Mirror finish with HSS tool bits

[Parlo]

So what's wrong with very high speed on HSS but very light cuts? I mean HSS doesn't really burn up that easily anyways. We're not talking about high carbon steel here.

Sometimes very light cuts can have a detremental effect on surface finish because there is no loading on the machine to tighten up all the sliding parts.

 

[GunsOfNavarone]

One thing I'll add, don't buy hot rolled steel, use cold rolled when possible. PCD tools on aluminum, I get mirror finish, carbide on stainless or titanium and I get mirror finish. Heavy cuts on cold rolled and I get mirror finish. Hot rolled and 12L14, at best would be a satin finish, but more likely that torn finish. Now when I say, "mirror finish", I don't mean like chrome, but I could see a reflection of whatever I put up against the surface.
I hate HSS tools, I just can't find formulas that work, so if that's your tools of choice, I feel like you have your work cut out for you.

 

[jmkasunich]

Are you using cutting oil? One thing that causes crappy finishes is "built-up edge". That's where part of the chip that is being removed welds itself to the tip of the tool. For a brief time, the welded on chip is the "cutting edge" instead of the actual cutting edge. That usually cuts a little deeper and much rougher. Then the welded on chip breaks off and you are back to the original cutting edge, before another chip welds on again. This can happen many times per second. Cutting oil, especially with extreme pressure additives, prevents the chip welding and improves the finish.

Built up edge - Wikipedia

en.wikipedia.org

 

[GT-6 Racer]

There is some good information here. I would add the the formula for a good finish not only is material and tool dependent but also machine and coolant dependent along with cutting parameters. For example my big series 60 Monarch will peel .100” diameter off a big chunk of A36 and you can see yourself in it. Low SFM but higher feed seems best. The 10EE with a 0.050” diameter cut and much higher speed and less feed is best. The south bend 13 is hss tools at a low SFM and low feed with a 0.020” diameter depth and the it’s a satin rough finish. Carbide on the SB isn’t great either, can’t work it hard enough. Shear tool is by far best finish on the SB with any steel. Also the last 3 cuts at equal depth rule also helps. Most of time a very fine Final Cut leaves a poor finish as Parlo points out.

Chip welding drives me nuts on the EE as I tend to run faster which gives a better finish with carbide but then welds a chip and gouges things. No coolant on that machine. Tap magic EP extra thick helps some. Also at high speeds the carbide coating make a huge difference. Choose wisely by manufacturers recommended use and it works great. Big spend though especially if works several materials and you need multiple types of coatings

Just methodically work from the recommended speeds and feeds for your material and tooling. W/O Flood coolant you really need to slow down for some operations. I get my feeds speeds from old guides. Modern guides expect big spindle speeds and coolant. Takes patience and experience.

Not so cookbook as it is with high power CNC with flood coolant and high $ exotic tools.

 

[brino]

@mikey has lead that big huge thread on sharpening HSS lathe tools....... it is full of great techniques and advice.
I wonder if he has some knowledge to add here.
Brian

 

[taiwanluthiers]

There is some good information here. I would add the the formula for a good finish not only is material and tool dependent but also machine and coolant dependent along with cutting parameters. For example my big series 60 Monarch will peel .100” diameter off a big chunk of A36 and you can see yourself in it. Low SFM but higher feed seems best. The 10EE with a 0.050” diameter cut and much higher speed and less feed is best. The south bend 13 is hss tools at a low SFM and low feed with a 0.020” diameter depth and the it’s a satin rough finish. Carbide on the SB isn’t great either, can’t work it hard enough. Shear tool is by far best finish on the SB with any steel. Also the last 3 cuts at equal depth rule also helps. Most of time a very fine Final Cut leaves a poor finish as Parlo points out.

Chip welding drives me nuts on the EE as I tend to run faster which gives a better finish with carbide but then welds a chip and gouges things. No coolant on that machine. Tap magic EP extra thick helps some. Also at high speeds the carbide coating make a huge difference. Choose wisely by manufacturers recommended use and it works great. Big spend though especially if works several materials and you need multiple types of coatings

Just methodically work from the recommended speeds and feeds for your material and tooling. W/O Flood coolant you really need to slow down for some operations. I get my feeds speeds from old guides. Modern guides expect big spindle speeds and coolant. Takes patience and experience.

Not so cookbook as it is with high power CNC with flood coolant and high $ exotic tools.

I got a victor lathe, I can easily take off 4mm of steel on it without a hint of slow down. I rather not take that much off at once though mainly because I hate scrapping parts. The lathe rigidity isn't really an issue, bigger issue is part flex and chuck slipping.

I've experimented taking off about 3mm at a time on a piece of 4140 and on "roughing" inserts it gives great finish.

 

[ddickey]

@taiwanluthiers Do you mean 4mm depth of cut?

 

[taiwanluthiers]

@taiwanluthiers Do you mean 4mm depth of cut?

I mean 4mm off the diameter.

 

[cazclocker]

Mirror finish with HSS is very unlikely to happen, or with carbide either, that is what grinding, polishing and lapping is for.

I get mirror finish on my HSS cutters all the time. I just hand-polish with successive grades of wet/dry 3M sandpaper, ending with 3000 grit. The mirror finish begins to appear with 1200 grit, and only gets better from there. But I have a ton of patience so that helps. And I don't have anyone telling me to hurry up.

 

[benmychree]

All this discussion of high finishes on tools is in my opinion, akin to "gilding the lily" I have never found it necessary to any more than grinding a tool in the ordinary fashion to achieve an acceptable surface finish.