What am I doing wrong

Hi all I'm supposed to be an engineer by trade but I have two old lathes one is a challenger which is very old and not very rigid the other is the so call RR of model engineers lathes Myford. I've clocked them all up spindles and all. I just cannot stop the chattering please see photo attached. What am I doing so wrong?

Edited By JasonB on 31/07/2017 07:32:48

Edited By Neil Wyatt on 31/07/2017 10:56:06

Well I wouldn't call the Myford the RR of model engineering, they were after all built down to a price! My fight with chatter was only overcome on one Myford,, by getting the mandrel bearings sorted out and then eliminating the play in all of the slideways. Even then, you could not take too big a cut, but after all it wasn't an industrial lathe!

Even now I only take small cuts as I feel the lathe will last a damn sight longer than me and save me the cost of yet another overhaul before I exit this world!

Andrew.

Before rebuilding the lathe I'd look at the tool. Assuming that the material is steel the tool angles are wrong. Fine for brass, but not for steel. The top of the tool needs to slope away from the work by far more, say 15° or so.

Andrew

Been through all this on my 1930s Drummond. As Andrew J says, the tool rake angles for these small lathes is much more than an experienced engineer would be used to using on larger industrial machines. LH Sparey recommends 15 degrees side rake on the top surface and about the same clearance on the side, giving an "angle of keen-ness" of about 60 degrees, conveniently measured with a screwcutting tool sharpening gauge.

The other trap to look for, providing headstock bearings and ways and dovetails etc are all reaosnably serviceable, is a bellmouthed chuck. You will never get rid of chatter if the chuck is bellmouthed and not holding the job firmly at the outer limits of the jaws. Old chucks can be reground with a dremel type grinder mounted on the toolpost after putting suitable packers or 'clover ring" between the jaws to pushe them outwards into the operatiing position.

My old Drummond will take a .100" deep cut in steel without chatter, at a decent old feed rate, provided a tailstock centre is used on medium to long jobs since I did all of the above.

Edited By Hopper on 31/07/2017 06:42:15

Edited By Hopper on 31/07/2017 06:43:13

The appearance is a, 'Cyclic' chatter and no doubt emanates from the lathe spindle bearings or end float. Further check of belts etc to see if they are stiff from being in one stopped position for a long time. Tool geometry does not cause this type of chatter. Tools need at least 12 deg. clearance and back rake, the simplest tool angles. Refinements in angles to suit the materiel being turned. Most lathes in good fettle will turn quite well with any tool with clearance.

Clive

The tool needs to be rigidly supported too, ie not rocking. Colin

A few obvious things to check;

• Tool height is critical. The point should be set as close as possible at the mid-point of the rod, 9 O'Clock. (The tool looks high in the photo and may be rubbing);
• Tool should be sharp.
• motor in forward rather than reverse (the chuck should spin anti-clockwise).

Any chance of a better photo? The camera has auto focussed on the slide, leaving the rod blurred. Holding a sheet of paper close under the rod should force the camera to focus on the chatter.

That two lathes both have the same fault suggests bad luck or the same 'mistake' when setting up. The 'mistake' may simply be what your test rod is made of. I've had bad experiences trying to turn random scrap and now buy new metal specified for machinability.

Dave

Edited By SillyOldDuffer on 31/07/2017 09:52:24

Thanks for the feedback.

Clive do I need to put any leverage on the spindle bore when clocking as when checking with a clock spinning the spindle it runs spot on so I'm really confused. Are there any instruction on spindle inspection and dovetail adjustment I can download or buy?

Regards

Andy

The tool looks to be too far to the left of the cross slide to me. I would set it up so that the carriage was getting as far to the left as possible without the chuck hitting it. Then set the tool post on the slide in a position that allows the required cut to be made. That way the forces on the tool tip are less likely to be trying to lift the right hand side of the slide up.

Martin C

Welcome to the world of smaller lathes!

What sort of cut are you taking, and what feedrate? The swarf looks very fine and granular. What type of steel are you cutting?

Does the tool have pointed end it looks very sharp - if so try putting on a small radius, making sure it doesn't rub beneath the tip. It may be that the sharp tip is breaking down rapidly and then rubbing rather than cutting.

I find a constant 10 degrees for all the angles of an HSS knife too works well as a general purpose one for most materials, bigger for aluminium and plastic, less for brass when after a really good finish.

Check all your slideways are well adjusted too.

Neil

Edited By Neil Wyatt on 31/07/2017 11:00:44

Try this, set up the Dti, on the lathe body so that the plunger/lever is lightly resting on the spindle. Get a bar and using as a lever attempt to lift the spindle by leverage. All being well the reading should be minute.

Then place Dti. with plunger against the should of the spindle and again using a lever try to move the spindle axially, again minimal deflection. This sis just to satisfy the spindle condition, reading does not matter as you are only trying to see if it will move.

Clive

Thank you Clive I will give that a go.

Regards Andy

Another simple suggestion. A 4-jaw chuck will chatter if two jaws end up doing most of the holding because the other pair are slightly loose. The slack jaws allow the work to 'flap' under tool pressure as the chuck rotates. I suppose a damaged chuck might cause the same effect.

Andy: you seem to be focussing on the spindle, but haven't said what other checks you've done. Forgive me for asking but are you the kind of 'engineer by trade' who knows about lathes? I ask in case I'm telling granny how to suck eggs. I once found myself explaining 3-pin plugs to an Electrical Engineer. He thought it was hilarious; I was embarrassed...

Dave

Hi Dave,

Yes I'm a press tool maker by trade serving my time in an old fashioned tool room but it,s been 20 plus years. I understand the mechanic of them and I've always enjoyed turning but I just can't the feel right with the smaller lathes. I'm keen to know how people set the saddle, cross slide and top slides up I've never been able to master it on a model lathe give me a Colchester or Harrison any day. I think maybe it's me trying to get to much from a small machine but I haven't got the time to take .005" cuts when I need to remove 10mm + on a job. I know the machine are very old and maybe I need to strip them down and start again?

Regards Andy