Rear mounted parting blade.

[DPittman]

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.

 

[TorontoBuilder]

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....

 

[Susquatch]

On the rear mounted upside down blade the tool does not dig in.

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.

 

[Xyphota]

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.

 

[TorontoBuilder]

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.

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

 

[DPittman]

@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?

Just because I had the 4way tool holder sitting around and it wasn't going to be used for anything else.

 

[Susquatch]

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

Glad you clarified..... I was gunna jump all over you. All 1966 except els, dro, vfd, etc etc etc

 

[DPittman]

Ha ha, I got the April/May issue of "Machinist's Workshop" in the mail today and there is an article on making a rear parting tool post!