First project-sheave

[JohnCT]

Tried upping the speed a little, different cutter, different geometry, still getting a really ugly finish

 

[francist]

So what's changed? Obviously something has, you're getting poor results where you know you've done better before. What's different? Work through everything step by step.

Is the metal the same, is it held firmly in the chuck (sometimes bell mouth chuck jaws can be deceiving), is the tool post solid with no crud underneath, is the cutter on centre height, is the stick-out on the tool minimal, is the grind on the cutter good, is there a built-up edge on the tool tip, is your rpm/turning speed good (why did you change from faster before to slower now?), what is different that's not present now?

You got it once, and it could not have been all luck, so something has changed. Find it.

-frank

 

[JohnCT]

well pretty much everything has changed, the machine has been cleaned, oiled, mounted to a stand, belt replaced, other then looking at pictures, I don't know if my cutters are properly ground. I had it slowed way down to work some steel, that wasn't going as well as I would have liked either.

Last part I turned, the lathe was still on the transport dolly in the hallway, I ran a cord to it, stuck a piece in an went at it, so yeah, beginners luck.

 

[Dave Paine]

You have a few pieces, it is possible that the metal is contributing to the bad finish. Try mounting another piece in the lathe and take a light cut or face the end and compare.

 

[JohnCT]

Well it's functional, but 1.5 mm under what I wanted for finish thickness. I'll try another one

 

[Dave Paine]

Looks decent to me. Good practice and back-up if you make a better one on the next attempt.

 

[BtoVin83]

Like my dad always said when us kids screwed up "oh well you needed the practice"

 

[whitmore]

Thanks, I'll see what I can come up with. My overall finish is really poor, even on the facing and sizing cuts.

Actually, that's not too bad; the wire rope is supposed to turn the sheave, after all, it doesn't hurt
for the finish to have a little 'tooth'. It's the center pivot that has to run smooth.
A 1/8" wire rope has 1/8" circular diameter, but when bent around the sheave takes on
an oval (same area, different shape) as it slightly flattens against the sheave. So, the bottom
of the cut will be maybe 0.160" diamater, to allow the wire rope to not bind...
and a 0.160" wide plunge cut with a form tool is unlikely to leave a perfect finish, the chip
clearance is slightly problematic.

 

[JohnCT]

Round 2 and back in it's home.

 

[Dave Paine]

Glad that round 2 worked. The weather may even warm up soon so you can get the boat on the water.