PM1236 gears

[Larry$]

Perhaps you can post your lathe manual and pictures of the gear tables that are on the front of the machine so that I could understand better.

On this image columns 1 to 8 are positions on the lower gear box. Gear positions and # of teeth are shown on the left side with 127 idler gear. Input on the top gear, out put on the lower gear. Leaver with position A or B is a doubler on the output of the main gear box. Lever positions C & E output the lower gear box to the threading shaft. Positions D & F out put to the feed shaft. #s above the diagonal line represent the carriage travel along the ways in "/rev of the spindle. #s below the line are cross feed movements "/per rev of the spindle.

The right hand image shows the travel of the carriage in mm per rev of the spindle. The change gear diagram shows that the upper, input, gear is driving the 127 tooth idler and the 120 idler gear which is fixed to the 127 gear is driving the lower change gear. #'d columns are the lower gear box knob position for the gears in there. Example: both change gears 40 tooth, out put lever C and upper gear box out put B gives a thread pitch of 2.4mm. There are some common metric thread pitches missing.

I had thought of making change gears for some of the misssing mm threads but to get an even # of teeth the gears got too large.

 

[B2]

Hi @Larry$

Your lathe controls operates considerably different from the ones I have been working with. I did manage download the manual from PM. (They had removed the link on the web page showing the lathe, but had not removed it from their server. ) So when I googled the lathe model I found the file. However, the manual is pretty sketchy. There are no, good ,pictures of the front of the lathe and so it is very difficult to see the knobs etc. as to the details of the gears operations. I figured out a little from your posting above.

On this image columns 1 to 8

But still do not have a sufficient concept of the operation. If you want me to take a look at it for you please provide a number of pictures of the front controls (all of them) which are sufficiently clear that I can read the settings, letters, numbers, etc. Right now I do not even know which knobs have which settings.

Anyway, it appears you have a Norton gear box 1-8. This is very handy and means that you potentially have lots of hidden gears settings. It also looks like there is a knob that must be labeled A, D, E, and F? If that is true than you should have at least 8*4 =32 fundamental thread setting plus the doubling factors. Plus there seems to be stuff that I do not understand yet.

Dave L.

 

[Larry$]

please provide a number of pictures of the front controls (all of them) which are sufficiently clear that I can read the settings, letters, numbers, etc. Right now I do not even know which knobs have which settings.

First photo shows the lower gear box, the left lower corner knob is what engages the connection to the knob labeled 1>8. The right hand knob selects the feed shaft or threading shaft and its speed (just double or 1/2.) O is both shafts disconnected (CE & DF for threading or power feeding on the charts.)

The Rt, photo shows the 3 spindle speed selector levers @ the top. The lower concentric levers show the A/B from the charts (doubling or 1/2 out put to the lower gear box) The other concentric lever is for reversing the feed shafts.

Spindle speeds are shown.

 

[epanzella]

I have a PM1236 on order as well. I think there are minor gear changes needed. If it really starts driving you crazy you could do an electronic lead screw upgrade (ELS).

I think to completely get away from gear changes you have to get into the really big (and expensive) lathes.

The Grizzly 12x36 (G4003G) does all imperial pitches from 4 to 112 tpi without swapping gears. Metric pitches require a few gear changes. I always thought the PM and the Grizzly were nearly identical but I guess there are some differences. Not a big deal to change gears if they have a decent slip fit. My gears were tight enough to require a puller and that definitely suck. I bored a thousndth or two out of each one and now they change fast.

 

[B2]

Hi @Larry$

the left lower corner knob is what engages the connection to the knob labeled 1>8.

I have a couple of questions:
1) I do not under stand the function of the "left lower corner knob". If all that it does is turns off the function of knob 1-8 does this mean that in one position the lower left knob stops all the gear motion, i.e. the lead screw from turning and the Feed bar from turning? But isn't this what the "O" position on the C-D-O-E-F knob does? Having this knob and the O knob setting would seem to be functionally redundant.???

2) I would like to confirm what you said about the C-D-O-E-F. You should turn on the lathe and check, do not just rely on what the manual or chart shows. The answer is important to determine if there are any hidden threading values that can be reached via the gear box knobs.
i)---- In the O Position, neither the Lead screw nor the feed bar is turning?
ii)---- In the C and E positions, ONLY the Lead screw is turning?
iii)---- In the D and F positions, Only the feed bar is turning?
iv)---- What I am really asking is: Is any positions, of any set of levers and knobs, where the Lead screw the feed bar both turn at the same time? If they never turn at the same time then it appears that the lathe only has the one set of gears (1-8) where the non-factor of two rates are changing and all other conditions are just multiples of 2, or one must change the external gears to change the rates. The multiples of 2 show up in the charts via lever A-B (x2), or by changing from C-E (x4) of by changing the external gears by ratios of multiples of 2 (25T/50T Vs. 40T/40T) in the pictures of the charts). While the metric chart only shows a few values for any set of external gears, there are metric rates for each of the Knob positions (1-8), they are just not the standard values and are not listed in the charts. My spread sheet will generate then as well as all possible values using the external gears.

3) Is your PM-1440HD lead screw 8TPI?

4) The manuals imply that the external gears that came with the lathe were 25T, 30T, 32T, 40T, 50T plus the 120/127 exchange gear. Is this correct? Do you have others that should be put into the spread sheet?

5) I searched on 1440HD found a lot of search hits, but little new information. So the PM manual shows that the concentric levers (A-B lever in your photo of the top have of the lathe controls) has three positions for the outer handle not just two. Are there three positions, but only two letter labels. If so what does it do? So it appears the the manual I found on the PM1440HD at the PM site is not exactly your lathe! Is that the same manual that you have?

Comment: The feed and X-feed rates listed in the table are only good to 2-2.5 digits while the X-Feed rates are only good to 1.5-2 digits. The leading zeros do not count in the accuracy. Unless we know the exact gears and their arrangement in the carriage we can only use the numbers in the Feed/X-Feed tables to estimate the over all gear ratio. If you were to try to use the feed bar and and feed rates to make threads then the predicted accuracy would be no better.


Dave L.

 

[Larry$]

I have a couple of questions:

1. True, it stops all gears, shafts down stream from turning. the O knob setting would seem to be functionally redundant.? True I don't use that.
2. iv) True only the shafts shown turn, not both. True about all of the doubling locations. Using more than one doubling is useful: 8-16-32-64-128 are all common threads.
"there are metric rates for each of the Knob positions (1-8), they are just not the standard values and are not listed in the charts." True.
3. "Is your PM-1440HD lead screw 8TPI?" Yes
4. your list of change gears is true, there are two 40 tooth gears.
5. the center position of A>B just has neither engaged. It prevents simultaneous engagement.
I think the various locations where the center positions disconnect everything are simply to make sure that both locations don't get engaged half way & cause something to break. On the CDOEF control it is possible to connect both C&D and both shafts spin but that is just the result of the gears sliding form one to the other, there is no detent there and no harm since it drives two separate shafts and nothing can get locked up that would cause a problem.
"there are metric rates for each of the Knob positions (1-8), they are just not the standard values and are not listed in the charts." True.
"The leading zeros do not count in the accuracy." I think I have to debate that statement. The zeros after the decimal point and before the significant numbers indicate an order of magnitude difference in accuracy for the significant numbers. If on a drawing you see 0.0001 it means holding an accuracy of tenths as opposed to if they wrote .1 but if they wrote .1000 it would then indicate an intended accuracy of tenths. Zeros do count!

 

[B2]

Hi @Larry$

Thanks. I need to think about what happens when both C & D are engaged. It is possible that it might be useful. If the contacting gears on both the lead screw and the Feed bar are the same then I would expect them to both turn at the same RPM and if this RPM is ratios are the same 2x found in E/C & F/D then maybe there is nothing to be achieved by using this intermediate C & D engagement.
Anyway, this flaw was not what I had in mind when I ask the question.

Anyway, based upon my estimates from the feed rates. I think the carriage Feed rate has a similar set of gears in it as my PM1440GT which are also the same in the PM1340GT. In this case the gear train ratio back to the main gear box was found to be: (1/18)*(22/44)*(22/50)*(13)*1.5*PI()/25.4 . Where the last term, 1.5*PI()/25.4, is the connection to the rack teeth. The 1/18 is the connection to the worm gear at the lead screw. Likewise, I was able to compare my 1440GT X-feed drive gear train ratios and believe that yours is slightly different from mine, but can be expressed as: (1/18)*(22/44)*(44/18)/8 . Where the last (1/8) is the TPI of your x-feed lead screw and the last 18T gear connects to that x-feed lead screw. Anyway, these two expressions seem to yield the values in the tables to within acceptable accuracy of our knowledge of the table values. Perhaps they are exact???!!! Until you take your carriage and the saddle apart and analyze the connections, or find a believable and understandable parts diagram, we will not know for sure. There are not parts drawings in the PM manual that I managed to download.

Since at the carriage control you have a choice of whether you connect to the lead screw (standard threading) or to the Feed bar you then have the choice of using either to actually make threads. Using the thread bar may not be the standard, or the good way, to make threads, but it does move the carriage and some sort of a thread will result. These are usually at a higher TPI rate than maybe useful to you because the lead screw is 8TPI and the feed bar is sort of like 1/infinity TPI. I have an old Southbend lathe and it does not have a Feed bar, only a lead screw. One feeds and threads with the single lead screw. However, it has a compound Norton Gear box where one of them provides 7 factors of 2 and the other one provides 10 separate gears similar to your 8. It has an extra 6.75 and a 7.5 TPI . I wish I had this on my 1440GT. The last, and finest, thread in the label is 480TPI or a feed rate of 0.0007in/turn. There are probably few people who need that dense and, by definition, shallow a thread.

Comment: When I used the word accuracy in the feed tables I meant to be referring to how well we knew the value. For example, if the listed cross feed rate is 0.0014 we do not really know if it is 0.00144999 or if it might be 0.00135000 we also do not know if they rounded up, rounded down, or just truncated to get the 0.0014 in making the table. However it appears, by comparing their numbers as the use factors of 2 in gears, that they use the standard convention that a remainder of .5 or greater is rounded up and less that .5 is rounded down. So this means that the accuracy in our knowledge is (0.00144999-0.00135000)/0.0014 or ~0.0001/0.0014 or 1/14 = 7.14% error. You might not want to have to tolerate that on a thread.

I worked on it quite a while this today so I will see if I can finish generating an Excel work book for you.

Dave L.

 

[B2]

Oh, by the way, I came across and old advertisement for a GRIP-1440HD LATHE

KBC,GRIP-1440HD LATHE W/NEWALL NMS300,6-269-007-N3,KBC Tools & Machinery

KBC,GRIP-1440HD LATHE W/NEWALL NMS300,6-269-007-N3,KBC Tools & Machinery

www.kbctools.com

Which appears to have a similar gear box to your 1440HD.

There are a lot of 1440HD lathes listed on the web, but most of them do not look like yours.

 

[Larry$]

You might not want to have to tolerate that on a thread.

Understood.
Thanks, Looking forward to trying the spread sheet. I'm running open office for spread sheet. I think it runs the same as Excel.
I'm making bread right now, just came out of the machine, damn it smells good.
Amazon just delivered some stuff I ordered for my metal working. Got a small set of imperial spiral taps for power taping on the mill. Made in Korea. They look good. Power taping always has some risks!

 

[B2]

Love to have a piece of homemade bread!

I think I totally screwed up the guess on the x-feed gears. What I had gave me the wrong number as indicated in the tables. However, on other lathe models I commonly see poor values for the x-feed tables. This is going to take a bit longer than I though!

Power taping.... I have done a lot of mill hand tapping. Mostly 1/4-20 or 6-32. I have always wished I had that power tapping ability, but I have little control on the speed/phase of my spindle. Just a VFD into an inductive motor. I have a PM940-VS-CNC. (Spindle is gear driven not belt.) What do you use at the Mill?