Machining with coolant

[hdshinn]

OK, I'm hoping 1) there are some machinists that hang around here and 2) this is a safe spot to ask the question.

I'm very much a hobbyist when it comes to working with metal. I have an engine lathe, nothing to speak of but it does stuff for me. Should I be using coolant when cutting with carbide cutters? I've read pros and cons. I've also read that carbide should be used at high speed with heavy roughing cuts. es/no?

I recently fell heir to some HS steel cutters that seemed to perform (on mild steel) better than the carbide I've been using. I used coolant with and was surprised how well they performed in comparison.

Thanks for any guidance.

 

[Steve from Socal]

Hello Dennis,

Using carbide tooling on many lathes has qualifiers. As you noted carbide exceeds at high chip loading and high speeds. To get good results you need HP, RPM AND, the rigidity to support the tool. HSS sharpened correctly will give good results on most metals and is better for light finish passes and lower speeds.

As far as coolant; HSS is probably more critical due to the heat rise in the part, carbide should remove most of the hot metal in the chip. I use coolant with both types of tools depending on the nature of the work. With HSS the coolant not only cools the work but it keeps the HSS from becoming over heated. Carbide is not as sensitive to cutting edge temperature. Coolant is messy and water based coolants seem to get into places and cause corrosion no matter what they claim. I use Jet-A or Kerosene as a coolant in my lathe, it is not an ideal coolant but it is stable and cools well.

Steve

 

[toolchaser]

I use the tan chip rule for both Carbide & HSS. Cardide does NOT like temp fluctuations. If it gets hot, rapid cooling can cause micro-cracking

 

[Jim Johnstone]

Here at work, we cut steel dry with solid carbide tools. The only time we use coolant is on aluminum and that is more for chip flush than cooling, as aluminum likes to gum up the works, so to speak.

On HSS tooling, coolant would likely be very helpful.

And you are correct, push carbides hard, they work better than way.

 

[Ign]

Coolant on an open machine is impractical at best anyhow. Use some cutting oil applied w an acid brush if you choose, but don't bother w carbide tooling.

Coolant is very nice on stainless as it gets hot in a hurry and holds heat for a long time. Your part can easily grow a couple thou after just one or two passes, so if it's critical wait until it cools before measuring and determining finish cut.

 

[hunter1151]

If you are talking about a manual lathe, I would never use water based coolant. They were not made for water based coolant and will end up rusting the entire piece. Use oil on an engine lathe. That being said be careful when using carbide with oil as you can in some cases catch stuff on fire with the hot chips that can come off of carbide. If you get the right carbide you can cut it dry. The other problem is rigidity, on a lot of engine lathes you would have better luck with a negative rake tool(carbide). Alot depends on the lathe itself.

 

[hdshinn]

Wow!

Thanks everyone for all the tips!!