Anybody familiar with Drukov grinder? - Page 3
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  1. #41
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    It did fix the bell mouth. Nice even grip now, the test piece I chucked had the same runout near the chuck and 6" out. I ground the faces of the jaws today, they were beat all to hell as well. The finish on the jaws both ID and face is great, couldn't ask for better. I tested pinion to pinion today and marked the most consistent one with a stamped 'M' for master. Reground the jaws with that one tightened. Now runout is within about .003" at all the different sizes I checked, that will have to do. It will be a huge improvement over having to bang the part around with a dead blow every time it was turned around and having to pussy-foot depth of cut and feed when there was no center in for fear of moving the part and losing concentricity. Gotta do the 4-jaw on the bigger lathe yet, it's in similar shape bellmouth-wise.

    And yikes, a thou per inch on facing is not very good. At least it's concave. On your grinder, .0002" isn't terrible, I think mine runs out a tenth or so and it doesn't cause any problems.

    I had to deal with alignment issues on the tailstocks of both of these lathes until recently also. The owner did not want to turcite and scrape the bases, so I just split the tailstocks and shimmed them. They are lined up much more closely than they were now, parallel to the spindle axis and on center within a couple thousandths. The one lathe center was something like .025" low when retracted and pointed . 010" down in 6" at the headstock end when extended. At least it's an improvement, they drill much more nicely now.

  2. #42
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    After repeated mentions of the Grizzly grinder being similar to this one, I just went and downloaded the manual and parts diagram for that grinder. It is not the same in any meaningful way. Similar format but most toolpost grinders are. The eccentric worm adjustment mechanism on the Drukov is not present on the Grizzly. The Grizzly has a little adjuster in a similar location but it does not function like the Drukov. The Grizzly's adjuster moves the entire spindle straight up and down relative to lathe centerline on a dovetail slide. It apparently has about 1⅝" of height adjustment. After adjusting the height there's a clamp that clamps the dovetail to lock it in place. Personally I'd prefer the solid mount and shim to height, likely far more rigid.

    Anyway, I started pulling the Drukov O.D. spindle apart the other day but quit when I got to the first open bearing. I can't tell if its angular contact or not without pulling it all the way out, there were no numbers on the side I was able to see. So I just flushed the bearings and re-oiled them and reassembled. Spins smooth as heck and grinds well, so must not be too bad. I don't particularly care for the complete lack of any seals whatsoever though. The grinder appears to rely on a total loss oil setup and what is basically a slinger to prevent ingress of contaminants. The spindles on mine get slightly warm during use but not uncomfortably so, so at least the bearings are in decent shape.

  3. #43
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    I was referring to the surface grinder I'm repairing, being the same as Grizzly's current import G5963, it is identical, even the parts diagram (since 1991). And I bet it's got the same deep groove bearing setup. My only complaint with mine is the poor surface finish. OK the downfeed is troublesome, and I have a 2 inch travel digital indicator that displays tenths to control (sorta, as it needs a gib lock) the grind depth. The dial on it is calibrated in hundredths, so you're using your eye guesstimator if you want sub hundredths feed.

    I did 'dump' some #20 oil in my tool post grinder, but have not run it since doing that. Still working on the mandrel to balance wheels. My scrap bin had a 4 foot piece of 7/8" Monel. That stuff is hard to machine. Very stringy. I read not machine a high removal rate, as it will work harden. It's what I had, at least it won't rust.

    The tool post serial number has the date of manufacture coded into it, mine is 90307, made in 1990. Enco had a good price if I remember ($600).

  4. #44
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    Ahh, I see. Missed that, thought you were talking about the Drukov. FYI the parts manual from the Grizzly toolpost grinder does spec angular contact bearings - a pair at each of the inboard and outboard ends. I lucked out on my surface grinder and snagged a fully hydraulic/automatic Brown and Sharpe Micromaster II 8"x18" for $100.

    Any chance you could post a picture of the setup you've got for attaching the toolpost grinder to the compound? Your setup sounds much different than what I've got. I am curious about it. Like I said, I just made what looks about like a round t-nut with the bottom portion the correct thickness to get the grinder spindle on center with the lathe spindle - in this case .891" thickness - and the upper portion 1⅛" to be a semi-close fit through the slot in the grinder. The stud from the QCTP is ¾" diameter, so I made the hole through the mount 49/64" that way I could just use that. Then stacked a couple spacers on top to take up a little extra room under the nut since the stud was pretty long.

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    Got a pic of the mount today. And here's the finished grind on the jaws too.

    20210120_100115.jpg

    20210120_100109.jpg

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  7. #46
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    Damn, I wish I thought of reusing the QCTP, it's right in front of me.
    I still need to find the correct length hardware.
    I took these photos just a bit ago on first fit up,
    20210120_104743.jpg
    20210120_104805.jpg
    20210120_104940.jpg
    20210120_105131.jpg
    Note I made an attempt to be able to clamp a sine bar to the side of the compound, issue is it wants to twist the sine bar at a slight angle, and that kills accuracy, as well keeping it parallel with the top of the compound slide is an issue.

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    Yeah, I wanted to keep the ability to turn the grinder independently from the compound, helps to get clearance sometimes or if you need to do a little bit of side-wheeling. That method also allows the grinder to be slid fore and aft if a little more clearance is needed since it has that elongated slot.

    For the sine bar you might be able to just use two parallels secured to the sine bar through the holes at either extreme end over the top of the compound to keep it level and just secure it to the side of the compound with something like a rubber band through the middle hole.

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    I'll probably make another change and copy your solution, as I'm now stuck with the compound slot alignment.

    So back to making the wheel balancing arbor.
    However, I'm trying to install a brake resistor on the VFD on this lathe. Mitsubishi want's way too much for them, and I'm not finding the value for a 5.5Kw VFD. Somewhere in the 20-30 ohms is what I see other drives using (@240VAC input, @480VAC input 55 ohm, this adds to the confusion when generic sites have resistor values as a function of driver HP rating). But I can't find any published information on minimum resistance. I don't want to burn the output transistor dumping this energy on the brake resistor. I'm not impressed with the documentation from Mitsubishi.

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    I had a similar problem finding the minimum resistance specs on my Hitachi VFD for the braking resistor. I finally found the spec buried in fine print somewhere in a pdf. I think they just want you to buy part number such and such and be done with it. I will look up what the Hitachi manual says and let you know. I just used an old electric baseboard heater for my resistor, fell into the right resistance range and works fine.

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    Looks like for the 240 version of a 5.5kw Hitachi, at a maximum of 10% duty cycle the maximum braking torque setting is 80% and for that, minimum resistance is 20 ohms. For 100% duty cycle, max braking torque is to be set at no higher than 30% and minimum resistance is 64 ohms.

    If you have the 480 version, at a maximum 10% duty cycle, max brake torque of 80% and minimum resistance of 70 ohms. For 100% duty cycle, max brake torque of 40% and minimum resistance of 222 ohms.

  12. #51
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    So many years ago, I purchase a resistor load bank from inventory disposal, being the hoarder I am.
    Attachment 311177
    There are 21 resistors of 10 ohms each, so I wired them to be 7 in series, and 3 banks of these in parallel ~23ohms or so. Still can't put the deceleration time to .5 seconds. From 1150 RPM with a 12inch chuck, It trips out if less then 2 seconds deceleration time. What I don't like about VFDs, that time is fixed no matter what speed your decelerating from. The software is design to decelerator over that time period. Unless I'm missing some area in the parameters where you can make that a function of what Hz is being generated. However in the lathe it stays set to 60Hz. There is a parameter that it will accelerate and decelerate at the limits of the inverter (parameter 60, set to 11), but I think that stresses the input diodes, as I'm powering with single phase. It's a 7.5HP drive, running a 7.5HP motor, and I know it needs to be oversized for single phase input. But I bought this back in 2004, and didn't know that at the time. I don't want to burn the drive up, and the soft start is a good thing. I did try that mode yesterday, and the lights dimmed when starting the motor. But I fear that will damage the input diodes.


    That's good to know to use a baseboard heater, I see the local home supply, 2000 watt $65. I was seeing OEM for $500+ on eBay. I guess I lucked out with the load bank having values I could use.

    Oh, those 10 ohm resistors are 113watts each. I shouldn't burn that up.

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    I was seeing in the tables that 480 inverters had the minimum resistor at twice the size of 240 volt. I guess that makes sense as the current is the same, and I'm guessing that transistor that dumps the regenerative energy into the DC bus, is the same size in either class of drive voltage.
    My previous VFD settings were to just let is coast to a stop. Seems that puts the least stress on the VFD. Now I'll see if I burn it up.
    Now I can get back to the task at hand. The wheel balancing mandrel.
    I made just the slightest change to the sine bar clamp, and used pin gauges to find the angle of the Drukov taper. I put the hub that holds the cup wheel in the lathe chuck and swept that angle with the compound. The sine bar is 5 inch, and the pin gauge was .441". I think that's 5.06 degrees. It's close, but will see what the other grinding wheel hub sweeps out at.
    20210120_213413_hdr.jpg
    20210120_213406.jpg
    Those holes in the sine bar are not quite .375. Maybe .3745, so a piece of drill rod does not fit in them. I used some crocus cloth to whittle the the bar stock down, but I was not consistent with that machining method. So the bar did not fit all the way down in the hole on the sine bar. You can see here that 3/8" drill rod is now proud of the 1/2" square bar (which looks like shit as it's a piece of hot rolled that was covered in thick scale), I machined it off just enough so I could chuck it in a 5C collet I got last month for square and hex stock. We'll see how many times they get used before my big estate sale.
    Now the sine bar is flush with the top edge of the compound slide top. So it's easy to verify it's not at an angle relative to the top of the compound. It's not an optimal setup, as there's probably some compliance in the 3/8" pin, so the sine bar may not be sitting flush to the side of the compound.

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  15. #53
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    Yes running the 7.5 HP motor with a 7.5 HP VFD from single phase is not good for it. I'm sort of surprised it doesn't fault out on acceleration. I only have a 5 HP motor on my lathe and I also run my VFDs from single phase. For the lathe and the hydraulics on the surface grinder I use a 25 HP Baldor drive and only run one at a time. The Baldor gets derated 40% running on single phase. Plenty of power to spare. I run the spindle of the surface grinder (2 HP) with a separate 5 HP Yaskawa drive. On my mill I've got the Hitachi VFD but it's designed and rated to run on single phase input and rated for 3 HP when running on single phase, which is what the drive motor on my mill is. (The Hitachi is probably a converted higher horsepower 3-phase drive in reality). I use a separate 5 HP Yaskawa drive for the toolpost grinder, which is a ¾ HP motor.

    Regarding the variable braking from different speeds - usually you can do this in the VFD parameters but it's going to be under the DC injection braking settings rather than the regenerative braking ones. The VFD doesn't have any indication of the lathe spindle speed without feedback, it can only tell the speed of the drive motor, so high inertia braking like stopping a heavy large chuck from high speed can cause braking faults with settings that are too aggressive. Pretty sure my VFDs all have settings for variable DC injection braking based on the current frequency setting of the drive when you hit the 'Stop' button. I know the Baldor does for sure and I'm pretty sure I saw it on the others.

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    I see the Error on the display during acceleration, but the drive does not trip out. For some reason I had it in my head it was a 10HP drive all these years. It came in a steel enclosure, packaged by Mitsubishi for environmental location. It was the last item that Mitsubishi sold on eBay, as they were auctions of new equipment, and "loosing their shirt" I think I got it for under $400 back in 2004. They've (VFDs) come down in price since then.

    I had originally tried to power the lathe with a home built RPC. That did not go well, and ended up damaging one of the contactors in the lathe. It developed a phase to phase short in the plastic insulator. So there must have been some sort of metal in the plastic injection machine that made a hard carbon trail. I integrated the lathe controls with the VFD, so just FWD/REV are the remote signals. I hope 23 ohms brake resistor does not damage the drive. We shall see.

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    Good luck! I have remote pods on the lathe, mill and grinder with Fwd/Rev, Jog and Start/Stop along with a speed pot. Don't use them on the surface grinder or toolpost grinder though, I just use the front-mounted panel for those.

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    So I got better finish by running the lathe in reverse, and at 300RPM.
    20210121_200030.jpg
    I'm not impressed with the wheel balancer I got off ebay this past summer. It is of the disk wheel type. And seems to only detect a massive out of balance condition.
    20200815_192337.jpg
    I got it used, cost $500, uses ball bearings Koyo 608ZL, the L being some plastic ball carrier designator, two per disk. The disks all appear to spin normal. I thought it would work better then it does.
    I did get the surface grinder back together last night, minus the TEFC cooling fan and shroud housing, as the one off the motor runs with a horible wobble.
    The surface finish is better, but still has much smaller ripples that I can see. And the spindle seems tight. I hope I don't have too much nonadjustable preload on the bearings, as the assembly is, install the bearing into the motor housing, and a preload nut to hold them in. Then press the shaft into that. There's no way to adjust what that does other then a rubber mallet to wack it back, but I could not generate enough impulse to do anything. The spindle was too stiff to start up. It's an odd motor as it uses a plastic can capacitor, with no centrifugal switch, so some sort of permanent split phase, but I always see oil filled capacitors for those sorts of motors in my AC condenser fans or compressors. To free up the spindle enough I put it on my lathe to do a run in, as the shaft was too big to mount in a electric drill chuck, even the hole hawg has only 1/2" chuck (I tried thinking it has a 5/8" Jacobs chuck).

    https://youtu.be/oEHKz1HbzWA

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    Yeah the finish on the video looks like you're getting there. With such a machine the wheel balancing will probably help a lot. Like a lot a lot. I haven't bothered to balance the wheels on my grinder but I think I might eventually. Mine finishes pretty good without balancing but can't hurt to make it even better.

    20210101_144110.jpg

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  21. #58
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    That's the finish I was hoping for.
    It may be the cheep ass surface grinder I have just is not stiff enough to prevent vibration from disturbing the grind.

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    Those flimsy ones do make it a challenge but I'm sure you can get it dialed in pretty well. I think you probably should use a different wheel balancer though. I think I would steer clear of anything with bearings and just go with the levelled parallel knife edge type approach. You can make a balancing arbor and the knife part of one of those without too much trouble.

    There's also the vibration analysis method that Conrad uses, that might be worth looking into as well.

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    The idea was to not screw around with leveling some fixture, or having to manufacture that sort of wheel balancer. There are many youtube videos of the making of one. I thought for sure the disk type balancer designed and manufacture for just this sort of balancing would have worked without screwing around.
    I can't see any real issues with the bearings in this, but small out of balance wheels will not be detected with this. And I give a little spin just to get past any stiction issues. Being a used balancer, has the grease become too viscous in the bearings? is one thought. I certainly can remove the sheet metal shields from the bearings, that are under the covered side plates, and spray with starter fluid to flush them, then use some synthetic clock oil to relube them. When I search for 608Z bearings, the hits are all these roller blade or skate board bearings that use this same size, and then the ABEC debacle argument about what is better in that usage. The Koyo bearings in their present form I believe to be part of the original manufacture of the balancer. The idea of the disk is to give a fulcrum mechanical advantage to overcome friction. This should work!
    The level balancing fixture has it's issues as well, as any small surface dent or scratch can result in the same hung rotation.

    Just what I need is to make the task even funner with some sort of electronic accelerometer. I see I've been to that link before,
    Grinding Wheel Balancing

    I'll have to read it fully to see just how damn complex I can make my life.

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