Pull Stud Torque

gkoenig · Jun 24, 2018

So, I'm now super confused on this...

Yamazen's kick ass installer guy was wiring up my new Speedio and we got to looking over the killer deal on some ER8 Lindex holders I snagged on eBay, and he took one look at them and said "These weren't used much, but someone overtorqued the pull studs." He based the diagnosis by the uneven wear pattern on the taper - top and bottom, nothing in the middle.

The obvious next question I asked was "Well, what's proper pull stud torque for a BT30?" His reply? 8-10ft lb!

That seems fuckin' low, Frank @ Maritool lists 25-35lb on his website. This man knows tooling, tapers, pull studs...

Low and behold, Frank's high-strength pull studs (J&M built) come with a little insert that says that with 800 pounds of retention pull, you need 8ft_lb on the pull stud. (J&M's Pull Stud Torque Guide: http://www.onlybusiness.com/Member/...tention Knob Tightening Torque Chart_2017.pdf)

In summary, multiple sources I tend to trust seem to be all over the map on this topic. 8ft_lb to 35ft_lb. What to do?

Tonytn36 · Jun 24, 2018

I use a 3" long wrench and a small dab of loctite, not sure of the actual torque, but it isn't much at all.

Vancbiker · Jun 24, 2018

I do pretty much the same as Tonytn36, drop of blue loctite and lightly tightened. Probably less than 5 lb ft.

Kaszub · Jun 24, 2018

For my CAT40 use 35

Matt@RFR · Jun 24, 2018

Tonytn36 said:
I use a 3" long wrench and a small dab of loctite, not sure of the actual torque, but it isn't much at all.

Basically the same here, we hand clean everything really well, hand tighten, then use an end wrench to just barely sinch the pull stud down and no more. We do not use any loctite and have not had a problem in maybe 3-4 years of doing this. We do the exact same procedure on 30 and 40 taper, solid holders, ER40 down to ER11.

DMF_TomB · Jun 25, 2018

Matt@RFR said:
Basically the same here, we hand clean everything really well, hand tighten, then use an end wrench to just barely sinch the pull stud down and no more. We do not use any loctite and have not had a problem in maybe 3-4 years of doing this. We do the exact same procedure on 30 and 40 taper, solid holders, ER40 down to ER11.

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i have only seen anti seez compound on pull studs so they dont rust on and can be removed later. never seen one loose but i have seen plenty too tight. i got a special wrench 2 foot long and if i got to use a hammer on wrench they diffidently too tight.
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on a optical too setter i put all tools in taper holder and tap back and forth sideways to look for taper swelled bigger at retention stud end which causes poor fit in taper then you get increased dynamic run out, that is when tool under load the run out increases far above what you would get measuring run out with no load on the tool.
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i get worst tool holders with excess runout and have the taper reground. i have seen .020" dia runout before. i have checked tools probably over 5000 times by now. some tools dont care much about runout. some tools like short carbide drills though will break if runout too much. and even if drill dont break you get bigger holes than the drill dia if runout too high , a few .001" dont matter but obviously dont want holes way off size

riabma77 · Jun 25, 2018

gkoenig said:
In summary, multiple sources I tend to trust seem to be all over the map on this topic. 8ft_lb to 35ft_lb. What to do?

I would follow the torque specs from the pull stud manufacturer.

I agree it's confusing. My first pull studs for my Haas MiniMill were MariTool. If I remember correctly, there were tightened to 60 ft_lb? 1 year later I tried the "high-torque" from J&M, with a torque of 20-25 ft_lb. I was confused in the beginning, but I never had any issue during the next years. In fact, the taper contact pattern was more uniform.

35 ft_lb for a 30 taper seems a few high to me.

For my new Speedio, I'm going to try the NT pull studs recommended by Yamazen. I don't have any spec yet, but I'm sure it's going to be more close to 8-10 ft_lb than 35.

I never tightened them by hand, or use any Loctite. Just a torque wrench.

2outof3 · Jun 25, 2018

gkoenig said:
So, I'm now super confused on this...

Yamazen's kick ass installer guy was wiring up my new Speedio and we got to looking over the killer deal on some ER8 Lindex holders I snagged on eBay, and he took one look at them and said "These weren't used much, but someone overtorqued the pull studs." He based the diagnosis by the uneven wear pattern on the taper - top and bottom, nothing in the middle.

The obvious next question I asked was "Well, what's proper pull stud torque for a BT30?" His reply? 8-10ft lb!

That seems fuckin' low, Frank @ Maritool lists 25-35lb on his website. This man knows tooling, tapers, pull studs...

Low and behold, Frank's high-strength pull studs (J&M built) come with a little insert that says that with 800 pounds of retention pull, you need 8ft_lb on the pull stud. (J&M's Pull Stud Torque Guide: http://www.onlybusiness.com/Member/...tention Knob Tightening Torque Chart_2017.pdf)

In summary, multiple sources I tend to trust seem to be all over the map on this topic. 8ft_lb to 35ft_lb. What to do?

Being careful is prudent. We did have a customer lose a 27,000 RPM spindle from intensive fretting from an over tightened pull stud. You just spend a heck of a lot of money on that new beast and I would hate to have you cranky because of the choice of used holders. Just be careful.

DMF_TomB · Jun 25, 2018

2outof3 said:
Being careful is prudent. We did have a customer lose a 27,000 RPM spindle from intensive fretting from an over tightened pull stud. You just spend a heck of a lot of money on that new beast and I would hate to have you cranky because of the choice of used holders. Just be careful.

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never saw machine yet with perfect alignment of arm holding tool going into spindle. basically getting slammed into spindle the taper is deteriorating every time.

riabma77 · Jun 25, 2018

DMF_TomB said:
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never saw machine yet with perfect alignment of arm holding tool going into spindle. basically getting slammed into spindle the taper is deteriorating every time.

Brother Speedios don't have an arm to change tools. It's a carousel mounted into the spindle head. Servo driven, so the tool holder is always perfectly aligned during tool changes. Mechanically just perfect.

Mud · Jun 25, 2018

DMF_TomB said:
. never saw machine yet with perfect alignment of arm holding tool going into spindle. basically getting slammed into spindle the taper is deteriorating every time.

Then you need to adjust your machine better. . https://www.practicalmachinist.com/vb/attachment.php?attachmentid=231536&d=1529941383

gkoenig · Jun 25, 2018

2outof3 said:
Being careful is prudent. We did have a customer lose a 27,000 RPM spindle from intensive fretting from an over tightened pull stud. You just spend a heck of a lot of money on that new beast and I would hate to have you cranky because of the choice of used holders. Just be careful.

Ngon said they were good-to-go. The "wear" on them is almost nothing, but the pattern told the story that led to the pull stud question.

Finally starting to get her dialed in:

@lumalabs on Instagram: “My god, it’s full of stars here...”

DMF_TomB · Jun 25, 2018

riabma77 said:
Brother machines don't have an arm to change tools. It's a carousel mounted into the spindle head. Servo driven, so the tool holder is always perfectly aligned during tool changes. Mechanically just perfect.

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so machine does not follow the laws of the universe that things change size alignment changes as temperature changes ?? the machine is precise temperature controlled ?? i have seen many machine alignments change as machine warms up and change alignment as temperature varies cause of various loads causing different temperatures
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i have heard of many things supposedly perfect machines. never measured one as perfect.
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had a machine where machine alignment seemed off and every time checked it measured perfect. i bolted on precision level and saw level change every minute. parts were bending under load as most parts do and alignment changed when machine was running under load. the Swiss kept saying machine was perfect. the precision level bolted on was saying different literally every minute its imperfections were plainly seen under dynamic loads.

art.h · Jun 25, 2018

It would make sense not to over tighten screw threads in general are the least likely to offer good alignment, any miss align or angular deviation will create a permanent high spot hit. In the long run wear on the spindle socket but more so on the holder itself.

gkoenig · Jun 25, 2018

art.h said:
It would make sense not to over tighten screw threads in general are the least likely to offer good alignment, any miss align or angular deviation will create a permanent high spot hit. In the long run wear on the spindle socket but more so on the holder itself.

That's true!
But the normal tightening torque for an M12 thread (as found on the ass end of a BT30 tool holder) is 165Nm, or 122 ft_lb.

Even at the high end of the torque spec (the 35ft_lb on Maritool's documentation), we're a whole world away from standard torque on a pull stud's threads.

Mud · Jun 25, 2018

DMF_TomB said:
. . so machine does not follow the laws of the universe that things change size alignment changes as temperature changes ?? the machine is precise temperature controlled ?? i have seen many machine alignments change as machine warms up and change alignment as temperature varies cause of various loads causing different temperatures . i have heard of many things supposedly perfect machines. never measured one as perfect. . had a machine where machine alignment seemed off and every time checked it measured perfect. i bolted on precision level and saw level change every minute. parts were bending under load as most parts do and alignment changed when machine was running under load. the Swiss kept saying machine was perfect. the precision level bolted on was saying different literally every minute its imperfections were plainly seen under dynamic loads.

So you can hold .0002" over 40' on a 20 ton part, but you can't keep a toolchanger from rubbing a tool against the side of a spindle taper? I'm disappointed.

Unahorn · Jun 25, 2018

riabma77 said:
Brother machines don't have an arm to change tools. It's a carousel mounted into the spindle head. Servo driven, so the tool holder is always perfectly aligned during tool changes. Mechanically just perfect.

Hmm I have 3 brothers. 2 of them have tool change arms.

riabma77 · Jun 26, 2018

Unahorn said:
Hmm I have 3 brothers. 2 of them have tool change arms.

OP mentioned a Speedio and it's what I was referring. I corrected my post.

Fal Grunt · Jun 26, 2018

Anyone else having issues posting on their desktop? Am I the only one still using a desktop?

I had this issue a few years ago with a new Cat 40 machine. We were BREAKING pull studs, something I had never experienced. Much to the anger of my boss I spent hours researching it and making phone calls. Numbers were all over the map. Manufacturer said they broke because we over torqued them, I say they broke because they had cracks, manufacturer said they broke due to our drawbar pressure being too high. Blah blah blah on it went. Owner wouldn't pay to buy top quality pull studs, so I bought them for our heavy roughing tools.

Ultimately I torqued them to whatever the manufacturer spec was. We never had any fretting issues while I was there.

I am HOPEFULLY getting a Speedio 700 next year, so I will be paying close attention to what you find out.

gkoenig · Jun 26, 2018

Fal Grunt said:
I am HOPEFULLY getting a Speedio 700 next year, so I will be paying close attention to what you find out.

Just loaded up the turret for the first time. I thought I made enough inventory to give me a couple of weeks to just fuck around with the Speedio and dial a bunch of stuff in (including some dead sexy Lang workholding, and a customized vise from Eric with Lang studs on them). Alas, a small rush borked my inventory so the old Orange is on the table along with the old fixture, and we're gonna let her rip.

Pull stud torque I'm running is 15. Not trying to split the difference between all the numbers I've seen, but my 10-80lb 3/8" torque wrench is sub optimal on the 10ft_lb stop, so I gave it half a turn.

I'm also considering Vibra Tite VC3 as an alternative to blue LocTite. This is a sticky acrylic product with micro beads in it; they wedge themselves into the thread faces to dampen the vibration that loosens threads. Neat thing about VC3 is that it is totally reuseable on the thread (up to 6 times) and doesn't care about oil or contamination. It's a neat product, and it sounds optimal for this application.

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