adjustable tailstock for 4th axis
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    Default adjustable tailstock for 4th axis

    morning fellas.
    i'm looking for a quickly adjustable tailstock for machining different length parts in a 4th axis. something that doesnt need to be aligned back in every time you change part length. does anything like this exist off the shelf or am i going to have to build it myself using linear rails etc?

    thanks!

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    Quote Originally Posted by empwoer View Post
    morning fellas.
    i'm looking for a quickly adjustable tailstock for machining different length parts in a 4th axis. something that doesnt need to be aligned back in every time you change part length. does anything like this exist off the shelf or am i going to have to build it myself using linear rails etc?

    thanks!
    You need more precision than the tee slot?

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    Quote Originally Posted by gregormarwick View Post
    You need more precision than the tee slot?
    yes....... stupid 10 char limit

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    Hardinge make/made some. Manual or pneumatic.

    https://www.shophardinge.com/assets/docs/B159.pdf

    You might be able to find one on Ebay.

    See below. You could ask Steve for more info.

    Inexpensive tailstock for 4th axis

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    Quill tailstocks are common enough, I assume op needs more stroke than that?

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    My tailstock is good for a few tenths using the t-slots. How much deviation are you trying to hold? If you get too much shit between the tailstock center and table you will start adding deviation from a lack of stiffness.

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    Quote Originally Posted by gregormarwick View Post
    Quill tailstocks are common enough, I assume op needs more stroke than that?
    Got it. I wasn't sure how much stroke he was thinking. Probably have to build something if you need a foot of stroke.

    Otherwise just throw money at the problem and get a B axis lathe with a tail stock.

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    Quote Originally Posted by gregormarwick View Post
    Quill tailstocks are common enough, I assume op needs more stroke than that?
    i'm looking for ~12 inches of adjustment

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    Haas makes one that has roughly 3" (I think without checking..) of stroke. Activated by a simple toggle switch, adjustable air pressure to change holding force. Love ours.

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    Quote Originally Posted by empwoer View Post
    i'm looking for ~12 inches of adjustment
    Discount my previous post then.

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    Quote Originally Posted by DavidScott View Post
    My tailstock is good for a few tenths using the t-slots. How much deviation are you trying to hold? If you get too much shit between the tailstock center and table you will start adding deviation from a lack of stiffness.
    your t slot nuts are that tight to the slots? maybe i'm missing something, how do you get it to stay aligned that tight in t slots?

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    I run my indexer and tailstock on a subplate that has a long large slot milled for the tailstock to slide in with holes every couple inches to bolt it down. It's a rather large MT4 tailstock off a CNC flat bed lathe that I milled the sides of the casting square to the quill.

    The Alca 5 subplate is dowelled to go on a pallet so it's dedicated work offsets are spot on every time.

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    Quote Originally Posted by empwoer View Post
    your t slot nuts are that tight to the slots? maybe i'm missing something, how do you get it to stay aligned that tight in t slots?
    The ones I have used had keys bolted to the bottom to keep it running in the slots. Definitely not tight enough for tenths, but good enough you could slide it down 6" and get most jobs done.

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    any suggestions on how i'd go about building something on linear rails?

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    What machine are you intending to use this on?

    Do you want to buy an off the shelf tail stock and mount that on you're carriage?

    How often will you take in on and off?

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    Quote Originally Posted by J Gilles View Post
    What machine are you intending to use this on?

    Do you want to buy an off the shelf tail stock and mount that on you're carriage?

    How often will you take in on and off?
    doosan DNM4500. it has a tailstock that came with the 4th, i'm thinking build a subplate on with both the 4th and tailstock mount, and put linear rails on for the tailstock to slide on, use preset holes to lock in position or something like that

    most likely will not be removed much, if at all

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    Quote Originally Posted by empwoer View Post
    any suggestions on how i'd go about building something on linear rails?

    Many different ways to go about it. At the end of the day you need to sit down and list your minimum requirements:

    What size and length parts do I need?
    What type of center or locating device will be engaging the part?
    How quickly do I need to reposition?
    Will it need to be automated/integrated with the control to prevent loading errors?
    "Quill", Carriage, or both?
    Do I need to limit the stroke?

    If you answer these and more, you will find your design options narrowed down vastly.

    I have built this very thing in the past. Actually will probably build another one soon. I hemmed and hawed over details for a while, but eventually it just settled into a given form. From there is was just selecting hardware and building around what was available. If it does exactly what you need, chances are the cost is irrelevant or negligible. Don't worry about making it super accurate as a bolt on assembly. Consider building it up as you go using the machine for measuring and qualifying certain + tolerance features or "machinable adjustments" in place. Makes it much cheaper to build, and gives you the best end result. All you have to do is keep it within your capabilities.

    Everyone wants something that runs perfectly true. But at the end of the day, how good does it really need to be?

    For mine I machined the "spindle" base height to control the center height and XZ plane error, but have adjustment screws along x that control the rotation about z and y axis center position. It run's pretty good. The base plate the the rails bolt to was surface ground and within the range that we cut parts in had about .0003" of center deviation, that would be combined vertical and horizontal change, as measured using an indicator on the spindle head traversing the X in multiple locations. There was a little rise of about a thou at the end of travel, but we never cut parts that small. That would also be .001" over 25" in this case which IMHO would be very acceptable in most cases, especially in this one if we ever cut a part that long.

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    Quote Originally Posted by empwoer View Post
    doosan DNM4500. it has a tailstock that came with the 4th, i'm thinking build a subplate on with both the 4th and tailstock mount, and put linear rails on for the tailstock to slide on, use preset holes to lock in position or something like that

    most likely will not be removed much, if at all
    Sounds like a good plan.

    If you want infinite adustability without the pin holes you can get locks for common linear rail sizes. They aren't cheap, but can make sense in some applications.

    Longer rails and mounting plate that extend under the parts should help against side loading/twisting. Assuming you never use it on really short parts.

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    Quote Originally Posted by huskermcdoogle View Post
    Many different ways to go about it. At the end of the day you need to sit down and list your minimum requirements:

    What size and length parts do I need?
    What type of center or locating device will be engaging the part?
    How quickly do I need to reposition?
    Will it need to be automated/integrated with the control to prevent loading errors?
    "Quill", Carriage, or both?
    Do I need to limit the stroke?

    If you answer these and more, you will find your design options narrowed down vastly.

    I have built this very thing in the past. Actually will probably build another one soon. I hemmed and hawed over details for a while, but eventually it just settled into a given form. From there is was just selecting hardware and building around what was available. If it does exactly what you need, chances are the cost is irrelevant or negligible. Don't worry about making it super accurate as a bolt on assembly. Consider building it up as you go using the machine for measuring and qualifying certain + tolerance features or "machinable adjustments" in place. Makes it much cheaper to build, and gives you the best end result. All you have to do is keep it within your capabilities.

    Everyone wants something that runs perfectly true. But at the end of the day, how good does it really need to be?

    For mine I machined the "spindle" base height to control the center height and XZ plane error, but have adjustment screws along x that control the rotation about z and y axis center position. It run's pretty good. The base plate the the rails bolt to was surface ground and within the range that we cut parts in had about .0003" of center deviation, that would be combined vertical and horizontal change, as measured using an indicator on the spindle head traversing the X in multiple locations. There was a little rise of about a thou at the end of travel, but we never cut parts that small. That would also be .001" over 25" in this case which IMHO would be very acceptable in most cases, especially in this one if we ever cut a part that long.
    good stuff! any chance you could share some pics of that setup to get my brain storming?

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    Quote Originally Posted by empwoer View Post
    good stuff! any chance you could share some pics of that setup to get my brain storming?
    All I have is a video of it running a part. Feel free to send me a PM with you cell # and I can text it to you. I hesitate though to share that video online. I have to review some of the design stuff later this week to send out for quote, maybe I can post some solidworks screenshots here as they won't reveal anything about the process. The design is pretty simple at the end of the day. I avoided using rail locks as I didn't feel they would have the level of robustness I was looking for. I put a t-slot in the base plate which has a stop block in it, then the stop rod interfaces with that and the actuation cylinder creating the travel limit stops. The rails are the quill, eliminating extra moving parts. Instead of a dead MT type center receiver, it has a live "spindle" with an H7 bore and bolt flange face. The "centers" we used are sometimes part specific, therefore we make our own as needed. Dead simple and easy to build without a requiring grinder. The spindle had some runout (about .0001"-.0002") and that was mostly in the bearings as indicated by the high spot moving. Not ideal, but fine for our and most applications. It would not be great if you were doing continuous rotary surfacing of metals as you would see that in the finish. In our cast we were doing that in wood, so it was not noticeable at all.

    Best of luck.


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