Grinding a dovetail endmill
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  1. #1
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    Default Grinding a dovetail endmill

    I need a 50deg cutter for a dovetail I need to true up for scraping, I got a quote from AB Tools for 625.00 to grind a cutter. That is not going to work for me, so I am left with several 45deg endmills that I have on hand. I want to try to increase the cutting angle from 45deg to 50deg, I have my Brown & Sharpe #13 to do the work with, I just can't find any guidance on how to do an sngle this steep. Does anyone out there have any suggestions or guidance they can provide on how to go about this? I have a few endmills that are in bad shape and I can use for practice before I try a good one.

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    Have you considered a different approach, like using the 45° cutter and nodding the milling head or setting up the piece with the dovetail at 5°?

    Otherwise, I'd suggest you to search for the PDF of the No. 2 Cincinnati T&C grinder or similar publications, which have plenty of information on how to set the work head and the spindle for grinding a variety of cutters.

    Just my 2c

    Paolo

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    Made this one from a el cheapo carbide router bit from Sears for the dovetail for the inserted bronze tooth. Hand held and diamond wheel did what was needed

    Only two requirements - angle near what was wanted and cutting clearance behind cutting edge
    Attached Thumbnails Attached Thumbnails dcp_1209.jpg  

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    I normally would have gone about it by tilting the head with a 45deg, but right now my knee mill is out of action and I am working with my Fadal. I thought about using a sine plate to set the 5 deg tilt but my sine plate is too small and everything on Ebay is way overpriced for a tool that gets used but a few times in a career. I will have to check out the Cincinnati manual for some setup suggestions. There isn't much information out there on the setup and operation for the B&S13 universal, not that I have come across at least.

    I had considered making my own 50deg endmill, setup a program to rough it out of a piece of A2 then braze in some carbide blanks, but still the setup comes into question. I will have to think about this for a little, but I am going to see what I can do with the Biax. Maybe I can move enough material, that with the straight edge and scraper I can get to where I want it to be.

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    Quote Originally Posted by SShep71 View Post
    ...I thought about using a sine plate to set the 5 deg tilt but my sine plate is too small and everything on Ebay is way overpriced for a tool that gets used but a few times in a career....
    The very part could be your "sine plate": measure the distance between where it rests on the table and where you would have to put the "blocks", and you can calculate how high your blocks/machinist jacks need to be in order to incline the part 5°

    However, John posted the most sensible solution: for one-off job, your cutter could have a single tooth (i.e. like a fly-cutter) and, anyhow, the angle needs to be approximate. If you're talking about scraping, likely you have to mill/scrape the mating surface too.

    Paolo

    PS Dovetails are a place where I rarely use my Biax and, if I use, I use it only far enough from the point of the V and scrape the rest by hand.

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    Could you start with a modified woodruff cutter of appreciate size and whittle away at the job? The cnc mill should handle the steps well enough.

    Sent from my SM-G973U using Tapatalk

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    PM Sent....

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    The cutting flute edge is often an an odd helix or angle due to the way it is cut-in and the included angle needed to go from the tooth edge and where it is cut into.
    Best solution is to spin or circle grind all the flutes together to the desired angle, then with perhaps 6 to 9 degrees primary clearance grind the clearance up to just make sharp. Very often you will knock or tweak the angle perhaps 1/2 degree to the right and left a little to make the land straight at the edge..
    Yes often a secondary is put under the primary..perhaps 15 degrees.
    Be very sure you grind the angle the right way because it is not uncommon for a guy not used to cutters to grind it 5* the wrong way..Hold it to the part and mark it with a shrpie where you see the grinding to be more and less.

    Circle grinding makes all the cutting edges very accurate and to the correct angle. The shear effect of a better angle cutter makes a slight very slow radius to the cutting edge but not to the cut angle and that is why you need to bump the angle to make a straight cutting edge to the part.
    *Agree to test the existing because you want to match that..good to test the male and female existing to decide what angle to make the cutter.

    55* (?)
    https://www.amazon.com/WUPYI-Degree-...strial&sr=1-43


    HSS 45deg Dovetail Milling Cutter, 1-7/8" size, 7/8" shank - 65-183-6 - Penn Tool Co., Inc
    Last edited by michiganbuck; 10-13-2019 at 07:24 PM.

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    Guess I should and that fitting/feeling the cutter into the part for determining the correct angle often does not work well. The cutter flutes may not be exactly at/on center for the length of the flute.
    Better to make a template or measure the part taper with taper per inch or the like...and then with rolling the cutter on its center axis under an indicator find the same/needed taper on the shank or on the flutes..

    Also swinging a protractor base work head is often not exact..The lines are often very good but setting the zero at an exact right angle or square to the machine is needed in most cases... and then you are lucky to get less than .005 with eve ball alone.

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    With having a 13 grinder you can use the machine as a precision measuring device. Set the part on the table squared up perhaps clamped to an angle plate...and then with an indicator mounted to the wheel head touch the angle and zero the indicator with noting the down dial number....then cross travel one inch, a half inch or a quarter inch.. and down dial there, with noting the down feed travel to make zero..to find taper per the distance cross traveled..

    Then with setting the cutter held between centers or on a spin device like a work head to make a circle grind to the cutter like an OD grind but on the desired taper..Then back off clearance to just come up to sharp...with knocking a little if needed to make a straight land at various places on the flute...then add a secondary so no heal will rub.

    Same method of measuring a step or an angle can be used on a decent surface grinder...and to measure a part feature with long axis travel a stack of jo-blocks or one side of 1-2-3 blocks set to the long travel stop with a indicator or just a parked wheel rub makes a good measuring machine out of many grinders. Yes, with a down travel for the travel distance.

    QT: [I got a quote from AB Tools for 625.00 to grind a cutter.] That seems high..perhaps they are CNC grinding and so wish to charge high, or making the whole cutter .. On a cini #2 (or the like) one should be able to make an altered standard or sharpen a used cutter with changing the angle 5* in less than an hour..

    13 grinder is not as fast as a #2

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    A recess wheel can be put on a 13 grinder so the wheel holding nut does not stick out and then the 13 grinder can grind a short dovetail with the part fixtured.
    long travel about 22" so a 20" long part might run.

    NORTON 7"X1"X1-1/4" GRINDING WHEEL 32A46-IBVE REC.2-3/4X1/2 SURFACE BENCH RECESS | eBay

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    I was thinking along the lines of grinding the angle into the stone with a sine plate on my surface grinder, then transferring the wheel to the #13. That way I would be sure that everything was in parallel and concentric to the center line. However, I got a itch last weekend and just spent the time with the Biax and knocked it all out. I still have some fine adjustments to make to the contact area and PPI, but it will have to wait until net weekend. Ill post pictures, but I still intend on moving forward with grinding this tool, good practice of sorts. I thought about machining a blank, brazing carbide into it, then grinding everything after heat treat. Haven't decided which way I want to go, I just won several machines at a local auction and they are in the way. So I have to dedicate some time to that.


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