Shop disagreement on rigid tapping, your thoughts?

[Chriseg1]

I was curious to get peoples thought on this, We have a disagreement in the shop.

Should these be peck tapped, or finished in one shot? About 250 holes for each.

Machine is a TM1-P with rigid tapping

1st:
Vanadium Steel Spiral Point Tap for Aluminum 1/4"-20, H3 Pitch Dia, 3-Flute, 3.150" L O'all,
hole is 0.201" thru, 3/8" 6061.

2nd:
Vanadium Steel Spiral Point Tap for Aluminum 10-32, H3 Pitch Dia, 3-Flute, 2.76" L O'all
hole 0.159" thru 1/4" 6061

[Machineit]

I'd shoot them straight through!

Mike

[Delw]

roll tap them straight through especially on the 10-32

[Matt@RFR]

One shot. If you peck tap things like that, I'd like to bid against you!

[Chriseg1]

Just a bit more info, the tooling is what I have. And the whole peck tap thing is coming from the kid that designed the parts. He is telling me that the holes are deeper than the Dia. of the tap, so they have to be peck tapped.... ? this is what they taught him in school?

[underthetire]

I agree. Straight through, especially if its not a blind hole. Peck tapping is usually for hard materials.

[Machineit]

Just a bit more info, the tooling is what I have. And the whole peck tap thing is coming from the kid that designed the parts. He is telling me that the holes are deeper than the Dia. of the tap, so they have to be peck tapped.... ? this is what they taught him in school?

Ah yes, our great school system!

[KenFoulks]

Straight Through.

Make sure you have:
Good coolant concentration
Good coolant flow
Good drilled hole size

[Machineit]

Please remember the following too:

My version of Machinery's Handbook is #23. Starting on page #1654 there is a chart of "Recommended Hole Size Limits Before Tapping Unified Threads"

It has them listed by Classes, 1B-2B and class 3B. 1B and 2B are in one column and 3B is under another column. The hole sizes are listed in four depths each, To and including 1/3 D, above 1/3 D to 2/3 D, 2/3 to 1 1/2D, and 1 1/2 to 3D. D=the tap size, such as 1/4 inch.

I'll list an example below of class 3B thread holes:

-----------To 1/3 D,--------above 1/3 to 2/3 D-------2/3 to 1 1/2D,-----1 1/2 to 3D
-
-------------Min Max-------------Min Max--------------Mini Max---------Min Max

1/4-20-----.1960 .2013---------.1986 .2040 --------.2013 .2067-------.2040 .2094

As you can see a 1/4-20 tap run in only .400 deep can use a .2094 hole and still be a legal class 3B. It is much easier to tap too.

Using the largest hole possible and also within class limits will make the job a lot easier. This is especially important in tough to tap materials and small taps. We did a lot of 4-40's in excess of .450 deep in stainless and going to the larger hole size saved a bunch of broke taps. Just 1 or 2 thousands makes a tremendous difference in ease of tapping since the root of the tap on a 1/4-20 is larger than .201 inch.

Most of the machinists I have worked with didn't know this, they only used the standard chart for tapping. So every hole for a 1/4-20 was the #7 drill, no matter how deep it was. On your holes just going to .203 for the 1/4 inch tap really relieves the pressure on the tap and has no effect on the strength of the thread.

Mike

[azmachining]

Just give away some what of a trade secret, that's cool (sarcasm)...

[NWSERVICEGUY]

I have trained at many community colleges and must say that few of them actually understand CNC. They mostly teach manual machining with a term or two of CNC. My 17 yo son is wanting to get into the industry. He brought me a community college class schedule and I read through it and was not impressed. I got him a job at a very nice shop that will teach him more in 1 month than 2 years at a community college.

[haastec]

this is what they taught him in school?

Time to school him some more!