New to Milling

[freudianfloyd]

I have been doing fabrication for the past several years, but most of my experience is with welding and the lathe. I am trying to get a hang of using a mill but have been having some issues.

First off the "mill" I am using is a Jet JMD-15 so I know it is limited in what it can do.

I am trying to mill down a 3/4" parting tool holder to fit in my 5/8" tool post. I first tried using a 3/4" endmill with a .125" depth cut, but the machine was making all kinds of noise so I backed off. The material is cold rolled by the way.

I switched to a 3/8" endmill to make multiple passes, and it worked if I made really shallow cuts, but after I made a couple, the start of my cuts were lower than the end of my cuts, and the first pass was lower than my second. Basically every cut was making a stair step. Is there something I am doing wrong, is it a limitation of the machine? The part I was milling was firmly in the vise on a set of parallels. Is it possible the end mill is sliding inside the collet?

Any advice would be appreciated.

Also, I was running a 3/8" roughing end mill at around 300rpm and feeding it manually.

 

[rsanter]

Because of the angle of the cutting edge it can happen that the cutter is being pulled down.
Did you have the quill of the machine locked? How tight was it?
How tight did you have the bit clamped into the machine? Was it really tight? Was it tightened into a chuck or collet?

On a mill you will need to feed slower than you may feel like compared with a lathe. When you have a limited machine like you have you have to reduce the depth of cut and the feed rate

Bob

 

[larry_g]

Confirm it is stair step and not sawtooth. If it is stair step then yes the bit could be slipping. make your cuts then move back to the first step and measure if there is clearance between the bit and the material. If so then something is moving, bit, spindle, or the whole head sliding up. Could also be your part moving.

If it is sawtooth then the head could be out of tram. Pictures of the problem and your setup would help.

lg
no neat sig line

 

[freudianfloyd]

Because of the angle of the cutting edge it can happen that the cutter is being pulled down.
Did you have the quill of the machine locked? How tight was it?
How tight did you have the bit clamped into the machine? Was it really tight? Was it tightened into a chuck or collet?

On a mill you will need to feed slower than you may feel like compared with a lathe. When you have a limited machine like you have you have to reduce the depth of cut and the feed rate

Bob

Thank you for the replies. I talked to our mill operator in a different building, and he let me show him what I was doing with his mill, we think it is a combination of my feed speed, and the limitations of the machine. I had the end mill in a collet, and tightened down as much as possible, but it was still slipping.

 

[galute]

Someone correct me here as I'm new to milling also but isn't 300 rpm on a 3/8 bit too slow on cold rolled? Maybe causing the bit to dig in?

 

[kazlx]

You 100% sure that parting tool holder is CRS? Unless you made it, most of those are hardened....BTDT. I had to grind one I got from a friend to take a few thou off to fit my tool holder.

Other than that, could be the limits of the machine. Are you using a HSS cutter?

 

[freudianfloyd]

You 100% sure that parting tool holder is CRS? Unless you made it, most of those are hardened....BTDT. I had to grind one I got from a friend to take a few thou off to fit my tool holder.

Other than that, could be the limits of the machine. Are you using a HSS cutter?

No it is not hardened, a dull file made a big gouge in it as I was thinking the same thing. The real mill we have here was able to take a 1/4" deep cut with a 3/4" end mill in one pass, this little jet couldn't take a .125" cut with a 3/8" end mill though.

 

[kazlx]

There you go...just too big of a cut. The machine is moving around.

 

[tdkkart]

.125" deep in steel is a BIG cut for a mill-drill.
.030" would be more like it.

 

[APEowner]

Is it possible the end mill is sliding inside the collet

As has been discussed, it's not only possible but probable.

With some experience you'll get a feel for when you can get away with making end cuts with an end mill in a collet the correct tool holder for that application is an end mill holder.

 

[bmxdad]

Looks like the bed is fixed, and the z axis is on on the quill. If that is the case, do you have any way of getting the vice up? Maybe a solid spacer so the quill is high as it can go.

Rpm for a .75 end mill should be around 500 rpm. .100 deep cut. Use a spray mist if you can, otherwise flood it.

Also, don't climb cut with a light machine like that ... conventional cut is best.

 

[Kevin54]

First off, a JET isn't going to be a Bridgeport or better. So expect less. What you can do is make sure your endmill is tight in the collet. Secondly, semi tighten your locks on your table. This will take some of the slop out of it. Thirdly, make smaller passes. And if you are using a good sharp endmill, increase your speed of your cutter just a little. Maybe around 600 rpm's to see how it acts.

If you are cutting left to right, then lock your table for front to back until you are ready to move the table front to back. This should help you out.

I've told many people that I have trained to machine......you have to become one with the machine. (laugh if you must) but when you learn what the machine does, it will tell you what you need to do. Learn to "read" you material after you make a cut. If you have "chatter", then you have to read the machine to learn where that chatter is coming from. It's not complicated, and don't try to make it so. If you cutter is moving in your collet when you are cutting, you need to look at the cutter like a large screw with threads. You move too fast, and too deep, it will want to screw itself into the material. If the cutter pushes up, then you have a dull cutter. I've ran mills for 35 years and have taught many, and I tell everyone the same thing. Become one with the machine. Learn to read it, learn to read your material, learn to read your cutters. Understand what goes on when an endmill is going through a piece of material. It will bend, flex, push up, push down. That is when you have to learn when to speed things up and slow things down. Learn to read the chips that come off of the material. If you are cutting steel, a clean silver chip is what you want. Blue is too fast. Red is way too fast. And if one jumps down your neck and is white hot.......well.....you're going to have a blister or two.

 

[Steevo]

I have a Grizzly knee mill, and if I get too aggressive with endmill size or depth of cut, it actually lifts the table as it cuts. It took a while to figure out what was going on, as everything would measure out fine before and after, but I'd get inconsistent cuts that "stair-stepped" or varied both up and down across a piece.
I finally figured it out by stacking 100# of weight on each end of the table to stabilize it, then slowly working backwards to figure out how deep a cut or large a bit was "too much for it and caused it to lift when cutting.

 

[Ed ke6bnl]

You 100% sure that parting tool holder is CRS? Unless you made it, most of those are hardened....BTDT. I had to grind one I got from a friend to take a few thou off to fit my tool holder.

Other than that, could be the limits of the machine. Are you using a HSS cutter?

I agree it is probably hardened