Turning finish

[WobblyHand]

You mean you don’t have additional gears with which to change the threading pitch or power-feed ratio?

He can change threading pitch. Power-feed ratio is fixed, unless he buys a slower gear set, which I linked earlier in this thread. Natively, a mini-lathe cannot change power-feed ratio.

 

[njblignaut]

I have found that a lack of tool pressure can also lead to a bad surface finish with build-up on the cutting tools. Micro oscillations in your machine due to rubbing and no cutting. The higher the tool pressure the better the finish. Have a look at Jon's Workshop on balanced cuts.

 

[kmanuele]

Yes I do, but they would still be geared to spindle speed.

I've seen a few folks remove the change gears and drive the thread/power feeds with a separate motor. Then you could have control of those independent of spindle speed.

Man ! Did I get hammered on this one

Think before you speak.

 

[mikey]

Yes I do, but they would still be geared to spindle speed.

I've seen a few folks remove the change gears and drive the thread/power feeds with a separate motor. Then you could have control of those independent of spindle speed.

Man ! Did I get hammered on this one

Think before you speak.

I hope you really are joking about feeling hammered. The guys are trying to help, and guess how we all know about what to say? We've all been exactly where you are so please don't hold back with any questions you may have.

Your power feed is indeed tied to your spindle rpm through your gearing. All lathes are like this except for manual lathes like Sherline lathes. You can modify the feed rate by changing gears as noted above or buy a lathe with a quick change gear box that does the same thing with levers/knobs. You should also know that very accurate cuts and fine finishes can be achieved with manual feeds.

Take your time, learn about the geometry of your turning tools and how their edges are used. Try to stick with HSS for the more common materials, especially while you're learning to use the lathe. Time spent on basic skills will pay off in the long run.

And if you don't understand something, ask.

 

[kmanuele]

This where I am on finishing. Tool ground to about 10-12 degrees for all rakes and reliefs. All edges and the nose honed. Nose radius is about 0.050".

Photo on the left shows turning first at 0.0025 IPR, about 500 RPM, with tool perpendicular to the work. Fingernail test included .

Then I rotated the tool as shown, turned at a higher feed rate - 0.050 IPR, and a very good finish. The photo doesn't do it justice. Zero fingernail scraping. It looks like the work is seeing a large radius on the trailing edge of the nose -- accidental, but something to remember for future grinds and/or tool post rotation.

I still don't understand why the perpendicular case, with nose radius 20 times feed rate, doesn't have a better finish. Am I expecting too much?

Photo on the right shows a subtle repeating pattern. I think this is due to one of my change gears out-of-round or bored slightly off-center. I can watch it oscillate. Needs replacement.

 

[kmanuele]

I hope you really are joking about feeling hammered. The guys are trying to help, and guess how we all know about what to say? We've all been exactly where you are so please don't hold back with any questions you may have.

Your power feed is indeed tied to your spindle rpm through your gearing. All lathes are like this except for manual lathes like Sherline lathes. You can modify the feed rate by changing gears as noted above or buy a lathe with a quick change gear box that does the same thing with levers/knobs. You should also know that very accurate cuts and fine finishes can be achieved with manual feeds.

Take your time, learn about the geometry of your turning tools and how their edges are used. Try to stick with HSS for the more common materials, especially while you're learning to use the lathe. Time spent on basic skills will pay off in the long run.

And if you don't understand something, ask.

Thanks for this, and yes the hammered comment was in jest.

Tone doesn't often come across with text. This is a great site, and everyone has been helpful.

K

 

[kmanuele]

This where I am on finishing. Tool ground to about 10-12 degrees for all rakes and reliefs. All edges and the nose honed. Nose radius is about 0.050".

Photo on the left shows turning first at 0.0025 IPR, about 500 RPM, with tool perpendicular to the work. Fingernail test included .

Then I rotated the tool as shown, turned at a higher feed rate - 0.050 IPR, and a very good finish. The photo doesn't do it justice. Zero fingernail scraping. It looks like the work is seeing a large radius on the trailing edge of the nose -- accidental, but something to remember for future grinds and/or tool post rotation.

I still don't understand why the perpendicular case, with nose radius 20 times feed rate, doesn't have a better finish. Am I expecting too much?

Photo on the right shows a subtle repeating pattern. I think this is due to one of my change gears out-of-round or bored slightly off-center. I can watch it oscillate. Needs replacement.

View attachment 403659View attachment 403656

I rotated the tool a bit further and got lots of chatter.

Then put the tool back perpendicular, turned RPMs down to 250 and a great finish again. 300 RPM seems to work also.

So, a solution

Note that I am taking very shallow cuts -- 0.005" DOC or less, to creep up on final dims.

 

[SLK001]

Have a look at this grinding guide: