When it comes to parting off a 2" diameter piece of hot rolled steel my little mini lathe likes to chatter a bit. I built a parting tool spring type holder similar to the ones I have seen on the net. This one is different. It will mount up flush with the QCTP block and you will not loose any cross slide travel. It is made for the smaller tool holders like the HESS 250-00x holders and mounts up fine on the mini lathe. Using a 5/32" by 1/2" blade it cuts like butter without chatter. Just a bit of noise but it is the best parting off I have had with this lathe in the last 2 years.
So you need some steel
one block 1" x3.75" x 2"
one plate 1/8" x 2" x 1.2"
one 5/64" x 1/2" x 4.5" cutoff tool
6- 8-32 button head screws
3- 8-32 flat head screws
1- 3/8" x 7/8" spring pin
1- piece 1018 1/2" square
The outboard plate that clamps the cutoff tool works very well. I was concerned that it might allow the tool to move but it is rock solid.
Short video of the tool at work.
Last edited by jjr2001; 04-21-2017 at 07:24 AM.
Nice work JR
This certainly reduces the tendency for the tool to dig in and grab any backlash in feed screws.
Have you thought about achieving the same result with a rear tool post, both approaches will allow the tool to move away from the work under cutting forces. I use tipped inserts in my parting tool and have parted of 3 inch blanks with auto feed on occasions in my SB, it has plain bearings and is one of the few times I think it may help with less vibration.
Thanks for posting.
Hi Dan, Thanks for the tip on the rear mounted tool for parting off. I have seen that method on the net
and it looks like a good idea. I was torn between that fix and the spring tool. Thought the spring tool
would be a bit easier to do since my cross slide is pretty small. Either way both methods have merits.
I had never bumped into this and did a search because you said JR you'd seen it else where. Looking at it I had an inkling, but I wanted to make sure. What an interesting fix. Just out of curiosity did you try it without the spring pin, just the hole? For whatever reason I can't get that it really does add "spring".
My lathe does indeed put up a chatter when trying to part off. Soon as I can figure out where I can get a chunk of steel like that this is going on the must make pile.
Thanks for the plans, parts list and pix, good job.
Hi C-Bag, I have seen similar types on eBay usually under the brand Williams, Atlas, or Armstrong.
They are from the old days when lantern tool post ruled. Tom Lipton of Oxtools has one he made
years ago and explained it like this. The pivot point is above the tool bit so the torquing force tends
to move the tool bit, when under extreme load, away from the work instead of into the work like
a normal tool setup.
In my testing I did use it without the roll pin and it was just too free and the tool bit seemed
to jump around. The parting tool I was using chattered a lot when I used it in a standard
tool holder but when I used it in the spring holder with the roll pin the chatter was gone.
I could feed in and curl off chips quite well on the 2" blank I was testing it on. I have seen
versions of this tool without the roll pin.
I suppose tool rigidity depend on the steel used. I just had a piece of hot rolled and
found that the pin does make it work better. I could see an entire build of several of these trying out
different diameter holes starting with say 1/4" and working up to find a sweet spot for the particular
setup and lathe in use. The other thing in my version is the long "key" that can be adjusted in or out
for different extensions toward the work being turned. This gives some latitude in setup and the
ability to "tune" the tool in case harmonics start to give a problem. However the main reason for the long
"key" is so the tool can be set flush with the forward face of the QCTP.
Ah, so many tools to build and so little time!
My .01 cent worth, discount for cash. Hot rolled steel is fine. I'd venture the web of flex hole would fracture, but the roll pin distributes the load and absorbs the flex. I like the hole and profile aren't concentric.
A back tool post offers the backlash advantage, saves toolholder space and changes, can be set close to the material to save cranking the crosslide, and chips fall out of the cut.
Just keep the gravity switch on.
...we'll learn more by wandering than searching...
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