Help Needed: Eriksen Lathe Thread Cutting

[Stustoys]

I'm assuming for metric you have to drive the 63 toothed gear(should you mix different module?)

That would at least explain the reversing ratios I was talking about, which was the only way I could come up with an answer but I didn't really think it could be right lol.

[Jekyll and Hyde]

If you were to flip the 48 change gear, and the 117/74, it looks possible that the 117/74 might engage both the 63 and the 74 (117 would drive 72, and and 74 would drive 63)?

That might explain it if Mk1_OZ has the power flow correct... DO NOT POWER IT ON in this configuration, only turn it by hand at first and see how things work, as it may cause the whole thing to lock up....

*edit* This would of course rely on some extra trickery happening in the 1-10 gear train, a one way clutch or something. And looking at it closer, you'd have to swap the 48 with the 72. I'm not convinced about that power flow drawn at the moment anyway, need to think some more...

*further* scratch that, the 63 is completely in the wrong plane of course. But the washer on it and the 48 aren't the right ones...

[Jekyll and Hyde]

Ok this is doing my head in and I am likely missing something simple. Been looking at this to long.

How can the direction of the ratio change of the box change?
nml A lever 2 on W
spring trigger 1 = 4 TPI 6.35mm pitch
spring trigger 10 = 7 TPI 3.63mm pitch
For the same input the output must decrease to go from 6.35mm to 3.63mm pitch.

nml A lever 2 on M
spring trigger 1 = 4mm pitch
spring trigger 10 = 7mm pitch
For the same input the output must increase to go from 4mm to 7mm pitch.
Right?
What am I missing?

Who's the idiot now? lol

And it doesn't really help anyway

Thanks for that. Now my brain is really bleeding - I was going to point out what you were missing, and then I realised that the 1-10 numbers on the chart are inverted between metric/imperial. I feel like all the clues are here now, but just have to piece them together....

I find it really hard to believe if change gears were required, they wouldn't be mentioned on the chart (as they are in the TOS manual I have, which also has a metric/imperial lever). So we're missing something critical about the power flow. It seems most likely that it's supposed to be driven off the 63 tooth gear at all times, but I can't see enough clearance in the housing to set that up?

What drives the... tumbler gear? on the 1-10 change lever? It appears to sit in front of the splined shaft, so something must interface between that shaft and the tumbler gear...

[Stustoys]

I think there will be a change gear setup that that lets you have both imp and metric setup at the same time. You can only select one shaft to "drive" at a time.
I like his power flow drawing as it explains the ratio reversing
My current guess is there is(or should be) another gear behind the 72 tooth that drives the 63 tooth(which explains the different module)

Once we get consistent pitch numbers working out where the change gears should be "should be" easy
There is a lot of adjustment on the banjo

p.s. oil your QCGB in position 1

[Stustoys]

Thanks for that. Now my brain is really bleeding

Didn't want to be the only one

I find it really hard to believe if change gears were required, they wouldn't be mentioned on the chart

yeah there is a long of extra stuff in there if you have to mess with the change gears anyway

[Jekyll and Hyde]

I think there will be a change gear setup that that lets you have both imp and metric setup at the same time. You can only select one shaft to "drive" at a time.
I like his power flow drawing as it explains the ratio reversing
My current guess is there is(or should be) another gear behind the 72 tooth that drives the 63 tooth(which explains the different module)

Once we get consistent pitch numbers working out where the change gears should be "should be" easy
There is a lot of adjustment on the banjo

p.s. oil your QCGB in position 1

I started looking at the ratio reversing thing from a different angle. If you assume the 63 is driven for metric, and the 74 for imperial, that ratio reversing makes perfect sense at the 1-10 selector.

But now I've come completely unglued figuring out if that holds through the next step. We know that 'C' should be a 4:1 reduction from 'A' - but where is this happening? All the gears look to be pretty much the same size in there, no way in hell there's a 4 reduction going on just from where the A-D tumbler engages?

The only way I can see that is if all the gears in that section compound, so that in position A you're driving straight off the shaft, but in position C it looks more like the below?

[Michael G]

I was threading a 300mm section of rod and a reasonably fast spindle speed with a large thread pitch meaning the carriage moved like lightening = easy to crash.

Change the spindle speed. The leadscrew gearing should run off the spindle, so changing that will not alter the fun and games that you are having...

Michael

[Jekyll and Hyde]

And further to my previous post, following this theory a little more - the power flow as indicated earlier between metric/imperial must almost certainly be slightly wrong. That 4:1 relationship between A and C with C being a finer pitch remains the same on the imperial threading chart, so the powerflow through the section I've indicated surely must always be as I indicated? If it started on the top shaft, the 4:1 relationship between A and C should reverse to A being the finer pitch?

I just tried reversing the flow for imperial as below, but that can't work - position A wouldn't DO anything, as far as I can figure out? The red line is effectively a dead end?

*Edit* Also just rechecked the metric chart - each letter step is a reduction of 2 from the previous - which is why all the gears look the same size (they are!)

[Michael G]

Does this give the 2.5mm pitch? (my reading of the charts suggest it should)
worm1.jpg
Michael

[Jekyll and Hyde]

Does this give the 2.5mm pitch? (my reading of the charts suggest it should)
worm1.jpg
Michael

I believe this is the correct setting. I've just been squinting at the module charts.

I'm pretty certain that the coarse/fine lever, when set to fine, gives a further 4:1 reduction in order to cut the threads as per the module table. So ANYTHING in the metric table uses the coarse setting.

So close to having this thing fully nutted out, what is missing....

If we (well, one of us!) counted the internal change gear teeth (and tumbler teeth) for whichever of the 1-10 pin position gives 1/2" pitch, we should be able to work out the required change gears on the back now, no? We know what reductions are created by any position of A-D, and the coarse/fine lever.

So between that, and whatever the ratio is for the 1/2 pitch position, we should be able to figure out the combination of change gears required to give 1:1 rotation with the spindle?

[Stustoys]

I just tried reversing the flow for imperial as below, but that can't work - position A wouldn't DO anything, as far as I can figure out? The red line is effectively a dead end?

how about this?

[Jekyll and Hyde]

how about this?

The first one would give a different ratio between A and B than all the other positions, I think?

And the second is basically the same as my metric version, just with D as the 1:1 position instead of A? Still needs the bottom shaft to be the driver....

[Stustoys]

The first pic is my Metric leads, top shaft driver. Notice I've paired(compounded?) the gears differently so there is no dead end. I think my pairings match the OP's

The first one would give a different ratio between A and B than all the other positions, I think?

No I think its the same, it's just that the driver gear comes in in the middle of the ratio change. Each ratio change is done in two steps.
So with the dog ring A driving it goes through half the ratio change to get to position A on shaft B Or(ok not drawn that well) half the ratio change to get to position B.
half and half is one.

And the second is basically the same as my metric version, just with D as the 1:1 position instead of A? Still needs the bottom shaft to be the driver....

Second pic does use the bottom shaft as that driver its for imp.

[steran50]

I believe this is the correct setting. I've just been squinting at the module charts.

I'm pretty certain that the coarse/fine lever, when set to fine, gives a further 4:1 reduction in order to cut the threads as per the module table. So ANYTHING in the metric table uses the coarse setting.

So close to having this thing fully nutted out, what is missing....

If we (well, one of us!) counted the internal change gear teeth (and tumbler teeth) for whichever of the 1-10 pin position gives 1/2" pitch, we should be able to work out the required change gears on the back now, no? We know what reductions are created by any position of A-D, and the coarse/fine lever.

So between that, and whatever the ratio is for the 1/2 pitch position, we should be able to figure out the combination of change gears required to give 1:1 rotation with the spindle?

Your picture is exactly what I said. If the change gears have been played with, then although the set up in the picture is correct to what you and I believe then the thread is not going to be 2.5 metric. I personally would try it at those positions and if it's not right then only alter the change gears and try again until the thread is correct.

[Jekyll and Hyde]

The first pic is my Metric leads, top shaft driver. Notice I've paired(compounded?) the gears differently so there is no dead end. I think my pairings match the OP's


No I think its the same, it's just that the driver gear comes in in the middle of the ratio change. Each ratio change is done in two steps.
So with the dog ring A driving it goes through half the ratio change to get to position A on shaft B Or(ok not drawn that well) half the ratio change to get to position B.
half and half is one.

Yeah, but what about compared to C and D? If I'm not mistaken, the step from B-C has a different reduction to from A-B in your diagram, and possibly C-D works out different to B-C?

If I slightly rewrite the threading chart for NML, pin 1 position:

A: 4mm
B: 2mm
C: 1mm
D: 0.5mm

Each letter you advance has to change the ratio from the previous by 2, I don't think that's happening in your diagram? And the same applies to the imperial threading.

Second pic does use the bottom shaft as that driver its for imp.

Bit lost here now - are you assuming the metric/imperial inputs are flipped from the way Mk1_OZ wrote them?