At a complete loss for ideas

+1 for Bi11Hudson comment. I use my HSS shear tool regularly to achieve fantastic finishes. Remember to take VERY light cuts .001-.002 with a slow feed rate.
 
Scott-ak said:
... Anything less than about 5 thou depth of cut results in a surface with grooves and such with 2 thou differences over the length. ... This pic is of my 4th attempt to cut a 3/4" diameter for an arbor.

...

The pic is 2" round bar. The left side was cut with the same carbide tool as the right. Same DOC & feed rate.
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That looks like a short piece. Are you saying you were getting a taper of .002 over that short distance? Was that also resolved with the HSS tool?
 
I generally get better finish with HSS with a large radius

That could be hot rolled steel also
 
Smaller radius for sure BUT...hot rolled anything, not to mention 1018 and I challenge anyone to get a mirror finish!
 
Also when turning on the PM1440GT run the compound parallel or perpendicular to the travel. If you have the compound set near 30 deg for threading, one of the t-nuts that hold the compound to the cross slide is in the access hole slot for the t-nut which affects rigidity. Generally the compound is the weak link for rigidity on this lathe. I eventually removed the compound on mine and replaced it with a solid tool post riser. I rarely use the compound except for short tapers I cannot do with a form tool. Carbide insert cutters for steel need more rigidity than properly ground HSS. I can get great finishes on 1018 and A36 with inserts and the solid tool post riser but they need to be run deep, hard and fast.

This post shows the solid tool post riser and the finish improvement.
 
I wouldn't have thought you'd have rigidity problems with something as big as the PM1440.
 
The compound really is the weak link in the rigidity - even if you position it so the t-nuts are not straddling the mounting holes. Like Jay, I implemented a solid tool post and wow - what a difference in rigidity. It really helps with parting and finishing on 1018. This post shows the implementation for the BXA solid tool post on the 1340. It's been over a year since I had the compound on the machine. Thanks Jay for the encouragement to go this direction. It was actually a very fun build.
 
Pcmaker said:
I wouldn't have thought you'd have rigidity problems with something as big as the PM1440.
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It's not limited to the PM1440GT but more a function of the style/design of cross slide and compound on a lot of the import machines. At the end of the day it is still a hobby class lathe, though quite capable for it's size, there are areas that can be improved to squeeze out more performance.
 
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