Drilling holes

[BobWarfield]

I missed hearing a conclusion on the tram?

FWIW, I would try to find a way to measure repeatability at 2 different Z heights for the IH mill head. I assume, particularly with a big Albrecht in there, that there is a significant Z difference for the head in the 2 operations?

It would be interesting, for example, to try boring a hole with a center cutting end mill at the two different heights or even a test bar of some kind and find out if there is any shift as the Z is moving.

The head may be trammed, but is the column squared, in other words?

One test would be to put a DTI in the spindle and measure against a vertical reference (cylindrical square, angle plate, or something that's really perpendicular to the table) and see how much the DTI deflects as you move the head up and down.

If this is the issue, the next step is to either correct the problem or perform the two operations with the head moving as little in Z as possible. On the latter, put a screw machine length bit in an end mill holder instead of Albrecht chuck.

Just a few thoughts...

BTW, fascinating looking part, what is it?

Best,

BW

[wildcat]

Ok, I see. If zero degree is along the horizontal axis and on the right side and increase in the counterclockwise direction when viewed from above (all standard IMHO then these were started at 180 for the CAM generated program and 90 for the human generated program. Both were complete in a single full circle G2. Mach3 1.84 is the control software. The OD is pretty consistent...

When you cut outside the limits on the machines that don't like full circles do they not cut all the way or the path oblonged or something else?

Originally Posted by HIRAH I know that a few of our milling machines won't cut correctly more than 90° and less than 180, or more than 180° and less than 360°.

[wildcat]

Bob - I had another problem with this part. After cleaning out the space the mill came back to clean up the holes. The first time I ran this I retracted and tried to come back to -.125. Unfortunately, the mill overshot a little and little diamonds were left between the holes (neat look but not what I really wanted). This lead me to put a height gage on the table and measure against the head at a few different locations. I found there was .0020-.0035 of backlash which has partially been corrected in Mach3. The second run instead of retracting the mill zig-zagged between the holes back to the first hole so I didn't really test if Mach3's backlash corrected the problem but regardless the part turned out better. So, testing with the height gauge (a Fowler - I didn't break the bank on the height gauge front) the head seems pretty good at repeating position over a large range and now most backlash is compensated for. I had used a test indicator previously, zero it on the table, go up a few inches and rapid down to zero. No broken test indicator and the reading was dead on.

You have a very interesting suggestion about making test cuts at different levels... have to think about how to do that at reasonable cost.

I did measure with a test indicator against a 2-4-6 block (got a set after seeing them on your site actually) and please remember these are no-name Enco 2-4-6 blocks so I don't know their true squareness. Anyway, measuring with a test indicator against them along the 6" there is roughly .003 different in both axis (I think I previously wrote the exact values in this thread). Measuring with a dial indicator (not a test indicator) against a square shows no measurable difference in 6". Which measurement is to be trusted? Cylindrical squares are probably the best but they must be made out of gold.

I previously ignored the small tram errors like in the above paragraph simply because my parts are not that thick so a .003 difference over 6" is nothing over 1/2". I never gave much thought to how it might affect relative positions between tools (in this case a drill and a small end mill). Very interesting.

Unrelated to this thread really but perhaps interesting - Another unexpected source of error has come from my vise. I use a Kurt 688 vise and previously really tighten it down on the part. Well, as material is milled away so is the strength. I have actually measured error introduced by deformation caused by the force of the vise. In the worse case while cutting a slot at full depth I had the slot compress and pinch the 1/4 endmill till it broke. Now, I tighten it a lot more gently.

The part is my attempt at a part made in house for lab equipment. I was not involved with it so I don't know the lab but I do know that when built with a 3D printer it did not build properly. Hey, I had a weekend - if I was not doing this I might have been watching TV

In search of precision...

[CountZero]

@wildcat

Just a tip on slot milling, try to plan the cuts so the slot won't be compressed(make it in the y instead of x direction for example).

@BobWarfield

You have an amazing collection of information on your site, wonderful!

[wildcat]

That's a great idea. Difficult for circles but point well taken. It just shows the tricks one picks up with experience. I watched a training video recently and the guy said that he tries to write the programs to make cuts, when possible, right to left (or was it left to right?) so the chips are thrown away from the operator. It would have taken me years of being beat with hot chips to realize that And that stuff (illusive common sense), doesn't seem to be taught much. I picked up a book recently "Machine Shop Trade Secrets" by Harvey that is full of stuff like this.

Originally Posted by CountZero @wildcat Just a tip on slot milling, try to plan the cuts so the slot won't be compressed(make it in the y instead of x direction for example).

[BobWarfield]

Wildcat, you are going to learn it all in the best possible way--through experience!

It sounds like things are not quite square as you move up and down in Z based on the measurements you are getting. Your next question will be whether you want to try to minimize z movements by using shorter tooling for drilling (just to get the job done), or whether you want to start shimming your column until things get really square for the Z moves (a more permanent solution).

I love that you worked on this part even though it wasn't really a "pride and joy" project. Chalk it up as valuable experimentation and learning. I try to set aside a little of my time just to go out in the shop and try things. I usually learn more at those times than when I am on a project. With the project, if something measures out wrong, I just fudge it and push on in order to get done. With experiments, there is no point in fudging it because you are there to learn.

CountZero, thank you for your kind words!

Best,

BW

[ctate2000]

Not a drilling problem. You have a interpolation issue. Check your code for math errors. Check x axis for backlash. Check roundness of OD. Place indicator in spindle locate center of hole then indicate OD and check for out of round condition. The consistancy of the error is indicative of the too problems I suggest you check for.