Turning Question: Fine Chatter / Wave Pattern

[DiogenesParticipant @diogenes]

Banding can be caused by oscillation of the work as well as the ‘tracking’ of the tool point, maybe a consideration in this case where you were using a somewhat elderly (did you say?) rotating centre for offset turning – the point might turn once a rev, but the balls will be cycling the track at a much slower rate..

..this is an ‘ask how I know..’ comment..

 

[Nigel Graham 2Participant @nigelgraham2]

Thankyou Diogenes.

A good point, given the unknown age and provenance of all this equipment. I will follow that by examining the device. I don’t know how or if I can dismantle it, though

 

I spent a peaceful couple of Christmas morning hours giving the lathe’s lead-screw, feed-shaft and rack-&-pinion a good cleaning and oiling. Whether it would have made any difference to work quality I cannot say, but it would have done more good than harm.

To clean them I drenched them in WD-40 (whose MSDS tells it is really only thin oil in white spirit) then used a worn-out paintbrush and tissue-paper (not cloth!) wipes to chase the muck out.

Wipe down, then squirt oil over the pinion, along the screw and down all the oil-holes I could find.

Finally, I verified the headstock still holds enough oil for the largest internal gear to pick up and fling all over the works.

[Nigel McBurney 1Participant @nigelmcburney1]

I think your problem is the use of a 6 mm dia cutter which is in effect a form tool,and its being used on a small diameter workpiece and using the least rigid on any set up on a lathe,ie set over tailstock with work between centres, dsecribed in many engineering text books but I do wonder if the writers of these books have actually carried out this method,and it stems back to victorian times when the faceplate and between centres working were the principle workholding methods and using carbon steel cutting tools, Now on your lathe would you consider using a parting tool 6mm wide,no you would you would use a 3mm tool.you are expecting too much from the circular insert.use a hss tool bit with a rad of around 1 mm . I would put the job in a three jaw supported by tail stock centre,then turn the taper with the top slide ok the travel is limited so do it in two bites and carefully blend in the two cuts.  I had a job come in to make a Crossley oil engine con rod from solid about 30 inches overall,using 51/2 inch bar ,the customer insisted on it being from solid rather than two ends welded on, so i had to do it between centres with tail stock set over,to start each end was machined first ,ncluding the bullk of the large blend radii the centre section turned down parallel to nearly the largest dia the the tapered part the holding on the parallel centre sectionof the centre machined off the ends to give the flat areas,then i mounted the rod between centres ,tail stock set over, and roughed out the taper with carbide tooling. Finished off with  HSS tool with minimum rad,even with a large job in a 71/2 inch Colchester it is very easy to get tool chatter so feeds and speeds are kept low.In over 60 odd years of engineering I have found the majority of vibration and chatter marks and simlar finish problems are due to too high speed,too high feed, and expecting too much from tools with large rads or other forms, its better to get forms on large poorly supported rads by twidling the handles on cross and sliding feeds. By the way the clicking that was mentioned in a geared headstock can be due to the tooth on a gear or pair of gears (Hardened & ground)being slightly distorted due to a crash caused by an accident with a workpiece coming into violent contact with the bed or saddle of the lathe, and its nigh impossible to locate the distorted tooth as the damage does not show,the distortion can be minimal but it will click .

[Nigel Graham 2Participant @nigelgraham2]

Bit of an IT hiatus but managed to sort that with advice from the Forum management.

Sometimes I think using a computer is analogous to needing know how the lathe was designed when I only want to face the end of a bar.

Anyway, I’ve not actually measured the marking and rack but they do look suspiciously similar. I can’t detect any unwanted play anywhere, but neither have I discovered any adjustment. It looks as if the saddle is guided simply by a single inverted-Vee, own weight and a restraining bar under the rear bed overhang.

I’ll try consulting the manual again to see if I have missed something.

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