measuring mill wear

Discussion on all milling machines vertical & horizontal, including but not limited to Bridgeports, Hardinge, South Bend, Clausing, Van Norman, including imports.

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TRX
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measuring mill wear

Post by TRX » Wed May 10, 2017 8:59 pm

I have an elderly vertical mill that needs some work. Before I commit to that I need to measure the amount of table and knee wear. The spindle is the part that obviously needs work, so I'm mostly interested in the table bits.

It *seems* simple. Put an indicator in the spindle, run the table across the X and Y axes to measure wear. Clamp a square to the table and run the knee up and down to see if the knee ways are worn.

Is this a valid way to check for table wear?

"Better to ask and be thought a fool than forge ahead and remove all doubt..."

Harold_V
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Re: measuring mill wear

Post by Harold_V » Wed May 10, 2017 9:04 pm

Wear of ways is a little more involved than the simple approach you've mentioned. As ways wear, they become loose in the center, so you can't tighten the gibs enough to eliminate clearance that is sure to plague you in use of the machine. One of them that is really irritating is the cross slide, which tends to shift side to side as you reverse travel. That causes cuts to be out of square.

What you expect from the machine is important in any decision you make. I tend to demand perfection, and am not happy with machines that have experienced rust or considerable wear, as each of them eliminates the very thing that makes a machine tool expensive---precision.

It does little good to do superficial repairs on machine tools. You can make them look better, but they may not perform to your expectations.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

TRX
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Re: measuring mill wear

Post by TRX » Wed May 10, 2017 10:51 pm

So, what kind of setup would you use to measure that?

spro
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Re: measuring mill wear

Post by spro » Thu May 11, 2017 12:19 am

What do you think Harold? A long sweep from tightened spindle of quill would measure but he already said the spindle bearings are shot.

spro
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Re: measuring mill wear

Post by spro » Thu May 11, 2017 12:25 am

Oh heck,

Harold_V
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Re: measuring mill wear

Post by Harold_V » Thu May 11, 2017 3:16 am

Worn machines tend to be in general poor condition, which is likely no surprise to you. All I know is that when they aren't fit, they are not reliable, and can be very frustrating to use when you're trying to work to specific dimensions, especially with tight tolerances. That's where my experience lies---I am not a machine rebuilder, nor am I privy to the methods of such people. However, I am in the middle of reading Edward F. Connelly's 1955 book, Machine Tool Reconditioning, as I own a B&S surface grinder which requires attention. His book details how one goes about assessing a machine tool, which includes the visual inspection of scraped ways. It would be my recommendation that you pursue the proper methods, so you can make an informed decision in how you should move forward on any machine tool. To do otherwise is not a great choice, as you can put lipstick on a pig, but in the end you still have a pig, but with lipstick.

Having experience the use of a Gorton 8-D mill, both before and after a full mechanical restoration, I can attest that a junk machine can be fully restored to usefulness, possibly even better than original condition. The problem is it's VERY labor intensive, and would require the replacement of screws and nuts, as well as realignment of their relationship to the now changed slides. It is not for the faint of heart, and requires a considerable investment of time and money to acquire the proper tools and skills required.

Harold
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TRX
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Re: measuring mill wear

Post by TRX » Thu May 11, 2017 8:34 am

What I want to determine is *how* worn the ways are.

If it's .001" across 12", that's good enough for what I do. If it's .010" across 12", I have better things to do with my time.

For that matter, if I bought a brand new machine, how do I verify its accuracy? It's the same thing.

John Hasler
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Re: measuring mill wear

Post by John Hasler » Thu May 11, 2017 9:05 am

Lock the Y. Run the X to one end and tighten the gibs until the table will just move. Move it to center and see if you can wiggle it, and see how much the gibs have to be tightened to lock it. Do the same from the other end. Repeat with the Y after locking the X.

John Evans
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Re: measuring mill wear

Post by John Evans » Thu May 11, 2017 10:50 am

Yep,John H has the method I use. I call that wear Bridgeportitis ! Usually caused by mounting the vise in the center of the table and doing all work in the center third or so of table travel.
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pete
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Re: measuring mill wear

Post by pete » Thu May 11, 2017 11:04 am

Testing for proper machine tool alignments and wear is a lot more complex than average hobbyist seems to think. Luckily there's a least one free online reference source I know of that should really help. Google Dr. Georg Schlesinger, then you should see a link to Totally Screwed Machine Shop .com Read that through a few times until it's clear about exactly why each test is being performed. The standard machinists square is always going to have some deviation in it. Mitutoyo and Starrett list the allowable out of square condition for there brand new squares that still fall within the allowable limits. Ideally you need two known to be good reference surfaces before you can start to test what you have. A surface plate is your basic building block and at least a shop made or commercial cylindrical square that have been tested and any deviations noted and at what point they are. Don Baily at Suburban Tools shows a real good video on Youtube about testing cylindrical squares. And The Tool & Die guy also on YT shows using a slightly modified surface marking gauge with a 10ths reading test indicator that gets zeroed to the cylindrical square first so true 90 degree angles can be checked. That would be used to check your squares first.

Since nothing is ever perfect if your measuring equipment has enough accuracy. Then even brand new top quality Swiss, German ect machine tools will still have very slight but still measurable misalignments. Harolds mention of that MTR book is in my opion well worth the almost $100 it costs. Very dry and boring to read, but at the minimum it would change anyones opinions about how clean and well lubricated any machine tool needs to be to expect a good long life from it. The books mostly about the rebuilding of machine tools and how critical it is to maintain a machines alignments in 3 dimensions as material is removed or in the case of something like moglice added to bring components like lathe carriages back to there proper elevation after a lathe bed has been reground. The Practical Machinist sub forum about Machine Tool Rebuilding has a great deal of information as well. YT has some great rebuilding videos done by people who do understand what there doing. There's also a great many that aren't so good. Hand lapping parts togeather especially for the cheaper small Chinese machine tools is advocated by far to many that just don't understand there's no control over where and how much metal is being removed. Yes it helps make the machine feel smoother to use, and the slides movements might be a little more predictable. But it's almost 100% for sure you'd make the machine more inaccurate. Hand or power scraping parts to known flat reference surfaces while maintaining there alignments and using a great deal of skill and experience is how it's done. If that lapping worked at all then professional machine tool rebuilders would certainly use it and they don't.

Running a proper series of tests isn't a waste of time. If you don't know where and how much the machine is out then there's no hope of even trying to correct for them while using the machine. Minor adjustments can help a lot sometimes. Regrinding ways without further hand scraping can be more than accurate for what most of us really need. Even Bridgeports are have only ground ways with oil flaking added that many confuse with scraped ways.

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GlennW
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Re: measuring mill wear

Post by GlennW » Thu May 11, 2017 11:42 am

pete wrote: And The Tool & Die guy also on YT shows using a slightly modified surface marking gauge with a 10ths reading test indicator that gets zeroed to the cylindrical square first so true 90 degree angles can be checked. That would be used to check your squares first.
This is a pretty simple method of checking a square without needing a reference such as a cylindrical square as long as the blade is parallel:

First mic the blade width to verify that the blade edges are parallel, and if so...

Then set up a few 1-2-3 blocks and a DTI on a magnetic base.

Then check one side of the square by bringing the blade up against the 1-2-3 block and zero the DTI reading.
Image

Flip the square over and check the other side.

Image

The error will be 1/2 of the indicator reading, so this square is off by just over a tenth.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

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SteveHGraham
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Re: measuring mill wear

Post by SteveHGraham » Thu May 11, 2017 12:55 pm

Regarding squares, I wonder what people think of heavy angle plates. I got a Japanese one cheap from Ebay. It's what I use to tram the head of my mill. I would think it would be pretty hard to knock one out of square!

https://www.mscdirect.com/product/details/70149042

I know nearly nothing about metrology, but I've gotten good results with this, and it saves me a huge amount of time. You can even run a fly-cutter after using it. I can always get out the Indicol if I need to be more rigorous. I can't remember the last time I did that.
Every hard-fried egg began life sunny-side up.

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