Machining tips for Chrome Moly

[SnakeyJ]

Some time ago I took a punt and brought some 3' of 2 1/4" of steel bar stock. I was not sure what grade of steel, but nice, shiny and it cost less than the postage.

It is quite hard and generates a lot of heat when cutting, with long unbroken chips that tangle up around the cutter. That said it takes a good cut with carbide inserts and leaves a good surface finish with flood cooling and automatic feeds.


I can mill it, gently with carbide endmills and made a nice fly cutter, but burnt a lot of oil as I don't have flood or must cooling on the mill (yet).

I can cut with bandsaw ok and it drills ok with cobalt drills.

I'm pretty sure this is chrome moly and just seeking any advice/tips on machining. Speeds, feeds and tools. Advice on buying 'pigs in pokes' is less useful, but likely deserved!

 

[Karl_T]

chrome molly or 4340 has a maintainability rating of about 60% IIRC. It is used a lot where an assembly will be welded. Now the weld can be harder than a hooker's heart.

4340 machining properties - Google Search

 

[GeneT45]

I'm wondering if what you have is 17-4 PH? The Cr-Mo I've used (mostly 4140) cut pretty easily when using carbide. It would cut well with a broad range of speeds and feeds.

GsT

 

[Winegrower]

I had some material that sounded like that, long stringy tough chips... this is what happened to me:

 

[mmcmdl]

I had some material that sounded like that, long stringy tough chips... this is what happened to me:

I remember when you did that .

 

[SnakeyJ]

I had some material that sounded like that, long stringy tough chips... this is what happened to me:

View attachment 451207

That does look pretty similar - it does machine better with flood coolant to keep it cool and I can break the chips with a brush if I push them down. But occasionally they just run away and wrap around everything.

 

[SnakeyJ]

I'm wondering if what you have is 17-4 PH? The Cr-Mo I've used (mostly 4140) cut pretty easily when using carbide. It would cut well with a broad range of speeds and feeds.

GsT

I did buy some 17-4 ph stainless a couple of years back to make some counterweights for a telescope mount - definitely easier to machine that the chrome moly! I haven't got hardness files, but might try scratching with a few known metals in my scrap box to see if I can bracket. I'm guessing it's at the harder end, 4140 or similar?