surface. So we are really both doing the same thing. I just am doing it all with our 3/8" HSS bits.

From contributor C:
I guess it all comes down to time versus money. If using the correct carbide bit, you could run longer without change and without grinding the bits. But the carbide ones can be ground also if needed.