Help with poor finish when cutting with the side of the cutter

This topic has 17 replies, 9 voices, and was last updated 1 January 2012 at 21:52 by Jim Greethead.

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30 December 2011 at 18:17 #5824
nic
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@nic
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30 December 2011 at 18:17 #80849
nic
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@nic
Hi there,

I’ve just milled the first test cuts on my new Super X3 on a block of aluminium and I’m surprised at how much poorer peripheral (side) cuts are compared to top cuts. For example, using a 50mm indexable end mill I can get a virtual mirror finish on the top, but when cutting the side, a 16mm 4 flute HSS end mill leaves the surface marked with many vertical lines, often wavy. Other cutters show the same problem.

I think the side cuts should be as good as top cuts, so what’s going on?

Any help greatly appreciated.

Thanks,

Nic
30 December 2011 at 18:28 #80850
JasonB
Moderator
@jasonb
What depth of cut and how thick is the material?

Wavy lines suggest chatter.

Have you checked teh spindle bearings for play, when my X3 arrived I could move it 0.030″ from side to side, the lock nuts were completely loose.

J
30 December 2011 at 19:35 #80857
nic
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@nic
Hi there,

I can’t measure any play in the spindle bearings, I have just tried locking all gib screws except the axis i’m traversing and those ones were done up extra tight and i’m still having the same problem.

All were very light finishing cuts, the aluminium is approx 75mm square.

Thanks
30 December 2011 at 19:40 #80858
JasonB
Moderator
@jasonb
How much of the 75mm side are you trying to cut in one go eg what length of the side of the 16mm cutter is actually cutting.

What speed are you using?

Any cutting fluid, if so what?
30 December 2011 at 19:44 #80860
nic
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@nic
Hi there,

At most 10mm depth.

1700rpm

WD40

Cheers.
30 December 2011 at 19:47 #80861
JasonB
Moderator
@jasonb
Try halving the speed.

J
30 December 2011 at 19:49 #80862
Jim Greethead
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@jimgreethead
Good question Nick, I have the same problem but I didn’t think to ask. I will be watching with interest to see if there is anything I can do to improve the finish. It could save a lot of filing and polishing.

Thanks for the interest Jason, I have a feeling that you might be able to help here as you have in other threads.

Jim
30 December 2011 at 20:52 #80870
Chris Gunn
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@chrisgunn36534
If you are running a 16mm cutter along the side of your block 10mm deep, each tooth is trying to take a 10mm long cut, even though it may not be a deep cut. When you are face milling each tooth is only taking a cut of a few thou.

This leads to chatter on a hobby machine, however good the set up and the bearings are. Every vertical miller I have had gives a similar result.

Industrial machines have a much better spindle than hobby machines and are much heavier all round.

The marks can be minimised by getting the speed right and taking a very fine cut to finish, but you will still get a ripple.

In the good old days a horizontal miller would have been used to mill the sides of your block, and you would then be back to a few thou a tooth and a good finish. The answer is, if the finish is vital, dont do it, turn the workpiece around and do it with your face mill if possible.

Chris Gunn
30 December 2011 at 20:59 #80873
Sub Mandrel
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@submandrel
I’ve notioced this on my X2, as the wavy effect is very regular and can be reduced by changing speed (up or down) I think its possible a resonance effect.

You could try changing your feedrate as well.

Neil
31 December 2011 at 10:53 #80906
mgj
Participant
@mgj
If its resonance, or flexing , then the other solution might be to change the number of teeth on the cutter. I know most endmills are 4 tooth, but some of the indexable ones have varying numbers of teeth, and you can often find 3 tooth cutters around.

One other solution might be to increase depth of cut, so that the helix of tooth A has not left the work before tooth B engages. That cuts down vibration and improves finish, if the size of job permits.(and the shape/helix of the cutter). The small FC3 cutters always seem to produce a very good finish, and that, I think is/may be one of the reasons.

I think its also important to realise when milling that the depth of cut is determined by the feed – or more specifically the tooth load per rev, so just because one is taking a deep (long) cut, doesn’t mean to say that the cutter is seeing a deep (big) cut. Tooth loads are generally within a couple of thou per tooth per rev – but then if you have a lot of teeth you can feed very fast. What may well be happening is that you are using too low a feed, and the cutter is skidding initially and then digging and engaging, so you end up with peaks and troughs. (and a blunt cutter can do this too – blunt cutters need higher feeds).

If you look at Tubal Cains book Milling Operations in The Lathe, the whole business of tooth load and feed rates is explained very well. Its getting a little long in the tooth, since it predated carbide cutters (toothload figures for which should be available from the suppliers, manufacturers web site), but its first calss on the principles one needs to understand, and where to start.
31 December 2011 at 11:12 #80908
Roderick Jenkins
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@roderickjenkins93242
I’d just like to reinforce MGJ’s recommendation of Tubal Cain’s book “Milling Operations in The Lathe”. This is a very good treatise on the technicalities of milling. I’m sure Tubal Cain would have written a book on vertical milling if Arnold Throp’s rather superficial “Vertical Milling in the Home Workshop” wasn’t already in the Workshop Practice series.

Rod
31 December 2011 at 11:59 #80910
Tony Pratt 1
Participant
@tonypratt1
Ric, as has been said try halving your speed to get rid of any resonance and check your spindle bearings aren’t too loose. Check that the axis you are using is correctly adjusted, smooth in operation but not tight or loose. Take a small cut with a sharp cutter in the conventional direction ie feed the work against the cutter rotation, then reverse the feed and go back across the machined surface[this is climb milling] without adding a cut, you may notice some small amout of material being removed and perhaps the finish improving?

Tony
31 December 2011 at 12:56 #80913
MICHAEL WILLIAMS
Participant
@michaelwilliams41215
Given that your set up is reasonably rigid and that the cutter is sharp the fine rack like cutter marks which you describe indicate that you are cutting on a dominant tooth . That is one tooth on the cutter is working much harder than the others . This arises sometimes when the cutter has teeth sharpened to variable depth or because the cutter is banana shaped but more commonly it is when any component of spindle , arbour , chuck , collet or cutter is running eccentrically .

This eccentricity only has to be very slight – half a thou will ruin the cutting action . This eccentricity may be in one component (cheap milling chuck is always favourite) or may result from accumulation of tiny errors in several parts .
1 January 2012 at 10:06 #80960
Jim Greethead
Participant
@jimgreethead
Thank you all for your good advice to Nic which I have also taken on board.

There are many things to try and I have found that a climb milling cut on the same setting improves the finish as does the use of WD40.

I have ordered a copy of Tubal Cain’s book and will examine it with pleasure when it arrives.

Ultimately, I suspect that Chris Gunn’s advice will prevail but I will have learned something on the way. And that is part of the pleasure.

Happy New Year to all of you.

Jim
1 January 2012 at 11:42 #80969
MICHAEL WILLIAMS
Participant
@michaelwilliams41215
Preamble :

If its a resonant effect it will occur at some specific speeds and not at others . Cutter will produce regular Moire silk like patterns superimposed on any other cutter marks .

If its an eccentric cutting action it will occur at all speeds . Cutter marks are usually sort of upright but can be sloped or curved backwards or forwards as well .

Tests :

(1) With proper regard to safety clock the cutting teeth on the end mill as installed in chuck and spindle .

(2) With a constant feed rate and depth of cut do some cutting at different speeds and note those speeds where the cutting action is good and those where it isn’t .

If cutting action is bad at some particular speed see in particular if it occurs again at the fifth and octave speed either side of problem speeds and disappears elsewhere .

(3) Listen to the machine and feel the sensation in the feed handles .

Eccentric cutter produces sound which is sort of bump-bump-bump at lower speeds . Also at lower speeds there can be a sensation at the feed handles as each bump occurs ..

Resonant condition usually produces ‘buzzing’ sound and feel .

Notes :

(a) It is perfectly possible for eccentric cutting and resonance to occur together .

(b) There are other possible causes such as loose quill problems discussed in a previous thread though this should be an unlikely cause on a new machine .

MW

Edited By MICHAEL WILLIAMS on 01/01/2012 11:54:23
1 January 2012 at 17:51 #81000
nic
Participant
@nic
Hi there,

Thankyou so much for your help so far, I have only just managed to get back to the computer, new year and all!

I will be reading through all your advice but in the mean time I came across this page:

http://www.practicalmachinist.com/vb/cnc-machining/surface-finish-issues-while-sidemilling-aluminum-118921/

Again I have not read all the way through it but someone does talk about a carbide end mill specifically designed for cutting aluminium.

I have gone ahead and bought one from ebay to eliminate the cutter being the problem and I will report back when it arrives, has anyone else tried this type of cutter?

Thanks again

Nic
1 January 2012 at 21:52 #81018
Jim Greethead
Participant
@jimgreethead
Hi Nic,

Thanks for the link, I did read all the way to the finish. He decided that the problem was that the taper was bellmouthed and that the solution to this (and other) problems was to have the spindle rebuilt.

But then we did not get the results from all that. A recent post has asked for the outcome so we may yet find out.

BTW, I get this type of finish and I also get it when I use a woodworking router bit to round off the edges of my engine bases. The bit is a two blade carbide so I was not surprised to see chatter marks. But perhaps it is just the limitations of the HM45.

I will be interested to see the results you get with the carbide end mill.

Jim
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