# Which parting blade thickness should I go with?



## Wonderclam (Oct 16, 2019)

I have a PM1127 lathe and I'm looking to buy a parting blade for my parting tool holder. I'm looking to get the "T" shaped parting blades, and the ones with cobalt mixed in.

I'm trying to decide which thickness I should go with. 1/8, 3/32 or some other thickness? I think I remember seeing a Tubalcain video where he recommended not to get the 1/8, and to get the 3/32 instead or was it the other way around?

Also, another unrelated question:

How much diameter should I be turning on my lathe at max? I've been weary of doing more than .050 as I'm not sure how thick of a cut my lathe can handle and I don't want to break anything.


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## ddickey (Oct 16, 2019)

3/32" is a good width. 
Never run an 1127 so can't comment.


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## benmychree (Oct 16, 2019)

There is less chance of chatter on small lathes using narrow parting tools.


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## T Bredehoft (Oct 16, 2019)

I use a 3/32 by 1/2 (concave grind on both sides)   on my 1030, but I cannot feed it as heavy as I'd like, it stalls the drive. It could be I'm cutting 4140 half hard. I tried the one that came with the machine, it's aobut .140 wide, It either chatters or stalls.


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## Chewy (Oct 16, 2019)

I use the Shars posted below on a 1228 Lathe.  Works great.  Don't buy cheaper straight parting tool. Mine is in junk drawer. I  turn 1018 a lot.  Charles









						SHARS P2 "P" Type Type 3/32 x 1/2" x 4-1/2" M42 Cobalt Cut-off Blade NEW !{  | eBay
					

Find many great new & used options and get the best deals for SHARS P2 "P" Type Type 3/32 x 1/2" x 4-1/2" M42 Cobalt Cut-off Blade NEW !{ at the best online prices at eBay! Free shipping for many products!



					www.ebay.com


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## ttabbal (Oct 16, 2019)

On my 1127 I use a AR Warner HSS blade from littlemachineshop.com. I don't remember the thickness. 

I found the biggest improvement by far was a rear mounted tool holder for it. The compound just lets it flop around too much.


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## mikey (Oct 16, 2019)

I would try a P1 (1/16" wide) blade first and go to a P2 (3/32" wide) only if the P1 doesn't work. The narrower blade will cut with lower cutting forces and will work on pieces up to 1.5" OD or more. Your set up must be rigid, the tool must be on center and perpendicular to the work and the tool must be sharp. 

As @ttabbal said, a rear mounted tool will work best.


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## pontiac428 (Oct 16, 2019)

My workhorse parting tool for my Atlas is P2.  Small lathes don't like thick parting tools.  I run P1 when I can get away with it.  I really like way the 1mm (.040) blades from Shars cut, but they explode into a hundred tiny knives if they get bound up.  So my go-to is P2.


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## Pcmaker (Oct 16, 2019)

mikey said:


> I would try a P1 (1/16" wide) blade first and go to a P2 (3/32" wide) only if the P1 doesn't work. The narrower blade will cut with lower cutting forces and will work on pieces up to 1.5" OD or more. Your set up must be rigid, the tool must be on center and perpendicular to the work and the tool must be sharp.
> 
> As @ttabbal said, a rear mounted tool will work best.


 what's a rear mounted tool?


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## ttabbal (Oct 16, 2019)

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.


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## ezduzit (Oct 16, 2019)

ttabbal said:


> 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.


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## ttabbal (Oct 17, 2019)

ezduzit said:


> 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.


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## mikey (Oct 17, 2019)

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.


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## ezduzit (Oct 17, 2019)

mikey said:


> 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.


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## mikey (Oct 17, 2019)

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.


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## stioc (Oct 17, 2019)

@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.


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## darkzero (Oct 17, 2019)

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.


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## ttabbal (Oct 17, 2019)

@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.


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## stioc (Oct 17, 2019)

@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?


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## Wonderclam (Oct 17, 2019)

stioc said:


> @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?


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## ttabbal (Oct 17, 2019)

stioc said:


> @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?



Pretty much. There is a through hole for the t-nut, I just used a piece of threaded rod with a nut and washer on the top to hold it to the carriage. There are two smaller holes toward the blade that are threaded under the slot and clearance above to tighten the blade. I believe I used 1/4-20, mostly because I already had a tap and bolts that size.


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## stioc (Oct 17, 2019)

Wonderclam said:


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



Yes hence the 3/32" over the 5/64" but up to a limit of what your lathe and workholding can handle. Pushing a thick blade into the workpiece can knock it out of the chuck if the workholding isn't optimal.


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## mikey (Oct 17, 2019)

Wonderclam said:


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



In my opinion, a slightly thinner blade is useful when parting from the front IF the lathe is tight and the blade is held rigidly, perpendicular to the work and is dead on center height. I prefer a P1 (1/16" thick) on my Emco Super 11 and it cuts well from the front on that lathe. Thinner blades cut with lower cutting forces. I have parting blades from P1-N to P3 and inserted carbide blade at 1/8" wide. I've used them all to see what they're like and thinner blades are better if your lathe can handle them.

When parting from the rear, thinner blades are definitely better. I use a P1-N for all work on my Sherline and it cuts anything that I can fit on that lathe with no issues (up to 2" OD). The tool holder design holds the blade rigidly, vertically and does not allow it to turn. This allows the girder design of a P-type blade to excel, even when extended far beyond the length needed for a cut. 

So, I suggest using the thinnest blade you can get away with.


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## stioc (Oct 21, 2019)

ttabbal said:


> Pretty much. There is a through hole for the t-nut, I just used a piece of threaded rod with a nut and washer on the top to hold it to the carriage. There are two smaller holes toward the blade that are threaded under the slot and clearance above to tighten the blade. I believe I used 1/4-20, mostly because I already had a tap and bolts that size.



I copied your design right down to the step on the left side, thanks for the pics and info  The only issue I had was I couldn't clamp down the blade because the two bolts just didn't have the leverage with just the saw kerf to bend the top of the post. So I lopped off the top from being 1/2" thick to a 1/4" thick. That didn't do anything. Then I ran the saw from the opposite side like you did but that didn't help either. I finally decided to drill the end of the saw kerf and that made the top just springy enough to get a good clamping force going with the two 1/4-20 bolts.

As far as how well it cuts it's hard to say because I didn't really have time to play with it but it cut the aluminum washer ok in my test (shown in the pic) but it had a lot of squealing even with WD40. The cutting edge is exactly in the center of the workpiece and everthing is clamped down tight. I'll try to sharpen the bladen and see what happens.


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## ttabbal (Oct 21, 2019)

Looks like you're on the way! I'm glad my posts were helpful. Hopefully your parting is improved as mine is.


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## macardoso (Oct 21, 2019)

I use a 1/8" blade on my 12x36 and wouldn't go any larger. Smaller blade equals less forces and a better cutting experience. You don't *need* a rear mounted tool post to get good results although many produce evidence that they work very well. If you can part using power cross feed, I find the results to be very consistent.  

Get a good tapping oil to use while parting off. It makes a difference over coolant or cutting dry.

Just my personal thoughts, thousand ways to skin a cat.


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