Any tips on getting a good finish on drill rod ?

M

matchman

Guest
Im trying to get set up to do single point neck turning in my lathe.
Using HSS tool on drill rod to make a mandrel . "Crap finish". Tool set on center. 700rpm, slow feed. The finish is almost fuzzy . I turned within .001 of finish and used 600 grit paper to finish to diameter and end up .002 under size and still not smooth.
I can post a pic of how the tool is ground and the finish if that will help.
Thanks for any help.
Adam
 
Drill rod does not like to be single point machined. Cylindrical grinding is about the only way to get a really good finish on drill rod.

For a turning mandrel, Class 6 or Class 8 bolt shanks do best. They are rigid but they must still be polished. I turn the spot on the mandrel to about 0.001" over, then use a Pattern File or similar and bring the mandrel down to about 0.0002" over, then 240-280 grit wet-or-dry to finish.

If you will finish this area to EXACTLY the diameter of your bullets then the finished case neck will be exactly what you measure, and the exact diameter of a case neck with a seated bullet.
 
I use drill rod all of the time …

… to make parts or tooling. You can get a real nice turned finish with drill rod but you need to get the surface speed up there and use positive rake carbide inserts. For turning necks on a lathe I use stress proof or 4140 to make the mandrel. Stress proof is free machining and 4140 machines real well too. Both polish up real nice and I have those materials it in the shop readily available. The grade 8 bolt is a great idea, I LIKE IT!!

Nic.
 
Niccolo said:
… to make parts or tooling. You can get a real nice turned finish with drill rod but you need to get the surface speed up there and use positive rake carbide inserts. For turning necks on a lathe I use stress proof or 4140 to make the mandrel. Stress proof is free machining and 4140 machines real well too. Both polish up real nice and I have those materials it in the shop readily available. The grade 8 bolt is a great idea, I LIKE IT!!

Nic.
Click to expand...

I do the exact opposite on drill rod I use a low surface speed and use a negative rake finishing insert. High speeds and feeds will most likely brake the inserts because the drill rod is to tough. I am turning on a CNC with inserts, from what I have noticed what I consider low many manual lathe guys with HSS tooling would consider high. Just to give you a idea 300-350 SFM is about normal. 100 SFM would be low. 400+ SFM would be low.

Here is a arc that I turned on 1/4" O-1, after turning it was heat treated and lightly sand blasted. The only noticeable marks near the center line where surface speed is approaching 0 SFM.

IMG_0098.jpg
 
Thanks Guys.
Jerry the grade 8 bolt worked great!
adam
 
+ 1 on the grade 8 bolt, been using them for years, there is a size for every cal., I also use a collet instead of a chuck, you can get the carriage so much closer.!
 
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