Making a couple of 1/4" linkage rods out of stainless. Using the 'start from this side' side of the die it quickly started seizing. Using liquid wrench and bearing grease for lube. Almost got it stuck. Turned the tap over and it cut great, no seizing at all. Thought I might have a dull die but it cut my standard steel mock up rod easily using the correct orientation. So what's the tip for tapping stainless, other than what I did?
I will be fascinated by the results of your question as I had a real dickens of a time cutting threads in these radiator support rods. The originals were too short for the jog I had to put in them so I bought long rods, bent them and cut to fit then had to add the threads. What a task, ended up ruining one of them and had to buy another rod (not cheap). I too thought my tap was dull or work out, bought a new one. Used a lot of thread cutting oil and took my time making quarter turns, backing it off, another quarter turn, so on. It worked but what a task.
You really need a specialty cutting fluid for stainless; a 'standard' cutting oil literally won't cut it. Need a sharp tap or die too. Stainless galls easily, I've literally seen a stainless nut threaded on a stainless bolt by hand seize and take the threads off when trying to remove it. Rapid-tap and anti-seize are your best friends when using stainless...
I like to use Butterfield drilling and taping fluid on stainless steel. I find it provides a better cut with less sticking due to it's lubricating properties. I use Rapid Tap for most everything else. When threading stainless I only turn the die/tap until it just starts to cut then back of. Quarter turns are too much and will cause the stainless to bunch up and gall instead of cut cleanly.
Don't know, salvage yard scrap. Non magnetic. I sometimes have the need to cut down or extend thread on hardware store SS bolts. What alloy or grade would that be?
300 series is non magnetic. But the differences are pretty big after that. 316 is is much tougher than 303 for example. And 310 is crazy tougher than 316
Most common stainless is either 18-8 or 316. Keep in mind that cut threads are considerably weaker than rolled threads, and stainless is weaker than regular steel. Most rolled-thread stainless bolts are not quite equivalent to a grade 5 bolt, cut threads drops it to a grade 3. Not a material you want to use in any critical fastening applications... Grade 8 stainless is available, but usually has to be gotten from a specialty supplier.
The die you are using is better suited for chasing threads rather than cutting threads. A round ,split die has a screw for adjustability so you can start a little larger and adjust the die down for easier thread cutting. Another thing is bolts are usually about .005 under the nominal size on the od. example: a 1/4 - 20 bolt will measure about .245 on the od. As stated above, Moly Dee(made by Castrol) is excellent cutting oil for stainless but it is not cheap. Regular cutting oil or Rapid Tap will work better than liquid wrench or bearing grease.
Bevel the edge that is being threaded a little bit, this will help you get the die centered and straight. As others said lots of oil and go slow back and forth, eventually you’ll get there. Hope this helps you. Edit: You could also bevel it to a point, then cut it to length when you’re satisfied with thread length
Use never seize instead of cutting oil , works for cutting thread and for drilling , seriously , try it !
Just a thought. I recently attempted to threat some 1/4 round rod I had on hand. this rod was bought as 1/4 '' in lengths When the die nut was run down it make a total mess of the thread cut. After careful examination the 1/4 rod was found a bit to big in diameter to let the tap cut properly. It galled and tried to twist ect. perhaps your rod is a bit large in diameter as well?
These are all great tips, my two cents are that you can't use cheap dies or taps, I undersize a little, since stainless work hardens quickly, slow speed with fast penetration, lots of cutting fluid and 303 is a better machinable stainless over 304 stainless. 303 doesn't weld as nice as 304. The never seize sounds like a good idea, I will have to try that and the Moley Dee. And treading is a lot easier on a lathe when doing round stock.
The most common is 304. Use sulphur based cutting fluid. As has been said measure it first to make sure it's not oversized. Taps got in a hole, dies go over a rod. And as has been said you have a thread chaser not even a die. A chaser doesn't like to cut a new thread just repair a damaged one.
That is what I mainly use, Castrol bought them out but still good stuff. I have a bottle of Anchor Lube that is also good with SS, that can be thinned with water if desired.
300 series is slightly magnetic. 316 is more of a specialty alloy and not easy to come by, but McMaster Carr will have it. For car use, I'll avoid 316. I have loads of 303 and 304 leftover from paying jobs, it cuts well on a lathe, 304 cuts better than 303 which is a little gummy. 301 and 302 mainly comes in sheet form and is loaded with hard spots, so is 316. I had a nice sheet of 303 stock at work, 3/32" thick. I used it a lot for brackets on my cars.
Most grade-8 stainless is alloy A286, which is a tough nickel alloy. It has great strength at high temperature and high tensile strength around 160-180 ksi for what we buy for hardware at work. Fastenal will have it mostly in MIL numbers. BUT... Ace Hardware at least by me carries it. Great for exhaust hardware, it will discolor a tad, but it will never rust.
Thanks for all the replies. I changed the title to reflect cutting internal as well as external threads, which of course I meant, just couldn't think of the term (Dieing Threads?). I do have some split dies but didn't know the die I was using was just a thread chaser. I have cut many threads with them over the years without problem, and as I said it cut effortlessly backwards. Another point brought up was the diameter, and after measuring this morning the stainless rod does in fact measure .2515".
.2515 is a little high for a 1/4" thread. Although it should work. I would make threading blanks for that size around .245 to .248.
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