What Measurements Are Important

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RONALD
Posts: 754
Joined: Sun Oct 26, 2003 7:27 am

What Measurements Are Important

Post by RONALD »

In the General Section that discussion about TIR is only one of the many measurements you can make on a lathe.

Here are the sheets that I got with my new Harrison VS330TR in 1994.

Harold, or anybody else can set up all those tests shown and be assured they have made all the measurements that can be done for a manual lathe.

Because Harrison is in the UK, all measurements are in Millimeters, I converted a few into Inches.

From what I was told only their VS TR series warranted such measurements.
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Mr Ron
Posts: 2126
Joined: Tue Dec 22, 2009 12:36 pm
Location: Vancleave, Mississippi

Re: What Measurements Are Important

Post by Mr Ron »

All measurements are important, but if a machine has been manufactured and certified to the standards specified in the test sheets, then it would be easy to replicate the tests to check if the measurements have strayed from the original tests. If they have strayed, what does that tell you? It is not easy to correct as it can mean re-machining and grinding. A machine starts to wear once put into service, but good maintenance will extend the life for a long time. When parts do wear down to the point where they deviate from the original test results, you usually make allowances for wear rather than to try to restore to original measurements. In short, a worn machine can still produce precision results by factoring in allowances. It just takes a bit more time.
Mr.Ron from South Mississippi
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: What Measurements Are Important

Post by pete »

A great set of charts showing the proper tests Ron.

Dr. Georg Schlesinger pretty much wrote the book on machine tool alignment and testing. There's a couple of websites with copies of his work online if you run a search using his name and possibly adding Testing Machine Tools they should come up as downloadable PDF's. The actual hard copy books seem to be fairly rare. But reading and understanding what he wrote and why each test is run and exactly what the results are showing probably should be on anyones reading list that's interested in obtaining any sort of accuracy. Lathe bed leveling or getting the bed into a neutral untwisted position is one of the most misunderstood procedures on almost any machinist forum on the net. And it's only one step in a fairly lengthly process to properly test and set up a new or used machine. It's very likely Harrison's tests were taken directly from Schlesingers work. My Chinese lathes test certificate certainly was.

While they are about checking and aligning a Fadal CNC bedmill, At-man Unlimited series of videos about doing so on Youtube are extremely informative and most of the checks could be directly applied to even manual Bridgeport type mills. He points out that tramming the spindle to the table is pretty much the very last step verses what most do as the only step while checking there mills. It's a lot more complex process than I'd thought and I learned a great deal while watching them. Once the checks and any adjustments if possible are made then normal spindle tramming is about all that's needed for future checks for a very long time. I'd go as far as saying that it's probable that 90% or more posts about lathe or mill alignment on most forums are either incorrect or far from complete.
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