Need Help!- Need to know how to remove X amount material

[Coldwave]

I am still a newb with machining parts and well I need to know how to remove like say .020" of material off a piece of stock that is .375" thick. Do I touch the bit to the surface and then move it off to the side and then turn it on and start moving the Z-axis dial little by little as I make small passes to remove the material until I get the .020" worth of turning on the dial? What is getting me is the fact that I cannot figure out that if the cutting piece is suppose to touch the part so that you will have a your "zero" reference point to know how much material you removed.

I would also like to know of some textbooks that could help. The ones I have do not take the baby steps for me like "The Home Machinist Handbook" and the "Table Top Machining" which plunge you straight in without taking baby steps. I need the small baby steps since I cannot learn very fast.

[roninB4]

More info is required here. What sort of machining operation are you doing? Is it .020 of a counterbore? Is it off the entire face of the plate or the side? What sort of material is it? What machine are you using? What cutting tool do you have? What measuring instruments do you have to verify that .020 has been removed? What is your tolerance range for this? Does the piece get heat treated after machining? Is thermal expansion a potential issue here?

More info would be needed to give you a proper reply but the standard operating procedure for most any operation is to establish zero, take a partial cut, verify by measurement, adjust per your reading and then finish to the target dimension.

What sort of job do you have that requires you to cut metal? Is this a regular part of your duties? What have you done to educate yourself? Bought any books? Which ones? Do you know how to calculate speeds and feeds? Do you know how to stay safe around machinery?

I ask all these questions because I'm trying to steer you in the right direction and give you a good answer that will establish good work habits. I must also state that the machine shop can be a very dangerous place and if you don't know what you're doing you can sustain serious injury. I don't want to see that happen if it doesn't have to happen.

[Coldwave]

Originally Posted by roninB4 More info is required here. What sort of machining operation are you doing? Is it .020 of a counterbore? Is it off the entire face of the plate or the side? What sort of material is it? What machine are you using? What cutting tool do you have? What measuring instruments do you have to verify that .020 has been removed? What is your tolerance range for this? Does the piece get heat treated after machining? Is thermal expansion a potential issue here?

I only have a small hobby mill made by Sherline that is the 5000 series. It is all hand wheels with no ability to zero the wheels since I did not order that option.

It is removing .020" of surface material from a 2" by 1" piece of flat rectangular aluminum that is .375" thick. I am doing this for beginning training for myself. I take baby steps. I need to be able to correctly know how to remove a certain depth of material that you simply cannot do that without having a reference point to start from which in this case would be the surface as my "zero" which from here would be .020" of space once the .020" of material is removed.

The only way I can think of doing this is by having the cutting tool touch the surface and see what reading I get on the Z-Axis wheel and then move either the X or Y-axis wheels enough turns such that the cutting tool is away from the material to be shaved down and then start up the machine and run the cutting tool down a depth at .005" of material removal from the face of the rectangular shape at a time.I know you may be thinking if I do not raise up the cutting tool when I use it to find the reference point that I will scratch the surface of the material but in this case it is not important, but in future machining operations it could be, but I do not want to run into backlash errors.

My measuring instruments are a Starret 1" micrometer, Starret Edge finder, and Starret "Last Word" dial indicator. I also have a set of Machinists squares.

Originally Posted by roninB4 More info would be needed to give you a proper reply but the standard operating procedure for most any operation is to establish zero, take a partial cut, verify by measurement, adjust per your reading and then finish to the target dimension.

What if I must take off very little material then? Would the test cut technique work if I needed to take off .003" as an example if tolerance requirements were tight?

Originally Posted by roninB4 What sort of job do you have that requires you to cut metal? Is this a regular part of your duties? What have you done to educate yourself? Bought any books? Which ones? Do you know how to calculate speeds and feeds? Do you know how to stay safe around machinery?

Trying to teach myself to be a decent hobbyist machinist so I can make parts that I do not feel like paying someone $100 to do for me. I have lots of electric motors, but my ability to make adapter plates for them to bolt up to is zero. The books I have are the two mentioned above and the Machinery's Handbook that is as thick as a bible! If you could, please tell me of some books that do not plunge newbies into projects without doing the baby steps first so that the very basics are understood.

Originally Posted by roninB4 I ask all these questions because I'm trying to steer you in the right direction and give you a good answer that will establish good work habits. I must also state that the machine shop can be a very dangerous place and if you don't know what you're doing you can sustain serious injury. I don't want to see that happen if it doesn't have to happen.

I know of the dangers. Common sense does not elude me. Just some of the technical babble does of machining parts.

[djr76]

Use the top surface a Z0. reference, then either move the quill down .02 or move the table up .02, take it off all in 1 cut. Thats normal practice to use the top surface as a Z point reference.

or you can take the stock out, touch off on the surface that that the stock rest on, raise the quill .355 or lower the table .355 since you are working with .375 thick plate.

[mfgbydesign]

I use a shim (feeler gage) or gage block. If by "machinist squares" you mean 1-2-3 blocks you can use one of those.
1. Manually drop the tool over the work until it touches the shim or the gage block will not go under.
2. Raise the tool up ever so slightly until the shim glides smoothly or the gage block slides under the tool.
3. Move the tool over so it clears the workpiece.
4. Drop the tool by the thickness of the shim or gage block you used. It is now in line with the top of the work without drag marks or chipped cutting edges. This is where you set Z-zero for an incremental amount of material removal.

You might also consider touching off the locating surface using the same technique to establish an absolute zero for machining to a specific height. Particularly if you are machining several pieces or using CNC.

For the edge finder:
1. run it in a collet about 200 RPM
2. Jog it down (in Z) so the tip is below the top of the work (off to the side), but the larger diameter is above the work.
3. jog (X or Y) the tip against the workpiece (or locator) until the tip offsets from the larger diameter.
4. Raise is it in Z above the workpiece.
5. Move it another 0.100 inches in the same direction as step 3. Your spindle centerline is now in line with the edge of the piece.

[Ed from NY]

There is a good chance that what you want is not to remove 0.020" of material but to end up with a block that is 0.355" in height. In that case take a first cut that you know will fall short, measure how much you have left and adjust your depth to compensate for the difference. Same as a "trial cut" on a lathe.

[packrat]

A good source of books is, Lindsay's books; Lindsay: Milling Machine How-To Books Most are from ages past, but the basics of running a machine haven't changed, just the technology.

As far as your original question, do like Ed from NY said.
1. With the cutter turning,and over the part about 1/16", slowly move your 'Z' axis until it starts to mark the surface.

2. Move the cutter away from work in the 'X' and change the setting by about half of what you want to remove. And take a cut.

3. Measure part, adjust depth to remove the remaining stock and take the cut.

Just take your time and have fun!! If you make a mistake, they have more metal!

[roninB4]

Not being familiar with the mill you have I'd only have a few generalities to offer.

1) Vibration will be a factor due to the small size of your mill. I say that not as a knock against your machine but more as a condition you'll have to learn to deal with when it rears it's ugly head. It's the same for larger machines too.

2) Your set up/fixturing will be be important. How you set up a work piece (WP) will make a big difference in ease of machining and accuracy.

3) Your level of accuracy needs to be established. You can probably bang out a tolerance of +/- .003 with no trouble but attempting tighter tolerances than that may prove to be difficult. This is where your fixturing and realistic tolerance goals will help you.


For taking off "X" amount of material, most of the previous posters have already explained what they do and I do the same most of the time. An old shop adage is "Check twice, cut once". That means check and re-check your measurements, don't just trust the dials alone. I would think that (I may be wrong here) that for motor mounts you'll want to have some level of parallel tolerance for the plates. Your work holding methods, head tram, fixture (vise?) accuracy, and tooling will all conspire to help or defeat your tolerance goal as the weakest link will decide your results. For determining "zero" on the WP there are many methods but working with a total cut of less than .005 becomes more difficult with a small machine like a Sherline or Taig. The amount is always relative to the accuracy of the machine itself and depth of cut. For taking .0002 I've used a magic marker and brought the cutter/wheel to where it just wiped it off to establish "zero". I've verified "zero" by taking the cutter/wheel over the surface and observed for metal removal to verify rather than trust what "should be". The temperature of the WP can make a huge difference too as odd as that sounds. Thermal expansion can cause the WP to "grow" up into the cutter/wheel and material will be removed where you don't want it to.

[roninB4]

There are also other factors you'll need to consider. Warp of the material after machining can greatly affect your results/accuracy. The more material you remove AND the location of the cut on the WP can cause warp. I refer to it as The Potato Chip Factor. I've made cuts on a plate, pulled it out of the vise and it bowed/warped beyond the tolerance range. Each material behaves differently and sometimes the individual piece itself can have internal stresses that are released after the cut, wood behaves the same way sometimes.

I didn't intend to infer that you weren't smart enough to avoid being hurt. I had no way of knowing if you worked in a large shop with large machinery. I've seen several industrial accidents and they're awful to witness, just didn't want to see that happening to someone trying to learn.

I'll apologize for not getting back here sooner, I'm building a shop and it takes a lot of my time. As for the random sequence of my answers, I've not had enough coffee yet and I may not have properly answered your questions. Your own personal observations, experiences, and advice from others will help you greatly in the learning curve. Post up when you have questions, perhaps one of us can help. Good luck.