Torque specs-dry vs oil 1

[qtrhorse]

I have CAT-50 tool holders that have a 1"-8 thread pull stud with a 110 ft.lbs. max. torque spec. This seems quite sufficient if the threads were always dry. However, between the spindle oil and the oil in the coolant, in takes about 150 ft.lbs. to get the same results, a formula or lab test backed data sheet would be nice to justify.

 

[NickE]

WE dont like double posting...

 

[MintJulep]

It generally takes less torque to achieve the same pre-load if the threads are lubricated, so I don't quite understand.

It is unlikely that you will find any published test data for a stud lubricated with a combination of oil and coolant, so if you want to know, do your own testing.

 

[JJPellin]

That seems like a very low torque for a stud that large. We use a program to determine torque based on size, thread and lubricant. The numbers for 50% yield on a 1" - 8 tpi-UNC, B7 stud are as follows:

Dry - 1378 ft-lbs
Oil - 551 ft-lbs
Ni Lube - 413 ft-lbs
Mo Lube - 248 ft-lbs

These values are based on tests with new fasteners, in test-lab conditions.

For any size and thread, the ratios are always the same. To get the value for oil, use the number dry times 40%.
To get the value for Ni, use the number dry times 30%.
To get the value for Mo, use the number dry times 18%.

 

[qtrhorse]

Sorry NickE, I see automotive and manufacturing as different disciplines however, I thought changing the senario to suit the discipline was ok.

 

[byrdj]

"to get the same results"
I think a diffintion of what results you are looking for?
I can not think of what "results" you are reffering too.


as stated by above postings, If the amount of tension in the stud is the limiting factor then you are definately over stressing the component. If the manufactor says 110 ft-lbs dry is the MAX (to provide a given loading) the same torque with lubed threads will provide a load greater than MAX.

Could your desired results be some how related to prevent backing off during operation? If so (and if there is a real limitation of 110 ft-lb dry loading), a alternative locking method not dependant on thread friction may be needed if threads will always be wet

 

[qtrhorse]

JJ, My application is on a pull stud on a CNC machine holder, we have found that it takes about 150 ft. lbs. to keep the oily stud from coming loose however, the manufactures spec is 110 ft.lbs. max., I don't know if that is dry or wet.

If we torque to full spec, it will distort the machine taper. I know what works, just trying to justify it.

What program do you use?

Can I get a list of other size torque specs?

 

[Tmoose]

The last time I looked at tooling pull studs/retention knobs the torque spec seemed to be trying for an initial tension just a bit higher than the drawbar force. I don't recall if the specs were for lubricated or unlubricated threads.

A loose knob results in lower retention force that quickly results in wiggling tapers and a damaged spindle.

As others mentioned my expectation would be for a lubricated thread to clamp tighter at a given torque and be more secure. My personal preference is to always put some lube on threads, and even under bolt heads and washers.

This source offers torque, but no lube explanation.

http://www.commandtool.com/ctstore/showdetl.cfm?&offerings_ID=254&ObjectGroup_ID=73&CATID=16

 

[pdybeck]

According to data collected and analyzed by Shigley and Mischke, there is not a correlation to an average difference in torque to tension of dry vs. lubricated fasteners. What the data indicated was that lubed fasteners acheive a desired preload at a much more consistent torque value. Applied torques on "Dry" fasteners on average yield roughly the same preload, but there is a much greater deviation from that mean or average value from dry fastener to dry fastener vs. lubed fastener to lubed fastener. If you are looking to control preload in fasteners to a tighter range, then lubricating them prior to torque will give more predictable results, not higher values compared to dry conditions - according to Shigley and Mischke

 

[dimjim]

What I have for a grade 2 bolt
60000psi Tensile and 33000psi Yield
list 160 lubed and 220 ft-lbs dry.
Is this tensile and yield about the
right strength for the material that
you have?

 

[pdybeck]

dimjim,

What is the size of the bolt? That is needed for an answer to your question.

 

[dimjim]

pdybeck

1" 8 tpi as first stated.
I was trying to reply to the
request for torque values.

 

[pdybeck]

dimjim,

The torques you mentioned would be safe for Grade 2 material. Values of 250 lb-ft (dry) and 160 lb-ft (lubed) will give about 15,000 lbs of clamp load. These values are considered the maximum recommended for grade 2 material. The values you gave are slightly below this and would provide about 13,200 lbs of clamp load.

Pete

 

[qtrhorse]

Thanks for all the great input!

When tightening the pull stud it distorts the taper on the holder, the tighter you go, the worst it gets. Yet, you must torque to 150 ftlb. to keep from coming loose.

Only option is to tighten to spec and use a Loctite 371 or 377 to keep it from loosening.

If someone knows of a better, more vibration-proof threadlocker that will hold in the oily environment.

 

[MintJulep]

No chemical thread locking compound will work on a fastener contaminated with oil and coolant.

 

[Tmoose]

Who makes your retention knobs?
Who makes your tools?
I'd expect good quality parts to tighten correctly first time, and stay secure. Power or manual drawbar ?

If the threads in either part are especially rough, or if the contact faces aren't true they would have a greater tendency to embed or relax.

I'd coat threads and faces with grease, moly or graphite, and torque and loosen the stud 10 or 15 times to ease down the high spots. Then I'd clean the threads, paint or pencil a few stripes on the contact faces assemble and torque the parts dry. Disassemble and Look at the face stripes to confirm at least 80% contact.

 

[Tunalover]

For about 100 $US you can buy TORKSENSE. It's offered by BOLT SCIENCE, a UK firm. Do a GOOGLE on TORKSENSE and this will get your where you need to be. Another program they offer (<$300) TORQUE is more expensive yet more capable. I think that one or both of them have an extensive database encompassing many materials, finishes, and lubricants. Of course there are easy ways to provide your own inputs (you don't have to use what's in the database). Either program can be purchased on-line and downloaded.



Tunalover