oversize tapped hole question?

[rgollar]

I am machining 6150 alloy steel that is getting harden (quench & temper) to Rc 54-56. Should I over size the tapped holes? The sizes are M6 x 1.0 and M16 x 1.0. 

[Thad]

We use +.005 taps on all heat treated details in a die shop environment.

[Machineguy]

Call your heat treater and ask him what the specs are for shrinkage.  Normally its not bad, but you need to ask.

[jeff]

Yes oversize them.

[Newbeeee™]

We use +.005 taps on all heat treated details in a die shop environment.

Thad,

I'm assuming you're talking microns - ie 2tenths of a thousands of an inch?

 

Do you do this fro all thread sizes or have a range ie the bigger the thread the more the oversize?

[Rstewart]

Thad,

I'm assuming you're talking microns - ie 2tenths of a thousands of an inch?

 

Do you do this fro all thread sizes or have a range ie the bigger the thread the more the oversize?

 

Na, I think they are .005" over.   Holes Shrink when heat treated, some more than others.

[Newbeeee™]

Na, I think they are .005" over.   Holes Shrink when heat treated, some more than others.

What on a 1/4" tap? 5 thou???

[Rstewart]

What on a 1/4" tap? 5 thou???

 

 

Oversize Taps are .003" to .005" larger than the standard pitch diameter.

[Newbeeee™]

Oversize Taps are .003" to .005" larger than the standard pitch diameter.

I thought that was for plating build-up though, not shrinkage?

[jeff]

I thought that was for plating build-up though, not shrinkage?

It's for whatever you need it to be for.  

We always use +.005 over for HT shrinkage. 

[crazy^millman]

Threads have a tolerance on them look on the go/no-go gauge. The PD numbers is the tolerance zone for the threads. Class 2 threads and larger threads have more and class 3 and smaller threads have less. Part shrinks .002 that extra .003 is going to be huge help.

[Newbeeee™]

Everday's a school day.

I never knew heat treat shrunk that amount - so if a 1/4 hole shrinks 5thou, is that equivalent to the overall part shrinking 20thou per inch?

[MotorCityMinion]

"is that equivalent to the overall part shrinking 20thou per inch?"

 

Nope.  The hole (ID), shrinks because the material grows.  External features will get bigger.  It's not always a 1 to 1 ratio either.

[jeff]

Everday's a school day.

I never knew heat treat shrunk that amount - so if a 1/4 hole shrinks 5thou, is that equivalent to the overall part shrinking 20thou per inch?

It also depends on what heat treat process you use. If it's carb & harden then expect it to grow about .001"/.002" per side. 

[Newbeeee™]

"is that equivalent to the overall part shrinking 20thou per inch?"

 

Nope.  The hole (ID), shrinks because the material grows.  External features will get bigger.  It's not always a 1 to 1 ratio either.

Haha - DOH moment!

I meant the length/width growing not shrinking

But it was the 1 to 1 ratio I was asking about as I was amazed threads shrunk that much (small ones anyway).

[The Cathedral]

Threads usually shrink/grow at a 4:1 ratio. Whether it's heat treat or plating.

[Newbeeee™]

Threads usually shrink/grow at a 4:1 ratio. Whether it's heat treat or plating.

Yes, understand 4:1 with plating as flank angle build up (trig etc).

But it surprised me with the shrink rates and that's a straight diameter like for like ie 5thou oversize tap so part shrinks 5 thou.

[The Cathedral]

Yes, understand 4:1 with plating as flank angle build up (trig etc).

But it surprised me with the shrink rates and that's a straight diameter like for like ie 5thou oversize tap so part shrinks 5 thou.

 

huh?