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    Default Machinists Want Blank Parts

    As the title describes, recently a couple of machinist have decided that they do not want parts with precut lead holes from our CNC cutting tables. Instead, would rather start any hole of any tolerance from scratch with a center drill or centercut endmill.

    I have inspected the parts off the table and found nothing out of tolerance and have only been told its "easier" to start with a blank. From a time perspective, I cannot understand why you would want to start with a blank plate every time. For example, laser cutting a 3.25" lead hole in 1/2" A-36 to be finished at 3.505" would take significantly less time than roughing in one on a VMC from scratch.

    Can someone give me some clues as to why you would want a blank plate every time?

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    Maybe they are like DMFTom and need a ton of overtime... ya know, so they can make more than programmers, and contribute more to their 401k, maybe even make $100k/year working 70 hours a week...

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    Quote Originally Posted by AJT View Post
    As the title describes, recently a couple of machinist have decided that they do not want parts with precut lead holes from our CNC cutting tables. Instead, would rather start any hole of any tolerance from scratch with a center drill or centercut endmill.

    I have inspected the parts off the table and found nothing out of tolerance and have only been told its "easier" to start with a blank. From a time perspective, I cannot understand why you would want to start with a blank plate every time. For example, laser cutting a 3.25" lead hole in 1/2" A-36 to be finished at 3.505" would take significantly less time than roughing in one on a VMC from scratch.

    Can someone give me some clues as to why you would want a blank plate every time?
    It all depends on part shape, hole size,location from datum, material, etc..
    But in the example described above hell yes I would laser a hole that size to within 1/4".
    Although on some materials the flame cut edges can be more of a pain than it's worth because they can get hard. Is the A36 annealed?

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    Quote Originally Posted by Mike1974 View Post
    Maybe they are like DMFTom and need a ton of overtime... ya know, so they can make more than programmers, and contribute more to their 401k, maybe even make $100k/year working 70 hours a week...
    But watch out for hard spots they can chip an insert before you know it and then you wasted a $2000 part to save 5 minutes, I tell you it's just not worth it. And remember that 3x the stickout is 3x3x3=27x less rigid..........

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    Quote Originally Posted by ChipSplitter View Post
    But watch out for hard spots they can chip an insert before you know it and then you wasted a $2000 part to save 5 minutes, I tell you it's just not worth it. And remember that 3x the stickout is 3x3x3=27x less rigid..........
    Dang! I knew I was forgetting something... HARD SPOTS~!

    (and flatness to .000000001" over 300")

    can't seem to find that picture of the broken drill in the control though...

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    I totally agree, in most cases dealing with some shit flame cut part just isn't worth the hassle

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    I HATE it when the blanks come with holes already in them.

    HATE IT!!!!

    90% of the time they tried to hit them right on size and
    what could have been a quick slam slam job turns into a
    fricken nightmare.

    Give me a 3" hole to make a 3.5" hole, I'm cool with that, as
    long as the material isn't going to turn into glass, I really
    HATE that.

    I've got one coming this week that will be water jet. 3/4"
    holes. But this time, they will be waterjet to 5/8" not a
    tapered 3/4". It will now be a slam slam job.

    One of my customers recently got a plasma table, and I don't
    know how they lived without it for so long. But its been a
    learning curve as to when and when not to put holes in things.
    No fault of theirs, just trying stuff out to see what the
    machine can, and can't do. Mangled holes in 1/2" 304 are a
    bitch to clean up.

    My suggestion is that when the machinist says they don't want
    holes, don't put holes. When they say they want holes, ask
    them what size they want them.. And then do what they say.
    There are reasons.

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    Quote Originally Posted by Mike1974 View Post
    Dang! I knew I was forgetting something... HARD SPOTS~!

    (and flatness to .000000001" over 300")

    can't seem to find that picture of the broken drill in the control though...

    Here you go....

    Flying Broken Tooling

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    We've run into this before and It kinda depends on the part. Lots of programmers will burn out a "finished" part all on size and then send it to the machinist for follow up ops, but they miss that if any of the features are receiving any follow-up machining, they are not burning out a finished part, they are burning out a "blank" and as such need to leave material to cut in places.

    A good way to think about it is that burning out features to machine often will not save you any time (burning a hole with follow-up drilling vs. drilling a hole from scratch), but it can save you material (nesting pieces together and such). If you are not saving material, you're better off leaving it there for the mill to cut away. This is overly generalized, but point is that both process's have their place but you can't replace a mills finish accuracy with a plasma table.

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    Quote Originally Posted by Bobw View Post
    I HATE it when the blanks come with holes already in them.

    HATE IT!!!!

    90% of the time they tried to hit them right on size and
    what could have been a quick slam slam job turns into a
    fricken nightmare.

    Give me a 3" hole to make a 3.5" hole, I'm cool with that, as
    long as the material isn't going to turn into glass, I really
    HATE that.

    I've got one coming this week that will be water jet. 3/4"
    holes. But this time, they will be waterjet to 5/8" not a
    tapered 3/4". It will now be a slam slam job.

    One of my customers recently got a plasma table, and I don't
    know how they lived without it for so long. But its been a
    learning curve as to when and when not to put holes in things.
    No fault of theirs, just trying stuff out to see what the
    machine can, and can't do. Mangled holes in 1/2" 304 are a
    bitch to clean up.

    My suggestion is that when the machinist says they don't want
    holes, don't put holes. When they say they want holes, ask
    them what size they want them.. And then do what they say.
    There are reasons.
    Not going to argue about trying to clean up a hole that doesn't have enough stock. But your last sentence.... Sure there are definitely reasons to approach jobs differently, but having a reason does not make it a good reason.

    I was having some fun at Tom's expense earlier, but I have seen guys that would milk jobs to get overtime. Not you as an owner, of course, you want to do it as fast as possible, but the unscrupulous hourly guy might not think the same....

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    I think it's simply that I don't like needing to adapt to what's already done. BUT I'm a true jobber. I get to build a part from start to finish, through all the different machines and processes. I don't like getting parts from the Mill guy or the Lathe guy, then needing to finish it off.

    That is a preference though. And preferences are for spoiled people.

    R

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    The fab shop I was working in as a laser operator used almost exclusively chinese steel. Anything that needed to be machined after laser cutting got left a WIDE margin for HAZ, Random areas of wildly different hardness made clean up pretty difficult, and often even mild steel got glass hard. The quality of your material makes a big difference.

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    A36 gets a bark on the entry side of a flame cut hole & the best answer used to be 4-6XX neg/neg rake inserts with large depth of cuts (first pass). Don’t know if plasma or laser does the same.

    If it’s not welded later, people who made LOTS of a part used to sub 1119 or 1120 resulfurized plate which for some reason doesn’t get the hard bark on top and more (much more) than pays for the steel price with increased speeds, feed rates and better finishes.

    Good luck,
    Matt

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    Quote Originally Posted by AJT View Post
    .......Can someone give me some clues as to why you would want a blank plate every time?
    What answers did your machinists give you when you asked them? You did ask them didn't you?

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    I have no experience with that material.
    Makes me wonder if the roughing process does something to the steel??? Does it make it harder...shitty burr to dela with....warpage????
    Step one should probably be to sit down with them and ask them why they dont want it roughed out.
    Maybe it makes sense....maybe its bullshit....but I would put them on the record with a reason why.

    One thing about milling a large diameter hole to finish is most of the time you need to mill it from center or risk having a slug break your tool.....(unless of course you clamp it or something similar

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    It all depends what they want to do and what machine they have. If they have a 50-taper boxway VMC they can drill a 3" hole and finish it with an endmill before you know what happened. The heat-affected-zone in A-36 is nothing to sneeze at. It likes carbide for a snack..... We have a job similar to this except we're profiling an outside contour with a 1/2" 4 flute EM running 400 SFM, 0.1" WOC, and .003 IPT. Tool life suffers even at those numbers. Slotting at 600 SFM would actually do better on tool life.

    All that said, there are cases where a carving the meat out with a laser is better, especially with large holes.

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    I absolutely cringe when customer says "we'll provide the blank from our burn table".
    Id rather do it from solid for a couple reasons.

    1 - Knowing where there is actually stock without spending 2 hours measuring and laying the damned thing out
    2 - HAZ on a lot of stuff is terrible, especially the crap Chinese "steel" these clowns provide. If I blow up an $800 endmill, or spend 8 hours z level roughing with inserts, whats better?

    If they would waterjet stuff, theyd save so much money, but the initial cost is what scares them. They dont realize having to stop and change inserts, z level roughing < HEM with a nice big endmill....

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    Quote Originally Posted by macds View Post
    I absolutely cringe when customer says "we'll provide the blank from our burn table".
    Id rather do it from solid for a couple reasons.

    1 - Knowing where there is actually stock without spending 2 hours measuring and laying the damned thing out
    2 - HAZ on a lot of stuff is terrible, especially the crap Chinese "steel" these clowns provide. If I blow up an $800 endmill, or spend 8 hours z level roughing with inserts, whats better?

    If they would waterjet stuff, theyd save so much money, but the initial cost is what scares them. They dont realize having to stop and change inserts, z level roughing < HEM with a nice big endmill....
    Well sheesh?! Don't use diamond or ceramic or pcd for A36 then!!

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    Quote Originally Posted by macds View Post
    If I blow up an $800 endmill
    What end mills are you buying that cost $800?

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    Quote Originally Posted by Mike1974 View Post
    Well sheesh?! Don't use diamond or ceramic or pcd for A36 then!!
    Large corncob body loaded with inserts? If it's a reputable brand, that's $800 easy for a "regular" cutter.


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