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Cross slide lifts when parting off

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Martin Brundell02/05/2011 13:39:56
29 forum posts
Hi, I have a problem with the cross-slide lifting when Im parting off Mild Steel (EN1A free cutting).
 
I have tightened and aligned the adjuster at the side so that it's almost to tight to move the cross-slide - but it still lifts!
 
How can I stop this?
 
thanks
 
PS WM280VF lathe
maurice bennie02/05/2011 14:37:57
164 forum posts
1 photos
Hi Martin. Have you checked that the carriage is not lifting.
best wishes Maurice.
john swift 102/05/2011 14:55:16
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318 forum posts
183 photos

Hi Martin ,
 
my first attempts parting off on a CL300M minilathe didn't go well
 
the tool was deflected downwards even after tightening the gibs on the top and cross slides
 
re-grinding the tool to make it thinner helped
 
but in the end ,I replaced the original bent and miss shaped low grade steel gibbs with new brass ones from Arc Euro Trade
 
I also changed the method of adjusting the plates holding the saddle down to the bed
removing the 2 jacking screws from each plate and inserting a shim to set the clamping pressure between the saddle plate and the bed
 
this link shows the original saddle clamps
 
I don't know if brass gibbs are avialable for your machine but at least you need to check
the fit of the gibbs on you machine

Edited By john swift 1 on 02/05/2011 15:17:04

Edited By john swift 1 on 02/05/2011 15:18:07

Edited By john swift 1 on 02/05/2011 15:18:35

Edited By john swift 1 on 02/05/2011 15:27:04

Martin Brundell02/05/2011 15:38:25
29 forum posts
Posted by maurice bennie on 02/05/2011 14:37:57:
Hi Martin. Have you checked that the carriage is not lifting.
best wishes Maurice.
 
 
 
Hi, I can actually see the top slide moving up and down. But how exactly can I tighten up the main carraige as well?

thanks

Martin Brundell02/05/2011 15:45:26
29 forum posts
Hi John thanks for the reply and will ring Arc Euro tomorrow about the gibs
 
However a bit lost with the sadlle info you have mentioned... bit new to lathes. I am trying to look for info now.
 
thanks
 
Martin W02/05/2011 15:54:27
856 forum posts
29 photos
Martin
 
Are you parting off from the front or from the rear like some advocate. If from the front then all the forces should be acting more or less into the bed of the machine, however if from the rear then there will be a lifting force. Using a similar but smaller version of this lathe I have had no problem parting from the front and so have not tried parting from the rear. I believe that at the rear of the saddle, under the rear edge, there are a set of gib adjusters that control the saddle clearance. Secondly is there a saddle locking screw which clamps the saddle securely to the bed, if so then it might be worth locking this when parting off.
 
Cheers
 
Martin
JasonB02/05/2011 17:14:53
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I have the same lathe and don't have a problem parting off.
 
The saddle can be locked by tightening the allen screw that is just under the cross slide gib adjusting screws, the one nearest the bed of the three on the right top surface of the saddle though I seldom need to do this.
 
You may need to adjust the gibs on the cross slide if that is lifting, use the three screws that have the lock nuts, the one without a locknut is just to lock the cross slid ein a set position.
 
Check the tool is not above centre height as this will tend to push teh toolpost away from the work and lift the cross slide.
 
What type of parting tool are you using, what dia is the steel what speed and feed  are you using and what cutting fluid? answer these and it will help us to help you.
 
You should not need to replace the gibs or saddle fixings.
 
Jason

 

Edited By JasonB on 02/05/2011 17:18:14

Martin Brundell02/05/2011 17:52:54
29 forum posts


Posted by JasonB on 02/05/2011 17:14:53
:
Hi Jason, I have adjusted the gib screws but still no go. I am cutting off from the front and left hand side as I stand looking at the lathe. When cutting you can pysically see the toolpost dipping forwards. I have checked the toolpost etc an that is solid with no movement - however you can see the cross-slide lifting on the right side (were the gib is) I am using cutting fluid with a pump. The tool is spot on centre on the work piece, but when the post dips it makes the tool go lower than centre and then dig.
Cutting with a HSS blade that is very sharp - but also have a carbine insert system, but this does exactly the same.
I will try tightening the apron tomorrow but at the end of the day the cross-slide if definitely lifting.
Martin Brundell02/05/2011 17:56:51
29 forum posts
The steel I am using is EN1A feee cutting leaded steel at 20mm diameter. Speed at approx 120 rpm and using the finest feed "C" on my machine. When it does cut it does it lovely but I really think the movement is bodging it up most of the time.
 
I agree I should not need to change the gibs or saddle fixings, but I have tried adjusting until I am blue in the face
Martin Brundell02/05/2011 17:59:58
29 forum posts
BTW thanks for the replies - I am taking it all in slowly.
 
Been at it all day so going to try again tomorrow now. It just seems like the gibs mechanisn isnt doing much apart from making the cross-side stiffer to operate, it does not seem to be locking the topslide down much at all.
 
thanks again
JasonB02/05/2011 18:02:01
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19098 forum posts
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You have not said what dia the steel is or the speed and feed you are using.
 
I tend to use the slowest gear combination which is what the lathe comes set up with and the lever in the "C" position as this gives the finest feed rate, speed depends on dia but I can part off 1" steel at around 500rpm with a 3/32" wide Eclipse HSS blade.
 
Maybe take the cross slide off and check there is no muck under the gib strip stopping it seating properly- just keep winding it towards the back until the screw disengages with teh nut. If teh gibs are tight the slide should not be able to lift.
 
J
 
EDIT Cross post there, only other thing is to make sure the tool is perfectly at right angles to teh lathe axis so the sides are not rubbing.

Edited By JasonB on 02/05/2011 18:04:22

Martin Brundell02/05/2011 18:08:15
29 forum posts
Hi Jason, my cutting blade is 2mm and is square (I square it with the chuck face).
 
500rpm - I can only dream of parting off at that speed LOL
 
I will take the cross-slide off tomorrow and clean it all out - thanks for the tips.
john swift 102/05/2011 22:10:33
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318 forum posts
183 photos

Hi Martin ,
 
I failed to find the manual for your lathe but if you look at pictures 2 and 14 here :--
 
 
( they look more like your lathe than the CL300M !! )
 
you will see "L" shaped pieces that hold under the front and rear edges of the bed
 
assuming the parting off tool at the rear , have a look at the rear rear clamp adjusters ,
the 5 screws hidden underneath
see picture 14, may be easier with the rear splash guard removed
 
the front clamp looks its in 2 parts , looking at the marks in picture 10
these clamp just under the front inverted "V" on the bed
 
John
ady02/05/2011 23:45:11
612 forum posts
50 photos
I haven't tried it yet but the turret lathe boxes always had a steady over the workpiece for parting off.
 
The problems are hundredths of a millimeter but they employ large forces and unless your lathe is "perfect" you will get issues.
 
A steady across the top of the workpiece apparently makes a huge difference for parting off. Nowadays instead of a block lubricated with whale oil and tallow we can use a couple of one dollar bearings to secure the workpiece.
 
2cents(buddy)
john swift 103/05/2011 00:31:27
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318 forum posts
183 photos

Hi Martin ,
 
just a thought , you don't have the parting off tool too far out ??
 
if it is just long enough you reduce the leverage on the tool post
 
also don't part off too far away from the chuck or collet than you need to
 
 
Hi Ady ,
 
I've not seen steadys used when parting off
 
but have seen rollerboxes used to turn small diameters down in one pass
 
 
at school ( a long time ago !) the parting off tools on the Myford 7 lathes had a very short life
( 2 or 3 tools to partoff one piece )
 
years later I used an old Ward 2D capstan lathe once !
 
what a difference ,no deflection of the tool or workpiece
parted off several dozen parts without breaking the parting off tool
 
 
John

Edited By john swift 1 on 03/05/2011 00:35:41

ady03/05/2011 00:53:59
612 forum posts
50 photos
"Cross slide lifts when parting off"
 
This really shouldn't happen ever, for any reason.
 
Take it off and clean it up.
Edited By ady on 03/05/2011 00:59:13
 
These lathes aren't very old, they should be fine, a quarter of a ton with an MT4 spindle...holy smoke
 
Model No.  
Distance between centers
700mm
Swing over bed
280mm
Swing over cross slide
165mm
Taper of spindle bore
MT4
Spindle bore
26mm
Number of spindle speeds
6/Variable
Range of spindle speeds
125~2000/50~2000rpm
Range of cross feeds
0.02~0.28mm/r
Range of longitudinal feeds
0.07-0.20mm/r
Range of inch threads
8-56T.P.I
Range of metric threads
0.2-3.5mm
Top Slide travel
50mm
Cross slide travel
140mm
Tailstock quill travel
80mm
Taper of tailstock quill
MT2
Motor
0.75/1.1KW
Packing size
1400 x 700 x 680mm
Net weight
210kgs

Edited By ady on 03/05/2011 01:02:17

ady03/05/2011 01:04:01
612 forum posts
50 photos
Give you a giant tip.
 
Lose the compound and replace with a big 4 way tool post. bolted directly to the cross slide.
 
Only ever use the compound for tapers.

Edited By ady on 03/05/2011 01:10:56

ady03/05/2011 01:14:50
612 forum posts
50 photos
I havent done it yet but sparey bought a parting tool and placed it on the back side of the cross slide, upside down, bolted it to an angle plate and reinforced the open side with a steel plate which secured the parting tool to the angle plate.
 
Horrible to look at but apparently very effective.
Pat03/05/2011 05:07:45
94 forum posts
1 photos
Hi Martin
 
Your lathe will part off more easily if you invert the parting off tool and run in reverse. This causes the tool to lift away from the work rather than dig in. The tool still needs to be on center height and correctly adjusted so that there is no side cutting. (Reverse running is not recommended and can be down right dangerous for lathes with chucks that are screwed on to a threaded nose piece. Yours uses bolt on chucks so reverse running is OK.
 
A further refinement is the index-able tip parting off tools which are widely available (Chronos) in sizes suitable for your lathe.
 
Also when parting off plunge the tool into the work with continuous pressure as a diffident feed rate can induce chatter and dig in problems. Depending on what you are cutting use the appropriate feed rate / speed and some lubricant.
 
Hope this helps as you should not be having problems if the gibs are reasonably tight. There is a tendency to have the gibs too loose and the smaller the machine the tighter the gib needs to be comparable to the machine size as there is less mass in the cross slide and saddle. I have a similar machine and no problems reverse parting off.
 
Regards - Pat
 

 

Edited By Pat on 03/05/2011 05:08:17

chris stephens03/05/2011 12:21:51
1047 forum posts
1 photos
I don't know if this is the case with your lathe, but on the "mini-lathe" there seems to be a design/manufacturing fault with the top slide dovetails. The problem is that there is a sharp corner which has to fit in a rounded "vee", so there is only a line contact not full flank engagement. The remedy, on the mini-lathe at least, is to file away the sharp edge to allow the dovetail to do its proper job.
chriStephens

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