OT. Coarse Or Fine Threads?.. your help please.

[Limy Sami]

I have to make some ''end mill'' type coupling (side screw, whistle notch etc etc) for 1" shaft.

The max ''body'' dia of the coupling is 2" which means only a 1/2" wall.

The material is our EN24 T which I think?? = your 4340 prehard.

Coupling on a machine run by semi skilled + labour,..... AKA they don't break much

1/2" thread, and I'm concerned about wear,..... so do I go 13 tpi or 20 tpi?

Thanking you for your time.

Sami.

[David Utidjian]

Limy,

I have a Royal brand R8 endmill holder for 1" Weldon shanks. It is 2.125" in diameter. Royal saw fit to use two 5/8-18 set screws (big fat grub screws to you) to hold the tool. I would guess that the material and duty is similar for your application.

-DU-

[L Vanice]

I would use the 1/2-20 and put anti-seize grease on the screw.

But I am curious why a Brit would not suggest metric or 1/2-12? I am (obviously) out of touch with current UK fastener practice and preference.

Larry

[Limy Sami]

Originally Posted by L Vanice

I would use the 1/2-20 and put anti-seize grease on the screw.

But I am curious why a Brit would not suggest metric or 1/2-12? I am (obviously) out of touch with current UK fastener practice and preference.

Larry

12 mm ISO is 1.75 pitch (app 14 tpi-ish) and readily available.

Fine rate metrics are hard to find, worse in small quant's and cost the earth.

Both UNC & UNF are common & plentiful, sensibly priced and acceptable to customer.

1/2" 12 is BSW which to all intents and purposes is considered obselete nowdays.

[Mark Rand]

I'd go for 1/2"BSF in EN24T. Use coarse threads in soft stuff and cast iron, fine threads in harder stuff. BSW and UNC are too coarse.

If you really must use foreign threads, then go for UNF

[John Welden]

Originally Posted by Limy Sami

The max ''body'' dia of the coupling is 2" which means only a 1/2" wall.

Sami.

Only 1/2" ? That's enough meat to survive a nuclear explosion. You'd have to try damn hard to strip out a 1/2 13 thread. It would take a cheater bar.

[WILLEO6709]

Originally Posted by John Welden

Only 1/2" ? That's enough meat to survive a nuclear explosion. You'd have to try damn hard to strip out a 1/2 13 thread. It would take a cheater bar.

pose that challenge to any operator and within 7 minutes he'll come carrying baCK A TOTALLY stripped, thrashed, and unrecognizable pice of magnetic something with 3 holes in it......

[willbird]

Honestly I would search around a little bit and find a nice screw in an existing type of holder, say a Parlec straight shank endmill holder, buy the replacement screw, and tap your device to fit it. The screws they sell for replacement parts are a REALLY nice part in my experience, and probably way under-priced for the quality level.

Bill

[Tonytn36]

Originally Posted by WILLEO6709

pose that challenge to any operator and within 7 minutes he'll come carrying baCK A TOTALLY stripped, thrashed, and unrecognizable pice of magnetic something with 3 holes in it......

The operators & so called set-up people I work with can *DESTROY* a steel anvil with a RUBBER HAMMER....

I have no idea how they do it...but....sheesh...

[Mud]

I'd use the fine thread. And I'd forgo the antisieze. Antisieze greatly reduces the friction in the threads which increases the chance of stripping. Counterintuitive, but it's true, most noticeable in aluminum. It the monkeys are fond of long wrenches and extensions, let it be hard to tighten, maybe put oil on it.

[gregormarwick]

Originally Posted by Limy Sami

Fine rate metrics are hard to find, worse in small quant's and cost the earth.

Both UNC & UNF are common & plentiful, sensibly priced and acceptable to customer.

This is the polar opposite of what I've found. Imperial cap screws especially are really hard to find around here.

Gregor

[PhillipM]

Hmm, loads of both around here Imperial or metric, course or fine, never had a problem finding any (well, bar an M18 fine thread, that's a fun one)

[gregormarwick]

If you need a couple of hundred 1 1/2 UNC setscrews, that's no problem. However, if you go asking for a half a dozen 3/16 UNC socket caps to replace the slideway wipers on the old kearns borer (for example ) everyone looks at you like you just requested a solution to world conflict. Seriously.

[Mark McGrath]

Off course the old Kearns borer should have BSW screws in it.
I`ve got plenty BSW and BSF socket caps in 3/8",7/16" and 1/2" diameters.
Comes from running BSA multis.

[gregormarwick]

Originally Posted by Mark McGrath

Off course the old Kearns borer should have BSW screws in it.

That is a distinct possibility. However I doubt it minded too much, especially after running for god knows how long with missing wipers...

[PhillipM]

Originally Posted by gregormarwick

If you need a couple of hundred 1 1/2 UNC setscrews, that's no problem. However, if you go asking for a half a dozen 3/16 UNC socket caps to replace the slideway wipers on the old kearns borer (for example ) everyone looks at you like you just requested a solution to world conflict. Seriously.

www.shop4fasteners.co.uk & www.stagonset.co.uk

Sorted.

[js412000]

I have found that a coarse thread is more rugged and will tolerate more rust, dirt and abuse than a fine thread.

A fine thread is better to resist unscrewing caused by vibration.

[tdmidget]

A coarse thread is stronger than a fine thread. A fine thread does not weaken the fastener as much because the minor diameter is greater. Thus fine thread = stronger fastener. Coarse thread = stronger threads. In any case you need at least one diameter of thread length to achieve full strength.

[peterve]

Originally Posted by tdmidget

A coarse thread is stronger than a fine thread. A fine thread does not weaken the fastener as much because the minor diameter is greater. Thus fine thread = stronger fastener. Coarse thread = stronger threads. In any case you need at least one diameter of thread length to achieve full strength.

I always thought it was 0.8xdiamater
That is why a nut is 0.8 x diameter
Please correct me if I am wrong

Peter from Holland

[Limy Sami]

Thanks for all your help, I'll be going for 1/2 x 20.