Milling machine question

cazclocker

cazclocker

Purveyor of cheese.
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I have a Little Machine Shop 3900 milling machine. Yesterday I did a small job that came out nicely, but I am certain that I could have done better. Basically, I had four pieces of 6105-T5 aluminum pre-made, but I wanted to remove some of, but not all, of a raised part, and I wanted to remove exactly the same amount from both sides, leaving the remaining raised part perfectly centered. Here is a picture of what I started with:
http://i1251.photobucket.com/albums...Project/IMG_0037_text added_3_zpsxuaphkza.jpg

So I fumbled around and tried to mill off exactly the same amount from the left side and the right side, of the "raised part" so that it would sit in the slot of the mating piece. It came out pretty nicely, but again, I know darned well there's a better way to do it. Here is my result:
http://i1251.photobucket.com/albums...t Project/IMG_0049_text added_zpsclrjacua.jpg

So my question really is this: how am I supposed to calculate the edge of the cutter I am using (in this case, I used a 5/8" four-flute cutter) so that I can use the little dial on the X-axis to go in exactly .218"? What I did, is I actually fired up the milling machine and slowly advanced the table along the X-axis until the cutter touched the work ....... then I stopped the machine and zeroed my X-axis dial. Then I figured out how many revolutions of the dial (3 complete revolutions of 60 thou = .180", plus .038" more = .218"). OK, but I didn't go the whole last .038" because I figured my initial zero point might be a bit off. Good thing I stopped short because sure enough I was off...so I just advanced the X-axis a couple thou at a time until my dial indicator told me I had cut enough.

Again - what's the right way to know that the edge of my cutter is at the edge of my work? Help! I'm making mountains out of molehills!

...Doug in Arizona
 
An edgefinder is often used in that application They even make one with a laser. I have both. I also converted my LMS mill to .05/rev on the dials to make it easier to figure. LMS sells the kit and it is reasonable and not too difficult to do.
 
Actually you did pretty good. I probably would have done just what you did. If it is needed to be accurate, I "sneak" up on the finish cut just like you did. When working with the dials, there is always a tiny bit of error, no matter how small. When working with dials, you have to compensate for back lash in the axis, wear in the machine, and any other mechanical errors that can throw you off. Yes, they are accurate if you do all that, but to me "sneaking up" on the finish cut is the best way to be accurate.(MY OPINION)
 
When an edge finder is not handy I will tear a strip of paper and put it between the cutter and part. Just holding one end of the paper I slowly advance the cutter to the part while running. Just as it touches the paper I will feel a tugging on the paper. That tells me I am about .003 away from the part and set my dial as such. I will usually be within .0005 of where I need to be.
I also use this method for finding a surface for depth. I will slide a piece of paper under the not running cutter as I lift the table slowly. When I feel drag on the paper I know I have to come up .003 to touch the surface.
 
Thanks guys. Hmm, I better look into an edge finder. As I sit here, I'm not even sure what one looks like. I'm confused by the fact that the spindle can be sitting in the exact same place, but the edge of an end mill will be different depending on the size end mill I'm using.
I like the piece of paper idea...that will certainly indicate the cutter is .003" away from the work. And I agree, "sneaking up" on my finish cut gives the best results. It's funny how the smoothest cuts happen when you're only taking .001" or .002" at a time to finish.
Thanks again!
...Doug in Arizona
 
the smoothest cuts happen when you're only taking .001" or .002"

Yup, that's when there is the least load on the machine, load can move things erratically. If there is any 'play' in the machine, it can be bouncing with each stroke of each flute of the cutter.
 
Jim Dawson, hey I have one of those! I'm just not sure how to use it. I have a video series by a guy called "Swarfrat" in which he explains their purpose and use. I think I'd better review it.
Thanks so much, everyone.
...Doug in Arizona
 
Doug I use the other end..the center finder, to find the original center of clock plate pivot holes and then a center cutting end mill to do the rough cutting for new bushings.

David
 
Hi Dave, that's brilliant. The cone-shape center finder would naturally settle in the original pivot hole center! Thanks for the tip - I usually broach them out by hand, and I've been wanting to find a way to use my milling machine.
...Doug
 
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