Turning from the rear on Sherline lathe.

[EricB]

So now I have to puzzle over why one tool "lifts" and and others "dig in." Thanks for setting me up with another week of obsessive mental torture. Lol.

On the front, the tool is pushed down into the crosslide and the work will climb the tool. On the back the tool is being pushed away from the machine and the work.

 

[fcs]

Give this a try and let us know how it goes.

I'm the OP so I guess I can butt in here and report.

Mikey is correct that I saw the rear mounted tool holder on the Sherline website and wondered what advantage it might have. I see that they are 3/8 inch so they would not work with my 1/4 inch tools anyway, without 1/8 inch of shimming. So I don't feel called to pursue this now.

I ground a right hand bit to Mikey's specs and it cuts the aluminum bronze much better than my round nose tool. I can take much deeper cuts and the surface finish is better. It does chatter when straight and needs to be at a slight angle to the work.

I am reluctant though to try his idea of making a shoulder cut with my rear mounted cutoff tool. First, I have honed a slight taper on the tool to take the button off the finished part (RHS) and leave it on the stock in the chuck. Second I distrust my ability to do most turning from the front and some from the back. I know I have a real good chance of screwing something up. And won't I need a left hand tool to cut into a shoulder cut from the left?

Anyway progress has been made. I can take stock down to the maximum dimension with the new tool. For the female ferrule where the shoulder is on the left it will also work well. I suppose there is a similar tool I could make for the compound slide. At the moment it makes my head hurt to visualize it.

Thanks.
Frank

 

[zondar]

On the front, the tool is pushed down into the crosslide and the work will climb the tool. On the back the tool is being pushed away from the machine and the work.

Yes, but the quote was that the parting tool lifts, not about what happens on one side or the other. So, my next puzzle was why does a parting tool "lift" but others do not?

 

[mikey]

It's not a matter of seeing, it's a matter of trying to understand the mechanics of it.

One more Q: If it's better for everything, why don't all lathes just put everything in the front, tools upside down, and spin the lathe "backwards?" Minor convenience, e.g. seeing the tool tip slightly easier, over superior rigidity? Just a long-standing convention from back in the days when all lathe tools were basically hand-held gravers?

Maybe try reading through this thread. It might give you a better idea of the issue.

 

[mikey]

I am reluctant though to try his idea of making a shoulder cut with my rear mounted cutoff tool. First, I have honed a slight taper on the tool to take the button off the finished part (RHS) and leave it on the stock in the chuck. Second I distrust my ability to do most turning from the front and some from the back. I know I have a real good chance of screwing something up. And won't I need a left hand tool to cut into a shoulder cut from the left?

Your rear mounted parting tool is much more than a parting tool. It is a precision demarkator, depth setter, groove maker and it also parts. I strongly suggest you grind off that taper at the tip. Grind it square across the face with a 7-8 degree relief angle under the end edge. Hone the top lightly and keep it burr-free. Then use the thing.

Need a shoulder a precise distance from the end of the work? Use the parting tool to demarcate it and take it to depth, then come back in with your turning tool and turn it. There will be times when this will save you time, such as when the OD of the work has to be accurate in the low tenths. Use the parting tool to take you to depth once and start measuring only when you approach the mark. Need two shoulders a precise distance apart? Cut it with your parting tool. Need an O-ring groove or a thread relief? Yup, parting tool.

You mention male and female ferrules. You can use the parting tool to demarcate and set depth for either, then use RH and LH tools to turn down the end of the work.

AND, as mentioned, when you're done you can part stuff off with your parting tool! It will part thin stuff, thick stuff and it will do it all at high speeds without chatter or fuss. If you have been stuck parting from the front, doing it from the rear will seem like nirvana.

 

[fcs]

Need a shoulder a precise distance from the end of the work? Use the parting tool to demarcate it and take it to depth, then come back in with your turning tool and turn it. There will be times when this will save you time, such as when the OD of the work has to be accurate in the low tenths. Use the parting tool to take you to depth once and start measuring only when you approach the mark.

What I don't see is how you can groove with the parting tool to an accurate depth. You have to judge when the tool just touches the work, not a thou too much or too little, then use the handwheel markings, which are 2 thou apart in OD, to get the depth "accurate in the low tenths." Are you using a dial indicator to measure the X movement?

Now I haven't tried this. Maybe it works better in reality than my imagination.

 

[mikey]

Yup, just using your eyeballs and the handwheels. Try it; it isn't difficult.

 

[mikey]

I meant to suggest that you check to see if the bottom of the blade slot of your tool post is on the exact centerline of your specific lathe. This is important to how well the tool functions.