# Pm-1340gt Vs Pm-1440gt



## dogma (May 1, 2016)

I have been researching my first, possibly last, lathe purchase for a couple of  months.  I thought I had settled on a 1340GT and contacted Matt @ QMT last week.  It was a fantastic pre-sales experience and Matt pointed me at this forum to research VFD conversion options.  This led to the discovery of @mksj's proximity sensor setup and that we live in close proximity.  @mksj was extremely generous and invited me over to view his setup yesterday (and endured a couple of hours of my naive questions -- for which I am extremely grateful).  As I was leaving, Mark mentioned that the PM-1440GT was shipping soon...   After viewing the 1440GT spec sheet, this set me to wondering if I need to better define my lathe requirements.  I've made a simple spreadsheet attempting to compare the the two machines "by the numbers".

https://docs.google.com/spreadsheets/d/15LhsoYRhdKQnq4hONc795D3LZFY7TPZd-HZoRTGIYiM/edit?usp=sharing

The 1440GT has 34% mass and 50% more power in approximately the same size envelope for a 35-40% cost premium.  However, there are some trade offs.  The bore is larger but the distance through the headstock is also 1.75" longer.  The 1340GT can cut a larger range of imperial threads and smaller imperial metric threads.  The 1440GT has much faster feed rates and considerably and a whopping 2.25" greater clearance over the cross slide.

The extra weight, and hopefully rigidity, of the 1440GT sound attractive to me but I am firmly in the unknown-unknown phase of learning to run a lathe.  I'm sure that either machine would exceed my needs but this is purchase that I may live with for decades -- I'd like to make the best choice among the available options.  I don't have well defined, or really any, requirements for threading capability.  Either machine is within my budget but going with the 1440GT would mean deferring all but very basic tooling for a month or two.

I am left trying to answer several questions:

What range of threads is reasonable for a generic usage lathe?

Is there any common use case for cutting a TPI > 56?
What sort of job in a machines of this size class would use 3HP?
Is it reasonable to assume that the 1440GT is more rigid under load? 

What would an example of a job that needs a 2" bore?
Any guidance would be greatly appreciated!


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## Dan_S (May 1, 2016)

dogma said:


> I am left trying to answer several questions:
> 
> What range of threads is reasonable for a generic usage lathe?
> 
> ...



my opinion/thoughts are as follows:

4-56 TPI & .4-7mm are both more than enough to cover just about everything you will ever want to make. 4 tpi at 52rpm  is still scary fast for threading. 56TPI is breakout out the magnifier territory. Above 40 tpi i just use a die.
3hp, is more about being able to take big cuts, than the actual size of the work piece. Lets say you need to take a 1" bar and turn a section of it down to 3/8". A 3Hp machine will let you do that in 3 or 4 cuts. On my 3/4 hp machine it would be more like 7 or 8 cuts.
Generally larger/heavier machines are more rigid. However, to be 100% sure it pays to look at the size/configuration of the spindle bearings and the thickness of the spindle walls.
A bigger bore is almost always better as long as spindle rigidity hasn't be sacrificed to get it. For example if you need to face a 1 foot long 2" bar to length on the 1340 you need to break out the steady rest, while you can just chuck it up through the head stock on the 1440.


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## dogma (May 1, 2016)

Dan_S said:


> 3hp, is more about being able to take big cuts, than the actual size of the work piece. Lets say you need to take a 1" bar and turn a section of it down to 3/8". A 3Hp machine will let you do that in 3 or 4 cuts. On my 3/4 hp machine it would be more like 7 or 8 cuts.



Whoa - 0.2" cuts blow my mind!  One day-dream project of mine would involve turning down a ~6" section of 1.75" 309/310 stainless to  0.75" and might evolve into a small production run of ~100 parts.


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## tmarks11 (May 1, 2016)

dogma said:


> The extra weight, and hopefully rigidity, of the 1440GT sound attractive to me...



Just to make your decision tougher: Matt is working on getting a one piece cast iron base made the the 1340GT, which would be a HUGE! improvement in weight and rigidity.

So you might ask him about the ETA of that option.

http://www.hobby-machinist.com/threads/arrrrrgg.45537/#post-388535


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## Dan_S (May 1, 2016)

dogma said:


> Whoa - 0.2" cuts blow my mind!  One day-dream project of mine would involve turning down a ~6" section of 1.75" 309/310 stainless to  0.75" and might evolve into a small production run of ~100 parts.



Keep in mind though, a .2" doc on a 6" bar requires a lot more power than a .2" doc on a 2" bar, because the MRR is much greater. MRR is really what what power buys you.


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## Chipper5783 (May 1, 2016)

Get the 14".  Waiting a few months for certain tooling on a machine you'll keep for the rest of your life - not really an issue.

The 14" has a more useful slow speed (52 rpm is still too fast for many operations).  Dan is absolutely correct.  I have threaded 3 tpi at 45 rpm - scary stuff (I popped the drive key).  One of my "some day" projects is to change my driven pulley - since I almost never use the top speeds.  My "new" - to me, little lathe goes down to 30 rpm - it is awsome.

I have not used a variable speed lathe, but I can imagine that being able to drop another 50% of the speed would be very nice (there should still be pretty good torque, the gearing is in your favor).

The 13" (as well as being too fast at the bottom end) isn't really fast enough at the top end.  I wouldn't use the 14" machinie's 2200 rpm very often, but something faster than 1600 rpm is occasionally nice to have.

Threading range?  Don't sweat it.  The range of 8 - 40 will cover 99.9% of conventional threading.  Pretty well any lathe will cut whatever other thread you want - just change the end gears (and there will be a chart in the manual).  I had to cut 3 tpi on my lathe, but my change box only went down to 4 tpi.  The manual didn't have a chart - so I had one gear made to double the speed into the threading box (I set the box at "6" tpi to = 3 tpi).

Metric threading on an Imperial lathe.  The data sheet is not giving you the whole story.  Sure, there is a lever that flips to "Metric" and a chart that gives you the advance per rev - but you will find there are very few useful metric threads.  Think about it, the box is designed to split a bunch of Imperial threads - just adding a 127 tooth gear is not going to magically give you a nice tidy range of metric threads on an Imperial lead screw.  In order to get a decent selection of Metric threads using an Imperial box & lead screw requires the 127 tooth wheel and probably 2 additional end gearing ratios.

What sort of jobs to use 3 HP?   I my world - less than 0.1%.  I have a 3 & 5 HP lathe, and I almost always run it on the 3 HP setting, because it is quiter and starts easier - it has my 3 favorite speeds.  I have maybe popped the overloads once or twice in 30+ years:  A. I am not in that big a hurry.  B. To use full power, you have to have a seriously solid set up - most work pieces are just not that solid.

The longer cross and compound slides are nice.
Some of the tooling on the 14" will be a little more expensive: D1-5 is bigger and not as common second hand.  You should consider going up a size in the QCTP (the smaller one will work, but there are advantages to using one as large as the lathe can comfortably handle - don't get too crazy).

Sure the 14" will be more rigid, but the 13" will be fine.  Occasionally you'll need to take one more pass.

The 2" spindle bore?  Unless you have a specific job, I would put that as a nice to have.  I have 1-1/2" spindle bore and it is fine - either there is lots of room, or it is way to small.  I suggest it will be rare that having that extra half inch will be a game changer.

If you can swing the 14" - go for it.


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## wrmiller (May 1, 2016)

Some folks need/want as big a machine as they can get. Some don't. I fall into the latter category. I have a 1340GT, modified with a VFD and it is plenty for me. Actually, I don't need a lathe this big, but went for it to get the step up in quality. On my 1340 I can spin over 2000 rpm or down under 100. I don't thread really coarse threads, so really low speeds are not something I need. The 1340GT has a two-step pulley on the motor and I spend 99% of my time in the high range. I only thread in inch and love the range of the Norton gearbox. If I ever do need to thread in metric I'll buy a tap or die. 

I am waiting for Matt to get the cast iron stands in for the 1340GT, I will upgrade to those (Matt is saying a few months) and then I will be done with the modifications to this thing. If you have larger projects that require a bigger lathe, go for the 14. I would have considered it had it been available at the time I bought the 13. Probably.


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## dave2176 (May 2, 2016)

PM has some great machines. If I were looking, things that would be big include bed width as in 10" and longitudinal feed down to .001". The gears that give you 56 tpi are the same ones that limit the feed to .0026" although change gears probably would get you much finer. For example,  my machine can do 112 tpi and a .0011" feed according to published info but change gears can get it to 288 tpi and closer to .0003" feed. The point being that there is ability in both those machines that is not typically published. Yes I love my D1-5, just seems more manly having 6 cams instead of 3 but I'm not sure it adds up to anything. Just recently I was wishing I had a 2" bore. I think I would love either of them. One thing to consider is that tooling will cost more than the machine by time you are through.
Enjoy the process. Dave


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## dogma (May 2, 2016)

Chipper5783 said:


> Get the 14". Waiting a few months for certain tooling on a machine you'll keep for the rest of your life - not really an issue.


I completely agree!


Chipper5783 said:


> I have not used a variable speed lathe, but I can imagine that being able to drop another 50% of the speed would be very nice (there should still be pretty good torque, the gearing is in your favor).
> 
> The 13" (as well as being too fast at the bottom end) isn't really fast enough at the top end. I wouldn't use the 14" machinie's 2200 rpm very often, but something faster than 1600 rpm is occasionally nice to have.


Neither have I but which ever way I go, I'm planning to do a VFD retrofit immediately.  One thing I just discovered is that 2k+ speeds require a steel chuck.

Thank you for your guidance.


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## dogma (May 2, 2016)

dave2176 said:


> If I were looking, things that would be big include bed width as in 10" and longitudinal feed down to .001".


What is the advantage of the a wider bed?  Less deflection of the carriage?  .001" seems like a very fine feed.  Is that useful for a fine cleanup pass?


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## dogma (May 2, 2016)

wrmiller said:


> am waiting for Matt to get the cast iron stands in for the 1340GT, I will upgrade to those (Matt is saying a few months) and then I will be done with the modifications to this thing. If you have larger projects that require a bigger lathe, go for the 14. I would have considered it had it been available at the time I bought the 13. Probably.


I've heard of various issues with the stand.  Are you having trouble with specific resonance modes or general lack of rigidity?


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## dogma (May 2, 2016)

dave2176 said:


> For example, my machine can do 112 tpi and a .0011" feed according to published info but change gears can get it to 288 tpi and closer to .0003" feed. The point being that there is ability in both those machines that is not typically published.


So what your saying is, I also need a horizontal mill to cut gears?


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## Rich V (May 2, 2016)

Dogma, welcome to the site!
To help answer your questions we would need to know what your plans are in metal working.
The only real benefits I see for the 1440 is the increased bore and larger swing. The extra power and possible rigidity increase may be useful but only if you plan on optimizing cutting for production of multiple parts. Most hobbyists will seldom use a lathe the size of the 1340 to it's maximum cutting potential since it takes time and effort to find the max cut. Most of us will be done with the cutting operation before we find the max cutting for a given setup. Such is the nature of one off part making.

Now the head bore size can be very useful and can never be 'too large' in my opinion. The only down side is larger bore usually translates to longer length of bore. If you plan on doing any gun barrel type work then a short bore length is very useful. 
Same goes for how large a piece you can swing over the cross slide. You never know how big a piece you may want to work on so larger is better. 

As for the 1440 being more rigid, if your comparison table is correct the 1340 & 1440 have the same size bed so there will be no increase in rigidity from that aspect. If the cross slide is larger/beefier on the 1440 then that will help in increasing rigidity. Again any increase in rigidity from the 1440 will be only useful on heavy cuts so the benefit if real will only be useful on occasion.

I have the 1340gt and I'm very happy with it.
You won't go wrong on either of these lathes, they are well built and both should last you a lifetime.

Oh just to make your decision harder there is another PM lathe you can look at, the ERL1340
http://www.hobby-machinist.com/threads/erl-1340.39331/ it is very similar to the 1340gt but much more heavily built.


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## wrmiller (May 2, 2016)

dogma said:


> I've heard of various issues with the stand.  Are you having trouble with specific resonance modes or general lack of rigidity?



A few folks had issues with the stand. I've had none so far. Reason I want the extra weight/mass of the iron stand is because I spin a heavy 8" set-tru above 2000rpm at times and believe it will help when spinning unbalanced parts.

I'd forgotten about this since buying my lathe, but someone here mentioned fine feeds.  This was one of my main desires, and a lathe that will only thread to fifty something tpi is way too coarse a feed for me. I specifically looked for a Norton gearbox so I could get the 112 tpi/feed rate I wanted. Larger lathes have fewer/coarser feed rates.


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## dogma (May 2, 2016)

Rich V said:


> Oh just to make your decision harder there is another PM lathe you can look at, the ERL1340
> http://www.hobby-machinist.com/threads/erl-1340.39331/ it is very similar to the 1340gt but much more heavily built.


Gee, thanks... 

Matt told me this morning that the PM-1440GT is back ordered until September, so it may make this decision a bit easier.


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## sanddan (May 2, 2016)

dogma said:


> I've heard of various issues with the stand.  Are you having trouble with specific resonance modes or general lack of rigidity?



I was one of the unfortunate ones to have issues with resonance nodes. The current stand can be modified to stiffen up the mounting pads which will eliminate the flex, not a hard job or excessively expensive. The cast iron stand came about as a factory solution (per Matt's suggestion). I built my own stand so I could add storage as well as increase stiffness and mass. Not a reason to not buy the 1340GT if this is the size that works best for you.

I've tried .100" DOC in aluminum, I could tell the lathe was working hard but it did it without a lot of drama. On that job I settled on .050" DOC (.100" total stock removal) at a higher feed rate. Still made short work of the necessary stock removal. I doubt I am pushing my machines very hard, still learning. LOL


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## mksj (May 2, 2016)

The ERl-1340 would be on my short list (but has a smaller spindle bore of 1.57"), but probably looking at just as many months as the 1440GT. Did Matt mention the ETA for stocking the cast iron base for the 1340GT? Mass adds to rigidity and less vibration issues.

Similar to Dan, I usually do 0.050" DOC (0.100 total) in aluminum, 0.050-0.060" total stock removal in steel with no problems on the 1340GT. Type of tool holder/insert make a difference in how hard you can push it. Rigidity wise I would think the 1440GT would get the nod, if some of the added weight equates to heavier structural castings.  Speed wise, they are basically the same with a VFD, a reasonable range for both would be 50-2000 RPM, you could go slower if needed. Since you mentioned you would go with the VFD, and probably a proximity sensor stop, having a very low RPM for threading is negated. There are a few times where I wish the feed rate had one step/slower gearing, but you get use to each machine. Not sure about needing very high TPI's, anything below 56 is all I have needed, but then I do nothing fancy with mine.



dave2176 said:


> One thing to consider is that tooling will cost more than the machine by time you are through.


Agree, this was a real eye opener for me, but if you stay with the similar size machine 1340/1440 the tooling should be interchangeable if you decide to go beefer later.  If you are planning on machining larger stock, then the 2" spindle hole may be the game changer.


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## sanddan (May 2, 2016)

It's funny, I think I do more small parts than big. Just the opposite of what I thought before getting into machining. The 1340 seems big sometimes, or maybe just right.

Of course, bigger is _always_ better! LOL


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## dogma (May 2, 2016)

mksj said:


> Did Matt mention the ETA for stocking the cast iron base for the 1340GT? Mass adds to rigidity and less vibration issues.


I just asked that question (waiting on response).  However, I think it might be a fun project to weld up a heavy duty stand. IMS (a local metal supplier) has delivered heavy stock to the house for something like a $50 surcharge.


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## dogma (May 2, 2016)

sanddan said:


> Of course, bigger is _always_ better! LOL


I continue to be amazed by the wide range of project sizes a lathe (or a machining center) can accommodate.  It's somewhat constitutive based on experience with [power] hand tools.


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## dave2176 (May 2, 2016)

dogma said:


> What is the advantage of the a wider bed?  Less deflection of the carriage?  .001" seems like a very fine feed.  Is that useful for a fine cleanup pass?


The advantage would be overall rigidity improvements. I don't use very fine feeds unless I am doing something very small and fine. For most things a couple strokes with a lathe file followed by emery cloth works great. Just nice to have ability to do very fine work when the need arises.



dogma said:


> So what your saying is, I also need a horizontal mill to cut gears?


Well of course you do, who doesn't "need" one. What I was referring to however is all the gaps or blank spaces in the threading charts. My lathe uses a 40 tooth on F and a 40 on G by default which provides all the "published" American threads from 4-112 tpi but it only gives me a couple metric threads that are useful. So if I want a 0.635mm pitch it's the same gears and position as 40tpi, one of the standard threads. My lathe didn't come with a 27tpi which is useful for a number of things so by changing gears, specifically leaving on F and putting the 60 on G I have 27 tpi on C2. So with my QCGB having 40 possibilities and 24 options of change gears I have 960 possible threads which also translate to feed rates. Any other lathe with change gears has many more possibilities than what is what is published on the charts.


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## dogma (May 2, 2016)

dave2176 said:


> My lathe uses a 40 tooth on F and a 40 on G by default which provides all the "published" American threads from 4-112 tpi but it only gives me a couple metric threads that are useful.


Is there a good reference to read up on various lathe threading gear box designs?  I am completely ignorant of how they operate.


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## dogma (May 2, 2016)

mksj said:


> Similar to Dan, I usually do 0.050" DOC (0.100 total) in aluminum, 0.050-0.060" total stock removal in steel with no problems on the 1340GT. Type of tool holder/insert make a difference in how hard you can push it.


I'm still a bit fuzzy on the relationship between longitudinal feeds, spindle speed (obviously, linear surface speed is what maters), and DOC translate into required power (per material).  I have a fancy android app that does it but if there a good resource to learn the theory?


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## dogma (May 2, 2016)

dogma said:


> However, I think it might be a fun project to weld up a heavy duty stand. IMS (a local metal supplier) has delivered heavy stock to the house for something like a $50 surcharge.


I've done a little bit of reading on this and it seems that gray cast iron is preferred for this sort of  construction due to it's vibration dampening properties and IMS doesn't stock CI flats.  Sandwiching some sort of elastomer between steel plates might work.  Will have to see if I can get someone at work to do an FEA...


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## mksj (May 2, 2016)

Cast iron is the preferred material, Meehanite cast iron used in the ERL-1340 and 1440GT is denser and has more ideal strength and dampening properties. Wouldn't chase your tail with FEA. On feed and speed, there is a lot published, I loosely use some of the manufactures recommendations for speed and feed, in general, you will be probably be at 50% SFM of published table attached (or lower RPM and faster feed), and way under those published if using  inserts. Most of the feed rates fall into the 0.001-0.004 IPR. The lowest IPR on the 1340GT is 0.002, so lower RPM and slighter faster feed. Just a rough calculation, a 1" bar at 1000 RPM would have a SFM of 262, the same bar at 250 RPM would have a SFM 65. The DOC, varies on materials, IPR,  Hp and cutter, working with different materials, you start to get a feel when you are pushing the DOC for stock removal. Just some thoughts, there are much more scientific formulas on all this stuff.

After awhile, you get a better feel of the cutting speed and feed, this is also affected by the cutter and the finish you need. I tend to push harder to remove material, then do a skim cut for for close to the final finish. There is minimum cut for different cutting tools, so taking like a 0.001" cut may not work very well. The cross slide feed is 1/2 the Z axis (longitudinal), when doing cut off I slow the speed down 300-450 RPM and feed manually, just need that tactile feedback. The nice thing when using a VFD, you can really find that sweet spot for the machine, I am always amazed that small changes in the RPM make a large change in the cutting performance/chatter, especially when boring/drilling.


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## jbolt (May 3, 2016)

dogma said:


> Matt told me this morning that the PM-1440GT is back ordered until September, so it may make this decision a bit easier.



Sounds like he has completely sold out the first batch. He said those were supposed to be finished in May. Not sure yet what that actually means for receiving and delivery. That will be about a two month slip in the original schedule when I ordered mine.

September sounds like is a "best guess".  I'm sure it is a real challenge to work with overseas manufacturers who are building machines for multiple customers.


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## wrmiller (May 3, 2016)

Matt always tries to give a "best guess" to his customers, but it is based on what information he is getting from his manufacturers. If they are overly 'optimistic' when communicating their delivery schedules...then as they say, the "big round brown ball" rolls downhill. But having said that, Matt appears to be getting better at translating his manufacturers delivery communications. Only one of my three machines I've bought from Matt over the years was delayed, and that was only a few months. That was a long few months though...  

He also told me that it would be a "few months" for the cast iron stands to become available for the 1340GT, and that extras would be available for existing customers. But, I automatically translated that into 'may be available by the end of summer'. I'm hoping I'm wrong though, as he (Matt) is having these stands done here in the US.


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## jbolt (May 3, 2016)

This got me thinking about the executive office build out I did for Hyundai corporate back in the 90's. All the cultural hoops I had to go through was nuts.


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## qualitymachinetools (May 8, 2016)

"I'm hoping I'm wrong though, as he (Matt) is having these stands done here in the US"

Yeah we are waiting on our pattern guy for the castings, its no difference, overseas or in the US.


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## GA Gyro (May 8, 2016)

Hey Matt,

Way to go on the cast iron base for the 1340...
Please put me down for one also!

Any rough idea of weight of the base (base alone)?  

THX

John/GA


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## wrmiller (May 8, 2016)

qualitymachinetools said:


> Yeah we are waiting on our pattern guy for the castings, its no difference, overseas or in the US.



Except for waiting for that 'slow boat' once they are ready.

I'm stockpiling my pennies in anticipation...


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## tailoredpencompany (Oct 20, 2022)

dogma said:


> Is there a good reference to read up on various lathe threading gear box designs?  I am completely ignorant of how they operate.


Does anyone have a published gear box conversion table worked up?


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## B2 (Oct 25, 2022)

Hi,  Nor for sure what you mean by  


tailoredpencompany said:


> Does anyone have a published gear box conversion table worked up?


If you mean the possible generated TPI there are various tables for various lathes listed on this forum.  My own version tries to enable most lathe models:  








						TPI Feeds X-Feeds: Generalized Excel file for your Lathe
					

TPI Feeds X-Feeds: Generalized Excel file for your Lathe  Hi Folks,  My PM1440GT lathe manual only showed a few of the possible threading values and it appeared to me that the Feed rates were incorrect.  They were.   Hence, I set about to figure out what all possible TPI could be achieved via...




					www.hobby-machinist.com
				




If you are asking how the gears are laid out inside the gear box you can search on Norton gear box and see one approach that is easy to understand, how ever many lathes do not use the Norton box look at the manuals to "sort of see" the arrangements of gears in various lathes.  My own limited experience is that these drawing are commonly in error and do not make sense on the lathes commonly discussed on this forum.

Dave L.


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