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Re: machining 4140
: machining 4140 -- popethom	Post Reply	Top of thread	Engineering Forum

Posted by: randykimball ® 04/18/2006, 19:28:07 Author Profile eMail author Edit

I'm going to guess that you are drilling a hole in 4140 HT. If using carbide you need to be up around 1600 RPM or higher. However, I'm wondering if you are drilling with the drill wobbling, ... the drill needs to run true. If using cobalt drop the RPM down to around 620. If power feeding you should feed at around .003" per revolution. These settings may vary greatly based on your coolant, machine steadiness, machine type, drill point style, your experience, and actual hardness of the 4140. The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.

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Re: machining 4140
: Re: machining 4140 -- randykimball	Post Reply	Top of thread	Engineering Forum

Posted by: Kelly_Bramble ® Administrator 04/19/2006, 08:45:58 Author Profile eMail author Edit

I'm no expert (complete amateur) on drilling in 4140, however I have drilled a few holes in this material and 4130 steel. I know that the right type of drill bit, and adequate cooling is required. You don't want to get into it too fast or with a worn bit. I remember having to replace the drill bit after drilling several holes. Seems to me that I have broke a tap or two in this material as well. I was using a 1950's vintage drill press and drilling/tapping thru about 1.5 thick material. Tough stuff..

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Re: machining 4140
: Re: machining 4140 -- Kelly_Bramble	Post Reply	Top of thread	Engineering Forum

Posted by: randykimball ® 04/19/2006, 23:08:03 Author Profile eMail author Edit

You are "right on". A dull drill will work harden a hole, this is not good. However, the hole is usually still workable, ... if you are skilled enough, using colbalt or carbide drills. Also, very much agreed, you do not want any drill to get too hot. Although there are several materials tougher and of which work harden more readily, it is a strong consideration while machining 4140 steel. One reason is because poor drilling methods (or with dull drills) may weld or embed protions of the drill itself into the work area. This creates a serious problem often resulting in the work being scraped. Unless completely removed, and only if it has caused no stress fractures in the billet, you can bet it is no longer useful as an aircraft or other life safety part. The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them. Modified by randykimball at Wed, Apr 19, 2006, 23:10:28

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Re: Re: machining 4140
: Re: machining 4140 -- randykimball	Post Reply	Top of thread	Engineering Forum

Posted by: bobss396 ® 05/02/2006, 13:58:46 Author Profile eMail author Edit

SAE 4140 has a machineability of around 66%, suggested surface speed is 110 ft/minute. The as-supplied hardness is somewhere around rc28-36. I would put a call into Guhring for their opinion. I would suggest a 135 degree split point drill which is Tin coated. This coating helps a lot to extend drill life. I assume that you are using a big enough spot drill and flood coolant. Calculate for a .003-004 chip load (to start) and use a peck cycle if you're using a CNC mill or lathe. Start with a .5 diameter peck and increase it if the drills holds up better than what you were using. Bob

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: Re: Re: machining 4140
: Re: Re: machining 4140 -- bobss396	Post Reply	Top of thread	Engineering Forum

Posted by: WOOLEY ® 03/13/2009, 02:54:27 Author Profile eMail author Edit

Hi, CAN 4140HT BE FORM TAPPED? I AM MAKING REDUCER BUSHINGS, USING A GEOMETRIC DIE HEAD FOR THE OUTSIDE THREADS AND TAPPING 3/4" X 10 ON THE INSIDE. THE FINISH IS UGLY ON BOTH, BUT WORSE FOR THE TAP. (5 hp ENGINE LATHE WITH #3 MORSE TAP DRIVER IN TAILSTOCK) Modified by WOOLEY at Fri, Mar 13, 2009, 10:28:27

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