Lathe really crap finish – Myford ML4

This topic has 14 replies, 11 voices, and was last updated 11 October 2012 at 16:28 by Martin W.

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30 September 2012 at 23:04 #99777
Dean Godfrey-Cooke
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@deangodfrey-cooke74440
Hi All

I finally got around to playing with my lathe at the weekend. I was just getting some practice with the new HSS tools I have, cutting a few grooves in some aluminium I had knocking around.

It was chucked in and held by a rotating centre but whenever I tried a finishing pass the surface was just shocking, uneven ridges all teh way along. I tightened up the jibs to see if it was a little loose but no luck

Where do I look next? The tools were new and sharp.

Cheers

Dean
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30 September 2012 at 23:04 #6367
Dean Godfrey-Cooke
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@deangodfrey-cooke74440
1 October 2012 at 00:21 #99779
Martin W
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@martinw
Dean

Do you know what grade the aluminium is? If not dump it and buy or get some that you know is good for turning. Something like HE30 normally turns nicely especially if you use WD40 or white spirit as a cutting lubricant, this can be applied using a small brush.

If this doesn't do the trick then check your tools to make sure they are really sharp. Try reducing the cut depth and feed rate to see if this helps. It's worth noting that tools with very sharp points/noses, non radiused cutting ends, can leave a trace on the surface like a fine screw thread.

Cheers

Martin
1 October 2012 at 08:08 #99785
JasonB
Moderator
@jasonb
Make sure the cutting edge is exactly on centre height and also use some form of cutting fluid WD40 or Parrafin work well on ali
1 October 2012 at 09:08 #99788
jim both
Participant
@jimboth37830
It could be the Ally. We had a job at work with some free issue (customer supplied) Ally, job looked a doodle. Turned out to be the worst maching metal i'd come accross in 30 years. it cut like LEAD!!!

i made sure non of the bar ends fell into my bag on that job!!!!
1 October 2012 at 10:09 #99792
Boiler Bri
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@boilerbri
If you pm me i will send you a sample of HE30.

Bri
1 October 2012 at 13:07 #99804
Phil H 1
Participant
@philh1
Dean,

You might laugh at this and I hate to admit it but I was very puzzled one day at the poor finish until I realised the spindle was rotating backwards!!!!

Otherwise, the usual checks like centre height, spindle speed, rigidity of the tool and workpiece etc.

Phil H
1 October 2012 at 14:00 #99805
Andyf
Participant
@andyf
For aluminium, a much greater top rake than that used for steel is often recommended – at least 15 deg, and up to as much as 35 deg. If your tools were pre-ground for steel, .the angle will be much less.

That said, I don't use anything special for Al, and my results are OK (though my standards are not terribly high!).

Are you using a fine power feed, or winding the saddle along by hand? If the latter, try cranking very slowly indeed.

One problem with Al is that it is gummy, and a blob of it can build up on the tool tip, altering the geometry and impeding chip clearance. Using WD40 or paraffin helps to prevent the build-up.

Andy.
1 October 2012 at 15:34 #99810
KWIL
Participant
@kwil
It is not that Ali is "gummy" it just happens to have a relatively low melting point and "welds" itself to the tool if the tool is not correct or in some circumstances not lubricated.
1 October 2012 at 16:47 #99814
Wolfie
Participant
@wolfie
I had this problem and in my case my lathe tool was too sharp!
1 October 2012 at 19:45 #99819
ianj
Participant
@ians
Posted by Phil H 1 on 01/10/2012 13:07:16:

Dean,

You might laugh at this and I hate to admit it but I was very puzzled one day at the poor finish until I realised the spindle was rotating backwards!!!!

Otherwise, the usual checks like centre height, spindle speed, rigidity of the tool and workpiece etc.

Phil H

I can remember once at work one chap drilling some mildsteel angle iron cursing the crap drill bits until it was pointed out he had the drill on reverse !!

Ian
11 October 2012 at 14:19 #100506
Dean Godfrey-Cooke
Participant
@deangodfrey-cooke74440
Thanks for all the responses guys.

When I get some time I'll try some other Alu and the suggestions above. I wasn't using any lube so it could be that simple, though the spindle was going the right way 😀

Wolfie, too sharp?

I bought the tools from RDG on their recommendations for Alu, I also have some Warco Indexable tipped tools but haven't tried them yet.

Cheers

Dean
11 October 2012 at 15:31 #100513
Terryd
Participant
@terryd72465
Sorry – error

Edited By Terryd on 11/10/2012 15:39:17
11 October 2012 at 16:22 #100515
KWIL
Participant
@kwil
CCGT-AK tips for aluminium are extremely sharp with a high top rake.
11 October 2012 at 16:28 #100516
Martin W
Participant
@martinw
Dean

I think Wolfie is referring to the point I made in my initial post on this thread that if a tool has a pointed cutting end rather than a radiused cutting end then it can leave fine grooves in the turned piece. Often to get a really smooth surface it is necessary to grind a small radius on the end of the tool. The cutting edge still needs to be sharp with a rake ground on the top surface. There are many books and tables that give these relief angles for different materials etc.

Indexable tools will have as part of their reference code a number/letter which which defines the tip radius, so by picking a larger radius tip you can effectively make a smoother cut at the same tool traverse speed.

Hope this helps

Regards

Martin

Edited By Martin W on 11/10/2012 16:30:17
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