Getting a smooth finish on threads

[envirotronics]

Hi, I have been testing the thread cutting feature on my new HAFCO AL960-B Lathe.
The threads work OK but the finish is terribly rough looking.
I am running the speed at 170RPM -3/4" BSP 14TPI - Tool steel.
I have watched Videos and amazed at how smooth the results others can get.
I am using proper thread cutting tool (60deg)
Any clues?
Regards- Graham Hobbs

[snapatap]

first off, wrong angle for bsp needs to be 55 not 60 degree. I'm assuming by proper threading tool you mean a carbide insert type tool? If so i have found that running dead slow 50ish or less revs can give a good finish, as the recommend cutting speeds aren't achievable on a manual lathe.

[morrisman]

Sounds like the tool isn't sharp enough ? If using a HSS tool, a slight bit of side rake helps ( depending on the direction of the cut ) plus use a proper cutting fluid ie tap magic

[Sterob]

I would have thought using cutting fluid would help?

[pipeclay]

Are you plunge cutting or coming in at an angle using the compound?

[envirotronics]

Thanks everyone for your response.
I am using a carbide insert tool.
I will try the 55 degree tip as suggested and also try a better cutting fluid
I will also drop the speed (if possible)
Regards
Graham

[Michael G]

Before doing any of that I would look at the material you are using. If it is just some garden variety 'mild steel' then it is quite likely that the threads will look torn. It's not always easy to find but if you want smooth looking threads then some 1214 (or 1214L) steel will give a nicer result.

Michael

[envirotronics]

Thanks Michael.
I am using Tool Steel.
I have also tried a variety of materials with similar results.
Cheers
Graham

[bob ward]

My preferred method of single pointing threads is to cut 95% of thread depth on the lathe and then finish/polish with a die, assuming of course I have the correct die.

An 85% deep cut allows you to cut most of a 55° thread with a 60° tool.

[AlexD]

I’ve done a fair amount of threading on my AL-960B using both inserts and HSS tools on different materials, and usually achieve reasonable results. One thing I always do if possible is use a live or dead centre to support the free end of the work piece, and of course make sure the gibs are tight and the tooling is exactly on centre height. Also having a variable speed drive helps a lot – lets me slow things right down when threading up to a shoulder then speed up when reversing back. I haven’t really noticed any difference in the finish depending on speed – more a function of the material and sharpness of the tooling.