Slipjoint long pull question

Stang Bladeworks

KNIFE MAKER
Hi Guys,

I just got a mill and I have been looking for any excuse to use it. I decided to use a 1/16 end mill to mill long pulls in my slipjoints. Due to my process I need to mill this after hardening. I run my cpm154 at 62HRC so it is a bit of a challenge. I bought a carbide end mill on amazon for this task. I got one done but my endmill snapped. I am wondering if anyone has any tips or tricks for an operation like this. I am hoping to get more than one knife per endmill. For this time I ran about 2500rpm with .005" depth of cut. Is there a specific type of end mill that would excel at this? can I reasonably get multiple knives out of one endmill? should I adjust my parameters? For this one I used rapid tap but I imagine I should use some coolant or at least air to help. The chips started to pile up badly. These small endmills snap like toothpicks and they are not cheap. I am open to any suggestions, I have no machining experience so I have a lot to learn / spend...
Thanks.
69368
 

John Wilson

Well-Known Member
I make my long pulls on the mill with a dremel cutoff wheel. I chuck up the cutoff wheel and position the blade in the vise. Advance .005 go left, advance .005 go right... repeat until I get the depth I want.
 

Jason Volkert

KNIFE MAKER
@Stang Bladeworks I don't have any experience with milling "long pulls" but I do have some experience with endmills. I found that cheap Chinese endmills are really made out of chinesium. A American made end mill from places like lake shore carbide are worth the extra money. They last 2 to 3 times longer for me in my shop.
 

Stang Bladeworks

KNIFE MAKER
@Stang Bladeworks I don't have any experience with milling "long pulls" but I do have some experience with endmills. I found that cheap Chinese endmills are really made out of chinesium. A American made end mill from places like lake shore carbide are worth the extra money. They last 2 to 3 times longer for me in my shop.
I dont doubt that. The worst part is these chinese ones were more expensive than lakeshore i just needed them right away. Any advice on rpm or depth of cut on something that small?
Thanks
 

Jason Volkert

KNIFE MAKER
I don't usually mill anything that is already hardened. So I don't have any good advice on the subject. If I had to do it I would probably have my mill at full speed for a endmill that small and do like 5thou depth of cuts and see how my mill handled it.
 

KenH

Well-Known Member
Derek, something as small as you're using for milling those long pulls will require high RPM and shallow cuts. You might take a look at this page: https://www.whitneytool.com/SpeedAndFeedCalculator.aspx This calculator doesn't factor in depth of cut and width of cut, but will give you an idea of starting place for RPM.

You would select the type of endmill (carbide), then the type of material, and it looks like "ALLOY AND MED. CARBON HEAT TREATED (Rc 48+)" might be close? Enter endmill diameter you're using (3/32"?) and SFM rate selected from the alloy chosen. Since you're cutting a deep slot (nail pull) it says to reduce SFM by 20 to 40%, so let's use 60

So, with a .093" diameter and 60 as the SFM would give an RPM of 2464 rpm.
 
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Stang Bladeworks

KNIFE MAKER
Thanks for the info Ken.
My mill only goes to 2500 rpm. I thought a 5 thou cut was conservative. My feed rate is slow (by hand) i will try a higher quality end mill. Hopefully i can find one that works good. I like the end result but adding $20 to each knife is not ideal. I will also add some air to evacuate chips.
 

tkroenlein

Well-Known Member
I'm not a master of machining, but when I see carbide that's working like it should, you get "swarf" as opposed to chips or curls. Whenever you see a chip or curl, tool failure is just ahead.
 

John Wilson

Well-Known Member
Sometimes when i set the open postion the blade is canted slightly so i grind everything perfectly straight. If i make the long pull parallel to start with it may be slightly off when im done. Hope this makes sense.
I do that, too. But I have had luck doing that before HT. I can’t open and close the knife while the spring is soft, of course, so I remove the pin and reposition the blade in each position. That way the geometry is solved and complete before HT. The nail nick is the last thing I do. Then I heat treat the blade and spring.
 
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