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Facing Cuts - Requires the Carriage to be Locked?

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EtheAv8r05/05/2011 10:21:40
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I have now had my shiny new Wabeco D6000E lathe and stand delivered the week-end before Easter and it was installed in my workshop over the Easter holidays. I have a problem and want to seek the opinions of you chaps who know about this sort of thing.

I cannot take a facing cut that is true, the result is a dome because the carriage is pushing back as the cutting tool traverses the bar being faced - no matter how light the cut. The only solution is to lock the carriage, take the cut, unlock the carriage, move forward the required distance, lock the carriage and take the next cut… etc. The carriage lock is via a hex cap screw that requires a 6mm allen key – and at present is inaccessible due to the Newall Microsyn encoder for the DRO readout being mounted across the very end of it at a tangent to the outside edge of the cap screw and this in turn is covered with an aluminium angle protective cover!

Now the only limited experience I have of using a lathe is a Myford at a Friday evening class and I do not have to lock the carriage to take a facing cut – nor have I been advised to do so, nor have I read any such guidance in my recent reading to learn about this turning malarkey. However the Wabeco agent has come back to me and said that the carriage must be locked for each facing cut – and as he supplied and installed the Newall DRO pre delivery, and specified the location of the Microsyn encoder is arranging for his man to visit and re-locate the Newall Microsyn (which incidentally also currently prevents the tailstock moving as far forward as it should – and subsequently making turning between centres very difficult as the cutting tool would be too far forward to reach the tail end and if the tool holder is rotated 180 to mount the tool at the rear, then will not cut to anywhere near the chuck, making it necessary to use an excessively long ‘tail’ for holding in the chuck to be cut off after).

There is no slop or movement in the carriage, but it can easily be pushed back, and the dealer tells me he has checked all his display machines and they are all the same, so the carriage must be locked for each facing cut pass – is this normal?

Edited By EtheAv8r on 05/05/2011 10:45:00

Steve Garnett05/05/2011 10:47:34
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Posted by EtheAv8r on 05/05/2011 10:21:40: so the carriage must be locked for each facing cut pass – is this normal?
 
Have to say that if you want a really accurate result, then generally the answer is yes - that's why a locking facility is fitted. And this does apply to almost all lathes, I think. There are one or two things you can do to relieve the situation slightly, but at best they represent dubious practice. So if I tell you what the obvious one is, then I also have to say - Don't Do It. If you engage the half-nuts used for threading without the leadscrew turning, this will prevent the saddle moving. But on a new precision lathe (good choice, by the way), you really shouldn't be using the threading lead screw for anything other than thread turning. The other thing you could do which is more acceptable (only I gather that this would be a problem too at present) would be to bring the tailstock up to the rear of the saddle, and lock it there. Also a bit of a pain when it comes to repositioning.
 
They've clearly not mounted the Newall encoder in an optimum position, considering that saddle locking is clearly indicated - so yes, they need to sort that out for you or the lathe isn't really fit for purpose.
 
 

Edited By Steve Garnett on 05/05/2011 10:51:38

Andrew Johnston05/05/2011 10:55:04
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Hi Edmund,
 
No it is not normal. I only lock the carriage on facing cuts when I want to use the top slide to put on a specific (accurate) cut and I don't want to move the carriage by accidentally nudging the carriage handle.
 
Incidentally the lathe cross slide should be set up to face from flat to slightly concave, but never convex.
 
Apart from that, how do you like the lathe?
 
Regards,
 
Andrew
blowlamp05/05/2011 10:55:14
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I'm not having a go, but you can't have it all ways.
 
In one sense, you want free movement (virtually frictionless) of the carriage for accurate turning, but at the same time want things to stay put (due to friction), when it's convenient for you for facing.
 
So, you can use the carriage lock and apply an infeed with the top slide, or engage the screw-cutting clasp-nut and use the leadscrew to apply a feed.
 
If you don't want to do any of that, then you could tighten the carriage gibs to create more friction to hold it when facing.
Steve Garnett05/05/2011 11:05:41
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Blowlamp, I agree - you can't have it both ways - unless you have a lathe with a permanently engaged threading drive, that is. And that is exactly what the Hobbymat has (and it's a pain), which is why it's not fitted with a carriage lock. As for tightening the gib strip every time you want to take an accurate facing cut - well that would be a pain too, so you'd have to leave the gib tight all of the time. Which is going to increase the wear rate over a long period, so doesn't sound like a good idea anyway.
 
Wabeco provided a lock, and clearly they intended it to be used.
blowlamp05/05/2011 11:23:12
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Posted by Steve Garnett on 05/05/2011 11:05:41:
... so you'd have to leave the gib tight all of the time. Which is going to increase the wear rate over a long period, so doesn't sound like a good idea anyway.
 
Wabeco provided a lock, and clearly they intended it to be used.
 
 
Hi Steve.
Yes agreed, but in view of my preceding comments, my last paragraph was more intended to be thought provoking, rather than a recommendation.
 
Martin.
NJH05/05/2011 12:00:02
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Hi
I use the carriage lock on facing cuts and
especially when parting off. However forget the Allen key approach if
possible ( you can never find the right one when you want it!) and make
yourself up a little lever like this :-
 
 

Edited By NJH on 05/05/2011 12:00:18

Steve Garnett05/05/2011 12:04:01
837 forum posts
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Norman, that's what my Kerry has on the rear of the saddle as a standard fitting.
Pat05/05/2011 12:12:36
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The problems you are having with making a facing cut indicate that the gibs are out of adjustment. The drag imposed by the gibs should be noticeable but not excessive. The adjustment requires to be done in the correct order to ensure the gib has a uniform clamping force throughout its length. I suggest you use a lubricant that is formulated for dovetail slides and reduces the stick slip which can be very annoying as well as masking sloppy gibs.
 
Also check if you have the tool mounted from the compound slide that the slide is not over extended and its gibs are adjusted correctly as well as those on the saddle and the cross slide.
 
I am not saying that you are doing this BUT there is a tendancy to set the gibs so that the hand wheel can be spun merrily. The arbiter of correct setting is that the tool post does not move under reasonable hand pressure. The slides will almost certainly not spin merrily if this condition is satisfied! To anyone who has had formal training the checking of the tool post for free movement would be second nature along with tool height angle etc.
 
Unfortunately it takes time to get familiar with setting up gibs and differentiating between adjustment faults and problems with the actual machine construction. You should be OK with a new machine from a good dealer such as Wabeco as far as construction faults. Adjustments are down to you to perform correctly. It is a pity that your machining course did not cover the setting up of the slides and checking that they are adjusted correctly.
 
The locks come into their own for repetition work or for use where there are very heavy loads being imposed as in metal spinning, heavy drilling / milling from the cross slide etc.
 
Hope you soon get the lathe set up correctly. - Regards - Pat

Edited By Pat on 05/05/2011 12:14:27

WALLACE05/05/2011 13:19:05
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Wouldn't the tool shape make a difference ? A round tool with a obtuse (that the right term ?) angle be more liable to being pushed sideways - as opposed to a relatively sharp tool with an obtuse angle ?
 
 
W
EtheAv8r05/05/2011 13:28:29
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Well some interesting and different responses, but clearly the suggestion that I should lock the carriage for each facing cut is not as startling as I first perceived it to be as this view is supported by a good percentage.

I will definitely be looking at making a handle as shown and recommended by NJH – thank you very much for that, for me a picture is so much more useful than a description as I am so very new to this hobby with no previous machining experience or background.

The DRO encoder is being re-located on Monday, so that will resolve some of the issues, the present installation location is very neat and out of the way, but creates so many other problems that I as a know-nothing very quickly discovered in my early experiments with the machine that I am surprised it is the way the dealer recommended… maybe that will change for future installations.

The initial oil on the machine is as it was provided – all set-up and ready to go by the dealer . I have purchased slideway oil (Castrol Magna DB68 slideway oil) that I believe is a lubricant that is formulated for dovetail slides. As this is not a budget machine I expected the setup to be spot-on, but maybe the gibs might need finessing, but this is a skill that completely alien to me at present. I did not attend a formal machining course; it is rather an informal evening class at a well-equipped school in Cambridge.

Andrew – after some initial doubts over the week-end that I had made a very expensive mistake with this purchase, it would seem that all will be well – I just have to learn the ropes, and there are some different twists comapred to the ropes that I have learned so far. The machine appears to be very fine, and I am sure I will learn to love it. There are not many with a 5 year warrenty.

For instance the leadscrew is permanently driven and I would have liked a lever to engage/disengage it as required. However it is but a 1 minute (maybe 2 minutes) process to disconnect the drive belt, but the dealer recommends leaving it driven all the time, any comment on this?

Edited By EtheAv8r on 05/05/2011 13:30:40

Pat05/05/2011 14:59:06
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Yes Castrol Magna DB68 is a good slideway oil.
 
However as the machine may have been sent out with something different I would clean the gibs and re oil.
 
On small machines my preference is for an aerosol formulation such as Rocol Ultraglide spray as this gives a thin film of lubricant that is persistent and penetrates well. The bulk oils tend to leave a thicker film which is OK on big machines which will probably have central oiling systems on their dovetail slides. I also find the aerosol Ultraglide is a help in keeping tools in good condition and a quick squirt prior to storage works as well as WD40 without the gunge.
 
You have a good quality small lathe so Google - Mini Lathe.com - this is not your lathe but the cross slide and compound gib adjustment instructions apply. Enjoy the fact that your lathe is better made and finished. Follow the instructions which are well illustrated. - take your time to adjust both cross and compound slides (Leave the saddle gibs alone as yours should be OK assuming the machine has not been roughed up in transit to your bench.) - relax and enjoy making swarf. The web site quoted and the web ring associated with 'Mini Lathe.UK' should help extend your lathe skills.
 
Regards - Pat
 
 
EtheAv8r05/05/2011 15:22:24
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Pat
 
Thank you for your advice. I will source some Rocol Ultraglide spray and check out the gib adjustment guide.
 
Regards
 
Edmund
Steve Garnett05/05/2011 15:34:12
837 forum posts
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Posted by EtheAv8r on 05/05/2011 13:28:29:
For instance the leadscrew is permanently driven and I would have liked a lever to engage/disengage it as required. However it is but a 1 minute (maybe 2 minutes) process to disconnect the drive belt, but the dealer recommends leaving it driven all the time, any comment on this?


That's interesting, because as far as I can tell from the spec, this lathe is equipped with a tumbler gear to reverse the direction of lead-screw travel. And it's generally the case that these have a centre-off detent position. In order to work correctly, the gearing has to be driven directly from the headstock - you can't have a belt in the drive to the lead-screw because you'd never be able to guarantee repeat positioning of screw cuts.
 
So how does this work out on this particular lathe? I can't immediately find a manual available for it.
chris stephens05/05/2011 15:40:15
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Of course there is nothing to stop you taking a cut from centre to outer edge, no matter what some dullards would have you believe
Does your lathe have power cross feed? If so you can always keep some pressure on the carriage wheel while taking a facing cut. Another way around the problem would be to make a saddle stop and keep the saddle firmly against it with hand wheel. . A saddle stop is something that I would not now be without for general turning, so you might find one useful too. If you only make a simple block type stop, with no built in adjustment, there is nothing to stop you putting on extra cut with the top slide, something you can also do when you lock your saddle with your soon to be liberated carriage lock. I fail to see why you would want to release the carriage lock to put on more cut, when you have a top slide which will just as well, don't think that you can only work with your DROs, there are other measuring instruments.
 
Just looked up your machine and I am slightly jealous. I think though you may have to learn to love you left hand being showered in hot chips! Why do otherwise sensible manufacturers put the carriage hand wheel on the wrong end of the carriage? I know there is an American chap on You Tube who insists that you should never buy any lathe with a right hand operated hand wheel, but I am sure I can see men in white coats waiting to take him back to the asylum.
chriStephens
Ian S C05/05/2011 15:43:31
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NJH, I must make up a little leaver for my saddle lock, after twenty years the allen head cap screw is a bit tatty, and has always been hard to get at. Ian S C
Gordon A05/05/2011 16:14:44
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Greetings All.
 
On the subject of a carriage locking lever, if you are not confident enough (like me) to produce a neat little handle like NJH that will lock in just the right position; a small indexable handle from somewhere like Arceurotrade will probably be suitable.
If the handle, when locked is in the way, it can be lifted and moved to a better position without releasing the lock.
 
Gordon A
JasonB05/05/2011 16:23:07
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I generally don't lock the carrage maybe only on intermittant cuts or very hard materials.
 
Even if you do need to lock the carrage you should not need to do it for every cut as the tool can be advanced using teh top slide to put on the cut, this is also easier to see the depth of cut as its easier to read a topsilde handwheel with small increments than the carrage wheel.
 
I had a very similar Emco Ecomat 8.6 for a number of years and again seldom locked the carrage, as said above a blunt or poorly set up tool will also tend to push the carrage away, if you are using insert tooling this may be part of the cause, try a nice sharp HSS tool.
 
Have a look through KWIL's photos he has a low profile saddle lock that would also work an the Wabeco
 
Jason
EtheAv8r05/05/2011 16:26:52
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Steve - you can see a picture of the gear arrangements here http://www.lathes.co.uk/wabeco/page2.html - yes the is a tumble/reverse... but all drive is via toothed belts. When screw-cutting once you engage the half-nuts for threading you do not disengage them until you have finnished, you select forward to cut the first pass and you select stop at the end of the thread, wind out, select reverse to drive the carriage back to the start, wind in to the next cut depth, select forward to cut the second pass etc.
 
Chris - the lathe does not have power cross feed. I appreciate that I don't have to work with the DRO and can use the top slide but this is a bit a a waste of having a DRO - and it is extreamly accurate - and I and not young and have a lot to learn - and do, in a short time.... so would like to use the DRO whwnever possible.
Steve Garnett05/05/2011 16:52:26
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Ah, toothed belts - that makes a lot more sense. The awkward bit though, seems to be (as Tony puts it):
 
"Unfortunately, to reset the tumble reverse for neutral or left-hand threads, an inaccessible nut has to be released."
 
And I can see how, from this situation, it's not going to be easy anyway to use the lead screw as a means of preventing saddle movement. So I'd say that yes, some sort of saddle-clamping arrangement is called for. The arguments about tightening the gib screws really boil down to a simple consideration - if you are going to take any significant amount off in a facing cut, the gib has to be tight enough to resist the outward force from whatever tool you are using, or it is going to allow the saddle to move. If you are only going to take very light cuts, then you won't need the gib screws ridiculously tight - but if you are, then the saddle lock looks like a much better bet.

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