# Shars retrofit parting blade



## Ken226 (Jun 22, 2021)

I've been using one of these for a long time:


shell gas station open near me


It was a big upgrade from HSS blades and made parting quite a bit easier,  but I kinda always wondered how the same gtn-2 inserts would work if it wasn't extended so far from the toolpost.  It always seemed to kinda suck for rigidity.

I came across one of these retrofit blades which allowed me to use gtn-2 inserts with the HSS blades holder.  It moves the blade about 1-1/4" closer to the toolpost.

I just finished taking my first cut with it, and am very impressed.   The extra rigidity made a significant difference.   It was definitely worth the price.

Anyone else using one?  Opinions and experience?


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## RandyWilson (Jun 22, 2021)

I have the -3 version. I haven't snapped a HSS blade since. I still suck at parting, but I haven't broken anything with the GTN-3.


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## Ken226 (Jun 22, 2021)

RandyWilson said:


> I have the -3 version. I haven't snapped a HSS blade since. I still suck at parting, but I haven't broken anything with the GTN-3.




I'm loving it so-far.    I've been using the same inserts for a long time,  but having the blade over an inch closer to the toolpost center made a remarkable difference.


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## Ulma Doctor (Jun 22, 2021)

i should reevaluate carbide parting tools
i purchased a used blade, new inserts , and found it to be less than stellar on my 1236 lathe
maybe a new blade with new inserts may be the answer 
thanks for the report!


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## Ken226 (Jun 22, 2021)

I think the difference I'm seeing is due to the new blade being much closer to the toolpost.  Less cantilevered length along the z axis.



The flexural rigidity of a cantilevered beam is a function of (elastic modulus times second moment of area) divided by length cubed.

So, the denominator being a cubed number (length cubed),  a small change in the amount of offset would have a huge effect on rigidity.

At least, that's my theory anyway.  

The old blade had 2" of offset, and the new blade has 1".     According to that formula, reducing the offset by half should make it 8x more rigid.  Along the z axis anyway.    
      It would probably be alot more accurate to find the distance from each blade to the toolposts center of moments,  and calculate the difference based on that, but I don't know where that is.  Whatever the actual amount,  I'm sure it's a good bit more rigid.

My blade stickem-out on the X axis is the same on both, so that shouldn't have anything to do with it 

It seems to cut about 8x better anyway. 





The new blade sits in the holder with a few degrees of rake as well, rather than horizontally.  That could be playing a role as well.

Kinda makes me wonder. How many loved or hated tools/inserts may have performed just based on how they were mounted.

Edited to add a correction:
Earlier I guestimated about 1-1/4" difference in offset.   Looks like 15/16" is more accurate.


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## Firstram (Jun 23, 2021)

15/16" is a huge improvement, thanks for the heads up!


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## RandyWilson (Jun 23, 2021)

As I understand it, the tool blade is designed specifically to mount in the angled/raked BXA holder. The cutting insert is held with less rake than a normal tool so it's relative position to the work ends up as intended.


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## Ken226 (Jun 23, 2021)

RandyWilson said:


> As I understand it, the tool blade is designed specifically to mount in the angled/raked BXA holder. The cutting insert is held with less rake than a normal tool so it's relative position to the work ends up as intended.



Since you mention it, I went and eyeballed them side by side.  

Your absolutely right,  I can clearly see that the insert fits into the new blade at at an angle to the blade,  keeping it's rake relative to the part the same.


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## hman (Jun 24, 2021)

@Ken226 - Please give us a link to this parting holder.   I've tried searching the Shars website for "P3N" ... no joy.  Thanks!


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## KevinM (Jun 24, 2021)

hman said:


> @Ken226 - Please give us a link to this parting holder.   I've tried searching the Shars website for "P3N" ... no joy.  Thanks!



I bought one.  It is a little hard to find.






						Search results for: 'retrofit'
					

Shars Tool




					www.shars.com


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## Ken226 (Jun 24, 2021)

KevinM said:


> I bought one.  It is a little hard to find.
> 
> 
> 
> ...



Yes,  that's it.  Mine is the narrower BXA size 11/16, for gtn-2 inserts.   I picked mine up on ebay.


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## Video_man (Jun 26, 2021)

Ken226 said:


> I've been using one of these for a long time:
> 
> 
> shell gas station open near me
> ...


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## Video_man (Jun 26, 2021)

Ordered one today, thanks for the tip!


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## Cadillac STS (Jun 26, 2021)

I got one of those and it solved all issues with parting for me.


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## Ken226 (Jun 26, 2021)

Cadillac STS said:


> I got one of those and it solved all issues with parting for me.




What inserts are you using?

The Shars inserts that came with it seem to work pretty good.


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## Cadillac STS (Jun 27, 2021)

Ken226 said:


> What inserts are you using?
> 
> The Shars inserts that came with it seem to work pretty good.


The ones that came with it.  Comes with ten and they last a very long time


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## Cadillac STS (Jun 27, 2021)

An important consideration with parting is that if possible take the part out and cut it with the bandsaw then face off the edges. Nothing wrong with that.


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## Christianstark (Aug 11, 2021)

GTN 2 vs 3 for a PM 1340GT?


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## Janderso (Aug 11, 2021)

I have to agree, this set up makes parting effortless with a rigid lathe.


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## xr650rRider (Aug 11, 2021)

Christianstark said:


> GTN 2 vs 3 for a PM 1340GT?



I use the GTN 3 it's 1/8" wide and I've had better luck with 1/8" in other parting tools.


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