Help with tapping problems
Help with tapping problems
(OP)
I have a small manual mill that I use with a tapmatic head to make some steel parts. My parts are initially cut for me, from 1/4" thick cold rolled material with a waterjet. I finish drill the holes to be tapped on the mill, then tap.
I use a non-sulpher cutting fluid manually applied to tap and hole. I've made hundreds of these things but the last 2 batches have given me a lot of trouble. Today while trying to figure out how to solve it, I've broken 4 taps.
I am drilling a 10-32 and a M6 hole.
I used a guide (my notes say from USCTI) to choose the drill size. I wanted a high percentage thread.
For the 10-32 I chose a #23 drill (0.154) which the guide said my probable hole size would be .1578. That would give a 79% thread.
I haven't changed anything in my process except obviously the steel may be slightly different from batch to batch, but it is cold rolled. I could have changed drill bits due to wear, not sure there, and the resulting finish hole could be different. I don't have a good way to gauge the true hole size. The #23 bit is a snug fit by hand.
I do not know what speed is best to use for this tap and material. I used to run at about 500-600rpm and didn't have problems, but as I was having problems lately, I tried to slow the speed. Initially that seemed to help, but then I broke some more taps.
Usually the tap wants to hang part way through the cut. Once it hangs, it's difficult to get out.
Can someone tell me what the correct rpm is for tapping a 10-32, and M6 holes, in 1/4" cold rolled should be?
And if my drill selection looks wrong, can someone offer any advise on the correct hole size to produce a high percentage thread that is close tolerance/tight?
Thanks,
Scott
I use a non-sulpher cutting fluid manually applied to tap and hole. I've made hundreds of these things but the last 2 batches have given me a lot of trouble. Today while trying to figure out how to solve it, I've broken 4 taps.
I am drilling a 10-32 and a M6 hole.
I used a guide (my notes say from USCTI) to choose the drill size. I wanted a high percentage thread.
For the 10-32 I chose a #23 drill (0.154) which the guide said my probable hole size would be .1578. That would give a 79% thread.
I haven't changed anything in my process except obviously the steel may be slightly different from batch to batch, but it is cold rolled. I could have changed drill bits due to wear, not sure there, and the resulting finish hole could be different. I don't have a good way to gauge the true hole size. The #23 bit is a snug fit by hand.
I do not know what speed is best to use for this tap and material. I used to run at about 500-600rpm and didn't have problems, but as I was having problems lately, I tried to slow the speed. Initially that seemed to help, but then I broke some more taps.
Usually the tap wants to hang part way through the cut. Once it hangs, it's difficult to get out.
Can someone tell me what the correct rpm is for tapping a 10-32, and M6 holes, in 1/4" cold rolled should be?
And if my drill selection looks wrong, can someone offer any advise on the correct hole size to produce a high percentage thread that is close tolerance/tight?
Thanks,
Scott





RE: Help with tapping problems
RE: Help with tapping problems
My USCTI chart shows the following for a 10-32 threaded hole:
Tap drill size Theo. % thread
-------------- ------------
5/32 83
#22 81
#21 76
For an M6 threaded hole:
Tap drill size Theo. % thread
--------------- ------------
#10 84
#9 79
5 mm 77
RE: Help with tapping problems
Coreypad: Thanks.
* Is the USCTI chart on line somewhere?
I've got the Machinists Handbook, in case it's in there. But I didn't see it.
Looks like your smallest drill is bigger than what I'm using in both cases. I've been using a #11 for the M6. Perhaps that's part of my problem, particularly if the steel is harder that will aggravate the problem. I'll order some of those drill bits with my new tap order.
* any suggestion on taps or coatings for this potentally harder thatn spec steel?
* What about cutting speed? What rpm should I cut these at?
Thanks guys for the help.
RE: Help with tapping problems
I have the 20th edition of Machinery's Handbook. It has recommended tap drill hole sizes in Table 2 of Section 10 Threads and Threading.
I recommend you work with high-end tap manufacturers like Emuge, OSG, and Sandvik for a specific tap and coating.
RE: Help with tapping problems
RE: Help with tapping problems
10-32 uses a 5/32 drill, while an M6 uses a 5 mm hole.
RE: Help with tapping problems
RE: Help with tapping problems
http:/
Ted
RE: Help with tapping problems
Software For Metalworking
http://closetolerancesoftware.com
RE: Help with tapping problems
RE: Help with tapping problems
I have not tried thread forming. Figured that would be harder with a manual maill and limited lubrication abilities. I do need full strength and an excellent fit for the application.
RE: Help with tapping problems
Ted, thanks, that was very helpful. Drill sizes with expected %thread results, and a nice recommended rpm table by material and hole sizes.
It looks to my one of my root problems may be determining what size hole my drills are actually producing. I'm using modern, high quality coated screw machine drills in a presicion chuck, so maybe I'm getting better results than the theoretical .003 oversize.
But I don't know how to measure the holes accurately. Can someone advise the correct (and most affordable) way to check hole diameters for this application?
Thanks guys for all the help.
Scott
RE: Help with tapping problems
Ted
RE: Help with tapping problems
http
A.R. "Andy" Nelson
Engineering Consultant
anelson@arnengineering.com
RE: Help with tapping problems
RE: Help with tapping problems
Thanks for the suggestions.
RE: Help with tapping problems
RE: Help with tapping problems
Thanks guys.
Scott