Drive dogs, what's their intended purpose?

[DennisCA]

I would say that it is in the name ! Thats what they are for !
The argument about whether they are needed or not is rediculas

It clearly isn't given that it's on going and the pros with long experiences in the business have differing opinions on the matter. So I'm trying to make heads or tails out of this.

And you can't take too much from a name either.

[Paul Alciatore]

I resisted jumping in at first because I have not used the 30,40, and 50 tapers, but I have used R8s and MTs. So I will now say the following.

R8s and MTs are very different animals. MTs are a self holding taper as witnessed by so many drill presses and other machines that use them. There are even tapered keys that are used to remove a MT from a spindle and those keys are definitely needed. So they really do not need a drive dog if the tapers are in good condition and they are installed properly.

R8s on the other hand have a much steeper taper and could easily drop out from vibration if not held firmly by a draw bar or similar device. That is why they have threads at the rear and why all R8 milling machines have drawbars.

The PIN in an R8 spindle is about 1/8" or 3mm in diameter and usually made of soft steel. It is definitely not intended to serve as a drive dog and many of these pins have been sheared off in an instant when the R8 tool or collet became loose in the taper. Some R8 spindles do not even have a pin installed by the factory. These pins are a convenient way of holding the tool or collet from rotating while the first few tightening strokes are applied to the draw bar or during the start of an automatic draw bar's tightening cycle. They also facilitate the last few rotations of the operation of removing the tool or collet as it would just spin without it and the operator would need to hold it by hand during that period. Once friction starts to take hold, the pin is no longer needed.

The only logical conclusion is that the R8 tooling MUST be drawn tight enough to prevent it from spinning in the R8 spindle. If this is not done then the pin will likely shear off and the taper will need some maintenance while the collet or tool will probably be trash. I do not think that many who have used the R8 tooling for long would disagree with this. Personally I would not call the key in an R8 spindle a drive dog. It merely facilitates installation and removal.

But, and it is a big but, things get a little bit blurred when we move to an MT taper. Yes, the reason for a tang on an MT taper is to allow a key to be used to remove the taper from a spindle. The MT spindles usually have a pair of slots on the sides which allow these tapered tools to be inserted and hammered to loosen the MT taper's grip. Then the MT taper just drops out of the spindle.

However it is curious that MT tapers are made with tangs, which are the full width or almost the full width of the MT at that point. A male MT is traditionally made in a lathe with a taper attachment. Almost every MT that I have has the center holes on both ends where it was held between lathe centers when it was made and that includes some that are of fairly recent manufacture. But that full width is NOT needed for removing a MT. And, in fact to make the full width tang the MT (adopters) had to be moved from the lathe where virtually all the other work was done to a milling machine. They had to be mounted in a manner so that the rear end could be milled down on BOTH sides to make the flat tang that we see on all these tools. Undoubtedly a special fixture was used to hold it for this work. NO factory in their right mind would do this if it was not really necessary.

When I started to purchase MT tooling for my lathe I found that some of it had the traditional tang and some did not. I made the mistake of purchasing a MT adopter for my tailstock chuck that did not have a tang and found that I had a devil of a time every time I tried to remove it. The tailstock had a self ejecting feature where by simply backing up the screw enough, the tang of the adopter hit a hard point and the MT was loosened. But that did not work without a tang. So I decided to add a tang to that MT adopter. But I quickly saw that a full tang was not really needed just to facilitate the ejection from the grip of the taper. In fact only a round PIN at the center of the tapered section would suffice quite well and that would be a lot easier to make and add. So, that is what I added to that MT: a central pin. And it works perfectly for ejecting the MT from the tail stock spindle.

Now I must ask, if a full tang is not really required for removing a MT from it's grip in the spindle, they WHY do ALL the manufacturers of these tapers go to all the trouble to make them. That REQUIRES a separate operation in a different machine. That costs time and MONEY! They must do it for some reason.

I am sure that some standard exists that specifies the tang. But that just moves the question of "WHY?" back a step from the actual manufacturers to the designers of the MT and of it's features. And if, in spite of a standard, a MT can be made without a tang at all, when why can they not be made with just a pin shaped protrusion? A pin shaped protrusion can be made as a last operation in the lathe where all the other features of the MT are formed and moving the part to another machine (milling machine) would not be necessary at all. That would save time and dollars. Surely I am not the first one to see that.

I can not but help to think that there must have been some reason for the full tang as opposed to just a central pin. So do I dare even suggest, very quietly that the reason for the tang was to provide a more firm connection between the MT and the spindle? Do I dare? If I shouldn't, then I won't. But then, please, PLEASE tell me why a full tang is specified or at least universally used. WHY?

....................

Without explaining why I do so, I will admit that when I install a MT in my lathe tailstock, I make sure to rotate it so that the tang makes firm contact with the screws installed in that ram that prevent it from rotating.

No I will not admit to installing those screws. Lets just say they ARE there.

Well that's a different take than what I've hard so far that's for sure. I googled on PM and Forest Addy there said the R8 keys where useless too. It's clear this is an area of differing opinions.

For what it's worth, I don't use drive dogs with my deckel which has a 40 taper. And I notice the deckel collets for it, which interface directly to the taper, cannot take a drive dog.

[strokersix]

MT tang:

The slot in the spindle for removal wedge weakens the spindle. A narrow slot and tang weakens the spindle less than a larger full round would. Also, the angled edges of the tang provide better contact with the removal wedge.

Just a guess. I don't know.

[SVS]

Do the math on cross section area. If either half of the MT taper is poor the tang on a larger drill bit will twist off. If the tapers are good the tang is there for alignment (if needed) and for removal, and because that’s the way the standard was written.

Hit reply to soon!

I think some of the big old horizontal mills with larger B&S spindles had drive slots, which is surprising in that B&S is even more self holding than MT and they all had drawbars.

[eKretz]

It clearly isn't given that it's on going and the pros with long experiences in the business have differing opinions on the matter. So I'm trying to make heads or tails out of this.

And you can't take too much from a name either.

It should be a given. And after long experience in the manufacturing industry: there are many "pros" who don't know all that much. Take what most say with a grain of salt. Look up the information yourself. Think. Would the drive keys be there if they weren't intended to serve a purpose?

As already mentioned multiple times here, when using a tiny little cutting tool this might be fine. When using a tool of any size or using a lot of horsepower, use the drive keys. It's a very good idea to use the drive keys for any type of tool that needs to be indexed for accuracy as well - like Stefan's boring head for instance. Just like on the lathe where we match mark our spindle mounted workholding devices to ensure minimal runout, on the mill keeping that boring head indexed with the same orientation to the spindle every time it's removed and inserted will keep it cutting repeatably at the same diameter. Randomly orienting will cause bore size to deviate. Same goes for endmills cutting to the right size at the same dial or DRO numbers if you don't have zero runout and a perfect spindle taper. Repeatability is the name of the game if you're making multiple parts.

[andywander]

Correct. The tang on those Morse taper tools that actually do have a tang only "engages" with the removal wedge, nothing else. I have cut off the tang on an MT3 drill chuck adapter so that the lathe tail stock could read "0" rather than starting at about 5/8in. All the holding on MT is provided by its shallow taper, and in fact in many cases you could shorten the taper by a fair bit and still have plenty of holding power.

Hmmmm...many of the MT spindles I have seen do have an internal "slot" that engages the tang on a tool. That seems to indicate that, at least when they were invented, the tang was meant to be used to drive the tool. I suppose it's possible that the internal "slot" is merely a by-product of making the removal wedge slot, but to do so you need to make the internal taper only as deep as the "non-tang" portion of the tool.

I agree that they do seem to hold just fine without the tang, for the most part. I have had slippage problems when using large drills in my lathe tailstock MT3 taper, until I installed two large set screws to make a "slot" for the tang to engage.

[MrWhoopee]

Well that's a different take than what I've hard so far that's for sure. I googled on PM and Forest Addy there said the R8 keys where useless too. It's clear this is an area of differing opinions.

The set-screw/key in an R8 is worse than useless. It serves no real purpose and has the potential to cause real problems. When in the trade, we removed them from all our mills. Had one shear with a large cutter and jam the shank in the spindle to the point it required major surgery to get the tool out.

[DR]

Not to start an argument on this, but Morse tapers are self holding. It sure is odd tailstock quills occasionally need reaming to remove burrs.

I shudder when I see someone turning (as opposed to precision grinding) Morse taper shanks on homemade tools then using them in their tailstocks.

[eKretz]

Not to start an argument on this, but Morse tapers are self holding. It sure is odd tailstock quills occasionally need reaming to remove burrs.

I shudder when I see someone turning (as opposed to precision grinding) Morse taper shanks on homemade tools then using them in their tailstocks.

Yes it is odd, isn't it? Even in most working shops. Just goes to show how little care most "pros" give these pieces of precision equipment. Seating shanks with burrs, raised dings and even chips/grit on them. Leaving the taper socket open to debris when the machine isn't in use (or even when it is!), Then seating a tool without cleaning the socket, etc. I've seen it all.

A Morse taper is intended to be a self-holding taper - but there is a prerequisite to that working out: the tapers (male and female) must both be in good enough shape to ensure solid contact and full seating. The tang will never hold up to as much torque as a fully seated taper shank. If the taper unseats, the tang will twist off before the tool also in almost every case since it's soft.

[BCRider]

..... I shudder when I see someone turning (as opposed to precision grinding) Morse taper shanks on homemade tools then using them in their tailstocks.

As someone that did three of my own MT3's in the past on my lathe I'd offer up a counterpoint. While I agree that it's not reasonable other than by shear luck to go directly from turning to use there is a way to get a very good fit that is a match for a ground item.

When I turned some MT3 tapers I used an MT3 socket as a test master. The final fit was tested by running a couple of felt pen strokes along the taper then fitting the socket lightly and giving it a twist. The high bands on the circumference which smeared away the felt marker were then given a light filing with my big broad lathe file. The marking, socket rubbing and light filing were repeated until the socket twist showed a fairly even smearing of the marker lines along the full length. At that point I found that a very light seating bump of the socket required a far heavier bump to free the lock. The results matching well the degree of locking from the same test with commercial ground MT3 tapers in the same socket.

So one does not need a cylinder grinder to do Morse tapers. Just method and a master socket to use for testing and tuning.

__________

Hey, MrWhoopee, I know that the R8 taper is close to the critical angle for self locking. I understand it was picked on purpose for that. So MOST of the time a little upward pressure would be enough to let the drawbar get a hold and set the locking pressure. But did you find that now and then one of the arbors would not self grab all that well?

[mickeyf]

When I started to purchase MT tooling for my lathe I found that some of it had the traditional tang and some did not. I made the mistake of purchasing a MT adopter for my tailstock chuck that did not have a tang and found that I had a devil of a time every time I tried to remove it. The tailstock had a self ejecting feature where by simply backing up the screw enough, the tang of the adopter hit a hard point and the MT was loosened. But that did not work without a tang. So I decided to add a tang to that MT adopter

Hah! The only reason I bought a drill chuck adapter with a tang was because I could not find one without, and in my case I cut it off (as described above), and still had plenty to self-eject when retracting the tail stock. I guess all lathes are not created equal.

So one does not need a cylinder grinder to do Morse tapers. Just method and a master socket to use for testing and tuning.

I have also made several by testing with a commercially made socket. They all are for use on my milling machine, have a thread for a draw bar rather than a tang. All work just fine.

[Rich Carlstedt]

Yes it is odd, isn't it? Even in most working shops. Just goes to show how little care most "pros" give these pieces of precision equipment. Seating shanks with burrs, raised dings and even chips/grit on them. Leaving the taper socket open to debris when the machine isn't in use (or even when it is!), Then seating a tool without cleaning the socket, etc. I've seen it all.........................................A Morse taper is intended to be a self-holding taper - but there is a prerequisite to that working out: the tapers (male and female) must both be in good enough shape to ensure solid contact and full seating. The tang will never hold up to as much torque as a fully seated taper shank. If the taper unseats, the tang will twist off before the tool also in almost every case since it's soft.

+100 % !

Yes, there are machinists and there are machinists ! and working in a shop for 50 years has shown me that alot of them have no idea of what is going on...
Did you know if you run a convertible at 254 MPH you get sucked out of the drivers seat ?

Now, before the argument may start, i just threw that out because some guys will be experts and say "Yes, it's true" or some will say "No, thats impossible.
But will any of them know the physics of the statement ?

So lets look at the physics of the Drive Dog question.
First of all, know that any taper angle of less than 7 degrees is known as a "Locking Taper"- and above 7 it becomes a "fast Taper" ...meaning it needs a draw-bar or screw
Also know that the smaller the taper angle the greater the lock !
So when you look at tool holders, the amount of "Lock" varies with its angle
ALSO the surface area of the taper determines how much it will hold.!

now look at fast Tapers, like R8 or a NMTM 50 ......which is a great side track here.. What is NMTM ?
It's the Association tool makers....the ..National Machine Tool Manufacturers association
What does that have to do with iit ? Well, all these tool makers got together and created standards....do you think they just through them out there ?...NO !
They did studies and tests and determined what was needed on a 5 or 10 or 50 HP Spindle to keep the tool holder from coming loose
now that meant determining the loads and HP capabilities and then they said (improvised explanation here ) "We can run a CAT 23 holder to 8.5 HP without drive lugs IF
the taper is engaged at 200 Foot pounds , and with Lugs, we get 11.6 HP....... So the Tool Builder then has an idea of the limits he can design to ...
Do you understand ? It takes 3 variables ...HP,and Draw-bar Force and Taper( angle and area)... and all that ALSO assumes the taper is clean and smooth.

SO the individual machine tool builder looks at what HP he is going to put in his mill and then determines the spindle HP and Forces AND then decides the taper he wants...
So when you hear some guy say XYZ .................it's best to know if he understands what he is talking about
Go get a copy of the "Tool Engineers Handbook " and do some research. ISBN07-001524-4

For me---When i hear of a R8 having the key sheared off and removed, I think... Stupidity !......., sorry if you are offended, but it only happens when the draw-bar is not tightened properly
or the tapered surfaces or tool had damaged surfaces ! Put crap in and you get Crap out . Of course if you are dumb enough to replace a Bridgeport motor with a 5 HP unit , then it applies
to you. Now , I have been in shops where the boss was the stupid one '" I don't care Joe, just push it on the Bridgeport " and the machinist does it.. but that my friends does not make it right.
So i have a 1943 Bridgeport with a 1956 J head and...It still has the key in the spindle, and i intend to keep it that way.
The key allows all your tools to be exposed to the exact same surface area each time and like CSI (TV) it is just like each bullet matches a rifle barrel it came from.. so your collets/tool holders pick up the same pattern. The key is not a "Shear key " as some un- knowledgeable people believe, it is there to minimize "Fretting" of the tapered surfaces ..so when it's "gone" so goes your tapered surfaces on the spindle and the tools..and your loss is ...............Less power before slippage...take your pick

There is another variable with CNC macines and the is when they use a knob on the tool and rely on air/hydralics for retention ..

Rich

[Tundra Twin Track]

I’m assuming the tang on MT is a spot for drift key to contact for removing from spindle.

[Bented]

I resisted jumping in at first because I have not used the 30,40, and 50 tapers, but I have used R8s and MTs. So I will now say the following.

R8s and MTs are very different animals. MTs are a self holding taper as witnessed by so many drill presses and other machines that use them. There are even tapered keys that are used to remove a MT from a spindle and those keys are definitely needed. So they really do not need a drive dog if the tapers are in good condition and they are installed properly.

R8s on the other hand have a much steeper taper and could easily drop out from vibration if not held firmly by a draw bar or similar device. That is why they have threads at the rear and why all R8 milling machines have drawbars.

The PIN in an R8 spindle is about 1/8" or 3mm in diameter and usually made of soft steel. It is definitely not intended to serve as a drive dog and many of these pins have been sheared off in an instant when the R8 tool or collet became loose in the taper. Some R8 spindles do not even have a pin installed by the factory. These pins are a convenient way of holding the tool or collet from rotating while the first few tightening strokes are applied to the draw bar or during the start of an automatic draw bar's tightening cycle. They also facilitate the last few rotations of the operation of removing the tool or collet as it would just spin without it and the operator would need to hold it by hand during that period. Once friction starts to take hold, the pin is no longer needed.

The only logical conclusion is that the R8 tooling MUST be drawn tight enough to prevent it from spinning in the R8 spindle. If this is not done then the pin will likely shear off and the taper will need some maintenance while the collet or tool will probably be trash. I do not think that many who have used the R8 tooling for long would disagree with this. Personally I would not call the key in an R8 spindle a drive dog. It merely facilitates installation and removal.

But, and it is a big but, things get a little bit blurred when we move to an MT taper. Yes, the reason for a tang on an MT taper is to allow a key to be used to remove the taper from a spindle. The MT spindles usually have a pair of slots on the sides which allow these tapered tools to be inserted and hammered to loosen the MT taper's grip. Then the MT taper just drops out of the spindle.

However it is curious that MT tapers are made with tangs, which are the full width or almost the full width of the MT at that point. A male MT is traditionally made in a lathe with a taper attachment. Almost every MT that I have has the center holes on both ends where it was held between lathe centers when it was made and that includes some that are of fairly recent manufacture. But that full width is NOT needed for removing a MT. And, in fact to make the full width tang the MT (adopters) had to be moved from the lathe where virtually all the other work was done to a milling machine. They had to be mounted in a manner so that the rear end could be milled down on BOTH sides to make the flat tang that we see on all these tools. Undoubtedly a special fixture was used to hold it for this work. NO factory in their right mind would do this if it was not really necessary.

When I started to purchase MT tooling for my lathe I found that some of it had the traditional tang and some did not. I made the mistake of purchasing a MT adopter for my tailstock chuck that did not have a tang and found that I had a devil of a time every time I tried to remove it. The tailstock had a self ejecting feature where by simply backing up the screw enough, the tang of the adopter hit a hard point and the MT was loosened. But that did not work without a tang. So I decided to add a tang to that MT adopter. But I quickly saw that a full tang was not really needed just to facilitate the ejection from the grip of the taper. In fact only a round PIN at the center of the tapered section would suffice quite well and that would be a lot easier to make and add. So, that is what I added to that MT: a central pin. And it works perfectly for ejecting the MT from the tail stock spindle.

Now I must ask, if a full tang is not really required for removing a MT from it's grip in the spindle, they WHY do ALL the manufacturers of these tapers go to all the trouble to make them. That REQUIRES a separate operation in a different machine. That costs time and MONEY! They must do it for some reason.

I am sure that some standard exists that specifies the tang. But that just moves the question of "WHY?" back a step from the actual manufacturers to the designers of the MT and of it's features. And if, in spite of a standard, a MT can be made without a tang at all, when why can they not be made with just a pin shaped protrusion? A pin shaped protrusion can be made as a last operation in the lathe where all the other features of the MT are formed and moving the part to another machine (milling machine) would not be necessary at all. That would save time and dollars. Surely I am not the first one to see that.

I can not but help to think that there must have been some reason for the full tang as opposed to just a central pin. So do I dare even suggest, very quietly that the reason for the tang was to provide a more firm connection between the MT and the spindle? Do I dare? If I shouldn't, then I won't. But then, please, PLEASE tell me why a full tang is specified or at least universally used. WHY?

Could you please elaborate further?

[skunkworks]

Could you please elaborate further?

Lol... You sir are a comedic genius...