Machining 4140

[Cross Slide]

I have had a 5C Collet Chuck for a couple years that I need to machine a backing plate for. 
Unfortunately in my area metal suppliers are limited that have good selection and will sell short pieces. 
I managed to get my hands on a 5.5”x2” piece of solid round 4140.
I have heard 4140 is great to machine and I have heard it’s a nightmare to machine. 
What do I need to know before I try machining and screwing up a nice piece of 4140?
Thanks
Trevor

[Dr Stan]

Use good sharp carbide tools.  Rough it in about .050" oversize then let it cool off to room temp.  For roughing use a .062" radius on the tip and finishing .032" or less. Start with .010" feed and increase it until your getting nice 6's and 9's.

You didn't indicate if you have carbide insert tooling or if you need to use cemented carbide.  Another factor is the size and condition of your lathe so I cannot recommend depth of cut.  If you have a nice tight American Pacemaker you can take .250" deep cuts with the right tooling.  A 13" South Bend is going to balk at .050".  BTW, I've taken .500" deep cuts in aluminum bronze with a MoMax HSS 1" square tool ground with a chip breaker that would throw the chips off to my right in a Pacemaker.  Machine tool and tooling make a big difference as the ensign who was getting under my feet found out.   BTW, I was a Second class Machinery Repairman (E-5) with less than 90 days remaining in my enlistment. and I didn't give a da#n.

[Cross Slide]

I do have some carbide insert tooling. I really haven’t used any of them yet. I mainly use HSS.
My lathe is a smaller lathe. It’s a Craftex CX701 12x24”. It’s the Canadian version of the Precision Matthews PM-1127VF-LB. I’m not sure how deep of a cut I can actually take with a lathe this size.

On my invoice it says I purchased 5-1/2” HR Round HTSR 4140 R/L
I don’t know if the HTSR will give any more info.
Also. What does the R/L stand for?

Trevor

[EdK]

(07-04-2020, 09:28 AM)Cross Slide Wrote: I do have some carbide insert tooling. I really haven’t used any of them yet. I mainly use HSS.
My lathe is a smaller lathe. It’s a Craftex CX701 12x24”. It’s the Canadian version of the Precision Matthews PM-1127VF-LB. I’m not sure how deep of a cut I can actually take with a lathe this size.

On my invoice it says I purchased 5-1/2” HR Round HTSR 4140 R/L
I don’t know if the HTSR will give any more info.
Also. What does the R/L stand for?

Trevor

Hopefully the "HR" doesn't stand for hardened.

Ed

[Cross Slide]

(07-04-2020, 10:40 AM)EdK Wrote:

(07-04-2020, 09:28 AM)Cross Slide Wrote: I do have some carbide insert tooling. I really haven’t used any of them yet. I mainly use HSS.
My lathe is a smaller lathe. It’s a Craftex CX701 12x24”. It’s the Canadian version of the Precision Matthews PM-1127VF-LB. I’m not sure how deep of a cut I can actually take with a lathe this size.

On my invoice it says I purchased 5-1/2” HR Round HTSR 4140 R/L
I don’t know if the HTSR will give any more info.
Also. What does the R/L stand for?

Trevor

Hopefully the "HR" doesn't stand for hardened.  

Ed

I’m pretty sure the HR is Hot Roll. It definitely has the Hot Roll Steel look to it.

[f350ca]

Even prehardened isn't that tough to machine with carbide. You have to take reasonable heavy cuts to get a good finish. If you come up shy and have to remove 1 or 2 thou the finish sucks.

[Dr Stan]

You're probably not going to be able to take anymore than .050" DOC (Depth of Cut) and possibly only about half that amount.  Do you have access to another lathe that can take a deeper DOC?  If so rough it out there.  BTW, you'll want to finish it mounted on your spindle to make it as true as possible to your machine.  Also use a center punch to show its mounting position.  I always make 4 little center punch marks to show alignment/location on the spindle nose.

[Cross Slide]

(07-04-2020, 08:42 PM)Dr Stan Wrote: You're probably not going to be able to take anymore than .050" DOC (Depth of Cut) and possibly only about half that amount.  Do you have access to another lathe that can take a deeper DOC?  If so rough it out there.  BTW, you'll want to finish it mounted on your spindle to make it as true as possible to your machine.  Also use a center punch to show its mounting position.  I always make 4 little center punch marks to show alignment/location on the spindle nose.

Definitely can’t pull off .050 with my lathe. But I was able to do .030. I’m very happy with the finish I got. I will definitely be finishing it up attached to the spindle. I currently have one side faced and the bore done so it will fit snug on the spindle register. Last weekend I made a gauge that is the exact size as the spindle register, so I had something to test fit without needing to pull my 4 jaw chuck off to test fit it. Next I will fit Put it on my mill and set my DRO for a bolt circle and drill and tap the holes. Then bolt it to the spindle an machine the second side to fit the collet chuck. I will definitely mark it’s location to the spindle. My 3 jaw chuck has a 0 on the chuck and the backing plate that correspond to a 0 on the spindle. 
Trevor

[Cross Slide]

   

   

   

   

[EdK]

You're getting a good finish.

Ed