Levelling and Alignment - Is this run out due to bed wear?

Excuse me but your test is giving you false readings. Aluminum is the best material for this because if you use steel and a carbide tool bit if you drag the tool backwards it may chip and a HSS bit will dull in steel. . If you use steel, use leaded cold roll. That bar is 2 times longer then it needs to be. The push away on that will be so severe. Cut it in 2 (shorter) and do it again. Also cut a lower land near the chuck, so when you take a cut and you are near the chuck the tool end in a low area. Take a .005" cut on the 2 lands and when you are off the right hand land, shut off the feed and crank it to the next land and cut it making sure not to touch the cross feed. Once you enter the lower under cut land nearest the chuck, you shut off the feed, shut off the spindle, DO NOT touch the cross feed crank. stop and then crank the saddle back and you will see the tool scratch the 2 lands and after it is off the right side, turn on the spindle and again DON'T touch the cross feed dial and turn on the feed and cut it again and take a clean up pass. This will eliminate any push away do to dull tool. I sometimes do it a 3 rd time. I have been using this technique for decades and it works. Please follow the directions I am giving and not try to reinvent the wheel. I am going to try to attach some info and test sheets. Note the machine the bar is a 16 x 36 Heavy Duty lathe. Go to page 5 of this manual. It is for a bigger machine but the principal is the same. http://www.vintagemachinery.org/pubs/2261/16506.pdf
 

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Richard King 2 said:
Excuse me but your test is giving you false readings. Aluminum is the best material for this because if you use steel and a carbide tool bit if you drag the tool backwards it may chip and a HSS bit will dull in steel. . If you use steel, use leaded cold roll. That bar is 2 times longer then it needs to be. The push away on that will be so severe. Cut it in 2 (shorter) and do it again. Also cut a lower land near the chuck, so when you take a cut and you are near the chuck the tool end in a low area. Take a .005" cut on the 2 lands and when you are off the right hand land, shut off the feed and crank it to the next land and cut it making sure not to touch the cross feed. Once you enter the lower under cut land nearest the chuck, you shut off the feed, shut off the spindle, DO NOT touch the cross feed crank. stop and then crank the saddle back and you will see the tool scratch the 2 lands and after it is off the right side, turn on the spindle and again DON'T touch the cross feed dial and turn on the feed and cut it again and take a clean up pass. This will eliminate any push away do to dull tool. I sometimes do it a 3 rd time. I have been using this technique for decades and it works. Please follow the directions I am giving and not try to reinvent the wheel. I am going to try to attach some info and test sheets. Note the machine the bar is a 16 x 36 Heavy Duty lathe. Go to page 5 of this manual. It is for a bigger machine but the principal is the same. http://www.vintagemachinery.org/pubs/2261/16506.pdf
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Richard, thank you for such a detail response and points noted - I don't have any suitable aluminium bar stock, but have just ordered a couple of 1.5" x 8" lengths and will redo this following your instructions on arrival. I have to say the Warner and Swasey service manual is a thing of beauty, both in glorious art deco style and the clarity of the prose - now if only the Chinese could learn to emulate this ;)

I have to say I've managed to get a much nicer result this afternoon working on a 8 x 1" steel bar, no idea of grade but after cleaning up the rust and peeling chrome, I turned the insert to a fresh edge and turned the suds on. It machine really nicely and I surfaced the entire length of the bar in a single cut. It has helped a great deal to have a slight tension on the carriage lock nut, not enough to feel resistance when manually racking the carriage, but it certainly takes the slop out of the carriage.

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The taper is 0.1mm over 150mm or around 4/1000" over 6"

 
My aluminium stock arrived this morning and have faced and surfaced this twice. I did single surface feeds along the full length under power feed as I wanted to check if there was any variation along the length. The result was absolutely bang on at least to .01mm (.0004") over the full length 6.5", with my verniers and micrometer - the finish looks pretty good, though this wasn't a new insert it looked pretty good and gave a better finish than my home ground HSS (which definitely needs sharpening)! The new HBM 125mm chuck is a huge improvement over the original Pratt Burnerd (with worn abused jaws) - certainly not the same quality and doubtless won't last 50 years, but it is accurate and true for the time being.

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Richard King. Just as an aside I spent most of my working life as a Marine Engineer on Cargo ships not navy. We often had to machine parts on board. Some of the ships I served on had very well equipped workshops, but machining when underway was always a problem.

Contending with vibrations particularly from main engines, large low speed diesel engines, typically around 80 RPM. plus harmonics from propellers and other machinery, but always managed to get the job done. The rolling and pitching of the ship didn't help.

I never had to relevel a lathe on a ship we just used them as is, and compromised when we had to. a good file and emery tape was always our friend.
 
I have also talked to USA Navy guys who said they usually never ran machines in heavy seas... I also always say you can tell how good a machinist is running on crap machines. Or rocking and rolling machines :)
 
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