Using Carbide Milling Cutters

[DaveH]

How to use Carbide Milling Cutters

Carbide milling cutters are becoming more and more prevalent in the Home Workshop. So with the Home Workshop in mind may I offer the following.

Carbide cutters are used extensively in Industry, they remove material 2 – 3 times faster than HSS this is one of their main advantage to industry.

Carbide cutters are very hard but brittle and one sure way to break them is SHOCK.
Mechanical shock
Thermal shock

Mechanical shock – When the cutter first starts cutting you must take it easy, feed it in slowly. Once it is past it’s ½ diameter into the work piece then you can increase the Feed. Also when exiting the work piece slow down – take it easy.
   
Thermal shock – Spraying the hot cutter ( the cutting edge might be hot) with the occasional fluid will kill it. Not necessarily immediately but it causes ‘micro cracks’ which lead to eventual breakage.   
So it is really a FLOOD coolant/cutting fluid or NONE

Using a carbide cutter.
So how do we use them – Use the same Depth of Cut you would for your HSS cutters increase your Spindle speed by 50% so long as your mill is not vibrating too much – more if your mill is happy but be careful. Now it is possible to increase the Feed because your spindle speed has increased.  That being said you don’t have to increase spindle speed keep it has you do for HSS cutters with the same Feed, they will last (stay sharper) longer.

Chips (with everything) – Get rid of them, applies to HSS cutters as well. They cause bad finishes and can break your cutter. One way is to use a low pressure blow. Another way is to use a small brush (paint brush) but be very careful the bristles can easily get caught although no damage may result – it will make you jump.

Small diameter cutters below 3mm diameter may break so I only use a low pressure air blow to clear the chips it is really important to clear the chips away on small diameter cutters otherwise breakage will occur, especially with carbide mills.



Some use a cutting fluid (not a coolant) this is applied to the area to be cut first before the mill starts cutting, the cut then proceeds. At the end of the cut and stopped clean the mill and the work piece of any chips, and repeat the process. This can be beneficial with finishing cuts. Extreme care is required in cutting closed slots as the chip build up can be much greater and really needs to be cleaned out with a low pressure blow continually.

Feel free to ask, I may not be able to answer but someone will 
 

Happy Milling  

DaveH

[slowcoach]

Great write up DaveH  , I use carbide cutters at work and yes you have to exercise caution when using them to stop them from breaking, I find that when flooding with coolant it's really difficult to see the job your cutting, so I use the method you mentioned in your post and use a cutting fluid when manually milling with them and then clean chips away before the next pass.
I hate breaking them, because then I have to take the long walk to the boss's office to order another, It dont go down to well 

Rob

[DaveH]

Rob,

Just great minds .......... that's all

I hate breaking them, because then I have to take the long walk to the boss's office to order another, It dont go down to well 
Rob

Tis the shelling out of money that tick's me off

DaveH

[sparky961]

I've never had a lot of luck machining steel with HSS end mills.  I don't think I have the patience and my machine is not at all rigid.

With that said, I find with carbide 4-flute end mills I can just buzz right through it almost as easily as aluminum with a HSS end mill.

I was a bit anxious to try this, but I figured I had little to lose and everything to gain.... I decided to crank my mill to it's maximum speed (3k RPM) with a 1/2" solid carbide end mill, and see how well it cut some 44W HR material.  With my teeth clenched, and my full-face shield on, I carefully entered the material taking about 1/8" deep cut.  I sped up the feed gradually, more ... and more ..... and more and more..... and wow, I was just zipping right though the stuff like it was butter!  There did seem to be an upper limit to my feed where the machine wanted to shake violently, but just below that and it just purred along spitting hot chips everywhere.

YMMV, but I find machining steel dry works reasonably well.  We'll have to see how the tool life treats me, but I'm not trying to get production-style life out of my tools and I'm not noticing any problems yet.

-Sparky

[Bogstandard]

Very nicely composed and explained Dave. 

There are lots of myths and legends that surround different types of cutting materials, you have now dispelled a few of them. 


Ralph and myself had a session yesterday afternoon with two sets of jaws off his 3 jaw chucks. Cutting back the angled sides of the tips so that he could regrind them without leaving too wide a gripping face.

One good quality carbide cutter soon had all twelve faces cut down to perfection just by listening and looking at how it was cutting, with no coolant or lube used at all. The cutter was untouched and the surface finish on the jaws was like it had been done on the surface grinder, but done in a fraction of the time and a lot less trouble.

This was one of those times when carbide was the only real solution, and he has already let me know that our work wasn't in vain. He burned the midnight oil last night and reground one set of jaws, and up to now, at least one dead chuck has been resurrected to live another day. 


John

[DaveH]

Sparky,
   I like the full face shield. Purring is good.

John, Thanks

DaveH

[DaveH]

Just a little more on milling in the Home Workshop.

It is important to Look, Listen and Feel your machine,  John has an industrial milling machine (don’t know about Sparky’s machine) nevertheless John said in his post “listening and looking at how it was cutting” This is one of the most important parts of milling, if the machine seems happy then all is good. If the machine feels jerky, noisy, and is vibrating, then reduce the depth of cut, still vibrating reduce the spindle speed.

Always start with a slow spindle speed and a small depth of cut with a low feed rate.

Just remember slow spindle speed “equals”  small depth of cut. You cannot have a big depth of cut with a slow spindle speed.
So to increase the depth of cut the spindle speed nearly always has to increase, this can cause vibrations, so we are in a bit of a catch 22 situation. This is where the rigid Industrial machines score.

All milling machine are different some perform well at 3000 rmp, 6mm cutter ½ mm depth of cut, some wont. Some are happy at 1000rmp,12mm cutter ½ mm depth of cut.

So fast / slow are relative to your machine

Look, Listen and Feel.  Take care of your one good eye.

 
DaveH