End Mill isssue

[Todd_71]

Ok I have a newbie question.

I was playing around making some chips fly last weekend. I was playing with end milling and side milling with a 3/8" and 1/2" HSS end mill on a piece of 2" thick mild steel. I was side milling and getting a fair amount of chatter (enough to shake things and feeling it in the table). So much I was afraid I was going to break damage something. Just a .010 cut would be make things pretty rough. Additionally as proceeding with the cut the end mill would start slipping out of the collet.
I tried varying the RPM between 700 and 1200 RPM but I never felt good about the way it was cutting.
I will note that the surface was rough and uneven (I was trying to square things up).
I pretty much destroyed one end mill. My fault probably going to fast.

Things I have tried so far:
I bought a spindle wrench to help facilitate getting a good hold on the end mill. I cleaned up the collet to ensure it was free of oil, using a couple blasts of CRC. I using collets that bought with the mill from QMT. I gave it another try last night and I think it is better (using the spindle wrench to get a bit more torque) but I still seem to be getting some slipping of the end mill in the collet. I'll try a new end mill today when it arrives but was hoping for some feedback if anyone has any.

My question is should I get an end mill holder rather than using collets?
Should I use roughing end mills for uneven surfaces?
What is a good reference for how deep a cut I can take when end milling & side milling.

I'm good with trial and error but hate to spend more than I need too.

 

[T Bredehoft]

We need a bit more information. What is your mill? Is it heavy enough for what you are doing?

3/8 end mill in mild steel, no faster than 800 rpm, 1/2 end mill no faster than 700. The heat generated will anneal the cutting edge otherwise. Cutting aluminum, with a bit of something to lubricate it, any speed is possible.

Length/depth of cut, this is a function of the solidity of your machine. I would not expect my PM25 to be able to take a reasonable cut with a 2 1/2 inch long 1/2 inch end mill. It would chatter. I would expect it to take one inch in aluminum, but not in steel.

 

[mikey]

Todd, a bit more info would help us to help you:

• Which mill are you using and are the gibs adjusted well?
• Were the end mills in good condition or worn?
• What kind of collets are you using?
• Were you conventional milling or climb milling?
• Were you feeding manually or power feeding?

In general, a collet will be more accurate than an end mill holder. Roughing end mills are better for roughing, which is what you were doing. For some general guidelines on speeds/feeds for different materials, see the third post in this thread: http://www.hobby-machinist.com/threads/milling-speeds.55436/

 

[Billh50]

Also check the sharpening of the endmill. I have gotten some were they had no relief at all. Especially some of the cheap no name brand end mills. drills are even worse. Buddy of mine bought what he thought was good deal on a set of drills. The relief on all of them was the wrong way. Had to resharpen every one of them.

 

[jlsmithseven]

A 6" vise is overkill for a RF45 style mill. A 4" is more appropiate for that size mill & IMO 5" max. I have a 5" GMT vise on my PM45 & it's slightly too big. Not enough Y axis travel to make use of the 5" full capacity. Better to save your money rather than getting something too big & most importantly the weight. I take my vise of the table quite often, a 6" is still light enough for me to be carried by hand but I'm glad I have a 5". I also have a 4" vise as well. I prefer the 5" though.

But those GMT 6" Premium vises are pretty nice. I'd love to have one but don't need one on my current mill. But if you plan on upgrading to a full size knee mill in the future than the 6" will be perfect.


Here's what the 5" looks like on my mill.



I couldn't even complete this cut without my bellows & DRO scale getting in the way. Not enough Y travel & the 5" vise is not even maxed out.



Here's what a 6" vise looks like on another PM45 (gt40's)
View attachment 253544

 

[Todd_71]

• Which mill are you using and are the gibs adjusted well? > PM932V which is essentially the PM932 PDF with variable speed. As for the gibs, I think so but I haven't played with them honestly since receiving the machine.
• Were the end mills in good condition or worn? > Brand new
• What kind of collets are you using? > Not sure what brand. I purchased them from QMT when buying the mill.
• Were you conventional milling or climb milling? > Started with conventional, but I also tried climb. Climb seemed a bit better actually but I took a smaller.
• Were you feeding manually or power feeding? > Manually

 

[Todd_71]

Good question. Let me help you out since I have experienced similar things. I'm in my second semester at school but I've definitely been where you are.

Let me make this simple for what I think is happening.

1) I think your draw bar in the machine is bad. Can you see the top of the draw bar and how it spins? If it's going haywire, that could be your issue.
2) I usually use my .750 HSS end mill when I'm side milling my ends, especially on saw cut material where it's very rough. A roughing end mill used instead could remedy your problem though. You can take .040 passes with that thing if you want, then clean it up with the 3/8" end mill.
3) You are climb milling and not conventional milling. I can definitely feel the difference If I'm climbing vs conventional.
4) Make sure your end mill is spinning clockwise.

Solution: Use a collet with a 1/2" or bigger roughing endmill. Clean up the sides and tops with it until you're relatively close to your measurement. Replace it with your 3/8" and smaller end milling to clean everything up. I think you will get much better results. Also, look up climb milling vs conventional milling.

I'm still a beginner as you can see, but I think my solution will help you a lot.
To answer your question, I've taken like .025 passes with my .750 end mill. One time I went higher and it kicked the piece out so I don't try anything higher now LOL.

The draw bar comment is interesting. It isn't a tight fit in the spindle so it is never perfect centered and spins as such.
It was a rather rough finish and I was considering a roughing end mill.
Noted on the rest of your comments, I'm confident on those two.

 

[jlsmithseven]

Made a picture in my previous post to show other beginners what I'm talking about. You seem like you know that much. Anyways, what type of collet they probably meant like 5C collets or what type, not the brand name? let me ask something else, what type of machine are you using LOL. is it a very old Bridgeport? just a hunch. I honestly feel that how you're describing the finish on the piece is that a roughing end mill will do a much better job, Once it's semi smooth go for your regular end mills. Try it out!


Pull the draw bar out and take a look at it. It might be the culprit.

 

[Todd_71]

Made a picture in my previous post to show other beginners what I'm talking about. You seem like you know that much. Anyways, what type of collet they probably meant like 5C collets or what type, not the brand name? let me ask something else, what type of machine are you using LOL. is it a very old Bridgeport? just a hunch. I honestly feel that how you're describing the finish on the piece is that a roughing end mill will do a much better job, Once it's semi smooth go for your regular end mills. Try it out!


Pull the draw bar out and take a look at it. It might be the culprit.

Thanks!
5&6 = yes I have avoided/eliminated those possibilities.
5C collet? Not sure, but I believe so... I assume (because I'm ignorant here), that is the number of slots cut in the collet.

The draw bar is one diameter the entire length and threaded on each end. Can't exactly tell but it looks like the stock ones that I have seen others here replace. I don't have a lathe to make a new one so I'm stuck with it for now.

No not an old BP, it is a Precision Matthiews PM932m.

I'll try order a roughing bit. I think that may be the case because I used a 1/4" end mill to slot a square in the same piece of steel with out much trouble, but I did use the keyless chuck for that. I thought the collet would be better.

 

[JR49]

Just a quick thought. Is that rough edge you're cleaning up a result of being flame cut or plasma cut? If so that will eat up your cutter pretty fast. JR49

EDIT, Just saw your last post. I too have a PM 932m and also use the R8 collets from QMT. I have never had a problem with an end mill slipping in the collet. Oh, and I am still using the draw bar that came with the mill, but I did find a make a bushing to keep the draw bar centered at the top of the spindle.
I don't feel that I tighten the draw bar nut all that tight, but I do use 2 wrenches, one too hold the draw bar from turning (top nut with roll pin through it). And, with the other, I tighten the other nut below it Hope this helps.