MACOR GLASS CERAMIC advice needed - VMC
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  1. #1
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    Default MACOR GLASS CERAMIC advice needed - VMC

    I've been asked to quote this. We would run these in the Haas VF-2ss which has 12,000 RPM and thru coolant. I have never dealt with this material before, but there is quite a bit of information online. I gather 20-30 SFM with uncoated carbide endmills and drills and lots of coolant is where it's at. We are quoting quantities of 2, 10, 40 and 200.


    glass-ceramic-pm.jpg

    There are several things that scare me. I'm reading that chipping is a major concern, and the .013" thru holes are only drilling through .009" of material, so if it chips, I suspect we will lose the entire bottom of the counterbore, which forces 100% visual inspection of every hole. Or, we could make the side with the step in it last so the drilled holes don't actually go through the rough material, but I'm still concerned about chipping those same holes when it comes to facing the step in op 2.

    Then there's the +.0004" Ø.044" thru hole and its .039" slot cousin. No choice but to finish that slot with an endmill obviously, which is how I would go about that hole as well normally. But I wonder how this material likes spring passes.

    And the last major question is tool life for all of the above. I mean, are we looking at replacing drills and finishing endmills during each part? After each part? After several parts? I have no idea, but my instinct is telling me each part is going to eat at least $150 of tooling.

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    Macor is a weird crunchy material to machine. I did a few pieces using recommended SFM and flood coolant. The more flood the better. I did 2 duplicate jobs spaced about 6 months apart. The first time worked fine, the second time using same parameters, i got minor breakout, chipping of edges. Don't know if it was inconsistency in stock or what, but the customer didn't care anyway.

    I don't think I'll ever machine it again
    It makes a mess of ceramic sand in the machine. Whatever it's made of, reacts with steel. My vise's were permanently etched/stained after a few parts. I can't speak to tool wear as I only did 6 parts total.

    Yuck.

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    Pick up a Harvey tool catalog I suspect their diamond coated tools might be of help. also fresh sacrificial back plates will be needed for each part. Macor can be present fun interesting challenges. chipping can be a problem, but thats the nature of Macor. Controlled fracturing is how its actually cutting so thought needs to go into each tool path. climb cuts only. swarf containment is critical for your machines sake.

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    Sounds like a pass* to me, unless you are going to quote waayy inflated to CYA!

    I've done more than a few jobs that were not a fit for us/our equipment over the years. It always ended in a pissing/shouting match about losing money.

    *Obviously you know your business better than anyone. If it is something you want to tackle and become a "specialist" in this material and add it to your capabilities list, go for it.

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    Hi [email protected]:
    I agree with your instinct and the opinions of the others here that this job is going to be a big challenge and your scrap rate will be very high.
    I'm concerned about the 0.007" wall thickness between the counterbores...one tiny misadventure and you'll scrap a part.
    I couldn't find a counterbore diameter on the drawing but they look to be about 0.025" diameter, so you're not spoiled for choice on how you make them...they'll have to be drilled.
    How will you get the flat bottom?
    How will you keep a flat bottomed drill from catching on the corner (as you first drop it down the hole) and wiping out the corner?

    I've found with Macor (the few times I've taken it on) that drilling from both sides has been the secret to avoid chipping on the exit.
    A backup plate has been hit or miss...sometimes the exit corners would crumble anyway, just from the change in hardness and ductility as the drill exits the Macor and enters the backup plate.

    I've also been somewhat successful surface grinding Macor when I wanted to get accurately square blanks right to size, but I was not able to grind it like grinding graphite with wide wheels and massively deep cuts.
    It glazes very easily and I had better success with silicon carbide than with aluminum oxide.
    I never tried diamond wheels.
    However, diamond coated cutters like those used for cutting graphite sinker trodes were helpful too, but even though it cuts like it should be super abrasive, it's actually not that bad.
    Dull tools however are death for Macor parts...any side loads will kill you quickly

    A last note, be SURE to verify with the customer that coolant contamination will not be an issue...the Macor literature SAYS it's not porous, but I scrapped some parts once because I stupidly marked them with felt pen and then couldn't get the marks off again afterward...so take that for what it's worth.
    I've always cut it dry since then (not that I've used it a lot or anything).
    The literature recommends water soluble coolants specially formulated for grinding glass or ceramic.
    The skanky crap living in the bottom of your coolant tank might not be suitable for your needs.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    My first project out of college was an assembly composed of Macor and 316 SS that I designed. I got a bunch of "No Quotes" and decided I was a smart guy and could figure out anything on God's green earth, I could build it myself... let's just say the final product didn't look too much like the original drawings. I haven't touched that nasty shit since. I seem to recall that if I was successful at getting the endmill to cut at all, it would induce enough heat to crack the entire part in half. Flood coolant, glacial RPMs and a well rounded scrap bucket.

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    As much as I enjoy learning new things and being the hero to our customers, I no-quoted this one. Thanks a lot for all the advice fellas, and have a good weekend.

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    It looks like a test socket of some type holding spring pins - maybe they can use Torlon - it's what I've seen used in the past for RF test sockets that test tight pitch QFN components.

    Matt

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    Quote Originally Posted by [email protected] View Post
    As much as I enjoy learning new things and being the hero to our customers, I no-quoted this one. Thanks a lot for all the advice fellas, and have a good weekend.
    I see several places(google) that advertise machining Macor...
    Maybe send it out for quotes ?

    I would love to see the #'s on those parts.

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    Quote Originally Posted by messar View Post
    It looks like a test socket of some type holding spring pins - maybe they can use Torlon - it's what I've seen used in the past for RF test sockets that test tight pitch QFN components.
    You got the application, more or less. We have made Torlon parts for this customer before and make Ultem stuff for them constantly. They have been doing this stuff for decades, so I trust that the material choice was driven by design constraints they couldn't get around.

    Quote Originally Posted by cmccull166 View Post
    I see several places(google) that advertise machining Macor...
    Maybe send it out for quotes ?
    Given my terrible luck with 95% of the shops I've outsourced to in the past, I'll stick with my no quote. More than likely, my no quote will trigger a meeting about which meeting to have so they can discuss design issues in a meeting after all the different departments have meetings about when they can all be in the same meeting at the same time. I'll probably see an RFQ very similar to this in the next month or two in a different material.

    For what it's worth (and keep in mind the overall size of this part), material prices were:

    16 pcs $31.13 per pc
    30 pcs $23.32 per pc
    65 pcs $18.81 per pc
    230 pcs $16.61 per pc

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    It sounds like it would be interesting to play with, with proper machine guarding, oh and don't use your good vise! Considering the material prices what would they pay for them? I know not gonna say but I get $20 for a single soft stone switchplate which carbide wouldn't make but a few at best and hold less than .001" on some features. A good enough price and if there would be more those parts, and parts like them, could look really interesting.


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