Milling machine question

[RJSakowski]

Hi Doug,

I use an edge finder as my preferred means of setting x and y positions. Used carefully, you can achieve repeatability to a ten thousandth.

Some things to remember about using:

I use a small amount of light machining oil to lubricate the edge finder; just a light film on the mating surfaces and wipe any excess off. You want the exterior dry. Set the spindle speed fairly low, around 750 rpm. I usually try to engage between .1 and .2" of the edge finder and to keep the consistent if I am locating the center of a piece. They work best with smooth surfaces.

When finding an edge, advance to the surface until it deflects. Note the position and back off. Come up on the edge again very slowly. You will see the edge finder runout gradually decrease as you approach the edge. The reason for doing this is that the fist contact with the edge will kick it out and you want the edge finder running true to the spindle axis. The correct position is the one closest. Repeat the process until you are satisfied with your position.

With a DRO, this process is slick. I have a Grizzly DRO on my old mill/drill and finding the center of a workpiece is apiece of cake. Find one edge, zero the DRO and find the opposite edge. Hit the 1/2 button and the DRO is centered on your workpiece. My Tormach CNC requires doing some math but works the same.

I find that the effective edge finder diameter varies slightly from the nominal. A .5000" diameter edge finder should be .2500" from the edge when it deflects but depending on rpm, surface condition, depth of engagement, etc. it will vary slightly, usually a few ten thousandths. For most work it is sufficient. Milling cutters will also cut a different diameter from their nominal depending upon runout, tool deflection and actual diameter. For precision work, it is best to sneak up with your cut as you have done.

 

[cazclocker]

...I use a small amount of light machining oil to lubricate the edge finder; just a light film on the mating surfaces and wipe any excess off. You want the exterior dry. Set the spindle speed fairly low, around 750 rpm. I usually try to engage between .1 and .2" of the edge finder and to keep the consistent if I am locating the center of a piece. They work best with smooth surfaces.

When finding an edge, advance to the surface until it deflects. Note the position and back off. Come up on the edge again very slowly. You will see the edge finder runout gradually decrease as you approach the edge. The reason for doing this is that the fist contact with the edge will kick it out and you want the edge finder running true to the spindle axis. The correct position is the one closest. Repeat the process until you are satisfied with your position.

With a DRO, this process is slick. I have a Grizzly DRO on my old mill/drill and finding the center of a workpiece is apiece of cake. Find one edge, zero the DRO and find the opposite edge. Hit the 1/2 button and the DRO is centered on your workpiece. My Tormach CNC requires doing some math but works the same.

I find that the effective edge finder diameter varies slightly from the nominal. A .5000" diameter edge finder should be .2500" from the edge when it deflects but depending on rpm, surface condition, depth of engagement, etc. it will vary slightly, usually a few ten thousandths. For most work it is sufficient. Milling cutters will also cut a different diameter from their nominal depending upon runout, tool deflection and actual diameter. For precision work, it is best to sneak up with your cut as you have done.

RJ, thanks for that. I don't have CNC, so I don't have the luxury of a DRO either. But I just reviewed the section from the my DVD "Milling 101" by Swarfrat, and I still have one more question. He mentions that to find a flat edge, he sticks the cone end of the edgefinder in a chuck - leaving the .200" cylindrical end to do the edgefinding. I guess I'm thrown by realizing that if I use my 3-jaw chuck to hold the edgefinder, and then I use one of my R8 collets (my LMS milling machine uses the R8 system), what if there's a discrepancy between centering between my 3-jaw and my collet? I thought it was well known that 3-jaw chucks inherently have a few thou of runout. Should I get an R8 collet that can hold the edgefinder's body? I know that the edgefinder's body is fairly thin-walled, so I'd have to finger-tighten only, whatever I use to hold it in the spindle.

...Doug

 

[RJSakowski]

RJ, thanks for that. I don't have CNC, so I don't have the luxury of a DRO either. But I just reviewed the section from the my DVD "Milling 101" by Swarfrat, and I still have one more question. He mentions that to find a flat edge, he sticks the cone end of the edgefinder in a chuck - leaving the .200" cylindrical end to do the edgefinding. I guess I'm thrown by realizing that if I use my 3-jaw chuck to hold the edgefinder, and then I use one of my R8 collets (my LMS milling machine uses the R8 system), what if there's a discrepancy between centering between my 3-jaw and my collet? I thought it was well known that 3-jaw chucks inherently have a few thou of runout. Should I get an R8 collet that can hold the edgefinder's body? I know that the edgefinder's body is fairly thin-walled, so I'd have to finger-tighten only, whatever I use to hold it in the spindle.

...Doug

The beauty of the edge finder is that it doesn't care about runout. As you advance the edge finder it will center itself perfectly before it jumps. The location of the jump is coincident with the spindle axis in the direction you are moving.

 

[JimDawson]

RJ, thanks for that. I don't have CNC, so I don't have the luxury of a DRO either. But I just reviewed the section from the my DVD "Milling 101" by Swarfrat, and I still have one more question. He mentions that to find a flat edge, he sticks the cone end of the edgefinder in a chuck - leaving the .200" cylindrical end to do the edgefinding. I guess I'm thrown by realizing that if I use my 3-jaw chuck to hold the edgefinder, and then I use one of my R8 collets (my LMS milling machine uses the R8 system), what if there's a discrepancy between centering between my 3-jaw and my collet? I thought it was well known that 3-jaw chucks inherently have a few thou of runout. Should I get an R8 collet that can hold the edgefinder's body? I know that the edgefinder's body is fairly thin-walled, so I'd have to finger-tighten only, whatever I use to hold it in the spindle.

...Doug

There may be some runout on your drill chuck and that will effect the edge finding. If I need to get really accurate I do use a collet. I worked for years without a DRO, just using the dials on the machine, you just have to remove the backlash and always approach the work from the same direction and remove the backlash by cranking out a ways then cranking back in. I've been doing that for so many years that it is just automatic for me to do it even on a zero lash machine.

 

[RJSakowski]

RJ, thanks for that. I don't have CNC, so I don't have the luxury of a DRO either. But I just reviewed the section from the my DVD "Milling 101" by Swarfrat, and I still have one more question. He mentions that to find a flat edge, he sticks the cone end of the edgefinder in a chuck - leaving the .200" cylindrical end to do the edgefinding. I guess I'm thrown by realizing that if I use my 3-jaw chuck to hold the edgefinder, and then I use one of my R8 collets (my LMS milling machine uses the R8 system), what if there's a discrepancy between centering between my 3-jaw and my collet? I thought it was well known that 3-jaw chucks inherently have a few thou of runout. Should I get an R8 collet that can hold the edgefinder's body? I know that the edgefinder's body is fairly thin-walled, so I'd have to finger-tighten only, whatever I use to hold it in the spindle.

...Doug

The edge finder body is hardened steel so you can tighten it securely. I keep my half inch mounted permanently in it's own 1/2" end mill holder. I use the 1/2" finder more than the .2" because it seems to be more sensitive and introduces less error if I am finding the edge of a small diameter cylinder.
One other note is there is a sound made when the edge finder jumps so you can watch your dial rather than the finder. Play around it it. You will like it!

 

[cazclocker]

OK, I've grasped the concept enough to give it a whirl. Thanks so much! I'll report back in a little while after I practice a little...
...Doug

 

[darkzero]

Here's another video by good ol' TubalCain:

In addition to the conventional edge finders which I use the most, I also sometimes use the electronic contact edge finders in cases where I don't want to mark the final finish. There are visual types & audible types, I prefer the visual type myself (LED lights up) as it can be too noisy at times to hear the audible ones. Fowler offers one that is not expensive compared to the break away ball type which costs 2-3 times more. Care must be used with the straight tip type as the tip does not break away, advancing too far after contact may damage it. If you do decide to ever get the electronic type, I recommend staying away from the metric ones as referencing the radius can be annoying, that is if you use imperial measurements & have imperial dials (since you mentioned no DRO).

 

[cazclocker]

Darkzero, thank you for that advice. I forgot about what a great resource ol' TubalCain is! And I was certainly not aware of the visual or the audible edge finders. Very slick. You are correct about the dials on my LMS mill - they are indeed imperial (English), not metric. Although I'm very comfortable with metric measurements having spent my career operating German printing presses, I still prefer the system I learned growing up in America.

I spent some time in my shop practicing edgefinding. I got some scrap brass and one piece of aluminum block. I tried both my cheapie edgefinder (which works just great), and the method mentioned by billh50 above - I just held a scrap of paper to the work's edge and slowly advanced the work into the slowly-spinning cutter (about 750 rpm) and sure enough, at some point I could feel the cutter starting to grab the paper. Of course, then I have to advance the table another .0035" (the thickness of the paper) and then half the cutter's diameter. That worked VERY nicely. I mentioned that I also practiced a bit with my conventional edgefinder - that worked beautifully too. I ended up using a 3/8" R8 collet since the edgefinder's body is 3/8" diameter. It was a bit of a trick to "wait for the jump", but it's easy after doing a few times. Then advance again .100", and voila...there's the edge.

I think that both methods work well for me. The advantage that I can see of just using a scrap of paper is that there's no changing collets - I just mount my cutter and proceed to find the edge. With the edgefinder, I have to change collets - the 3/8" R8 for the edgefinder, and another collet for the cutter I need. Changing collets is not much of an actual disadvantage since I'm not doing production, but it is an extra step nevertheless.

This is Doug in Arizona saying, so long for now. (TubalCain joke)