Machining Aluminum #122 - Sydney, Australia

[racedirector]

Wow its been a while since I updated things.

The Big Red beast is still going, been cutting a little here and there but nothing major.

My future plans call for stability and accuracy so I went ahead and started the twin 6mm mdf gantry revealing job and almost have it done. This last effort is to take 1.8mm out of one of the front wheels, just having a brain fade on which one

I have also ordered the Wixey WR525 digital measuring kit to get my distances spot on, hopefully that will arrive soon.

And the big one is I have just ordered a Centroid Acorn kit, a Mill Pro licence and one of their Wireless pendants, all a bit exy here in Aus ($AUD975.00) but I hope things will improve over using LinuxCNC/Pathpilot. Expensive mistake if it doesn't!

With Acorn I just have to figure out how to set the Axis "steps", Acorn does it differently than every other piece of software out there. The Rack & Pinion thing has me stumped at the moment, especially since I am using metric racks, metric pinion and pullies, Mod 1 to be exact. All part of the deep learning curve to come....

Cheers

[racedirector]

Got a few goodies from Centroid, my wireless MPG, Acorn board, Power Supply and 8 relay board for the outputs. I am waiting on a new computer to run CNC12 but that should be with me tomorrow.

[racedirector]

Slowly getting things happening with Centroid Acorn control. Heres a quick video air cutting a Mayan Calendar....

https://youtu.be/3DKkDJY7OFE

Getting there slowly

[MetalHead]

Thanks for the details on the Acorn. Would love to see a picture of the cabinet.

[racedirector]

I'll grab a shot once I am finished in there, still need to wire up the spindle/VFD under Acorn PWM control.

That video is an air cut of a 600mm Mayan calendar. I ran that under LinuxCNC using Tormach Pathpilot software and it took 2.5 hours. My aircut finished in 1:41, a full 50 minutes faster. That is with Smoothing on in CNC12. I will run another once the spindle is up and running for real and see if there is a difference in quality.

I have read multiple times that Acorn improves cut time, I wondered if it was true - it definitely is!

Cheers

[racedirector]

Hi all

Been having issues lately with accuracy, The weird thing is the machine was told top cut 1090mm and it did it perfectly yet when it was told to cut 12.5mm, it cut 11.8 and then was told to cut 16mm andit cut 15.25.

I have 30 tooth pinions on a metric rack and do not get what is happening. Do I need smaller pinions? I want this machine to be as accurate as possible so am lost as to what is going on.....

Any suggestion or info would be appreciated.

Cheers

[Surfcnc]

Hi Bruce can't remember anything about our machine and too lazy to bone up on your build BUT

The machine has more torque (significantly more) at low feed speeds.
Torque is best described as falling off a cliff as the traverse speed increases.
Slow the machine right down and make your cuts again to ensure there are no missed steps.
Cut something soft like MDF to give it an easy job to do.
Or traverse the machine from point to point and check the distances x and y.

Next put the machine under load.
Fast traverse deep cuts to show up mechanical issues.

A mechanical problem probably pinions loose slipping under higher load is my best quess.
You should have two grub screws per pinion to ensure they are locked in properly.
If you have any belts and pulleys on reduction drives check they are also tight.

Cheers

[Surfcnc]

Measure your cutters with a micrometer.

[racedirector]

Hi Ross

Weird thing is I was cutting MDF and only cutting at 80ipm. I will check the pinions are tight and everything else in the drive line is OK. About to buy a Mitutoyo caliper so will measure the tool I was using too.

Cheers
Bruce

[bradm]

The first thing I notice is that you're saying you were off by 0mm, then 0.7mm, then 0.75mm. The 0mm occurred on a very large cut (1090mm), and it isn't clear to me that you would be able to accurately notice a 0.7mm error on that. So I'm going to assume you have a fairly consistent 0.7mm error, probably in one axis.

Since it doesn't vary with distance, presumably all your ratio calculations are correct.

Does it occur only on one axis? Is the error just along the X or Y direction, but not the other?

Have you tried climb vs conventional milling to see if it changes the outcome?

I'll make a wild leap here based on a bunch of assumptions: You have a little bit of slop in the Y axis, moving the car across the gantry. Either that Y gear isn't tight to the pinion, or there's a little wiggle in the spider when extended to cutting depth ( remove bit, extend, push with hand ), or the tool mounting was imperfect.

[racedirector]

HI Brad

I had just recalculated the steps so they are correct. The 1090mm was in the Y direction as were all the rest. Thats what I find weird, why it cuts larger distances correctly yet it doesn't cut smaller distances. I run a 2.2Kw spindle with ER20 collets, so that rules out the tool mounting, I always make sure the collets are done up tight. All these cuts were completed with a CMT downcut 0.25" bit.

I use Fusion 360 to supply my gcode and always select conventional milling versus climb.

I will check slop in the Y and the Z in the morning, the machine hasn't been used for over 10months while I waited for my garage to be built. It could be from not being used that it is punishing me for not using it

Cheers

[bradm]

Sure, take away all the easy answers, Bruce.

So, I'd definitely try climb milling a test piece. If it's still under, we're looking for axis slop somewhere or tool size. If it's now oversize, then you've got tool deflection potential.

You might also consider trying a roughing pass 1-2 mm out, and then a finishing pass to see if the accuracy improves.

No other differences in cutting ( slot vs edging, etc ) on your large vs small cut?

[racedirector]

I will try all that and report the results

The 1090mm was the overall width of the part, the 12 & 16mm were pockets. To add to the strangeness it cut the length perfectly also at 2200mm

Cheers

[bradm]

Pockets, you say? And you were moving in the direction that tends to deflect the bit into the material, and not away from the material?

Since I'm going out on limbs this morning (here), I'm now hot on the bit deflection theory. Reverse direction in your pockets and/or cut it with two passes ( can be the same location for a climbing bit ), and I'm guessing it just works.

[racedirector]

Well, well.... found 1 X-axis motor with both a loose pinion and loose drive pullies. I am going to check all motors etc and try things again.

[racedirector]

Close but not yet exact......

Recut the pockets with climb cutting at 80ipm 16000 rpm. Designed as 16.5 wide and 12.3 wide at 6mm deep. Came out at 16.15 and 12.1 at 6.4 deep. Will recalulate the steps involved along with accurate measuring with my Wixey system and restest after that.