Bad finish

I'm doing my first experiences with the lathe. This aluminum part was machined at 1500 RPMs lubricated with WD40 and with CCGX09T304 for aluminum.

As you can see in the photo the finish is not the best. Any clue to what I'm doing wrong?

Vasco Reis

Pausing the feed as you reposition your hand causes banding like this. Unless you have a lathe with a taper turning attachment you can't use power feed which would help with finish. You need to practice keeping the feed constant.

Martin

It seems like I'm going to have a lot to practice. I've tried the power feed and the finish is perfect.

It is not easy because it does not have a smooth movement, I guess it needs tuning...

Thank you

You could try a small electric drill to power the top slide instead of winding it by hand (if it is actually the feeding that is the problem).

Martin is right, of course ... and the problem might be to do with the design of the handwheel [or whatever], or the way that you are holding it. But you may also get some improvement by adjusting the gib 'just right'.

What lathe is it ?

MichaelG.

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Edit: Good suggestion, Steve 

Edited By Michael Gilligan on 20/11/2016 22:06:32

It is the feeding that is the problem. It does not have a smooth movement at all and it is very difficult to maintain a constant movement.

Maybe I'll fit a small stepper motor. First I will try to fine-tune the movement (and the hand)

An EMCO Compact 5

Vasco Reis

I was taught by to feed gently using two hands, use the ring of the handwheel rather than the knob and keep feeding it through both hands a little at a time. Keeping the pressure even on the transfer is the trick. Like all skills it is a case of practice.

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Excellent idea to fit the stepper motor.

I've just looked at some photos of the EMCO Compact 5 topslide ... I would avoid using the handle on that little wheel [in fact, I would probably remove it]; I think you will get much better control using the wheel as a knob.

MichaelG.

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Edit: Marcel posted before me ... We are saying the same thing, but unfortunately using different terminology.

Edited By Michael Gilligan on 20/11/2016 22:25:54

Not at all convenient ...

Vasco Reis

Fitting a stepper motor to a sticky slide is not really the solution. You need to pull the slide off off and clean and lubricate the moving surfaces, remove all burrs etc beforehand, then reassemble carefully and adjust the gib strip adjusting screws until you get an absence of shake but a nice free motion. If you flick the handwheel it should spin freely for half a turn or more after your finger is removed.

Then use a two-handed method to continously turn the handwheel without pausing and turn it nice and slowly.

I'm with Marcel looks like you were feeding using the handle which tends to lift and then lower the end of teh topslide which gives the regular rings you are getting. This is OK for roughing out but for finished cuts two hands are needed on the wheel rim to give a constant even feed.

Also make sure the gib is not loose.

Small electric screwdriver with a socket on the end to fit the handle nut will do the job of driving the topslide if you must use power feed and it it easily removed so won't get in the way.

VCR,

You are probably using the wrong shaped tool. Try one that has a "flat" behind the cutting edge that follows along the required shape. Hand to explain but is a type of cutter recommended for fine finish on many materials.

Lampton the CC shape insert mentioned in the first post has an 85degree corner so should not be a problem.

That is provided it is mounted at the correct angle, VCR can you post a photo of how the tool is positioned when cutting the taper

On a small lathe cutting aluminium I think VCR would be better advised to use a really sharp HSS tool ground to the appropriate shape with paraffin as a lubricant.

No mention is made of the grade of alu. I would expect this on soft alu. I would use an HHS tool with a steep top rake and the speed sounds ok.

Clive

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... but VCR has shown us the excellent finish obtained on the same workpiece under power-feed.

MichaelG.

Am I the only one who would just rest a file on it whilst it's still turning ?

Did i just say that?

Its a first attempt ,everyone has to start somewhere,power feed is not the answer,to get good at turning you should be able to turn any work to good finish by hand,and until you can leave the power feed alone.To improve matters the top slide must be free to slide easily,and the the handle free to turn without any tight spots or jerkiness, A second handle 180 degrees opposite to the first one can make it easier to manipulate with two hands,Colchester lathes have this feature. The now regarded as old fashioned ball handles are far easier to rotate with the fingers of both hands,my Myford has these handles and I have never wanted power feed on either top or cross slide,but there again I started my training nearly 60 years ago and was in a workshop where you could watch other operators,learning in isolation is not easy. The only time that we rotated the top slide by just winding the handle was on the German 5 inch c/h plain instrument lathe where the top slide was very long and travelled very smoothly,when turning the od of nickel silver eyepiece tubes the lathe was on top speed at around 3500 rpm and the handle wound really fast,it produced a superb finish.

Hi Vasco. I recently had to improve my taper turning skills in order to successfully make steam cocks for my Loco. I tried many techniques, most of which ended up looking like yours! In the end I had to tighten all gibs and as others have said already, use both hands to give as smooth as possible turning action - the key step was that the final few cuts were taken by dragging the tool rather than pushing it. Tool starts at the thick end and finishes at the thin end. I suddenly had a near perfect finish. Hope this helps.

On my top slide I have cut down the supplied handle, about half way. Then fitted another handle opposite, does help in smoother turning.