tapping of 4140 steel 1

[par96]

Is it possible to tap 4140 steel in the field? Is it possible to tap 4140 steel in general? I have a filler plate that i need to attach to a piece of 4140 steel, but this filler plate needs to be interchangeable with a thicker plate so welding is out of the question.

thanks

 

[unclesyd]

Generally yes. You can tap up Rc 42 without much trouble.

Come back with the tap size and hardness of the 4140 if known.
Any more information about the hole will be helpful

 

[par96]

unclesyd,

I was planning on specifing a 5/8" dia. countersunk bolt w/ 11 unc (1 1/2" of thread). Approximate bolt length of 2". Tapping approx. a 2" long hole into the piece of 4140 steel. The existing drawings call out for the clamp (4140 stl.) to be heat treated to 275-300 B.H.N. before machining.

The adjoining piece of steel will be 1/2" thick. My steel design manual indicates a countersunk height of 5/16" for a 5/8" dia. bolt. Would the following be an appropriate call out on the drawings; "TAP 5/8"x2"-11UNC DEEP HOLE & COUNTERSUNK 5/16" DEEP FOR 5/8"x2"-11UNC COUNTERSUNK SLOTTED HEAD BOLT".

Is there a web site that references appropriate designations for tapping holes and threaded fasteners?

Once again thanks for the help.

 

[CoryPad]

par96,

I don't know of a web site that has designation information. According to Handbook of Bolts and Bolted Joints, an appropriate designation for the thread is 5/8-11UNC-2A (you can change the class to whatever you want). For the hole, you can add depth information(fully threaded, partially threaded, unthreaded) after the thread designation.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patdaly]

par96

Cory is correct on his nomenclature. You will likely have to drill the hole 2-1/2" deep if you need 2" of thread engagement, to allow for the imperfect threads of the taper tap ( I wouldnt really suggest using a bottom tap in 4140 unless in the annealed state.) and to allow chip clearance.

Couple of other things to consider, I would look at an Allen head bolt, I cannot recall finding slotted head fasteners that large, and you have to be very careful about any loads this filler might see, countersunk bolts aren't really structural in nature, they will fasten a filler piece on just fine, but any loads subjected to the filler could cause failure.

 

[BillPSU]

Whenever tapping a hole clearance in the bottom allows for a place for chips to go. Drill the hole through if possible.
The callout should be 5/8-11UNC-2B x 1.5" MFT(minimum full thread). 2A is an external thread tolerance and 2B is an internal thread tolerance. The fastener having 1 1/2" of thread 1.5" MFT would be sufficient.

Are you tapping this part on the machine or on a drill press in a shop? Hand tapping on the machine in the field will present some challenges.

 

[unclesyd]

As posted above just check your dimensions.
The countersink as stated will not clear a 5/8" Standard height bolt head. As posted by patdaly[/] the use of a low head socket head cap screw might be more appropriate if the head has to be flush. Any type slotted head fastener could be extremely hard to remove.
Just remember that one of the plates has to have clearance for the bolt, normally 1/16" on the dia.

Come back with a little more description of the bolt you a planning to use and the thickness of the two plates

 

[diamondjim]

Looks like you are talking about
an 80 degree countersunk bolt
rather than a counterdrilled
hole for a socket head bolt.
We generally drill the tap drill
an extra depth of (7 divided by
the pitch of thread) to allow for
the tapered lead on the tap for
most commercial jobs.
I think machineries handbook
recommends at least (5 divided by
the pitch of thread) extra depth.

 

[jetmaker]

2 cents worth,

Having worked with high strength steels in the past, it is good practice to avoid blind threaded holes. If at all possible, drill a through hole, and then use a nut/bolt combination to connect the plates together. This is better for fatigue and possibly ultimate strength.

If the nut retension is an issue, then weld the nut to the bottom of the thicker plate.

Regards,

jetmaker