Gunsmithing Any drawback using carbide coolant fed bits in dry machining?

[Phil1]

Is there any drawback to using coolant fed bits for dry machining other that possibly plugging the coolant hole? Obviously the bit would be used in a machine without coolant feed capability.

Obviously the life of the bit would be less due to lost capability to clear chips and heating.

 

[persistant7500]

As far as I know in a continuous cutting action like turning the life of the carbide insert will be shortened slightly because of the potential for heat stress. However I have been taught that in interrupted cutting operations like milling the shock of repeated heating and cooling will kill and insert prematurely. I have some shell mills and other insert cutters that I run dry in my mills and have not had to replace any because of wear, now if I could just get the guys to be more careful when touching off.............

 

[LRI]

There's a great many variables at play here. Here's a few to consider.

Coolant fed carbide drills exist to evacuate chips from the bore. The coolant does aid in mitigating heat, however the primary function is to clear the debris field. This also brings up another subject that is important to consider.

Pecking with carbide drills. DONT DO IT. That will ruin the carbide faster than anything else. Reasons are simple. Once loaded, keep the cutting surface cutting. The initial bite is hard on the edge. Work hardening your material is another reason to stay in the hole. When you peck you give the material time to develop a hardened shell that you now have to poke through to get to softer material. Again, its going to accelerate the wear/tear on the drills cutting surfaces.

You need to keep the tool cutting at a pace that's ahead of the thermal wave running through the material as you drill. Speed and feed charts along with chip load and SFM exist for a reason. Learn to use them!

Turning inserts for a lathe.

Grades of carbide are important. If your attempting to thread a barrel tennon for instance you want a harder grade of carbide that will take a sharper edge. This will mitigate work hardening your threads as you sneak up on your final pitch diameters to get that good tennon fit with the receiver. It's not free however. The harder carbide is more likely to chip and erode faster than a softer one with a bigger fillet. It's a trade off and the only way to sort it out is to buy some inserts and start fitting up sticks.

End Mills. If you are cutting steel I'd encourage you to consider TIALN coated tooling. Run the tool DRY! Leave the coolant off! You'll be amazed at how aggressive you push these little bastages. I just ran a batch of recoil lugs in the shop here at over 725SFM to rough and 1050SFM while finishing. My step overs were 20% of tool dia and a 5% for finishing.

The game has changed significantly over the years. pretty cool stuff.

Hope this helps.


When in doubt, call the tooling tech support guys before you buy. Tell them the application and they'll get you squared away. Very knowledgeable folks!

C.

 

[Horseheadman]

Depending on the material you're cutting, the cutting point angles and rakes can effect your success. Chad covered things pretty well...