Never machined p20 --- NEED HELP ASAP!!!
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  1. #1
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    Default Never machined p20 --- NEED HELP ASAP!!!

    we have a rush job that needs machining tonight (friday)... and i've been nominated to do it... however it is p20 and i've never machined p20 before, or anything hardened for that matter.

    right now someone else is working on it and i am to take over, however they are just working on picking up locations, and setup... and no doubt i'll have to do most if not all of the machining.

    the machining itself is relatively simple work, however tedious.

    we have plugged 6 positions on a mould, which are 90 degress 3 axis work. they were welded in. they are on angled faces which need to have the weld machined out of them, as well as machine down the plugs to match the faces.

    the faces will probably need to be machined with ball nose cutters 3d work..

    the plugs also need a 7mm hole put in them as a "die button" which has to mate with punches in the other half of the mould. we've ordered a carbide 7mm reamer as well as a .010" - .015" carbide drill which is under 7mm (can't recall the exact size off the top of my head).

    i do not think we have through spindle coolant. SO.. with the carbide drill, i know with TSC drills you can not peck and the coolant still gets through obviously... but with just a standard carbide drill, do you still not peck?? will the drill not get severely hot if not/weld chips/etc? i'm not sure on the exact depth of the holes, as this is all being thrown at me today (friday afternoon)... the other guy ordered a spot drill... but as is my understanding you do NOT spot with carbide drills or it'll wreck the edges pretty quick, and that carbide drills hold their location without spotting. but since location is critical, perhaps if i just do a SMALL spot, just enough more to guild the middle of the drill, not enough that the edges will cut into the chamfer of the spot drill? then we are following it with the 7mm carbide reamer.

    what sort of speeds and feeds can i look at? peck with said drill or no? spot or no? how about the reamer? never ran a carbide reamer before... treat it just like a HSS reamer but the fact that it's carbide allows it to machine hardened peices?

    how about the welding, how hard is it to machine? have never machined it before... what sort of speed/feed can i start with as a starting point for my ballnose cutter?

    i know Speed and feed is all "estimate" untill in the actual situation... but i need help desperately as to where to even begin, so any suggestions would be great....

    ANY Help at all will be greatly appreciated... as i'll be working on this in a few hours... i'm not looking forward to it and don't have a good feeling about it, as i've never done work like this before... the last thing i want to do is break a carbide reamer or drill inside these holes... but also not breka the tooling cutting edges as, you guessed it, we only are getting one of each...


    Thank you! I'll be checking back in a couple of hours!

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    Not hard material to machine just a little gummy and abrasive. We used to machine p20 all day long and we made pump bodies that held .0002 over 450 degrees. Check with online speed and feed charts if you worried and try not to work harden the material. You will find its more like a harder mild steel than anything.

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    P20 is not 'too' bad as far as machinability goes

    Ok yes it work hardens to some extent, but not as much as other tool steels that harden as soon as you even think about machining them

    I used to do punch and stripper plates out of P20 drilling 2000 0.050" odd holes in each
    What we used to do was use a proper BS style center drill eg a BS 1 center drill and drill the center so that the hole dia at the top was slightly smaller than the finished size of the hole, then run the drill in pecking 1 D deep , keeping the RPM low and the feed high (4"/min rings a bell, but dont quote me on that)
    With a 7mm hole I'd be tempted with a BS4 center drill, followed by a 6.8 drill, then the carbide reamer.
    The only real advantage we find with the crabide reamers is that they tend to hold their size better than the HSS ones in a production enviroment

    Boris

    "free cookie for spotting the spelling mistake"

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    Quote Originally Posted by Boris View Post
    P20 is not 'too' bad as far as machinability goes

    Ok yes it work hardens to some extent, but not as much as other tool steels that harden as soon as you even think about machining them

    I used to do punch and stripper plates out of P20 drilling 2000 0.050" odd holes in each
    What we used to do was use a proper BS style center drill eg a BS 1 center drill and drill the center so that the hole dia at the top was slightly smaller than the finished size of the hole, then run the drill in pecking 1 D deep , keeping the RPM low and the feed high (4"/min rings a bell, but dont quote me on that)
    With a 7mm hole I'd be tempted with a BS4 center drill, followed by a 6.8 drill, then the carbide reamer.
    The only real advantage we find with the crabide reamers is that they tend to hold their size better than the HSS ones in a production enviroment

    Boris

    "free cookie for spotting the spelling mistake"
    Crabide reamers...

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    Quote Originally Posted by Dave Cross View Post
    Crabide reamers...
    Of course, how easy to spot. You spelled reemor wrong!

    Ray

    Where's my cookie?

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    Quote Originally Posted by IAMATT View Post
    Not hard material to machine just a little gummy and abrasive. We used to machine p20 all day long and we made pump bodies that held .0002 over 450 degrees. Check with online speed and feed charts if you worried and try not to work harden the material. You will find its more like a harder mild steel than anything.


    0.0002" over 450 degrees is pretty good

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    Quote Originally Posted by Slapstick View Post
    however it is p20 and i've never machined p20 before, or anything hardened for that matter.
    Hardened to what?

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    Quote Originally Posted by Boris View Post
    P20 is not 'too' bad as far as machinability goes

    Ok yes it work hardens to some extent, but not as much as other tool steels that harden as soon as you even think about machining them
    "
    Thankfully none of those (P20 or any tool steel) work harden as high or easily as 304 and most other 300 series stainless steels!

    Jeff

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    Default machining P-20

    Hi Slapstick:
    You may find that the areas around the welds are hard compared to the rest of the block...P-20 is often deliberately flame hardened in wear areas like shutoffs by moldmakers who want to give a cheap mold a longer lifespan.
    I do a lot of laser mold welding and it definitely is harder around the weld than elsewhere on the block.
    The large mass of the block and the small size of the weld means that the weld will be quenched by the block drawing the heat away almost as quickly as an oil quench.
    Expect to go through a few cutters as you cross the weld zone.
    If you're lucky it won't be too bad, but buy a few extra cutters just in case.
    Cheeres

    Marcus
    www.implant-mechanix.com

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    Thanks guys for the reply.

    Everything went ok. We decided that rather having me stay late friday night burned out, that i would put the holes in, while another guy came in saturday morning for the ballnose work.

    since i had no experience with this before (though i have read up on it), i followed what the other guy told me to do.

    The spot drill broke... i had a feeling it would as the relief angles were pretty steep and it didn't have much meat behind the cutting edge. i ran it at 1200 rpm and 2 IPM feed rate. We also could not use coolant since there was electrical work inside that could not get wet.

    But i knew the carbide drill is rigid enough without spotting... i ran it at 1000 rpm and 2ipm feed as well. using 2mm pecks dry, and a total depth of 1.5". The drill survived but one cutting edge was crumbled and the other was a little worn.

    Now i did what the other guy told me to do, as he was more in charge of the work, and despite me not agreeing with him... if anything went wrong... i wanted to do it the way he told me, not that i did it my own way, and someting messed up.

    if i were to have done it my own way, i would have skipped the spotting all together. i would have NOT pecked with the carbide drill. As both spotting and pecking are not reccomended for carbide drills, but he didn't seem to know this when i mentioned it. I have experience with TSC carbide drills, and not pecking, but would have been a little nervous not to peck with no TSC running through the drill.. but pecking causes chipping when chips get stuck under the cutting edge, and spotting causes chipping as there are the two different angles... but, i did what he told me to do just in case anything went wrong.

    Thanks all for the help.

    with that, my question still stands... with TSC carbide drills not pecking isn't a problem since the coolant is getting right to the front... with non TSC carbide drills... what do you do? no coolant is getting to the cutting edge, but pecking is bad... so which is better?

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    carbide eg should be e.g.

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    Quote Originally Posted by thndrbug4u View Post
    carbide eg should be e.g.
    thanks, I've been confused for the last 11 years.

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    Quote Originally Posted by thndrbug4u View Post
    carbide eg should be e.g.

    Was this a "better late than never?" moment, or just a random drive-by editing?

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    Hey Boris, forget the cookie: I'll take a crab salad, thank you. :-)


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