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Cross slide lifts when parting off

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john swift 103/05/2011 12:59:49
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318 forum posts
183 photos

Hi Chris ,
 
thats why some people treat these lathes as an assembled kit of parts to be
 
taken apart ,cleaned and then fitted together
 
not some thing everbody will want to do when they first get a lathe !
 
 
John
 
chris stephens03/05/2011 13:27:55
1048 forum posts
1 photos
Hi John,
Indeed it is, but I question (slightly tongue in cheek) whether this counts as "merchantable quality". The trouble is retailers can't say "buy our lathes and spent many happy hours making it work properly" but then if it was in "Full" working order the price would be commensurate with that quality.
How do the retailers get across the fact that a customer is buying a semi-finished machine, without loosing a potential sale? To my mind there is nothing wrong with stating the truth but then I can fix the problems, whereas a newbie buying his first machine might not be capable of doing so. I suppose they could give a fee copy of the WPS book on the "mini-lathe" with each one, but it smacks a bit of "rotting fish for sale"!
chriStephens
Martin Brundell03/05/2011 14:06:31
29 forum posts
Yes this is the exact machine I have




Edited By Martin Brundell on 03/05/2011 14:08:19

Martin W03/05/2011 15:36:07
863 forum posts
29 photos
Interesting comments re 'merchantable quality'. I have bought a lathe from Chester, smaller cousin to this, and a mill from Warco and both items went from box to bench to working with only minor adjustments; namely gib adjustments to suit me and tramming the mill.
 
To date with the subject lathe it has not been, as far as I can see, categorically proven by measurement that the top slide is moving and if so by how much. Surely the thing to do is set up a dial indicator and measure any deflection of the top/cross slide or saddle relative to the bed and then if proven contact the supplier.
 
It could be that the, depending on how far from the chuck the cut is being made, it is the metal that is deflecting. Another thing to try is to support the work, already suggested, but using the tail stock and see if that improves the situation.
 
Just a few thoughts
 
Martin
mick03/05/2011 16:18:03
398 forum posts
44 photos
Have you tried increasing the top rake angle to assist the swarf to curl, as it sounds like a tool problem. speed is far too slow for a 20mm bar, try at least doubling it and hand feed in, this gives you time to react to any change in the tool cutting behaviour. I know it sounds wrong but Increasing feed and speed will quite often cure machining problems. Minium tool overhang, only enough unsupported blade to cut through, the blade must be completely parrallel to the chuck, part as close to the chuck as possible, if you have a live back centre use a pressure pad to help absorb any vibration, plenty of coolent delivered via a hand held oil can. If the tool still dips I think I might resort to a hacksaw
Donald Wittmann03/05/2011 17:27:13
40 forum posts
Martin B.
If you have the scope of adjustment as regards tool height you could try inverting the parting tool and running the lathe in reverse [ok with bolted on or Camlok chucks] also for en1a steel you should try using the inserts that have a positive cutting geometry they are usually uncoated and very sharp with very low cutting forces. The type specified for non ferrous metals, a good grade will last you long enough on en1
also when parting off the worst thing you can do is approach the task with trepidation parting off calls for a fairly heavy feed and constant cutting. NEVER use a tailstock centre when parting off or the problems you are having just now will be the least of them.
Also for Ø20mm you should up your speed to about 250-300 rpm and flood coolant.
Donald.
Martin Brundell03/05/2011 18:15:25
29 forum posts
UPDATE:
 
Thanks to all for your suggestions and help - I've cracked it!!! (well you cracked it)
 
Took the crossslide off cleaned up and re-seated, upped the speed to 250rpm - this alone helped, it worked 50% better after that but still flexing slightly.
 
I then reduced the tool overhang and made sure the toolpost was more central. 75% better.
 
Then I inverted the parting tool, reversed the chuck rotation - 85% better
 
Then I dug out my carbide tipped parting tool (3mm tip) that I have never been able to use because it chattered like a bugger, inverted. PERFECT - went through it like butter!!!
 
Thanks again for all your help - I am a happy bunny again!
 
PS has anyone got a turning speed chart for EN1A - 303 free cutting stainless etc in RPM??? All I can find is metres or feet and I can't find out how to translate.
 
Again thanks, it really is much appreciated
 
JasonB03/05/2011 18:22:39
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This is a reasonable table in easy to work out RPM, use it as a basis as each machine will be a bit different depending on its power and rigidity.
 
 
One thing I didn't add was that I tend to use the lathe with the topslide about 3" in from the front of the cross slide, this keeps more of the slide engaged in the dovetail and saves exposing the screw when turning small diameters.
 
J

Edited By JasonB on 03/05/2011 18:23:29

Martin Brundell03/05/2011 18:28:53
29 forum posts
Brilliant Jason - thank you

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