Turning Upside-Down

[ELM6061]

As I read through all the different threads/posts and checkout all the great photo's. I have noticed on a couple of occasions, that lathe tools have been inserted "upside-down" to complete some turning/parting etc and it has me very curious why.
I am sure I have seen it done in three different threads, but sorry I am unable to recall which ones to add a link.
I distinctly remember one being mentioned as a parting tool, and the second being a turning tool (not threading). The third I think was for a left hand thread, which at the time, I sort of got my head around, but as I think about it more, struggle to make sense of it as well.

So, after all that;
What is the purpose of using a lathe tool upside-down & when would you need to do it?

And would I be correct in assuming, if you do use a lathe tool upside-down;
You would have to have your lathe spinning in reverse, which would put all the pressure on your tool post bolt, rather than the compound supporting both the tool post and cutting tool? (open to great flex and less accurate tolerances).
PS: I will keep looking for the posts where I saw this.

Eddie

 

[kvom]

Some lathes can mount a parting tool on the back of the crossfeed. If standard rotation is used then the tool must be upside-down.

 

[Herbiev]

Or if you live in Australia

 

[ELM6061]

Or if you live in Australia

I was starting to wonder whether it was due to global position.

@kvom so you mean the tool is at the back of the work piece and not the front? Be a pain to see where you are cutting wound it not?

Eddie

 

[chbeyer]

Hi Eddie,

mounting upside down is a good idea for parting or grooving tools because:

The chips fall out of the groove thanks to gravity and can not interfere in any way with your cutting.

The setup gets more rigid because the counter-cutting-force (Sorry for my english, hope you get what I mean) pulls the crossfeed into the dove tails instead of pushing it downwords on the carriage. Which means you avoid any play in the setup and have a bigger chance for a non-chattering cut.

If you have a threaded chuck mounted on your machine it is not a good idea of course to change the sense of rotation (necessary with an upside down mounted tool) because you risk to loosen the chuck. Solution: Put the upside down mounted tool on the other side of the chuck, on the back of the crossfeed so you can keep the sense of rotation.

In addition it is nice to have a correctly adjusted parting tool mounted at hand when needed. You need a large crossfeed of cause to do so...

hope this helped

cheers
christoph

 

[lensman57]

Hi,

A rear mounted tool ( up side down ) works well for parting operations, in theory you should be able to part larger diameter work piece due to the more rigid set up, I do not see any advantage for normal turning. I do not like the way the tip of the tool is sort of obscured from vision. you can adapt any lathe to cut up side down but then you need to make a new tool post to bring the tool tip to center height.

Regards,

A.G

 

[rkepler]

I sometimes turn upside down when threading to a shoulder - I just put a stop on the ways for the carriage and use that as the point where I form the rest groove for the threading tool.That lets me form a complete thread all the way down to the shoulder and not have to pop the tool out perfectly (sure, I can do it 3-4 times in a row but not 30-40 times).

I have a 3/8 washer to put under the toolpost to get the tool to the right height when turning upside down. Still have to pack on top of the tool in the bottom of the tool holder slot, and you'll want to have everything roughed in beforehand.

 

[digiex-chris]

matching inside and outside tapers!

Set the compound, cut your outside taper on part A with the regular way. Flip the tool upside down, leave the compound the same, bore the matching inside taper of part B on the back side. Part A will be a perfect angle to fit part B. This not only matches the taper, but lets you work through the wide end of the bore instead of the narrow end.

 

[ELM6061]

Ok, so there are some real benefits, interesting that your tool is also supported better (not that I have my head around that yet).

So if I was planning to make an adjustable tool post for my lathe anyway, what changes would I need to implement, so I could also turn upside-down (mind you, I do have lousy balance and a dicky shoulder, so hand stands are out).

My lathe is a Hafco AL960B.

 

[chbeyer]

Hi Eddie,

no need for changes at all. You should be able to put the reversed tool on the correct hight of course so maybe you need to construct one special holder for your regular toolpost to achieve that ...

cheers
christoph

 

[jerryc]

Many turret lathes, Warner&Swasey, etc used a tool mounted upside down in the back of the machine . Worked quite well as I remember.

 

[digiex-chris]

yeah, I've got an adjustable height tool post and that's how I do it when I'm matching tapers. Do the outside as normal, then remove the tool insert a boring bar upside down, and crank the height up till it's on center, and do the inside taper. I usually just use my normal boring bar holder and reset it for upside down work.

 

[ELM6061]

Sorry I am still a little confused here. With the lathes that allow you to do this, does your cross slide have enough travel to allow you to get the tool post behind the chuck or is it how you hold the tool in the post.

My lathe will only allow one side of the tool post, to go just past the center of the chuck, not behind.
I assume with mine, it cannot be done?

 

[chbeyer]

Hi,

at least your cross slide is not prepared for a rear tool post. You would need some t-slots ore anything to fix a toolpost with.

You still can turn the parting tool upside down and use the regular tool post if you are able to put the chuck rotation in reverse sense ...

cheers
christoph

 

[chipenter]

You have two cap head screws at the back of the cross slide , use these to fix a plate and build a toolpost , there is usualy a forum for youre lathe were ideas and mods are posted .

 

[chbeyer]

Hi Eddie,

reverse parting of is not a must ! A lot of people are just happy with parting tools mounted the right way. If the toolholder on the pic is the one you use you should rather think about a quickchange toolholder with a couple of inserts to keep some tools ready and on the correct hight. If you have severe problems with parting off you can still try the revers-tool-method

(just my 2 cent)

cheers
christoph

 

[Tin Falcon]

ELM :
I have been lurking on this one. I think this is a case of if you have to ask why. you probably do not need to set up this way. Nothing against learning or curiosity.
IMMHO the main reason for an upside down tool is to use a tool holder on the back side of the part. especial having one in front and one in back . this saves time in a production environmental. this was especially useful before the advent perfection and low cost of QC tool holder.
when you use a upside down tool in a front tool holder you must have a positive lock of some type on the chuck. Ie bolt on like a 7x10 or a cam lock set up . It looks like yours is cam lock. do not reverse the spindle on a screw on chuck like a south bend or a 9 x20.
that said I have done threading on my 7x with the tool upside down this allows threading from the chuck side out. less chance of a crash.

In most cases in a home shop you do not need dual tool posts. this is a hobby and your journey so you ust choose your path.
Tin

 

[ELM6061]

G'day all and again, thanks for your comments.

@chbeyer, Yes I get what you are saying, now that I understand there is a second tool post involved, and the lathes are built for it. Quick change tool post has been on my to do list, and I thought if it was just a simple a case, making further modification while building one, then I would consider it. Clearly that is not the case. I find it strange that the manual for my lathe state's it takes 12mm tools, yet a 12mm tool is no where near center and needs to be packed, what a pain having to pack everything, grrrr. Have since met one of the forum members (Swifty) for coffee, and kindly invited to check out his workshop one day. While there, I was shown how he has fitted the spacers needed, permanently to the tool, while it is probably not as good as a quick change tool post, it will surly be better than what I am doing at present.

Tim, you pretty much hit the nail on the head. This thread was mostly a curiosity and just trying to learn. I am not running any coolant on my lathe and my last few efforts at parting have not been too successful. I took particular interest when it was mentioned, "when parting, the chips just fall away, with the tool upside-down". I posted the images of my lathe, as I could not understand how the tools were being supported, knowing "my" cross slide did not allow the tool post to get behind the chuck, and had not picked up on the fact, that there was a second tool post being used (slow , I know).
Now this thread is just a case of; Move on, nothing more to see here!!!! HaHa

Thanks again for all the info everyone.

Eddie

 

[chbeyer]

Hi Eddie,

don't worry, everyone has to start at a point

For the toolpost you should try to find someone with a similar lathe and have a look at the setup. The mercedes of toolpost is the swiss made 'multifix' which really restores the tool within thou after a toolchange. But also cheap models like this are completely OK to work with:

http://www.rdgtools.co.uk/acatalog/Quick_Change_Toolposts__Complete_Sets_.html

You will want to have a couple of those holders so it is nice when you can afford a lot of them

Before buying you have to check carefully that the toolpost matches the hight of your crossslide ...

chers
christoph