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Help. Machining an Alloy Steel Socket Head Screw

blackwolf4278

Aluminum
Joined
Oct 1, 2020
Hi all. I’m running into an issue turning a Steel Screw. I’m not exactly sure what kind of material it is, I can only say that it is a Black (Alloy Steel) Screw, with we all widely use. I don’t know how hard they are, but I’m having a big issue turning down a 8” long 12-13 screw. I need to turn about 6 inches of the thread to a .375 DIA and leave the 2” thread as is. My inserts keep breaking, and I keep having a horrible finish.

Any ideas? Thanks!!!
 

Orange Vise

Stainless
Joined
Feb 10, 2012
Location
California
They're around HRC40. Thru-hardened 4140 or similar material.

Carbide should easily cut it with tailstock support. The harder part is getting rid of the burr where 3/8" transitions to 1/2" thread.
 

blackwolf4278

Aluminum
Joined
Oct 1, 2020
That’s exactly what I do. I have a tail stock, I made a small “bushing” that I screw onto the thread, and then press onto it with a tailstock.
 

cyanidekid

Titanium
Joined
Jun 4, 2016
Location
Brooklyn NYC
tailstock support (could also be conical cavity type live center) [as mb said]
follow rest, brass tipped,
positive rake insert for aluminum?
polish the major dia. of the threads with some 800 paper.
shallow cuts, and of course lock anything not being used, with the helix, its not only an interrupted cut, but also exerting force on the Z axis.
 
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blackwolf4278

Aluminum
Joined
Oct 1, 2020
tailstock support (could also be conical cavity type live center) [as mb said]
follow rest, brass tipped,
positive rake insert for aluminum?
polish the major dia. of the threads with some 800 paper.
shallow cuts, and of course lock anything not being used, with the helix, its not only an interrupted cut, but also exerting force on the Z axis.
Thank you.
What do you mean by brass tipped and/or positive rake insert for aluminum?
 

sfriedberg

Diamond
Joined
Oct 14, 2010
Location
Oregon, USA
What do you mean by brass tipped and/or positive rake insert for aluminum?
He meant using a follower rest with brass tips on the fingers. A follower rest (as an alternative to the tailstock) to fix your high length-to-diameter stickout issue. Brass tips on the fingers to avoid galling your workpiece.
He meant using a sharp, positive rake insert intended for aluminum instead of a negative rake insert intended for steel. A sharp, positive rake insert to reduce cutting forces, which would also help with your high length-to-diameter stickout issue.
All of his suggestions were aimed at reducing the deflection which is causing you problems: Resist the cutting force, reduce the cutting force.
 

DDoug

Diamond
Joined
Oct 18, 2005
Location
NW Pa
Yup, set-up sounds shaky all around.
How is the tool holding set-up ?
Insert radius ?
Angles ?

Post some pix.
 
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MrWhoopee

Hot Rolled
Joined
Nov 8, 2017
The diameter is small compared to the length. Even with tailstock support it's going to jump around and chatter. A follower rest would help if such you have. Inserts for aluminum (positive rake with sharp edge) would be best if they can hold up to the material. Any positive rake insert (CCMT, DCMT, even TPG) would be better than negative. Small nose radius would also help, as would holding short, turning a section then pulling out a little more etc.
 

guythatbrews

Cast Iron
Joined
Dec 14, 2017
Location
MO, USA
More info would help a lot. How many pieces are you making? Are you chucking on the head or the major diameter? What diametral tolerance?

As said previously way big l/d ratio. If only making a few chuck on major diameter not head, center, and do a few inches at a time. Won't work well if high qty or close tolerance.

If high qty maybe someone can centerless grind.

More info helps people help you.
 

Scottl

Diamond
Joined
Nov 3, 2013
Location
Eastern Massachusetts, USA
They're around HRC40. Thru-hardened 4140 or similar material.

Carbide should easily cut it with tailstock support. The harder part is getting rid of the burr where 3/8" transitions to 1/2" thread.
What I've found in such situations is that you need to leave the straight section a little short and then make final passes cutting in toward the tailstock so any burrs are pushed away from the end of the thread section. It also helps to gently wire brush the cut end of the threads using a fine gauge wire wheel after machining. I keep a carding wheel (fine wire - typically used for wire brushing during rust blue process) on one end of a bench grinder and always use it on any threads that have been shortened or otherwise cut.

A follower rest would definitely be a good idea when trying to turn a 6" length down to .375 inches.
 

FredC

Titanium
Joined
Oct 29, 2010
Location
Dewees Texas
I have turned thousands of commercial Allen screws making oil field J-bolts. I thought they were case hardened alloy similar to 8620. 8620 mock hardens to fairly high strength and yield values so case hardened anything made from 8620 will be hard and tough all the way through. On these J-bolts the ones I made were fairly short so I purchased overly long screws machined the head end then cut them off. Inserts need to be appropriate for hard allow steel. The Op will need some kind of support to make it work. On a few of these specialty Allen drive screws that we made using off the shelf was too difficult and we made them from ETD which did machine easier than the commercial screws. On the threads we turned from the outside towards the shank and never had to brush the threads.


Jbolts.jpg.
 

swarfless

Cast Iron
Joined
Aug 31, 2005
Location
South Australia
As often the case not enough info. Add to all the suggestions re work support maybe your SFM is too low, a big part of carbide's advantage is simply being able to tolerate a higher cutting edge temperature than the workpiece can. If not too many pieces were involved I'd simply grind them .. & I only have a T & C grinder.
 

blackwolf4278

Aluminum
Joined
Oct 1, 2020
Thank you for all of the advises? I will be trying all of them until i get to the bottom of this! Thanks again
 

kenton

Hot Rolled
Joined
Dec 15, 2015
I guess I take a different approach than most. When I have modify fasteners I usually use a TPG insert with a .015" nose radius and cut to finished size in one pass to get under the hardened rolled threads. Having a solid lathe and supporting your workpiece are obviously very important to this approach.

I use a buffing wheel to knock the burrs off the threads, usually a harder one meant for deburring steel.
 








 
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