# R8 Insert Deflection



## Bill Kirkley (Oct 13, 2019)

As indicated in other threads, I bored out the upper end of my PM-833T's spindle socket so it would accept my Interstate collets.

It was pointed out that the threaded end of an R8 insert is precision ground. The explication being there is a tight fit between the insert and the spindle. This is presumably to counteract insert deflection under load.

As pictured below I made a devise to measure R8 insert deflection under load. The measured deflection was .00075" for torques ranging from 88 inch pounds to 946 inch pounds. The torque was created by placing a 44 pound weight on a half inch rod secured in an R8 collet.

Varying the torque had no affect on the deflection. One explanation is that any load settled the apparatus, not the collet, causing an initial deflection. If this is the case, it could be argued that loads in the range tested result in no deflection of the insert.

If the deflection is a result of collet movement then a wide range of loads result in a deflection of .00075".


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## Bill Kirkley (Oct 13, 2019)

Bill Kirkley said:


> As indicated in other threads, I bored out the upper end of my PM-833T's spindle socket so it would accept my Interstate collets.
> 
> It was pointed out that the threaded end of an R8 insert is precision ground. The explication being there is a tight fit between the insert and the spindle. This is presumably to counteract insert deflection under load.
> 
> ...


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## Bill Kirkley (Oct 13, 2019)

I realized that the deflection is negative. If I am not mistaken, the loads should have resulted in a positive deflection.  The devise is clamped to a 1/4" plate. The plate may sag slightly under load, resulting in the observed negative deflection. 

If that is in fact the case then loads in the range tested do not deflect the collet.


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## mksj (Oct 13, 2019)

At the end of the day I would not worry about determining the magnitude of deflection and if it will have an ill effect. The apparatus is not going to be able to determine in a static mode of what is going to be happening in a dynamic mode. About all I can suggest is measure the diameter of you tooling and the ID of the milled spindle and see what the difference is between the two. Maybe a few other people can measure the upper R8 ID of their spindle for comparison. 

My main concern would be that you could have introduce some skew in the spindle, this would be seen a worsening TIR as you get further away from the collet/chuck while rotating the spindle. I typically prefer to use an ER32 system clamping some precision ground rod because it tends to have the lower runout vs. R8 and tends to me more uniform in arbors/collets as to TIR. You could also try milling a slot, with a known movement in the Y axis and compare the actual width to the movement.  If you are not doing tight tolerance work it may not matter anyway.


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## Bill Kirkley (Oct 13, 2019)

When a rotating end mill is fed into a workpiece there is a force exerted on the end mill perpendicular to the long axis of the end mill. The rotation makes no difference other than the fact that the force is applied 360 degrees as the cutter rotates. If at any time you could stop the action, there would be a load perpendicular to the end mill.

The rotation and cutting might add a vector of force but you still have a load perpendicular to the long axis of the end mill.

The reason it is significant is that it implies a loose fit between the threaded end of the R8 insert and the spindle will have no ill affect on performance.  It also implies that the contact between the R8 bevel of the spindle and insert is the only thing that affects stability and performance.


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## davidpbest (Oct 14, 2019)

If you really want to test this, put an end mill in the spindle using whatever type of tool holder you prefer, and slot some material at a depth of 1.5X the diameter of the end mill.   Then measure (using gauge pins or gauge blocks) the resulting width of the slot and compare that to the published OD of the end mill.   That will give you some real world indication of the spindle & tool holder TIR, along with some indication of the rigidity of the machine.   If you want to see the real world "skew" or deflection of the tool under load, side-face the width of some thick material using an end mill and measure the resulting width top and bottom, or check it on a surface plate with a squareness gauge to see if you're getting a square result.   While I admire the lengths you have gone to in your tests, I don't really understand how useful those load test results are in practice.   As I said in your original post, I still think you should replace the spindle with one that has not been bored out to accept out-of-spec collets - at some point you'll be glad you did.


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## Bill Kirkley (Oct 14, 2019)

Davidpbest,  the problem with the tests you propose is they are pass fail. If you fail they don't tell you why.

Is the tool you are using within specs?
Is your tool holder socket out of round?
Is your spindles bevel out of round?
Is there a poor fit of the spindle bearing
Is there too much space between the threaded end of your tool holder and the spindle?

Many of you use static testing to check the spindle bevel's runout.

I have a space of about .001 inches between the threaded end of my tool holder and the spindle. The test I did eliminates this as a potential cause of tilt of a tool under load in the range I tested.

Many have indicated they bought tools that wouldn't fit their spindle. I would imagine the culprit is the threaded end of the tool holder. It is too large for the spindle. My test shows manufacturers can make that portion of the spindle one to two thousands larger so it will accept any tooling and have no affect on the machines performance.


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## matthewsx (Oct 14, 2019)

One thing I really like about forums is you get to see the work others have done, the advice they’ve given and learn about their thought processes.

Davidpbest has posted some pretty impressive stuff on here and I would count him as someone to look at for making the PM tools as accurate and repeatable as possible. I’m not sure what his background is but he definitely works with master machinists to make his shop really, really nice.

I looked at your test rig and I wondered exactly what it was testing, just as I read the earlier post about enlarging the spindle on your machine and wondered why you took that approach to collets that seemed too large.

When I post things online I do so to learn from those with more experience or different perspectives than I have. I really like this forum because unlike so many others it seems like most of the people on here have the same attitude and are willing to both learn and share their knowledge.

If your machine does the work you need it to do then there is no need for further tests IMHO. If not there are plenty here willing to help.

Cheers,

John


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## higgite (Oct 14, 2019)

Bill Kirkley said:


> I realized that the deflection is negative. If I am not mistaken, the loads should have resulted in a positive deflection.  The devise is clamped to a 1/4" plate. The plate may sag slightly under load, resulting in the observed negative deflection.
> 
> If that is in fact the case then loads in the range tested do not deflect the collet.


So, if there is no deflection, a logical conclusion of your test would be that R8 mill manufacturers and R8 collet manufacturers are wasting time and adding additional cost by boring spindles to a precise ID and grinding collets to a precise OD? Sorry, but with all due respect, I’m skeptical.

Tom


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## Bill Kirkley (Oct 14, 2019)

There are parts of a machine that need to be precise. There are parts that don't need to be precise. This test indicates the upper bore of a machine doesn't have to be precise. 

RJSakowski posted in another thread that manufacturers are in fact not precise with this dimension: 



RJSakowski said:


> 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.


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## shooter123456 (Oct 14, 2019)

Bill Kirkley said:


> There are parts of a machine that need to be precise. There are parts that don't need to be precise. This test indicates the upper bore of a machine doesn't have to be precise.
> 
> RJSakowski posted in another thread that manufacturers are in fact not precise with this dimension:


Two things: Bridgeport designed the R8 taper, so their specifications would be THE specifications.  The fact that there isn't a standardization is not an indication that the dimensions aren't critical.  

Second, the lack of consistency between manufacturers is also not an indication that the dimension is not critical.  There are differences in holding force, longevity, run out, surface finish, etc between different collets.  The fact that some work better than others can likely be attributed to the fit between the collet and spindle.

And as someone else noted, the fact that manufacturers go through the trouble of grinding both those surfaces can't be ignored.  If it really made no difference, they wouldn't be doing it.


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## Bill Kirkley (Oct 14, 2019)

Shooter 123456,  as stated, all of these machines are derived from the Bridgeport standard, so great care is taken in maintaining that standard. 

What may not have been considered is weather or not some of the specs are critical. Machines evolve over time based on new findings through testing, innovations, materials, etc. I believe it is possible no one ever considered whether or not the dimension in question is critical. 

The test clearly indicates a load on a cutting tool does not deflect or tilt the tool holder. If you accept that, then the ID of the upper part of the spindle is in fact not critical.


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## matthewsx (Oct 14, 2019)

Bill Kirkley said:


> Shooter 123456,  as stated, all of these machines are derived from the Bridgeport standard, so great care is taken in maintaining that standard.
> 
> What may not have been considered is weather or not some of the specs are critical. Machines evolve over time based on new findings through testing, innovations, materials, etc. I believe it is possible no one ever considered whether or not the dimension in question is critical.
> 
> The test clearly indicates a load on a cutting tool does not deflect or tilt the tool holder. If you accept that, then the ID of the upper part of the spindle is in fact not critical.



I seriously doubt that engineers at Bridgeport and Precision Matthews have never considered if any spindle dimension is critical, most likely they have specs and tolerances that parts are manufactured to in order to keep their products performing as designed.

Both companies are still in business so if you have any questions perhaps asking their customer service departments would give a definitive answer.

John


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## RJSakowski (Oct 14, 2019)

Bill Kirkley said:


> There are parts of a machine that need to be precise. There are parts that don't need to be precise. This test indicates the upper bore of a machine doesn't have to be precise.
> 
> RJSakowski posted in another thread that manufacturers are in fact not precise with this dimension:


Manufacturers may  be precise in this dimension not not accurate.  Precision and accuracy are two different animals.  

The problem that arises isthat given no "official" specifcation outside of Bridgeport, other manufacturers had to reverse engineer. the parts.  This typically involves making a number of measurements of existing "good" parts and attempting to recreate the Bridgeport spec.  If a large number of parts are measured, there is a fairly good probability that one can have a good value for the internal diameter of the top of the Bridgeport socket.  There is also a small but finite probability that the value will be out in left field.  

If a manufacturer wanted to determine a spec. for the Bridgeport R8 socket, he should measure a sufficiently large sample of Bridgeport machines.  This is not really a practical situation and more then likely various manufacturers would skimp on sample size, increasing the probability of an erroneous value.  Note that the measurements should only be made on Bridgeport machines as any other machine could be tainted by there own reverse engineering.

Measuring R8 collets/adapters is not the best way to set the standard as well as they should only be manufactured by Bridgeport or one of their subcontractors privy to the internal Bridgeport spec. and even then, the specification for fit with the socket is unknown.


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## shooter123456 (Oct 14, 2019)

Bill Kirkley said:


> Shooter 123456,  as stated, all of these machines are derived from the Bridgeport standard, so great care is taken in maintaining that standard.
> 
> What may not have been considered is weather or not some of the specs are critical. Machines evolve over time based on new findings through testing, innovations, materials, etc. I believe it is possible no one ever considered whether or not the dimension in question is critical.
> 
> The test clearly indicates a load on a cutting tool does not deflect or tilt the tool holder. If you accept that, then the ID of the upper part of the spindle is in fact not critical.


That is based on the assumption that the only function of that face is to prevent static deflection of the tool.  It could play a part in concentricity, repeatability, wear, vibration resistance, etc.  It could also be to help transmit radial loads to the upper spindle bearings instead of just the lower ones.  I could also be that it doesn't become important until more force is exerted.

I think what everyone is saying is that one test to measure one factor isn't enough to conclude that some of the largest machine tool manufacturers in the world have failed to consider that they could be saving time and money with no detriment to performance if they just made that part oversized and didn't worry about it.


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## Bill Kirkley (Oct 14, 2019)

Unless someone can find fault with my methodology, the test shows that a load applied to a tool in an R8 tool holder, resulting in a torque of 946 inch pounds, causes no deflection of the threaded end of an R8 tool holder.

It appears there is disagreement as to the ramifications of this finding.


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## mksj (Oct 14, 2019)

Clearly the specs for the R8 collet are well known and published by Bridgeport, Hardinge and no doubt multiple other manufactures of premium collets. The spec. for the R8 collet OD limit is 0.9495", the degree that a collet producer adheres to this spec, their tolerance limits, and their QC varies by manufacture. On Hardinge R8 collets the spec. is +0.0000 -0.0003. When I measured my Lyndex and Royal (Crawford)  R8 collets they were all 0.9495 or slightly under. The spindle ID is manufacturer specific.  If your collets meet this spec. and the spindle did not fit it,  then clearly the spindle was faulty and should have been replaced under warranty. If you now feel that the spindle OD is bored concentrically and too the proper dimension then end of story. I have yet to see that you evaluated any axial deviation measurement at say 3-4" from the collet with an accurate test gauge. I can assure you that you need a gauge that can measure down to 0.0001" to have any meaningful results. Repeat the test pulling the drawbar up and down several times. If they are reproducible then you are should be OK as too the vertical collet alignment in the static mode.






Given that the R8 collets has been around for a long time  requirements for manufacturing are quite tight, I seriously doubt the it is just haphazardly decided as to what the spindle bore should be and that the upper dimension can be whatever they decide on that day. If this was the case the surfaces would not be precisely ground to interface with the corresponding spindle interface. I have had no "zero" issues with quality collets and arbors AND have only had issues with generic collets like the Interstate for whatever reason. Other problems I have seen is the guide pin is set too deep (or is too wide) or the threaded portion of some arbors is not deep enough preventing the drawbar from not being able to pull the collet completely vertically.

If you look at other similar collets like the 5C, the rear ground surface is precisely ground despite being pulled back by a threaded portion similar to the R8, any small deviation in axial play results in measurable skew. The back interface on my Bison 5C chuck is very tight, previous Chinese chucks less so and it showed more inconsistency in  axial deviation. There are also limitations to R8 system because of the nature of the collapsible interface of collets as compared to other collet systems/spindle interfaces which offer far better concentricity and rigidity.

The R8 drawbar is not precisely located and it is made to pull up on the collet, and not provide a lateral position of the collet. In my mill it rattled around until I modified the spacers. A small deviation at the top of the collet when the collet is drawn up of say 0.001" would result in a corresponding runout/wobble at the cutter tip. When milling there are vibration/oscillating forces, with corresponding movement/deflections at the end mill tip. The forces and effects can only be determined in a dynamic situation and is specific to the cutter type, collet, clearances, rigidity, etc.  It is a known fact that runout of endmills corresponds to endmill life in a production environment, as well as the accuracy of the finished product. Clearly these are not issues in your situation.


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## mikey (Oct 14, 2019)

Bill Kirkley said:


> Unless someone can find fault with my methodology, the test shows that a load applied to a tool in an R8 tool holder, resulting in a torque of 946 inch pounds, causes no deflection of the threaded end of an R8 tool holder.
> 
> It appears there is disagreement as to the ramifications of this finding.



Bill, just a few points to ponder:

How exactly did you enlarge your upper spindle? I'm curious because it appears you did this without removing the spindle from the machine.
The upper spindle is intended to resist radial forces. The force required to break an end mill varies with the size of the end mill, of course, but the force to break a 1/2" end mill is in the neighborhood of 116,000 - 200,000 pounds-force/inch squared. I've broken 1/2" end mills before so I know that the forces experienced by a cutter are considerably higher than what you're using in your tests. They can be even higher if you use a large face mill or even a large diameter fly cutter due to shock loads. You asked about ramifications ... here it is.
You seem to be trying to make yourself feel better about modifying your spindle. That's okay because as you said, its good enough for what you do and nobody can gainsay that. I think what at least some of us are saying is that another option is to just replace the spindle and use good quality collets ... and then move on, with a lesson having been learned. I assure you that we're trying to help you.


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## RJSakowski (Oct 14, 2019)

mksj said:


> Clearly the specs for the R8 collet are well known and published by Bridgeport, Hardinge and no doubt multiple other manufactures of premium collets. The spec. for the R8 collet OD limit is 0.9495", the degree that a collet producer adheres to this spec, their tolerance limits, and their QC varies by manufacture. On Hardinge R8 collets the spec. is +0.0000 -0.0003. When I measured my Lyndex and Royal (Crawford)  R8 collets they were all 0.9495 or slightly under. The spindle ID is manufacturer specific.  If your collets meet this spec. and the spindle did not fit it,  then clearly the spindle was faulty and should have been replaced under warranty. If you now feel that the spindle OD is bored concentrically and too the proper dimension then end of story. I have yet to see that you evaluated any axial deviation measurement at say 3-4" from the collet with an accurate test gauge. I can assure you that you need a gauge that can measure down to 0.0001" to have any meaningful results. Repeat the test pulling the drawbar up and down several times. If they are reproducible then you are should be OK as too the vertical collet alignment in the static mode.
> View attachment 303846
> 
> 
> ...


Interesting that the Hardinge drawing has the half angle of the taper when the angle of the taper is actually 16º 51' for a half angle of 8.425º.  

From what I have been able to find, the diameter of the cylindrical section is .9495 +0000/-.0003" or .9496 +0000/-.0003".  However, I have been unable to find any direct reference to an actual Bridgeport spec.  After extensive searching, it appears that many others have tried and failed as well.

FWIW, my two machines have a socket dimension greater than .9494" (slip fit) .  A .9495" cylinder is a light press fit. A 9505 was a no go.  Neither are Bridgeports though.


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## mksj (Oct 14, 2019)

Specific to RJ's comment about the Bridgeport spec. for the R8, there is information that was posted elsewhere which is informative/provides the reference spec. and also some discussion of the female receiver dimensions although that seems to be more opinion then a standard. I am using quotes below to provide credit to the individual who posted the information. This is a similar situation to many of the import 123 blocks, which although the external dimensions are accurate, the holes for bolting them to other blocks of fixtures are undersized and the bolts do not pass through these holes. Regardless of who made the the R8 collets, if they were no larger than  0.9495", then your spindle dimension may have been ground incorrectly. How this is addressed is clearly your choice.






						R8 Taper socket dimensions? - RC Groups
					

R8 Taper socket dimensions? uk.rec.models.engineering




					www.rcgroups.com
				




"Ok we need to look at a bit of history here to get the full picture.
The R8 collet was devised by Bridgeport back around WW2, before that they were using the B&S collets or sometimes the Morse. All this is rather hazy due to licensing agreements.

Because the R8 was classed as a proprietary taper it was never listed in places like Machinery Handbook, to my knowledge unless it's in V27 it still isn't.

Many people have listed various drawings for the R8 some very crude and some with a few major dimensions on them as a guide. many of the collet manufacturers have them on line.

The first recorded entry I can find on the FULL specs is in a 1952 edition of the National Machine Tool Builders manual. This was a professional body of interested people who went about setting various standards, machine noses and tapers being one.

Incidentally the initials NMTB is still prevalent today as a standard taper although it has also been superseded by the term INT

Here's a copy of that drawing hosted by Scott Logan of Logan lathe fame. http://www.loganact.com/tips/r8.htm

So now we had a standard and all was fine - until.............

Sometime with the last three of four years with the import of tools from the far east a certain American manufacturer who was building his version of a machine with an R8 taper sent a sample to China for collets to be made. Unfortunately due to a lack of published standards his spindle wasn't standard so the Chinese working with what they had made collets up to fit this spindle. The Yank was pleased as he now had a supply of collets but in the process had ****** up the whole shooting match.

So what has now happened is that in certain provinces they are making collets to the Twonk spec and in other provinces they are making collets to the correct spec.

The importers know this problem but it depends on where they are buying from whether they admit to knowing about this.

Over the last couple of years I have bought about 12 pieces of R8 tooling from collets to boring heads, all have fitted my Adcock and Shipley built Bridgy with no problems so watch where you buy from.

Regards,
John Stevenson
Nottingham, England."


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## Grandpop (Oct 14, 2019)

I am at least the 2nd owner on an Enco 8 x 28 knee mill. I came with 3 R8 collets that all went in and out easily.

One of the first things I bought was a set of R8 end mill holders. Imagine my surprise when none of them fit up inside the spindle! After a lot of investigation it appeared that the holders did meet the Bridgeport specs for the end diameter, and the spindle bore was .0005 too small. The PO had ground the end of his collets down to fit!

After a lot of head scratching, my father suggested taking a length of wood dowel, slotting it to hold a piece of Emory paper, putting the emory in the slot and wrapping a turn or two around the diameter. I turned the end of the dowel down to fit a cordless drill to drive it. I didn't have a great expectation for success, but with nothing to loose, I wrapped a piece of 220 grit around it a gave it a try.

I was amazed that after a few minutes of up and down in the bore my smallest end mill holder was starting to fit. I ran the drill a little faster, swapped in anew new emory, and a few minutes later they all fit just right. 

I have no way to get up in there to measure the bore accurately, but the largest end mill holder is a nice slip fit. To be clear, I would not be concerned if the bore ended up .001 over. Nothing I will ever make ever make on this hobby machine would be affected.


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## mikey (Oct 14, 2019)

I have a RF-31 and use Crawford collets, a Tormach collet and ETM tooling in it and all fit without any issues. If something doesn't fit I would suspect the thing I'm trying to insert before modifying my spindle. But that's just me.


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## wrmiller (Oct 14, 2019)

mikey said:


> I have a RF-31 and use Crawford collets, a Tormach collet and ETM tooling in it and all fit without any issues. If something doesn't fit I would suspect the thing I'm trying to insert before modifying my spindle. But that's just me.



Yea, that is kinda what I was thinking.


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## RJSakowski (Oct 14, 2019)

For reference, the quote in post #20 is dated 2006.  I had run across the same thread. I would be interested in seeing that R8 spec in the 1952 edition of the National Machine Tool Builders manual. 

I am curious as to who the Yank that was responsible for the Twonk spec was.  A little later in the same thread was a suggestion that the Asian collet manufacturers might be grinding the R8 taper to 3-1/2"/ft. which would be a half angle of 8.297º rather than the accepted taper of 16º51'/2 or 8.425º.  
One issue that I have with my Tormach mill is that the collets make contact at the large end of the taper which would mean the socket taper angle is too small.  I had thought that this was a manufacturing error but now it seems that it may be a design error resulting from the Twonk spec. Hmmm.


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## Doubleeboy (Oct 14, 2019)

Interstate stuff can be hit or miss .  Lyndex is good and not too expensive.


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## wrmiller (Oct 14, 2019)

Doubleeboy said:


> Interstate stuff can be hit or miss .  Lyndex is good and not too expensive.



I bought the ultra precision set from PM at the same time I bought my mill. Collets are Taiwan made and have near unmeasurable runout. Well at least none I could detect with my equipment anyway. 

I did have to back out the keyway pin a bit though.


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## Bill Kirkley (Oct 15, 2019)

Mikey,  I am trying to determine if what I did had any affect on the precision of the spindle. The results do make me feel better. It indicates enlarging the upper end of the spindle has no affect on the stability of a tool in an R8 collet. 

I used a scale to test the force on a tool. I determined this by the resistance I felt turning the handle, mimicking the resistance I feel running the machine. The range was about 115 to 196 pounds force. Cranking the handle much harder than I ever would the force was about 246 pounds. 

I weighted the weight. It is actually 43.8 pounds. In my test, at a distance of 21.5 inches, there was a torque on the collet of 941.7 inch pounds. If you feed the tip of an end mill 3 inches long measuring from the end of a collet, this torque would place a force on the mill of 313.9 pounds (941.7/3). This is greater than the extreme force I measured (246 pounds). 

So, I am relieved that boring out the spindle will have no adverse affect on its function. 

Below are photos of my force measurement and  my setup for boring the spindle.


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## Bill Kirkley (Oct 15, 2019)

mksj said:


> If they are reproducible then you are should be OK as too the vertical collet alignment in the static mode.


 
I believe it is the R8 bevel that determines the alignment of the insert. For all practical purposes it is a wedge. If the two components mate properly, there can be no tilting. That is why from the beginning I didn't think the upper end of the spindle had any impact on performance.


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## mikey (Oct 15, 2019)

Bill Kirkley said:


> Mikey,  I am trying to determine if what I did had any affect on the precision of the spindle. The results do make me feel better. It indicates enlarging the upper end of the spindle has no affect on the stability of a tool in an R8 collet.
> 
> So, I am relieved that boring out the spindle will have no adverse affect on its function.



Bill, I understand the intent of your tests and I'm glad your tests give you confidence. In the end, it is your machine and as long as it performs to your satisfaction then that's what counts.


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## jknc (Nov 15, 2021)

Grandpop said:


> I am at least the 2nd owner on an Enco 8 x 28 knee mill. I came with 3 R8 collets that all went in and out easily.
> 
> One of the first things I bought was a set of R8 end mill holders. Imagine my surprise when none of them fit up inside the spindle! After a lot of investigation it appeared that the holders did meet the Bridgeport specs for the end diameter, and the spindle bore was .0005 too small. The PO had ground the end of his collets down to fit!
> 
> ...


I know this is an old thread at this point - but this method worked amazingly well for me on my PM727.  After bluing I felt like my spindle was concentric.  I checked the collets for size and they were 0.949 - well within spec.  Oddly over the past year of use the spindle was getting tighter.  I used a dowel and some emory cloth and it cleaned it up perfectly.  The collets slip right in now (it had gotten where I needed to use a soft blow hammer to get them in). 

Instead of using a drill I just ran the mill about 200rpm and moved the dowel by hand up and down in the spindle bore.


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## Winegrower (Nov 15, 2021)

Yep, an old thread, but kind of interesting.   If my Asian brand collets didn't fit, boring out the inside of my spindle would be one of the last things I'd think of.      If ever.


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## tq60 (Nov 15, 2021)

Have not read all but some general comments.

OP stated 44 pounds applied force and interstate collets. 

Is interstate a brand or type?

If it is labeled as R8 and does not fit then either collet is bad or mill is bad, easy.

Get a known good brand, does not need to be bridgeport. Harding or many others. 

We have assorted Chinese and American from the used parts bin and new and all fit the bridgeport fine.

If the good one fits then mill good collet bad, ifnofitthen warranty.

Never modify the machine to fit the tooling.

44 pounds side loading...the servo power feed is rated in fairly high torque combined with the gear ratio of the lead screw.

Side load is much higher than 44 pounds.

Combine the actual cutter interface load it can be more.

Place a 1/2 inch dull end mill in your fixture and see how much weight it takes to break it, likely more than 44 pounds.

Sent from my SM-G781V using Tapatalk
Just noticed very old thread...oops...

Still, never modify the machine to fit the tooling, the tooling is throw away so modify that or toss it.

If new send back...


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## Bill Kirkley (Nov 16, 2021)

jknc said:


> I know this is an old thread at this point - but this method worked amazingly well for me on my PM727.  After bluing I felt like my spindle was concentric.  I checked the collets for size and they were 0.949 - well within spec.  Oddly over the past year of use the spindle was getting tighter.  I used a dowel and some emory cloth and it cleaned it up perfectly.  The collets slip right in now (it had gotten where I needed to use a soft blow hammer to get them in).
> 
> Instead of using a drill I just ran the mill about 200rpm and moved the dowel by hand up and down in the spindle bore.


Your fix was simpler than mine!


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## Bill Kirkley (Nov 16, 2021)

tq60 said:


> Have not read all but some general comments.
> 
> OP stated 44 pounds applied force and interstate collets.
> 
> ...


Never Say Never!

PM wanted me to take the mill apart and send them the spindle. That was something I did not feel comfortable doing.

As for sending it back, that would entail rehiring a rigger to remove the machine, then paying to have it shipped. 

Modifying the machine was the simplest solution. It not only worked, it was cheap.

No doubt most think this was a radicle solution, but for me it was an easy fix, it solved the problem and it was fun!


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