G4003g: 91 and 86 End Gears

[Splat]

The 86/91 gear can be flipped with either the 91 0r the 86 on the inside. Mine came with the 91 in but I've used it both ways depending on the thread.

So I understand you correctly here, are you saying you can cut metric with either gear on the inside? Not talking about feeding, only threading. It was my understanding it had to be the 91T on the inside to cut metric. Thanks.

 

[epanzella]

So I understand you correctly here, are you saying you can cut metric with either gear on the inside? Not talking about feeding, only threading. It was my understanding it had to be the 91T on the inside to cut metric. Thanks.

What I'm say is that you need to mesh the gears that the chart calls for to do a particular thread and how the gears were when you got the machine doesn't matter. If you can't make it work one way flip the gear over and do it the other way.

 

[Splat]

What I'm say is that you need to mesh the gears that the chart calls for to do a particular thread and how the gears were when you got the machine doesn't matter. If you can't make it work one way flip the gear over and do it the other way.

Yes, I understand that. I thought you meant it didn't matter re: the middle gears. That's actually what one would believe if they read the crappy manual I got with the machine. They corrected many errors in the next, 2010, edition, btw.

 

[Superburban]

Yea, my lathe also says "any" in the chart, but the diagram to the left shows the spindle gear "F", mating with the 91 tooth gear, and the QCGB gear "G" mating with the 86 tooth side.

 

[epanzella]

Yes, I understand that. I thought you meant it didn't matter re: the middle gears. That's actually what one would believe if they read the crappy manual I got with the machine. They corrected many errors in the next, 2010, edition, btw.

When ever you use one gear as the middle gear it doesn't matter how many teeth it is as it changes nothing. eg; 40/91/60 is the same as 40/86/60 or 40/25/60. That's why the top section of my chart shows "any". The bottom four parts of my chart also shows "any" which is incorrect. The picture in the far left column correctly shows the F gear meshed to the 91T and the G gear meshed with the 86T. That's definitely not "any".

 

[Splat]

When ever you use one gear as the middle gear it doesn't matter how many teeth it is as it changes nothing. eg; 40/91/60 is the same as 40/86/60 or 40/25/60. That's why the top section of my chart shows "any". The bottom four parts of my chart also shows "any" which is incorrect. The picture in the far left column correctly shows the F gear meshed to the 91T and the G gear meshed with the 86T. That's definitely not "any".

I see. I'm not too up on gearing so didn't figure about the middle gear not mattering if both F and G gears mesh with it. Thank you.

 

[B2]

So I go to change my G4003g's F and G gears and I notice the 91 and 86 tooth gears aren't right. The 91 is on the outside and 86 on inside. This is opposite of what the manual shows. Can anyone please verify the position of their 91 and 86 gears on their G4003g? Thanks.

@Splat

I worked on a similar problem for @TakeDeadAim last night. You will find that thread at:

Ok, I did a little spread sheet testing and it looks like the G4003 uses the same gear ratios as the PM1340GT. So the spread sheet should work for you. However, the external gears are a bit different, as is the 91/86 exchange gear. I will run my program and see what come out. I found a different manual for the G4003 and is has the supplied external gears listed: 26, 27, 35, 36, 40, 40, 45, 50, 60, 86/91

So on an Imperial lathe one can very seldom find get exact metric thread mm/T values using an exchange gear. This is probably because the lead screw is not metric! Nevertheless, near approximations are available and this is what we cut and is what the manufacturer advertises as exact.

I took the spread sheet and ran it looking for approximations to 1.25mm/T values. Below is a screen shot of the results. You read the gear positions as follows. Consider the first value, line 3. From right to left. The metric thread value is in yellow and is noted to be 1.24047. Column U: 27T is the gear at the spindle. Column T: 86T is 1/2 of the exchange gear and it is in contact with the 27T. Column S: 91T is the other half of the exchange gear and it is in contact with the 45T gear which is at the gear box (bottom gear) . This is noted at Column N. The gear box is set to B and 7, which are noted at columns H and M, respectively.

If you scan down to the middle of the list you will find the Metric thread value of 1.25023mm/T. This is the closest approximation to 1.25mm/T.
You will see that there are alternative external gear arrangements corresponding to different gear box lever settings. Each of these calls for the 91T exchange gear to be in contact with the spindle gear (Column U). However, since these are all close approximations there is nothing requiring the manual to choose these arrangements. For example they could have chosen line 20 or 21 where the 86T gear is contacting the spindle gear.

You may also note that the workbook considers what one would get if he were to use the feed bar rather than the lead screw to cut the thread. Since I do not know the gearing in the saddle these may not be correct, but look to line 22 where the exchange gear is not actually used except to transfer the motion. Here one can use either the 91T or the 86T to contact both the upper(spindle) and lower(gear box) gears.

Can you tell me if the exchange gears can fit on the upper or lower gear axles? That is, are the axles the same diameter and the same keying? If so then their are even more possibilities where the 91T or 86T could be located at the upper or lower gear position and smaller gears could be located at the exchange gear axle. Then the physical swing of the exchange gear axle may determine what is physically possible.




Dave L.

 

[B2]

The workbook was posted at:

Nov. 6 2023 Excel workbook file name: TPI_ManyLathesRev1 NB06_0054.xlsm

The fundamental worksheet format and Macros have not changed, but
I added a couple of lathe sheets to the TPI generating Excel workbook. So I thought I would just post the current workbook.
It now has lathe sheets for the following lathes, but many other lathe models are similar or the same...just by different names.

NB06: Currently Available, LatheModel TPI sheets:
PM1440GT
PM1440HD - ( @Larry$ @verbotenwhisky )
PM1340GT_PM1236T
PM1236-1236M
JET-BD1340
Atlas618
MMLB-Norton - ((MetalMax) @Provincial )
MM1340LB-Lever - (MetalMax)
PM1228VF-LB - ( @LROYSON , @Aurelius )
G4003G=G4003 - (waiting feedback from @TakeDeadAim)
PM1130V - (TBD: @JPMachine to review. Remove some gears before running the GenAllTPI_14V2 macro)

Dave L.

 

[B2]

@Splat

Did you find the workbook that I posted as an attachment. After I initially posted it I found that the gears that I had used in the G4003G spread sheet were too extensive so I EDITED the posting so that the corrected Workbook replaced the intial one. I did this within a few moments, but hopefully you would find the correct one. You will find it at the following posting. Please let me know if you get it or not. If you need help figuring it out just let me know.

Hi Folks,
Comments regarding experiences, additions, improvements made etc. about this project/Workbook would be appreciated.

Nov. 6 2023 Excel workbook file name: TPI_ManyLathesRev1 NB06_0054.xlsm

Edit: Corrected lathe sheet G4003G and so changed the file and its name to: TPI_ManyLathesRev1 NB06_2023
I got more info about the gears available in the the G4003G