Crazy Threads...

Tozguy said:
While we are on a roll, could we try the same 64 turns but at 10 TPI settings and measure carriage travel?
Needless to say that all backlash has to be taken up before marking the start.
Anybody want to predict the result?
Click to expand...

it moved aprox 6.800"
 
So I did my own math for once. I learned it from tubalcain!
So i need a 54 tooth gear at 3.5" with a 16 pitch.
Now... just need someone to make it.
 
Hukshawn said:
it moved aprox 6.800"
Click to expand...

Thank you Shawn, the 10 TPI test is more accurate than the 16 TPI one. It also proved that the first confirmation of 54T gear theory was repeatable.

Re the thread dial this is what mine looks like. I don't know how (yet) to use one that is not numbered.
The thread dial gear is 16T. If it is an option for you to adapt that gear to your machine then I could give you the part number and where to order from.


There should be a 54T drive gear out there somewhere for you. Maybe quicker and less expensive if you can find one already made that can be bored to the right dimension. Unfortunately the gears on my lathe are lighter than yours but if someone here has a similar size gear on their lathe and can provide the part number it might be an option to buy one of those.

IMG_0050.JPG

IMG_0052.JPG
 
Yes I'll take that part number for the thread dial gear. I'm sure I can make it work. I suppose as long as the teeth mesh properly.

As far as the 54t gear. I was looking on eBay, but barely anyone lists the pitch, only what machine it's designed for. makes me weary
 
Going back and looking at the pictures you have posted. There is one piece of information that is missing. You only show partial pictures of the threading chart on the gear box. You only show the picture of the gear arrangement for metric threading. Should be a picture of the gear arrangement for imperial threading. Plus a 54 tooth gear is not going to solve your problem. Yes, it will get you cutting imperial pitches, but will not be in line with the threading chart on your gear box. I suspect the gear is there in your gear train that you need. Just have to rearrange the gearing to get it cutting imperial pitches. I agree the 51 tooth gear is out. Maybe able to take one of the compound gears and use it on the leadscrew. Definitely needs a gear with an even number of teeth. Ken
 
Shawn,
My lead screw is 8 TPI Acme thread. Dial gear mesh does not seem to be all that critical as there is not much power transmitted to drive the dial.
I will call the supplier tomorrow to find out availability, price and delivery of the dial gear.
It is better that I do it, with manual and parts list in hand, so we can identify the part clearly.
Will follow up with you in private conversation or by email

Blairzrx@hotmail.com
 
I thought I posted these already.
I'm not sure what I'd change in the gear train. the only gears capable of changing are the three change gears. all others are not adjustable and likely nothing else would fit

IMAG0685.jpg

IMAG0683.jpg

IMAG0680.jpg
 
What if I switched the 34t at the top of the chain with the suspect 32t behind the 74?
 
higgite said:
Short version:
Tozguy is spot on. Replace the 51T gear with a 54T gear and you will get Imperial threads so close to perfect you won’t know the difference. Without altering the gear box or the leadscrew.

Long version:
When the metric leadscrew (3mm pitch) was replaced with an Imperial leadscrew (8 TPI = 3.175mm pitch), the carriage moved farther for each revolution of the leadscrew than it did originally, which means it also moved farther for each revolution of the spindle than it did originally. To correct that error, the original 34T gear was replaced with a 32T gear to slow the leadscrew down when cutting metric threads. With the 32T gear, the 3mm gear box setting actually results in a 2.988 mm thread. The 1mm setting will produce a 0.996 mm thread. And so on. Plenty close enough for government work.

The original 51T gear hasn't been changed, hence the lathe still cuts Imperial threads with too much pitch. To get it back on track for Imperial threads, you need to replace the 51T gear with a 54T gear. That will result in a thread with so little error that it’s practically immeasurable. Something like 15.99+ TPI for the 16 TPI gear box setting.

I think the thread dial, as is, will be useless for both metric and Imperial. You might cut an 8T or 16T gear and get it to work for Imperial threads, but I think you're stuck with leaving the half nuts engaged to cut metric threads.

Tom
Click to expand...

Tom, thanks for doing the numbers.
The scenario it implies is interesting:
* metric lead screw had to be changed because.....??(reason is left to the imagination)
*only could get an inch lead screw to replace the original one (changes drive ratio by +1.058)
*changed from 34T to 32T in metric mode to correct ratio (changes metric ratio back by -1.062)
* left the correction of inch ratio from 51T to 54T to the next owner (changes inch ratio back by-1,059)
Back in business soon.

How would you explain the 14T dial gear with the original lead screw?

Mike
 
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