What is my best choice for this job

[hswaters]

Ok so my Grizzly mill has arrived and I have at last got it on the workbench. That was one big job too. I got a harbor freight shop crane and it was strong enough to lift it onto the bench but it was just about 4 inches too long on the legs and they hit the wall behind the workbench, stopped me cold. I had to put a come along on the mill and attach to the wall to get it all the way onto the bench. Setting it up is another story.

Anyway I am now working on the first cut. I have a piece of steel of unknown type that is about 2"x3"x8" and it has a rough gouged edge where it was cut with a torch. There are sort of bubbles and deep ridges in this surface. I would like to mill it off so the piece is smooth on that side. A 3" 4 tooth facing cutter came with the mill and I gave it a try with that but it sure does throw off some hot chips even on very slow feed, almost on the stop setting. I was wondering if maybe a fly cutter would be better for this sort of thing. Or maybe I am cutting too deep. I was making a cut about fifty thousandths but it seems to bog the mill down and the chips come off yellow hot.

[Hawkeye]

Your RPM is way too high. Often, areas where a cutting torch was used cool off quite quickly. This hardens the steel, if it has any amount of carbon in it. Harder means slower.

Also, carbide doesn't like interrupted cuts. The roughness of the hardened area can cause carbide to chip. 50 thou is a pretty heavy cut for a light machine. (You haven't said what mill you have.)

For that size cutter, try 900 RPM (carbide) or 130 RPM for HSS. Any time it's throwing sparks, stop and change something. Carbide can cut blue or straw-coloured chips, but no glowing ones. If HSS is causing chips to change colour, slow it down.

[PixMan]

Unless I missed it, you haven't said what cutting speed (rpm nor sfm) you are using. I assume feed rate is by hand also.

Is the cutter a solid high speed steel one or a carbide insert type? As Mike stated, carbide can run quite a bit higher speed than HSS tools. I'm not sure the average uncoated insert in a budget-oriented milling cutter would be able to take 706 sfm (which is what 900 rpm on a 3" cutter is), so you might start at about half that speed. Getting the flame cut kerf off with a disk grinder would also help preserve cutting tools. If the flame cut slag is still there when you cut with carbide, it would not be unusual to see some sparks and that's not always a sign of impending doom.

Lastly, expect hot chips. It's going to happen if you expect to get material off at a reasonable rate and becomes a matter of managing the flow. As in, stay clear of it.

[Highpower]

(02-11-2014, 07:42 AM)PixMan Wrote: ...... Getting the flame cut kerf off with a disk grinder would also help preserve cutting tools.

I agree with Ken 110%. Grind it off first, then machine. Saves time and your tooling.

[stevec]

It's a Given!

[hswaters]

Now that we have discussed cutters I think it is time to discuss cooling. I have been watching youtube videos when I should have been working on getting my garage set up and I notice some people are using a coolant that appears to be air or else it is something that does not show up on a video. Can a stream of air be a good coolant? Do people already use that? I am looking for some way around the water oil mixture and the mess.

[Hawkeye]

A well-aimed blast of compressed air will always provide some cooling, due to decompression cooling. Not as good as water, but some help.

Another advantage of air is it's ability to clear chips out of the cut. This helps give you a better finish. I use it on my X2 CNC mill.

For most of my milling cuts, I don't use any coolant. I'm more likely to use cutting oil or Crisco as a lubricant, especially with aluminum.

[hswaters]

(02-25-2014, 11:04 PM)Hawkeye Wrote: A well-aimed blast of compressed air will always provide some cooling, due to decompression cooling. Not as good as water, but some help.

Another advantage of air is it's ability to clear chips out of the cut. This helps give you a better finish. I use it on my X2 CNC mill.

For most of my milling cuts, I don't use any coolant. I'm more likely to use cutting oil or Crisco as a lubricant, especially with aluminum.

Thanks Hawkeye. I will start working on setting up some air.