Post PM-833T Spindle Bore Runout

I can understand the reluctance, Bill, but as David said, it is the right move to make ... every single cut you make with a tool held in an R8 collet will be affected by that spindle. Besides, its an opportunity to learn how to remove and replace the spindle, check the bearings and make sure your bearing preload is good. If you can, put the new spindle on V-blocks and check it with a tenths-reading DTI so you know it is straight and that the spindle taper runs true. If you do the same thing at each step of the installation then if one component is off you will know exactly what it is.

To clarify, check the spindle first. Then install it in the quill and check the run out of the spindle in the quill with the quill locked down on the work bench. This tells you that the spindle bearings are aligned and the spindle runs true in them. Then install the quill and check it again. If run out is consistent with what you got before then you're good; if it increases wildly then your drive sleeve bearings are suspect. Get it?

I'm not sure how you're checking your spindle concentricity but this procedure from an older thread works well:

Just thought I would give you a simple procedure for checking concentricity with reasonable reliability.

  • Clean everything - the thing to be checked, any tapered thing, the indicator base and indicator tip. No oil anywhere.
  • Always check the foundation. If you're checking something that fits in the spindle then you have to check the concentricity of the spindle first. If mounting something that contacts the spindle register, check the register. If mounting something inside the Morse taper then you have to check that, too.
  • Use a Sharpie and mark the thing that is being checked and another reference mark in line with it that is on something stationary. This is really important. Try to make your marks in such a way that you minimize parallax. That is, when they line up, you're sure they line up.
  • Mount the indicator correctly (angle of the indicator arm correct for that indicator) and preload it so there is some tension on the internal springs. I usually preload to at least 0.050", then zero the dial. If I tap the indicator and the needle jumps around and doesn't return to exactly where I set it then I know I need to re-configure the holder so it is solid. When you zero the needle, it needs to be dead center on some unit so you know exactly where your starting point is; no guessing allowed.
  • With your reference marks lined up, manually turn the thing you're measuring one full revolution and be certain the indicator needle returns exactly to your starting point when your Sharpie marks align. If they do, this tells you your set up is repeatable and you can rely on it. If they don't then you need to reconfigure it more solidly or change indicators.
  • Now, make one more revolution manually but slowly and note the maximum deviation of the needle. If you can, Sharpie mark the turning thing so you know where that deviation is. Come back to your reference marks and check that you hit zero. Now repeat to see if the deviation is in the same place and of the same magnitude. If it is, then that is the amount your concentricity is out.
  • It is a good idea to check a thing in multiple places - at least three spots on a spindle or taper (near the outer end, a bit of the way in and way in). That way you are sure the defect is over the whole surface and not at one spot.
  • When using a D1 camlock attachment, like a chuck, it is a good idea to check your run out in all of the possible mounting positions so you know which one is the best and then put a witness mark on the chuck so you can always remount it for best accuracy. This assumes the run out is acceptable and you're going to keep it.
This is not perfect but it is the best you can usually do in a hobby shop. At least you'll know, with a reasonable degree of certainty, that something has such and such amount of run out and you'll have a good idea which component it is and how bad it is. We frequently see run out being checked under power on Youtube; not sure what you can tell when doing that but it isn't concentricity of the component being checked - too unreliable, too many interfaces.


 
Mikey, thanks for the post. At this time I don't want to deal with the procedure of replacing the spindle. Maybe sometime in the future. My current setup works for me. Besides, I'm a firm believer in Murphy's Law!
 
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As far as I know, there is no official specification for the R8 taper outside of Bridgeport. As such, all specifications are derived from reverse engineered products. Consequently, there will be some dimensional variation between manufacturers. Interchangeability if parts requires that all parts be made to a set of tolerances such that the worst case pass of one part will mate with the worst case pass of the mating part. Without a set of consistent specifications between manufacturers, there is no guarantee that parts from different manufacturers will mate.

I had this problem with the keyway on R8 collets. Some collets would fit while others jammed up. On the other hand, the bad collets worked with no problem on another mill. The issue was a slightly shallow keyway. A bit of stoning to increase the slot depth solved the problem.
 
Bill Kirkley said:
Mikey, thanks for the post. At this time I don't want to deal with the procedure of replacing the spindle. Maybe sometime in the future. My current setup works for me. Besides, I'm a firm believer in Murphy's Law!
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It is probably also possible to bore out the spindle bigger, glue in a sleeve, and then bore the sleeve in place to be concentric and to just fit all your collets. That is not a newbie job, pretty fussy work. Still, if you are ever thinking of throwing the spindle away, first consider fixing it...
 
Bob, I have no idea what diameter I finally ended up with, as I don't know where I started. I have used the machine and found no problems. It could be I'm on the upper end of one of RJSakowski's manufacturers acceptable specs.

I didn't look at all of Davidpbest's videos. If he didn't find a way to measure the ID of the part of his spindle that mates with the threaded end of his R8 inserts, based on RJSakowski's post, there is no telling what it may be.

I deflected a stationary end mill one thousandth an inch putting a far heaver load on it than I ever would. If it took cranking a piece of wood hard against an end mill to deflect it one thousandth an inch, normal use likely causes no problem.

So, I don't feel the spindle is ruined. If I were making parts for a high precision device it may not be adequate. For what I do it is great.

There is a mix of people who post here. For some everything needs to be as perfect as possible. For others good is good enough. For some anything is better than nothing.

For now, at least, good is good enough for me. One day I may decide to try my hand at replacing the spindle.
 
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If the mill is working adequately for you, then yes, leave it alone. We can spend all of our time fiddling with machines instead of actually making something. The only point of my post was that a new spindle may not be a requirement if you want to tighten it up.

Personally, I find it very satisfying bringing damaged equipment back to good usable condition without buying anything, or very little. I also enjoy making nice work with used machines and tooling that were formerly in bad condition. I like it more than buying new stuff, especially when I would have to rehab it as well...

I also find that taking things apart, seeing how they work, looking for issues and addressing them, and just making sure everything is OK, all let me use those things like I am part of them, not just a driver.
 
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Bob, I have a friend who, like you, loves bringing old machines back to life. Me, I like designing and making gadgets for personal use. Very few require tight tolerances.
 
Bill Kirkley said:
Bob, I have a friend who, like you, loves bringing old machines back to life. Me, I like designing and making gadgets for personal use. Very few require tight tolerances.
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No problem with that, Bill. Do what you enjoy, and enjoy what you do.
 
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