Who can make sense of this?

[PeterT]

I have this funky chart too & assumed it is feed rates? They show the headstock gear combination but no mention of which corresponding leadscrew (8 TPI or 3mm).
This has always puzzled me thinking there should be some math correlation to a longitudinal feed value on this table and screw pitch on prior table, assuming the same lever combination. But I cant see anything that computes. So either I'm not getting it, or maybe under powerfeed (vs threading select) a different or default drive gear is coming into play? Fortunately I never pay attention to feed rates haha

EDIT
There probably should be no correlation to feed rates & some multiple of thread pitch because the powerfeed bar is driving completely different set of gears in the apron in order to traverse the carriage & cross slide.

 

[PeterT]

This is what I'm referring to. I don't see any mathematical connection to feed chart and like 1/TPI on the thread chart. Hence wondering if they are even comparable?

EDIT. There probably should be no correlation to feed rates & some multiple of thread pitch because the powerfeed bar is driving completely different set of gears in the apron in order to traverse the carriage & cross slide.

 

[Tinker]

This is interesting. So PeterT, are you telling me that the chart you posted (#6) is wrong. But when I tested C6, I was spot on with 1mm and B6 was exactly 2mm. Are we over analyzing this? Should I have made the gear representation as Brent had hand drawn? You know, really, I'm happy I can do 1 and especially 2mm threads without changing any gears around. I never would of figured this out without your help. I mean everyone. I will do more testing and hopefully everything works out. I will modify my chart accordingly and post my final results.

 

[Tinker]

Ha Ha Ha reading post #21 reminded me of what the original manual that came with the lathe was like. The direct translation from mandarin to english is Noooooooo............. good. It was very hard to make any sense of anything.

 

[PeterT]

This is interesting. So PeterT, are you telling me that the chart you posted (#6) is wrong. But when I tested C6, I was spot on with 1mm and B6 was exactly 2mm.

No, I don't think they are wrong. At least for my 14x40 & we are hoping yours is the same. The Fig-11 chart in post 5 & 6 shows the metric pitch threads that can be cut with different headstock gear arrangements involving different combinations of 127,120,40,32,30 gears AND presuming the 8TPI leadscrew which you have established. So what my recent comments were about is

1) Disregard the equivalent chart that may be nailed on your lathe showing TPI & mm pitches that assume the 3mm pitch leadscrew. You cannot get those pitches (at least using those gear combinations) unless you have a 3mm leadscrew. I guess the manufacturers thought it best to publish both on plate & cover their bases regardless of how the lathe left the building, 8TPI or 3mm

2) The other chart we were trying to make sense I'm saying I have one of those too (post #21 & 22). But I think this is feed rate = how much distance traversed per revolution. Notice they provide both directions, longitudinal & cross feed. But this is automatic power feed mode. So in my case I switch a knob from thread mode to power feed mode & the threading half nut is of course not engaged to the threading leadscrew. And now that I think about it, there probably should be no correlation direct match to feed rates & some multiple of thread pitch because the powerfeed bar is driving completely different set of gears in the apron in order to traverse the carriage & cross slide. DUH, I took mine apart, I should know that. Sorry for the mental lapse I had gear ratios & threading on the brain. I amended the posts so it doesn't haunt me later.

 

[Brent H]

@PeterT and @Tinker : seems both of you have some unexplained chart work - but, the good thing is, both your lathes can do metric and imperial threading with little changes to the back end gearing.

The feed rate chart has to take into account the gear reductions that happen in the apron and feed box when you engage the feed verses the treading. there will be some ratio that then further changes the feed rates. On my lathe the cross feed is 1/2 the longitudinal feed so another gear reduction happens there.

Both of you have an 8 tpi lead screw it would seem so I would make up a Metric and Imperial threading chart that reflects that and if you are so inclined, a feed chart that reflects both the imperial and metric depending on you gearing configuration.


Reading through your chart though, there are some pretty strange numbers - typically the longitudinal feed and the cross feed will be some ratio that does not change - like mine states the cross feed is 1/2 the longitudinal feed. On the chart you guys have the cross feeds listed at C-2 and D-2 must be errors - they just do not fit the math.

Cross Feed should be :

C-2 = 0.06
D-2 = 0.03

C-3 = 0.056
D-3 = 0.028

They must have done some rounding off that went squirrely as the gear ratios are close together. Only way to really get it figured would be to know what the gear ratio's are and calculate things out

 

[RobinHood]

And now that I think about it, there probably should be no correlation to feed rates & some multiple of thread pitch because the powerfeed bar is driving completely different set of gears in the apron in order to traverse the carriage & cross slide

But there is: taking the 3MM lead screw (and the corresponding tables from post #22 above), the threading ratio to longitudinal feed is 2.7272:1. The ratio of long. feed to cross feed is about 8.1666:1. (There are lots of errors (decimal places in the wrong spot) and probably rounding errors as well). Yes, feed rod and threading lead screw are separate shafts, but they come out of the same gear box, so there is always some ratio between them as they have at least some of the gears in common.

Just as an aside: you can use the lead screw as a longitudinal feed. For the SAE system just take 1/tpi to give you the inch/rev. (eg: 128tpi = 0.0078 in/rev). In Metric the thread pitch is equal to longitudinal travel (eg: 0.7mm thread pitch = 0.7mm/rev).

as Brent sais: probably time to calculate whole new tables and take off the original ones - they are too confusing (and full of errors).

 

[PeterT]

Both of you have an 8 tpi lead screw it would seem so I would make up a Metric and Imperial threading chart that reflects that and if you are so inclined, a feed chart that reflects both the imperial and metric depending on you gearing configuration.

Regarding threading, I think you are saying the same thing as me. In my case, I don't think a new chart is required, just recognize the lower chart relating to 3mm leadscrew doesn't apply.
Regarding feed rates, yes I think table might be messed up.

Website is freezing right now, cant seem to upload pic. I'll try later