Which parting blade thickness should I go with?

[ezduzit]

The tool is mounted on the back of the work, upside down. The forces and flex are different and seem less prone to chatter and catching. Gravity helps evacuate chips. The is less flex as it is generally a solid mount, no compound or QCTP flex.

Here's a photo of mine.

View attachment 304089

Too much stick-out for this operation.

I part on the normal side of the machine and prefer the 3/32" HSS parting tool over the 1/8" carbide inserted one, even in stainless steel.

 

[ttabbal]

Too much stick-out for this operation.

I part on the normal side of the machine and prefer the 3/32" HSS parting tool over the 1/8" carbide inserted one, even in stainless steel.

Quite so. Yet it worked fine. It was part of the test to have it hanging out too far. Normally, I do set it properly to just clear the DOC.

I'm not of the opinion that there is "one true way". This worked best for me, even with the stick out. I tried a QCTP holder on the compound, didn't like it. On a plinth it worked pretty well. The rear mount improved further. And of course it was on my particular lathe, gibs set a certain way etc.. There are always variables.

Perhaps there is another method that I will like better in the future. Always willing to learn.

 

[mikey]

Unlike a front mounted tool, stick out is not usually an issue with a well designed rear mounted parting tool. I've been using one for many years, don't pay much attention to stick out and have never had it dig or chatter.

 

[ezduzit]

Unlike a front mounted tool, stick out is not usually an issue with a well designed rear mounted parting tool...

Regardless of where the parting tool is mounted, stick-out should be adjusted properly. That has nothing at all to do with the side from which the tool is mounted.

 

[mikey]

I beg to differ. If parting from the front then minimizing overhang is important. However, when parting from the rear, my tests suggests that overhang is not critical. I've tried varying the amount of extension to see if I could get the parting tool to chatter, deflect or break and have seen no adverse effects as stick out increases.

I've shown these pics before but they're the only ones I have of these tests so it will have to do.

This is a rear mounted parting tool extended about 5 times the extension needed to make this groove in mild steel. It is a P1-N tool about 0.040" thick and it has made two side by side cuts to produce this groove.



There was no chatter at all. Look at the finish inside the groove:



This same work piece was later parted off about 1" from the chuck and came off without incident. Speed is 1200 rpm and feed was manual.

This same Sherline lathe would require very slow speeds and minimum stick out if trying to do this from the front so where the tool is mounted does make a difference and stick out in a rear mounted tool is not critical.

 

[stioc]

@ttabbal - do you have more pics or info on the rear toolpost? It's been on my to-do list but wasn't sure if aluminum will work and whether to make a modular holder or a specific one for a fixed thickness blade?

As for the blade thickness mrpete22 of YTube fame says to use 3/32" on smaller lathes because the flex will shatter a thin blade. I found that out myself with the 5/64 blade. I now use the shars posted above in 3/32" thickness, so far so good.

 

[darkzero]

My favorite "parting blade" is 0.035" thick.... on my bandsaw. I prefer to use the bandsaw when I can.

But seriously, I have a 12x lathe & 1/8" is the thickest I use. I rarely use it though, I prefer & mostly use 3/32" Manchester tool. I also use thinner, down to 0.019" with my Nikcole Mini Systems tools but mostly use those for grooving.

 

[ttabbal]

@mikey posted an article in another thread that I based mine on. I bet he'll post it here.

I used aluminum, and it seems to be working well. I went with 1/2" blades as I already have some. I considered making it possible to have bigger blades, but I decided that they are pretty simple so I will make another one if I want a different size. I also like that there are no parts to move around. Just a block of metal with a slot for the blade.

Here's a photo that gives a better view of the whole thing.

 

[stioc]

@ttabbal thanks for posting a close up pic. That's an interesting design- simple too just a 2x2 block of aluminum with a single hole at the top that threads into the T-nut at the bottom?

 

[Wonderclam]

@ttabbal - do you have more pics or info on the rear toolpost? It's been on my to-do list but wasn't sure if aluminum will work and whether to make a modular holder or a specific one for a fixed thickness blade?

As for the blade thickness mrpete22 of YTube fame says to use 3/32" on smaller lathes because the flex will shatter a thin blade. I found that out myself with the 5/64 blade. I now use the shars posted above in 3/32" thickness, so far so good.

If thin blades shatter, don't you want to use a thicker one like a 1/8th?