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Rear mounted parting blade.

DPittman

DPittman

Ultra Member
I've messed around with a couple of different variations of using a parting blade on my small lathe. I changed out the original 4 way tool post for a quick change tool post on my compound slide and used that for while for parting.

I then made a mount for the qctp that eliminated the compound and that did improve the rigidity. However I find I like having the compound on much of the time despite the reduced rigidity.

I also experimented with an upside down parting blade in the front and running the lathe I reverse. I believe there is some benefit to this as the chips fall away from the blade quickly.

I now have made a mounting base to utilize the original 4 way tool holder that attaches on the back side of the lathe saddle. I mount the blade upside down again and run the lathe in forward. This allows me increased rigidity when I really need it (parting off) but I can leave my qctp and compound in place. I remove the 4way tool holder from its mounting base when not in use just to give more room around the work.

We will see if it was worth it.
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from my understanding the rear mounted upside down parting blade is the best option.

Mark Presling has a good videos that explains exactly why rear mounting parting is superior


It comes down to this though. Mounted normally the parting blade wants to dig into the piece when things flex. On the rear mounted upside down blade the tool does not dig in.

So even with a very tall post that may not improve rigidity it should be superior

It is the only way to fly....
 
TorontoBuilder said:
On the rear mounted upside down blade the tool does not dig in.
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I've been parting upside down on the front for a decade. Works great. Same principal as others have described for parting upside down in forward gear.

But I fail to see the advantage of a rear mount other than for lathes that cannot be run in reverse.

I do see why @DPittman did it that way though because he wanted to preserve his front mount.

@DPittman - I'm also wondering why you went to all the trouble of a full blown four way tool post back there. Why not a dedicated parting tool post?

@DPittman - I'm really jealous of the T-slots you have in your cross slide. I can't do that, but I may put in a dedicated tool post of some kind when I install my DRO Scale.
 
I had to do something similar a few weeks ago. I normally have a QCTP rigidly mounted to the cross slide, but I needed to make a batch of tapered parts so I re-installed the topslide and moved the QCTP to the back. The myford lathes have threaded chucks so running them in reverse under load is not a good idea. I have a hemmingway kit to make a dedicated upside down parting tool holder which I need to put together.
 
Susquatch said:
I've been parting upside down on the front for a decade. Works great.

But I fail to see the advantage of a rear mount other than for lathes that cannot be run in reverse.

I do see why @DPittman did it that way though because he wanted to preserve his front mount.

@DPittman - I'm also wondering why you went to all the trouble of a full blown four way tool post back there. Why not a dedicated parting tool post?

@DPittman - I'm really jealous of the T-slots you have in your cross slide. I can't do that, but I may put in a dedicated tool post of some kind when I install my DRO Scale.
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Colchester lathes had a popular option of a rear tool post that remains mounted all the time. Every Colchester I've seen with the rear post always had the parting blade installed permanently, so speed may be one reason this remains popular. And I'd say fashion and the desire for historical accuracy may play a role for people like me... I'm going all 1966 with my machine. Well no, that's a lie. I'm going to heavily modify my lathe but still have the solid rear tool post and parting blade for greater rigidity and to save using a tool holder for something more vital
 
TorontoBuilder said:
I'm going to heavily modify my lathe but still have the solid rear tool post and parting blade for greater rigidity and to save using a tool holder for something more vital
Click to expand...

Glad you clarified..... I was gunna jump all over you. All 1966 except els, dro, vfd, etc etc etc:D:p;)
 
Excuse my ignorance….. is the rear or backwards parting deal just more ridgid? I get away with the conventional way on my SM…..

Just wondering what the advantages are?
 
BaitMaster said:
Excuse my ignorance….. is the rear or backwards parting deal just more ridgid? I get away with the conventional way on my SM…..

Just wondering what the advantages are?
Click to expand...
not just more rigid but the cutting force direction tries to push the cutter away rather than into the workpiece causing it to bind. Watch Mark's video for the detailed cutting dynamics
 
TorontoBuilder said:
not just more rigid but the cutting force direction tries to push the cutter away rather than into the workpiece causing it to bind. Watch Mark's video for the detailed cutting dynamics
Click to expand...

@BaitMaster - ^ what @TorontoBuilder said.

But I would add that a rear mount has the same result and dynamics as a front mount upside down in reverse. It's a lot easier to do the front version, but not all lathes can run in reverse without risking the chuck coming loose. It's nice to have options.

@PeterT did some drawings a while back that were really good. As usual, I can't find them. Maybe one of the librarian gurus can help.

My preferred way to part used to be upside down on the front. However, another member gave me a carbide insert tool that was too big for his lathe. It works extremely well parting normally on my lathe. As a result, I seldom use the upside down trick anymore. But when nothing else works, parting upside down in reverse will ALWAYS clobber the problem.
 
StevSmar said:
I have their tangential tool holder which is excellent. So easy to sharpen the tools.
Click to expand...

You are the second to mention tangential tools that I've seen. @RobinHood was the first. I believe his was Australian based too - but that might just be an impression.

I'm not familiar with them at all so I'd really like to know more about them. Especially the turning geometry that makes them work.

Any additional info you could provide would be appreciated.
 
Susquatch said:
I'm not familiar with them at all so I'd really like to know more about them. Especially the turning geometry that makes them work.
Click to expand...
I thought you mentioned in the past that you owned one of these also? They are also called diamond tool holders. I thought you commented that it was odd that we both owned these and a Mesa Tool holder. Guess it must of been somebody else, my memory fails me too. :(
 
DPittman said:
I thought you mentioned in the past that you owned one of these also? They are also called diamond tool holders. I thought you commented that it was odd that we both owned these and a Mesa Tool holder. Guess it must of been somebody else, my memory fails me too. :(
Click to expand...

Yes, I own a Mesa. And yes I recall being surprised that you had one too. Perhaps you are thinking about the Warner tool I also have?

I think this was discussed long before @RobinHood straightened me out by telling me that a tangential tool was not the same as a shear tool. Up till that point, I thought that a tangential tool was just another name for a shear tool - because the cutting edge is tangent to the part surface. I even had the balls to suggest that RobinHood might have meant shear tool when he mentioned tangential.

So lord knows what we were talking about back then! It would be interesting to review it and maybe even correct any error I might have made back then.

Suffice to say here, that I don't think that tangential tools and I have ever worked together..... But it seems like a tool I could be friends with so I'd like to know a bit more about its character before I let the darn thing into my shop..... LOL!
 
Susquatch said:
Yes, I own a Mesa. And yes I recall being surprised that you had one too. Perhaps you are thinking about the Warner tool I also have?
Click to expand...
Ah yes I think you are right!
I think you would like a tangential tool holder as well as you like hss. They are super simple easy to sharpen and are quite versatile. They are also very suitable for smaller lathes as the geometry allows heavier cuts than you'd expect.
Eccentric Engineering website has a video that showcases them pretty well.
 
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