Milling Problem

HBilly1022

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I wanted to make a hex ER40 collet block and mounted a piece of mystery steel in the RT chuck, with TS support but I couldn't take very many cuts before the end mill was dull. I have 2 - 3/4" HSS end mills and dulled both of them in only a few short passes on this stuff. I resharpened both and tried again with the same results. I can't get 3 - 0.025" DOC passes over this short piece before the end mill is dull again. Here are a couple of pics.

First one is of the first 0.025" with a freshly sharpened end mill.
1510456235928.png

this one is of the 3rd 0.025" pass (ie a total DOC of 0.075") and I couldn't finish it.
1510456428814.png

I turned this stuff down from some 2 1/2" rusty round bar and it didn't seem to be unusually hard. Yet I can't mill the stuff. Any ideas?
 
What RPM are you using? Are you using any coolant or cutting oil?

On your end mill, your primary grind looks a little wide, should only be about a max of .030"-.040". The nasty burr it's leaving is telling me that your primary and secondary angles may not be great enough, that could be causing the endmill to dull quickly. Not knowing what kind of mill you are using, for me, I would take the entire cut, leaving about .010-.015" for a finish cut, instead of stepping it as you have done. Your RPM's should be around 200 give or take a little and fee as much as the machine will handle along with some kind cutting oil or coolant. Ken
 
You didn't mention your RPM. That (and cutter diameter) will give your surface feet per minute. That could be critical.

-brino
 
Gotta use oil for sure and a slow speed. If you had a cobalt M42 end mill it would help a lot- a roughing mill for example
Mark S.
 
How did the chips on the lathe cuts act and color , what tool hss or carbide.? If you cut it on lathe it'll cut on mill. Try a fly cutter with carbide lathe tool .
 
Thanks so much for the reply's. I'll try to answer all of the questions.

The end mill is 3/4" diameter HSS with 4 flutes, it was running at 475 rpm, which is close to what I calculated using the typical formula (did I get it wrong?). I started the feed at about 5" per minute but quickly slowed way down because the chips started coming off blue. The thing I find weird is that these are the same end mills I used to surface a 4" x 6" block of steel yesterday and that went well using the same speed and feed rates, using one end mill for both sides. Different piece of material though. The end mills were sharpened using the same jig, with the same angles, for both projects but for some reason this one is not going well.

The mill is a King PDM 30 ( same as an RF30 / 31, I think).

I'm not using any lube or coolant. I don't use any on the lathe either and it seemed to work ok there (not an excuse; just pointing out the way I do it .... right or wrong). Although I did have to resharpen the HSS cutter many times during the cutting operation. Is there something I can brush on? I'm not set up to use flood coolant on either machine.

Ken, I'll check the width and angles tomorrow.
 
it was running at 475 rpm, which is close to what I calculated using the typical formula (did I get it wrong?)

Nope not wrong, I get about 400 rpm for those parameters too.

Is there something I can brush on?

For cutting steel, I use a can of this from the local hardware store in the area with black pipe and fittings.
They sell it for pipe threading.
http://homehardware.ca/en/rec/index...7n/No-216/Ntk-All_EN/R-I1142043?Ntt=oil&Num=0

-brino
 
My methods are not always perfect, but I would definitely be using some sort of coolant or cutting fluid. You might want to build or purchase a no fog coolant mister and use something like Koolmist or Rustlick Syncool. Optionally, you can use a cutting oil like Mobilmet 766, available from Amazon, McMaster-Carr, or MSC. Another cutting lube that works very well, especially on hard materials, is Anchorlube. It is a green paste-like substance that you brush on, a bit expensive, but great stuff just the same. If worst comes to worst, you can always use plain old dark cutting oil, often available at your local hardware store or plumbing supply. It tends to smoke quite a bit though and creates a rather nasty smell in the air, definitely not recommended if your shop is in your basement.
 
From reading this thread. I would think the endmills do not have the right reliefs. That or the material is work hardening from lack of coolant.
 
How big a bite are you taking (depth of cut)? If your end mill is dulling quickly can you be rubbing on the work and not really cutting?
 
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