Internal rolled threads 2

[awol]

I am manufacturing an internal ACME thread using two methods; single point and thread tap. Both are producing "chatter" on the thread face, making the part unusable. The material is Inconel. Has anyone found a vendor that can roll internal threads? Or can polish internal threads?

 

[Kenneth]

I don't think you're going to have much luck finding anyone to "roll" internal acme threads. Even "standard" (60°) thread forms would be extremely difficult (if not "impossible&quot to "roll" using "thread forming" taps in high strength, difficult-to-machine materials like inconel. Were you using a "tandem" tap when you attempted to tap these threads? I have even seen "roughing", "semi-finish" and "finish" taps made for acme threads (

http://www.natool.com/products.cfm#Acme).

What specific inconel alloy and material condition are you trying to tap? Cutting fluids, etc. are very impotratnt when machining these materials...



To quote one tap vendor (

http://www.roton.com/taps.jsp):

"We recommend using tandem style taps for tapping power transmission thread forms. This style of tap has both a roughing and a finishing section (see Figure 13). This allows the user to tap a nut in a single pass. Tandem Acme and Hilead taps dimensioned on the backside may be used for nuts with a maximum thread length of twice the nominal diameter and for nut materials of brass, bronze, mild steel and cast iron. For longer nuts or nuts made from alloy steel, stainless steel or other alloys with low machinability, special taps may be required."

I think a reputable tap manufacturer may be be your best source of information.

 

If your finish and tolerance requirements are that critical, you might try having the threads ground by a good job shop. You could also go to a specialty tap maker and have them grind a tap with the correct geometry for you. One note, is the tap galling on reversal, or is it actually "chatter"?

 

[TVP]

To reinforce what Kenneth said, you need to be aware of what condition the Inconel is in (annealed, heat treated, etc.) and what type of lubricant is being used during the tapping process, in addition to the specific tap geometry and rolling procedure. Feel free to post additional information and we can respond again. Also, this topic has been discussed on Eng-Tips previously-- see the following thread:

thread281-22444

 

[awol]

reply for ornery norsk :
The tap is leaving actual "chatter" marks on the thread face.
I have never seen this before. We tapped the last one by hand (with a big wrench). This attempt left chatter marks to the point I couldn't tell when the turning started and stopped.
They are very uniform. And completely unusable.
To all: Thanks for the great response. I have contacted a company that grinds internal ACME threads.
-awol

 

[dlewin]

I am not sure what size thread you are machining or if you have access to a machining center, but we have used the thread milling process to generate difficult threads in a variety of material and I know that inserts are available for ACME threads. The process involves a custom cutting tool and a machine with helical interpolation ability. I am not sure but I would assume that thread milling would be more cost effective than grinding. Here is a link that overviews the process.

good luck

http://www.carboloy.com/News/news/Technical/tapping/

 

[JOVATO8]

AWOL
Try roughing then finishing the threads.
Set-up a tool for roughing the thread and an other for
finishing.Works for me, I had the same problem.
I assume you are threading on a CNC lathe.
Make sure to adjust your tool to have your threads match.

Later
JOE

 

[basanga]

one way to combat this problem is to strike out the thread first by single point cutting(screw cutting), obviously the cutting fluid will play a big part in giving the required finish. I usually try to leave .005" max to remove by the finishing tap.

if you have a recomended cutting oil for this mtl, try utilising it in an undiluted format.