Have you ever tried this?

[T Bredehoft]

I have a 10-30 Precision Matthews Lathe, hence the forum this is posted in. It's using the lathe in an unintended way, I have a cut-off tool mounted upside-down on the back of my cross slide, for ease of removing a finished piece, whatever it is. I got to wondering, since cutting upside down works so well, why don't we do it from the front.
I hunted around, found a HSS 3/8 tool ground to cut to the right, turned it upside down, put a piece of 3/4 Ledloy in the chuck and at .0035 feed, cut a very nice .050 on a side. no struggle, nothing, I cranked it in to .100 on a side, no problem, it cut like butter, (keep in mind that I wouldn't have thought to do this right side up. ) OK, what'll it take to stall this. I turned it to .014 feed, and sure enough it stalled. At .007 it walked through it like cheesecake. And the chips just fell into the chip pan, no spray at all.

Should we have been doing this all along? I can see threading from the shoulder out as another benefit.

Looking for reasons NOT to do this, else I'm going to continue. Your advice solicited.

 

[Weldingrod1]

It depends on how tight your hold down stuff is and the saddle weight vs cutting force ratio. Of course, back side cutting and normal rotation has the same issues... dunno.

Sent from my SM-G892A using Tapatalk

 

[Jubil]

I don’t see any reason not to do as you are, except if your chuck is a screw on. It could possibly unscrew with some really bad outcomes.
Part of the reason for mounting cutoff on rear of cross slide is to omit the compound and whatever flex is in it.
If it’s working for you, that’s what matters.

Chuck

 

[T Bredehoft]

PM's chucks, at least the ones I have are mounted on quick change plates, no threads to be concerned about.

 

[Superburban]

Cutting the normal way, all the forces get pushed downward into the compound, the saddle, and then to the ways. The other way, everything is pulled upwards. take a look at the surfaces on the bottom of the saddle, and te ways. Now take a look underneath, and see the two small tabs that keep the saddle from lifting. Also note that those surfaces are not well machined, definitely not to the standards the top of the ways are.

For a cutting tool on the back side, where you are not moving the saddle, and not looking for a fine finish, it works. I would not try it for the front side and look for any great finish, or longevity of the lathe.

 

[maspann]

Here is Joe Pie's technique for threading.

 

[T Bredehoft]

Thanks for Joe's tutorial. You may have noticed that I said in the first post "I can see threading from the shoulder out as another benefit."

At my age I don't think wearing out the lathe is an option. but Yeah, I'll keep it in mind.

 

[GunsOfNavarone]

If I could figure out a way to mount a cut off tool from backside of my g0602, I'd be all over that.

 

[T Bredehoft]

mount a cut off tool from backside of my g0602,

PM's lathes, at least the 10-22-30 size have a machined surface there with T-slots. Just another perk, I guess.

 

[Tipton1965]

Turning a threading tool upside down and running the lathe backward to thread is one of the oldest tricks in the book. It goes back generations in the machinist trade. I was shown that technique back in the 80's when I worked as a machinist. The guy who showed me was retirement age and he probably learned it from someone when he was first starting out. It is a clever way to thread when you have a pesky shoulder to deal with.