# Torque needed for MT3 drawbar?



## zoltan (Mar 10, 2015)

Pretty simple question: how much torque is needed for the MT3 drawbar on my mini mill? I hate doing things by feel.


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## RonGinger (Mar 10, 2015)

I am not sure about the MT3, but I was just today reading an article on the Tormach site about R8 drawbars and they suggest 30 ft-lbs. That would seem pretty close for an MT3.

MT tapers are locking tapers, so its going to take force to get it loose- some drawbars have a shoulder so you can apply force with the wrench, some just expect you to whack it with a hammer. It always bothered me to be whacking on my spindle, but its the only way. That does help you learn to not make it to tight.


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## TorontoBuilder (Mar 10, 2015)

zoltan said:


> Pretty simple question: how much torque is needed for the MT3 drawbar on my mini mill? I hate doing things by feel.



wait, you mean I'm supposed to be using a torque wrench on my drawbars? Oh dear. Well good thing I haven't used my mill much yet


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## Swifty (Mar 11, 2015)

You got me wondering, so I tightened my R8 collet on a cutter, used the ring spanner and tightened it up like I always do. I then checked it with my torque wrench, it was 30 ft/lbs.

Paul.


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## Blogwitch (Mar 11, 2015)

You should find that most general purpose spanners come in standard lengths.

There is a reason for this. 

When an 'average' person tightens up a nut or bolt with an 'average' sort of force, you should be within the torque range for that said nut or bolt. All this was worked out many years before torque wrenches were used, and as mentioned above, is why many spanners come in standard lengths.

Or just measure up the length of the spanner and use a spring balance to work out how much force should be used.

If you are anything like myself, white knuckles is the usual setting.

John


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## hanermo3 (Mar 11, 2015)

The A is very little.
R8 and MT3 are completely different.

MT tapers need a lot less force, as they are locking tapers.
1-2 Nm on MT2 on a bridgeport is enough.

1-2 Nm (just push/slap it in) on an MT3 on my lathe (350 kg) is enough.


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## Swifty (Mar 11, 2015)

Hanermo3, I understand what you are saying, but there are MT collets available that need to be tight enough to hold the cutters. If it's just a MT shank on the end of a collet holder, that's a different situation.

Paul.


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## Forestgnome (Mar 16, 2015)

Swifty said:


> Hanermo3, I understand what you are saying, but there are MT collets available that need to be tight enough to hold the cutters. If it's just a MT shank on the end of a collet holder, that's a different situation.
> 
> Paul.



No, it's pretty much the same. It takes very little tension on the drawbar to hold a cutter in a Morse or B&S collet, unless you just like beating on the end of the drawbar.


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## velocette (Mar 17, 2015)

zoltan said:


> Pretty simple question: how much torque is needed for the MT3 drawbar on my mini mill? I hate doing things by feel.



Hi zoltan
Engineering is all about hands on and using the hands to feel.
Firm but gentle hands will help get things done.

Eric


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## zoltan (Apr 15, 2015)

I think the issue I'm having isn't the drawbar being too loose, but that the drawbar keeps loosening up on me while being used. I think I'll try Loctite on the drawbar to keep it in place.


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## rodw (Apr 15, 2015)

zoltan said:


> I think the issue I'm having isn't the drawbar being too loose, but that the drawbar keeps loosening up on me while being used. I think I'll try Loctite on the drawbar to keep it in place.



If you do, get the one that is designed for adjustment screws that wicks in. 290 I think.


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## digiex-chris (Apr 15, 2015)

if it's an endmill holder, just enough to keep it from coming loose. If it's a collet, just enough to hang on to the part or endmill. I find that a morse taper will stay put properly all by itself if you slap it in there, the draw bar is just to prevent it from loosening up from side forces. Definitely less for a morse taper than an R8 or 30 taper, way different angles. I would imagine loctite on a drawbar would be annoying when trying to remove a flush collet. 

I often slap the endmill holder in, then tighten the draw bar by hand till it stops, then tighten it 1/4 or 1/3 what I'd feel on a similarly sized fastener. Collets are a bit of an experience thing. Just enough that it'll hang on to whatever you need to hang on to, and just loose enough that you can still get it out with a reasonable tap on the draw bar. If you have to really slug it hard to get it out, try a bit looser next time.

It's tough to find drawbar torque numbers published for morse tapers. Like many things that were spec'ed out when Morse tapers were new, it's a feel thing.


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## Charles Lamont (Apr 15, 2015)

zoltan said:


> I think the issue I'm having isn't the drawbar being too loose, but that the drawbar keeps loosening up on me while being used. I think I'll try Loctite on the drawbar to keep it in place.


Loctite what exactly? This should not be necessary. If the drawbar is coming loose there is something wrong.


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## zoltan (Apr 15, 2015)

Charles Lamont said:


> Loctite what exactly? This should not be necessary. If the drawbar is coming loose there is something wrong.


Loctite on the drawbar threads. It doesn't surprise me that it's loosening considering it's not very tight, is spinning at 1,000RPM, and the head can vibrate.


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## BaronJ (Apr 15, 2015)

zoltan said:


> Loctite on the drawbar threads. It doesn't surprise me that it's loosening considering it's not very tight, is spinning at 1,000RPM, and the head can vibrate.



Hi,
If its any help I have a "T" key that has a four inch tommy bar, two inches on either side for tightening the drawbar on my mill, which is MT3.


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## Charles Lamont (Apr 15, 2015)

zoltan said:


> Loctite on the drawbar threads. It doesn't surprise me that it's loosening considering it's not very tight, is spinning at 1,000RPM, and the head can vibrate.


As I don't know your level of knowledge I am asking probably dumb questions to try to make sure we are all singing from the same sheet to get to the bottom of this for you.

Which threads? The drawbar should have threads at both ends, at the bottom to screw into the back of the taper you want to hold, and at the top to allow the retaining nut to be screwed down onto the top of the spindle to tighten the assembly. Is your configuration in some way different? 

Is your technique right? I was taught to screw the nut well up the threads so you can screw the bar down until it bottoms in the taper, back off two turns, then screw the nut down and tighten it moderately.

The threads at both ends need to be used every time you change tooling, so I don't understand why you would want to use Loctite. The drawbar should be tight, but not very tight, and not come loose. The length of the drawbar should provide enough elasticity that vibration is not a problem. Do your tapers fit properly?


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## velocette (Apr 15, 2015)

Hi Zoltan
What is the condition of the Morse tapers both in the spindle and the surface of the external taper as any burrs or swarf will not allow them to seat properly and may be the cause of the vibrations.
Remember thumb on the wrench head that is on the lock bolt and use small digits to nip up the bolt is normally enough to secure it.
Is the collar that is in the top of the spindle in place and lightly oiled.
Check your spindle speed and feed rate for the size of the cutter and the hardness of the metal that is being milled as this is often a cause of vibration.

Eric


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## zoltan (Apr 16, 2015)

Charles Lamont said:


> As I don't know your level of knowledge I am asking probably dumb questions to try to make sure we are all singing from the same sheet to get to the bottom of this for you.
> 
> Which threads? The drawbar should have threads at both ends, at the bottom to screw into the back of the taper you want to hold, and at the top to allow the retaining nut to be screwed down onto the top of the spindle to tighten the assembly. Is your configuration in some way different?


I just have a X2 mini mill and its drawbar is only threaded on the end which engages the tool, like this:






I'm going to put some blue Loctite on those thread to keep it from loosening from the tool. I could tighten the drawbar more to keep it from loosening, but at that point it becomes very difficult to release the tool from the taper.


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## zoltan (Apr 16, 2015)

velocette said:


> Hi Zoltan
> What is the condition of the Morse tapers both in the spindle and the surface of the external taper as any burrs or swarf will not allow them to seat properly and may be the cause of the vibrations.
> Remember thumb on the wrench head that is on the lock bolt and use small digits to nip up the bolt is normally enough to secure it.
> Is the collar that is in the top of the spindle in place and lightly oiled.
> ...


Tapers are in good shape. In fact, I just replaced the spindle.


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## digiex-chris (Apr 16, 2015)

the drawbar isn't bent or anything? the flat at the top that bears against the top of the spindle is square to the drawbar shaft? The top of the spindle is smooth and flat? The drawbar threads are smooth and in good shape? The collet or endmill holder or whatever is in the taper has threads that are smooth and in good shape?

I'm curious if a split style lock washer under the top of the drawbar would be a good idea or not. Would at least make it less trouble than untreading a loctite'd thread I think.


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## Charles Lamont (Apr 17, 2015)

Ah, I have not seen a drawbar like that before. I am still convinced that something is wrong, but I don't know what to advise, except that using Loctite is not really a solution. Have you tried some engineer's blue on the tapers to make sure they match?

In removing a tight morse taper tool, I find a tap with a big hammer more effective than a whack with a little one.


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## digiex-chris (Apr 17, 2015)

Charles Lamont said:


> In removing a tight morse taper tool, I find a tap with a big hammer more effective than a whack with a little one.


Agreed. A good clonk with a heavy chunk of brass. Not a deadblow hammer, it absorbs the shock too much. Repeated tapping with the bearings in the same place is harder on them than a single slightly harder tap.


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## zoltan (Apr 17, 2015)

I really don't think anything is wrong, and my loosening problems stem from the drawbar being barely tightened. I doubt I'd see these problems with an R8 spindle since the drawbar is tightened down much harder with those.

I think I've worked out an alternative method for releasing the tool from the spindle, and will try to post a couple pictures later this evening.


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## zoltan (Apr 20, 2015)

For the MT3 spindle release I took an 8" C clamp and modified the modified it to fit between the spindle and tooling:






I then removed the pad from the clamp's screw, leaving just the ball end:





Then I turned a partial spherical dimple in the end of the drawbar:





Now when I want to release the tooling I loosen the draw bar, mate the clamp's ball end to the drawbar dimple, slip the bottom of the clamp between the spindle and tooling, and tighten the clamp until the tooling is ejected:


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## velocette (Apr 20, 2015)

Hi Zoltan
Excellent solution to release morse taper from spindle. 
This can be used on all lock bolts regardless of what the thread pitch.
Having a number of different pitch lock bolts this helps make it simpler.
Well Done Zoltan

Eric


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## rodw (Apr 21, 2015)

I'm sorry, but I'm really at a loss to understand why people bother with all these creative ways to remove MT tooling. If you loosen the drawbar a thread or two and give it a whack, how does that impact on the bearings? Think about it. The only thing you whack is the drawbar and the only thing it is touching is the taper. The bearings are not part of the equation and if the spindle does move down at all in unison with the whack, it is designed to slide up and down anyway so the bearings are not impacted. There might be a bit of a jolt on the spindle rack gears but nothing's going to get damaged as it is free to move.

We are talking about a sharp whack to provide enough inertia to pop out the taper, not belt the machine to pieces.


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## digiex-chris (Apr 21, 2015)

The taper is locked into the spindle, so if the tool doesn't come out of the taper, the force is transferred to the spindle, and then to the bearings supporting the spindle.

I've yet to have a problem though. I have to whack the drawbar on my lathe surprisingly hard to get my MT collets to release, and after 3 years of doing that, I took the head apart to make sure I wasn't doing damage. Not a single sign of problems with the bearings. Properly adjusted bearings might be a factor though. For oil lubricated tapered roller bearing there shouldn't be any slack so the weight of the spindle can't accelerate axially when the draw bar is struck and so the rollers are properly seated all the way around and not concentrating force on the roller at the bottom. In a vertical mill, gravity pulls the top bearing down into full contact with it's race, so it's not a problem there.

Your mileage may vary.


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## zoltan (Apr 21, 2015)

rodw said:


> I'm sorry, but I'm really at a loss to understand why people bother with all these creative ways to remove MT tooling. If you loosen the drawbar a thread or two and give it a whack, how does that impact on the bearings? Think about it. The only thing you whack is the drawbar and the only thing it is touching is the taper. The bearings are not part of the equation and if the spindle does move down at all in unison with the whack, it is designed to slide up and down anyway so the bearings are not impacted. There might be a bit of a jolt on the spindle rack gears but nothing's going to get damaged as it is free to move.


The spindle is only supported by the bearings, and does not slide up or down in the bearings. So any impact to the spindle is directly transmitted to the bearings. In fact, due to bearing preload, the entirety of a hammer blow to the drawbar is absorbed by just the top bearing.


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## zoltan (Apr 21, 2015)

digiex-chris said:


> I've yet to have a problem though. I have to whack the drawbar on my lathe surprisingly hard to get my MT collets to release, and after 3 years of doing that, I took the head apart to make sure I wasn't doing damage. Not a single sign of problems with the bearings. Properly adjusted bearings might be a factor though. For oil lubricated tapered roller bearing there shouldn't be any slack so the weight of the spindle can't accelerate axially when the draw bar is struck and so the rollers are properly seated all the way around and not concentrating force on the roller at the bottom. In a vertical mill, gravity pulls the top bearing down into full contact with it's race, so it's not a problem there.



If you're using tapered roller bearings in your lathe that's probably why they were fine even if you hammering on them. They have a line contact with the race, as opposed to a ball bearing's point contact, so it takes significantly more force to damage the race or rolling elements. My mill uses deep groove ball bearings, and the original top bearing was already developing a slight indexing when I upgraded them, hence my reluctance to continue hammering on the drawbar. If my mill used tapered roller bearings I wouldn't have much issue just  hammering the drawbar.


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## pete (Jun 4, 2015)

Try Googleing the term "brinelling" along with "bearing's", there obviously not referring to the barely automotive quality bearings in something like the smaller Seig mills. But for very high precision spindle bearings it can take as little as 4 ft. pounds of shock force to get that brinelling process started. It's NEVER a good procedure to subject any bearing to any type of shock force. There not designed for or intended to take that. Having a morse taper internal taper on any mill today without also having a built in screw type ejection to release the male taper is just amazingly poor design and engineering in my opinion. 

Pete


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## velocette (Jun 4, 2015)

Hi All
I have followed this thread with interest  from the start on the varied ideas and opinions.
Pete sums it up nicely with the "If you bash them you can bust them" approach.

The attached photos will show my approach to the problem.

Eric


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## zoltan (Jun 5, 2015)

velocette said:


> Hi All
> I have followed this thread with interest  from the start on the varied ideas and opinions.
> Pete sums it up nicely with the "If you bash them you can bust them" approach.
> 
> ...


I love this solution. It's elegant.


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## bobsymack (Jun 6, 2015)

Car and trucks use taper roller bearings in the wheel hubs and have about 3 thou floating clearance when assembled and they put up with severe punishment from the road surface without any diverse affects so I don't think a whack of a hammer to release the morse taper in the spindle would harm them.
Vince


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## zoltan (Jun 6, 2015)

bobsymack said:


> Car and trucks use taper roller bearings in the wheel hubs and have about 3 thou floating clearance when assembled and they put up with severe punishment from the road surface without any diverse affects so I don't think a whack of a hammer to release the morse taper in the spindle would harm them.
> Vince


The X2 comes stock with deep groove ball bearings. I've upgraded my mill to angular contact bearings. Neither tolerate shock loads nearly as well as low tolerance tapered roller wheel bearings.


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## bobsymack (Jun 6, 2015)

Sorry I just presumed your spindle ran on taper bearings (should have read the whole thread)
Vince


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## digiex-chris (Jun 6, 2015)

I wonder how difficult a retrofit to taper bearings would be


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## velocette (Jun 7, 2015)

digiex-chris said:


> I wonder how difficult a retrofit to taper bearings would be



Hi to All  with apologies to Zoltan.
Just had to run with this 
This is not to difficult But will need a couple of mods See attached files.
You will need to fabricate brass shim shields to help retain the grease in the bearings.
The taper rollers are 17.25 mm wide as opposed to the Ball races that are 16 mm wide
The Shim is .25 mm  THICK NOT  as shown on the file so you need to Bore the outer bearing housing another 1.5 mm deeper OR  Grind off 1.5 mm from the inner race of the bearing.
Grinding the inner race must be perfectly true and square to the bore.

To swap for Shielded angular contact bearing is a straight swap with no mods.
Either method will give much better performance than the original ball races.

Eric


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## zoltan (Jun 7, 2015)

You don't need to bring the bearings or bore the bearing seat deeper. You only have an extra 1.5mm extra on each end and it's fairly easy to deal with. 

For the shields I prefer to use HDPE from an empty milk jug. It's very easy to cut using a simple compass cutter. It works very well.

Of you go to tapered roller bearings don't just buy wheel bearings as they have a max TIR OF 0.0007". Instead spend a little extra and buy P6 grade (or C grade) bearings from your local bearing supplier as they only cost a little more but have a max TIR of only 0.0002&#8221;.


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## Cogsy (Jun 7, 2015)

The part number of the bearing yoiu want is a 30206 - that's an ISO standard number and will be recognised at any bearing supplier. Buy a quality brand like SKF, FAG or even NTN. In a spindle application the bearing should be carefully adjusted into a very small preload condition not only for maximum load capacity but for maximum precision as well. The 30206 manufactured by SKF has a maximum side runout of 10 microns (0.01mm or 0.0004").

If you could somehow use it, the 32006X is a higher precision bearing and would normally be the choice for a spindle bearing. Dynamic load rating is the same but the critical dimensions are 30mm ID 55mm OD and 17mm thick.


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## zoltan (Jun 7, 2015)

Per the SKF catalog it looks like their automotive grade 30206 has a max TIR of 0.0007". 

The 30206 is only if you have a MT3 spindle. If you have a R8 then the bottom bearing is 32007.


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## Cogsy (Jun 7, 2015)

Interesting, I'm using an old general catalogue but I didn't think they'd down-rate them. Wish I'd kept my precision books but I never thought I'd need the things again.

As for the sizes/part numbers, I should have said as per the dimensions in post #37 - I haven't got one of these mills I was just going off the drawings - sorry for any confusion I caused.


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