Too tight is definitely a no no. I was planning on using a dial indicator to read the end play and leave a couple tenths for heat. I don't know what the minimum is. It cannot be too tight.
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Thornton mechanical lab surface grinder
- Thread starter Batmanacw
- Start date
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- Nov 24, 2014
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The shaft knurling suggests that a bearing locked up, at some time in the past, and the journal was damaged. I suppose it's possible that the knurling is original to the manufacture of the shaft (to save a out-of-spec part?). The shaft might not even be original to the machine.
I would put it together (without bearing retaining compound) and survey at least two widely spaced circular elements of the wheel mounting taper with a .0001" (or better) reading indicator. I would want to know what I was working with before I tried to "fix" it.
Here are two possible options for a retaining compound. Neither are suggestions. Just options for your consideration.
Amazon.com: Loctite-66010 Retaining Compound, QuickMetal(R), 6mLTube, Silver : Industrial & Scientific
Amazon.com: Loctite-66010 Retaining Compound, QuickMetal(R), 6mLTube, Silver : Industrial & Scientific
www.amazon.com
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It's absolutely "OK" (in a properly designed system). PRELOAD is the condition where an axial force, beyond zero clearance, is resisting an opposite load that would cause bearing clearance.
I'll assemble it and test it before I do anything.
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- Nov 24, 2014
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Clearance equals RATTLE equals CHATTER and bearing damage. Leaving axial clearance in the shaft is definitely, IMO, wrong.
I suggest adjusting the nut to ZERO shaft end play and just a bit more preload. One way to know the actual preload is, with the housing rigidly mounted, apply an increasing axial force to the preloaded shaft until axial motion is detected. Easier said than done in most hobby shops.
I got the spindle cleaned up and reinstalled. Turns out the rear bearing has a spring mechanism that sets the preload tension. That actually made things easy.
I put the felt seals in pretty snug although that doesn't interfere with the spindle other than contacting the spindle diameter in two spots. The seals are snug enough that if you push in the ball oiler type drain on the spindle barrel the oil won't come out unless you open the filler cap. I put enough oil in that it leaked quite a bit and then ran it until it stopped.
The spindle is just a bit louder but running very smooth. After running 30 minutes there was very, very little temperature change on the spindle.
I checked run-out with a mitutoyo tenths indicator on the taper in two spots. I could make out a wiggle but less than a tenth of a tenth. I put axial pressure on it and could not detect axial movement at all. The last time I checked the spindle I had 0.0015" in run out. Now even the grinding wheel adapter is less than 0.0001" run out on the diameter and face.
The surface finish is not as good as it was but it's not terrible. Definitely a bit more chatter. I need to clock the wheel, dress the wheel, and try again. Once the bearings run a bit the chatter will probably improve. I don't need perfect finish and the accuracy is good. The piece of hss I ground for the picture came out 0.4994" in 3 measurements. I could not tell any difference.
So far everything is going well. I'm hoping to see a bit less chatter but the machine is still running pretty good.
I put the felt seals in pretty snug although that doesn't interfere with the spindle other than contacting the spindle diameter in two spots. The seals are snug enough that if you push in the ball oiler type drain on the spindle barrel the oil won't come out unless you open the filler cap. I put enough oil in that it leaked quite a bit and then ran it until it stopped.
The spindle is just a bit louder but running very smooth. After running 30 minutes there was very, very little temperature change on the spindle.
I checked run-out with a mitutoyo tenths indicator on the taper in two spots. I could make out a wiggle but less than a tenth of a tenth. I put axial pressure on it and could not detect axial movement at all. The last time I checked the spindle I had 0.0015" in run out. Now even the grinding wheel adapter is less than 0.0001" run out on the diameter and face.
The surface finish is not as good as it was but it's not terrible. Definitely a bit more chatter. I need to clock the wheel, dress the wheel, and try again. Once the bearings run a bit the chatter will probably improve. I don't need perfect finish and the accuracy is good. The piece of hss I ground for the picture came out 0.4994" in 3 measurements. I could not tell any difference.
So far everything is going well. I'm hoping to see a bit less chatter but the machine is still running pretty good.
Thank you for the advice. It did help to know basically what I'm looking for.
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- Nov 24, 2014
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There is a bit more too it than has been discussed. Further help would require you being willing to disassemble the spindle and post pictures of the spindle parts (including both bearings (both sides of each). Lots of details are involved in assembly of a precision spindle.
It's good to read the spindle taper runout was very very little.