# Fly Cutting On The Pm 940



## Subwayrocket (Aug 16, 2016)

A short vid , fly cutting jaws of an old vise I found at the scrap yard . The aluminum jaws were kind of chewed up and a few places where cutters cut into the jaws. Welded those over then milled and fly cut them.
No clue what make or model this vise is...was on an old Supermill at the junk yard .






Before





One Jaw down , other one started welding up the cuts and dings


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## Dan_S (Aug 16, 2016)

That left a really nice finish!


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## Subwayrocket (Aug 16, 2016)

Thanks Dan_S .  I roughed it down just skimming off the anodizing and taking off the welds, then came back over it with the fly cutter 0.005" then again at 0.004" to remove the last of evidence of dings. The right RPM and feed makes it like glass . I practiced on a few of my aluminum chill blocks.  Only prob is that I wish I could run it at higher Rpm , but it's a heavy unbalanced cutter and vibrates in the machine at H1 , 650 rpm so I run on L3 370 rpm (no vibration) and a a lower table feed of 2 on the power feed .  You can see in the vid, the X handle rotating SLOWLY .
 I was thinking about maybe tapping the back end of the bar and adding a bolt that I could add weights to as an adjustable counterbalance .  ???   idk  Any thoughts anyone ?? 
Yes it leaves a nice finish , but it's very slow going at 370 RPM


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## Dan_S (Aug 17, 2016)

Subwayrocket said:


> I was thinking about maybe tapping the back end of the bar and adding a bolt that I could add weights to as an adjustable counterbalance .  ???   idk  Any thoughts anyone ??
> Yes it leaves a nice finish , but it's very slow going at 370 RPM



I'd avoid that, as the bar is probably hardened.


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## Subwayrocket (Aug 17, 2016)

I'm talking about the back part that hangs out the back of the cutter, not the cutting end. I have M42 bits that would probably cut it....idk if my taps would tap it though ...the other option is to drill a hold, then weld a nut to the back of the bar over that hold. Anything to allow me to add counter weight.  I may call Suburban today and inquire about this .  More expensive option is to but the 7" bar which I could just slide in more , then have more equal weighted amounts sticking out each side.  With this 5" bar, I've got about a 3/4" steel cube sticking out one side, and nothing on the other to balance it .


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## Dan_S (Aug 17, 2016)

what kind of chipload & sfpm are you running right now?


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## Subwayrocket (Aug 17, 2016)

Dan_S said:


> what kind of chipload & sfpm are you running right now?


Dan , so far I have not calculated it. I started slow and did it by feel and watched for good finish. On my PM940 in the above vid, i'm taking a 0.005" cut at 370 Rpm and the power feed dial on approx # 2 .
If I go above 2 on the power feed, I start seeing more lines and less mirror ...and slower than 2 , (from what I see in the finish)  I think it's mushing over the same place to much .
Anyway, i'm not sure what that calculates to .  I first ran a 1" end mill at 1300 Rpm , roughing over the welds hand feeding ... then I skimmed the entire surface level with the same end mill at 1300 Rpm and taking about 30 thousandths with the dial at 3 or 4 on the power feed .  Sorry I don't have those numbers . I am still learning


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## Dan_S (Aug 17, 2016)

try the calculator hear.
http://www.carbidedepot.com/formulas-milling.htm

my concern would be that you might not be able to go much faster, before you reach the limits of the insert.


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## Subwayrocket (Aug 17, 2016)

Dan_S said:


> try the calculator hear.
> http://www.carbidedepot.com/formulas-milling.htm
> 
> my concern would be that you might not be able to go much faster, before you reach the limits of the insert.



I will try that calculator. Thank you !  When I did run it at 650 Rpm it still left a mirror finish with the power feed at around 3  . Wish this machine had a speed between L3 370 Rpm and H1 650 Rpm  
...I think on their website they say not to exceed 1300 on any machine .


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