# Funny Snafu With My Pm-1340gt



## AirWolf (Dec 25, 2015)

Although I have had my lathe up and running for a month or so - just noticed today the rather odd numbering snafu on the handwheel dial... maybe the engraver operator had a hick-up or sneezed?    Anyone else have one like this?


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## ogberi (Dec 25, 2015)

I can just hear the conversation you have with yourself..."Okay, just 12 thou more, so that's 48."   (makes cut, mikes part) "DANGIT!  The *OTHER* 48!


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## kd4gij (Dec 25, 2015)

Install a DRO and you will never look at that again. Or call Matt he should send you a new dial.


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## rwm (Dec 25, 2015)

It was made friday at 4:50 PM.
R


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## AirWolf (Dec 25, 2015)

kd4gij said:


> Install a DRO and you will never look at that again. Or call Matt he should send you a new dial.


 I do have a DRO - probably why I never noticed this before...


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## Bob Korves (Dec 26, 2015)

A bit off topic, but why didn't they use a lead screw that would have 100 graduations per revolution?  And why do the graduations not add up between the stamped markings?  How do you get 10 graduations between .48 and .56?  I have no idea what brand of mill it is or where it was made, but that dial tells me it is a POS!


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## AirWolf (Dec 26, 2015)

No, it is NOT a POS... It's a VERY NICE  PM-1340GT - as clearly stated in the heading of the thread.
It's just a simple snafu dude... and if you take a minute and look at the graduations - they are .004 each... some very basic math IF you use the correct .48... and not the second "mistake" one.


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## Bob Korves (Dec 27, 2015)

AirWolf said:


> No, it is NOT a POS... It's a VERY NICE  PM-1340GT - as clearly stated in the heading of the thread.
> It's just a simple snafu dude... and if you take a minute and look at the graduations - they are .004 each... some very basic math IF you use the correct .48... and not the second "mistake" one.


I take back the POS statement, AirWolf.  Uncalled for and I apologize sincerely.  I actually know nothing about that machine beyond the picture of the dial you have posted.  Still, why would one revolution be .58 of whatever units they are supposed to indicate?  Is there some usefulness to that?  Dial up 2.424 units for me real quick...


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## Bob Korves (Dec 27, 2015)

OK, I have figured out that you have a 13x40 lathe, and that is the carriage hand wheel in the pic.  I get it, and I feel some deja vu coming on.  I have a Kent KLS-1340A (13x40") lathe with a carriage hand wheel which reads 55 units of .005" per revolution, along with a metric dial as well that does not come out to anything useful at all.  When I first saw that on my lathe I said "What a POS!"  Good enough words for that design on my lathe...

Now I have a magnetic back long travel dial indicator indicating the carriage movement so I can get some useful idea of how far I am moving the carriage.  Sure can't figure it out from the hand wheel dials...


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## joshua43214 (Dec 27, 2015)

Bob Korves said:


> I take back the POS statement, AirWolf.  Uncalled for and I apologize sincerely.  I actually know nothing about that machine beyond the picture of the dial you have posted.  Still, why would one revolution be .58 of whatever units they are supposed to indicate?  Is there some usefulness to that?  Dial up 2.424 units for me real quick...


This is the carriage feed, they are usually something odd in terms of distance per revolution.
It actually moves 0.600" per revolution, not 0.58". So 2.424" would just be 4 turns + 6 ticks.
The pic does not show that the minor ticks are 0.004", and 0.020" per major tick.
I admit it is odd, but if you are smarter than the machine it is not difficult.

It is really impressive how smooth and precise the carriage wheel it on this lathe


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## Bob Korves (Dec 27, 2015)

joshua43214 said:


> This is the carriage feed, they are usually something odd in terms of distance per revolution.
> It actually moves 0.600" per revolution, not 0.58". So 2.424" would just be 4 turns + 6 ticks.
> The pic does not show that the minor ticks are 0.004", and 0.020" per major tick.
> I admit it is odd, but if you are smarter than the machine it is not difficult.
> ...


It looks like the handwheel should have been marked .48, .52, .56, and then there is a half distance interval that would be .58.  If it is truly supposed to be .60 then the entire graduation is wrong.

It is not about whether you are smarter than the machine, it is about how many parts end up in your scrap bin due to confusion resulting from poor design.  This is not a metric conversion issue, the rack is pretty obviously imperial.  For less than one revolution it works OK.   I can go three turns of .55, 1.10, 1.65 on MY 13x40 import lathe, and then add seven .005 graduations to reach .200, but it is quite easy to screw that process up.  It is just poor design.  On my mill I crank the X handle around one full turn for .200, five full turns for an inch.  Stick a fork in me, I'm done...


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## mksj (Dec 27, 2015)

I have to agree with Bob K on the dial issue, it is 0.580" per evolution on this machine, which seems quite odd. Trying to keep track at 0.004" per mark is pretty tough over distance, I could have something to do with the feed gearing/travel when it is engaged? After a couple revolutions of a dial these days, I loose track if it was 3 or 4 turns, let alone counting the marks (if I could see them). On my mill they have metric pitch leadscrews with imperial dials, couldn't figure why the dials where off until I found that they didn't have imperial leadscrews. The mill manufacturer (Optimum) never corrected the problem and still sells the same machine these days. Thank god for DROs. I still would request a replacement dial to make the machine correct.


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## sanddan (Dec 27, 2015)

mksj said:


> After a couple revolutions of a dial these days, I loose track if it was 3 or 4 turns, let alone counting the marks (if I could see them).



That's me to a tee! It's the biggest thing I struggle with machining without a DRO. My Enco 12x36 lathe has graduations that are about a 1/4" apart. I've never looked at them when running the lathe I either mark the part for length or use a mag backed dial indicator. Can't wait to have a DRO on the lathe too.


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## RJSakowski (Dec 27, 2015)

The Grizzly machines have metric lead screw with SAE approximations.  The G0602 lathe has dials marked with .001" divisions but they are actually .025mm or .000984".  Not a problem when you're only moving a few thousandths but a .006" error over an inch.  AS I recall, the G4000 lathe and the G0755 mill have the same setup.  

It isn't too bad to deal with because if you interpret the dial literally, you will end up slightly short.  After a quick measurement, it leaves material for a final pass.  However, the manuals don't state that this is an approximation which could lead a neophyte to believe that they were doing something wrong.  If fact, the manual states that the compound travel is .o40"/revolution  or 1.02mm/revolution when if fact, the travel is 1.00mm/revolution.  Similarly for the crossfeed dial, it states a travel of 1.52mm/ revolution when is actually moves 1.50mm.


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## joshua43214 (Dec 27, 2015)

mksj said:


> I have to agree with Bob K on the dial issue, it is 0.580" per evolution on this machine, which seems quite odd. Trying to keep track at 0.004" per mark is pretty tough over distance, I could have something to do with the feed gearing/travel when it is engaged? After a couple revolutions of a dial these days, I loose track if it was 3 or 4 turns, let alone counting the marks (if I could see them). On my mill they have metric pitch leadscrews with imperial dials, couldn't figure why the dials where off until I found that they didn't have imperial leadscrews. The mill manufacturer (Optimum) never corrected the problem and still sells the same machine these days. Thank god for DROs. I still would request a replacement dial to make the machine correct.


Doh! You are correct. I never actually use this wheel for measuring distance any way, I just use a dial indicator if I need more precision that cutting to a scribed line.
The OP's lathe just has an extra 0.48 stamped on it. Other than that the dial is correctly made

I was actually wishing for a DRO on the lathe the other day. I want one so seldomly that it has been pretty low priority though.


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## wrmiller (Dec 27, 2015)

I mounted a DRO on my lathe before I ever used it, so didn't notice the graduations on the carriage handwheel. I did notice the .002 graduations on the cross slide and would not have been happy if I had to use that dial either. There have been some other issues with my lathe as well, but overall I am happy with it.


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## lpeedin (Dec 28, 2015)

On my 1127VF-LB, the hand wheel has an odd number of graduations as well.  I believe one full revolution is 1.190" IIRC.  It really threw me off when I first got it and didn't notice it.  I was using the hand dials for roughing something to length and keep coming out way off, even for roughing.  I believe this is due to them using an Imperial conversion handwheel on a metric set of gears in the apron.  There was also a metal "sticker" on top of the handwheel bracket that said      II = .020" indication that it was .020" between marks, which checks out pretty close against a dial indicator.  Then after that "sticker" got some oil on it and came off, I saw that the actual handwheel bracket was engraved with   II = .05 MM.   If you do the math, .05mm = .0019685" or .020" if you round up.  I still use the handwheel graduations for roughing and just reset it to zero each time I reach the supposed 1.000" mark.  Then for actual measurements, I use a magnetic backed dial indicator since I don't have a DRO.


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## RJSakowski (Dec 28, 2015)

Something has been bothering me about the OP's picture.  

The dial on the  crank is supposedly reading in inches but it appears to have .58" inches per revolution.  That is one coarse lead screw: less than 2 tpi.  Additionally, .58" does not work out to a nice simple number of mm pitches as all common metric threads are.  If it were actually reading mm, the pitch looks better but is till not a nice simple mm spacing.  

I took a look at some pictures of the PM1340gt lathe on the machine tools online website and the cross feed and compound feed dials have both inch and mm graduations.  However, there is also a dial on the carriage crank and it appears to have a single scale on it.  

Now it makes sense.  A single turn of the carriage crank on my G060602 produces .95" of travel.  The exact distance being determined by the pitch on the bed  rack and gear train used to connect to the crank.  Like many lathes that I have seen, it has no dial so I never concerned myself with the amount of travel per revolution.

Bob


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## wrmiller (Dec 28, 2015)

What would be cool is if the carriage handwheel had a push or pull feature to change from a coarse feed to a fine. Probably doable, but not sure I'd tackle it.


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## tmarks11 (Dec 28, 2015)

Are you remarking on the 0.580"/revolution as weird, or the fact that you have two 0.480" positions?  The latter sounds like a late Friday night blooper, but the former (as others have stated) is fairly normal.

My G0709 is exactly the same way (and the exact same weird number).  It doesn't equate cleanly to a metric number either as far as I can tell (0.580 = 14.73 mm).  It would be understandable if it was 0.590" per revolution (almost exactly 15 mm).


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## joshua43214 (Dec 28, 2015)

You folks are headed off in the wrong direction about looking for a metric equivalent.
It is a rack and pinion system with a gear reduction in the carriage.
The travel distance will be a function of the pitch diameter of the pinion, so it will be something irrational provided the radius is rational.
One could engineer it so that the gear reduction will work out to an approximation of some whole number. It would be a tricky puzzle to work out the math for the proper gear reduction and pinion size to provide some reasonable distance per turn given a set of size constraints for the gears and shafts. 0.58" is close enough to 0.50 that that could be used as a target for the solution. Probably easiest to just solve it numerically, rather than find it with calculus.


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## tmarks11 (Dec 28, 2015)

Not really that tough of an equation to solve. This isn't rocket science.

M7 G0709 goes from a 14T:60T then to a 13T to drive the rack. The diameter and # of teeth (13T) is what is the driving part of the equation for distance travel per revolution. An that is not that tricky.  One turn of the hand wheel drives the 13T drive gear 1/4.285 of a rotation.  0.580" per revolution of the hand wheel means that every revolution of the drive gear travels 2.486" along the carriage.  That makes that drive gear 0.791" in diameter (20.09mm...hmm...close), and the pitch of the rack has to be 5.23 TPI.

No quadratic equations required.  Didn't even need to pull out a scientific calculator. Although I might need a pencil and paper to determine the profile of the gear.

To get 0.500" per revolution, I would need a drive gear that was 0.682" in diameter, and a rack that was  6.068 TPI.  I probably wouldn't do that, but would change my first reduction to get a beefier diameter drive gear.

The strange thing is that NO attempt seems to be made to achieve a "countable" value with EITHER imperial or metric values.

I just call this sloppy engineering personally.  It would be no harder or more expensive  to cut the gears to get a clean 0.500" that an offbeat 0.580".  You can't tell me that a rack with 5.23 TPI is an off the shelf item.  And since other lathes manage to do it...


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## joshua43214 (Dec 28, 2015)

hmmmm
Not an expert on gears, but I do know that pitch Diameter = Number of teeth/Diametrical Pitch, and there are standard DP's. This means that unless you plan to use custom ground gear cutters, pitch diameter is constrained to set values depending on the DP and the number of teeth. This is why outfits like Boston Gear can publish gear templates that you can lay any standard random gear on top of to find the PA and DP. Likewise, racks have a fixed number of teeth per inch for a given DP and PA - and this TPI will almost always be some weird irrational number (because pi is used in the calculation). For a manufacturer, the cost difference between custom tooling and standard off the shelf tooling can be very substantial, not to mention the potential difficulties in sourcing.

I'm not an engineer, I just picked up a BS in math for fun when I was doing my real major, so I am probably showing some true ignorance here about tool manufacturing.
I admit up front that I have limited experience with gearing, and I know very little about actual manufacturing methods. I have no doubt that CNC machined precision gears can be just about anything a person wants. But I am pretty sure that this is just a standard grade 3 or 5 rack and pinion and just made with some mass manufacturing process. This means standard tooling, on old fashioned automated machines.
So:
13teeth/.791diameter = 16.4349 diametrical pitch
not exactly a standard DP...
16 is a standard DP though
13/16 = .8125 diameter
.8125*pi = 2.552" of travel per revolution of the pinion.
So for 1/2" travel for 1 rev of the handwheel we need calculate a gear ratio by 2.552x = .5 -> x = .19588.
39/200 = .195. .195*2.225 = .4976 (0.0024" error)
Pretty sure you won't get a 200 tooth gear in that apron though...
10/51 = .1961, but .1961*2.552 = .4907" (big error) and a 10 tooth wheel is awkward...
Seems this might not be so simple after all.
I also neglected to calculate transmission losses because I do not know how it is done, or if it is appropriate in this situation.
No idea if a 16DP is even appropriate for this situation. I know 16 and 20 are commonly used in linear motion though, so probably best to stick with one of those.
This is even assuming the whole thing even uses the DP system. I know there are other systems for designing this sort of thing. Dunno if they are better or worse, or anything about the cost of these systems.

I figure I already paid $6K for this lathe. I would not pay another $1k just so the hand wheel came out to 1/2" per revolution.
I will agree up to a point that there might be some lazy engineering here. It would take me less than an hour to write up some code that could find all possible solutions given a set of DP's and diameter constraints. It is entirely possible this was done and that no solution exists that does not entail either custom tooling or large error, and they just opted for a solution that had the least error and came out to some random 1/100" ( in this case 0.58).


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## BGHansen (Dec 28, 2015)

Sure seems like Matt would send you a replacement wheel.  Like tmarks11 mentioned on the G0709, odd 0.580 per turn.  Seems like that's a function of the number of teeth on the longitudinal hand wheel and the rack.

Bruce


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## tmarks11 (Dec 28, 2015)

joshua43214 said:


> 16 is a standard DP though
> 13/16 = .8125 diameter
> .8125*pi = 2.552" of travel per revolution of the pinion.


So I just double checked my G0709.

Not 0.580 per revolution.  An even more convenient value... 0.565.  Put a test indicator on it to confirm that the hand wheel marking was accurate... and it was.

Frequently cheaper chinese machines "achieve" imperial values by marking the hand wheels as if they are imperial when they are actually metric... and you find that four turns of the 0.250"/rev hand wheel gives you 1.016" instead of the 1.000" you were expecting... since it is actually a 25mm.rev hand wheel.

Using your math, my gear ratios doen't work out to DP16 (0.595 per hand wheel turn) or DP17 (0.560 per hand wheel turn).  So we are obviously looking at a different profile drive gear.

Anybody have a parts list for the PM1340GT?  I would be interested in what gear ratios they have in the apron for the hand wheel.


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## derf (Dec 28, 2015)

A good machinist wouldn't pay no nevermind to those numbers and lines. It could be worse....instead of arabic numerals, it could be chinese chicken scratchin'!


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## RJSakowski (Dec 28, 2015)

The problem is easily resolved by removing the dial completely.  My 50+ year old Atlas and 2 year old Grizzly don't have a dial on the carriage crank  so no issues.


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## joshua43214 (Dec 29, 2015)

Here is the page from the manual. The shaft A is the hand wheel, and B is the pinion drive.
The parts list just calls them "GEARS." for instance, part #8 is
8 | 3310 | GEAR
I count 34 teeth on the picture, no idea if that is what the gear actually has.
The gear that drives it has 5 visible teeth, so if the image is correct, that is a 10 tooth gear.
The teeth on the pinion are not really countable in the pic, but it appears to have between 13 and 18 teeth.
The pinion is buried far enough into the saddle I would have to put my head in the chip pan to get a good look at it.
The center distance between shaft A and B is about 2.3" by eyeball with a caliper.

given an approximate center distance of 2.3, we can approximate the number of teeth for 2 equal sized gears by 20DP*2.3 = 46 teeth, or 16DP*2.3 = 36.8
So I would take as a given that there is between 70 and 100 teeth total on both gears in the reduction depending on the DP. This is also consistent with the 60:14 ratio on G0709 which has a very similar looking apron.
If we assume 14 and 60 teeth and a 16DP
center distance = (60 + 14)/(2*16) = 2.3125" which sounds pretty good to me, and is nicely consistent with tmarks' calculation.
The circular pitch is pi/diametrical pitch = pi/16 = .1964 which is fairly close to the difference between the .565 of the G0709 and the .58 of the PM1340GT, the error is probably attributable to lash. Sounds like the PM just has one more tooth than the Grizzly.

Not sure what any of this actually means though, but math is always fun


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## AirWolf (Dec 29, 2015)

I sent the photo to Matt... he was really surprised by it as well stating he has never seen a mistake like that before. He is sending a new one... and this one will find a place among my collection of oddball things from other hobbies and life's experiences.


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## pstemari (May 6, 2016)

Looking at the OP dial, there's another five ticks between 0.560" and 0.000".  I'm guessing that it's really 0.600" per turn, with 0.040" between major ticks and 0.080" between numbered ones.  Then you've got 15 major ticks going around, of which 8 are numbered.

The weird thing is dividing the major ticks into 5 minor ticks, each being 0.008", for a total of 75 ticks.  If there were 4 minor ticks per major, each one would be a nice even 0.01".  Instead, the minor ticks go 0.480", 0.488", 0.492", 0.496", etc.  4 minor ticks per major would give you 60 ticks total, a nice even number for a dividing head.


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