Rough Milling

[WolfieParticipant @wolfie]

Heres the pics, this is what set me off worrying about it again

I have since skimmed this again with an endmill that hasn't been used before. It was quite small though and took ages. Its a much better finish but is still showing a few circular lines.

This is what it looks like after much sanding, you can still see circles in the metal grrrr

This is what I meant by 'notches' in the mill ends, a bit blurry but you can make them out in the circles on the endmill on the right. It can't be blunt as its never been used, my collet set doesn't quite go that big. The endmill on the left is the one guilty of the messy milling this time. Note it only has one notch in it not all 4??

[Anonymous]

Hi Wolfie,

Good grief, that's a mess and a half! The 'notches' on the end of the cutter are a consequence of the clearance angles ground on the flutes. The fact that 3 of the notches are missing is down to non-existent quality control. Personally I'd say that the poor finish is due to poor quality cutters.

My advice would be to bin them and buy a cutter of a recognised professional make and try it before mucking about with mill itself. Assuming the workpiece is steel, what feeds and speeds were you using?

One other point; has the mill ever produced a good finish, and if so what changed when you started getting a poor finish?

Regards,

Andrew

[JasonBModerator @jasonb]

OK the notches are just the way the bit is ground, it gives a slight positive rake to the edges.

On the smaller cutter it looks like the corner may be worn, the one nearest the large cutter which has lost the coating.

But looking at the marks I woulkd say you have some play somewhere in the machine, it may be the gibs on the ways need adjusting or I think more likely the spindle bearings have bedded in a bit now and need some play taking out, as Ketan said there is a nut & lock nut at the top of the spindle to adjust the bearings. When the guy can to check it over did he actually take any test cuts of just see if there was anything out of line?

J

[Steve GarnettParticipant @stevegarnett62550]

Yeah, the circles are round – that's more than back cutting, isn't it? I agree with Jason – looks like a combination of issues here – both with the cutter itself, and the way the mill's set up.

[JasonBModerator @jasonb]

Andrew, this may answer your question to what changed from an earlier post in this thread

"There is no doubt in my mind that this mill hasn't cut as well since the bottom half (base, slides and upright) acidentally rolled off my workbench when I was trying to replace the depth stop of all things. It dropped onto a concrete floor……………………"

The circles would suggest the cutter is being pushed away from the work when making a cut but as Wolfie stops feeding the cutter spins in the same place and cuts more in that position. either due to bluntness or play

J

Edited By JasonB on 01/08/2012 19:56:39

[Michael GilliganParticipant @michaelgilligan61133]

If there are some [almost] full circles remaining "after much sanding" then methinks the cutter must be floating vertically. … So; either the quill or the main head is moving, or the bearings are not properly loaded.

MichaelG.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Wolfie ,

Cutters are not exactly blunt – more that cutting edges not shaped properly .

One tooth on cutter used is higher than the others and dominating the cutting . This tooth is also a little higher on outer edge than inner hence cutting sharp rings on the corner . Probably all the cutters have similar defect .

Cutter used is gagging . That is it is dragging swarf into the central area where it is temporarily trapped causing both scratch marks and causing cutter to randomly lift / clear / drop / repeat .

Cutters could be recovered with first a grind to reshape the cutting edges and then a sharpening grind .

Separate to the gagging effect the cutters are lifting and dropping randomly .

Investigate all potential sources of cutter lift in your machine . In any case lock as many things as you can when milling .

Apart from cutter lifting problem no sign of any major machine defects .

One incidental problem is operator hesitation – always keep a nice even feed . I think you may have been speeding up and slowing down and in one place you very briefly stopped .

Try using cutting oil next time .

Refards ,

Michael Williams .

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

PS :

When milling broad areas you will probably have more success in any case with a flycutter . Easy enough to make and easy to resharpen the cutters as often as needed .

[Harold Hall 1Participant @haroldhall1]

For me, the fact that some of the circles are continuous is significant, you do not normally get such pronounced circles as that with back cutting.

Even if the bearings need any end float taken out, the upward load on the spindle by the cutting action would help to keep it up, at least partially, providing that is that the feed rate is sufficient. If though the feed is taken off momentarily then the load is taken off the cutter and the spindle will have time to fall completely.

I feel therefore that it is possibly a combination of bearings needing adjustment and the feed not being continuous with the first being by far the most important.

When you get this sorted out Wolfie do make some test cuts both left to right and right to left to determine if there is any differences, such information information is all part of knowing your machine.

Incidentally, I know you are making my grinding rest, are you using 230M07 steel as I quote on the drawings? This is the same as the free cutting steel best used on the lathe. Other than round and hexagonal, it is only available in squares which is why much of the design is based on square material.

If you decided to purchase some other grade what is it? If though you purchased "bright mild steel", do not do that again as you have no idea what you are getting. If that is all the supplier quotes, go somewhere else for your material.

Harold

[NobbyParticipant @nobby]

HI

I agree with Michael . On areas like thet block a fly cutter would be ideal . & helps keep the cost down believe it or not but I sharpen 2 flute slot drills freehand but make sure the center is lower Ie like small fly cutter it works great for me

Nobby

[Anonymous]

Posted by JasonB on 01/08/2012 19:53:51:

"There is no doubt in my mind that this mill hasn't cut as well since the bottom half (base, slides and upright) acidentally rolled off my workbench when I was trying to replace the depth stop of all things. It dropped onto a concrete floor……………………"

J

Quite so, but presumably not including the spindle? Perhaps Wolfie can elucidate on this point.

Regards,

Andrew

[Harold Hall 1Participant @haroldhall1]

You state Michael ( W) " This tooth is also a little higher on outer edge than inner hence cutting sharp rings on the corner".

It maybe that I am misunderstanding this comment, if so my apologies, It is though essential that the outer end of a cutter's edge is higher than at the inner end. For want of a better explanation, the end of an end mill must be concave.

Harold

Edited By Harold Hall 1 on 01/08/2012 22:54:23

Edited By Harold Hall 1 on 01/08/2012 22:55:31

[Ady1Participant @ady1]

you can still see circles in the metal grrrr

Get a shaper… and be amazed by your incredibleness

 

My first ever job on a shaper almost looked like it had been finished on a grinder

 

IMO mills are for production line work

Do the job on a 2 ton mill then finish on a million pound grinder setup

Edited By Ady1 on 02/08/2012 00:53:17

[Ady1Participant @ady1]

you can still see circles in the metal grrrr

Witha shaper… you can shave some circles away… and leave the others as a pretty pattern

IMO there's no contest as a hobbyist

[JonParticipant @jon]

As Michael and Jason have stated theres movement in the machine or vice. By that a lot more than a few thou of spindle drop/play.

Used to have exactly the same problem on a Wabeco cnc mill, you could actually see the head and upright casting flex with gibs locked down. Of course this machine flex rapidly wears and or breaks cutters almost as quick as you can slap a new one in an ER collet.

Remedy was to junk the Wabeco and take a hit on £5k, we got £1k back 12 months old and put it towards a more robust cheaper machine from Chester.

[blowlampParticipant @blowlamp]

Can you do the test on a bit of brass and let us know what the finish is like. Some steel is hard to machine nicely and you might just have a piece of the more unforgiving stuff there. If you can try the brass, then I'd suggest you use a few different cutters and see how the finish varies.

Martin.

[Michael GilliganParticipant @michaelgilligan61133]

Wolfie,

As Michael (W) and Nobby have mentioned; a fly-cutter would have been better for that particular job … or, of course, you could have faced it off in the lathe.

BUT that's not really the issue here: We are trying to work out why this job went wrong.

As Harold and Martin have both said; it could have a lot to do with the material.

Follow Martin's suggestion and try milling a bit of good Brass [or some hard Aluminium Alloy] … you can check the quality of the material first, by facing a test-piece in your lovely lathe.

MichaelG.

 

Edited By Michael Gilligan on 02/08/2012 08:20:26

[JDEngParticipant @jdeng]

Wolfie,

Just thought I'd stick my two pennorth in.

What speeds and feeds are you using? From memory Presto recommend a feed of about 0.003" per tooth when end milling; this equates to 0.012" per rev. For mild steel using a 1/2" cutter this means running at about 750 rpm with a feed rate of 9" per minute. If you reduce the feed rate there is a tendency for the cutter to "rub" which results in poor finish and premature failure of the cutting edge. Coolant is useful if you have it; helps chip flow over the cutting edge and flushes swarf away. If you reduce your rpm you still need to keep the feed at 0.003" per tooth.

Make sure all slides except the one you are actually moving are locked.

What type of steel is it? Some mild steel is extremely difficult to get a good finish on due to poor or indifferent quality control.

If you want to check for play in bearings etc use a clock gauge if possible. It will give a reliable reading from a known point which makes it easier to assess what is (or isn't!) going on.

Regards,

John.

[mickParticipant @mick65121]

I've been a bit reluctant to post on this subject, as milling is such a complex topic, with everyone having their own theory, which I feel only goes to cloud the issue.

I know only too well what it feels like to be at the lower end of a complex learning curve, as I'm currently trying to master fishing with light rock tackle and my posts on fishing forums sometimes ask questions that turn out to be blindingly obvious.

Having looked at the photos the first thing to say is in order to produce a decent flat surface the cutter must be feed completely around the outside edges at a 50% step over and continue in this "conventinual" milling pattern at 50% step over untill the cutter reaches the centre of the job.

Next the cutter must be feed from left to right looking at the machine, this is known as conventinual milling.

To feed from right to left is known as climb milling, as you are in fact asking the cutter to climb over the work.

Lastly the choice of cutter. For this type of milling I would say sharp HSS milling cutters with coolant applied either by brush, or directed from an oil can are better. TicN coated cutters are designed to be used at high RPM and are ideal foruse on CNC machine tools and are not really suitable for use at low RPM.

I suspect I may have put the Puma amongst the Penguins here, but I feel this to be fundumental to the topic under discussion.

 

Edited By mick on 02/08/2012 09:34:25

Edited By mick on 02/08/2012 09:35:46

[WolfieParticipant @wolfie]

Posted by Andrew Johnston on 01/08/2012 22:34:23:

Posted by JasonB on 01/08/2012 19:53:51:

"There is no doubt in my mind that this mill hasn't cut as well since the bottom half (base, slides and upright) acidentally rolled off my workbench when I was trying to replace the depth stop of all things. It dropped onto a concrete floor……………………"

J

Quite so, but presumably not including the spindle? Perhaps Wolfie can elucidate on this point.

No the head wasn't on the body when it fell. Yesterday I dismantled the bottom half completely, cleaned all the slides etc put in new grubs for the gibs etc (why is chinese steel so crap?).

It was my club meeting last night and I took the newly skimmed block and my endmills. The general consensus was that the finish was as good as I could expect from a cheap mill and that the endmills weren't good. I'm not convinced though.

Harold it is 230M07 as required

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Harold Hall :

Specific cutter being talked about has one tooth significantly higher than the others . It is also ground in the concave way that you mention but ground concave much more steeply than is desireable – hence sharp corner . The one tooth is acting like a fly cutter – but not a very good one .

Never been very convinced about merits of grinding end teeth of end mills significantly concave . A few thou difference in height inside to outside maybe but no more . Relieving the central zone where the teeth come together is more effective for getting good cutting action and makes grinding much easier .

General :

Wherever possible I grind end mills with a radius on the tooth corners – need not be perfect but any rounding of the corner makes a big difference to cutting action and prolongs tool life considerably .

Any larger end mills ideally have teeth with two slopes ( not talking about concavity now but the actual chisel shape of cutting edges ) – one to form the sharp cutting edge and one much steeper one to provde clearance behind the tooth to clear swarf .

Regards ,

Michael Williams .

[David Clark 13Participant @davidclark13]

Hi Woolfie

Do you have an old cutter, a decent size?

If so, procede as follows.

Grind away 3 of the teeth.

Carefully sharpen the 4th tooth on the hand grinder.

Then put a small chamfer on the tooth, say 20 thou at about 45 degrees.

Carefully run all over the block with the cutter. That should give a good finish.

Basically, you would be using the cutter as a small flycutter.

Ideally, to get a good finish, a flycutter would be best.

Looking at the material, I think it is a crap bit of material. I used to get finishes like that on rough stuff.

Right, finish milling. When taking a fine cut, a couple of thou for finishing, I would go about 3/4 the width of the cutter and use the cutter so it is cutting into the edge (climb milling).

Then run back down the far side doing the same.

Then clean up the middle.

That way, you are pushing the material onto the work and there will be minimum burr.

Do it the normal way and the burr is thrown over the edge.

Climb milling is ok when you are only a thou or two deep and you nip the table lock up very lightly.

regards David

[Ady1Participant @ady1]

as milling is such a complex topic

There seems to be quite a bit of skill required to get a critical cut right on a hobbyist setup, particularly a decent finish

I do still mill on the lathe and find it particularly handy for making deep slots, but it's only for doing rough work and removing material

For finish and accuracy I use the shaper

[David LittlewoodParticipant @davidlittlewood51847]

Mick,

You correctly advised that climb milling should be avoided (except, as DC pointed out, for very small cuts) but your description of what it was is confusing. Conventional milling has the tooth sweep up the curved surface from what might be called the bottom of the cut; climb milling has the tooth hitting the top of the cut and sweeping down the curve and back.

The left-right and right-left bit is wrong; you can do conventional cutting in either direction: to move the metal L-R past the cutter, it must be at the front and the cutter behind, and R-L it must be at the back with the cutter at the front. Some people like to go round the outside and then inwards in a spiral, but I don't as I can only use power feed on the X axis, and that gives a much better finish.

David

Edited By David Littlewood on 02/08/2012 11:06:59

[David Clark 13Participant @davidclark13]

Hi David

I industry, we always milled standing at the right of the machine and the work went from left to right.

That way the swarf is thrown at the machine column and the wall, not at the operator, me.

Hence the tilt of the head in the direction suggested.

regards David

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