Threading gear selection and position.

watersteps

watersteps

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Hello All, I am new here on this forum and I need some information that I cannot find anywhere.
I have a small mini lathe MX180V there was no name on the lathe from new. I believe it would be considered a 7x10 lathe. The manufacturer sent me a manual with the lathe when new, it is not correct (WM180V). The manufacturer insists that it is correct, even with different model number, different threading gears, 220v verses 110v, and more.
This is my problem, see attached gear chart off of the lathe. (Not a good picture) I have 6 gear locations and not the correct gears. I want to turn a 1.0625 x 20 TPI thread on an air rifle end cap.
These are the gear sizes I have,20, 24,30,35,40,50,60,72,80,80. These came with the machine I did not loose any. The chart calls for different gears then I have. I went on line to the little machineshop web site and used their gear calculator and it only shows 4 gears so I am lost.
From what I can determine the lead screw is 16 TPI, there is a 40 tooth gear on the chuck spindle, that is fixed, not changeable.
Looking at the gear chart attached, at the upper right corner you can see the A,B,C,D,E,F gear loctaions.
Does anyone know what gears go in what locations to produce a 20 TPI part.

rsz_dscn8268.jpg

rsz_dscn8269.jpg
 
It looks like you need 4 gears and 2 spacers.

52 meshed to the fixed 40 with the 33 on top of the 52.

80 meshed to the 33 with a spacer under it.

40 meshed to the 80 and a spacer.

The spacers on top or bottom might need to changed depending on how the fixed sides line up.
 
The problem is I don't have a 52 or a 33 tooth gear, I was hoping there might be a different group of gears that will provide a 20 TPI out come.
 
That ratio doesn't work out. 40/52 * 33/40 = 0.635, which would be about right if the leadscrew pitch were 2mm, not 16 TPI. (0.05" = 0.635 * 2mm).

If it's a 16 TPI leadscrew, you need a gear reduction of 0.8 from the spindle to the leadscrew to cut a 20 TPI thread.

Sent from my Pixel XL using Tapatalk
 
Thanks a bunch but, 0.8 reduction from the 40 tooth spindle gear. I have no idea what gears I would use to get that reduction.
 
Are we sure it's an imperial leadscrew? Most of the little lathes are metric. I was just going from the chart in the picture. I missed the bit about not having the gears in the chart.

It's also not uncommon to find metric leadscrews with imperial dials, which seems like the worst of both worlds to me.

Do the gears from the LMS calculator exist in your stack? If so, you can stack them in the same order with spacers to try it. Test on scrap and check with a pitch gauge. I use small PVC pipe pieces I happen to have around. Cheap and easy to cut.
 
You may be right about the leadscrew being metric. I will stack the gears to produce the 1.25 reading on the chart, I have all of those gears. I was told that 1.27 is almost a perfect 20 TPI.
 
an interesting poser - the gears you have suggest you will only be able to make "good" threads in the system of the lead screw. Metric lead screw = metric threads. To go between SAE/imperial and metric or (inch and metric), they usually throw in a 127 tooth gear. on 7x10 lathes this is not so easy. a 120 / 127 tooth set is a great converter because 25.4 mm (one inch) can be factored into 2 and 127. That is the smallest gear that will do the conversion exactly. Other 7 x 10s have a 33, 55 and 57 tooth gears to make an approximate conversion.
Without knowing the pitch of the lead screw, I can't give you a really good answer.
other 7 x 10 lathe owners might be of more help.
 
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