How to stop juddering

[Peter Simpson 3Participant @petersimpson3]

Hi All,

I need to reduce the diameter of a 14″ long piece of tube.

The material in Bright mild steel 13mm OD and an approx ID of 3mm.

I have it secured in a collet chuck at the head stock end and secured at the tail stock end with a rotating centre. Taking quiet shallow cuts under power feed I get a horrible juddering type of cut as the tool approaches the 7″ position Do you need to use a traveling steady for this type of work, would a sharp HSS tool be better than an indexable tool ?

[JasonBModerator @jasonb]

Sharp tool either HSS or **GT type insert with 0.2mm corner radius.

You don’t say how much to come off or what sort of finish is required but you could do it in short lengths of say 30mm, moving it further out the collet once the previous section is down to size. This would also be the quickest way to rough it down to size then do a full length finish pass with a travelling steady.

[Peter Simpson 3Participant @petersimpson3]

 

 

 

 

 

 

 

 

 

 

 

 

 

The final OD will be 11mm and a good finish is required.

 

 

 

 

 

 

 

 

 

The finished diameter will be 11mm and a good finish is required.

 

 

 

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[Andrew CrowParticipant @andrewcrow91475]

I would agree that a travelling steady is essential for any chance of good finish and accurate size at that length of such a slender bar.

Andy.

[old martParticipant @oldmart]

As Jason mentions, very sharp tools and the –GT inserts made for aluminium of HO grade along with very small depths of cut. Try different speeds and steadies are a great help.

[alecsParticipant @alecs]

A temporary travelling steady can be lashed up in various ways, ranging from a block of hardwood or brass or ally  with a hole drilled in it and either clamped to the cross slide or in the toolpost, through to more deluxe fabricated efforts.

I saw one recently that was a simple piece of brass slid along a round steel bar mounted on the headstock. It pressed on the rear of the job in the middle of the long thin section and stayed in place, so not travelling.

 

[noel shelleyParticipant @noelshelley55608]

Using a fixed or travelling steady is fine BUT it needs to be properly adjusted to work well.  Noel.

[alecsParticipant @alecs]

This steady is mounted on steel bar attached to the tailstock for screwcutting 10mm Acme.

[Howard LewisParticipant @howardlewis46836]

What feeds and speeds are you using? Too high?

If the tube is steel, in view of your problems, I would suggest a maximum cutting speed of 20 metres per minute (Cautious, but the object is a fine finish not ten a minute)

You are looking to remove 1mm from each side

So you need to take ar least one roughing cut (say 0.50, then 0.30, before a fine finishing cut (no more than 0.1 mm)  at a slowest possible feed rate. (0.05 to 0.1 mm per rev)

Stating the obvious, the tool, needs to be sharp, and at centre height, with minimum overhang.

Possibly, lubrication for the finishing cut may help

Presunably the gibs are correctly set? Lack of rigidity will allow chatter to take place.

A worn or badly adjusted machine will rarely produce good work consistently

Let us know how you get on!

Howard

[Peter Simpson 3Participant @petersimpson3]

Job done, did what Jason suggested, cutting 30mm out from the collet chuck at time to reduce the diameter. Then set up my traveling steady to cut the full length in 0.010 cuts. Worked out a treat with a good finish. Thanks for all of your suggestions.

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