How much way wear is too much?

samthedog

samthedog

Token Aussie
Registered
Hello folks,

I just went over my lathe's ways to measure the wear. It registered at .01 of a mm or 0.00039 of an inch near the chuck. I originally replaced a fairly worn Maximat since it had a badly worn bed. This got me thinking... How much bed wear do you guys think is acceptable and at what point would you have the ways re-ground or scraped? This is for the hobby arena, not aerospace production. I know there is no hard and fast rule but I am interested in what others think on this topic.

Paul.
 
I am still working on getting the electrical fixed on the lathe so for a turned piece I couldn't say. The spindle has zero measurable runout with my indictor which measures in.01mm incriments. The length of the bed has no change until the last 2 inches directly under the chuck. All tolerances for the cross slide and compound slide are very tight.

To me this .01mm is acceptable, especially for a 48 year old lathe. What about for others here? I mean, for me the smoothness of the finish will have more effect than the .01 difference in the bed. I am just curious how others see this, especially since there are so many people buying second hand lathes that have seen use.

Paul.
 
You don't say how you tested the ways, but he ultimate test is by taking some test cuts. There are a couple of ways and the simplest is to turn a 1" x 8" piece of aluminum , insert 3" into the chuck, center your tool as close as possible, be sure it is sharp and has a rounded tip so you get a smooth cut. Take a .020" deep cut t clean up completely and the length say 4 1/2" long and at the chuck end cut a deeper groove, say 1/4" wide and .030" deep.

Then take another cut .020 deep. When the tool goes into the relief at the chuck end turn off the feed and spindle, DO NOT TOUCH THE CROSS-FEED HANDLE, DO NOT MOVE THE CROSS-FEED OUT. Then crank the saddle back toward the tail stock and it will leave a small scratch. Then turn on the spindle and take another "free" pass. You may have got a little push away and by not moving the cross-slide or compound and aking a free pass this will eliminate the push away. Mic the part. I will write more tonight, I have to get to work. But if it is tapered a little you can twis he bed a litlle to compensate for wear. Bu if you are getting .0003" that's pretty good as the bed is only off .00015. I am assuming you level and aligned the bed too? The rule of thumb is a conventional lathe accuracy is .0002" in 12" accuracy and a jig bore or super precision machine is .00005 / 12". The other test is a 2 collar test. Google that or I cn write about that tonight. It's 7:00 AM now and I have to scoot.
 
Wear can be corrected by a little filing while the part is still in the lathe. The trouble comes when you are trying to bore a hole like for a steam engine cylinder. The bored hole may not be accurate enough to work well. You need to determine what kind of work you'll be doing,if a lot of boring,it could be a problem. Also,does the lathe face flat? Are you going to be doing much facing where you need an accurately flat facing job? The cross slide may be worn also,if the bed is worn.
 
Hello Moparfever. I won't worry with my "new" Colchester. My Emco was about 6 times worse. The ways were visibly worn and for the price of regrinding, it was cheaper to just pass it on and get the Chipmaster I have now. I was just curiouswhat others thought because to me even though I don't need the accuracy, my time is so precious with a young family that when I get the chance to work on something, it's usually a very small window. This is one major reason why I need the lathe to make my life as easy as possible.

I know most of us are just hobbyists but it's interesting what people's perspective is on needed accuracy and tolerances of their machines.

Paul.
 
Paul, I'd honestly be surprised if many of the current imported machinery on the market is as good as 0.01mm. As already said, the real proof is in the cut. But if the bed is not twisted, I'd think you will be able to do accurate work on your lathe.
 
Machines twist. I am a professional machine rebuilder and know this for a fact!

I have a friend with 1020 Rivett lathe that is also a solid lathe and his bed had a twist. He had to pull it straight for months to get it to cut straight. The machine had been sitting in a twist for 20 years because it was not leveled properly and one tail-stock floor support pads was not touching.

Your statement about not twisting reminds me of a situation I had at a Technical College up here in MN that happened to me 20 or so years ago. I was in the machine shop classroom working on a hydraulic problem on a Heald grinder and the assistant instructor Carl walked up to me with a couple of students and said " You will never believe this, we took some test cuts on the new Leblond lathe and the head is crooket" .

We walked over to the lathe department and there was a brand new 16 x 36 machine. I looked down on the floor and the machine was not sitting on it's leveling pads and one leveling screw was screwed into the concrete floor. I said to "Carl the machine needs to be leveled and aligned" By then the whole class was there listening and he puffed up his chest and said " The head is crooked and I have been shimming the head of machines for years" (The more he talked the deeper he was digging his grave). I was trying not to embarrass him in front of the class and said" Let's find the leveling pads and level it and see".

He then said " There is no way the cast iron bed will bend" By then I was getting nauseated with him and said " I will bet you $1000.00 I can get the machine to cut straight by leveling / aligning it".

He said he never bet money....so I said " OK a no money bet then" he said "go for it" and laughed. The big shot stood there while my helper and I lifted the machine, leveled and aligned it. We left his test bar in and tool and when we were done I asked him to take another cut. He did and when he mic' d it he turned around red faced. Had a stupid look on his face and said "what did you do"? I said "I read the instruction manual and followed the factory leveling instructions". The next time I went down to that school Carl was gone. I often wondered how he could have qualified to teach. I wonder how many lathes are out their with the head shimmed and screwed up?
 
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The way I measured the wear was by setting up a dial indicator stand on the acrriage. I set the tip of the indicator on the way and ran the carriage towards the headstock. I did this on both faces of the way to check if there was any major variation. The reason I did it this way is that I figured I would pick up a change on the indicator since the needle will be over a surface before the carriage would be resting on it. This seemed to be the case.

The wear on my lathe was the 2 inches under the chuck, where you might expect the most wear to occur. rcflier is indeed correct about the Chipmaster bed. There is no way on God's green earth to twist this bed.

Paul.
 
samthedog said:
The way I measured the wear was by setting up a dial indicator stand on the acrriage. I set the tip of the indicator on the way and ran the carriage towards the headstock. I did this on both faces of the way to check if there was any major variation. The reason I did it this way is that I figured I would pick up a change on the indicator since the needle will be over a surface before the carriage would be resting on it. This seemed to be the case.

The wear on my lathe was the 2 inches under the chuck, where you might expect the most wear to occur. rcflier is indeed correct about the Chipmaster bed. There is no way on God's green earth to twist this bed.

Paul.
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________________________

That is your opinion, I have mine.
 
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