My thread is ugly

[EnderDRM]

1/2 -13 tap in a blind hole .75 deep in 8620 CR.
15-50 sfm. Good flood coolant.
11MM drill.
Lathe with floating holder indicated w/in .001.
Threads are badly galled looking.
Any help would be great.

 

[13engines]

"Good flood coolant" is a pretty open ended statement. Verify your drilled hole size, and try a tapping fluid of some type and see what that gets you.

New tap? Old? Unknown sharpness or history of use?

 

[litlerob1]

Type of tap? Condition of hole before tapping? Depth of Drilled hole? Why are you using a floating holder?

R

 

[yardbird]

Don't know how big 11mm is but I drill for 1/2-13 with 27/64"?

Sometimes CRS is a bitch to get shiny

Picture if you can may help folks see what's happening.

Brent

 

[13engines]

Drilled on size the 27/64 would give him 78% thread depth which is reaching for the high end. 11MM on size should give him 66% which should only be making his life easier.

 

[SeymourDumore]

1/2 -13 tap in a blind hole .75 deep in 8620 CR.
...
Threads are badly galled looking.

Blame the ancestors who decided what the imperial coarse thread pitches should be.
( May they forever be rolling in their graves, most notably the ones responsible for 6-32 and 10-24 !!!! )

 

[Mtndew]

15-50 sfm.

Which is it? 15 or 50?
Are you using a coated tap?
3 flute?
4 flute?
Spiral point?


Get yourself a good coated OSG, Guhring or Sandvik tap and run it 100sfpm.

oh and your drill size is a tad big, use a 27/64 drill (.421" diameter)

 

[DDoug]

Where is "Mr. I love MollyDee" these days ?

 

[FredC]

Mtndew's suggestion of different tap styles would have been my first suggestion, drop back and punt suggestions leaded 8620 if possible, probably too course to use a forming tap, thread milling that deep would be slow, on a lathe I think you would have to start at the bottom and work out to keep from filling the hole with chips.

 

[AARONT]

1/2 -13 tap in a blind hole .75 deep in 8620 CR.
15-50 sfm. Good flood coolant.
11MM drill.
Lathe with floating holder indicated w/in .001.
Threads are badly galled looking.
Any help would be great.

Switch to some anchor lube or squirt some oil in the hole before tapping.

 

[G00 Proto]

Where is "Mr. I love MollyDee" these days ?

I'm here, just slow on the uptake. Ms. Moly Dee will give you the best threads you can expect out of shitty cold rolled steel using general purpose taps that you have laying around. I use it anytime I have material conditions that don't yield good threads.

On the downside it stinks like ten day old crotch rot. My stray cat tipped over a jug of it and managed to get that stink all over her... I was hoping she would get sprayed by a skunk to make her smell better. The stench eventually went away, and since she is still alive, I don't think it is nearly as toxic as I used to think. I wonder where that piece of shit is hiding... she brought in a half eaten mouse yesterday and left it in one of the mill stations, so I know she is still alive

 

[ChipSplitter]

Like MtnDew said, use a high end tap and make sure you have a spiral point tap if the hole is thru or a spiral flute if it's blind. Also, you could try going a little higher on SFM if you don't have a tool life problem. Sometimes that helps too.

 

[CORONA VIRUS]

Drill size is correct. Use uncoated, spiral-flute tap. 260rpm (34sfpm)

 

[Ox]

Are you using a tap from the hardware?
Those are barely good enough to clean threads.

Almost anything else should be good enough?

How about we see your program?
Also - define what'chew mean by "floating holder" as it could mean a reamer type holder with a little wiggle room, or it could mean tension only, or tension/compression type holder.

It all changes the results.


---------------------

Think SnowEh!
Ox

 

[DDoug]

I'm here, just slow on the uptake. Ms. Moly Dee will give you the best threads you can expect out of shitty cold rolled steel using general purpose taps that you have laying around. I use it anytime I have material conditions that don't yield good threads.

On the downside it stinks like ten day old crotch rot. My stray cat tipped over a jug of it and managed to get that stink all over her... I was hoping she would get sprayed by a skunk to make her smell better. The stench eventually went away, and since she is still alive, I don't think it is nearly as toxic as I used to think. I wonder where that piece of shit is hiding... she brought in a half eaten mouse yesterday and left it in one of the mill stations, so I know she is still alive

Naw...Your not the one I was thinking of:
https://www.practicalmachinist.com/...let-me-count-ways-223073/?highlight=molly+dee

 

[Bobw]

Are you using a tap from the hardware?
Those are barely good enough to clean threads.

The biggest problem with those is that they are heat treated
after they are cut/ground, and the heat treat burns off the
sharp edges..

If you take a dremel tool with a cut off wheel, you can
sharpen them up enough to at least get you a few holes, and
maybe even make you through until Monday.

They still suck, but if you *have* to use one, it needs some
TLC before its put into service. Otherwise, its like trying to
tap with a bolt.