DIY inside grinding attachment for cylindrical grinder, what design? - Page 2
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  1. #21
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    Quote Originally Posted by Mr_CNC_guy View Post
    Don't enclose the motor too well, it needs to be cooled!
    I spent a few minutes looking at possible fan locations. Remember that I intend to enclose everything within a cover.

    I first thought about having the fan as below. The airpath is shown with the blue arrow. Cold air would be sucked in by the fan, would run upwards by the motor, and then would exit through vent holes on the right side of the shroud next to the motor pulley. In use this would work well because the air inlet would be facing the operator and well away from the grinding mess. The downside is that when the internal grinding attachment is rotated up and out of the way, then the air inlet would be facing directly upwards on the top of the outside grinding head. That's not good, it would fill up with coolant and grit. Yes, I could make a cover for it, but I'd forget to use it



    Maybe a better way to do it would be to mount the fan directly BELOW where I am holding it, onto the back plate. I could mill an inlet louver into the back plate, with slots opening downwards at 45 degrees. That location should be well protected against the coolant and grit mess. Then when I rotate the inside grinding attachment up and out of the way, the fan opening is facing downwards, and is underneath the attachment rather than on top. That plus gravity would keep stuff from getting inside.

    The only downside I can see to this is that I would have to mill a bunch of air inlet slots in the back plate, which would make that plate more flexible and less rigid. Not sure if that matters, since the whole point of grinding is to keep the forces low.

    An alternative would be to mount the fan onto the outside of the cover on the right by the drive belt. That's well protected against coolant and grit ingress, but also means that removing the cover requires disconnecting wiring. I suppose if the cover hinged up that would not be so bad. But having the fan outside the shroud also puts it into a vulnerable location for damage compared with being mounted on the backplate.

    Decisions, decisions....

    Actually I like the idea of a cover that hinges up for access to the inside. One less thing kicking around on the bench during setup. I might try this.

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    ^ The high speed Heald grinding heads blew an oil fog through the unit to cool and lubricate the bearings.

    @ZK, you could always buy a container and park it out back

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    Most /all newbies try to make massive cuts like a lathe.....both internal and external.....all wrong......the motor should be supplying fractional horsepower,and and the wheel making just a tiny display of sparks ......not a stream like a Makita....I have always used water based coolant with internal grinding,and never had an issue with chatter or burning.

  4. #24
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    Heald grinding heads
    These folks must of been dead serious about ID grinding - I have the guts out of a fair sized RED HEAD. The hefty spindle has a short B&S 12 ID taper (1.797" big end) on the business end and the 2MM precision bearings are the 211 size. The casting that held all this machinery had to weigh 30 Lbs each

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  6. #25
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    Quote Originally Posted by cameraman View Post
    yup , now they pop into existence whereas before if I hit refresh and wait etc. the images don't 'Lay up" to the page ?

    Anyhoo lol.
    So I just reply and, presto!, the photos appear?

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    Lo! It is a miracle! I can see!

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    Not related exactly, but...
    I have a Brown Sharpe #13 grinder that I want to install an internal attachment on.
    On ebay I found a spindle (2 spindles actually) that were originally made to fit
    a Cincinnati #2 tool-cutter grinder. They are belt drive, and I think the taper
    is a #6 Brown Sharpe with 5/16-18 LH thread drawstud. I am going to fab a steel
    bracket and drive it with a flat belt from the right side of the main spindle.

    I also have a Heald #7 ID grinder that I am going to completely fix up some day.
    I think it is from the 1930s. Originally overhead driven for sure.
    If the plain workhead bushings are good and the ways look good (when I take the
    table off), it should make a fine machine. It has a Parker (pre-Majestic??)
    spindle cartridge, that mounts with a dovetail, just like a RedHead spindle.
    I was thinking I might buy one or more RedHead spindles off ebay if I see them
    cheap, but I need to assess the machine better first. I must say this Heald is
    a work of mechanical art. Very massive construction, should be very resistant
    to chatter. They really put all their efforts into this machine when they
    designed it.

    --Doozer

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  10. #28
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    I didn't like the first version of the cover and threw it in the trash. Now working on version 2. Basic idea is to enclose as much as possible. So on the grind side all that is going to be visible is the spindle protruding:



    Yeah, it looks like a box, but if I end up with a cover like this I'll round out the corners so it matches the machine underneath.

    On the tailstock side I'm mounting a pair of 92mm/3.625" fans. The bottom one (left in photo) will blow in cold air above the spindle and below the motor, and the top one (right in photo) will suck out the hot air just above the motor.



    I'll put grills onto the fans to protect against fingers. My expectation is that on this side and in this location they will be reasonably protected from the mess. Also easy to keep an eye on them.



    The cover will hinge up more than 180 degrees and will then just rest in position out of the way. Just now it's blocked by a piece I added to extend the range over which I can move the motor up and down to accommodate larger and smaller pulleys. That's on the list of things to fix. That way I can change pulleys or spindles with two rather than three hands.

    I'll run the fan wiring with flex cable so that the wiring won't need to be touched when opening/closing.



    Here it is locked in the "out of use" position. I've left just enough clearance underneath for the handle which moves the cross slide back and forth.



    Next step is to see if I can get the electronics fitted inside, rather than mounting them outside. IMO that's preferable, to keep things compact.

    Still need to figure out a safety hook or latch to retain this in the "up" position even if the hinge shaft comes loose.

    I also need to give some thought to how to fabricate/reinforce/brace the cover so that it doesn't vibrate or resonate.

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  12. #29
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    Still too busy to spend much time on this. Here is how the mock-up currently looks from the outside. Botton fan blows air in and the top fan pulls air out:



    Here is on the spindle side. Nothing is exposed apart from the spindle itself.



    For the inside, the drive electronics is going to sit on top near the exhaust fan. It has a temperature sensor inside so if it gets too hot in that location it will shut things down. The controls for speed/on-off/CW-CCW will be accessible at the top when the cover is closed.



    Next step is for me to get the wiring and controls laid out. Only things running into the box will be 48VDC power and a piece of 1/4" clear flexible tubing to carry compressed air/oil fog to high speed spindles. I've also decided to change the motor mounting so that I can tighten it into position entirely from the operator side. Finally need to add a "security hook" for locking the assembly in place when swung up and not in use.

    I might also add some "stiffeners" to the cover inside, laid out to direct cooling air in the correct places.

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    Hi Ballen:
    I've been looking at where this thread is going, and I have a really basic question to ask you about your design.
    You've designed your unit with an enclosure...I presume to keep the dirt and grinding swarf out of the guts .
    Then you punched a pair of big holes in it and made a system to pull the dirt and swarf right through the parts you were guarding.
    This strikes me as fundamentally wrong.

    As an alternative, have you considered enclosing the dirt-sensitive guts in a heat sink and blowing the fans over that instead? (Kind of like a TEFC motor is constructed)
    It would seem to make some sense, however you'd need to find a convenient way to access the heat sink so you could clean it from time to time, especially if you intend to run the grinder with coolant.

    To get an appreciation of my concern, open up your shop computer some time and see how nasty it has gotten in there, from the fans sucking in ambient air all the time.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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  15. #31
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    Hi Marcus,

    Thanks for the comments!

    It's a good question. I am hoping that by putting the fans on the far right hand side, away from the grinding mess and activity, they will not pull in gunk. And even if they do, I have a "plan B" which is to add some standard filters to the fans. If that doesn't work, then turning the cover into a big heat radiator is certainly an option. Or adding some cooling coils and running coolant through the coils to carry heat away.

    Yes, I am familiar with the enormous dust bunnies that can be found inside of computers and laptops. If this attachment was going to be operating 8 hours/day then it would be a valid concern. However this machine is not used for production, it is entirely for one-off parts. So I might end up running the ID grinder for 10 hours/year.

    I got to spend a couple of more hours on it today adding the wiring and controls. The top will have a power switch and LED power indicator, and the LCD motor speed display and potentiometer knob. I also have a 3-position toggle switch which will be for CW/OFF/CCW rotation. Initially I had planned to put this on top but I now leaning to putting it inside next to the spindle. The idea being that one never touches it except when the spindle is being changed. So getting it off the top where it might be bumped accidentally seems like a good idea.

    Hopefully the model will be finished tomorrow and I can turn to building the real thing. I'll post some more photos when the model is ready.

    Cheers,
    Bruce

    PS: input power to the box is 48VDC at up to about 10 amps. Can anyone recommend a 3-pin power connector for bringing the power/ground in? The connector should be reliable, splash-tight, compact, and have a good locking mechanism, like LEMO connectors.

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    OK, prototype is just about finished. Here is the wiring:

    48 VDC comes in the back along this white cable from a switching power supply:


    Electronics is in the top of the cover:

    On the left is the drive for the brushless DC motor, on the right is a 48V-12V buck downconverter to provide power for the fans and the LED indicator light.


    It's a bit tighter for space than I anticipated, so in the real thing I am going to make the unit 3cm higher and 1cm deeper.

    Here's the operator view:

    The rotary switch is on/off power, green LED is a power indicator. I think I am going to add a spindle on/off with a CW/CCW selector under the cover.

    Spindle side view:


    Front view:


    I just discovered that the upper fan is interfering with the cross slide coarse adjustment lever, need to move things up another 2cm:


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    I'm gradually turning this into metal. First step was to attach a clamping bracket to the front of the grinding head. I decided to do that with hand tools and a jig rather than removing the grinding head and putting it on my mill. Here's the spot-drill/drill/tap jig mounted to a moving table:



    (Yes, I isolated the inside behind where I was drilling to prevent chips from getting into the spindle bearings!)

    Here are the mounting holes



    Top hinge block and V-clamp block:



    Wooden mock-up for the hinged part:



    And in metal:



    A friend is going to vacuum braze this part (8/10/12/15mm mild steel) to make it very stiff. The internal grinding spindle will mount near the bottom of this plate, so this will give it a fairly rigid connection to the main grinding head.

    I've made everything out of steel to help match the thermal expansion coefficient of the machine. I'll need to fit an oil-damper to this hinged part because otherwise if it comes swinging down uncontrolled it will probably crack the casting for the wheel head.
    Last edited by ballen; 01-13-2020 at 01:39 AM.

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    I'm getting close to having something useable. The structure above finally came back from being brazed. Here it is, after some grinding, in the down position:



    and in the up position:



    Coming down:




    And from the side:



    In this last picture you can see I have added a hydraulic damper which slows the decent. (Note that this is not a "gas spring". It only slows the speed on the way down, but then does not exert any force.

    Next thing to make is the clamping system for the shaft. Then I can attach the sub-plate and the spindle holder (already finished but not shown here yet).
    Last edited by ballen; 02-17-2020 at 12:46 PM.

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    I'm almost ready to mount the motor, just need to finish the bottom part of the clamp. This will have an internal spring so that the clamping force holding the plate against the V-block is constant (operator-independent).

    I've tested this for rigidity and it looks good. Moderate finger pressure only deflects it a micron or two.

    Here it is in the vertical (operating) position:







    The large black bolt sticking out in the middle is where the clamping screw will go, that pushes the swivel bracket against the V-block. This will consist of a rod, threaded at the end, which carries a loosely-fitting spring. The spring has an ID of around 13mm, OD 18mm, length 25mm. The lower side of the spring bears against the cross-bar of the swivel bracket. The upper side of the spring will be pushed from behind by the clamping bolt. The idea is that when the clamping bolt is fully screwed down, it compresses the spring by around 5mm, which generates a about 250N of force (equivalent to about 25kg or 55 lbs). This has two advantages over a direct screw connection (no spring). First, whether the bolt is snug or a bit loose or quite tight, there will be the same force on the clamping bracket, as long as the bolt is bottomed out. Second, the flexibility of the spring at the bottom means that when I adjust the stops to center the spindle on the headstock/tailstock axes, the minor shift in angle on the cross bar will be taken up by the spring, and won't generate off-axis forces in the clamping system. I'll take some photos of this when it's finished. I had to mull it over quite a while before I found an approach that's simple enough to be practical in a grinder environment.



    Here it is in the swung-back position:







    I don't think I'll have it working by the end of the month, but surely sometime in March!

    In case you were wondering about the holes in the aluminium plate: I bought this on Ebay last week for about 1/4 the price of a pristine piece of 15mm plate.
    Last edited by ballen; 02-25-2020 at 01:20 AM.

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    nothing to add to the grinder, which looks super cool, but on the topic of the fans. One is that you could use smaller fans if that helps with fitment in the cover, though I'm guessing you're using what you have to hand. I'd also suggest some basic filtering, even just a layer of foam held a cm or so away from the fan.

    Another thing to think about is airflow and case pressure (I've built alot of quiet PCs). As set up, airflow will completely bypass the motor which is the target of the cooling, and it doesn't look like you can fit a baffle in between them as the belt will be in the way. I think you'd be better off with one fan blowing into the case and a baffled outlet in the cover above the motor - you can design the baffle so that it protects the outlet when in the upright position (I think I read that as a design criteria earlier on in the thread). That will also give you positive case pressure so you won't be pulling in dust or grit from any unsealed cast opening.

    Generally speaking stuff doesn't need alot of airflow to keep cool. The difference in heatsink temperature in still air vs. a CFM or so is enormous.

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    Thanks for your comment!

    Quote Originally Posted by mattthemuppet View Post
    nothing to add to the grinder, which looks super cool, but on the topic of the fans.
    I am going to first see if passive cooling (no fans) works. The different parts will all be in tight thermal contact, and the large aluminium plate should act as a good passive radiator. If that doesn't keep things cool enough, then I'll add fans, keeping your comments in mind.

    The total mass of aluminium, steel and cast iron is around 20kg which means the structure can absorb (say) 12kJ of energy per degree Celsius, which is about 200 Watts for a minute.

    Because brushless DC motors like the one I am using are 90-95% efficient, most of the heat is not coming from the motor itself, but from other components. I think the spindle (and the housing around it) are probably where much of the power will be flowing. When it's running flat out (say the motor consuming 300 Watts of electrical power) I estimate that the motor itself will be producing 25 Watts of heat, the spindle bearings, belt and pulley another 125 Watts and the grinding wheel itself 150 Watts.

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    Really like what you've done. Kudos. Very interested to see how it performs.

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    with that much surface area and mass, I think you would be fine with an external fan on low blowing over the housing. With a close fit between the cover (with the power supply) and base (spindle and motor) you should get passable thermal transfer between the two and probably between the whole unit and the grinder head. My "thermal" experience is only with high power LED lights, but a good rule of thumb is 10sq.in per watt of heat in still air to keep the LEDs below 70C. With moderate airflow (like riding at 10mph) you can halve that easily. Even something like a desktop fan on low should be fine.

    Obviously thermal expansion of the different components and its effect on precision is another topic and I don't have anything to offer on that front, but I would imagine running it for 30min no load with some airflow should get you into some kind of thermal steady state.

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    Quote Originally Posted by mattthemuppet View Post
    a good rule of thumb is 10sq.in per watt of heat in still air to keep the LEDs below 70C.
    Then I may have an issue. My baseplate is 35cm x 25cm, which is about 140 square inches. If multiply this by 3, to include the front and the sides, it gets me up to about 400 square inches. According to your rule of thumb, that's only enough to remove 40W of heat, not 300W.

    Are you sure that the rule isn't "1 square inch per watt"?


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