beej

ideas on how to cut this?

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I'm having problems cutting the thin rib on the end of this pin. the pin comes pre hardened 50Rc. the rib is .088x.275 it stands up 1.75 tall. Straight walls (no draft).  I'm stuck with the design. I only have 3 axis machines. We've been able to make them functionally right, but the customer is complaining about the chatter marks on the finish.

 

so far I've tried using Millstar Backdraft cutters and reduced shank endmills to try and keep the chatter down but so far not much has helped. 

 

I attached a jpeg file so you can see what I'm talking about.

 

Any ideas or processes that have helped you?

 

 

post-10280-0-05362000-1474374397_thumb.jpg

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rough, semifinish, finish, part off

 

depending on tolerances that is

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Can you buy a pin that is at least 1" longer and hold both ends while cutting the detail? Then wire off the extra material bringing the part to length. That way you are supported on both sides of the cut. It will be two setups but your part will turn out better. 

 

If you really want to stand it up to cut it, leave more stock for the finish pass and finish it in shorter sections. For example, rough and finish .25" lengths at a time. 

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If you really want to stand it up to cut it, leave more stock for the finish pass and finish it in shorter sections. For example, rough and finish .25" lengths at a time. 

that's a good idea, I'll give that a try. standing it up is the only option I have at the moment although it may come to getting a lathe with live tooling or a 4th axis

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You could also try ramping to keep your tool engaged.

 

Edit: You don't say which size endmill you are using. The smaller the better when trying to reduce chatter. Less surface contact will reduce chatter.

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wire edm a blade and core pin and silver solder them together.

 

then go slap the designer silly and tell him to use a narrower, off the shelf ejector blade the next time.

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You could also try ramping to keep your tool engaged.

 

Edit: You don't say which size endmill you are using. The smaller the better when trying to reduce chatter. Less surface contact will reduce chatter.

we have tried ramping and constant z cuts. about the same result both ways, but I thought, as you did, that ramping would be the way to go.

 

I have been using a 3/8 dia cutters with 5/16 shank.  That is bigger than I would like but, the overall length of the pin keeps me from going much smaller.

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wire edm a blade and core pin and silver solder them together.

 

then go slap the designer silly and tell him to use a narrower, off the shelf ejector blade the next time.

some Good ideas, guys, I appreciate the input.

 

I've been kicking that  wire edm idea around some too.

 

I can't blame the designer too much on this. These aren't ejector blades, they are punches on a Trim die.  Punching flash through a pocket on a casting.  there are lots of different shapes and sizes beside the one that I showed in the pic.

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i doubt you will ever get the chatter to stop being that tall and having it standing vertically, if possible bench the chatter out/ knock it down so its not as bad

id rough to +.005 and use 1/4 ball to finish it, try .025 stepdowns or less if it still chattered

 

if it was tight tolerance +/-.0005  id:

rough in the mill and finish grind it

or

wire from both sides and then cnc the radii

 

 

 

another idea would be to lay it down and do two operation and support the end(buy a longer pin and use the extra to hold it by and cut it off when youre done)

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some Good ideas, guys, I appreciate the input.

 

I've been kicking that  wire edm idea around some too.

 

I can't blame the designer too much on this. These aren't ejector blades, they are punches on a Trim die.  Punching flash through a pocket on a casting.  there are lots of different shapes and sizes beside the one that I showed in the pic.

 

 

a mould builder sees an ejector blade when it's actually a punch. imagine that. :lol:

 

assuming the punch his hardened, i'd contour it right to size using light depth cuts having the tool enter and exit the cut. surface contour or hsm waterline to avoid entering and exiting at the same position all the way down. ramping with the tool constantly engaged in the material would generate too much heat i think. use a necked bull nose tool with a small corner radius. you want only the end of the tool, say .05 up to .100 thou from the tip to cut. any more than that is going to want to rub, chatter, and generate heat.

 

edit:

 

now i actually read the first post instead of just looking at the photo. :blink: yes, is hardended. millstar backdraft tool, nope, not enough rake on them, they'll rub and chatter. yup, use solid carbide and neck the tool so only the very tip cuts, that should eliminate the chatter.

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Hi....Have you tried it with grinding?...We were machining/finishing similar type of pins on surface grinder.( by providing the form to grinding wheel).

 

I am not sure,,,,whether this option suits your requirements......Thanks ....N3 

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Make a split collet to hold onto the shank with just the rib sticking out?

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If I understand correctly this is an existing pin that is being modified.  With that said, you could try building a reservoir around the pin and fill with low melting point alloy, then finish with the alloy supporting the pin.  When complete, melt away the rest of the alloy.  I have modified pin heat sinks (1/16" dia pins, 1" tall) using this method and the results were PERFECT.

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Put that thing in a collet block and lay it down in the vise.   You'll have much less engagement on the endmill.  Use as small of an endmill as it takes to have no chatter.

 

Cut one side, then rotate the block 180 to do the bottom side.

 

Won't be fast but it'll work every time.

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Do you have to make them fast or something? I cut pins like this, with an amazing finish, but it is slow. The trick is to use a really small cutter engagment angle, which also includes reducing the axial length of flute that touches the part.

 

I would use a .25" or smaller endmill and relieve the shank and flutes so that I only have about .01" or so of actual flute that can cut at the end of the endmill. Then use a .5-2* engagement angle and Z ramp at 2* all the way down to keep the cutter engaged.

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I would relieve shank and flute so only 1mm (40 thou old money) cutting, and try conventional milling not climb milling ramping , and well supported

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We would call up Moeller or Dayton and tell them to make these. They are the professionals and they grind this stuff. Maybe they ruff them on the mill, but they always have a ground finish when we get them. Companies who make die components (ball lock retainers, buttons, punches, etc.) can do this stuff in their sleep. It's what they do.

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thanks for all the input guys.  A lot of really good ideas here.  More than one way to skin a cat, I see. not that I'm into cat skins and such. :laughing:

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