Thread cutting lube

[morrisman]

Whenever I cut a thead in the lathe , the cutting tool tends to tear the steel, rather than cut it with a smooth finish , the finish is rough .The bit is sharp as . I always use the lowest speed , 60rpm.

What is the most suitable lube for thread cutting .? .I've tried a few things, but none seem to work. The older books suggest lard of all things....

Mike

[pipeclay]

Solubile oil,straight cutting oil,tap magic,based on the information provided in your question I dont really think lube is the problem.

[Abratool]

Whenever I cut a thead in the lathe , the cutting tool tends to tear the steel, rather than cut it with a smooth finish , the finish is rough .The bit is sharp as . I always use the lowest speed , 60rpm.

What is the most suitable lube for thread cutting .? .I've tried a few things, but none seem to work. The older books suggest lard of all things....

Mike

Mike
This is my second contact with you today.I hope you do not think I am overdoing it.
When I cut threads on the lathe I angle the compound slide around to half the thread angle.For instance I would set the compound at 30 degrees for a 60 degree thread. For a 55 degree thread it would be set at 27 & a half degree.
The infeed for each successive cut is made by infeeding the compound slide, thus the toolbit is cutting on one side or the leading edge of the toolbit & not "crowding" the cut in a wedging action, & causing tearing of the thread. Small repetitive cuts of say a few thousands of an inch for each pass are made until the full thread depth is reached. The final one or two passes are made with the crossfeed infeed to obtain an accurate thread form from the toolbit cutting on both faces of its preground angle faces taking say a thou at a time.
Additional I have made a threadcutting stop for my 260 Hercus as shown in the attached photos. This has allowed a much more rapid threadcutting operation & reduces errors, by allowing the toolbit to rapidly be withdrawn at the end of the cut & then returning to its original stop position in readiness for the next cut.
I know all of the old books say to use Lard oil, but I have found Straight undiluted soluble cutting oil works well or a product called "Tap Magic" cutting oil is maybe a bit better. Others will have their own favourites, Im sure.
In past years I would use a Stock & Die to cut threads but these days The Lathe is quick & much more accurate in getting better results, than the old method.
Additional although it may seem extreme, I purchased a Thread Micrometer from "Tools4Cheap" in the USA. It uses interchangeable anvils to suit the thread pitch.Over the last week Im finding this is a great tool for getting accurate thread depths. It has taken some of the guess work out of the job.
regards
Bruce

[morrisman]

Thanks Bruce

I was doing it by the 'plunge method' -using the cross slide only . I will try the angled method compound in future.

I will have to drill/tap a hole for that stop gadget... as my lathe doesn't have a hole there for it.

Excellent advice ..ta

Mike

[pipeclay]

Before you start drilling holes make yourself aware of how the threading stop works and fits to the cross slide,there are no holes.

[Dropcat]

I will try the angled method compound in future

As Bruce said, the trick is to cut only one side of the thread. It is one of those 'not obvious' things. Find some plastic pipe (PVC etc) to practice on.

[pipeclay]

You would of thought in some of the books that were read the offset screw cutting method would of been mentioned,I myself use both methods with good results although experience plays a big part.

[Dropcat]

You would of thought in some of the books that were read the offset screw cutting method would of been mentioned

Not everyone reads the manual. Sounds like he being a bit enthusiastic (or the tool was blunt etc).

[Dave J]

I just use motor oil for lube and set the compound on most threads.

Dave

[Anorak Bob]

Mike,

What steel are you trying to thread, buttery 1214 or tough 4140? Shouldn't be any issues with the former, maybe some with the latter. If I have a suitable die, I'll run it over the lathe cut thread to clean it up.

Ten years ago, I used self ground HSS for all my threading. Nowdays I use indexable carbide inserts for most external threading and HSS internally. Sometimes I even use an old fashioned Lock offset toolholder in an old fashioned lantern toolpost when access is restricted.

Are you supporting the outer end of the work piece with your tailstock? Unsupported thin sections will deflect away from the cutter. Half dead centres come in handy.

Bob.

[unixbigot]

Do try the offset method, but as for cutting oil, I found a hint in one of the SI Workshop Practice Series that said "50/50 neatsfoot oil and paraffin" makes a good cutting fluid. Having some neatsfoot oil to hand, I gave it a try.

Being english, I think the writer meant kerosene, but I used paraffin *oil*, the stuff sold in chemists/supermarkets as "Paraffin BP" for use as a laxative. Neatsfoot can be obtained from hardware stores, or in bulk from equestrian suppliers.

The resulting brew is quite thick and can be applied by brush, sauce bottle or oilcan. Its good for hand tapping as it doesn't run far. It sticks to rotating work even under hundreds of RPM.

[wbleeker]

If you don't want to offset your compound slide, for every cut you take just move the compound half the crosslide infeed distance ie ten thou in and 5 thou along. Thats how we were taught as apprentices and it works.
Will

[.RC.]

I use trefolex.... Yea yea, I know it will kill me and make baby jesus cry... But then apparently so will beer, mobile phones, x-rays, ct scans, aircraft travel, meat, and about everything else.. For the half a dozen times a year I might use it, I will take the risk..

[Oldneweng]

As Bruce said, the trick is to cut only one side of the thread. It is one of those 'not obvious' things. Find some plastic pipe (PVC etc) to practice on.

Soon after I got my lathe I tried to cut a thread on a bit of inch stainless heavy wall pipe using the plunge method. First ever thread cutting on a lathe. Not a good result LOL. I haven't actually tried any since. Was using tool from one of those sets of 9 lathe tools which I have decided are rubbish. Plain carbide tips and a nice wooden box. Its a long story but I don't use them much and don't have another thread cutting tool yet except for a recently bought diamond tool holder which I have yet to set up for threads but will soon.

Dean

[azzrock]

hi. as a few people have said may be you should set the compound slide to 0. use a thread form gauge to set the angle of the tool. enshore you have the right clearances or rake. make one cut.
and for every say .010" after that.you move the tool in advance the compound slide 0.005". continue to do this for about 1/2 to 3/4 of thread depth .ill try and post a few p-hotos if my misses hasnt used all the batterys.