my new to me Jet 836 seems to have an under tolerance spindle grind. The top of some of my collets are very tight into the spindle to the point where it takes quite a lot of cranking to pull the collet up and get the bottom taper engaged. I put an endoscope in there and it is not the anti-twist nut or anything else. I made a small lap out of aluminum but i was scared to load it up with diamond paste and it only took a tiny bit off. Any ideas? Should I try harder lapping it or should I just try to grind the collets that are tight?
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R8 tolerance
- Thread starter greenail
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- Jan 31, 2016
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Did you check the threads in the collets ? You could mic the OD of the collets also which would tell you if they are big or not . I would leave the spindle alone . Once it is running out , it becomes a major issue bringing it back in true .
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- Sep 21, 2017
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Some thoughts:
Check your drawbar threads. If the drawbar was overtightened it could stretch the threads near the top and cause binding.
Check the alignment pin/key. If it's partially sheared from a hasty installation or abuse it could also cause binding.
Check the OD of your collets. If they are too large of course they will jam.
The likelihood of your spindle being out of spec is much lower than some other more common issues. I wouldn't lap the spindle. That's your absolute last resort!
Check your drawbar threads. If the drawbar was overtightened it could stretch the threads near the top and cause binding.
Check the alignment pin/key. If it's partially sheared from a hasty installation or abuse it could also cause binding.
Check the OD of your collets. If they are too large of course they will jam.
The likelihood of your spindle being out of spec is much lower than some other more common issues. I wouldn't lap the spindle. That's your absolute last resort!
the threads are fine. I wonder how much this "pilot" sizing actually effects the actual cutting dynamics. My r8 shell mill holder is down right loose at the top but it seems to cut fine. One of the tight ones measured about 5-18 microns big of the spec which says 9.490" or 24.1046mm. The problem with resizing the collets is how do you hold them? maybe my 4 jaw could do it...
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- Jan 31, 2016
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I would stone them . Shove them on an oversize piece of stock in the lathe and the friction would be enough for stoning them . Just don't spring them too much . If you have high spots , the stoning would let you know with the shiny spots .
I have a Grizzly mill that had the same problem. The guide pin in the spindle finally sheared off, marring the inside of the spindle. I replaced the spindle which cleared up a lot of the issue. The original spindle was on the tight side of spec and the new one is right in the middle.
I had previously chucked my problem collets in my lathe and polished them with 1200 grit to bring them into spec. I have also found that some of the offshore R8 tooling to be out of spec and all it takes is .0005 to make them tight.
You can just run them between centers to polish them.
I had previously chucked my problem collets in my lathe and polished them with 1200 grit to bring them into spec. I have also found that some of the offshore R8 tooling to be out of spec and all it takes is .0005 to make them tight.
You can just run them between centers to polish them.
- Joined
- Jan 20, 2016
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- 173
My MSC mill had the upper spindle bore .0005-.001 undersized when I bought it used. I found the R8 spec on line, so easy to check my collets. I had some undersized collets that the top diameter would slide right in, and other collets that were nearer to max in spec would not install.
Like you I had a choice to make. I was not about to mess with in tolerance collets/holders to make them undersize to fit my undersized spindle, so I wanted to fix my spindle to be able to use any R8 holder I might buy in future.
My dad suggested I cut slot in end of wood dowel and wrap sandpaper around it, then spin it with a battery powered drill to 'hone' it out. Can't really remember, but think I used 220 cloth strips about 1/2 wide. Only took a few minutes and 1 or 2 paper changes to get a collet on max tolerance to fit. Working fine for last 6 years now.
Like you I had a choice to make. I was not about to mess with in tolerance collets/holders to make them undersize to fit my undersized spindle, so I wanted to fix my spindle to be able to use any R8 holder I might buy in future.
My dad suggested I cut slot in end of wood dowel and wrap sandpaper around it, then spin it with a battery powered drill to 'hone' it out. Can't really remember, but think I used 220 cloth strips about 1/2 wide. Only took a few minutes and 1 or 2 paper changes to get a collet on max tolerance to fit. Working fine for last 6 years now.