Re: [PSUBS-MAILIST] Lathe Problems

["Jim Kocourek" <kocpnt@tds.net>]

Hi James,

While it is difficult to answer your question without knowing more, I think 
I might have some ideas.

It sounds and looks like chatter. The best machining happens when the work 
and Tool is VERY rigid. This means that the work extends very little from 
the chuck and the tool extends just a small amount from the tool post.

The possibility of chatter is also increased with high loads, as in heavy 
cuts, high feeds and dull or poorly positioned tool bits.

Try machining a piece with a very sharp tool that is somewhat pointed (a 
small area of contact between the tool and workpiece) The tool should be 
positioned just below the centerline for OD machining and the rpm should 
provide 250 - 350 feet per miniute depending on the type of steel. I have 
used many very old lathes in my time and never had problems, but it is 
possible that some gibs need to be adjusted up also.

Best Regards,

Jim K.


gs,.tfpmbe feedsos
Chatter is also increasc made heis VERY.
----- Original Message ----- 
From: <james@guernseysubmarine.com>
To: <personal_submersibles@psubs.org>
Sent: Tuesday, March 25, 2008 5:24 AM
Subject: [PSUBS-MAILIST] Lathe Problems


Hello All.

I have yet another problem someone could maybe help me with.
I really need to get my Lathe working properly.  You can see it here.

http://www.guernseysubmarine.com/index_files/Page10613.htm

Its an old one but apparently should be ok.  It has all the features i need 
and to by a new one that does the same things would be about $5000.
So ive really got to get it working.  I can get all the spares for it from 
the original factory.

Here is the problem.

Shoddy finish and dreadfull bad cutting.
Have a look at this picture and you can see what i mean.   My camera didnt 
like zooming in that close so its the best pic i could get.

http://guernseysubmarine.wordpress.com/

If i make a VERY shallow cut and go VERY slowly, it cuts ok ish, but still 
leaves a rough finish.  (like a very fine screw thread with burred edges).

If i make a deeper cut or slightly faster, it cuts a bit and then makes a 
hideous squeaking noise and produces the shown poor cut.

This is what ive done so far.

Eliminated all traces of splidle lift and end float on the main spindle.

Tightened up cross slide and sadle play.

Securly bolted machine to the floor and shimmed up the bed to flat.

Ive tried various different cutting tools of all shapes and sizes including 
brand new ones.

Tried different 4 jaw independant chuck.

Tried different speeds.

Speed is 640 RPM, tool brand new, centred and job material is low carbon 
steel.

Im almost sure the main spindle and chuck assembly is ok.  There is no play 
at all and it seems very good.

I believe the problem must be on the saddle/cross slide/tool post somewhere. 
I cant detect any vibration/movement, but it must be there somewhere.  There 
does seem to be backlash on the cross slide hand wheel, but then there 
always is.

I know these machines have to be reground sometimes and i suspect that may 
be needed.  There must have been a reason the college i got it from were 
getting rid of it....

I've done loads of lathe work before and im pretty sure its not my 
technique.  I've never had this problem before.

Am i just asking to much of a small machine?  Maybe its just "general 
vibration" over the whole machine.  It is 50 years old.

I could try and get a part exchange for a reconditioned one. 
http://www.myford.com/html/186801.pdf

Any ideas anyone before i go and turf it over the cliffs...?

Thanks
James







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