# X-Feed Rates on PM lathes



## B2 (Feb 9, 2022)

Hi Folks,

Have others measured their X-Feed rates on their PM lathes.  

I have a PM1440GT and it says on the front gear panel that the ratio of the Power Feed and the X-Feed rates are simply 2:1 (or 1/2) .   I think this is the common statement made for many lathes.  However,  I have made a quick attempt to measure these rates on my machine and I get a number more like 3.14:1 not the factor of 2.  I think the x-feed part of the table on the lathe is incorrect.  It is probably not something that most folks often even question as the distance traveled via the manual handle seems fine.  But when I look in the manual at the apron gear box I cannot make much sense of it.  I certainly cannot predict the Feed rates from looking at it.  The manual at least list gear dimensions, but I cannot tell how they are connected or even if they are all there... from the illustrations in the parts section.   

Has any one taken the gear box  (PM1440GT) apart to see if the drawings are close to really representing the gears?  Maybe some one else can figure out the gear arrangement and my lack of 3D imagination?   Has anyone measured the x-feed rates?  The table value for the Power Feed rates do seem close.  


Dave L.


----------



## T Bredehoft (Feb 9, 2022)

My lathe is a PM10-30, New last year.

Its' interesting you should bring this up. I'd been wondering, hadn't thought about putting an indicator on it. I just did, left and right movement (I dunno x and y and z on a lathe) in whatever gear set up I have for feeds, (ABC in C for the greatest movement) showed .0092, in and out showed .0021 (Starrett dial indicator, reads in tenths. ) That's 4.38 to 1 ratio.  Only direction of movement changed, no gears where changed in this experiment. That surely isn't 2:1.


----------



## Ischgl99 (Feb 9, 2022)

I just checked my 1236T, it’s supposed to be 1:3, but measured to 1:3.25, that’s close enough for government work.  Maybe yours is supposed to be 1:3 as well and they just miswrote it?


----------



## B2 (Feb 10, 2022)

Thanks folks,  So I am not going crazy.  Yes, government work and it may not matter much to others,  but do most of us even question the lathe plates?  I suspect that the 1:3.25 is more likely correct and that the 1:3 is just how they truncated the numbers.   Surely it is more exact and repeatable than just one digit!

Both the front panel label/plate and the manual for my PM1440GT says my x-feed rate is suppose to be 1/2 of the Power feed (z-axis).  Just to be sure I just went an remeasured it.  I have a counter connected to my spindle and a DRO on both axis so I used them.  If you want to understand how I put that in to my VFD control the posting is linked below.  A link to my VFD system  and its counter is noted below.  

I am going to set the factors of two on the gear box at 8x so as to cut the highest TPI or the slowest feed rate.  This makes the spindle turns higher and slows down the feed.  Then I will make a long feed run so as to get a high count with lots of digits... and see if I can get the numbers to higher accuracy.  I have a DRO on the machine and counter on my spindle so I will just turn it on and wait until it trips the proximity sensor.  Unfortunately there is no proximity sensor on the x-feed.  I will have to watch it more closely!



B2 said:


> adding a counter to my VFD converted PM1440GT



Dave L.


----------



## B2 (Feb 10, 2022)

Some of this discussion was occurring on an unrelated thread so I am moving it here.



Provincial said:


> Dave, on my Metal Max MM-1340LB (China-made Jet/Enco belt drive clone) the manual states that the carriage feed rates are 0.0036-0.1005 and the cross-feed rates are 0.0012-0.0345. That is pretty close to 1/3.



Hi @Provincial

Thanks for the information.  It is good to know that not every manual says the ratio is 2:1.  From above you will see that your value is also found by others. 

Yes, I would be interested to see your manual info. I googled your model number + manual but did not get hits.    But before you go to the trouble of photographing them...  Perhaps they are the same as others...  I did find a JET manual, but do not know if this is your lathe (see below).

You may be interested in looking at the on-line manual for the PM1340GT (link *HERE* ).  It may look the same as yours?  In the PM version of the manual, near the end, are illustrations of the drive train for both the main gears as well as the apron. Unfortunately in the parts list they do not give the tooth count on the gears.   I do not have the 1340 but a friend of mine does and he made a quick measurement and he said he did not the 1:2 ratio either.  I have the PM1440GT (link *HERE* ).  You can also look at its manual and you will find that the apron gear illustration appears to be the same as the 1340 illustration.  In the PM1440GT parts list many of the gear tooth count is provided.  PM removed the tooth count from a couple of head stock gear assemblies of the PM1440GT online manual, but I happen to have the printed manual that came from the factory and they are listed there.  Also, I found an old looking manual on-line for the  Eisen LD-1440E (link *HERE* )and it appears to be the same and is for both the 1340 and is more complete. It is also for both the English and Metric versions.  Perhaps it is the same as yours? 

There are several problems in trying to read these illustrations. One is that the parts lists never seem to give the TPI for the lead screws, the worm gears(not important), and the RACK on the bed and sometimes I think they are just incomplete.  Fortunately you can simply crank the handle a few times on the X-Feed and measure the distance traveled to get that lead screw. On the 1440GT (English) it is 10TPI.   I spent quite a bit of time trying to understand the main gear box in my 1440GT.  I finally got the numbers to all work out, but I had to physically re-arrange the positions of some of the gears in the illustration!  Even after all of that some of the gear positions would not clear each other as you moved the levers!

I really am coming to the conclusion that some of these illustrations are rather generic and may not even apply to the actual lathe that one has!  Perhaps the machines evolved and the manuals never kept pace?   I am not for sure what one does if he needs new parts! I may not get around to spending the time on it, but I looked at a JET version of the 1340 and 1440 (which may be yours?) and they are not laid out the same, but may provide insight into parts that are missing in my own lathe manual.  It is  *HERE* .  Also, this manual has a more extensive table of TPI and feed values at pages 16-17 and they support the feed rate ratio of around 3:1, ... not exact. 

By the way, my solid state VFD conversion is  *HERE*.   Others have ask me if I have made my hand wired electronics board in to a PCB that could be made available.  I am thinking of doing so.  It seems that a lot of folks are not familiar enough with electronics design to build the hand made board with confidence.  I am not really interested in doing conversions and selling them to folks, but I am willing to provide advice and encouragement on my design. 

Dave L.


----------



## Ischgl99 (Feb 10, 2022)

I kept it simple and put it in the highest gear and rotated the chuck by hand 10 times and then took the average after taking out the backlash.  The Z feed was dead on and the cross feed came out to 1:3.25 for the two feed rates I checked.  

I checked the PM manual for this lathe and it shows a picture of the feeds table and the cross feed should be 1:2, but the plate on my lathe shows 1:3.  I'm guessing they made a change somewhere along the line and never updated the manuals, and you happened to get one of the older thread and feed diagrams.


----------



## B2 (Feb 10, 2022)

Hi Guys,  

Thank you for your efforts.  

When I measure my ratio using ~ around 700 turns of the spindle,  I get:   1:3.1343    Could it be that your number is really more like mine or are you confident in the .25 part of your number?    However, I have some more work to do before I am totally confident of my number, it is conceivable that I have some noise in my measurement of the number of counts, ..... If I were getting extra counts that would drive my number down a bit.    I will try to check on this a bit more... later.  

Dave L.


----------



## Aurelius (Feb 10, 2022)

While I can't speak to your lathes, I can say that having worked as a tech writer in the past, it owuld not suprise me at all if someone simply didn't care enough to update the user manual.  It's unfortunately far more common than it should be.


----------



## Ischgl99 (Feb 10, 2022)

I’m very confident in mine. I set an indicator against my cross slide, turned the chuck until the dial started moving, zeroed it out and made a mark on the chuck, then spun it ten times and measured the displacement.  I did that for two different feed rates and it came out the same.  I tried using the gear ratios to verify it, but I was way off, so I think I need to spend more time figuring out how the gears engage in the apron.


----------



## Provincial (Feb 11, 2022)

B2, Here are the photos of the Metal Max manual pages.  I included page 7, which has the specifications.  I didn't include the cross slide pages, since there is no gear tooth information there.


----------



## Provincial (Feb 11, 2022)

The Jet BDB-1340A lathe seems the same as mine, except the quick change gearbox has been modernized, while mine has the Norton gearbox.  The parts list shows all the gear teeth that my manual shows.  No tooth count for the cross travel screw.

This link to the Jet manual should work:
content.jettools.com › assets › manuals › 321359A_man_EN.pdf

If not, search Jet BDB-1340A and you should see it.


----------



## B2 (Feb 11, 2022)

Hi Provincial,

Thanks.  The link l did not work, but with a little searching the model number did.  For others here is the links I got to work. 
https://www.jettools.com/us/en/p/bdb-1340a-belt-drive-bench-lathe/321360A   to the lathe, and the manual that it took me to:
https://jpw-assets.s3.amazonaws.com...4818d4c509187f3266a6bfd310_321360a_man_en.pdf

This manual's head stock gear box layout, both outside and for the most part on the inside, looks similar to my PM1440GT.  However the gear teeth and sizes numbers are not similar at all.  Later I may see if the gear numbers work out to yield the physical layout and thread lead screw motion.  From my gear teeth numbers I could get the TPI values, but I could not physically get the gears to shift pass one another!  Also, the gears were not in the right physical relationship to each other!  The apron gears are only vaguely similar seem to help me to understand my own a little bit more.  

Apron:  The big handle shaft has a gear on it, but it is not aligned to the Rack nor the worm gear that is shown in Fig. 12-1, Exploded view of the Apron so is not attached directly to the Rack, but is always attached to the Rack via so some gear.  It is locked to the rack when either feed mechanism is engaged.  However, when the worm gear is connected to the gear box then the Apron will not move via the handle.  I initially thought that maybe that big 60T gear was the upper circle that is sticking up (overall box sketch, below the gear layout, shown at the bottom of the figure, but as shaft B it is in the wrong location?   However, the letter B on this bottom sketch, is in the right location to engage the Rack!  

This worm gear attaches to the FEED drive rod( via the single slot.)  So that one turn of the feed rod will cause one turn of the worm gear which then translates to one thread of the which ever gear in the figure attached to it.  One might think that this is shaft D and gear item #31.  In the parts list this is the only 2mm gear.   Gear teeth are suppose to be the same size for matching to another gear so maybe this attaches to the worm.  This shaft would not move back and forth so is not the one couple to the FEED lever.  

Shaft E with its wide gear #33 would seem to be a coupling between a stationary set of gears on shaft D and the gears that might slight back and forth of Shaft C.  However, the draw it below the others in the exploded drawing.  I don't know if that has significance.  

This would leave shaft C to be the one that moves back and forth with the FEED lever. Also the part #11 appears to have a notch in it to allow the FEED handle to link to the shaft?  But I see not spline or key way for any gear to slide along and it would seem somewhat unreasonable that the entire shaft move.      The 44T gear #22 might be the one that couples to the Cross Feed lead screw via gear shaft #67 of Fig. 17.1 ? 

So the shaft F is a mystery as it is not clear how it fits in.  Also the bottom sketch shows it with dashed lines, I think, is this of significance?  

So maybe with more time I will figure this out entire gear path out. each gear on a shaft must match to another.  This means that if two gears on one shaft that move/shift (between Feed and X-Feed) requires two gears on another to some what match via summed diameters/radii.   

However, the gear teeth count and sizes to not match my 1440 so figuring out maybe not really help me with mine much.  

Dave L.


----------



## Ischgl99 (Feb 11, 2022)

I figured out what I did wrong with my gear calculations and come up with a cross feed ratio of 1:3.19.  I measured an actual 1:3.25.  I calculated the ratio after the worm gear since that is the same for both cross and longitudinal feeds.  The attached picture is what I believe to be the gear arrangement for my lathe.  The manual also shows a table with a 1:2 cross feed ratio, we know that is not correct, so the gears listed might not be accurate as well.


----------



## B2 (Feb 12, 2022)

Hi @Ischgl99 

Very nice sketch. I need to get you to sketch out my main gear box.  I got all of the gears numbers to agree with the final TPI, but I never did get teh physical layout such that the gears could actually shift positions without hitting one another.   

I think your apron gear layout must be the same as for the PM1440GT as all of the gear Teeth counts seem to be the same.   However, I am having a problem with the 50T gear shaft which shows the end of the shaft to have a M1.5 by 13T, as you note.  The problem here is that  I had measured the Rack earlier as my manual provided no info on it.  When I did this I laid along metal rule against it and it appeared that the tooth repeat pattern occurred at 70T/330mm, which is the same as 7/33, but went out a factor of 10 to get to 70T to be sure.  It was a little hard to judge, but I counted the teeth several times.  So this gives a pitch of 4.71428 mm/T.  This is similar to what I think you noted in your sketch, but did not apply units of mm.  This size does not match any metric gear that I am aware of.   So I think the diagram for the M1.5 13T shaft holding the 50T gear is incorrect.  There is no way that a 1.5mm gear tooth will fit a pitch of 4.714 mm rack pitch???   Maybe it is an English gear tooth size as they are not as straight forward to figure out.  I will work on this later.

Obviously the extra digits of my 70/330mm are suspect, but by no more than about 1/10 of a tooth and I really think it is better than this.  So ~330/70.1~ 4.708 and 330/69.9 ~4.721. This gear size, that is on the end of the 50T shaft is relevant to a final feed rate.  However it appears to be irrelevant to the x-cross feed rate.  I just measured by counting 100 turns of the FEED Bar and got 0.931"/100Feed Bar turns = 0.00931.  I suppose that I might have missed a little back lash or something so it might have been 0.0094 or so.  But it is close enough for now.  

If you look at your gear arrangement I think we should be able to predict the actual number.  But it is getting pretty late for me to even try.  Maybe you want to give it a try and maybe I could also in the light of day.  I  believe in my turns number as I have both my electronic counter counting and I have set up an old mechanical counter and they agreed on several runs where the total turns was a few hundred.  So maybe tomorrow I can make a run at 500 turns of the feed bar, which would represent about 5" of motion.  (When I set my gear box to AD and X, then I get 1 spindle turn per 1 Feed bar turn, so I do not actually have to count the revolutions..... just run the lathe slow so that the mechanical counter can keep up. )  Later I can change the gear box so that the feed bar rotations per spindle turn are less and go for even longer runs without running out of travel on the x-feed, and I could do runs for both feed rates.  

 Dave L.


----------



## B2 (Feb 12, 2022)

I went a head and made a pass at it.  x-Feed rate= {0.1"*(44)/(18*2*13)]/feed bar turn = 0.009401709"/Feed bar turn.  Where the 2 is from 44/22.    Close to my measurement.  Is this what you get?


----------



## Ischgl99 (Feb 12, 2022)

The pitch for a gear rack is simply the module times pi, so 1.5x3.1415=4.71mm for an M1.5 gear rack.  That matches taking the circumference of the pitch line of an M1.5 13T gear and dividing by 13 teeth.

For my calculations, I assumed one rotation of the 22T gear tied to the 18T gear that runs on the worm gear.  For the cross slide, that would be 22/44 x 44/13 x 0.1” (cross slide screw pitch) = .169” or 4.29mm

For the longitudinal feed, same 1 rotation of the 22T gear, 22/44 x 22/50 x 13 = 2.86 teeth of rotation of the 13T gear.  That translates to 2.86 x 4.71mm = 13.47mm travel.

Long/cross is 13.47/4.29=3.14 (I wrote 3.19 above, I must have rounded a number earlier that I didn’t this time).

We can’t blame the difference on a metric or imperial shaft since a 10 TPI shaft is almost exactly 2.5mm pitch, so it doesn’t come close to making it 1:3 instead of 1:3.14.  I think the difference is simply that this is as close to 1:3 they can get with common gears in the space they have.


----------



## B2 (Feb 12, 2022)

Good Morning @Ischgl99 
I am back at it.  Thanks.  I think we are in agreement!:

I like to relate to turns of the Power Feed Bar as this is what comes out of the gear box.  On the PM1440GT the setting of A-D, on the factors of 2 knobs,  and using the X lever setting results in a 1:1 ratio between the power feed bar turns and the spindle turns.  So this results in a x-feed rate that is generated by the spindle turns (for that gear box setting).  

X-Feed rate:  You used 22/44 x 44/13 x 0.1" = 0.169"/turn to get the X-feed distance of one turn of the 18T shaft.  I think to get this to the slotted FEED Bar turns you need to include the ratio of the 18T/22T that are on the 18T shaft.  Then you need to include the fact that one rotation of the worm gear represents one Thread on the 18T gear.  I collapsed some of this calculation in my previous note and this may have make it less than obvious.  My equation from last night is similar to your own with the 1/18 factor put in: {44/(18*2*13)}*0.1" =  (1/18)*(22/44)*(44/13)*0.1"  ~ (0.169/18)= 0.009401.  (Which is in close agreement to what I measured last night!) 

Power FEED rate:  So in your Power Feed calculation you have 22/44 x 22/50 x 13 = 2.86 teeth of rotation of the Rack, but to get this to the power feed bar I think we have to put in the 1/18 worm gear factor again.  So (1/18)(22/44)(22/50)(13)=0.1588888 teeth of the Rack.  Then 0.1588888...*1.5*Pi() = 0.74874625 mm or 0.029478" per FEED Bar turn( Z-FEED).   The lathe table says it should be 0.0295!  So this is in agreement.  

The Ratio is in agreement too: 0.029478/ 0.009401 =3.135624.  

But note that Pi()= 3.1415926...! Also note dividing the ratio by the Pi() factor yields 0.998031.  So all of these number are just a little less than Pi()!! ....and the final result is irrational due to the RACK!

So I think this settles this.  We make a pretty good team!

Conclusions (to a ridiculous number of digits, but which pop out of a spread sheet):  
X-Feed Rate per power bar turn is:  (1/18)*(22/44)*(44/13)*0.1" = 0.00940170940"/bar turn
Power Feed Rate per power bar turn is:  (1/18)*(22/44)*(22/50)*(13)*1.5*Pi()/25.4 =0.0294781988"/bar turn
Ratio: 3.13540842

Thanks!!!!

Dave L.


----------



## Ischgl99 (Feb 12, 2022)

B2 said:


> Good Morning @Ischgl99
> I am back at it.  Thanks.  I think we are in agreement!:
> 
> I like to relate to turns of the Power Feed Bar as this is what comes out of the gear box.  On the PM1440GT the setting of A-D, on the factors of 2 knobs,  and using the X lever setting results in a 1:1 ratio between the power feed bar turns and the spindle turns.  So this results in a x-feed rate that is generated by the spindle turns (for that gear box setting).
> ...


I try to keep things simple, so I only went as far back in the gear train where the driving gear was the same for both the cross and longitudinal feeds.  Since the feed shaft and worm are driving the 18T gear, and the 22T gear is attached to that shaft, I could eliminate any unknowns in the worm to calculate the cross to longitudinal ratio.  I also rounded some numbers since I felt two digits is plenty accurate for this.  Anyways, this has been enlightening and I have a much better understanding of how the apron gears work, so thank you for posting this.


----------



## aliva (Feb 13, 2022)

Why are you concerned with the feed rate ratio, by counting gear teeth and everything else. Seems like a waste of time. Or I'm missing something. Set the the feed rate in thousands  feed per revolution from the machine name plate . Who cares what the ratio may be. Adjust the feed to get the desired finish or chip formation and call it good. If you  really need to know, set your rpm, select a feed rate, and measure the travel. Even if the results don't match the name plate, it doesn't matter. The results is what is paramount


----------



## B2 (Feb 13, 2022)

Hi @aliva 

I do not disagree with your vision.   I too normally just guess, with some experience, until I find a feed that cuts nice for the current work material.   However, @davidpbest  provides, in his book,  some nice rules about what the feed rate "should be" for a given tool insert and its physical dimensions.  That would help a lot with the inital "guess".  Read on and you will see why...

However, the our two lathes PM1340GT and PM1440GT we found that the Power Feed rate to Cross Feed rate is NOT 1:2 as the lathe plate and the manual says. And this maybe of value to someone out there.   I have also studied the gearing diagrams for the 1440 at length and found it to be in error.  When I look at similar older models manuals they are wrong also.  So I suspect that it is something that just propagates.  

So I wanted to learn more about programing Excel spread sheets with macros which is to say is programing via Visual Basic for Applications, VBA.  As a vehicle to learn this I have been trying to write programs which both help me to learn as well as might be useful to someone.  My first attempt at this was to write some G-code in  a spread sheet and then to use the Macros code to generate a lathe front electronic panel for my VFD conversion.  The program allows one to make a round hole, with Keyways and/or flats on it of any size, orientation, and location.  You can make as many of these or any variation and place them in space.  In addition it does rectangular holes as well as Sub-D connector holes of the most common sizes.  Mix and match.  Obviously you can also make holes for other applications using the same program.  After you describe the number of holes and their other attributes of sizes, locations, orientations, flats etc. then the program automatically will generate the Gcode to make such a panel or other multi-hole device.  One can also add other shapes to the program.  If you have not seen it,  *HERE* is the thread for the VFD conversion which employees this control front panel for my lathe.  And,   *HERE* is the thread for the Excel Gcode generator.  

Having finished that to some degree I wanted to continue with my education.  So I have been working on an Excel spread sheet which will calculate all of the TPI values that one can obtain with a set of gears for a given lathe.  It also provides the TPI values that one would get if he were to use the Power Feed rather than the lead screw and 1/2 Nut.  Yes, I know there are reasons one might not want to do this, but when one is desperate he might use it and if so one would like to know the Feed rates to better than one or at most two digits.  I have found that what is on the front of the lathes is not very exact!  In doing so I decide to list the X-feed rates as well and I did not want to put out something that was wrong.  So away I went.  The exercise has also allowed @Ischgl99 and I , and hopefully now, others to develop an understand what is inside the apron gear box for these two lathes. 

So far my tool calculates the correct TPI for any set of external gears that one might have as well as all of the standard thread sizes.  It generates a large table of TPI values (and all other associated distances etc).  This can then be searched or just printed as a table for reference. I did these calculations for these two lathes using the external gears that come with them plus a 35T for the 1340.   For the simpler 1340GT there are 5122/2 TPI values using the split nut and the same number using the feed bar.  A minor fraction of these are redundant, but I will let the user deal with that.    The 1440GT has a different and more complex gear box and so it has 6144 using the split nut and 1536 using the Feed bar.  I have a program that will search this list and find all of the TPI values around a value of your choice.

Now I am trying to make the spread sheet as user friendly as I would want it to be.  After that I will post it for everyone to have and if someone wants to add another lathe that would be great.  I might even do it for them if I know what it is and how its gears etc are configured. 

I do not know what lathe you have, but would you be interested in getting a table, spread sheet, etc.  ?  With or without exact feed rates!


Dave L.


----------



## aliva (Feb 14, 2022)

*B2*
I will commend you on the amount of effort  and passion you've put into this. But at the end of the day, in my case , on my lathe I can't change any of the ratios as its preset by the gears installed. So I can't see the value of knowing the exact ratio. I'll grant you its a good exercise in ratios, but again in my case  no real value that I can see. 
Thank you for the offer of the table, spread sheet, etc. but I'll have to decline. I'm sure others may find that information useful.


----------



## B2 (Feb 14, 2022)

@aliva 
Thank you, and I am sorry you have no way to change external gears.  I understand you have declined the table offer.  No Problem.  

However, may I ask what model lathe you have and why you cannot change any of the gears.   Is it simply because you have no extra gears or is it the feature of the lathe?  If you can direct me to a manual for your lathe I would like to take a look at it.  I have been looking at several lathe versions to see how much they differ and if they can be incorporated into my spread sheet easily.  Usually the manuals are poorly written or incomplete and it is difficult without actually having the lathe to test.  Norton gear boxes are easy to incorporate, but the gear box is much more straight forward than that of my lathe.  

In addition to my PM1440GT I have an older South Bend 10K which I have had for several years and have enjoyed it a lot.  It has a great Norton Gear box on it along with 7 factors of 2 .... so that it allows a large number of threads and feed rates, 10x7=70.  However, I have no extra external gears so most metric threads have always been a poor approximation.  At some point I may recondition it so that the X-feed works much better and then I might get a 127/120 exchange gear and a few other external gears.  TBD.

Again, thank you for your comments.

Dave L.


----------



## Ischgl99 (Feb 14, 2022)

B2 said:


> @aliva
> Thank you, and I am sorry you have no way to change external gears.  I understand you have declined the table offer.  No Problem.
> 
> However, may I ask what model lathe you have and why you cannot change any of the gears.   Is it simply because you have no extra gears or is it the feature of the lathe?  If you can direct me to a manual for your lathe I would like to take a look at it.  I have been looking at several lathe versions to see how much they differ and if they can be incorporated into my spread sheet easily.  Usually the manuals are poorly written or incomplete and it is difficult without actually having the lathe to test.  Norton gear boxes are easy to incorporate, but the gear box is much more straight forward than that of my lathe.
> ...


Dave,
I think he was referring to the apron gears, since those are fixed, the ratio between the longitudinal feed and cross feed is also fixed.


----------



## B2 (Feb 14, 2022)

@Ischgl99 

Thanks, maybe your are right!?  None of us have much of any way to change the Apron gearing... or need to do so!  Either way I am still interested to know what kind of lathe he has.

Are you interested in my spread sheet?  At some point I will want a couple of people to check it for errors and to make suggestions to make it useful.  I have already put your PM1340GT properties in to it.  I do have a question however about the FEED settings. It is my understanding that the FEED rod turns no matter what position you have the gear box set to.  Also,  there is a rotating knob that has two positions, FEED or Lead screw.  However, I doubt that it affects the feed bar.  It probably only disengages the lead screw?  So the FEED bar rotational rate is both a function of the two parts of the Norton gear box.  IF so then the FEED bar rotational rate set has just as many rates as does the lead screw set? 

Dave L.


----------



## aliva (Feb 14, 2022)

Ischgl99 said:


> Dave,
> I think he was referring to the apron gears, since those are fixed, the ratio between the longitudinal feed and cross feed is also fixed.


IschgI99 is correct I'm referring to the apron gears. I can change the main gears in the head stock for metric threading if needed, which I've done once.
My lathe is a King industrial 12x36.
https://files.kingcanada.com/catalog/products/servicemanualxm/KC-1236ML service manual.pdf


----------



## B2 (Feb 14, 2022)

Thanks,  The apron gears look similar, but not the same tooth numbers as the PM1340/1440.  
Dave L.


----------



## Ischgl99 (Feb 14, 2022)

B2 said:


> @Ischgl99
> 
> Thanks, maybe your are right!?  None of us have much of any way to change the Apron gearing... or need to do so!  Either way I am still interested to know what kind of lathe he has.
> 
> ...


I have the 1236T, but everything we are discussing is the same as the 1340GT.

The feed shaft and the leadscrew do not rotate at the same time, the selection nob selects feed, none, or screw cutting.  There is a gear (#34) on shaft D of the attached drawing that slides to engage a corresponding gear on either the shaft for the leadscrew, or the feed screw.  

The power transmission through the Norton gearbox goes from shaft C to shaft F through the lever for selections A-E, shaft F turns gears #5 and 6, that then drives the output shaft of the gearbox that has the gears for speed positions 1-8, and is controlled by the selection lever for positions 1-8.  The shaft that carries the gears for 1-8 also has the output gear that drives the feed or leadscrew depending on the position of the output gear mentioned above.


----------



## B2 (Feb 17, 2022)

@Provincial


Provincial said:


> The Jet BDB-1340A lathe seems the same as mine, except the quick change gearbox has been modernized, while mine has the Norton gearbox.


After looking at the JET-BDB-1340A manual, ( I know your MM1340LB is different in that it has a Norton Gearbox, but that is an easy fix in my spreadsheet... if I know its values.) I think I figured out the FEED to X-FEED ratio and some other things. The main gear box is similar to my PM1440GT only in appearance, but I think I figured out the ratios for its operation. Also, the external gear list probably different from your machine.  The apron gear diagram is more complex and has completely different gears than in the PM1340GT/PM1440GT.  Furthermore the the cross feed gear tooth number is missing as is the TPI of its lead screw.    

Never the less, I was able to fit these all together and I have not put it into my spread workbook.  I have assumed that the cross feed gear tooth number and lead screw TPI (10) is the same as mine.  When I assume this, amazingly, the ratio of Feed rate to cross feed rate is identical to mine! This is even though the gear teeth numbers are considerably different!  I could hardly believe this.  Anyway, the manual had a few feed and cross feed rates shown on the face plate and when you take the ratios there it varies substantially with few digits.  One of them was way off compared to the others and by sort of averaging them it gave a ratio of 2.91.  However, my analysis gave the same as the other PM lathes I mentioned above, which is 3.1354084....

If you want to send me the Norton fundamental TPI values (commonly the top row of TPI values in a lathe table) and the factor of two values you have on the name plate as well as complete list of the external gears that you have then I will put that in to the spread sheet as well.   Then when I finally finish the thing and post it you will have it built in.  If you would rather send me a photo of the plate on the lathe with the external gear list I can use that.  

Dave L.


----------



## Provincial (Feb 17, 2022)

Dave L., Thanks for following up on this.  Since I posted, I noticed that my apron feed gear train does not have the extra countershaft (identified as F in the Jet BDB-1340A parts manual), and the lack of that gear train means the rest of the gearing is much different.  Also, my lead screw is 8 TPI, which could be different from the PM lathes.  I discovered that my cross feed screw also has 8 TPI, and the cross feed dial is graduated for two times the travel (reduction in diameter of the work), hence it has 250 graduations.

I just checked the apron cross feed reduction ratio.  For 10 turns of the feed shaft, the cross feed dial moves .370, or .037 per revolution, which is .0185 travel/revolution of the feed shaft.  This should be .148 turns of the cross feed screw per revolution of the feed shaft.  This could be off slightly, as I didn't have a precise reference point for rotating the feed shaft.

The gear train entering the Norton box breaks down to:
Spindle          50 tooth
Idler               26 tooth/21 tooth
Tumbler        50 tooth
Top change   40 tooth
Big Idler        127 tooth
Bottom Idler 40 tooth

I've attached photos of the Inch gear positions and the feed positions
I'll be out of the loop for about a week, starting Friday morning.

Jock


----------



## B2 (Feb 17, 2022)

@Provincial 

Jock, I will take a look.  Yes, the F shaft is an option and I do not find it being uses elsewhere either.  So I have been ignoring it.    I did not use it in my analysis of the JET machine either.   The 1340's have an 8 TPI lead screw but the 1440 has a 4 TPI lead screw.  Your name plate implies that your lead screw is 4.5TPI not 8 or 7.    The more important issue is that for the FEED drive both machines use the FEED bar which only has a notch down the center, no threads unless you want to call this a "0 TPI" lead screw.  I have been calling it the FEED Bar.  Also important is that your cross feed is an 8TPI where has the other machines are 10TPI. Are you sure about this?   From your plate you have 8 fundamental threads and 5 factors of two multiples, which is pretty standard. The PM1340 also has 8 and 5.   But the fundamentals for the PM1340 are:  4, 4.5, 4.75, 5, 5.5, 6, 6.5, 7. Your machine is slightly different:  4, 4.5, 5, 5.5, 5.75 6, 6.5, 7 as it is missing the 4.75 but has a 5.75 instead.  

I looked at the FEED rate table.  I believe that if you use the first row of the TPI table in the following formula you will get the exact FEED rates:
(0.1005/(TPI#)*(4)).   So if you use the exact number and take ratios x-feed rates you will find variations ranging from 2.809 to 3.071.  Some simple observations:  However if you only look at the TPI which are 4,5,5.75, and 6 you will find you get pretty good agreement at 2.903.  That is not to say that this number is correct.  It may just be a coincidence.  However for TPI 5,5.75, and 6 your get exactly the same number each time: 2.903043478.   However you will note I normalized these by the first feed rate of 0.1005/4.  If instead you used the 5 TPI value, to do the normalization 0.0805/5 you find similar effects but the ratio of feed rate to x-feed rate changes a bit to 2.913043478.   So who is to say which is correct.  I cannot say for sure if this is different from what you measured or not.  Maybe you can.  

I am not for sure how to proceed, since when I look at the photos in the JET book the spindle and change gears to not appear as you described. they look considerably different, but it could be that they just have different gears mounted.   Perhaps you could write this a bit differently for me telling me which gears touch the next gear when you are set up to get the 4 TPI thread.  Please make the Spindle gear the last one (50T) in a string of touching gears.    Or maybe a sketch of how they mesh.  If there is an intermediate gear between only two then it has no effect 40-127-40 on the over all turns ratio as the two 40T gears turn at the same rate. .   For example starting from the input to the gear box:  40 to 127 to 40 to 50 to 26 which is tied to 21  and then the 21 to 50 at the spindle? Or is it that the go 40 to 127 to 40 to 50 to 21 which it tied to 26 which touches the 50T spindle?   So in the first case the ratios read:  (40/127)*(127/40)*(40/50)*(50/21)*(26/50).  We see that the over all ratio is simply (40/21)*(26/50) .  i.e one turn of the shaft into the gear box results in (40/21)*(26/50) turns at the spindle or 0.8*(26/21)=0.9904.  Where as the alternative yields (0.8*(21/26) = 0.64615.  

Lastly you might count the length per tooth on the RACK.  It turns out to be important.  In the JET manual it says it is a 2mm thread so the length per tooth is just 2mm*Pi()=6.2832mm.  This 2mm comes from the JET manual 2mm, 13T gear that is suppose to be engaged to the RACK.  When I did mine I it seemed that the gear teeth repeated pretty well at 330mm with 70 teeth counted.  330/70=33/7=4.7143 ==> 1.5mm*pi()=4.712389mm.   

I too am going to be out of the loop for several days starting tomorrow.


----------



## Provincial (Feb 18, 2022)

Breaking this down to separate questions.   

I measured my lead screw, and confirmed that it is indeed 8 TPI.  I had measured the cross feed, and it moved exactly .125" for one turn of the screw, also 8 TPI.  I checked the rack, and it seems to be 6 TPI.  When I get a chance, I'll put a dial indicator on the carriage and see how far it moves for 10 turns of the FEED bar.

The tumbler gears (moved by the "forward/reverse" lever between the spindle and the gearbox operate differently in forward than they do in reverse.  In the forward position, the 26 tooth gear engages the 50 tooth spindle gear, and also the 50 tooth tumbler gear on the shaft the tumbler assembly pivots on.  The 26 tooth gear acts only as an idler, so it does not affect the reduction ratio of the gear train, and the tumbler gear rotates at the same speed as the spindle.  1:1.

When the lever is in the "reverse" position, the 21 tooth gear engages the spindle gear and also the 26 tooth gear.  The 26 tooth gear engages the 50 tooth tumbler gear.  The ratio should be 50/21*21/26*26/50, which is also 1:1, but makes the tumbler gear rotate in the opposite direction.

The tumbler gear is keyed to the 40 tooth "top" change gear, so that gear makes one rotation with each rotation of the spindle.  It seems to me that the first gear that needs to be considered in analyzing the gear system it that "top" change gear.  All the gears before the "top" change gear can be disregarded.

As long as the "top" and "bottom change gears have the same number of teeth, and both engage only the 127 tooth gear which is acting as an idler. the input ratio from the spindle to the gearbox is also 1:1.  Hence, the input shaft of the gearbox rotates at exactly the same speed as the spindle.

My gearbox with the Norton 2-lever system is quite different from the later Jet and PM units.  In practice, it works the same way, but the controls are different.  Separate from that, my system is laid out with slightly different gearing in order to cut 11-1/2 TPI for American NPT pipes.  I have not determined a use for any of the other threads available in the #5 column.  In doing this, they gave up having the 4.75, 9.5, 19, 38, 76 thread options.  I believe that PM (or more likely the OEM) decided that it was more important to have the 4.75 thread multiples available, than have the ability to cut 11-1/2 NPT threads.  David's excellent PDF of the PM1340 thread combinations does not show any use of the #3 column of options to cut a metric thread, and they do not show up in British Standard or Whitworth, so perhaps they are used somewhere else?  I am beginning to wonder it this is a holdover from someone (perhaps dyslexic, but more likely having a poor understanding of the English language) confusing "4-1/2" with "5-1/2" in the original Taiwan cloning process.  Since they were patterning on English machines, and the British Standard Pipe threads are 11 TPI instead of the 11-1/2 of NPT, the lack of that option may have been overlooked.

Interestingly, the Atlas 10" and 12" QCGB's have a 9th column, with threads of 7.5, 15, 30, 60, and 120!

At any rate, I discovered that the Metal Max metric thread chart shows that, using 40/127*120/40 gear train, setting C-6 cuts a 1.0MM thread.  C-6 is the 24 TPI setting.  This is identical to David's settings for the PM1340. This makes sense since they both have 8 TPI lead screws.  

I analyzed my feed box a little differently than you did.  I saw that position B-1 was 8 TPI, which matched my lead screw.  Your lead screw being 4 TPI made using A-1 logical for you.  I made a chart of the ratio of each position in relationship to the "root" setting.  I started converting it to revolutions of the lead screw per revolutions of the input shaft of the gearbox.  I call it "QCGB Analysis for Dummies" because it takes out the need to analyze each gear inside the gear box.  I assume it isn't precise, since the gears were chosen to be as close a practical from a manufacturing standpoint, but if it was close enough for a manufacturer, it should be close enough for us in the hinterlands.  by working backwards from the lead in inches of a metric thread, I should be able to find the input ratio needed to match a gear position.  

It will be a week before I can continue this.


----------



## B2 (Feb 19, 2022)

@Provincial

Thanks,  I will take a look when I can.  I think I can understand how you have explained it this time. Since the two 50T gears and the 21/26 gears never get changed I think your lathe functions just as the PM1340GT and the PM 1440GT.  etc.  

Do you have any change gears which you would switch out for the 40T and 127T gears so that you can make other threads.  I would think that your lathe originally came with a set of change gears.   If not would they be the same as in the JET lathe?   

When you return it will be nice to see your FEED rate data vs FEED bar rotation.  Of course we have what is on the lathe plate and if you are correct about the 8TPI (1-B gear setting) being the one where the spindle matches the Lead screw it may also be the setting where the Power Feed bar rotates once per Spindle turn.   When you return and I return....


Hi Folks, 

If you have a PM1340GT and have been following this thread you might be interested in this table that I just provided to another HM member at this original thread.


B2 said:


> Perhaps what I can send you, at this time, is a pdf print out of a table of all of the threading options/possibilities for the standard set of gears plus the 35T for the PM1340GT.


Dave L.


----------



## Provincial (Mar 1, 2022)

Dave, I got a chance to measure the feed rates on the Metal Max 1340.  I used 10 revolutions of travel and then divided the measurement by 10.  Here are the results. 

*Carriage Travel:*
Feed per revolution of Spindle with setting A-1 is 0.1005"
Feed per revolution of Spindle with setting A-1 according to the book is 0.1005"
Feed per revolution of the feed bar is 0.055"
Handwheel graduations are 0.010" per mark, 0.560" per revolution
Pinion gear (mating to rack) has 13 teeth.

*Cross Feed Travel:*
Feed per revolution of Spindle with setting A-1 is 0.0378"
Book Feed per revolution of Spindle with setting A-1 is 0.0345" 
Feed per revolution of feed bar with setting A-1 is 0.01875" (I think this is really 2:1 ratio)
Cross Feed screw has 8 threads per inch and travels 0.125" per revolution of the handwheel
Handwheel is graduated 0.250" per revolution, and 0.002" per graduation, which is proper for indicating diameter reduction of the work.

I used a cheap long travel dial indicator, so between alignment error and accuracy of the indicator, there is possibly considerable error.  The difference between book cross feed and measured cross feed is 0.033", which is far more than my margin of error.  I may have made a mistake in measuring or calculating, but I am sure that I took out all the backlash before starting to measure.  I'll have to repeat this measurement.  It is also possible that the book/plate on lathe is incorrect.

I used the A-1 setting because it was the coarsest feed gearing, and should show errors best.  I put marks on the chuck mounting surface and the bearing retainer for a spindle position reference.  I put a block next to the feed bar to reference off the keyway.  

I tried to measure the carriage travel for one rotation of the 13-tooth pinion, but I am not confident enough of my measurements to post them yet.  When I get reliable measurements, it should give an idea of the pitch of the rack, and help calculate the gear reduction of the drive.


----------



## jwmay (Mar 2, 2022)

Reading through this thread is like watching computers talk to each other. What an interesting experience! I'm gonna go make my lathe cut metal at whatever feed rate the last guy left it set for. Lol


----------



## B2 (Mar 2, 2022)

@jwmay

Let us know what cut that metal into!!!!

@Provincial

Hi,  I too have returned, but I have a lot on my plate for the next few of days.

Since your pinion gear is 13T then this would dictate the Rack tooth spacing to match.  This is as in your manual. It shows the pinion gear to be 1.5mmx 13T.  The length then of a tooth on the rack would be 1.5mm*Pi()=4.7124mm.  This would be the same as what @Ischgl99  found for his PM1340 and I found form my PM1440.  So I looked again at some of your lathe numbers and diagrams.  If you take the ratios of the all of the FEED to X-FEED numbers on your lathes plate you will find that it varies several percent.  These may just be the approximations that they made.  However, if you assume that the FEED numbers are pretty close, and they are if you accept that the number 3 gear setting value is correct,  0.0804.  I calculated what you would get for the other feeds as you changed the numbered gear levers and they in excellent agreement with the table values.  Any disagreement is in the 4 digit.  So even if these FEED rates have errors in them they are very consistent.    So accepted 0.0804 as been pretty good even if it is not necessarily accurate.  Try as I might I have not yet found a way to combined the gears in the apron to yield the FEED rates.

I then went back and looked at the gear diagram and it appeared to me that the gearing ratio for the X-FEED could be calculated to be:   =(1/22)*(40/46)*(46/13)*0.125=0.017482517= (0.034965/2).  (Note that this 0.034965 is very close to the x-feed rate table for gear handle position #1, 0.035.  The other table values are not as close, but I think this is probably because the table is not accurate.)   In this gearing ratio equation 1/22 represents the single thread that is turned on the gear touching the FEED BAR Worm gear per bar turn.  The (40/46) are the gear tooth counts for meshing parts #26 to #22 and then (46/13) is the part #22  driving the x-feed lead screw gear.  The 13T gear is a bit of a leap of faith as the diagram does not provide it, but this is the same number that is in the other lathes.   The 0.125" of course is the TPI on the x-feed.

I then took the ratios that this number and the 0.0804 number would yield as a function of the numbered gear levers and found that they, of course, were very constant.  That ratio is of FEED to x-FEED is  2.8743 exact.  However it would be nice if we could figure out the apron gearing for the FEED process.

So, I am going to seen to a private message with a spread sheet in it so that you can look these calculations over and tell me if you think they are ok.

Dave L.


----------

