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Thread: Large End Mill for Bridgeport

  1. #1
    Join Date
    Apr 2012
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    Medford Oregon USA
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    Default Large End Mill for Bridgeport

    I am slowly teaching myself to make parts. Almost every task, even simple ones brings up more questions. Last night I cut some hot rolled steel into the proper size blocks and then put it in the mill to even out the saw marks and true it up. A few setbacks popped up.

    The pieces once cut were about 2.75" x 1.5" I wanted them to look nice to I used a 1-1/2" end mill so the cut would go across the whole part. I was making .010 to .015 cuts with the power feed turned up to setting 3. Rpm was at the low end of high range. I think like 500 rpm. I was doing fine for maybe five passes then all of a sudden it started not cutting and generating a lot of heat if I did push it to cut. I think somehow I dulled the end mill. So I got a second used end mill about the same size and it did fine for two passes then started doing the same. It seemed to not like the mill scale? Not a huge deal, the large end mills were used eBay purchases and I think I may have $25 in each and they cut good for a few other projects. Still $50 in used end mills in one night, is something I don't want to do often. I looked online and did not see an easy way to restore them. Cheap, huge end mills are probably on eBay for a reason at those prices. One of the end mills was "resharpened" already so maybe the end mill was not that good when it got to me. I am thinking about the inserted face cutting end mills so at least the edges can be replaced. So that leads me to the question.

    I really like my HSS bits on the lathe now. With the advice here and basic grinder its so easy to get good cutting tools and a dull edge doesn't hurt at all savings wise. So I am wondering if going to carbide for the Bridgeport is a mistake? My Bridgeport is the 1969 model with a 3 ft table and a 1 hp motor. Its not a large mill by any standard. I did try fly cutting the blocks for practice. I did get a fairly nice finish, but its very, very slow and the cuts have to be light or the mill will start thumping when ever the tool contacts the part. It was a little faster to put them in the four jaw chuck and face them on the lathe.
    Last edited by donf; 06-10-2019 at 02:49 AM.

  2. #2
    Join Date
    Dec 2016
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    Helsinki, Finland, Europe
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    Default

    500rpm for 1.5" HSS end mill is on the fast side. Something like 200 rpm or even less would be a good starting point, on a sunny day you might get away with 400rpm (plenty of flood coolant, sharp HSS-CO tool, free machining or soft low carbon steel)

    If you want to try inserts you should probably look for 2" SEKT or SEHT insert face mill.
    Last edited by MattiJ; 06-10-2019 at 03:31 AM.

  3. #3
    Join Date
    Dec 2009
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    Stevens Point, WI
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    If you are looking to take skim cuts off the tops you might want to look at a small face mill or shell mill. I have a 3" that I just recently got an arbor for and set up. It has sort of round inserts in it so it is strictly for face finishing, try to take to much of a cut and it fights back.




    Andy

  4. #4
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    Jan 2002
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    Huntsville Ala
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    Default

    I must be a little dyslexic. I thought this was a "Large End Mill for Breakfast" discussion.

  5. #5
    Join Date
    Oct 2014
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    447

    Default

    Sounds like a job for a shaper. Good excuse to look for one. As for the end mills, you MAY be able to save them. Try clamping the shank in a small vise on your bench with the cutting end up. Keeping the relief angle in mind you can stone the end cutting edges. If the corners aren't too far gone this might work. And it won't make them like new but it might make them useful again. I have "sharpened" a lot of end mills this way. Larger ones are easier to see what you are doing but I have done some 1/4 or 5/16" I think.

  6. #6
    Join Date
    Apr 2017
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    Kelowna BC
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    CS x 4 divided by diameter .. CD = cutting Speed. in this case it's 100
    Use this formula to select your speed, BEFORE you cut.....always..

    You already know what happens if you don't !

  7. #7
    Join Date
    Feb 2015
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    NC
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    Quote Originally Posted by wdtom44 View Post
    Sounds like a job for a shaper.
    Yep.

  8. #8
    Join Date
    Apr 2012
    Location
    Medford Oregon USA
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    OK thank you for the advice. I looked this morning for feed and speed recommendations for the mill. http://www.hotteam67.org/Resources/M...nd%20Feeds.pdf I found this. When I did the math for HSS. I was way too fast. I will look for more replacement end mills and not be so hard on them next time. I have been using 10w oil for lube. I know its probably not the best. Would something like Sta-Lube SL2512 Soluble Oil, be suitable is a spray bottle for both the mill and lathe? The lathe is actually set up for coolant, but I never put the tank and pump back in as the recommendation seems to be no coolant needed for the speeds I work at.

  9. #9
    Join Date
    Dec 2015
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    Chilliwack, BC, Canada
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    HERE IS A SITE with a lot of handy tables. In particular note table 7-2 about 1/3 of the way down. It's a chart for surface feet per minute for cutting with HSS. Now by itself it's good but not all of the story. You need to tie that together with the circumference of the tool to learn what RPM to use to sit at or a bit lower than the noted SFPM. Sometimes also given as just SFM.

    You can either use the formula to calculate the RPM or you can use THIS CHART and just match the part that is turning to the diameter in the column labeled "Diameter in inches". And if you prefer metric I'm sure something similar is easily found.

    So using 80 SFM as the desirable cutting speed and looking at the diameter vs SFM chart for the 1.5" end mill I see that you should only be running the end mill at a max of around 200 RPM (204 by the chart). So that's a pretty obvious reason why your end mills both wore off the cutting tips in short order.

    The speeds for SFM are generally also chosen to achieve a reasonable tool life for production settings where they wish to balance the tool wear with the need to make money in a hurry. So in each case where a range of speed is given aiming for the lower side of the range will result in extending the tool life. And for a home shop I feel that's a great way to go so we can use the tools for longer. So faced with your situation I' likely aim for a speed that was a touch under 200 rpm and then set the feed rate so the chips are clean and crisp vs crumbled. And also for achieving a nice surface finish.

    The formulas work just fine. But I'd rather just look at a couple of charts when I'm in the shop instead of pulling out a calculator. Print 'em big so you can read them easily and pin them to the wall.

  10. #10
    Join Date
    Jul 2007
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    West Michigan
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    Do yourself a favor and get a carbide face mill.

    Brian
    OPEN EYES, OPEN EARS, OPEN MIND

    THINK HARDER

    BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

    MY NAME IS BRIAN AND I AM A TOOLOHOLIC

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