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Harig 612 Failed Lovejoy Coupler

akjeff

Aluminum
Joined
Nov 17, 2008
Location
AK
I think I found the source of a nagging surface finish issue with my Harig Super 612. Pulled the spindle, removed the motor( making note of the orientation of the Lovejoy coupler as its all balanced from the factory ) and found the rubber spider in the Lovejoy was mostly gone and the consistency of modeling clay! Found a NOS replacement on Ebay, and put it in this evening and did a test grind on a small block of 4140. Comparing it to a previous grind on a similar block with the same wheel looks promising. The spindle is now virtually silent, and taking a cut of a couple tenths up a half thou, I can't even feel it, and the sound level of the grind is way less than before. With the bad coupler, I could noticeable feel when the wheel was in the cut, and it was pretty loud. Basically with all that slop in the coupler, the wheel was being driven by an impact driver of sorts. There was just enough of the rubber left so there was never any metal on metal contact of the two halves of the Lovejoy. Pretty relieved to finally track down this last piece of the puzzle on this grinder.

Here's what I found when I separated the motor from the spindle. This has to be the original coupler/spider, as the relief grooves in the spindle only had a single, very crisp set of witness marks from the five set screws that secure it. This area of the spindle is dry, and there was no evidence of any chemicals or lubricant in there, that could have attacked the rubber spider( or urethane, or whatever it was made of ). I guess just old age. It was clay like, and smeared and flung all over the cavity its in.
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This is the NOS replacement I found. It is Buna-N rubber. Same manufacture as the original.
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This is the before/after test blocks of 4140. Wheel is a 5SG46-J with a pretty open dress. The block on the left was the before, and after on the right. Both were given a fresh rub with a flat stone before the photo. What isn't showing up well in the picture is on the before block; in addition to the long straight lines, there are ripple lines running perpendicular to them. On the after block, stoning it didn't cause anything to jump out. Just a nice uniform finish.
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This is the grinder. Took a lot of work to get it running. It was the victim of a tip over from the original owner( presumably not long after they bought it, as it has very little wear ). A friend got it after the school that owned it was going to scrap it. Then he got tired of it being in his way, and didn't have time to repair it, and gave it to me. All the control shafts were bent, cross slide lead screw bent, column lead screw was good fortunately, but the dust cover tube was folded over. Door missing from dust collector......Made all the new parts except for the oil pump/lines. Fun project, and a great little first grinder to learn on.
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Thanks. It was driving me nuts! Wish that I'd pulled the spindle sooner, it was about a 15 minute job removing it.
 
Thanks. It was driving me nuts! Wish that I'd pulled the spindle sooner, it was about a 15 minute job removing it.
Seems like those elastomeric couplers are not that great. I had a similar experience on a lathe, more advanced than a Lovejoy but same idea. After I finally figured it out, changing was quick and easy to replace the coupling filler every six months or so but still ... was an idea that looked good but turned out not so wonderful.
 
Seems like those elastomeric couplers are not that great. I had a similar experience on a lathe, more advanced than a Lovejoy but same idea. After I finally figured it out, changing was quick and easy to replace the coupling filler every six months or so but still ... was an idea that looked good but turned out not so wonderful.
I bought three of them to squirrel away a couple spares just in case. Not sure what the original blue one was made of. The three I bought were listed as Buna N rubber. Will see how it lasts.
 








 
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