Cutting Wing Rib Forms #118 - Oklahoma USA

[lonestaral]

Thanks for the concern Ken C.
It was to the North West of here.
Some felt the quake here but I was unaware of it.
One of the strongest for a long time.
The MM is fine and working well.

[pblackburn]

Congrats on 118

[IMMark]

Congrats on #118.....that's a fine number!
Mark

[racedirector]

Congrats on #118, I myself am aiming for 120.

[domino11]

Congrats!

[Tom Ayres]

Congrats DB! I was wondering who get the next number first. Sleepyhead Mike can go back to sleep now.

Oh, Bruce you can be number 119 if you want it bad enough...lol

[racedirector]

Not if the control box has its way Tom

[dbinokc]

I saw this video posted today on the welding tips and tricks channel on youtube.
A laser pointer is used to show how steel distorts as you weld it.

https://www.youtube.com/watch?v=0pf-qQDslhU

Next time I am welding something, I am going to attach a laser pointer to the piece to see how things move around as I weld.

[pblackburn]

That is the reason why when we need a precision part that requires a weld process, we allow a tolerance so it can be machined afterward. The tension that welding puts on steel is great. You can pull and push the motion somewhat but it all depends on the steel, the grade and quality. I have never seen a laser used to demonstrate it.

[dbinokc]

I got the PMDX-107 wired into the VFD yesterday. That will be nice. It was getting a little tedious to have to turn the spindle on and set the speed manually. The only thing I need to remember to do is make sure the spindle is not turned on when I am doing pen tests! I did not make that mistake, but I am afraid at some point I will forget.

I also dismounted the spindle to drill some mounting holes in the spindle mounting block for holding the pipe for the vacuum. I also drilled a few extra holes for any other things I may want to attach in the future. That is one nice about having the big hunk of aluminum block. Lots of meat to drill holes into.

Finally did some real airplane work today. I started drilling holes for four doublers in the center spar. This is basically a 1/4"x2" by 1014mm (mixed units I know) piece of aluminum bar. While I was not going to trust the mechmate to drilling these holes, I did use a pen to layout the holes in one piece and manually layed out the other. These are all match drilled. So the manually drilled the piece I layed out and clamped the other to it.

The result is the pic below. The lower is the mechmate layed out piece and the upper is the manual method. The holes were match drilled together. There is a little offset in the holes in the top compared the lines, because I align to line edges, not line centers.

The conclusion for me is that if I had used to MM to drill these holes, the piece would have been acceptable, but I would not have been happy with the accuracy. There was as much as a 1mm difference between my layout and the MM layout.

I think part of error is due to my not having the steps/mm quite right. I am waiting for a webcam to come in that I can attach to my MM to try to get a better indication of distance traveled.

Part of it also is that the surface of this bar stock is not perfectly smooth and the marker ink had a tendency wick along the grooves some. I think it also affected the tip of the pen.

Essentially there is more tuning to do. I want to see under .5mm error over the full dimension of the table.

[pblackburn]

You will have most likely 0.25mm backlash with using a spur gear drive. If you are using a planetary drive it will be less. I cannot read the specs on your steppers but I they look like steppers with spur gearbox. Only a belt drive will 'rein in' the backlash as a gearbox has to have backlash or it will tear itself apart. The tuning should be fairly easy to set using 0.005" V-bit and a certified tape. Run the steps per unit function starting at a mark at the front of the table and run the set distance to the end of the table. This will set your steps per inch or steps per mm as close as you are going to get. If you are do indeed have a spur gearbox, make sure you move axis in the direction of travel of the Steps per Unit function will be traveling first before running the function.

[dbinokc]

You are correct that that I have geared steppers and I did measure a backlash is about .25mm. I was giving some thought to trying beveled gear drive steppers.

[pblackburn]

Your only hope to reduce it is planetary (3 arc min), harmonic (0 arc min) or belt drive. Belt drive is the cheapest solution.

[KenC]

Belt drive also give more torque, if done properly, a few magnitude more.

[dbinokc]

I finally got a USB extension and was able to mount up my webcam to do some more calibration of the X and Y axis. The camera is a little microscope camera I have had for several years. It fits nicely in one of my extra connector glands.

I used an old eeePC for the camera display so as to not overload the Mach3 machine. I will try the Mach3 camera plugin later.

I am able to get under .25mm over the full range of my meter and 2-meter sticks now. I also checked my backlash. I have about .1mm on the X and about .25mm on the Y. That is going to be due to my using geared steppers instead of belt drives.

If you want to do similar tests be sure to get an active USB extension cable. The regular 15ft extension cables did not work for any of my devices. The active extension cable is basically a single port hub and gets detected by windows as such.

The lower picture shows by how much I am out of square over about 1500mm. So a little more shimming to do around the rollers.

[KenC]

Nice work!

[dbinokc]

The Y axis is finally squared to the X axis. What a PITA!
I did not think I was ever going to get it to come out right.

I used a combination of Gerald's instructions for shimming the gantry rollers and a test pattern of 4 X's 1 meter apart to measure diagonals.

[pblackburn]

That's awesome. I had my rails slotted a little on the Y. I screwed up on the markings for the holes and did not allow for the difference in using the bolt on V rail. In the end it helped for squaring the Y but Gerald's instructions are spot on if you have everything right.

[parrulho]

congratulations on your accurate machine.

[dbinokc]

I made my first attempt to cut some .025 inch aluminum with my downward cutting bit.

The results were not quite what I expected. The bit did not penetrate the aluminum on the first pass. After about three passes it finally broke through, but the behavior is not what I would have expected.

As far as I can tell, I have the bit turning the correct direction. Clockwise looking from above.

Any suggestions on why the bit would be riding over the top instead of cutting through?

The bit I am trying to use is at http://www.amazon.com/dp/B000P4NQGQ/..._26725410_item

[darren salyer]

My first question would be if you were ramping in, or just plunging the bit.
I've never cut aluminum but my gut says you'd want to ramp in, even though you have a shallow depth of cut per pass.
Speaking of, what was your depth per pass?

[dbinokc]

I was plunging instead of ramping. The depth of cut was the full .025 inch.

[darren salyer]

What software are you using?

[darren salyer]

I found this sentence describing the bit, which leads me to believe it may not plunge cut aluminum very well:

(precise hook angle - of bit allows for fast plunging - plywood, hardwood, and soft wood - table-mounted portable routers - kickback reducing design - )

Try to redo your file to allow a fairly shallow ramp in, to let the flute sides do the work.

Or, try a bit designed for aluminum.

[dbinokc]

I am using Aspire.
Any suggestions for a bit that may be more suitable for Al, if this one is not?

[darren salyer]

So you are familiar with ramping?
I'm going to have to let someone more familiar make a bit suggestion, or call a bit supplier tech line and ask.

[dbinokc]

Yes, I am familiar with ramping. The mechmate is not my first cnc machine. I also have a Taig CNC. I have used ramping for milling thicker pieces in the past, but did not think it would be needed for such a thin piece.

I used Mecsoft Visual Mill, but that copy of was over 10 years old and a little dated for features. After evaluating the latest versions of Visual Mill and Aspire, I decided Aspire was the better fit for the MM.

[darren salyer]

Ok, it was just a question. No offense meant.

[ger21]

Do NOT use downcut bits to cut aluminum. They don't work very well, and won;t last long.

Get a single flute "O" flute bit.

[dbinokc]

No offense taken. I apologize if my response came across as such.