Carbide mills on slow spindles

[Martin DowingParticipant @martindowing58466]

[Martin DowingParticipant @martindowing58466]

HSS mills are increasingly replaced by carbides and it may not be long before they are not easy to get, particularly those smaller diameters.

Yet if you have a slow spindle (my will go up to 1250 rpm) then carbides are not really good as they chip easy.

Even 1/4 inch carbide need something like 2500 rpm to work efficiently.

I have tried to buy 1/4 inch HSS bits from China.

I found an offer specifying $5 each, so got few. It was described "high speed tungsten steel" and you guess… carbides came.

Any ideas how to make intelligent use of them on slow spindle?

How fast plain bearing based on phosphor bronze and hardened spindle of 1-1/4 inch diameter can run?

My friend have tested one of these carbide mills at 3000 rpm on mild steel and it works really well.

What is a slowest rpm at which such 1/4" carbide mill can run without excessive risk of being destroyed on both mild steel and stainless?

Edited By Martin Dowing on 02/11/2020 12:40:15

[JasonBModerator @jasonb]

You should not have problems running them at HSS speeds of say 25-30m/min. (thats about 1250rpm with a 1/4" cutter) Have a watch of this to see that they work perfectly well and even cut better than HSS. Your machine is more likely to be what affects the cutters you can use rather than the cutters themselves, though who knows what you are getting with cheap "carbide" which could be another reason for them chipping..

Though I think 1/4" and other imperial sizes will become harder to get in teh future but  HSS metric cutters will still be easily available

 

Edited By JasonB on 02/11/2020 13:17:37

[Anonymous]

Posted by Martin Dowing on 02/11/2020 12:22:14:

Even 1/4 inch carbide need something like 2500 rpm to work efficiently.

Dunno where that came from but it's just plain wrong.

Carbide inserts for turning and milling often need minimum speeds, depth of cut and feeds to work properly. But the same is not true for "solid" (*) carbide cutters.

A 6mm carbide cutter will be fine at 1200rpm, provided the chip load, and hence feedrate, are appropriate. Of course the cutters can be run at higher spindle speeds, but it's not essential.

Charts from YG (sold by Cutwel) for their basic carbide cutters give a chip load of 0.018mm/tooth for low carbon steel and 0.019mm/tooth for stainless steel. Assuming a 3-flute cutter at 1200rpm that's a feedrate of about 66mm/min.

I don't see a problem with chipping on carbide cutters, although I use professional cutters. The biggest problem with cutters of any sort is too low a feedrate, spindle speed is way down the list.

Most commercial suppliers still sell HSS cutters, although as Jason says they're usually metric diameters.

Andrew

(*) Solid carbide cutters are not solid carbide, they consist of very small tungsten carbide particles in a metal (usually cobalt) matrix.

[Ady1Participant @ady1]

Chipping carbide at low speed often has two reasons on a hobby machine

Feed rate too high and a lack of stiffness

You can compensate for both with a slower feed rate

[OldironParticipant @oldiron]

Quote "It was described "high speed tungsten steel" and you guess… carbides came."

If I wanted HSS I would order HSS not Tungsten steel. The description Tungsten is most usually Tungsten Carbide.

Best to check that you know the description of whatever you really need to order. We used to get this all the time at the hydraulic company. Customer orders item A when it is sent and received they suddenly decide they needed item B. Could be a very costly mistake as we made many items to order. Always check the suppliers description as many just buy and sell on items and use the "usually Chinese" description which is not very accurate.

regards

[Martin DowingParticipant @martindowing58466]

Posted by Andrew Johnston on 02/11/2020 13:28:50:

carbide inserts for turning and milling often need minimum speeds, depth of cut and feeds to work properly. But the same is not true for "solid" (*) carbide cutters.

These are good news for me. I don't have much troubles with carbide inserts. They are running well on my machine including those from boring bars for indexable inserts while drilling 15mm holes and 40mm end mill for indexable inserts which can take 4mm cut in cast iron with a little squeaking but nothing chips.

I have broken sharp tips of solid carbide stub drills though and this observation was discouraging me from trying carbide mills.

So I will give a go for my new carbide mills. Maybe they are going to work and my problem was a bit psychological in nature.

Mind you, whats wrong with these sharp pointed carbide stub drills that their tip is getting broken so easy?

@Oldiron,

Very often it is impossible to find out what Chinese guy will sell you before you get it.

OK, HSS you can recognize by photo but if you are offered TiCN coated end mill described as "hight speed tungsten steel" selling well below a price of regular HSS here you are not suspecting that carbide will come.

Mind you, these mills are of rather high quality as determined by guy with big rigid machine.

[larry phelan 1Participant @larryphelan1]

With all the slagging you guys give the Chinese, it,s no wonder they get their own back by sending you the Virus post free !!

[JasonBModerator @jasonb]

Posted by larry phelan 1 on 02/11/2020 17:20:54:

With all the slagging you guys give the Chinese, it,s no wonder they get their own back by sending you the Virus post free !!

It's the cheap and nasty we are slagging off, not Chinese in particular. You can buy poor quality just about anywhere.

[Mick B1Participant @mickb1]

I treat my carbide endmills much the same as HSS, even though I know they can stand higher speeds. The finish they give is much the same, their sharpness and durability lots better. I mostly use an 8mm carbide endmill, and rarely exceed 1100 rpm.

[old martParticipant @oldmart]

I mostly use carbides as I am frightened of making HSS blunt and then being unable to sharpen them. I do use hss on aluminium with lubricant. Something to be careful of when handling carbide, they will be damaged if you drop them on the mill bed and the ends can chip if you touch down on steel when stationary.

[EmgeeParticipant @emgee]

I use mainly carbide but also get very good finish with HSS, sizes used from 16mm to 1.6mm slot drill, the max spindle speed is 2000rpm which I use with the small cutters but the feedrate may be as low as 25mm/min with 1.5mm DOC for some jobs using 6082T6 and 7075T6 aluminium.

Go to 5 mins in the video to see the 1.6mm slot drill cutting, finished ports in the picture.

Emgee

**LINK**

Edited By Emgee on 02/11/2020 19:26:55

[Anonymous]

For low carbon steel on the Bridgeport I'll run a 10mm cutter at 2000rpm and a 6mm cutter at 2500rpm. Could run faster but the Bridgeport gets a bit shake, rattle & roll at higher speeds.

On the CNC mill I'll run a 10mm cutter at 2200rpm and a 6mm cutter at 3800rpm. They seem to cut smoothly, if you get the feedrate correct, and leave a good finish.

The finish on these parts is straight off the mill:

Andrew

[Anonymous]

Posted by old mart on 02/11/2020 19:14:16:

…………the ends can chip if you touch down on steel when stationary.

Too true. I got so cheesed off chipping cutters when touching off on the CNC mill I bought an electronic tool heighht setter to deal with the problem once and for all.

Andrew

[Martin DowingParticipant @martindowing58466]

So what is wrong with solid carbide stub drills with sharp point? They look like regular twist drills but have a sharp point and are ground to 90 or even 60 deg angle.

This pointed end is so easy to chip off that I don't even know how to use them without breaking them.

This was discouraging me from using other carbide drills and mills for quite a while.

[Anonymous]

Are you sure they're drills? A quick look at my drills shows that carbide drills from a 10mm spot drill down to 1mm slow helix are all ground as per a normal drill – no sharp points. One carbide "drill" does have have a sharp 60 degree point. But it's not a drill; it's an engraving cutter.

Andrew

[old martParticipant @oldmart]

They sound like spotting drills, all the solid carbide twist drills I have look like regular hss drills.

[Clive HartlandParticipant @clivehartland94829]

Ifind the highly polished carbide shanks slip easily in the collets particularly poor quality collets. They pull down and cut the table.

They cut well and give clean surfaces for me, Mine are of Swiss make bought from Cromwell.

[JasonBModerator @jasonb]

Martin, a lot of carbide drills for harder materials have an blunter end of 135 deg, that may be why you are having problems in your other thread. Something like this would likley give a hole that would not even need reaming. If whatever you are using to drill with has any play then that may also be causing problems.

Clive are your cutters Swiss+tech, if so they have not been near Switzerland, Chromwell/zoro get them from China though they are to a reasonable quality

Edited By JasonB on 03/11/2020 07:16:35

[Clive HartlandParticipant @clivehartland94829]

Hi Jason, yes, Swiss tech. very good for what I do.on the Seig X3.

[old martParticipant @oldmart]

A little bit of rubbing on the shanks of the cutters with a very fine diamond lap would improve the grip in the collets. Remember to hold the sharp end in some old rags to protect your fingers.

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