Bridgeport M head Spindle spline repair
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    Default Bridgeport M head Spindle spline repair

    Guys,Can someone give me a measurement from nose to threaded end of m head spindle. A drawing would be great but beggers cant be too choosey. I am going to attempt to make a new spindle out of 4140. my shaft mics up fine with the exception of several inches broken of of the splined end. bought this little M head with thoughts of adding to my Diamond m-24 horizontal mill. As always Thanks,Blaine

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    I measured an M head I have and made a drawing for you. I included the spline as best I could measure. To me it looks like a straight side spline. But on the one I measured, one side of the spline is slightly wider than the other - due to wear? I doubt they would machine it off center?? On another M head it looks like the sides are both the same width.

    Irby





    Last edited by IrbyJones; 06-25-2019 at 11:35 PM. Reason: added possible cutter to drawing

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    Did you want measurement of the entire spindle? You have the spindle, so I figured you just needed the threaded part that was broken off.

    Irby

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    Irby, Thanks for the reply. I don't know exactly how much is broken off and that's why I needed the full length measurement. Thanks Blaine

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    More on the spline itself. I don't know anything about splines so I looked some up and found out this -

    There's a thread on this forum about cutting straight sided splines that should help you if you make or repair your spindle:

    6 Tooth Spline Shaft

    Rudd, on post #10 links to a pdf (http://ashgear.com/pdfs/f6.pdf) that lists cutters and one in particular (F6-087C) seems to be the one to cut this spline you need. BUT I wouldn't recommend using it. Using a cutter like that sets the width of the spline tooth itself by the depth of the cut. That's probably not the way you want to set the spine tooth width easily. In the thread above they suggest using an end mill in a vertical mill or a milling cutter like in post #13 in a horizontal mill to cut the spline teeth. You can set the teeth width more exactly that way. The valley between the teeth will not be correct when the teeth are cut that way, so you need to go back and cut it down some way, any way you choose. The way shown in post #13 is great if you have a horizontal mill, or an end mill small enough to fit between the teeth is fine if you just have a vertical mill. Overall that thread is great about telling you how to cut the spline!

    Here's a picture of my M head spindle and the mating drive pulley center part. You can see that the space between the spindle spline teeth has a clearance with the drive pulley part, so whatever you do to cut that space between the spline teeth is not critical. The spindle has a radius there as though a cutter like F6-087C was used, but that isn't critical. It could just as well be flat.



    Irby

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    Just for the heck of it, here's an updated drawing that shows the curved ID of the spline (which is like the spindle has), where the last drawing I did had it flat.

    Irby

    m-head-spindle-end-3.jpg
    Attached Thumbnails Attached Thumbnails m-head-spindle-end-3.jpg  

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    I forgot to extend the spline through the threaded section at the end of the spindle on my previous drawings, heck. Here's a corrected drawing. Now I'm done.

    Irby

    m-head-spindle-end-2.jpg
    Attached Thumbnails Attached Thumbnails m-head-spindle-end-2.jpg  

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    Quote Originally Posted by IrbyJones View Post
    I forgot to extend the spline through the threaded section at the end of the spindle on my previous drawings, heck. Here's a corrected drawing. Now I'm done.

    Irby

    Wow!Irby. This is super helpful information as reading a blueprint. It addresses the specific need.

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    Thanks Irby for your help. It's people like you make this forum.

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    Quote Originally Posted by IrbyJones View Post
    Here's a corrected drawing. Now I'm done.
    Well, maybe one more time

    Splines don't have an i.d. and an o.d., they have major diameter and minor diameter. They can fit on the major diameter, the minor diameter, or on the side. But you don't want to make them fit on two of the features, just one.

    In general, straight-sided splines are a major diameter fit. That's because grinding the o.d. of the mating shaft is easiest. If it's a minor diameter fit you can often tell because the roots of the male splines will be ground. As you can imagine, that's a lot more trouble and a lot more expensive so you don't see it often.

    Side fit is usually for a permanent fit and you don't see it much.

    For a sliding fit, there is class A, B and C. Basically that's just the amount of looseness.

    Looking at the numbers here, I'm going to go out on a limb and say this is a loose major diameter fit on the .872 feature. That would follow normal practice. That would make the major diameter of the female spline about .875.

    My criticism would be, your print has a .001" fit on the minor diameter. I do not think this is what Bridgeport intended and you could end up with the dimensions fighting each other. I don't have spline fit info handy but I'd make that minor diameter a good .015-.025" clearance. Maybe more, because unless they used an undercutting cutter on the spline, then the corners will have a radius and your pulley could hang up on the shaft. If you want to make it strong (why ? I guess it's a fixation with me !) just make that a nice radius. The smaller diameter on the shaft doesn't matter as much as the sharp corners do for life expectancy. Within reason, of course.

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    Quote Originally Posted by EmanuelGoldstein View Post
    Well, maybe one more time

    Splines don't have an i.d. and an o.d., they have major diameter and minor diameter. They can fit on the major diameter, the minor diameter, or on the side. But you don't want to make them fit on two of the features, just one.

    In general, straight-sided splines are a major diameter fit. That's because grinding the o.d. of the mating shaft is easiest. If it's a minor diameter fit you can often tell because the roots of the male splines will be ground. As you can imagine, that's a lot more trouble and a lot more expensive so you don't see it often.

    Side fit is usually for a permanent fit and you don't see it much.

    For a sliding fit, there is class A, B and C. Basically that's just the amount of looseness.

    Looking at the numbers here, I'm going to go out on a limb and say this is a loose major diameter fit on the .872 feature. That would follow normal practice. That would make the major diameter of the female spline about .875.

    My criticism would be, your print has a .001" fit on the minor diameter. I do not think this is what Bridgeport intended and you could end up with the dimensions fighting each other. I don't have spline fit info handy but I'd make that minor diameter a good .015-.025" clearance. Maybe more, because unless they used an undercutting cutter on the spline, then the corners will have a radius and your pulley could hang up on the shaft. If you want to make it strong (why ? I guess it's a fixation with me !) just make that a nice radius. The smaller diameter on the shaft doesn't matter as much as the sharp corners do for life expectancy. Within reason, of course.
    This is very revealing information. I do appreciate the knowledge and time to share it.

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    With a lot of help from you on this forum I am getting ready to machine this M head spindle. I have one more question before starting and is should I cut the 7/8-20 LH. threads On the end of the spindle first and then the splines or cut the splines first then the threads? Again Thanks for all your help.

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    Emanuel-
    Not sure why you are passing criticism on Irby's drawing.
    His dimensions appear to report sizes of an actual specimen.
    He makes no notation of tolerance or fit.
    It is not far to criticize something that was not in the vision
    of what was in your mind. Irby was not providing engineering data,
    and never represented as such.
    But thank you for adding your knowledge of fits and tolerance.
    I am sure it will be most helpful for anyone trying to replicate
    the spindle.

    --Doozer

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    Right! I liked it all as many experienced Irby's clear measurements and the cutting wheel profile. I would thread the end first and then machine the slots. They go right up into the threads but these can be dressed instead of interrupted thread cutting.

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    Quote Originally Posted by Doozer View Post
    Emanuel-
    Not sure why you are passing criticism on Irby's drawing.
    Because it was incorrect. And I didn't criticize him as a person, I tried to explain how splines fit.

    If you make something wrong but can't handle any corrections, then I feel sorry for you. Are you a millennial, by any chance ?

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    So then, you would thread the end first. That's the easy part. Your concise explanation of fit is similar to how gears are supposed to fit but it is different. Sliding surfaces and such call for what you posted.


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