Torque on Bridgeport R8

[dfwilbanks]

Has anyone used a torque wrench to measured the torque you apply to the R8 Bridgeport draw bar using a wrench or air tool? What torque did you go with? Why?

Thank you in advance.

 

[Winegrower]

I did not, because the torque varies depending on the collet, cut and cutter. After awhile, you develop a feel for what torque is needed, but not until you’ve had some end mills pull down into the work, possibly ruining the job.

 

[projectnut]

I don't use a torque wrench, but standard torque for a 7/16-20 thread is 41 ft. lbs. After doing it over 35 years I do it by feel and get pretty close to that value

 

[dfwilbanks]

I did not, because the torque varies depending on the collet, cut and cutter. After awhile, you develop a feel for what torque is needed, but not until you’ve had some end mills pull down into the work, possibly ruining the job.

HaHa. Good answer. But the pull out is what I want to avoid.

 

[benmychree]

Using setscrew style end mill adapters prevents pull out.

 

[dfwilbanks]

Using setscrew style end mill adapters prevents pull out.

Ok. Talking about R8, what sort of set screw adapter? I'm thinking more of the tool pulling out of the R8. In my case I will be using TTS. They are known to pull out if pushed hard. I'm looking to get a feel for what torque people use on R8 to control this. TTS or not.

 

[benmychree]

Ok. Talking about R8, what sort of set screw adapter? I'm thinking more of the tool pulling out of the R8. In my case I will be using TTS. They are known to pull out if pushed hard. I'm looking to get a feel for what torque people use on R8 to control this. TTS or not.

I am talking a solid R-8 adapter with a nicely fitted hole for the end mill and a cross drilled and tapped hole for a setscrew that locks into the flat milled into the end mill shank.

 

[dfwilbanks]

I don't use a torque wrench, but standard torque for a 7/16-20 thread is 41 ft. lbs. After doing it over 35 years I do it by feel and get pretty close to that value

There is no substitute for experience. I found this formula that converts bolt torque to clamping force. So 41 lbft would give about 375 lbs of force on the R8. That's very little when compared to the 2500 lbs some are getting using Belleville Washers and pneumatic cylinder. So I start to question my calculations. I hate that! The formula takes into account the diameter of the bolt but not length (twist), throws in a standard for friction, but does not account for thread pitch. Look like those things would matter.

 

[dfwilbanks]

I am talking a solid R-8 adapter with a nicely fitted hole for the end mill and a cross drilled and tapped hole for a setscrew that locks into the flat milled into the end mill shank.

That should work. So a solid R8 would not have the slits in it. Do you have an R8 for each tool or one of each size and change the tool with the set screw? No worse then what one has to do with TTS. I often wondered why Tormack didn't put a slot in the TTS holder, like the R8 has in the spindle and a pin in their R8 adaptor to prevent the tool holder from spinning.

 

[Cadillac]

I use German spec good n tight!