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Spindle Taper Maintenance

LocherInc

Plastic
Joined
Aug 1, 2011
Location
Lancaster, OH
Hey everyone. We're trying to get a little more active with the online community and this forum. We get a lot of questions about tapers as far as how accurate they need to be, how to tell if a spindle can be ground in-place, issues that can stem from a worn taper, etc. So I did a small write up with some general information for everyone. Please feel free to reach out if anyone has any questions. Take care.

Why Spindle Taper Maintenance is Important

Spindle tapers are typically an overlooked PM item on a machine tool. If there hasn’t been a wreck or clamping issues, there isn’t always a lot of thought about it, but the spindle taper is a wearing surface. Typically, what you will see as the taper wears is a condition called “Bell-Mouthing,” where the front (Major Diameter) side of the taper slowly opens up, costing you tool rigidity. A lot of times this won’t show up in just simply checking taper or tool runout. What bell-mouthing causes is tool instability due to the major supporting area being worn away. You’ll see shorter tool life, tool holder wear, and eventually it can get to the point where runout is no longer satisfactory or you’re having issues making cuts with the same kind of tool pressure. You’ll typically start to see fretting on the tool holders or taper surface. Fretting is a gold/copper colored pattern caused by high frequency vibration of the tool holder in the taper pulling metals to the surface. It can also indicate drawbar issues.

Where people can get into trouble is trying to address taper issues using hand tools like die grinders or other setups that aren’t designed to hold the types of tolerances required for a spindle taper. This happens a lot after a wreck to try and get the machine back into production. It is not recommended to use any kind of abrasives to try and polish the taper down. It’s a common misconception, but a spindle taper has the same tight manufacturing tolerances as the bearing journals on your spindle shaft. Being off even .010/.012mm or .0004-.0005” is completely out of spec. It requires the use of master plug gages or qualified air gages to hold the angle correctly. Incorrect angle, poor surface finish, or high spots can lead to premature wear of the taper and if too much material is removed, the spindle could be scrapped and need to be pulled for rebuild or replacement.

A correctly reground taper should not need to be ground yearly, unless under extreme cutting conditions, but periodic inspections should be done. These inspections include inspecting taper angle, measuring taper runout, inspecting runout using a precision test bar at the spindle face and 250-300mm from the spindle nose, measuring clamping pressure, and measuring gage line dimensions.

How do you measure “grind stock” or if a spindle even can be ground? A good base line measurement to use is “gage line.” This can be measured using a tool holder. Depth mic from the front side (part side) of the flange on the tool holder down to the spindle face. The amount you can grind and move this dimension will vary by machine and the drawbar setup, but a good rule of thumb is that you can be about -.015” before you’ll start to run into clamping pressure problems. That ultimate dimension will be determined by your clamping pressure. All machines utilizing CAT holders are going to have a .750” gage line. BT toolholders have a varying gage line and I’ve attached a .pdf with those dimensions. Machines utilizing Big Plus or other dual contact tool holders will again have a different gage line that will appear to be far minus as they are designed for a simultaneous fit. When grinding for dual contact, the face will need to also be ground to insure proper tool clearance. The amount of material removed should then be documented to track material removal. There are occasional outliers to these rules. When a spindle is rebuilt, some vendors or even OEM’s will not always grind and chrome plate the taper back to a standard gage line but set the drawbar up to work wherever the taper cleaned up. This isn’t a responsible practice as it can create issues with tool changers unless the machine was designed with that gage line in mind for clearance.
 

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"Occupation: Shop Manager for Locher, Inc"
Does the Owner how badly your damaging the company's reputation ?
Hey Doug. We ran the post by Practical Machinist before putting it up and they agreed with the educational content of it and gave us the go ahead to put it up. It was simply meant as providing information because we get these questions a lot. If the response from the community is that this isn't in the spirit of the forum or there is something wrong/misleading we will gladly take it down. The Carnac response/picture I just thought was joshing. Thanks.
 
I'll fill you in.

You're welcome here and all, but we often get spammy postings. Whether the "spammer" is the owner of some company simply posting about what they do, or paid-for bots that someone thought it would be a good idea to "advertise" here, on this free forum.

If that doesn't describe you, great. We hope you chime in from time to time. I see people asking about spindle grinding all the time. People spin holders, have runout issues after a crash, broken pullstuds causing a ton of damage. You name it.

There are many people who work for companies, or even own them, who post here regularly. Some of them occasionally post their product, but usually in response to someone else having a need. People like fmari, from Maritool, or OrangeVise (owner of Orange Vise), post here regularly off the top of my head. And they often are posting advice or suggestions that have 0 to do with what they sell, but rather their experience with machines, programming, tooling, etc. I hope you would do the same. If you came in here and said "oh god xyz machine tool doesn't harden their spindles very deep, so you would only be able to get it ground once without getting it chromed", that's the kind of insight that's super valuable to hear, as an example.

Your company comes in as the 2nd result on google when I google spindle grinding. The suggestion that you may damage some reputation is valid, provided you dont stick your head in now and then and give advice if you have any.
 
I'll fill you in.

You're welcome here and all, but we often get spammy postings. Whether the "spammer" is the owner of some company simply posting about what they do, or paid-for bots that someone thought it would be a good idea to "advertise" here, on this free forum.

If that doesn't describe you, great. We hope you chime in from time to time. I see people asking about spindle grinding all the time. People spin holders, have runout issues after a crash, broken pullstuds causing a ton of damage. You name it.

There are many people who work for companies, or even own them, who post here regularly. Some of them occasionally post their product, but usually in response to someone else having a need. People like fmari, from Maritool, or OrangeVise (owner of Orange Vise), post here regularly off the top of my head. And they often are posting advice or suggestions that have 0 to do with what they sell, but rather their experience with machines, programming, tooling, etc. I hope you would do the same. If you came in here and said "oh god xyz machine tool doesn't harden their spindles very deep, so you would only be able to get it ground once without getting it chromed", that's the kind of insight that's super valuable to hear, as an example.

Your company comes in as the 2nd result on google when I google spindle grinding. The suggestion that you may damage some reputation is valid, provided you dont stick your head in now and then and give advice if you have any.
Thanks and I definitely appreciate your input. The intention was certainly not to spam which is why I took an extra step to run it past Practical Machinist before I posted anything. We had seen some other informational posts on things like ballscrews and other areas of the machine and thought it might be somewhat valuable to someone looking for this kind of information because we get those phone calls a lot of people who just want some questions answered.

If it turns out this post is taken more negatively than I intended, I can certainly take it down. Spindles are the area we have the most experience, so it seemed that would be the obvious place to start with providing as much helpful information as possible. I would like to plan on continuing to contribute where at all possible instead of dropping a post and ghosting off into the distance.
 
The Carnack comment was only partly in jest. We are far to used to hit and run spammers. I will say yours is far less egregious than most.

A low key introduction is probably the best way to announce yourself.

Ed.
 
The Carnack comment was only partly in jest. We are far to used to hit and run spammers. I will say yours is far less egregious than most.

A low key introduction is probably the best way to announce yourself.

Ed.
Completely understand. Call it Naive and not giving it enough thought on how it could easily come across. Hope to be around on here for a while and pick up a few things for my own knowledge. Have a good one.
 
Completely understand. Call it Naive and not giving it enough thought on how it could easily come across. Hope to be around on here for a while and pick up a few things for my own knowledge. Have a good one.
I will chime in on this one, it sounds perfectly fine, Ill be it a bit spammy at first but educational for those who dont know or are looking for this information.

So question is this, as for tool holders, is there a list that you guys have tested and been reliably within tolerance enough that if you bought one new to check taper wear that it would be accurate enough to be a good example.
or better yet, what is the best set up to test tool holders if there are any tricks of the trade out there?
 
I will chime in on this one, it sounds perfectly fine, Ill be it a bit spammy at first but educational for those who dont know or are looking for this information.

So question is this, as for tool holders, is there a list that you guys have tested and been reliably within tolerance enough that if you bought one new to check taper wear that it would be accurate enough to be a good example.
or better yet, what is the best set up to test tool holders if there are any tricks of the trade out there?
I apologize in advance for the book I just wrote.....

Most of your reliable mainstream holder brands (Collis, Parlec, Maritool, Command, etc) are all going to be certified as holding about the same tolerances. Industry standard, where it is advertised, is typically an "AT3" spec tolerance for angle which correlates to a few tenths per foot or about twice standard spindle taper tolerance. So on a brand new 50 taper toolholder, you can expect the major/minor diameter to be within a tenth or two. Most of the holders we've taken the time to inspect from those brands are all pretty close to that. If you wanted to get a rough idea if you have a taper problem, using a brand new toolholder with a very light coating of Dykem #107 hi-spot, clamping that into the spindle, and looking at the contact pattern will typically give you a good idea. It's also important to remember that angle tolerances do not correlate to advertised runout tolerances.

One thing we recommend is typically picking a brand and sticking with that one rather than running several different brands. Consistency in manufacturing is always best. The tool holders are designed to be softer than the spindle itself. That's the reason when you spin a tool, the galling you see in the spindle taper is material from the tool holder built up on the surface, not so much where it has eaten into the harder material of spindle taper. This also makes them more prone to wear quicker than the taper surface. There are specific "tool holder inspection gauges" you can use if you are really trying to be diligent about monitoring tool holder wear. It is essentially 2 dial indicators setup at the major and minor diameter ends of a tapered socket that comes with a master plug to zero the indicators. You can then place your holders in the tapered socket and see if you have wear. We've had motivated customers actually make their own as well. Some wanted a third indicator to inspect the middle of the tool holder for added peace of mind. Even improperly torqueing your retention knobs can create issues with the taper. Over tightening can open up the smaller end of the taper causing improper fit.

Now when you get into something like "Big Plus" and dual contact holders it can get even hairier. Dual contact tooling has been around for over 50 years back when Ingersoll was manufacturing simul-fit tools. The tolerance for Big Plus specs only allows you about .00005" of room. The tools also need to be cycled out more regularly as you will slowly develop an issue where the tools hit more on the face of the spindle than the taper which can create vibration. A lot of shops will run both CAT and Big Plus tooling depending on the operation. They may have 90% CAT holders and then a few Big Plus where they need the added support. That's never a good idea because the CAT tooling will typically accelerate taper wear and then when you load the Big Plus tool, you run into that issue of face pressure. That can happen in as quick as 1-2 years of operation. .0001" of taper wear equates to .00035" of gage line movement in the tool. In that .0001" of wear, you're already out of spec as far as standard tolerance goes. There was an inspection report written a few years ago that analyzed a bunch of the "Big Plus" advertised tool holders on the market and something like 40% of them were out of spec from brand new. I'll have to see if I can dig that up somewhere.
 
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very interesting, this is the kind of thing we need more of, even the technical side of things, most appreciate the extra information like this of things we never run into day in and day out but can be important to the every day operation. im sure most people buy a tool holder once and run it till the end or till someone crashes it and never really think of it as a consumable with a life like the tool that it is holding. Most never seem to notice or even check until they get into major vibration or run out issues id bet.

as for the spindle grinding, what as been the worst taper wear that you have seen yet still ran fine?
 
very interesting, this is the kind of thing we need more of, even the technical side of things, most appreciate the extra information like this of things we never run into day in and day out but can be important to the every day operation. im sure most people buy a tool holder once and run it till the end or till someone crashes it and never really think of it as a consumable with a life like the tool that it is holding. Most never seem to notice or even check until they get into major vibration or run out issues id bet.

as for the spindle grinding, what as been the worst taper wear that you have seen yet still ran fine?
"Ran fine" is definitely a relative term lol. Depending on what kind operation you're running, you can either get away with a lot or you might start having problems very quickly. We've seen tapers where they had a wreck, ground it out with a die grinder and they've only got maybe a 1/4" of contact somewhere in the taper, the gage line is -.035", and they've got 500lbs of clamp force on a 50 taper tool but were still able to get a few parts done. I would say the most common thing is maybe they're down to 40-50% contact, the front of the taper has opened up and they're just getting chatter on the parts. They can usually get by adjusting the speeds and feeds for a bit, but that taper will wear faster and you're risking hurting your holders as well. If you've got 75-85% contact and aren't having any issues, you're probably fine for a while. We've also had spindles for rebuild come in where the tools are welded into the spindle taper and we have to machine the toolholders out.

Nowadays, production is king and guys have to do whatever they can to try and squeak by to get parts out the door. I'll never knock someone for doing what they need to do. Most of the time they honestly just didn't know how crucial that part of the machine really was. Like any thing, there is a real world and an ideal spec. Guys aren't going to just start tossing holders if they're out .0005". One important thing is that when you're doing proper PM's and grinding before you get to that failure point, you actually will get more life out of the spindle because you don't need to remove as much material per grind to bring the taper back and the taper doesn't wear as fast. Whereas if you wait until you're down to to almost no contact, you have to grind a lot more out. You only want to remove what is absolutely necessary to preserve spindle life.
 
I really like this. It’s quite interesting. I’ve always wondered about spindle grinding too. We have a lot of issues with tool stickage in our Haas VF3. But none of the other 5 Haas mills. Always figured all of our machines need reground, other than one that’s had its spindle replaced in the last few years, none of them have been looked at in 8 years. At least.

Edit: and I bet the results would be better than Haas factory spec. I checked the same VF3 with a brand new spindle probe gauge from Maritool, .0007” TIR at a 4” GL. I figured welp, maybe now I can justify getting this fixed. Then I was appalled to see that .0007 in 4” is within spec (.001 at 6”).
 
I really like this. It’s quite interesting. I’ve always wondered about spindle grinding too. We have a lot of issues with tool stickage in our Haas VF3. But none of the other 5 Haas mills. Always figured all of our machines need reground, other than one that’s had its spindle replaced in the last few years, none of them have been looked at in 8 years. At least.

Edit: and I bet the results would be better than Haas factory spec. I checked the same VF3 with a brand new spindle probe gauge from Maritool, .0007” TIR at a 4” GL. I figured welp, maybe now I can justify getting this fixed. Then I was appalled to see that .0007 in 4” is within spec (.001 at 6”).
Grinding the assembled spindle on the machine is definitely going to be the most accurate you can get. You're finishing to the true center of rotation with the bearings as long as your setup is correct. Even holding the correct tolerances in manufacturing, by the time you stack a tenth here or there, you can end up with a few tenths runout. .0007" at 4" seems on the high end to me. Usually what I've seen as acceptable factory tolerances are .0008"-.001" on a 12" test bar which is usually more than acceptable for most situations. Grinding you will certainly get more accurate runout than that, .0000-.0002" on the test bar is fairly normal, but that's just because the operation is accounting for all those stacked tolerances. I would never recommend someone pay to grind a new spindle to get rid of .0006" of runout at 12" unless they truly needed that running accuracy.
 
Grinding the assembled spindle on the machine is definitely going to be the most accurate you can get.
There is another opinion on this matter :) The geometric accuracy of the cone (roundness and straightness of the generatrix of the cone) when grinding on a grinding machine will be an order of magnitude more accurate than when grinding assembled on a milling machine.
 
There is another opinion on this matter :) The geometric accuracy of the cone (roundness and straightness of the generatrix of the cone) when grinding on a grinding machine will be an order of magnitude more accurate than when grinding assembled on a milling machine.

Might be easier to get it set to the right angle on a grinding machine, but with patience and knowhow, I think you could get just as accurate.

We had a spindle ground on a horizontal some years ago. Contrary to what I've seen suggested by people when they ruin their spindle, they did NOT use the machine axis (x/z) to generate the taper. They had a fixture with a quill set to the taper angle, and the quill moved in and out as the spindle was rotating at a slow rpm.

I assume most or all traveling spindle grinders do this?
 
There is another opinion on this matter :) The geometric accuracy of the cone (roundness and straightness of the generatrix of the cone) when grinding on a grinding machine will be an order of magnitude more accurate than when grinding assembled on a milling machine.
Depending on what kind of setup you are using to grind the taper and the running accuracy/condition of the spindle this can definitely be true. However, we are talking about the final running accuracy of a complete spindle assembly not just the spindle shaft itself. If you are grinding a stationary rotating spindle with bearings that are in good condition, only the running accuracy of the bearings is your limiting factor. Grinding a complete assembly will always be more "accurate" than the sum of the assembled individual pieces. With the angle, you are at the mercy of your gaging whether in the field or in the shop repairing a spindle shaft.

Might be easier to get it set to the right angle on a grinding machine, but with patience and knowhow, I think you could get just as accurate.

We had a spindle ground on a horizontal some years ago. Contrary to what I've seen suggested by people when they ruin their spindle, they did NOT use the machine axis (x/z) to generate the taper. They had a fixture with a quill set to the taper angle, and the quill moved in and out as the spindle was rotating at a slow rpm.

I assume most or all traveling spindle grinders do this?
There are different methods people use for grinding tapers in place. In my opinion, if you are moving the machine while grinding, you are introducing several additional points of error that aren't necessary. Skew, squareness, etc.
 








 
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