Endmill Chatter on Aluminum

[Downwindtracker2]

I'm making a jig to measure runout on rifle cartridge cases using 4 steel balls instead of a v-block. I had a 1/2" four flute endmill with a ball end, so that's what I used into an aluminum block. I noticed chatter, it was hard to miss, chuckle, and the finish was poor. It's not that critical, the steel balls will be epoxied in place, but maybe next time it will be. So what should I do to cut down on the chatter. Besides spending money on a 2 flute.

 

[Matt-Aburg]

2 flute, fast RPM, higher feedrate. If you don't have high enough rpm, (8000) then adjust accordingly...

 

[Former Member]

I have used a 1/2 4fl Carbide on Aluminium a lot. No chatter, 20IPM 0.050 depth 3000rpm upto full width pass.

I've just switched to a 3fl designed for Aluminium rougher/finisher run under the same setup. Even better finish. I've done a test run upto 30IPM, also good. When the mill is over hauled and ballscrews go in, it will be consider to increase production.

Now the question, Carbide or HS?

Aluminium is a grabby material that heats and sticks, so two things are required, Carbide (no flex), and flood cooling, reduces sticking. HS allows flex hence grab which translates as chatter, The second is the method of cooling/lube, not enough material and bit heat causing stick with increases flex and well.....chatter.

The other method to reduce it is slow your feed down and limit your RPM, less load, less flex, less heat.

 

[Dan Dubeau]

You're plunging a pocket for a ball right? Slow the rpm down, and feed too. ~3-400rpm and slow feed will limit the chatter. Lock the quill and feed with the knee also.

 

[Susquatch]

I'm making a jig to measure runout on rifle cartridge cases using 4 steel balls instead of a v-block.

Like this?

Show us a closeup photo of your chatter. It could be lots of things. Pictures tell stories.....

 

[Downwindtracker2]

My mill is a RF-45 mill/drill. A Thomas Skinner import. It's the square column original .It was well used when I bought it. I've replaced the lead screws and nuts . It's 100% better than it was. It has a 4 pole motor so the maximum rpm is 1500.

Yes, I'm plunge cutting. The endmill is carbide.

Yes that is the basic idea, but it is J. Belk's design . He was a gunsmith who posted a great deal on Mausers 20 some years ago when I first got on the 'net. He put the front steel balls together to stop the forward movement as the case shoulders butted up against them. He didn't have a stop like the pin on yours, so the cases can slide back and forth. The back balls were apart .200" and set so only 308 length cases balanced. I'll make two, another one for 30-06 length cases. With an adjustable stop, a flat head screw. A bit crude but within my skill set. My first attempt I just used a standard drill bit and Crazy Glue. I was working then, so the steel balls were from bearings. It didn't work that well.This time, the balls are from Amazon. I have a Starrett comparitor that was given to me, so I'll add 8mmx3mm magnets to the bottom.

 

[Susquatch]

He

He put the front steel balls together to stop the forward movement as the case shoulders butted up against them.

The reason mine has spaced balls at the front too is so that bullet runout can be fully compared to the case body. The shoulder does not get involved to mess up the measurement. I don't know how a measurement could be consistent with the balls acting as a stop for the shoulder.

The purpose of the pin is to maintain a constant reference on the base of the case.

What's missing in my photo is a seated bullet which is where the runout should be measured.

I shot competitive benchrest for many years and like many competitors, I built all my own rifles. I can't compete anymore - I'm just too old to be competitive. I developed bad vision, the shakes, and a really slow mind, but I can still shoot better than the average really good shot and I still build rifles for myself, my friends, and my family.

 

[Downwindtracker2]

I'm merely a hunter, just an odd club Farky Class competition. If I don't come in last, it's a good day. Reading a post on a hunting forum reloading section, a fellow complained of .007" runout on his 338-06 . He was using Redding dies, so I checked a couple of my cases, I was using inexpensive Lee dies. I got .003" . It was difficult to get a good reading with the J.Belk jig. I was displeased with the .003" . Well my rifle grouped around an inch,which is easily good'nuf for moose and elk. But I have factory rifles that group better. So the question of why. I had already bought a tubing mic to measure case neck thickness variation. I also bought another reloading die, RCBS, this time. After screwing up a die stem through my fault I like to have spare, of a different maker.

 

[Susquatch]

I know this game very very well having coached and helped countless new and old shooters and hunters for the better part of 50 years. That doesn't include my own teenage years and early 20s even though I was a damn good shot then too. It's just that nobody with any common sense listens to the opinions of a big hairy teenager. Nor does a hairy teenager have any interest in helping others..... LOL!

Do yourself a favour and put both sets of balls on floating plates so you can get past the shoulder onto something more consistent and less sensitive to position. The shoulder alone will include some wobble. Your goal is to measure bullet wobble not shoulder wobble.

Measuring case neck thickness will undoubtedly have you shopping for case neck turning tools.

But in my humble opinion, all this stuff is just a big waste of money and time in a hunting rifle. It's just too easy to think there are "magic bullets".

I'm here to tell you that case neck thickness and loaded round concentricity are meaningless to one inch groups. Powder load, bullet weight, case brand, primer type, seating depth, and rifle tuning are MUCH BIGGER FACTORS. The biggest factor of all is the shooter. In fact, a given shooter can shoot a nice group, take a break, and then shoot a crappy group with the same rifle and same loads - all because he changed how he sits or how he holds the rifle. Shooting well begins with consistency.

Despite my pessimism about the value of a concentricity gauge, I am actually impressed. Very few shooters would even think of such a thing let alone try to make one. This tells me that you are a curious bloke who is willing to experiment. That's the best start anyone could ever expect.

Nuff said.

Although a huge number of our members are shooters and enjoy gunsmithing, the forum isn't a shooting or gunsmithing forum. Discussions on these topics are discouraged. That policy predates me. So I'm going to send you a PM with more info in an effort to help a bit more.

We can continue the discussion about making your fixture here, but move discussion about using it and improving your rifle to the PM.

Anyone who wants to participate in the PM can request that they be added to our private discussion in a post below and I'll add them in.

Sound fair?

 

[mbond]

I have never fired a gun in my life, but I can attest to Susquatch's point from my other passion - golf. Being a player who can control the clubs with precision and consistency is _far_ more important to the results than the quality of the clubs / balls themselves.

Before I had cancer, I had about a 1% margin. Not good enough to be scratch, and no where good enough to be a pro, but good enough to know what makes the difference between good shots and bad. I have played with everything from the most expensive clubs to the cheapest stuff from Walmart. What you play with only matters at the very tippy top end

 

[Former Member]

Tooling is not sporting equipment and it does make a considerable difference whether you are a master machinist or raw beginner.

I've been up at the top in several sports (upto and including the world cup level), had kids that tried in one sport at did the same world cup and Olympic level. Once you progress beyond intermediate, you begin to notice and appreciate better equipment. In some cases not using the best actual hinders your progress as you are fighting the equipment.

In tools, poor/cheap tooling all you do is fight with it to get the result you want (beginner or master). Good tooling does what you want consistently. How good that result is depends on the skill level. How frustrating it is getting there is the quality of the tool.

So why fight, start with good tooling you will appreciate and progress faster.

 

[mbond]

I'm not sure if we are agreeing or disagreeing, but I think that bad players / machinists can use any equipment and produce bad results. And good players / machinists can use any equipment and produce results as good as the equipment can muster

 

[Susquatch]

The discussion was precision shooting. Not machining.

What you play with only matters at the very tippy top end

Right on.

I think that another way to say all this is that the weakest link is what defines the limits. Usually the weakest link is looking at us in the mirror. Few of us like to admit that but it is not until we ourselves are no longer the weakest link that the very best equipment starts to matter.

 

[Former Member]

Its more of a question how fast and easy they get to the end result, good or bad.

 

[Downwindtracker2]

It's my belief you can't make something accurately with out being able to measure it. That's all the jig is. Some years back, I had made a jig off plans on the 'net, but never used it. When curiosity got the better of me, I tried using it. I was able to get a measurement that I was happy with but it wasn't that easy. I saw the need for 3 or 4 improvements. When I make the jig this time, I hope without complaints from mill/drill, I'll add them.

Oh, I found a .003 discrepancy . The hobby machinist in me was not too impressed. I got to up my game.

 

[Susquatch]

Its more of a question how fast and easy they get to the end result, good or bad.

That's your question, not mine. Your time has a price tag on it - mine is whatever I feel like valuing it on that day.

I'd rather take my time the hard way getting to a more guaranteed good result than rush the easy way to a probable bad one.

 

[Former Member]

That's your question, not mine. Your time has a price tag on it - mine is whatever I feel like valuing it on that day.

I'd rather take my time the hard way getting to a more guaranteed good result than rush the easy way to a probable bad one.

Reading comprehension must not have been one your strong suits.

Good quality Carbide End mills just make life easier in your case (EASY) gives you a better finish, whether you take your time or not (obviously not FAST).

 

[trevj]

2 flute, fast RPM, higher feedrate. If you don't have high enough rpm, (8000) then adjust accordingly...

And here I was, based on my experience, about to recommend a lot LOWER RPM, and a fast feed rate! LOL!

I found that chatter came about from indecisiveness. Too slow a feed IN, gets you chatter, in a drilling with a mill situation, and feeding in hard and fast, and getting the hell out, has been the answer to that problem for me.

FWIW, for the purpose, I'd have probably chosen a drill or a spotting drill, instead of a milling cutter of any type! After all, the balls are being glued in anyways, and the end result is the same, no matter how bad you pooch the job, as four balls, at four different depths, will STILL provide you an accurate fixed reference point to spin your brass upon to check concentricity!

Well, as long as your brass is ROUND, anyways! LOL!

Which is to say, there may be more profitable lines to pursue...

 

[Downwindtracker2]

I used a drill for my first attempt at the jig. It wasn't my design. I found the balls weren't secure, they came off easily. My guess, not enough contact on such a smooth surface. This time I'll use epoxy instead of a industrial Crazy Glue.