# Post PM-833T Spindle Bore Runout



## Bill Kirkley (Oct 4, 2019)

I decided to check the runout after boring out the upper part of the R8 spindle. 

The Morse taper arbor PM supplied had at most two ten-thousands runout. (See attached video)

A 1/2" end mill

 shaft in the Interstate collet had about one thousands runout. 

I clamped a 1X2 board in the vise. Using the Y axis handle I pressed the board hard against the end mill. There was about one thousands deflection. 

I am not familiar with typical runout values. These seem pretty good to me. 

I have been of the opinion that a sloppy fit between the threaded end of an R8 insert and the spindle would have no adverse affects on performance. I think wedging the insert into the R8 taper with the draw bar is what produces stability, not the upper end of the insert. 





Your browser is not able to display this video.










Your browser is not able to display this video.









Your browser is not able to display this video.




















Your browser is not able to display this video.


----------



## davidpbest (Oct 4, 2019)

I am unable to see the videos you posted, but looking and what you wrote, I'm unimpressed.   I've posted the results of my PM935 spindle runout and end mill testing after a replacement head unit was provided by PM to correct for the original defective head.   Collet quality does matter.   *Results are here.*


----------



## Bob Korves (Oct 4, 2019)

If you want to vet the accuracy of your spindle, then test your spindle, not something stuck into it.  First, look carefully at the R8 taper in the spindle with a good light and look for damage or other problems.  If you find issues, fix them properly.  If the spindle taper looks OK, put a tenths indicator against the spindle taper and turn the spindle by hand.  A decent spindle should be within a couple tenths overall.  If that works and you still have a lot of runout out with collets, it might be the collets, it might be trash in the spindle recess, and it might be the anti rotation screw pressing too far into the key way of the collets.  

When measuring stuff, try to avoid using surrogates instead of the actual piece you want to know about.  It often only makes you more confused...


----------



## Bill Kirkley (Oct 4, 2019)

The question arose if enlarging the upper end of the R8 spindle would affect the spindles function. So I stuck an arbor in the spindle and found it deviates less than two ten thousands. 

Davidpbest stuck an end mill in a collet and had 4 ten thousands runout in the end mill if I read it correctly. 

Davidpbest. For what ever reason you have to be logged in. They worked for me.


----------



## davidpbest (Oct 4, 2019)

Bill Kirkley said:


> The question arose if enlarging the upper end of the R8 spindle would affect the spindles function. So I stuck an arbor in the spindle and found it deviates less than two ten thousands.
> 
> Davidpbest stuck an end mill in a collet and had 4 ten thousands runout in the end mill if I read it correctly.
> 
> Davidpbest. For what ever reason you have to be logged in. They worked for me.



I agree with Bob.   The critical reference surface of the spindle is the taper - the upper end shouldn't matter unless it's not concentric with the spindle rotation.   The TIR of my PM935 spindle as measured at the R8 taper is 0.0002".   With the best collet I can buy, I'm still at 0.0002" TIR on the OD of a 1/2" carbide end mill.   With lower quality collets, the TIR measured at the OD of an end mill bumps up to 0.001".


----------



## Bill Kirkley (Oct 4, 2019)

David, does the threaded end of an R8 insert contact the spindle wall?  If not, the inside diameter of the spindle or being concentric should matter.


----------



## ddickey (Oct 4, 2019)

It touches the wall of the spindle for stability. Blue it up and insert to check.


----------



## mksj (Oct 5, 2019)

The R8 collet touches the wall at the top and the bottom, there is typically a relief in the center of the collets/spindle. The top is precision ground to prevent lateral deflection and should be a close fit to the spindle wall. Otherwise you would get axial skew on tightening and deflection of the collet with milling. The draw bar provide vertical tension, but is not for significant axial deflection.  In tightening the bar there is no centering of the rod with respect to the collet other than screwing into the top of it. The top of the collet provides the centering.






The R-8 collet clamping range is very narrow, typically within 0.002". You may not be able to measure any noticeable runout at the collet tip holding a precision rod, but 2-3" out if the collet top is not aligned at the top, then you will see more runout at the cutting tip. As David pointed out and also mentioned previously, the cheaper R8 collets often have much worse TIR and sometimes collet fitment issues. I had problems until I got a set of Lyndex and royal R8 collets. It may also have something to do with the machine specific tolerances of the spindle. To measure runout of the spindle you want to  an indicator on the mating surface of the spindle.

I use two touch probes that require you align the tips to less than 0.0004" with a test indicator,  I use them with a R8  ER-32 collet setup which has a TIR of ~0.0002" out to about 3" from the collet. R-8 collets had too much runout.


----------



## Bill Kirkley (Oct 5, 2019)

Thanks, it would appear I rendered my spindle unstable by increasing the upper diameter by four thousandths so my Interstate collets would fit. 

In spite of this, it performs well for my purposes. The collets remain wedged in place after use and have to be tapped with a mallet to free them.


----------



## Bill Kirkley (Oct 5, 2019)

If my math is correct the tip of my half inch end mill will deflect .001 inches at an angle of .03 degrees. Fortunately, that is acceptable for the projects I do.


----------



## mikey (Oct 5, 2019)

If you actually bored out your spindle, that would also make any collet chuck you might have used inaccurate. A new spindle might be your best option. The amount of run-out you are citing is going to have a significant impact on end mill life, accuracy and finishes.


----------



## mikey (Oct 5, 2019)

Just curious ... why did you bore the upper spindle?


----------



## Bill Kirkley (Oct 5, 2019)

When I got the machine the Interstate collet would not insert. The threaded end measured maybe 2.5 ten thousandth inch under .949. From what I could find .949 to .9495 is the standard size for the threaded end of an R8 collet. I felt the spindle was slightly undersized. 

I only enlarged the upper end. I didn't machine the taper. So any deflection would occur with a lateral load. I don't think that will have any ill affects on the end mills. 




Your browser is not able to display this video.


----------



## Bill Kirkley (Oct 5, 2019)

I would be interested in the OD of the threaded end of a high precision collet. 

I also can not find the specs for the ID of the upper end of the spindle cavity. It would be interesting to know how close the collet and spindle measurements are to one another.


----------



## mksj (Oct 5, 2019)

All of my R8 collets measure between 0.94920-0.94945", the R8 collet specification is 0.94960" but probably varies by manufacturer. I would assume the spindle diameter would be 0.9500", spindle tolerance is usually within 0.0002" but once again is manufacturer dependent. The wiggle test doesn't really tell you much, it is all what the cutter does under load. In this setting the longevity of end mills will not be an issue, under CNC conditions it would be different. I think the bottom line is if something is not fitting in a new machine, I would work out/evaluate all other options including replace the spindle, before modifying  spindle to collet mating surfaces. If there was a defect then it should have been addressed by the manufacture. You also did not indicate if you remove the guide pin and if other R8 tooling did not fit. This was the differential for me when I had a problem with my initial R8  collets, other R8 tooling like drill chucks fit w/o any problems. Just my 2 cents on the issue.


----------



## Bill Kirkley (Oct 5, 2019)

The guide pin was out when the collet got stuck. The two arbors that came with the machine were a snug fit. The drill chuck was a smooth fit.

Based on your measurements your collets wouldn't have fit since mine is slightly smaller.

The manufacturer said I could return the spindle and they would check it out. Perhaps it was unwise but I didn't want to take the machine apart. I solved my problem by enlarging the upper end of the spindle.

I have milled the edges of a 1/2" flat bar with a 1/2" end mill. The operation was accurate and the adjacent faces square when compared to my Starrett ruler (I don't have a machinist square). I took .0625 inches off of the 1/2" edge with each pass.

The measurement of the upper and lower sides was within about a quarter thousandth inch top compared to bottom. 

I don't know how much pressure would be required to deflect the collet. The oversized upper end of the socket will not likely be a problem for the work I do.


----------



## Bill Kirkley (Oct 5, 2019)

mksj,  do your collets slip in easily or are they a snug fit?  I would think if your spindle is only two ten thousandth inch larger than your collet it would take some finagling to get them in.


----------



## mikey (Oct 6, 2019)

Bill Kirkley said:


> I would be interested in the OD of the threaded end of a high precision collet.



I use Crawford R8 collets. All measure between 0.9491-0.9493. I have one Yuasa collet at 0.9493". Hardinge collets are the standard in my opinion but Crawford and Yuasa are quite good as well. 

Its your call as to how accurate or inaccurate the spindle needs to be for what you're doing. For myself, I would bite the bullet and order a new spindle from PM and rectify the situation. Then I would buy a really good ER chuck and some good collets and be done with it.


----------



## davidpbest (Oct 6, 2019)

I agree with Mike - get a new spindle that is on-spec.   Sometime down the road you will be glad you did.


----------



## Bill Kirkley (Oct 6, 2019)

Thais for the help. I'll consider ordering a new spindle.


----------



## mikey (Oct 6, 2019)

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.


_


----------



## Bill Kirkley (Oct 6, 2019)

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!


----------



## RJSakowski (Oct 6, 2019)

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.


----------



## Bob Korves (Oct 6, 2019)

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!


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...


----------



## Bill Kirkley (Oct 7, 2019)

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.


----------



## Bob Korves (Oct 7, 2019)

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.


----------



## Bill Kirkley (Oct 7, 2019)

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.


----------



## Bob Korves (Oct 7, 2019)

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.


No problem with that, Bill.  Do what you enjoy, and enjoy what you do.


----------

