Threading stainless steel

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line runner

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I will say that I,m still a greenhorn at this.
I picked up a used lathe 2 yrs ago ... it is a Morton 16-40 D6 camlock , made in Taiwan, with a cast bed , It weighs approx. 3,500 lbs, quite solid and I think is good quality.It was built in 2002
I'm looking for advice when threading stainless steel (barrel grade stainless)

My threading comes out quite nice on steel like shafting, brass, aluminum.
I have tried the carbide inserts and also used HSS grounded at 60 deg.

On 60 deg. threads the coumpound set at slightly under 30 deg.... my first cut start at .005 and gradually work down to .001 and then it happens I get a tiny buidup of steel on the end ot the bit...I use a fine stone to remove this... but it does damage my threads some.
The oil used during threading is sulphur base and is brushed on at every pass.
Any advice would be much appreciated
 
Are you using coated (e.g. TiAlN) carbide, or uncoated carbide inserts? Or are you using just brazed toolbits? Brazed toolbits are usually zero-rake, and they're murder on stainless or aluminum. If you're really serious about it, check out proper indexable coated inserts and a good holder - and, as mentioned, some proper purpose-designed threadcutting lubricant (and LOTS of it) is never gonna hurt.

-M
 
line runner said:
I'm looking for advice when threading stainless steel (barrel grade stainless)
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I use HSS tools and cut an extra thread or so which I remove after finishing the threading process. I find slop in the lathe or something leaves the first thread a trifle out of kilter with the rest of the threads. Other than being tougher to cut, stainless is similar to other metals for threading, at least in my experience

cheers mooncoon
 
you will find the 416 stainless used for barrels quite easy to machine. It short chips nicely . Drills and reams well. Sulphur based cutting oils are great for this stuff .
If you want to use HSS keep it sharp and honed. You will find carbide is more user friendly as you gain experiance but doesn't like slow RPM's even for threading.
regards Randy
 
Maybe you need to adjust your half-nuts, if the first thread is always FU. Engage for threading then turn off the lathe and see if there is excessive amount of slop in the carriage.
HSS is technology from how many years ago?
Have a look in to coated inserts. Also worse case, you could save the last few thou on for chasing with a die.
 
Stainless comes in such a wide variety of alloys that all have such different qualities that asking about threading stainless in this sort of generic way is sort of asking what colour you should paint the living room. Perhaps that isn't a good comparison since usually the wife says what colour it'll be. But imagine if you were told you needed to pick the colour and it had to go with or compliment the existing colours in there. NOW you see what I mean? :D

You'll want to find out what alloy the barrel stock is and search or post back for specifics on that alloy. From there I'd suggest you obtain the exact same alloy and run some tests on some scrap to find the best cutting lubricant and fps cutting speed for the alloy when used with whichever style of tool you want to use. Then play with light vs heavier cuts to find which chips away better.

I haven't done a lot of machining with stainless but for the times I have you'd never know it was the same class of metal at all. Pretty much every piece I've ever worked with has had widely differing charactaristics to the point that what I learned on the last piece didn't do me any good at all with the next. But I'll admit that I have not ever gone looking for specific alloys. I just used what I either had on hand or whatever the local scrap yard had that was sized correctly.

The only time I ever threaded some stainless it worked just fine using normal methods but with a thick body synthetic cutting oil. I can't even tell you what it is since the lettering wore off the plastic bottle years ago. But I got it from KBC if that helps at all. It's a medium honey brown, not smelly like the sulphurated "black" oil and around the same consistency as 90 weight rear end oil.
 
Threading stainless rifle barrels is no big deal. They machine easily. I use HSS bits on center or just below center and cutting oil and about 100 RPM. I feed at 30 degrees and at first maybe 6 or 8 thou cuts and then as it gets close to finish 1 thou and then 1/2 thou. I very lightly run a smooth file on the top of the threads to clean very small roughness off the top. After fit is confirmed and I will spin in reverse at 300 RPM and run a folded piece of 320 grit paper in the thread from the shoulder backwards a few times and then on top... the threads always look great.

Looks is just looks though... as long as the pitch is correct and you can thread it easily by hand you are good to go. A slightly loose thread is better than a tight thread...
 
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Using carbide tooling, you will have much better success and a better finish if you thread at a higher speed. I thread at 240 Rpm. I use water based coolant on the threads. HSS bits will work well at slower speeds but even so, work better just a bit faster than many like to thread.
If the first thread is a bit off, the carriage can be snugged up on the bed a bit to load the leadscrew before the cut starts. Regards Bill.
 
if you are useing carbide thread at the fastest speed possible and still maintain controll wile threading as leeper said 240 rpm is an optimal speed i could give u a formula but 240 is a good speed
 
savage_shooter said:
if you are useing carbide thread at the fastest speed possible and still maintain controll wile threading as leeper said 240 rpm is an optimal speed i could give u a formula but 240 is a good speed
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Exactly! Actually this is all Greek to me:p

This place still amazes me with how many awesome guys around here will share their "trade secrets". Good going guys.
 
Not really trade secrets. Just carbide and metal machine shop 101.
Carbide produces the better finishes at higher RPMs. It's a known fact in the industry. HSS bits is old school tech that still works and for hobby folks with slower old lathes like mine it gets the job done and cheaper too. The art of grinding and shaping HSS bits is a treat. :)
 
Threading

We do a lot of threading on 300 and 400 series Stainless in our shop , Here are the part numbers of the tool that we have found work best for us , this tool can be used in a cnc as well as as conventional lathe
this is a SECO tool holder ** p/n CER 075 5-16 HD ** use coated insert
** p/n 16erag60 cp500 nitride coated ** We run VALCOOL coolant on the part while threading , i am not sure of the cost of the tool but it is used eveyday in our shop and has never failed and insert life is real good a tool like this would last you a life time as a hobbiest .
hope this helps
 
One day I'll graduate to a nice set of Aloris wedge tools and those coated inserts. They really are the way these days to speed up things.

I'm still using a Lantern toolpost with 5/16" HSS and carbide bits. An old habit from 1970's high school and apprentice machine shop days before the advent of CNC.
 
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