Lathe cutting out of true

[flintlockand steelParticipant @flintlockandsteel]

[flintlockand steelParticipant @flintlockandsteel]

I’ve just noticed my Clarke vari speed lathe is cutting out of true. It gets light use, mainly cutting new screws for old flintlocks etc, so it’s simple work.

Last night I spent an hour in a cold shed only to realise the 2 screws I’d cut tapered! Thicker at the live centre end.

About 0.02/3mm over 50mm

A while back I did swivel the tool post for an awkward cut. I thought I’d re-aligned it correctly on the scale. Perhaps not.

Is this the likely cause or is there something more serious going on.

Being awkward to adjust at the best of times how should I proceed to get it spot on again?

[Chris TriceParticipant @christrice43267]

Are you using a live centre in the tailstock? If yes, your tailstock is probably not lined up on the axis of rotation. If no, then it’s probably due to either the screw flexing away from the tool (this happens with long thin unsupported items) or your head stock is not parallel with the bed. Also check that your bed is not twisted either by it’s own weight or the way it might be bolted down.

Edited By Chris Trice on 02/12/2011 09:37:57

[TerrydParticipant @terryd72465]

Posted by flintlockand steel on 02/12/2011 09:11:32:

I’ve just noticed my Clarke vari speed lathe is cutting out of true. It gets light use, mainly cutting new screws for old flintlocks etc, so it’s simple work.

Last night I spent an hour in a cold shed only to realise the 2 screws I’d cut tapered! Thicker at the live centre end.

About 0.02/3mm over 50mm

A while back I did swivel the tool post for an awkward cut. I thought I’d re-aligned it correctly on the scale. Perhaps not.

Is this the likely cause or is there something more serious going on.

Being awkward to adjust at the best of times how should I proceed to get it spot on again?

 

Hi,

 

If you are using the saddle to cut the screw the angle of the toolpost is of no consequence. There are several possible causes. The main one being that the bed is twisted by not being set up correctly. This can be corrected by levelling, the use of shims under the feet and adjusting the tightness of the bolts. You can find some good advice here, here or here. Just try a Google search such as ‘setting up a lathe’ and you will find plenty of good advice and videos.

 

Best regards

 

Terry

[Clive BarkerParticipant @clivebarker72854]

Presumably it was the top slide that you moved and you are now questioning? (not the tool post whose postion wouldn’t affect parallel cuts, and doesn’t normally have an angular scale). If you are using the lathe’s leadscrew to cut screw threads (rather than a die) then the angular position of the top slide wouldn’t parallelism either. The only way I can see that the top slide could affect this is if you are turning to from the plaing outside diameter of the thread before using a die to cut the thread – you will need to confirm this.

 

If you are using the leadscrew to cut the thread then the slight taper then there are three possible reasons, none of which involve the top slide:

 

1. If you were using tailstock support with a centre then your tailstock might be slightly out of alignment. This can be easily corrected.

2. Some slight misalignment between the headstock and the bed – not normally so easy to correct

3. If the work is smaller in diameter closer to the headstock (left hand end) and the thread is slender without tailstock support, then the work could be deflecting under cutting forces. It seems however, that it is the other way round – larger nearer to the headstock. So perhaps not this.

 

The amount of taper you quoted is not going to make any difference to your screws if you have proper clearances which, in anycase, have a clearance between the male and female threads far in excess of 0.015mm on the radius.

 

Perhaps some clarification required of how you are making your threads.

 

Regards,

 

Clive.

[NJHParticipant @njh]

Hi Flintlock

 

It reads to me as if you may be using the top slide to make the cut. If so then having this set less than 2 degrees off parallel would produce this error. Make the cut by moving the carriage – if I am wrong and you are doing it this way then you will need to explore Terry & Clive’s suggestions. ( I hope I’m right as the solution will be much easier!)

 

Regards

 

Norman

[Ian S CParticipant @iansc]

I don’t know your lathe, but if its like my Taiwanese one the head stock is bolted to the bed, and has adjusting bolts back and front, mine did get out of adjustment a one stage. I suspect that I may need to do it again. Ian S C

[blowlampParticipant @blowlamp]

Is your lathe a Clarke CL 300?

 

Their top slides are very awkward to set parallel again because you have to wind them right back to reach the locking screws.

 

I’ve modified mine to get around this problem altogether – if you want to see some pics then let me know.

 

 

Martin.

[flintlockand steelParticipant @flintlockandsteel]

Had a bit of time to think it through and respond to your Q & A’s.

It is a Clarke CL300m.

As regards cutting I’m obviously going in with the compound slide and traversing either manually or engaging the screw cutter / leadscrew for auto traverse.

Threads are cut later with a die.

Using a live centre

I did wonder if the headstock had some play but nothing apparent there.

Last night I cut a 30mm screw to hold the frizzen (flash pan cover). This first passes through a saddle (steel spur projecting from the flash pan, through the frizzen then screws into the lock.

It starts fine and is a good fit in the saddle but not being parallel the pan is slack and wobbles and the screw undersized where it meets the lock. It’s only threaded where it meets the lock.

Now in daylight I can see that when I bring the live centre up to the bar it’s a hint off centre. This after drilling with a centering bit.

The tailstock bolts down solid onto the bed so where is my error arising?

Finally it was the upper compound slide that I rotated (very awkward to reach and adjust) to cut a bevel and it is this that I thought was causing the error despite it having been re-zeroed on the scale.

[TerrydParticipant @terryd72465]

Hi,

 

You can check your tailstock alignment by removing the chuck and fitting a centre in the tailstock and one in the headstock spindle. Bring the tailstock up to touch and see if they are in perfect alignment. You can then try the ‘two diameters’ test by turning a bar between the centres as shown on one of the websites I mentioned above. That will help to isolate the problem.

 

It is very difficult to analyse problems without being able to use the machine. If that is not done we are only shooting in the dark.

 

Terry

[Sub MandrelParticipant @submandrel]

Setting the CL300M topslide to turn parallel is child’s play.

 

Make sure the cross slide is very clean, and use a small square to set the topslide at 90 degrees to the front or rear edge of the cross slide.

 

If you do this and still get poor result, you probably need to re-adjust the gib strips in the slides or, just possibly, check the clamp holding of the carriage to the bed.

 

Neil

[Anthony KnightsParticipant @anthonyknights16741]

As supplied , the CL300 tailstock is a bitch to true up, because the locking screw is UNDERNEATH the bottom casting and virtually inaccessible when mounted on the bed.

I would recommend that you look at some of the web sites dedicated to the mini lathe.

My favorite is “mikesworkshop.weebly.com” (sorry, don’t seem to be able to insert a link), which among many other things, lists a series of mods to the tailstock, which makes it simplicity itself to set up. I know this because I have done it myself.

Hope this helps

regards Tony

[flintlockand steelParticipant @flintlockandsteel]

Thank you all for the valuable input. I’m almost out of time to do anything now before I go on holliday, but I’ll have a really good look at everything once I’m back.

Just goes to show how many potential variables there are with these things and even aparently solid imovable parts which one may accept initially as corect may be the cause of wasted time, frustration and grief.

Merry Christmas to all

Jon

[flintlockand steelParticipant @flintlockandsteel]

Hello again

Back from India which was a nice warm way to spend Christmas.

I,ve discovered the head and tail stock were about 2mm out of alignment!

Never assume a second hand lathe is set up properly.

I’ve now adjusted the tailstock (which is awkward to do) and got the centres to meet – looks spot on. So good, so far.

Set to turning a 10mm rod (using a live centre) and was surprised to find that I now appear to have the opposite problem to the one I started with. The turning looks to be about 0.4mm less at the tailstock end. I say looks to be as I only have a digital vernier gauge to hand and it can be a bit of a pig a) to read in poorer light and b) it doesn’t always reset to 0. Overall though, there is a difference.

I’m now thinking the tailstock might just be slightly over adjusted despite the centres looking good. I feel the tailstock is just that bit too close to the tool.

Any comments or confirmations greatly appreciated.

Jon

 

[michael howarth 1Participant @michaelhowarth1]

To check headstock mandrel / tailstock alignment I was told to insert a centre in each and bring them together with an old fashioned razor blade trapped between the two centre points. If there is perfect alignment the razor blade will be held perfectly vertically.

Any misalignment will result in the razor blade twisting……top to bottom or left to right. I have found that height alignment is usually good  and it is the left / right that needs adjustment. On my lathe it is then easy to adjust the tailstock unti the razor blade adopts the perfectly vertical position. Undoubtedly there are more accurate ways of testing alignment but as well as ease and rapidity I have found this method will produce pretty accurate results.

Edited By mick H on 05/01/2012 18:40:48

[Steve WithnellParticipant @stevewithnell34426]

The way I would do this is…

 

a) Put a six inch length of 3/4 inch bar in the chuck and centre, turn around and centre drill the other end. Then put it to one side as Delia might say.

 

b) Put a short length of say 0.5 inch bar in the chuck and turn a centre with a 60deg included angle.

 

c) Now set the one inch bar between the centres and take a light cut and use a micrometer to measure each end to establish the taper.

 

d) I’d use a DTI at the tailstock to setover the tailstock half the total taper you measured – if its “fat” at the tailstock move it toward the tool. If it’s thin, then move it away. Then take another light skim.

 

Sounds like you don’t have a DTI, so it will be more trial and error to get the taper sorted. Not sure where you are but I have one you could borrow if you are local.

[brickyParticipant @bricky]

Hello  Jon

The first thing to do is what has already been suggested,that is to read up on setting up a lathe as it appears that you have not set up properly before starting to use the lathe.

Setting over the tailstock should only be done after the bed has been assessed for twist with a level over the bed then turn a 8″ length of bar in the three jaw under power feed.,if this is not true keep adjusting the hold down bolts until you have truth. then proceed to the tailstock. Hope this helps.

Bricky 

[flintlockand steelParticipant @flintlockandsteel]

Thank you all for the valuable information.

Being a first (but second hand) lathe I had made assumptions as regarding it’s setup.

Taking all on board I now have managed to set it to an accuacy of 0.01mm in 75mm (the 75mm being the rod length).

Mounted on a leveled sheet of 18mm ply and a small adjustment to the tail stock, I achieved the above.

I think it would take too long to improve on this and without doing the really nice and useful modifications to the tailstock I saw on one recomended site I think this will have to do.

I only turn screws for my old flintlocks and a 0.01mm tolerence is fine.

Thank you

[Sub MandrelParticipant @submandrel]

0.01mm in 75mm is good, and you should be please with yourself.

 

I made a very simple mod to my tailstock – I widened the slot in the bottom and added a gib strip (even though the edges of the slot are straight, not angled) and an M6 screw through the side to lock it. Seeting the tailstock I just take light cuts and use the M6 screw and gib to keep it in place. Once happy with the result, I then lock it all out from underneath.

 

Neil

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