Milling – What am I doing wrong

[Chris GunnParticipant @chrisgunn36534]

Petrol head, If I were making tee nuts as you illustrate, I would start the "Perfect" side from the opposite end so feeding from right to left so the feed is going in the opposite direction than the cutter is trying to drag the work, and then tackle the opposite side in the reverse direction from left to right. Having the collet and quill locked up is essential too.

Chris Gunn

[Neil WyattModerator @neilwyatt]

Ah crossed posts! I suspected a loose quill.

If you have knocked off the sharp points of your end-mill don't despair, a quick and dirty fix from Tubal Cain is to relieve the corners to make a small facet at a 45 degree angle with a bit of relief*. You can't cut into a square corner and leave a sharp angle, but fine for most jobs (and a tiny fillet in a corner is often a good thing as it eliminates a stress riser).

Neil

*I've never had to resort to this…

[duncan webster 1Participant @duncanwebster1]

Your width of cut looks too wide. You should have no more than 1 tooth cutting at once, which more or less means the cut width should be less than 1/4 of cutter diameter. Half a millimeter depth of cut is very small, and is concentrating all the cutting on the corners of the end mill. To echo Martin Connelly, if your feed rate is too slow the cutter wil rub and go blunt very quickly. Aim for 0.004" per tooth per rev.

As a newcomer you would do well to buy a copy of either Arnold Throp or Harold Hall's books, they cost about the same as a coupe of cutters and will save you lots of blunt ones

**LINK**

**LINK**

[JasonBModerator @jasonb]

As you like a picture here are a couple of videos I did for another query, you can see the sort of feed rate I'm using, cutter is not as good as the Arc ones but leaves virtually no burr and makes decent size chips not iron filings. Slightly less powerful X3 mill

6mm wide cut, 16mm dia cutter 2mm deep EN3 steel, 750rpm

This time 2mm deep and a bit slower at 500rpm

Edited By JasonB on 03/03/2017 20:46:03

Edited By JasonB on 03/03/2017 20:48:17

[Chris Evans 6Participant @chrisevans6]

After 50 years of Bridgeport operation with R8 collets I know it takes a while to get the feel of how tight to tighten the cutter. Best to strip a draw bar thread than have a cutter pull down into the table. If I have any concerns of this happening I use a Clarkson chuck.

[SillyOldDufferModerator @sillyoldduffer]

I see petrolhead is using a cutter with a side slot in the shank. I have ER32 and have always wondered if that type are OK used in a straight collet, or is the collet's grip weakened by the slot? .

Dave

[petro1headParticipant @petro1head]

Jason were both Test Cut 1 and 2 at 2mm?

[petro1headParticipant @petro1head]

Posted by duncan webster on 03/03/2017 20:36:23:

Your width of cut looks too wide. You should have no more than 1 tooth cutting at once, which more or less means the cut width should be less than 1/4 of cutter diameter. Half a millimeter depth of cut is very small, and is concentrating all the cutting on the corners of the end mill. To echo Martin Connelly, if your feed rate is too slow the cutter wil rub and go blunt very quickly. Aim for 0.004" per tooth per rev.

As a newcomer you would do well to buy a copy of either Arnold Throp or Harold Hall's books, they cost about the same as a coupe of cutters and will save you lots of blunt ones

**LINK**

**LINK**

Any views on this book – **LINK**

[Mark RandParticipant @markrand96270]

Posted by petro1head on 03/03/2017 18:29:51:

I was take a .5mm cut. (when everthing is working fine could I take a deaper cut?

 

A good rule of thumb to work with is the full diameter of the cutter in width and half the diametar in depth or half the diameter of the cutter in width and the full diameter in depth. That'll give a reasonable load for an HSS cutter. or pro-rata!

In general, try to use as much depth as possible, since that's using more of the cutting edges on the flutes. the more use you get out of the sides of the cutter, the more metal you can remove with it before the corners go blunt and you have to get a new one.

Carbide can be worked harder.

Edited By Mark Rand on 04/03/2017 00:42:28

[JasonBModerator @jasonb]

Posted by petro1head on 03/03/2017 23:21:30:

Jason were both Test Cut 1 and 2 at 2mm?

Yes, if you look at the DRO after the first cut it was adjusted from 2mm to 4mm for the next cut and then at the end of the only cut in second video it is at 6mm. There is also a third video 19mm high and taking off 0.6mm

 

What diameter was teh cutter you were using?

Edited By JasonB on 04/03/2017 08:03:18

[RichardNParticipant @richardn]

Posted by petro1head on 03/03/2017 23:25:43:

Posted by duncan webster on 03/03/2017 20:36:23:

Your width of cut looks too wide. You should have no more than 1 tooth cutting at once, which more or less means the cut width should be less than 1/4 of cutter diameter. Half a millimeter depth of cut is very small, and is concentrating all the cutting on the corners of the end mill. To echo Martin Connelly, if your feed rate is too slow the cutter wil rub and go blunt very quickly. Aim for 0.004" per tooth per rev.

As a newcomer you would do well to buy a copy of either Arnold Throp or Harold Hall's books, they cost about the same as a coupe of cutters and will save you lots of blunt ones

**LINK**

**LINK**

Any views on this book – **LINK**

I don't have that book- but I believe it relates more about what machine and accessories to buy, whereas '35 Milling a Complete Course' **LINK** is excellent about techniques and skills, although primarily with a series of useful projects to make…

[Martin ConnellyParticipant @martinconnelly55370]

Harold Hall's website has a list of the contents of this book.

**LINK**

You can see if it suits your needs.

Martin

[petro1headParticipant @petro1head]

I was using a 14mm cutter.  Cutting 7mm wise which is the same width as one edge on the cutter

Bought Harold Halls book

 

Edited By petro1head on 04/03/2017 09:33:00

[petro1headParticipant @petro1head]

I removed the tool and took a couple of photos. oh dear its fooooked

So so far I have learned that I need to lock the quill etc. I must only take a max of one flute width off. I need to feed into the direction of the rotating tool. This however leads me to a question, on the job I was doing the bottom was correct, feeding into direction of rotation but how would you do the top?

I needed to machine down a total of 12mm, should I be taking heaver cuts, ie 2mm each time (Jason?)

I am going to need a new 14mm cutter, should I buy another HSS from ARC or a carbide cutter?

 

 

Edited By petro1head on 04/03/2017 09:47:07

[RICHARD GREEN 2Participant @richardgreen2]

In the first picture on this thread, the cutter is not square to the work, perhaps a swivelling head is rotating due to the feed forces,

[petro1headParticipant @petro1head]

Posted by RICHARD GREEN 2 on 04/03/2017 09:48:57:

In the first picture on this thread, the cutter is not square to the work, perhaps a swivelling head is rotating due to the feed forces,

I think its just a bad photo. Everthing was setup before use, but will check just in case, thanks

Edit: Just check and its ok

Edited By petro1head on 04/03/2017 10:16:42

[John RuddParticipant @johnrudd16576]

 

Here is my advice fwiw, others will no doubt tell you different.

I would in no particular order,

Buy a roughing mill cutter from Arc ( they are the dogs at removing metal fast)

Insert cutter into chuck and tighten.

Align new work piece.

Set the cutter for the first cut, lock Y axis and Z axis, use a reasonable cutting speed, and a decent feed rate. Listen to the machine, it will tell you if the feed is too fast or the speed is too fast ( or the opposite… ) ok this is subjective because you are inexperienced, but its a learning curve….

You may need to take several cuts to get near to size.

Once you are close to the finished size ( 10 thou….) use a normal 4 flute cutter to clean up to finished size….

Turn the part around and start the 2nd face/side whatever…..

In one of HH's books, there is an excercise on producing tee nuts, you'd do well to heed his instruction ( milling a complete course?)

[Anonymous]

Posted by petro1head on 04/03/2017 09:46:11:

…………. I must only take a max of one flute width off. ………..

That's wrong; you can take whatever width is required, although 50% is about the worst value to use. Width of cut should generally be less than 40% or more than 60% to minimise shock loading of the teeth. For shallow facing cuts I normally use around 75-80% WOC.

However, if you need to take off a depth of 12mm I'd be inclined to take pretty much full depth each pass and use smaller widths of cut. You're paying for the full length of the cutting flutes so you might as well use them rather than always use the bottom millimetre or two.

There are several rules associated with cutting tools:

1. Don't buy cheap cutters, they are often badly ground, will never give a good finish, and don't last

2. See rule 1

3. Cutters are consumable items -don't tiptoe about trying to make them last for ever, you'll just wear them out quicker

4. As mentioned above feedrate is single most important parameter – most people run too slowly with the result that the cutter rubs rather than cuts

For your case of a 14mm cutter I'd be running at 800rpm and 200-250mm/min feedrate.

Give it some welly! The same rule applies to chatter. Many people instinctively slow down, often the solution is to increase feedrate and make the cutter work. You're inevitably going to break cutters at some point, it's part of the real world learning process. Get it over with quickly and learn from it.

Andrew

[petro1headParticipant @petro1head]

Hi John, thanks

What be a good size rough cutter to buy?

I have ordered the book

[mechman48Participant @mechman48]

Hi

FYI …

​… from Model Engineers Handbook… Tubal Cain, 2nd edition

George.

[petro1headParticipant @petro1head]

Thanks, rotated so other may read it

[MuzzerParticipant @muzzer]

Strange advice from TC. Clearly practice has changed, as tooling and machine technology has evolved. Plenty of examples of end mills taking much deeper cuts out there, including slotting at 100% width.

For what it's worth, Mercans don't recognise the concept of the "slot drill" – everything on the other side of the Atlantic is an end mill although of course they have centre-cutting versions and the same choice of numbers of flutes.

Part of the learning process is exploring the limits of your machines. I suspect that machine could remove a lot more metal if the width and depth of cut were increased. At some point the motor will stall or the possibly the tool will break but before then it's likely that a glorious rate of removal will be seen. One clue might be the rating of the motor – how could you get anywhere near the rated power without taking enough of a cut?

My Bridgeport clone has a fairly modest 1.5hp motor but I have made full width slotting cuts with 12mm 3-flute HSS cutter at a depth of 15mm or so, using power feed for a consistent load. That was pretty much the limit and I used coolant otherwise I suspect the tool might have overheated before the full length of the lot was completed (about 300mm, roughing out a tee-slot). You may be surprised what your machine can achieve.

As pointed out, you should try to use as much of the flute edge as possible, otherwise most of your cutters will wear out near the corners and you will be paying for something you aren't using. And failing to take a heavy enough cut will increase wear due to rubbing, particularly if you use conventional milling. Climb milling isn't a problem if you tighten up the gibs just enough to overcome the self-feeding.

Murray

[BazyleParticipant @bazyle]

When Tubal Caine was writing no amateur had a one ton Bridgeport but would be using a 1/2 HP lathe with vertical slide or if lucky a Dore-westbury. Yes, times have changed.

A word of caution. When you move down to a 3mm cutter don't go hell for leather late on Saturday if you haven't got a few spares already in stock,

[John RuddParticipant @johnrudd16576]

If you can afford it, buy the full set….

I got a bit of discount doing it that way…

[Nick HulmeParticipant @nickhulme30114]

Posted by Martin King 2 on 03/03/2017 17:51:09:

Look up 'climb milling' that is whats wrong I am pretty sure.

It's about the cutter climbing into the cut in the X or Y plane, nothing to do with Z axis on a vertical mill

Edited By Nick Hulme on 04/03/2017 11:27:47

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