# Appropriate NMTB Size For New Mill...



## Ray C (Sep 7, 2013)

All,

I'm wondering what is an appropriate NMTB spindle size for the new mill I ordered (http://www.machinetoolonline.com/PM-45M-CNC.html) which has a 3HP motor.  By default, it comes with an R8 spindle but, is easily changed to an NMTB type.  I don't do heavy hogging operations on the mill and R8 has always been good enough but, it's fun to dream about an automatic tool changer were NMTB is more appropriate.  So, given the size/power of the machine, what would be most appropriate, a #30 or 40 size spindle?  These seem to be the more common sizes...

I was able to find this information (but not much else).  This fellow's idea of a medium machine is 20-50 horsepower...  http://www.tyler.net/drspiff/machining/collets/tapers.htm

Ray

PS:  I posted a similar question on a CNC-related web site and haven't gotten any replies...  Seems like a pretty basic question.


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## sdconcepts (Sep 7, 2013)

nmtb 30 is more than large enough.  I a little more rigid than r8.  nmtb40 is overkill unless  you have 15 hp.


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## ssaxer1 (Sep 7, 2013)

I have a 5HP CNC bed mill and it came stock with a NMTB 40 spindle. There many different brands of tool holders available from $ - $$$. I do not have a tool changer (would be cool) but I do have about 30 holders. I keep some permanently filled and loaded into my control ( I number them by 16th (ie a #4 is a 1/4 inch regular end mill.) For cases where I use a long aon a regular basis I number it with a 20 (24 is a 1/4 long). Makes it easy to remember when I am programming.


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## 110octane (Sep 7, 2013)

My 1944 Nichols "Hand Miller" came from the factory with what came to pass as a NMTB #40 spindle taper.  Nichols originally used the predecessor of the #40 but the drawbar threads were smaller than 5/8 - 11 tpi with something like a 1/2" diameter drawbar.  The overall taper and other details were worked out by the National Machine Tool Builder's Association in 1939 (this date may be incorrect, memory bad).  The #40 taper is very congruent with this smaller mill.

I truly like the NMTB #40.  A huge number of holders, arbors, collets, etc. are readily available for it and the overall picture of cost is reasonable.  It is a robust, solidly driven design.  My Nichols presently as a 2HP motor.  Think about obtaining Brown & Sharpe and other less ubiquitous tooling.  When CNC overwhelmed the manufacturing scene, tooling producers dumped tons of NMTB stuff.  I haven't looked much at the CAT 40 but I imagine that it would not require much modification to use it in an older "manual" machine.  The groove is incorporated for robotic tool changing and the drive tabs may be somewhat different (too lazy to research this).  The cost goes up, too, especially with the trough spindle coolant feature.  The "pull knob" on the rear of the CAT most always has 5/8 - 11 threads securing it to the drawbar hole in the holder, etc.

If there is room in the spindle, I would recommend the No. 40 NMTB features.
Geoff


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## Ray C (Sep 7, 2013)

Ok, so here's where my learning curve begins...  Thanks for all the replies.  It's truly appreciated.

Subsequent to posting my question, I've learned there is "BT" tooling which is similar but not compatible (due to the drawbar mechanism) to NMTB.  So, if you guys don't mind, I'll re-phrase the question...

For this machine, what spindle type (which might include BT or others) is best for this machine given it's size/horsepower taking into consideration the primary intention would be to support an automatic tool changer?  Also, what is the appropriate size?  (i.e. 30, 40)...

Sorry for not thinking this through the first time around but, there's a learning curve for me now...
As far as size, I don't necessarily prescribe to "bigger is better" and I think #30 is fine for a machine like this but, economics will be considered if it turns-out that #40 is a bunch cheaper and more available...


Ray


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## 110octane (Sep 7, 2013)

Ray C said:


> Ok, so here's where my learning curve begins...  Thanks for all the replies.  It's truly appreciated.
> 
> Subsequent to posting my question, I've learned there is "BT" tooling which is similar but not compatible (due to the drawbar mechanism) to NMTB.  So, if you guys don't mind, I'll re-phrase the question...
> 
> ...


Overall BT tooling is metric and CAT tooling inch.  The shoulder at the rear of the holder is of a different diameter and the drawbar setup slightly different.  There is a lengthy discussion about the dimensional differences and operational interface on another forum.  I am bound by agreement not to mention the post, but google will lead you to it.  Suffice to say that it looks as if the systems may be modified to interchange (at least from CAT to BT) but with some difficulty.

As a basic answer to your question, since you are in the US (?), I think that you should dismiss the BT tooling and stick with the CAT system.  As I understand it, the BT tooling is generally more expensive than CAT even if you are next door to the plant.
Geoff

- - - Updated - - -

Opps!  Forgot to say use size No. 40.  Best available and most economical.
Geoff


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## Dan_S (Sep 7, 2013)

Ray C said:


> For this machine, what spindle type (which might include BT or others) is best for this machine given it's size/horsepower taking into consideration the primary intention would be to support an automatic tool changer?  Also, what is the appropriate size?  (i.e. 30, 40)...
> 
> Sorry for not thinking this through the first time around but, there's a learning curve for me now...
> As far as size, I don't necessarily prescribe to "bigger is better" and I think #30 is fine for a machine like this but, economics will be considered if it turns-out that #40 is a bunch cheaper and more available...



I'M just a home shop guy, but everything I have read says that for a given taper all the different holder types are interchangeable if you are willing to make custom draw bars. I'm also considering going with a non R8 set up, and it looks like 40 taper is easier to find than 30, but either is more than enough than for a home shop machine. If you look at Hass for example they don't switch up to 50 taper, until the spindles get into the 30+ hp range.


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## benmychree (Sep 7, 2013)

For a 3 hp mill, 40 taper would be overkill; I have a Fray vertical mill that came with 30 taper, and it would be entirely adequate, and personally I like it lots better than R8.  I have found no difficulty finding adaptors for it on E Bay.  I have a Brown & Sharpe #2 universal horizontal mill also with 40 taper on the horiz. spindle and 30 camlock on the universal (all angle) head, which I retrofitted to take 30 drawbar adaptors as well as the camlock holders, which ARE not so easy to find.  With this modification, I can use the drawbar adaptors on both mills.  I find that the camlock holders are not easier or faster to change than the drawbar type.


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## Ray C (Sep 7, 2013)

LOL...  Head is spinning and I know for sure, I'm sticking to my plan -which was:  Order it with the R8 (because I have about $1500 in R8 tooling) then, upgrade it to something else when I get fancy enough for an auto tool changer.

Keep the replies coming and don't be shy to toss in other info as I'm on the steep side of the learning curve.

Ray


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## DMS (Sep 8, 2013)

The Tormach tool changer runs with the TTS toolholders on a machine with an R8 spindle. It's doable. Not going to be as robust as an 30 or 40 taper, but I don't know if you will be able to push it hard enough to matter. Course the Tormach only has a 1.5hp motor, if you are pushing 3hp, the TTS stuff may get away from you.

Personally, I would love to have a 30 or 40 taper spindle. If I could get one for my machine, I would base it on the price of tooling, and I think that would lean towards some flavor of 40 taper.


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## Mid Day Machining (Sep 8, 2013)

I have a Tormach PCNC 1100 in my garage and I use their TTS tool holders. My machine has their air operated power draw bar, and I can change a tool on about 3 seconds. If you only have 3 horsepower, NMTB30 tooling is way overkill, and if you have visions of building a ATC, your NMTB tooling will not work for that.

I considered the NMTB30 optopnal spindle when I bought my machine, but I decided the tool holders were far too expensive for what I wanted to do. I run my machine like a job shop machine, and have absolutely no regrets for my decision.


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## arvidj (Sep 8, 2013)

Ray,

you may want to double check to make sure a 40 taper is available as an option. When I was looking for a mill in that size R8 and 30 taper were the very common options but when I asked about 40 taper from multiple vendors it was not an option.

I went with 30 taper based on theoretical better rigidity and the shorter length. However, as everyone has suggested, the availability of inexpensive or used tooling is considerably less than 40 taper.

Just my experience, YMMV,
Arvid


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## GK1918 (Sep 8, 2013)

Ray C said:


> LOL...  Head is spinning and I know for sure, I'm sticking to my plan -which was:  Order it with the R8 (because I have about $1500 in R8 tooling) then, upgrade it to something else when I get fancy enough for an auto tool changer.
> 
> Keep the replies coming and don't be shy to toss in other info as I'm on the steep side of the learning curve.
> 
> Ray



Hey Ray your head spinnin,  auto tool changers ?  Power drawbars.  Thought I had spinning head problems so I make my own. Nice to do during a 
snow storm.  Whats a auto tool changer?  something from this century i guess. Nerer heard of it back in america (not this one the real one ,the twin
dimentional america)


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## Ray C (Sep 8, 2013)

If you get really fancy, believe it or not, a robotic arm grabs the tool on the spindle, a power drawbar mechanism unscrews the drawbar, the robotic arm puts the tool on a rack, it grabs the next desired tool, puts it in the spindle and the drawbar tightens up...  The the machine goes and does the next cuts until it needs a new tool.

Don't worry... I'll be changing tools manually for a while to come (I'm still pretty well grounded in the Old America).

Ray




GK1918 said:


> Hey Ray your head spinnin,  auto tool changers ?  Power drawbars.  Thought I had spinning head problems so I make my own. Nice to do during a
> snow storm.  Whats a auto tool changer?  something from this century i guess. Nerer heard of it back in america (not this one the real one ,the twin
> dimentional america)


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## Dan_S (Sep 9, 2013)

Ray C said:


> LOL... Head is spinning and I know for sure, I'm sticking to my plan -which was: Order it with the R8 (because I have about $1500 in R8 tooling) then, upgrade it to something else when I get fancy enough for an auto tool changer.





Ray C said:


> Keep the replies coming and don't be shy to toss in other info as I'm on the steep side of the learning curve.
> 
> [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Ray


[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]A machinist friend of mine recommends the opposite. his two main points are 30, 40, 50 taper machines all have larger tapered surface and are thus more rigid, he also mentioned that you can usually get less stick-out than you can with R8.[/FONT]


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## cjtoombs (Sep 9, 2013)

I am using the Tormach’s tooling system on my PCNC 1100 as well, and it seems to work well.  As far as the higher horsepower on your mill, it depends on how that horsepower is delivered.  I notice that the machine comes in a step pulley arrangement and a variable speed arrangement.  The 90 RPM speed on the step pulley means it is delivering that 90 RPM at a full 3 hp, which gives quite a lot of torque.  The PCNC uses a Variable Frequency Drive, so it has almost no torque at speeds below 200 RPM.  If you are opting for the variable speed machine, it depends on whether they use a variable pulley system or a VFD as to whether you have a lot of torque at the low speeds.  Low speed and high torque are the combination that makes using the NT tapers with their drive lugs worthwhile on smaller machines.  You see it on smaller horizontal mills, as even a relatively small horizontal mill might be swinging a 6" HSS cutter at 50 RPM and full hp.  I've used the TTS with up to 3/4" EM in mild steel with no problems.  I have to take very light cuts and run at about twice the recommended speed for a 4" HSS slitting saw in steel due to the low power at this speed, so there isn't much strain on the spindle that way.  I would determine if the mill you are getting will be the variable speed or not, and if so how that speed is varied.  If it uses the VFD for speed control, I think the TTS would do a good job for you.  Otherwise, the prior suggestions as to which you can obtain and has the cheapest tooling is valid.  If you decide on the TTS system or for anyone using collets, there is a good white paper on the Tormach website on proper preparation of collets for use.  I had some problems with tools coming out of collets until I read that and implemented the recommendations.  I have no problems with tools slipping now.


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## bloomingtonmike (Sep 11, 2013)

cjtoombs said:


> The PCNC uses a Variable Frequency Drive, so it has almost no torque at speeds below 200 RPM.



Many VFDs these days deliver full torque at .5hz (like my Hitachi WJ200s). What VFD does your tormach use?


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## cjtoombs (Sep 11, 2013)

The full torque at the motors rated speed.  For a 1 hp motor at 1750 RPM that would be 3 lb*ft of torque.  Horsepower is defined as (torque (in lb*ft) x RPM)/5252.  So what they claim is constant torque up to the motor design RPM, then constant Hp above that.  What that means is that with a 1750 RPM motor, at 875 RPM you will have half the horsepower.  The horsepower increases linearly from 0 RPM up to the design RPM, at which point the VFD limits current to maintain the design Hp of the motor, which reduces torque.  So if you are direct driving the spindle (1:1 ratio) then at 200 RPM with a 1750 RPM motor using a VFD you will have about a tenth of a Hp available.  Constant torque sounds good in the marketing literature, but what it means is the motor has very little power at low RPM.


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