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Tapping 304 Ss Help

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boostin53

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#1
I'm having a heck of a time tapping 304 SS. They are blind holes being tapped to m12x1.25 in 2" OD 304SS, 1.25" deep. I drilled to 27/64 for 75% thread, then failed. I then drilled up to 7/16 for 50% thread and failed again. I can get my tap started, but that's about it. It feels like the tap just wants to snap.

I know SS work hardens fairly fast. I step drilled up to the given sizes and made sure to use plenty of cutting oil and not let the bits dwell. The work never got too warm and neither did the bits.

What should I do differently? I know my taps aren't the best quality, but they cut threads in 303 SS with some effort. Am I just experiencing the less machinability of 304? Now might be a good time to warm up my internal single point threading skill (or lack of).
 

bss1

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#2
My recent experience is limited in ss304 to tapping about a half dozen through holes in some 1/4" material. It was a very slow process and. I'm glad they were through holes and only 1/4" deep. I had hand taps so I did the usual 1/4 to 1/2 turn and back-up. I'm sure I would have broken a tap in deeper holes as tough as the going was. I think it's just the difficulty with the material that is giving you problems. You mentioned using cutting oil when drilling. I'm sure you used it while tapping as well.

Maybe someone knows of a high end tap that would work better? I know some taps have coatings that are supposed to make them last longer, but not sure if they will make this specific job any easier.

My tap felt like it was going to snap as well but in my case I didn't have a lot to loose and twisted harder than I thought possible without breaking, but the same tap held up through 6 holes. In this case the tap was a 70's vintage craftsman brand. I'm sure there has to be some better taps available that may help.
 

boostin53

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#3
Yes, I used oil while attempting my tapping operation. If it's this hard to tap 304, I may just give up and change material or internal single point.
 

Ken from ontario

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#4
If you have the patience to watch the whole video in the following link, he gives some valuable info on what type of fluid you should be looking for, IIRC the we used to to use heavy tapping oil to tap 304 :

 

hman

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#5
The only thing I can think of is to buy a new, high quality tap. If you're having trouble with your existing tap in 303, I'd call that a clue indicating a dull tap.
 

Wreck™Wreck

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#6
I turn and tap 304 nearly everyday, a good quality sharp tap is important otherwise I have no problems with it.

By the way work hardening can happen with no heat generated, as its name implies it is deforming (working) the material that causes problems. Try machine tapping that size thread in one shot and use a spiral flute tap in a blind hole as they spit the chips out like a twist drill, a very nice tool for your application.
An example http://www.osgtool.com/Product-Group/threading
 

boostin53

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#7
A new tap might be what I need. Along with the OSG brand, what other brands should I be looking at for a quality tap?
 

Wreck™Wreck

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#8
A new tap might be what I need. Along with the OSG brand, what other brands should I be looking at for a quality tap?
PTD, Dormer and Guhring come to mind, you will find them a bit expensive by hobby standards however, steer clear of what home depot/ lowes/ace hardware offers, these tools are not intended for this sort of work.
 

boostin53

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#9
PTD, Dormer and Guhring come to mind, you will find them a bit expensive by hobby standards however, steer clear of what home depot/ lowes/ace hardware offers, these tools are not intended for this sort of work.
Yeah I expect a quality tap to be pricey for hobby use. But if I'm going to be using it often, which I will be, I rather pay the money for quality. Saves me future headaches. Thanks for the info Wreck!
 

Dan_S

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#11
Amazon is a good place to pick up taps. One of there arrived just the other day.
https://www.amazon.com/gp/product/B00F8TYPZO/

The thing with amazon is you have to be patient, I've gotten stuff at 75-90% off, and other times I've had to pay full retail. The sites that monitor prices for you can be a great help if you don't need something right away.
 

steelspray38

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#12
303 stainless steel is a free cutting grade i.e fairly easy to machine/drill/tap. Buy new fine thread M12 tap. 304 stainless is also fairly straight forward to machine.
You do not specify the number to be tapped. Another way to go is buy a top cutting fluid some are dedicated for difficult/tough metals sold in small can /dispensers.
It will make a world of difference and extend the life of your taps and reduce breakage ... reduced friction and torque and less likely that you will try to force the tap to cut.
Be careful to keep clearing the hole during tapping if you use hand taps. Though spiral taps are very good for blind ( non thro')holes and the way to go still needs care to avoid breakage since you are tapping a fair depth with a fine pitch tap. All the previous posts are very sound advice. Hope this helps
Apologies for a what might appear to be a rant.
 

Wreck™Wreck

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#13
A new tap might be what I need. Along with the OSG brand, what other brands should I be looking at for a quality tap?
If you do indeed spend $70.00 on a single tap please let everyone know how it worked from a hobbyists perspective, this may eliminate a good deal of broken/difficult to tap thread, threads.
 

boostin53

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#14
I just ran across this tap on the Motion Industries site. I have a great connection that has been working at Motion Industries for almost 25 years. And can get very good discounts on things. Anyways, this is a Morse brand tap and priced lower than I thought. Would this be a good choice? Screenshot_20170109-185229.png
 

boostin53

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#15
If you do indeed spend $70.00 on a single tap please let everyone know how it worked from a hobbyists perspective, this may eliminate a good deal of broken/difficult to tap thread, threads.
If I spend around that much money on a single tap, I will for sure let people know how well it worked. But it may not change the minds of some people. Not everybody is willing to spend that much on a tap. I don't see why not, if it makes the job easier and you have the extra funds.
 

Dan_S

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#16
Anyways, this is a Morse brand tap and priced lower than I thought. Would this be a good choice? View attachment 143428
The shank looks bigger than the threads so it might not work, you would need to look up the shank diameter and verify.

I found these 2 from Dormer they are about 50% off. You would need to look up recommended materials and coatings though.
https://www.amazon.com/Dormer-Powdered-Threading-Bottoming-M12-1-25mm/dp/B007IVHLK6/
https://www.amazon.com/Dormer-Powdered-Threading-Bottoming-M12-1-25mm/dp/B007IVI70O/

Also get yourself some tap majic, if memory serves this type is usually touted for stainless.
http://www.tapmagic.com/product/3/tap-magic-xtra-thick
 

Wreck™Wreck

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#17
Morse was a very highend tool company at one time, I do not recall using any of their tools often in the last 20 years.

The geometry looks correct so have at it, motion industries is geared toward automotive hobbyists as I recall.
 

boostin53

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#18
I have tap magic at work. I will grab some tomorrow. I just purchased a Guhring tap and will look into the ones in your links Dan. Doesn't hurt to have more than one good tap on hand!
 

boostin53

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#19
Morse was a very highend tool company at one time, I do not recall using any of their tools often in the last 20 years.

The geometry looks correct so have at it, motion industries is geared toward automotive hobbyists as I recall.
I ended up going with the Guhring instead. I may still end up purchasing a Morse tap in a different size since I can get them very cheap.
 

12bolts

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#20
I have a dwindling supply of Rocol RTD cutting oil that I use when working stainless. Its pretty $pendy, especially when used neat, but it does an excellent job. High sulphur.

Cheers Phil
 

george wilson

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#21
I just did a job all in 304. WHAT tough stuff that is!! I had to tap a 1/4-20 thd. hole in each piece. I used "Tap Magic" cutting fluid. I only used NEW HSS drills and NOS taps. I found a CARBON STEEL NOS tap,and actually managed to tap both holes with it after drilling with a new #7 drill. Some how the NOS carbon tap seemed to cut better than a NOS HSS tap!! Using a carbon tap sounds crazy,but it worked. Carbon gets just as hard as HSS. (HSS gets about 63 RC.) Just not as durable. But it lasted for the 2 holes,and still seems perfectly fine.

The carbon steel tap is probably from the 40's or 50's. I certainly would NOT recommend using a brand new carbon steel tap!

Understand,I am NOT recommending that you use a carbon steel tap for 304. It just happened to work the best for me in this particular case.

The trouble(among other things) with 304 is,every time you hesitate during cutting it,it will work harden.
 

EmilioG

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#22
I've always had good luck with Guhring and Emuge taps. For hard steels, I've used TiAiN, TiCn and Cobalt/TIN. Msc has pretty good prices on some these taps.
Would I spend $70 for one tap? Only if I was making a part that cost hundred or thousands of dollars, or something very near and dear. :)
Good luck.
 

Kroll

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#23
This was recommended by a member,for me it seems to work.So for myself combined with OSG tap it work for me,but just did acouple holes
$_57.JPG
 

boostin53

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#24
I'm going to try the Tap Magic first. Then maybe try the Anchorlube. I have several people requesting the same part, but with different exterior shapes. They all take a m12x1.25 internal thread.

They're simple shift knobs. While there are several companies that sell knobs for this application, the designs wanted are not produced. And all mainly stainless steel for the weight. My next order of SS will be the 303 grade. So I get to offer my friends a unique knob and get paid!
 

Kroll

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#25
That's a good plan,if us all could break even then that would be a profit.And its fun----kroll
 

boostin53

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#26
I don't want to say how much they're paying for each knob. But in the end, I will have made enough to easily cover the materials, tools used and some for my time. I'm doing this just because I can, not trying to make a killing with side jobs. It is fun though, plus gives me a valid reason to be in the shop, in my wifes eyes haha.
 

rick9345

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#27
Plain old fashioned cooking lard, and add a coupla drops of kerosene for tapping. A pound at the grocery store or wife’s baking supplies. I have the kind that does not need refrigeration(Armor brand)
 

boostin53

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#29
Took delivery of my Guhring tap today......I'm blown away! This is the first time I've used a quality tap. I hardly had to apply any force. It just seemed to cut the threads in this 304 like a hot knife thru butter! Needless to say, I will be buying more quality taps like this. WELL WORTH THE MONEY!
 

Bill Gruby

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#30
You get what you pay for with Guhring. Wait till you try one of their Drill bits.

"Billy G"
 
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