Friday, 26 October 2018

Fix Backlash - episode 222

Following on from the last video I explore further the problem of backlash on our CNC machines and how we can use backlash compensation to fix it. Before we start we first need to now what Backlash is and what causes it. 
Put simply backlash is the effective loss of steps when an axis changes direction. These steps are used to take up the slack in the system before it starts moving in the opposite direction. These steps are not translated into movement in the axis so it doesn't travel the full distance. Backlash is non cumulative so will not increase as the cut progresses.



Click to watch


Measuring
To measure this we need a dial who's resolution matches or is better than the axis it is measuring. 

Resolution = 1 / Steps per unit

X & Y axis
1mm / 75steps = 0.0133mm    or   1" / 1908steps = 0.0005"

Z axis
1mm / 315steps = 0.0032mm  or  1" / 8000 steps = 0.000125"

It is really important to have realistic expectations from Backlash compensation.
        The best you can hope for from Backlash compensation is 1/2 a step.
Divide the calculated figure by 2 and if you get better than that then you are like me, lucky.


Measuring tools
For this video I purchased a Digital Dial indicator. Up until now I have borrowed an analogue one but for this I decided a digital display was easier to read.  I have put a link below showing the dial indicator I purchased for this video.

Ebay Affiliate Links. By using this link a small commission is paid to me at no additional cost to you. There are many such dial indicators on the market and this is just the one I chose.

Dial Indicator
https://ebay.to/2yR4alc


Magnetic Dial Base
https://ebay.to/2q3rQit

Macros For UCCNC and Mach3
Thanks once again to John Revill for his work in making Macros for UCCNC and sharing them with us. Over the last few weeks he has made and shared several Macros that I am excited to be sharing with you soon. It is thanks to his Backlash measuring Macro that I was able to easily measure my Axis backlash and was inspired to try and replicate it in a Mach3 macro.

UCCNC Macro
http://bit.ly/2OFAJxd


Mach3 Macro
http://bit.ly/2PSXnP6


Installing the macros and running them is basically the same for both Mach3 and UCCNC.
It is surprising how similar these control systems are in their programming and us.
Just drag and drop the macro into the macro folder and Type M1040 into the MDI command line. If you find you already have a macro M1040 or want to call it something else just rename it as M followed by a number eg M666
So long as it isn't used for something else it should work for you.


The results
John sent me some photo's that illustrated the improvement he experienced by setting up Backlash compensation on his Stepcraft machine. The Laser really shows the backlash and I can see how this will make using the laser much better in the future.

Before Compensation applied 

After Compensation applied

You can see the lines are now aligned correctly compared to the before shot where there is a definite comb effect

How noticeable the effect will be in normal machining I don't know but I envisage it may show improvement in VCarve and PhotoVcarve machining where a fine cutter is used.

Final Thoughts
I have been using my machine for many years without thinking about backlash and I hadn't really noticed an issue. If John hadn't sent me the Macro I wouldn't have givenbacklasha 2nd thought but I'm glad I did.
It makes sense if you have a dial, to spend a little time and check each axis to see how much backlash you have and if you have a problem. Even if the dial you have doesn't have the needed resolution it will still show a major problem on an axis and may also allow you to get most backlash under control. The advantage of a lower resolution dial is it is easier to get those readings looking really good.

Cheers
Peter
















Sunday, 21 October 2018

Rack & Pinion or Leadscrew? - episode 221

Dan Zanotti asked me a little while ago a series of questions about my opinion on Rack & Pinion versus Leadscrew. While I'm happy to tell What I have and why I decided to go one way or the other I'm not usually happy to inflict my opinion on them. In this video I try and explain why I moved to Rack & Pinion and why I think that for my machine the combination of R&P on the X Y axis with Leadscrew on the Z is a good combination. I don't claim to be an expert on drive systems, I'm just a hobbyist like you.
In this video I start to explore Backlash which by my reckoning is the only real difference between the 2 systems that might make you think twice about Rack & Pinion.



Click to watch


Cost 
when trying to decide between the various drive systems cost can play a big part in your decision. It was probably the biggest factor for me because I had to import either Rack or Leadscrew and postage was the biggest factor. For a machine like mine I would have needed a 6 foot leadscrew or a 4 foot Rack and the shorter the package the cheaper it was to send. Rack has the advantage that if in the future I need a longer rack I can easily join it while with leadscrew I would need to replace what I have with something longer. Another issue with sending long packages through the mail system is then could easily get bent. A bend in a leadscrew no matter how slight can be difficult to remove while straightening a rack is easy. the disadvantage of Rack is i needed to buy the drive plate though it is also possible to make one if you know what you need. They are not that complex.

Resolution
Something I didn't really cover in the video is the resolution of each system. By that I mean how many steps per unit each system is. In my case the leadscrew has 4 times the resolution of the Rack & Pinion drive but when you consider that each step on the R&P is 0.013mm or 0.0005 inch then that should be all the resolution I will ever need. We are not building parts for NASA and the wood we use changes dimension by more then that depending on whether it is a wet or a fine day. 

Measuring tools
For this video I purchased a Digital Dial indicator. Up until now I have borrowed an analogue one but for this I decided a digital display was easier to read. the resolution on the dial far exceeds the machines capabilities. I have put a link below showing the dial indicator I purchased for this video.

Ebay Affiliate Links. By using this link a small proportion of any sale is credited to me at no additional cost to you. There are many such dial indicators on the market and this is just the one I chose.

Dial Indicator
https://ebay.to/2yR4alc


Magnetic Dial Base
https://ebay.to/2q3rQit


Macros For UCCNC and Mach3
Thanks once again to John Revill for his work in making Macros for UCCNC and sharing them with us. Over the last few weeks he has made and shared several Macros that I am excited to be sharing with you soon. It is thanks to his Backlash measuring Macro that I was able to easily measure my Axis backlash and in the next episode we will explore Installing  the macros then using them to eliminate system backlash.

UCCNC Macro
http://bit.ly/2OFAJxd


Mach3 Macro
http://bit.ly/2PSXnP6


Thanks to John's easy to follow Macro writing I was able to create a Mach3 version of the Macro that behaves the same. My first Macro written from the scratch. These are posted here for anyone who wishes to use them to measure their backlash. In the next episode I will be demonstrating how to install and use them so don't worry if you cannot figure them out right now.

Well that's all for now so until next time

Cheers
Peter

Sunday, 14 October 2018

Oil Filter Removal Tool - episode 220

Trying to do an oil change on my vehicle today and I couldn't get the oil filter off.
 Unfortunately I just couldn't break the seal holding it in place and my options were a bit limited. 

That's what I love about having a CNC machine. In this situation I would have been left with no choice but to resort to butchery or worse still buy the tool for removing the filter.  

It occured to me that I could try and make one. I know they aren't that expensive but why not make one. After all I'm changing the oil myself so I might as well save a few extra dollars if I can. Drawing it is not particularly dificult and as it turned out it only took 5 minutes to do. For the prototype I'm using some 12mm MDF which I have laying about the workshop. 
Because the shape has 15 flats on it I had dificulty measuring it properly so decided to cut the hole out first and could then test the new filter in the hole before proceeding with the final cutout. Just as well I did because I needed to enlargen the hole by 0.5mm to get a good fit. This is simply achieved by creating 2 profiles using the same tool but give the tool a different number between profiles. this will force the machine to stop at which time you can test the filter in the hole and if it fits then hit cycle start and the machine will continue with the cut. If it doesn't fit then hit the cycle stop, load a new file and recut.


Click to view


The Result
Well there is no doubt about it, the tool worked, even if it had to be shortened a bit. I have redrawn it and created a second tool for the smaller oil filter on Mrs CNCnutz car, just in case she needs it to change the filter.
After using it it looks like MDF is more than strong enough for the job unless the hulk does the next oil change and tightens the filter to excess. I can always cut one from plastic like HDPE if I need to.

Files
The files are available for download for anyone who wants them.

Toyota surf 1998             http://bit.ly/2On6Rpb

Toyota Corolla  1996       http://bit.ly/2PxvI6h
 




Cheers
Peter