mini lathe struggles with course threads

[Twinsquirrel]

Did a few practice runs cutting threads on my 7 x 14 mini lathe and noticed that when the change gears are set up for very course threads the machine really struggles even when it is not cutting, is this normal?

I cant find any binding on the lead screw and am at a bit of a loss as to why it should struggle so much.

David

 

[Bogstandard]

David,

The coarser you go, the more stress on the drive train. I had a bolt and holding bracket on my much larger lathe break because of the extra stress. I was trying to cut 2.5 TPI.

All you can do is make sure your change gears are not too tight together and not binding, and take much shallower cuts than normal.

In fact if you wanted to, and have a handle on your leadscrew, you could cut the threads without power, by turning the leadscrew. Doing it that way, and driving the spindle, takes all the pressure off the gear train in these high stress setups.

So there is most probably nothing wrong with your setup, just the way screwcutting works.

Hope this has helped.

John

 

[Twinsquirrel]

Thanks John, that's put my mind at rest. I like the idea of a handle on the leadscrew, I assume that I could also use that to do a very fine manual feed?

David

 

[mklotz]

http://www.homemodelenginemachinist.com/index.php?topic=1502.msg11045#msg11045

shows the lathe crank I built. Perhaps it will give you some ideas for making your own.

 

[Twinsquirrel]

Thanks Marv, my to-do list is getting longer by the day and you spindle crank looks ingenious and very useful, the problem is that what would take most of you guys an hour would take me a week to accomplish and would probably look like a road accident.

David

 

[chuck foster]

hey David
so what if it takes you longer and looks bad? as long as it works and you had fun doing it, who cares?
every one of us here has made and still makes stuff that looks horrible, but the more you make the better your workman ship gets.

now get out there and make that handle for your lathe .............. AND THATS AN ORDER!!!! ;D :big:

and could you please post some pictures of you adventure????

chuck

 

[rake60]

David you would have to look real hard to find a junked
parts that look bad in my basement hobby shop.

That's because the far corner of the basement with the paint
chipped off the concrete walls isn't very well lighted...
I tend to drop things on a horizontal plane sometimes. :

Rick