Help tapping in stainless?

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davestea
Posts: 260
Joined: Tue Feb 11, 2003 10:04 pm

Help tapping in stainless?

Post by davestea »

Need to know if there is anything special I need to do for tapping in some stainless I have.

Made an arbor (see previous post) and now need to put a 1/4x20 thread in the back end for a cap to hold it all together and to put a handle (tommy bar) in to turn the arbor.

Now this is some really stringy stainless - made some really long curls coming off the carbide tool I used.

Put a thread on with a 14x1mm die and took my time pulling on the chuck with the chuck key about 1/3 rev. at a time - back up the whole way back and forth a couple time then an another 1/3 rev. with the die. Gawd - glad it was only 1/2 inch of thread.. Pretty clean and smooth thread. Used kerosene - best stuff I've found so far.

Do I have to worry about using the next size drill for a looser clearance? Special lubes? I have two new taps bought special for this job. Broke 2 off in cheep steel already. Don't want to mess this one up. I"d like to get about .500" of thread. Can I get away with less?

Thanks for any help you can offer.
Dave
Smithy 3in1, Select Mill, Atlas 6" lathe
Rich_Carlstedt
Posts: 1754
Joined: Sat Dec 21, 2002 12:16 am
Location: Green Bay Wisconsin USA
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Re: Help tapping in stainless?

Post by Rich_Carlstedt »

Yes Dave
The first thing is you should drill out the hole for only 50 % thread on Stainless indstead of 70% as most charts show.
Read "Machinery's Handbook" and they explain why this is the NORMAL manufacturing procedure on tapping stainless.
Also be aware that 1/4-20 and 10-24 are the 2 most difficult threads to tap due to the ratio of Tap OD and thread root diameter. In other words, they are the easist to break in doing a job. A better choice is 1/4-28
A half inch deep should not be a problem and would give you maximum strength in the application
davestea
Posts: 260
Joined: Tue Feb 11, 2003 10:04 pm

Re: Help tapping in stainless?

Post by davestea »

thanks - can you tell me what drill size to use - don't have the handbool
Dave
Smithy 3in1, Select Mill, Atlas 6" lathe
Karl_Losely
Posts: 262
Joined: Sat Jan 04, 2003 10:54 pm
Location: Ohio, Lake County

Re: Help tapping in stainless?

Post by Karl_Losely »

Doug Alkire addressed tapping in 300 series stainless in the "Shop Talk" column in the March/April 2003 Live Steam. For a 32 pitch thread he recommends oversizing the tap drill by ~.004", half that for a 64 pitch thread and double for a 16 pitch thread.
Based on this info, I would use a #4 (.209") drill for tapping 1/4-20 in stainless. Standard tap drill for 1/4-20 in mild steel is #7 (.201").

Karl.
UnkaJesse
Posts: 4090
Joined: Sat Jan 04, 2003 10:29 pm
Location: Tennessee, Obion County, Town of Troy

Re: Help tapping in stainless?

Post by UnkaJesse »

Dave, If you can find it, the best ever tapping fluid is Perchlorethane or Trichlorethane based brake or electric motor cleaners, but our benevolant, beneficient all knowing government bureaucracy has about caused the makers of these cleaners to disappear. The last I was able to locate was at a NAPA auto parts store. Perchlorethane was once the main ingredient of the well known "Tap Magic" tapping fluid. [img]/ubb/images/graemlins/cool.gif"%20alt="[/img] They added a bit of oil of cinnamon and some red coloring (colouring fer yer TEL) to hide the principle active ingredient, but even they have got away from the Perc based fluid. [img]/ubb/images/graemlins/mad.gif"%20alt="[/img] One thing for sure, don't (repeat DO NOT) use this stuff on aluminum (Al-you-min-i-um,TEL) or you will be introduced to the vilest, most acrid smoke you ever had the displeasure to become acquainted with! [img]/ubb/images/graemlins/frown.gif"%20alt="[/img]

Unka (perchlorethane )Jesse
"The same hammer that breaks the glass, forges the steel" Russian proverb
Bruce_Mowbray
Posts: 705
Joined: Sat Jan 04, 2003 7:45 pm
Location: Pennsylvania

Re: Help tapping in stainless?

Post by Bruce_Mowbray »

Dave,
Sounds like fun. I use "Moly-Dee" (molybdinum disulfide based) tapping fluid whenever I tap stainless whether it be 303, 304, 17-4,18-8,etc. Always get good results with less tap breakage. This stuff is available through most machine shop suppliers.
Bruce Mowbray
Springville & Southern RR
TMB Manufacturing & Locomotive Works
davestea
Posts: 260
Joined: Tue Feb 11, 2003 10:04 pm

Re: Help tapping in stainless?

Post by davestea »

Yes, as I recall it was red - I just looked it up in a KBC catalog - can sure looks like I remember. It said for aluminum on it - after the first time it s'smoked' I read the can again. Bad smoke, black gunk on the tap and then it rusted badly in just a couple days. Yes, perclor is familiar - I used to use it to clean PC boards. I recall that smell from the tap magic -

thanks guys
Dave
Smithy 3in1, Select Mill, Atlas 6" lathe
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