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Thread: Fitting new chuck to backplate for beginners?

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    Cast Iron Splat's Avatar
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    Fitting new chuck to backplate for beginners?

    A friend of mine just got a "small SB lathe". He doens't know anything about it and neither do I since I've yet to go visit..pro'lly this weekend. So he's starting to ask me a skillion questions about lathes. I just refer him to SB's "HtRaL" and to this forum though he hasn't joined IIRC...don't know why either. But anyway he asked me about obtaining a chuck for it and what's needed to get the chuck working on the lathe. This got me thinking because down the road I'd maybe want to get a 4-jaw for my Heavy 10L. So in real beginner speak can someone advise what's needed and how to get the backplate mated with a chuck? Thanks.
    1953 Johansson B-12 mill
    1957 South Bend Heavy 10L with Teco NEV-101-H1 vfd

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    Re: Fitting new chuck to backplate for beginners?

    I'm no expert, but I have done this twice now, so for what it's worth....

    0. Buy a blank backplate to fit your spindle. (Yeah, you can machine from scratch before this step, but for your first chuck,... don't.)

    1. For a threaded spindle, the first goal is to get the backplate mounting flat against the shoulder of your spindle. That way, every time you mount it, it will end up in the same place.
    Mount the backplate "backwards" on the spindle; that is with the neck facing outwards towards the tailstock. Face off the surface that will meet the shoulder, and you may have to bore out a small depth inside to get it to fit.

    2. The second goal is to get the front face of the backplate perpendicular to the spindle axis. Turn the backplate around and mount it in its usual orientation. Face it off.

    3. Measure the recess (diameter and depth) on the back of your chuck. Also note where the flat surface on the chuck back is (the surface that you want your backplate to sit on), and where the mounting holes are.
    The usual situation is that the flat surface and mounting holes are outside (at larger diameter than) the recess. The next goal is to make a protruding boss (think of it as a very wide, very short peg) on which the chuck will sit.
    The boss should be a tiny bit shorter than the depth of the recess (so the mating surface meets) but the diameter of the boss needs to be as accurate as you can get it. Sneak up on it. Take your time. If you measured the recess diameter with the usual set of calipers, don't trust that measurement too much. Start taking a thou at a time well outside that diameter. Try the chuck after every little cut.

    4. Pat yourself on the back; it's easy from here on. The next goal is to mark the mounting holes. Take the backplate off the lathe and put it on the bench. Fit the chuck on top of it. Mark the mounting holes using a transfer punch through the chuck holes.

    5. Drill and thread the mounting holes. Good practice here helps. Good drill-press setup, and a tapping fixture will make sure you get nice perpendicular holes and threads. (This matters. (Ask me how I know. I have an extra set of &@%#$-ed up mounting holes on the first backplate I made.) The bolts pass a long way through the chuck, and there is very little tolerance for the mating thread to be out of perpendicular.)

    6. Bolt the chuck on.

    7. Open beverage of your choice.

  3. #3
    Titanium Ray C's Avatar
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    Re: Fitting new chuck to backplate for beginners?

    The previous poster provides a very good procedure. I would like to add a small step...

    Before you drill any holes in the plate, setup a static balance checking mechanism and find/mark the heavy ends, individually for both the back plate and chuck. When you finally position the two pieces to establish bolt holes, make sure you match the heavy side of one to the light side of the other. This will increase the chances that the overall setup, once assembled will be fairly well balanced when spinning at-speed.

    Let me know if you wish to see simple pictures of a decent static balancing setup.


    Ray
    ...and a rock feels no pain; and an island never cries.

    www.cmf-llc.com

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    Re: Fitting new chuck to backplate for beginners?

    Ray, I'd like to see the pictures on static balancing if you please.

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    Titanium Ray C's Avatar
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    Re: Fitting new chuck to backplate for beginners?

    Quote Originally Posted by Tozguy View Post
    Ray, I'd like to see the pictures on static balancing if you please.
    As you can see, it's a very simple setup with 4 inexpensive bearings attached with simple posts. With a 40lb (18kg) chuck, it can sense a little as a gram or two. When you make a rod for it, make sure it's well centered in the holes of the plate and chuck. You'll probably need to make an adapter from an aluminum disk etc for the center hole of the backplate. Does not need to be fancy as shown. What's shown is actually a part of that sheave. A 2" disk with say a 1/2" hole is fine. For the chuck, just center the rod in the jaws. The rod should have a smooth surface. A boring bar works very well.

    You should first find the heavy/light sides, assemble as mentioned then, test on the machine at all speed before doing any static balancing. Static balance does not guarantee good operational (dynamic) balance. Go back and make changes only if there's a problem. If there's a problem, first do a partial static balance of the plate, reassemble and check. If there's still a problem, do a little work on the chuck. Go back and forth like that until it's improved. If everything ends-up very well statically balanced and there's still a vibration, then, your chuck has a dynamic balance problem and this is the best it will be unless you know someone with a dynamic balance machine.

    You can drill divot holes on the heavy sides or add weight to the light side. If you drill divot holes, drill them near the outer edge on the inside face of the plate and chuck edge. That way, you won't ever accidentally get your fingertip caught (and ripped off) accidentally. To get a ballpark idea of how much weight to drill out (from some inconspicuous location), wrap a piece of tape all the way around the chuck and use coins. Please see the thread in the Metrology section titled to the effect of "D1-4 Chuck Measurement and Balance" for some additional insight.

    EDIT: When your testing the balance, proceed cautiously and always remember to snug-up the bolts adequately. A badly out-of balance chuck can scare the pants off you at 1200 RPM. Be ready with hand on the stop button.

    Ray


    Side2.jpgSide1.jpgBalance Beams.JPG
    ...and a rock feels no pain; and an island never cries.

    www.cmf-llc.com

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    Titanium Ray C's Avatar
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    Re: Fitting new chuck to backplate for beginners?

    Another point I'd like to add, is when checking balance at speed on the lathe, keep the balance bar locked in the jaws (which will likely be at a small diameter). Several reasons for this... Jaws tend to have weight variances and the further open they are, the more it impacts balance. It's not entirely necessary to have a perfectly balanced chuck when the jaws are wide open because of two reasons. 1) When you're working on such a large diameter piece, it's highly unlikely the stock is balanced -and all is for naught anyhow. 2) With larger diameter pieces, you won't need to spin as fast as your SFMs are in your favor. -And finally, with the bar clamped in the jaws, you're less likely to leave them open in a dangerous position.

    And finally, I've had situations where the stock was out of balance and causing problems. Try rotating and repositioning the piece... Seems to help about half the time.

    Ray
    ...and a rock feels no pain; and an island never cries.

    www.cmf-llc.com

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    Re: Fitting new chuck to backplate for beginners?

    Ray,
    Thanks for the pics and explanation. Same principal that I have been using for static balancing of motorcycle wheels and tires.
    Would there be any point to indicating runout of the chuck or backplate once it is on the balance stand to validate the mounting system?

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    Titanium Ray C's Avatar
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    Re: Fitting new chuck to backplate for beginners?

    Tozguy,

    Sadly I don't fully comprehend the question so please elaborate and we'll try to resolve it. For now, I'll additionally add that the balance mechanism has 3 bolts in the plate serving as a leveling means. Doesn't need ultra-fine leveling; a pocket spirit level will do fine. The riser arms on mine are adjustable because I sometimes need to work with (or make) shafts with multiple diameters. In the non-extended position, the arms are quite even.

    Also, I can't stress enough that any adapters to accommodate a shaft must be well centered and properly positioned ...I shoot for about 5 thou or better. Similarly, if you're balancing a 4J, mount it on the lathe temporarily and center the shaft WRT the side of the body as close as you can.

    If that didn't scratch the itch, let me know and we'll resolve it.

    Ray

    Quote Originally Posted by Tozguy View Post
    Ray,
    Thanks for the pics and explanation. Same principal that I have been using for static balancing of motorcycle wheels and tires.
    Would there be any point to indicating runout of the chuck or backplate once it is on the balance stand to validate the mounting system?
    ...and a rock feels no pain; and an island never cries.

    www.cmf-llc.com

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    Red face Re: Fitting new chuck to backplate for beginners?

    Ray,
    I apologize for being so brief the first time. My concern ishow close the static balancing system is to duplicating the same axis of theback plate or chuck when it is on the spindle. You mentioned that it isimportant to chuck up the axle on the lathe and make it concentric (w/no runout) so that the chuck spins on the same axis as when it is on the lathe. That goes a long way to ‘scratching my itch’.Thanks.
    Thanks also to splat for being so patient with me.


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    Titanium Ray C's Avatar
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    Re: Fitting new chuck to backplate for beginners?

    It's not that they have to spin on the same axis really.... If you make some kind of adapter and drill the hole off center, by definition, one side will be heavier and when you put it on the balance beams, you'll get flawed readings and make errant corrections.

    Putting it on the machine to mount the rod is just a convenient way to center a rod in a 4J. If it's a 3J, stick a rod in it and tighten e'r up right there on the bench. Same goes for a collet chuck -stick in the right size collet and you're done. With an independent 4J, you need a convenient way to spin while indicating the rod to see if it's centered so, putting in on the lathe is the easiest way to do that.

    With the back plate, you need to make an adapter, unless you have a piece of round stock the same diameter as the center hole. That's the only thing you really want to get pretty close.

    Does that make sense? If not, I'll try to re-word it.


    Quote Originally Posted by Tozguy View Post
    Ray,
    I apologize for being so brief the first time. My concern ishow close the static balancing system is to duplicating the same axis of theback plate or chuck when it is on the spindle. You mentioned that it isimportant to chuck up the axle on the lathe and make it concentric (w/no runout) so that the chuck spins on the same axis as when it is on the lathe. That goes a long way to ‘scratching my itch’.Thanks.
    Thanks also to splat for being so patient with me.
    ...and a rock feels no pain; and an island never cries.

    www.cmf-llc.com

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    Cast Iron Splat's Avatar
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    Re: Fitting new chuck to backplate for beginners?

    Thanks for all the info guys. I need to reread it all to absorb it. BTW, I found this little writeup about fitting lathe chucks and just wanted to link it for future reference.
    1953 Johansson B-12 mill
    1957 South Bend Heavy 10L with Teco NEV-101-H1 vfd

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