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Newbie with inaccurate machine looking for tips
« on: April 14, 2013, 09:08:07 PM »
Hello, my name is Chris and I am quite new to CNC.  I have no CNC background at all and am having some issues with our machine and hoping to find some help here. i have had a machine for around 4 years and used it very little for the first few.  It is a Vortech with 5x10 bed with stepper motors and at the time I didnt realize it is lkely a piece of junk, but I am getting ambitious about figuring this thing out. We have been using it regularly the past 6 months but it isnt very accurate and would like to try and dial things in if possible.

First main issue:  If cutting a rectangular part, it turns out to be out of square. For instance, I just cut out a part that is 29x15 with a bunch of 1/2" holes in it.  It comes out at 29x 15 1/16 and is 1/16 out of square. I tried tuning the motors to get them as accurate as possible already but am not fimiliar with all the different aspects.

Second issue is if I set my bit to zero on the corner of the material and run a program, instead of returning exactly to the zero point, it always comes back and sets the bit just short of 1/8" forward in the Y.

I am wondering if this is just a function of a poor machine or something I can adjust to compensate? I have poured over the forums trying to search out the answer and while I am sure it is there somewhere, I havent pinned it down yet.

Any help would be highly appreciated.

Anybody from this neck of the woods (west central Minnesota)willing to do some side work showing us the basics of Mach?

Chris

Starbuck, MN

Offline RICH

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Re: Newbie with inaccurate machine looking for tips
« Reply #1 on: April 14, 2013, 09:25:51 PM »
Make sure your steps per unit are correct. You can find info in Member's Doc's on how to calculate them or in the manual.
You can also use the axis calbrate feature in Mach. Click the Settings Tab ( ALT-6) and just above the reset button you will find the axis calibration. Also check for backlash, again info can be found in in Member's Doc's.

RICH
Re: Newbie with inaccurate machine looking for tips
« Reply #2 on: April 14, 2013, 10:10:10 PM »
Rich,

Thank you, where do I find Members Docs?

I attempted to set the steps/per manually by cutting a rectangle (many times) and then adjusting the steps until it was close.  Not site if this is the correct procedure or not but I did get things close when measuring a small part.

I was reading old posts and ran across one with a fellow who had a similar problem and resolved it when somebody had him change the CV angle.  what is this?

After running most any program the bit will home back to a position positive in the Y.  That distance is fairly constant regardless if it has run a short programor a long one.

Thank your your help, any responses are much appreciated.

Chris






Offline Tweakie.CNC

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Re: Newbie with inaccurate machine looking for tips
« Reply #3 on: April 15, 2013, 04:16:35 AM »
Hi Chris,

Welcome to the forum.
Members Docs. are here http://www.machsupport.com/forum/index.php/board,78.0.html

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Newbie with inaccurate machine looking for tips
« Reply #4 on: April 15, 2013, 06:17:03 AM »
Chris,
It's a long shot, but make sure someone has not enabled a formula in order to compensate for a mechanically out of square machine. 
John Champlain
Re: Newbie with inaccurate machine looking for tips
« Reply #5 on: April 15, 2013, 09:10:49 AM »
Thanks John,

I bought the machine new and nobody else has touched it so I don't think that could be set up to run out of square.  This machine has 2 stepper motors (one on each side) that runs the y-axis.  My suspicion is that one of them has some serious backlash so that they are not running in perfect sync.  Is there a way to compensate just one motor of the axis and not the other if this is the case? I ordered a dial indicator to check and thought I would check it with the motor on the left of the gantry and then on the right to see if there is a difference.

Chris

Offline stirling

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Re: Newbie with inaccurate machine looking for tips
« Reply #6 on: April 15, 2013, 10:04:40 AM »
if it's one of these (a link to what you have always helps) then I suspect they may be using the old double spur gear slightly out of phase ploy to reduce backlash on the r&p. You may find that one of them on one side has slipped or was not set up right. Worth checking anyway.

Ian
Re: Newbie with inaccurate machine looking for tips
« Reply #7 on: April 15, 2013, 10:30:59 AM »
Stirling,

Yep it is that machine. I have no experience with other machines and this is really the only one I have ever had my hands on but the gears on the machine (that the motor gears contact) are a plastic, not a metal.  Seems kinda shoddy though I have seen other claim that this same machine works well for them and is made the same way.

Which is the double spur gear and how do they set it to be out of phase? Asking so I can attempt to check it.

I will try and take pictures when I get a chance and post.............wondering if there is some way upgrading these parts of the machine by replacement of something better?

Thank you for your time, Chris

Offline stirling

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Re: Newbie with inaccurate machine looking for tips
« Reply #8 on: April 15, 2013, 11:24:15 AM »
but the gears on the machine (that the motor gears contact) are a plastic, not a metal.
You mean the racks? You sure? Please say t'aint so...

Which is the double spur gear and how do they set it to be out of phase? Asking so I can attempt to check it.
Well in their blurb they state "anti-backlash rack n pinion". Often this is acieved by having two gears on the same shaft mating with the rack, then one gear is rotated slightly with reference to the other which reduces the backlash that is inherent in all (AFAIK) r&p setups. Not saying this IS how they've done it - there are other ways - 'twas just a suggestion. - Still trying to get my head around plastic r&ps on a machine listed for $18.5K.

Ian
Re: Newbie with inaccurate machine looking for tips
« Reply #9 on: April 15, 2013, 10:21:19 PM »
Rich,

Found the member's doc's and did the calibration today on the motors using the function in Mach. (much easier than doing by cutting and manually changing the number) Thank you!

I will check for backlash in the next few days when I get a dial indicator. I did all checking today by rigging a 12" micrometer in a solid position and running the bit to open it. Did it many times and took an average and entered that reading into Mach to make the adjustment on the calibration.  It was only off a few thousandths.  I did notice that when running the micrometer open in the x-axis that the motor would stop and there would always be a few thousandths gap between the bit and the micrometer jaw, indicating that the bit was bouncing back a bit. This was under no load so I am sure when cutting material this gap may not happen, but it says to me that there is certainly some backlash?  Is this something that Mach can compensate for in the Backlash settings?

We ran a small part and it came out fairly accurate.  But if I run a bigger part, especially with some holes cut in it, the part comes back way out of square, 1/16" at least. I should mention that I am cutting cast acrylic, but that shouldnt have any effect on things.

Stirling,

The rack is not plastic, but the gear that the motor runs is some sort of plastic or fiber, not metal. It was originally on crooked (spun kinda like a bike tire with a bent rim). I shimmed it a bit to get it to turn smoother when I first checked things out. I attached a few pics showing the setup of how the motor turns this gear. There are 2 of these, one on each side of the gantry which runs the y-axis. Each motor has its own driver and while testing it today appeared to be somewhat accurate (not under any load) on both sides. But, when cutting parts (especially ones with any sort of circles) the parts are aout of square.  I am trying to narrow down if it is a mechanical problem or if it could be a driver/motor/other electrical issue.


A pic of the stepper running the x-axis is also attached.....same plastic gear.

This setup, with the plastic gear and the way it transfers the motion through the steel and to the rack, just doesnt seem like a precision way of building a precision machine.

So, my question is: Is there a way to retrofit this machine (without major rebuilding) to a system that might be more accurate? Would new drivers help?  The ones in there have to be some cheap Chinese ones.

Thank you all for the time to give me some advice...should have joined this forum 4 years ago when I got the machine! It has really helped.  Chris