lathe chatter

Talking of a few problems, how are things progressing at your Lacock/Lackham project?
wrote:


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
one word HACKSA
-- krame
----------------------------------------------------------------------- kramer's Profile: http://www.rcgroups.com/forums/member.php?action=getinfo&userid 25 View this thread: http://www.rcgroups.com/forums/showthread.php?threadid1773
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Four words UNCONTROLLED LINE OF CUT

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Airy R. Bean Wrote:

I use the hach saw on smaller parts ,I cut it off .25-.60" from where I want to be and face it off with a tool bit ,no chatter,no hastle.You have to let the weight of the saw feed the blade to take light cut and also have a slower rpm just to be safe
--
kramer


------------------------------------------------------------------------
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
That's all very well when you've got "slack".
Not possible when parting off near-disk-like objects which are well-nigh impossible to re-chuck (cue new thread?)

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
-- -- Dave Baker - Puma Race Engines (www.pumaracing.co.uk)

You must be pretty rough with a hacksaw if you need 1/4 to 1/2 an inch spare to clean up again. I can usually get to within 0.3mm if I'm careful with the saw :)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dave Baker Wrote:

025-.060 oops
--
kramer


------------------------------------------------------------------------
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Q-Cut insert parting tool (Greenwood).
Hold in a back toolpost if possible.
Run fast and feed fast and firm.
Don't, repeat, don't run the lathe backwards with tool held upside down. You will unscrew the chuck and disaster will surely follow!!!!
As an idea of speeds and feeds I would part off 1" dia brass bar on my Myford Super7 running at top speed (2200RPM) with a Q-Cut tool in the rear toolpost and feed in as fast as I can. Same with free cutting MS. I might drop the speed a bit if i was parting off silver steel or stainless.
snipped-for-privacy@tiscali.co.uk wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Practice on aluminium, about 2" diameter. HSS blade; about 30 deg rake, very little clearance; side rake; very sharp; tool just below centre; right way up and lathe running forward. When you can do that, nothing else is a problem!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dick Ganderton wrote:

i know what you are saying about chucks coming un-screwed, and must admit i have never thought of this as a problem, because normaly i use a chuck with D style clamping (pin and cam). I should have realised a lot of smaller lathes have a screw on chuck.
as a side note, if you have a secure chuck that will not unscrew, my method is very good at eliminating chatter while parting off, and is my prefered way of turning brass, save lots of little burns lol.
--
From the Keyboard of Tim Bird
Visit my updated website @ www.timbird.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks for all the tips. It is nice to know that I am not alone in finding parting-off a problem, although obviously you have all found your own various solutions. A Q-cut tool was mentioned several times. I have not heard of this. Many of the commercial parting-off tools are too big for a small lathe. Mine is a 3" from Axminster - probably Chinese. I did manage to get it to work after posting my query, but it still was not ideal and many of you suggested driving the tool hard against the work, which I haven't been doing. I think my main problem was that the ground angle at the end of the bit was not correct and the tool was simply rubbing against the work piece. I was also positioning the tool below the centre as recommended by one of my books. I have now placed it on the centre line. The regrinding and repositioning seems to work. I obviously need more practice to make sure that I have got it right. Thanks a lot, Eddie Price
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 4 Jan 2005 05:49:21 -0800, snipped-for-privacy@tiscali.co.uk wrote:

I think, sooner or later, everyone has a problem, with parting off. Brass is not normally too much of a problem but something like 3" diameter work hardening stainless steel can be a daunting task.
The the normal front mounted parting off setups need the setup of both the lathe and the workpiece to be exceptionally rigid. This is because any flexure increases the cut depth and this can be a recipe for chatter or even worse - catastrophic dig in!
A parting tool mounted upside down in a rear toolpost is much more forgiving because flexure decreases cut depth and this is an inherently stable configuration.
I regularly use a backmounted HSS cut off tool and the comparative freedom from tool jams and chatter is well worth the bother of providing the backmount facility.
An extra feature which works well on both front and back mounted parting tools is a longitudinal groove along the flat top face of the tool. Because the plunge cut chip of a parting tool is in an extreme state of compression its natural width is WIDER than the width of the cut and it will try real hard to jam against the sides of the cut. If the top of the tool is flat, the flat chip will try to form a close coiled swiss roll which is probably the worst possible shape for generating excessive side pressure.
The effect of the groove is to produce a chip which is curved across its width instead of flat and this curvature is more easily compressed by the sides of the cut. The shape of the groove doesn't seem to be very critical - I aim for a centred roughly semi circular groove a bit less than half the width of the top face. A tool and cutter grinder would make short work of this but I content myself with a cutoff disc in a dremel grinder and a fairly steady hand. I run the groove back for about 1/4" so that it survives several resharpenings.
Resharpen on the front face only - about 10 deg front clearance. Unless you're limiting cutting to small diameters with relatively wide blades keep the front face grind dead square on to the tool axis. Any angle here to move the final pip to waste or the workpiece generates undesirable sideways deflection
Because the side clearance on parting tool blanks is so small and there is no side rake it's important to be careful that the cutter is mounted truly vertical and accurately square on to the spindle axis. Even with the curved chip face there's still pretty severe pressure on the sides of the cut so continuous brush or drip oil feed lubrication is essential on difficult work material.
Jim
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.