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How Do You Create Class 3B Threads?


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 Our customers' quality standards changed where before they were ok with all threads being Class 2B (even though some prints called out 3B). Now they want the 3B's to be to print and I am having a hell of a time getting them right (always oversized), so I'm wondering what do you guys do to be successful? Material is 2024/6061/7075, threads are 4-40 up to 1/4-28, both standard and STI. They check fine with a 2B gage, so I'm close, but not close enough.

 I've used H2 taps, 2-3 flutes, spiral-straight, bright-steam oxide, solid holder-floating holder, 3-100sfm.

Follow up question- I've got 6-32 3B threads in Ti-6Al-4V where my go is tight, and my nogo is loose. I'm threadmilling these guys so it seems like maybe the major is collapsing more than the minor because of memory effect, but not sure how to solve this problem either.

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What thread percentage are you shooting for with the tapped threads? Using recommended drill sizes? Check to be sure drill isn't blowing out the holes. Shop I used to work at we had to make 3B threads quite often, and they usually took a little screwing around before they'd come out right. I know you probably already did this, but check for run out in both drills and taps. We always rigid tapped them, FWIW. A lot of the time (and I know this sucks) we had to put in M00s to have the operators apply some oil to all the threaded holes before tapping.

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36 minutes ago, C^Millman said:

Ream all your holes to the minor don't drill them.

We hold +/- .0005" on the diameter all day with carbide drills and get a good finish (for the first 75 minutes or so of feed time anyway), granted that they are some custom grind stub drills though.

 

Should work though. Tried that at my old shop, but boss said it took too long since we were making several thousand of those holes. If you got the time, that is also a good call. I even had a machinist that insisted on boring with an offset head as the only means of getting the necessary size, but those were the hard anodized 3B threads...

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9 minutes ago, MIL-TFP-41 said:

What brand of taps? I have found that the right tap for the right material can make a world of difference....well a thou or 2 of difference anyways. 

OSG. Everything from a General Purpose to a Exotap VA-3 to a HyPro AL.

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Working with those threads, any little thing can throw you off. Make sure your holes are clean, straight, and on size. Go as low (*thread percentage) as specs will allow on diameter. Depending on the machine... how many holes and what kind of pattern are you using to get around to them? If you are going through and drilling, then coming back to tap it couldn't hurt to make sure you're always approaching from the same direction, the tiniest bit of backlash can put you off location unless you always approach the holes from the same direction. I *think* MCam has a feature to make all drill/tap cycles approach from the same direction. 

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51 minutes ago, specv said:

What is the GH number on the taps you are purchasing? We cut 3B threads all the time and order our taps accordingly. The pitch changes .0005 for each GH number.

H2. Currently looking for a convenient supplier of H1's.

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43 minutes ago, McLaren said:

H2. Currently looking for a convenient supplier of H1's.

Lol yeah that's probably a better place to start.

 

I had issues with them because I was running them on a beat up old Haas and had to go through everything I mentioned. 

 

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Coolant strength up to around 10%?

Tap running spot on? For ally, bright finish. No treatment. Spiral point for through holes. Spiral flute for blind. Rigid tap preferred - the only time I've ever used a floaty is a fine (M10 x 1) in soft as sh1te ally extrusion. It was the only thing we could use to stop it tearing on the way out.

I'm assuming cut tap? You could roll the 6000 series, but not the 2024 (I wouldn't think - limited elongation and possible work harden?). Not sure about the 7000 elongation?

For reference, 3B has a larger core than 2B (to clear the increased root radius on the male part).

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7 hours ago, McLaren said:

Follow up question- I've got 6-32 3B threads in Ti-6Al-4V where my go is tight, and my nogo is loose.

^^this means your tool is worn beyond usage and your cutter comp is oversize.

Looking close at a plug gauge you should notice the no-go as being truncated on the major dia (i.e. thread doesn't come up to a point), unlike the go side.

this will tell you that it is not intended to gauge if your tool (tap or thread mill) has the tips worn-off. It is only to measure the pitch diameter. Therefore your cutter comp is over size and the tips are blown.

8 hours ago, McLaren said:

so I'm wondering what do you guys do to be successful? Material is 2024/6061/7075

Like newbeeee said, it's a lubrication issue or secondly a toolholder issue. Try using tapping fluid and blowing off the tap on each hole.

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13 minutes ago, McLaren said:

 That's what I was thinking as well, but I put in a brand new threadmill and same issue.

Hmmm. Perplexing.

What exact threadmill are you using?  post up your mastercam settings page or some NC code. There are some serious experts here.

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37 minutes ago, mkd said:

Hmmm. Perplexing.

What exact threadmill are you using?  post up your mastercam settings page or some NC code. There are some serious experts here.

#24 Drill - https://www.kyocera-sgstool.com/products/hi-percarb-series-135-5xd

32TPI Carmex Threadmill - http://www.carmexusa.com/default.aspx?page=item detail&itemcode=MTSH0250C4132UNMT9

6-32 STI Thread - 3900 RPM 2.0IPM

vzUV19r.png

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 The threadmill is in titanium, and those threadmills run CCW. Cutter comp is being applied during a lead in move.

%
O72202
G00 G90 G17 G20 G40 G80
G53 Z0.
G53 X-30. Y0.
N1
(6-32 STI THREADMILL B0C0)
(T37    - 6-32 STI CARMEX THREADMILL - H37    - D37    - DIA .146")
T37 M06
G00 G17 G90 G54
S3900 M04
B0. C0.
G254
B0. C0.
X-1.25 Y.56 M08
G43 H37 Z3.6
Z3.445
G94 G01 Z3.4328 F25.
G42 D37 Y.5665 F2.
G02 X-1.2335 Y.56 Z3.425 I.007 J-.0065
X-1.2335 Y.56 Z3.3937 I-.0165 J0.
X-1.2335 Y.56 Z3.3625 I-.0165 J0.
X-1.2335 Y.56 Z3.3312 I-.0165 J0.
X-1.2335 Y.56 Z3.3 I-.0165 J0.
X-1.2335 Y.56 Z3.2687 I-.0165 J0.
X-1.2335 Y.56 Z3.2375 I-.0165 J0.
X-1.2335 Y.56 Z3.2062 I-.0165 J0.
X-1.2335 Y.56 Z3.175 I-.0165 J0.
X-1.2335 Y.56 Z3.1437 I-.0165 J0.
X-1.2597 Y.5467 Z3.1328 I-.0165 J0.
X-1.2553 Y.5638 Z3.125 I.0056 J.0077
G01 G40 X-1.25 Y.56
Z3.4328 F25.
G42 D37 Y.5665 F3.
G02 X-1.2335 Y.56 Z3.425 I.007 J-.0065
X-1.2335 Y.56 Z3.3937 I-.0165 J0.
X-1.2335 Y.56 Z3.3625 I-.0165 J0.
X-1.2335 Y.56 Z3.3312 I-.0165 J0.
X-1.2335 Y.56 Z3.3 I-.0165 J0.
X-1.2335 Y.56 Z3.2687 I-.0165 J0.
X-1.2335 Y.56 Z3.2375 I-.0165 J0.
X-1.2335 Y.56 Z3.2062 I-.0165 J0.
X-1.2335 Y.56 Z3.175 I-.0165 J0.
X-1.2335 Y.56 Z3.1437 I-.0165 J0.
X-1.2597 Y.5467 Z3.1328 I-.0165 J0.
X-1.2553 Y.5638 Z3.125 I.0056 J.0077
G01 G40 X-1.25 Y.56
Z3.4328 F25.
G42 D37 Y.5665 F3.
G02 X-1.2335 Y.56 Z3.425 I.007 J-.0065
X-1.2335 Y.56 Z3.3937 I-.0165 J0.
X-1.2335 Y.56 Z3.3625 I-.0165 J0.
X-1.2335 Y.56 Z3.3312 I-.0165 J0.
X-1.2335 Y.56 Z3.3 I-.0165 J0.
X-1.2335 Y.56 Z3.2687 I-.0165 J0.
X-1.2335 Y.56 Z3.2375 I-.0165 J0.
X-1.2335 Y.56 Z3.2062 I-.0165 J0.
X-1.2335 Y.56 Z3.175 I-.0165 J0.
X-1.2335 Y.56 Z3.1437 I-.0165 J0.
X-1.2597 Y.5467 Z3.1328 I-.0165 J0.
X-1.2553 Y.5638 Z3.125 I.0056 J.0077
G01 G40 X-1.25 Y.56
G00 Z3.445
Z3.6
M09
M05
G255
G53 Z0.
G53 X-30. Y0.
B0. C0.
M30
%

 

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Originally I was doing 1 pass with 1 spring pass, and checking with a 2B gage they came out great. After changing to a 3B gage though I tried adding in the 3rd pass and removing some cutter comp. hoping to open up the major diameter without affecting the pitch diameter.

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W.A.G.: all I got is the tool is actually a right hand cut and you're rubbing it the wrong way.

These old eyes would need to look at that sucker under a microscope to be sure. i'm not seeing online catalog say left hand cut, but i know they exist.

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