Facets in my 16 TPI Threads - Need some help!

[davidpbest]

UPDATE:
I got the lathe back into position, leveled and tried threading with some barrel drops that Bamban gave me. Overall, vastly improved. I tried threading with just the cross-slide and a new AR Warner HSS tool / bit. 16 TPI at 65 RPM. I fed at 0.003 for 2 passes then 0.002 for 11 passes then 0.001 with a spring pass for 10 passes. Still feel some coarseness in the threading. Close inspection of the result reveals some surface irregularity that I can't figure out.

Which A.R.Warner insert are you using - TNMC or TPMC? Looks like tool chatter to me.

 

[mksj]

I would recommend taking deeper cut passes, if the depth is too shallow it wont cut and just push the metal. I take 0.01" per pass on the dross slide, then close to target 0.005" +/- and one spring pass using the cross slide. Multiple passes at the same or close to target depth decrease the finish. on steel. Cutter height and rigidity are also issues. I had better finish and inserts last longer with the lay-down type. Even wit HSS inserts I thing the cutting speeds are low and possibly need better lube. I would start with aluminum and then move to steel and and may need to do some adjustments.

Others have the 1236 and have gotten very good threading finish, but even between the same machine results can vary. Single phase motors are very susceptible to problems depending on the mount isolation and belt type/tension.

 

[macardoso]

UPDATE:
I got the lathe back into position, leveled and tried threading with some barrel drops that Bamban gave me. Overall, vastly improved. I tried threading with just the cross-slide and a new AR Warner HSS tool / bit. 16 TPI at 65 RPM. I fed at 0.003 for 2 passes then 0.002 for 11 passes then 0.001 with a spring pass for 10 passes. Still feel some coarseness in the threading. Close inspection of the result reveals some surface irregularity that I can't figure out.

Bummer, thought you had this all figured out

Looks way better than the samples you had in the original post. In the last picture above, it almost looks like your spindle side flank of the thread is tearing out while the tailstock flank just has the tiniest bit of chatter. The tearing would be my concern. What material is that? Stainless?

 

[Bamban]

Bummer, thought you had this all figured out

Looks way better than the samples you had in the original post. In the last picture above, it almost looks like your spindle side flank of the thread is tearing out while the tailstock flank just has the tiniest bit of chatter. The tearing would be my concern. What material is that? Stainless?

TXCowdoc may be busy, I will answer for him. The material is a barrel drop 416. I handed him a few to use while he is troubleshooting the problem.

 

[ChrisAttebery]

1. I would work out the process on some 1018 or HRS. Once you get it working on mild steel THEN try the 416 barrel drops.

2. Try using .010" DOC for all but the last pass. Use .005" and then a spring pass. Take more than one spring pass and see if that cleans them up.

3. Are you sure the tool is on center? Drop it down a bit and try again.

 

[Bamban]

1. I would work out the process on some 1018 or HRS. Once you get it working on mild steel THEN try the 416 barrel drops.

Just curious, why so?

 

[ChrisAttebery]

Just curious, why so?

1. Unless he has a bucket full of 416 drops it should be cheaper.
2. I would think that 1018 should be easier to thread than 416SS.

 

[davidpbest]

416 is gummy and difficult to thread. Not as difficult as 304 but close. I too recommend trying to get the threading issues worked out on another material first, then move on to SS. If you can't thread brass or 1018 without chatter marks, then there is something wrong with the setup (tool height, rigidity of the compound, too shallow of a cut, etc.). Diagnose this on a more forgiving material before diving into the deep end of the pool (416). I asked which of the A.R. Warner inserts you are using because a positive rake will work better in SS - it cuts cleaner than a neutral rake, but it does need enough DOC bite to cut instead of just rub intermittantly.

 

[Bamban]

1. Unless he has a bucket full of 416 drops it should be cheaper.
2. I would think that 1018 should be easier to thread than 416SS.

I got a bucket full for him. I just finished doing 28 barrels.

 

[Liljoebrshooter]

416r barrel steel threads very nice.
I remember going through the same issues when I started.
Keep trying different things and only change one thing at a time. I get the best result on my lathe with a Kennemetal NTP2R insert.
This was after trying about 5 other types.

Joe