Setting Up Endmill

[jmcmullan]

Got a lot of general metal shop time with hand tools & drill press, but have a new Enco mill-drill and am still learning (and having a blast). I've been struggling with this, thinking I ought to be able to figure it out, but I'm too old to waste time anymore, so here's my dumb question:

I'm just trying to take an accurate depth cut off the top of a piece of (flat) stock held securely in a milling vice. To set the depth of the cut, I'd run the tool down until it touches the workpiece (more later), set the downfeed dial to zero, move off the workpiece, dial in the depth of the cut, lock the quill and then mill-on. Got very poor results - mostly a deeper than expected cut by up to almost 10 thou.

At first I thought that there was axial play between the spindle and the quill. There was a little and I adjusted this out to less than .0005" - about as low as I can go without the bearings starting to get warm. This essentially had no effect on cut accuracy.

Finally I noticed (DUH!) that between when the end mill first touches the workpiece and when all the backlash is out of the quill downfeed is (guessing) several hundreths. So I tried lowering the tool down VERY firmly against the work to set the zero and then after I set the cut depth, press up on the tool with a piece of oak to take out the play while I lock the quill. This gets better results but still several thou of inconsistency. Most of all, this seems really awkward and I just don't ever remember seeing a machinist go through these contortions to set up a cut.

So hat in hand, I ask you all what the heck's the real way to set up a cut depth?

P.S. With my new found humility I might as well go ahead and ask what's a good book to learn this and other similar basic machining techniques?

Thanks,
Jay McMullan
Atlanta & Savannah GA

BTW, if ibewgypsy takes a look at this - drove through Tunnel Hill a few weeks ago on the way back from Jack's River. Really pretty country up there!

[Michael Az]

Here is how I do it. Lock down the quill. Take a small piece of paper and hold onto your workpiece under the cutter. Then with the spindle powered up I bring the table up until the cutter grabs the paper. You are now within a couple thousands. Move table so the work clears the cutter, reset your dial to zero and then move the table up whatever depth you need. Works very well for me.
Michael

[This message has been edited by Michael Az (edited 08-31-2004).]

[Allan Waterfall]

Jay,

I don't have a mill/drill but this seems to be a common problem.

One answer I've seen is to rig an external tension spring so that the quill is always pulled up against the rack.

Saw one once with a tensioning wire run up and over pulleys with a weight hanging down the back.

Allan

[nheng]

Jay: The best place for this info is in online forums and various magazine tip columns like HSM or MW. Unfortunately, the mill drills are not Bridgeports.

On my Jet (Rong-Fu) mill drill, I lightly lock the quill to introduce drag and then downfeed a slight amount and set zero. Lock it fully and make your cut. Loosen and repeat this process for each depth you want to hit. The idea is to keep some resistance between the micrometer downfeed handle and the quill.

Hope this helps.

added - combine this with Michael's paper trick to "kiss" the top of a workpiece (gently). What I've described is ok if you are first surfacing a piece of stock and then going for depth.

Den

[This message has been edited by nheng (edited 08-31-2004).]

[rbjscott]

I try to lock the quill in the most raised position possible to shorten the set up. Make sure the mill cutter is not creeping out of the collete or holder.
Use the table to set the desired depth of cut, leave the quill locked in place if possible.

[Joel]

Most mill-drills don't have a knee.

If your technique gives a consistent error, you can just subtract it from the dial reading.

Have you checked the accuracy of the divisions on your down feed?

You can always use a dial indicator for the precision cuts. Rough out your piece and leave your quill locked (locking the quill can move it a few thou), measure your part. Say you are .010 over size, set a plunger type indicator on a mag base so that it rides on the flat spot on the bottom of the quill (indicator upside-down). Zero the needle, unlock the quill, set your DOC to .010, and lock the quill making sure that your indicator maintains the same reading. It all goes pretty fast.

You can also get a cheap quill DRO for something like $35.00 IIRC.

[Joel]

Oh yeah, are you sure that your gibs are tight, that the table is locked, the head adjustment bolts are good and tight, and that the table is tramed in? If EVERYTHING isn’t tight and square, consistency can be hard to achieve.

[JRouche]

Hello, are you using an end mill holder (with set screw), a collet or drill chuck to hold yer bit? What size cutter including flutes? HSS or carbide. How deep a cut are you taking, I am assuming light? End mill pullout can become a problem if you are not using a holder (w/s.s). If its a collet most people don't tighten down the nut near enough. And unfortunately if you are using a drill chuck, all bets are off. Just measure the bit before cut and take a couple of nice cuts just for affect then remeasure the end mill stick out. And as stated by others, completely go through the machine and de burr, re tighten and knock off some of the razor edges left by the Chinese. There are some nice sites around totally dedicated to theses machines to make them nice mills to work on. JR

[moldmonkey]

I too have a mill-drill and had the same problem. The downfeed mechanism is poorly designed. I now use a indicator off the depth scale. I replaced the little arrow with a small piece of round stock with a flat facing down for the indicator point. I bolted a piece of slotted sq. stock to another piece that bolts into the two bottom tapped holes that hold the depth scale sheetmetal on. The slotted sq. stock sets to the side and is where I mount the 1" indicator. The slot allows me to move the indicator up and down to where the quill is at. Hope this makes sense I do not a future as a technical writer.

Another thing is it is good practice to take a cut at less than full depth measure and than move in. There are alot of variables that can throw you off.

Jon Bohlander

[This message has been edited by moldmonkey (edited 08-31-2004).]

[This message has been edited by moldmonkey (edited 08-31-2004).]

[PHiers]

I have a WT mill drill (rf45 clone)
I had this same problem at first, what I found was I needed was to tighened the spindle lock REAL TIGHT. I have a DRO on the quill so I know the beginning depth and the ending one. Also I found that if I lowered the quill to rest on the piece I wanted to mill and then moved it to the side, the quill would drop about 5 thou. I now have the spindle running as I lower it until it just kisses the metal then I set the depth I want and tighten the spindle lock real tight! Your mileage may vary.




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Paul in NE Ohio

[wierdscience]

Yep thats what I was going to say,lock the head and use a quill dro.Thats what I do and I have a b-port,even on those the knee cranks ain't that accurate.

[darryl]

It's a big plus to be able to read the relative motion of the quill when locking it. On my machine, locking the quill lowers it by about a thou. Not much, but it does move when tightening it. Also, I will lower the endmill to just touch the workpiece, raise it one thou, then tighten, checking to see that it comes into contact with the work, just barely. I then zero the dial indicator I installed to read the actual quill position. I pay no attention to the downfeed handle markings, since they are off so much that you couldn't rely on them to cut bread to fit a toaster. I like to leave the weight of the quill hanging on the rack gear that feeds it, since that can mean that it won't drop further into the work. If you push upwards on the quill to take out the play, that play can activate under loads and vibration, causing the endmill to go deeper than you wanted. Better to have a cutting force raise the cutter, taking off less than wanted, than to remove too much material, possibly wrecking the work.
Anyway, once the depth of cut is dialled in and checked when the quill it tight, the depth of cut can still change because of looseness in the tables' ways. An endmill may want to raise the material, depending partly on how sharp it is. Then too much material comes off. The vise's moveable jaw may want to flex up or down, and the material may want to settle into position once cutting forces come into play. The cutting forces may flex the table, causing the workpiece to spring around, though you wouldn't see a movement this small. omething else I've had happen on this round column mill is that the head will settle slightly on the column when the motor is started, unless I'm careful to tighten the head to column clamping bolts evenly and alternately. When I'm adjusting the vertical height of the head on the column, I always stop with a short raise of the head. In other words, my last crank of up or down will be up a small amount. I'll lower it to below where I want it, then raise it that anount before tightening the bolts. One last thing I'll mention is the fact that when the spindle and all heats up, there's a dimensional change that has to be accounted for. On my machine it's about 3 thou, in other words, the endmill will be cutting 3 thou deeper after it's been running awhile, with no other changes in position done by me.

The cutter can creep in the holder, for more than one reason. High cutting forces will flex the endmill, possibly causing it to slowly squeeze downwards. A too loose fit is almost a guarantee that you won't be able to keep the cutter from changing position in it's holder. If you're using a collet that's been damaged by being tightened on a rough or out of round workpiece, that can interfere with it holding a cutter securely enough so it won't creep.

I'm sure I haven't exhausted all the possible reasons for these problems, but I've gone on too long already, as I tend to do. Hope you nail your problem down, Jay.

[bar_acres]

I have a 2hp Harbor Freight Mill-Drill 600lb bench style. I've noticed and have learned to adjust accordingly, that when I use a vise under the workpiece that sometimes the vise cants the work several thousandths...I've learned that it's not the machinist's work you pay for...it's the setup time!

Just take your time and triple check everything you do. I can get my projects to within .002-.003 now. Good luck!