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Messages - klapa

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1
General Mach Discussion / Re: Calibration Issues - odd results
« on: June 18, 2011, 01:15:52 PM »
Quote
Are you doing the autocalibrate routine Huh  What are your axis specs  motor,gearing feedscrew , microstepping Huh?

What settings are in the config setup ?

(;-) TP

Well - I did not measure all the teeth and gear ratios - I first used the autocal routine in Mach3, and using that zeroed in on the steps per unit, and fine tuned it with measurements.

Yet - as mentioned - the perplexing part of this is that I have different results using a dial indicator vs. a steel rule.

I went through this process again Friday - I will setup the dial indicator by loading it with about 10 mil - then zero the dial - and then make a 500 mil move.  Here I am using the motor cal value (counts per unit) I obtained with the "ruler method".

When I make the 500 mil move - it is right on the money - yet when I return to zero - the thing will be 10 mil off.

If I make a 1000 mil (1") move with the dial indicator - and using the autocal routine setup the counts/unit in the config - both positive and negative moves will be within 1 mil - i.e. the dial indicator moves 1" and properly returns to zero.  For example - for such a move on the X-axis the counts/unit will be ~8750.  

Yet - using this value in my motor tuning config results in a GROSS error across a 4" move on the same axis - over 1/8" (125 mil). I can see the error with my eye - I don't even need to measure it.

Using the "ruler method" with my calibrated "carpenters eyeball" I will come up with a count/unit of ~1790.  Using this value in the config, I can move in 1000 mil increments across the full 8" of x-axis travel and cannot discern an error on my ruler which has graduations of 1/20" (50 mil) (using my eye).

I have just bought a 24" machinist rule from McMaster-Carr which is graduated in 50ths and 100ths of an inch.  I will scribe a small reference line on the bed rails for the y-axis - and the crosslide rails for the x-axis - and use that to calibrate it.  As we are an electronics manufacturer - I also have access to binocular inspection scopes which I can setup plumb and level - and use that to see the results on the rule.

It is really not "fair" that I am asking all these questions here on the Mach3 forum - as the software works very well - is straightforward to use - and really delivers allot of "bang for the buck" IMHO.

I need to read some books - but for the meantime this job needs to be done by next Wednesday.....

I will go to CNCZONE and see if they have a thread for "People who want to be a machinist but don't know their ass from a hole in the ground".  :)

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General Mach Discussion / Re: Calibration Issues - odd results
« on: June 14, 2011, 07:19:56 PM »
Yet that IS the problem - I do the cal with the dial indicator for a 1" move and I can get it correct withing 1 mil.

Yet using the value I obtain from that cal (for the pulses per unit) a big move will be off.

Yet if I use the ruler and cal for a big move - small moves - across the full travel of the axis - seem to be correct - much better than the gross error when using the value obtained with the small move and dial indicator.

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General Mach Discussion / Calibration Issues - odd results
« on: June 13, 2011, 09:19:57 PM »
I was trying to fine tune the calibration on our machine today.

I thought I had it nearly right-on for the X and y axis, but have some confusing results.

I am using two techniques for the calibration - as I don't have a set of gauge blocks I am "roughing in" with big moves and measuring with a ruler (1/20th" scale - 50 mil/division) and then finally "fine tuning" with short moves (<= 1") using a dial indicator and magnetic base.

The problem I have is that the measurements between the two techniques do not agree.  I don't think it is a machine problem - I think it is my measurement technique.

I can get the calibration right on the money either way - I can set the counts per inch using the dial indicator for a 1" move +/- 1 mil - and this is for both directions - I will measure 1" and then do the opposite move and return exactly to 0 - +/- 1 mil for the opposite direction move.  I have the same results with both G0 and G1 moves.

If I go with the numbers I get from the 1" move with the dial indicator - I will have, as a example for an 8" move on the X-axis, a bit more than a 1/8" error.  Yet I can return to zero position where I started and I've got a zero on the dial - and a 1" move will still yield +/- 1 mil - either direction.

Here the travel is too far - and the cal value for the counts per inch is ~8100.  I am using velocity between 10 and 20, based on how the stepper motors respond.

So - using the "ruler technique" - with a "calibrated eyeball" I will perform the cal again - and come up with something like 7975 counts/inch.  Now the 8" move is nearly perfect (with my eyeball) - and also incremental 250 mil, 500 mil, and 1000 mil move are right on the money!

I certainly understand that my eyeball is not as accurate a a dial indicator - yet am perplexed by my results - as certainly I can discern two divisions of the ruler (100 mil) with my eye.

As I have the same results in both directions on both X and Y axis - I don't think this is a mechanical thing like backlash - I think I have a flaw in my measurement technique.

Tomorrow I will first get the machine cleaned and lubricated - as I have found that the proper lubrication makes a big difference.  I have been just spraying WD-40 on the crosslide and bed rails for the short term, but the manual recommends 10 weight machine oil.

I will get this machine as clean as a rifle in boot camp, oil it well according to the manual, and try again.

Is white lithium grease OK for the drive screws?  This adheres better and longer in my experience with engines.

4
Quote
To take points in turn. If you need to rotate, make sure your fixture is repeatable. Without this, any accuracy in the machine is meaningless. Calibration looks good for what you are doing (Z doesn't need to be super accurate for drilling). Pan won't need to be punched. Use the correct drill bit and it will be OK. Use the shortest, stubbiest drill bit you can get and chuck it up as short as possible. Rigidity is your friend. A four facet point will help with centreing. Z is more conventionally set as zero at material surface; X and Y to suit yourself. Acceleration profile is quasi-independent of feedrate. Acceleration is how quickly the machine ramps up its speed from zero to the desired feedrate. I say 'quasi-independent' because if your acceleration is low, the feedrate is high and the move is short, the acceleration will govern the actual speed the machine reaches. You control it with the F-word (the G-code one!). E.g G01 Z-0.25 F60 would send the Z-axis 0.25 (inches) into the material at 60 inches per minute (i.e. 1 inch per second, or roughly 1/4 of a second for the manouvre). LittleMachineShop has an online speeds and feeds calculator, where you tell it material, tool type and diameter and it gives you a guideline feedrate.

Thanks for your response, djc.

I thought the fixture would be important.  The pans will come with two holes on each flange, for later mounting of the assembly to the finish frame, or bezel.  I plan to have a holding fixture with tapered steel dowel pins that fit those holes and locate the thing properly on the machine, with a couple of quick release type clamps to hold it from lifting or twisting.

Ultimately we will order the pans drilled from the fab shop - but will run a couple of hundred to finalize the design.

I'll try some of your suggestions today as I going to get some scrap material and start working on the program.

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General Mach Discussion / Is there a thread dedicated to n00bs here?
« on: June 12, 2011, 12:46:51 PM »
I mean like a thread for somebody like me that is not a machinist!

I design electronics for a living - but am currently tasked with getting a combo mill/lathe (Shoptask) machine up and running to run prototype quantities of mechanical parts for our products (LED lighting).

I need to get this done by next week - so no pressure :)

What I need to do here is use this machine as a sort of automated drill press to drill holes in a sheet metal "pan" that is ~18" square.  These holes will be for mounting 4X LED PCB to the pan - the finished product being a 24" square light fixture.

I would imagine that my required accuracy would be on the order of +/- 10 mil across a dimension of ~18" in the Y axis and ~8" in the X axis.  I am basing this requirement on the size of the fastener (screw) and the size of the hole in the PCB.  Due to the 10" limitation of movement about the X-axis - the pan will need to be rotated 180 degree during the process.

This machine has three stepper motors to drive three axis - X,Y, and Z.  Currently I just need to use for drilling sheet metal which I would imagine would be a maximum of 100 mil thickness (probably less) and the material would be steel.

I have managed to perform a cursory calibration of the machine as far as movement goes with the Mach3 software.  I do not have a set of gauge blocks so first "roughed in" the calibration using a steel ruler for 4" moves - and then fine tuned it using a dial indicator for 1" moves.  I currently have the Y-axis +/- 1 mil, X-axis +/- 3 mil (this can be improved), and Z-axis +/- 6 mil (the Z-axis on this machine has a problem).

Is this calibration technique adequate for my needs?

Will the "pan" need to be pre-punched to guide the drill?

Should I use normal drill bits or pilot drill bits?

Is there some "convention" as to what is "zero" for each axis?  I currently have dead center of the X and Y axis as zero - and Z-axis zero is fully retracted - i.e. Z only moves in a negative direction.  Is this "normal"?

What about feed rate?  I know from using a manual drill press that this matters - but I am not sure I understand the concept using Mach3.  Is this simply a function of the acceleration profile setup during the motor tuning calibration - or are there other ways to control this?

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Hello - I am klapa - tho actually that is my dog's name! haha

I am an electronics hardware designer by trade - not a machinist by any means.

I sort of got "roped in" to getting an old combo mill/lathe working to drill some sheet metal for initial prototype quantity runs of a product my company makes.

This machine is a "ShopTask" bought for $750 at some equipment auction.

I don't mind so much because I am also a "car nut" and am already thinking about all the custom parts I might make with this machine!

I was introduced to the Mach3 software by a guy I was referred to by the maker of the machine we have - this guy has a company called "Camtronics".

I also noticed that this same software, Mach3, is used on another machine we have - a selective soldering machine.

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