Rotary Grinding Fixture, Quick and Dirty -Talk me out of this
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  1. #1
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    Default Rotary Grinding Fixture, Quick and Dirty -Talk me out of this

    We need a rotary grinding fixture that will be set up for one specific job. It will never do anything but this one job. Ever. It does not have to do anything exceptionally well, just "well". I've been doing the task with a hand cranked Harig Grind-All, but it takes up way too much vertical space, and the hand cranking gets old. QUICKLY. I know we can purchase a motor and pulleys from Harig to overcome that, but that does not solve the work space issue.

    So, I thought purchase/murderfy something to suit. All it needs to do is to hold a part at approximately a 5° incline and spin at approximately 20 - 60 RPM. I am fine with accepting that some minor work will be necessary to insure good results. At first blush, it seemed too simple, and I quickly found two items that together would fill the purpose well when assembled together. My thought was to combine a small, tilting rotary table and an adjustable speed sewing machine motor. However, I admit that I am having a hard time swallowing the idea for personal reasons.

    These are what I am considering bodging together and connecting with a timing belt. My thought is to pull the handle from the table, replace it with a timing pulley, mount the motor to the side of the table, install a timing pulley on it, and connect the two with a suitable belt. Lastly, a small block will be mounted to the edge of the bottom face of the tilting member, opposite the hinge point, to set the angle.

    Tell me why this is a bad idea, or point me to a better idea in a similar price range.




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    Yes it will work and you'll be amazed how well.
    Also consider a E-yuck DC servo and a variable DC power supply.
    If you use a small self contained servo drive you can also index with it to grind on flats or such.
    Large selection of timing belts and pulleys from SDP.
    Wet or dry use? Where is the table bought from?
    Bob

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    Unless I've missed something you don't need a timing belt, a round belt (thing bloody great O ring) in VEE pulleys will do just as well and alignment will not be critical

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    Quote Originally Posted by Limy Sami View Post
    Unless I've missed something you don't need a timing belt, a round belt (thing bloody great O ring) in VEE pulleys will do just as well and alignment will not be critical
    Yes and for real easy a cordless drill with a socket to go on the the nut on the handle shaft works.
    Under years of use the worms go south first.
    Bob

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    Thank you for weighing in, gentlemen. See below...

    Quote Originally Posted by CarbideBob View Post
    Yes it will work and you'll be amazed how well.
    Also consider a E-yuck DC servo and a variable DC power supply.
    If you use a small self contained servo drive you can also index with it to grind on flats or such.
    Large selection of timing belts and pulleys from SDP.
    Wet or dry use? Where is the table bought from?
    Bob
    Hi Bob,

    You know what I'm doing. That is essentially what those sewing machine motors are. Both items are from ePay.

    Quote Originally Posted by Limy Sami View Post
    Unless I've missed something you don't need a timing belt, a round belt (thing bloody great O ring) in VEE pulleys will do just as well and alignment will not be critical
    Hi Sami,

    You are most assuredly correct. However, both cost about the same, and there can be a little drag encountered while performing the actual grinding, so my reasoning is that the timing pulley will help insure rotation without slippage, should it accidentally occur. I'm willing to be corrected, though.

    Quote Originally Posted by CarbideBob View Post
    Yes and for real easy a cordless drill with a socket to go on the the nut on the handle shaft works.
    Under years of use the worms go south first.
    Bob
    Yeah... I tried this with the Harig set up and have used same with other things over the years. It works, but it is not desirable for long term use. I'd rather spend the $100 on an actual motor that is more friendly to mount with some proper alignment, rigidity, and permanence than a drill motor.

    Back to the original concern, though - you guys don't think this is too cheesy? I mean... I'm looking at it and it sure looks like it should work, but I want to make sure I'm not being .... overly optimistic about the expectations given the origin of the bits. LOL.

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    Actually, this is a clever idea. Only suggestion I can make is put all the parts on a plate but then you probably already thought of that. The only flaw I can forsee is that the table have a sloppy center bearing or a worm and wheel with flaws in the thread/teeth.

    Tom

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    I still like the idea for a quick n dirty though what I would do is strip the rotab and if it hasn't got an oiler for the table interface find a way of drilling one and then rig up a simple gravity oil supply so there's a constant supply of fresh oil going in which should help keep coolant and crap out.

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    its not how cheesy it looks, its how it actually performs, isn't it?

    who cares how it looks, but you might want to put an indicator on it and crank it by hand and give it some side load to see if the little table is worth motorizing before you invest the time....

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    Skip the whole belt drive and related fab work outright.

    Under $80 found me a NOS Bison 90 VDC "gearmotor", hollow-shaft, with extra key-slotted reducer bushing. And mounting hardware in shiney-wood already fitted to the motor, plenty of space to drill for a mount.

    Speed control is not hard for either of a fractional HP DC or universal/series-wound motor. The 55 in/oz at the output ain't gonna hiccup keeping the goods turning. Worm drive means no kickback, either. Sealed "TENV" design, too, most are. No place for grit to do harm.

    Shaft doesn't HAVE to be directly close-coupled to the hollow. Nor even rigid material.

    Could git 'er done with a great deal less fab and cogitation hassle and for small money.

    Bodine or Bison gearmotor, either one could be pulled and put to work on all manner of OTHER gadgetry in between runs of this one.

    Worm ain't the smoothest? Nature of the beast they can sorta self-correct.

    Repaired a used "Ellis" DH/spacer bought from another PM member. Known to have had one tooth / set/ group impaired from overload. Smoothed itself out - per the Ellis manual, actually - by simply powering it and periodically taking up the pressure of engagement 'til it was smooth in manual use again.

    Mind - slow old gearmotor could also drive a Harig/clone or any other spindle'ish thingie directly, not even need the mini-tilting DH? The worm geared reduction is already "there". All yah need is tilt.

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    Quote Originally Posted by Limy Sami View Post
    I still like the idea for a quick n dirty though what I would do is strip the rotab and if it hasn't got an oiler for the table interface find a way of drilling one and then rig up a simple gravity oil supply so there's a constant supply of fresh oil going in which should help keep coolant and crap out.
    Yes, Sir. Also plan on an air fitting for minor positive pressure.

    And P.S., ... I'm back to favoring the oring belt for power transmission smoothness concerns.

    Quote Originally Posted by cyanidekid View Post
    its not how cheesy it looks, its how it actually performs, isn't it?
    who cares how it looks, but you might want to put an indicator on it and crank it by hand and give it some side load to see if the little table is worth motorizing before you invest the time....
    Good idea. I plan to. My experience in the past tells me that these things are usually half-arsed made decently. Where they lack is in the Worm & Wheel quality and any manner of decent cleanliness. Bearings are actually cheap enough these days that they end up using decent ones. Go figure.

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    I agree with pulling it apart to see what is in there. I'd make small wager there is no center bearing, just a shaft in cast iron housing. You may need serous belt reduction to get your sewing machine motor sufficiently slow. Maybe a jack shaft is needed.

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    Not to be a contrarian or anything but ...

    If this were just a quick hack for a single job, you would not have bothered to come here. You are looking for validation for a junky fixture for long-term use. Bad boy ! Bad boy ! Watcha gonna do when they come for you ?

    I've overbuilt fixtures for people - at a loss, of course, oh well - but some are still in use 40 years later. Now I wish I'd gone a little farther overboard.

    So think about this a minute ... spread out over ten years, what does that extra ten hours mean ?

    If using the thing will become faster and easier, that's an added bonus.

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    Quote Originally Posted by gbent View Post
    I agree with pulling it apart to see what is in there. I'd make small wager there is no center bearing, just a shaft in cast iron housing. You may need serous belt reduction to get your sewing machine motor sufficiently slow. Maybe a jack shaft is needed.
    ISTR my Bison dials-down to one rev every three or four minutes? This were an entirely "new" need, the Brothers Bodine wuddna had Bison, Dodge, Master, and a whole slew of others, globally pop-up to compete.

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    Cheesy? Gene Haas built his empire partly on a similar lashup. I had his 7" rotary which was similar except for a no name probably not Chinese table and a stepper motor. I bought it used, did quite a bit with it, broke it in a crash, fixed it, made a lot more parts with it, and resold it when I got a machine with a real 4th.
    There were no bearings in it, just a steel cone in cast iron.
    Build it, then if it lasts a year, buy a few more identical tables and set them aside for spares so you won't have to make new brackets if/when this one wears out.

    FWIW Dayton/Grainger sells gearmotors, I bought one to install in a welding positioner to slow it down.

    Photo borrowed from another thread
    272697d1576527762-old-haas-cnc-rotary-table-stepper-motors-haas.jpg

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    Quote Originally Posted by Mud View Post
    FWIW Dayton/Grainger sells gearmotors, I bought one to install in a welding positioner to slow it down.

    Photo borrowed from another thread
    272697d1576527762-old-haas-cnc-rotary-table-stepper-motors-haas.jpg
    +1

    Why take pulleys, sprockets, pinch-rollers, or gears of yer own devising near any sort of grinding when "sealed" is a freebie part of the package as has already solved a problem for yah?

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    Quote Originally Posted by gbent View Post
    I agree with pulling it apart to see what is in there. I'd make small wager there is no center bearing, just a shaft in cast iron housing. You may need serous belt reduction to get your sewing machine motor sufficiently slow. Maybe a jack shaft is needed.
    I've pulled some of those chinesium dividing heads apart for other companies, during projects, while making use of them in larger efforts. I was usually mortified at how much crap and casting sand was inside, and the Worm & Wheel were almost always poorly made, but everything else was always surprisingly decent.

    The sewing machine motor goes down to 350ish RPM, so there will be no jack shaft necessary.


    Quote Originally Posted by EmanuelGoldstein View Post
    Not to be a contrarian or anything but ...
    If this were just a quick hack for a single job, you would not have bothered to come here. You are looking for validation for a junky fixture for long-term use. Bad boy ! Bad boy ! Watcha gonna do when they come for you ?
    I've overbuilt fixtures for people - at a loss, of course, oh well - but some are still in use 40 years later. Now I wish I'd gone a little farther overboard.
    So think about this a minute ... spread out over ten years, what does that extra ten hours mean ?
    If using the thing will become faster and easier, that's an added bonus.
    I disagree with your assessment. I'm not asking for validation. I'm asking for a reality check of "Is it really possible to be this simple?" and "Show me a better option" in the price/time range.

    I am perfectly willing to spend another ten hours on it. Heck, I'd hand scrape the thing if it mattered. ( it does not ) But for what it's doing, and comparing it to what I've been using, it sure just seems like this would do fairly well.

    For the record, we actually did sit down and discuss making something from scratch. My reticence comes not from the parts that most people have issues with. ( The Worm & Wheel ) Rather, it's obtaining a lump of material, and then removing 90% of it to create the housing, along with making all the bits to make it effect the angle, and then adding all the motor and bits to it. And doing so without impacting working on actual paying, customer work.

    While looking for something else entirely, I tripped across a picture of one of these and the small, dimly glowing bulb appeared overhead. Just seemed a natural thing to do. Especially since I have done essentially the same thing with a Troyke rotary table and a motor, on a Bridgeport, in the past. So, I thought to make sure I'm not missing something obvious that would make it a non starter.

    Like I wrote, though - show me a better idea. Perfectly willing to entertain it.


    Quote Originally Posted by thermite View Post
    ISTR my Bison dials-down to one rev every three or four minutes? This were an entirely "new" need, the Brothers Bodine wuddna had Bison, Dodge, Master, and a whole slew of others, globally pop-up to compete.
    The issue I keep running into with this line of thought is that we still have to make some manner of mounting for the thing, and do so with provision for angling it, along with it having the motor away from the working side/end. Then, still make some manner of platform for the parts/tools to be ground, and yet still add some manner of variable speed control. All of that keeps adding up to much, much more than this idea.

    This proposal is a mounting adapter, two pulleys, a belt, an oil cup, and an air fitting. Then literally plug ( it in ) and play...


    No?

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    Quote Originally Posted by Zahnrad Kopf View Post
    This proposal is a mounting adapter, two pulleys, a belt, an oil cup, and an air fitting. Then literally plug ( it in ) and play...


    No?
    "No" is not at all hard-edged. Many things can work.

    All a purpose-built / stock gear-motor is going to save is the two pulleys, belt, a place to put them and the extra layer of mountings.

    Rotab avoidance only "maybe" - still need SOME kind of workholding and angle-setting, regardless.

    Open motor needing protection added is also only "maybe"..

    Not to forget that gearmotors, "PM" DC especially, tend to be HEAVY for their visible size, too. One of the other options in my Hell box is a Graham "ring drive" about the size of the average fist. Also heavy for its apparent size.

    OTOH? Resilient, non-synchro/toothed, flat, round, Vee, Poly//MicroVee belts do medium to higher speeds a great deal better than they do LOW speeds.

    So yeah.. not a huge difference. But is any of that an IMPORTANT difference?

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    I've been searching for one of these for AGES.... no luck.

    Belt driven, so no worries about eating up the gears.


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    I don't know enough about them to know whether this suggestion sucks or not, but rotary stages look interesting. There looks like some good deals to be had with careful shopping for used units. Quality and precision looks miles ahead of the Grizzly stuff. This thought would be just for grinding though (they don't look like they have the beef for milling).

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    Just another idea to throw at you. Servo powered.

    YouTube

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