Cool thread.. I am also going to add Roman Hall based limit and home switches..nice work on the machine by the way
http://free3dscans.blogspot.com/ http://my-woodcarving.blogspot.com/
http://my-diysolarwind.blogspot.com/
Since you are talking limit switches and I am working on the wiring of my new machine.....my Planet-CNC controller actually uses up to 4 of the 8 individual limit switch inputs also for the homing process. Sounds reasonable to me but what do I know. Is there a benefit to having separate home switches?
Thanks, JB
Hi Khalid!
http://www.cnczone.com/forums/open_s...made_easy.html
Hi JerryBurks, I just use 2 inputs for the homing switches for X and Y. Z does not need the hall switches as it has the z-axis tool zero setting sensor (earlier in this thread).
If you use the hall switches for limit switches they are accurate enough to use as homing sensors too.
One benefit of dedictaed homing sensors with the hall switches is that they can be placed in the MIDDLE of your axis, to "home" there. Then any error from heat expansion of your leadscrew etc will be half as it will be +/- error from the middle of the axis where it was homed. My new precision machine will not have limits, just a homing hall switch in the middle of the X and Y axes.
Also bear in mind that you can parallel the hall switches, so depending on your CNC software you might be able to put two X axis limit switches on one input terminal. The software then determines which switch is activated, by deduction.
Hi Roman,Originally Posted by RomanLini
Hi Khalid!
http://www.cnczone.com/forums/open_s...made_easy.html
.
I posses three CNC machines and no one have installed limit and home switches.. i will not installed the limit switch however i am going to install now the home switches..this is because i want to use Gerry screenset with auto-tool-zero... I will need your help how the home switches works and how to install
Regards
http://free3dscans.blogspot.com/ http://my-woodcarving.blogspot.com/
http://my-diysolarwind.blogspot.com/
Sounds good!
My ears perked up when Roman said: "One benefit of dedicated homing sensors with the hall switches is that they can be placed in the MIDDLE of your axis, to "home" there.
Also bear in mind that you can parallel the hall switches, so depending on your CNC software you might be able to put two X axis limit switches on one input terminal. The software then determines which switch is activated, by deduction."
Could there even be THREE home switches on an axis?
If so, I hope I hope I hope, there can be a defined area on my ShopDroid that does large parts; another defined area for smaller parts; and the area on the near end [near to keyboard and monitor] where parts are to be cut vertically [dovetails and box joints and such]. This would sure save a lot of time zeroing the axes between cuts! [The home switches on the ShopDroid are now planned for the upper left-hand corner].
I am using MACH3 and want to be come at least conversant with EMC2.
My cuts will have lots of circles, arcs and bezier curves of all sizes, and in 2D and 3D. On my small machine I home before each cut, mainly as it is necessary to be able to remove cut parts and insert stock to me cut.
If two or more home switches per axis is possible, would you please explain what this sentence means: "The software then determines which switch is activated, by deduction."
This is better than sliced bread and Christmas all together!!!!
There is no problem with the SENSORS doing that. You can parallel as many sensor outputs as you like. Only the sensor that has the magnet close to it will pull the output voltage low (to gnd). The other sensors are just ignored.
Interesting idea! There should not be a problem with the sensors doing that.
Ok, this is the issue. If your software is smart enough it knows which sensor is triggered by the homing sequence.
For example to home to sensor at the end of the X axis;
1. move to X = 1 inch
2. slowly move back towards X = 0, and;
3. when sensor goes low, home "X1" is detected
Now to home the machine to the sensor near the middle of the axis;
1. move to X = 21 inches
2. slowly move back towards X = 20, and;
3. when sensor goes low, home "X2" is detected
From the small amount I know of Mach3, the homing is done by a macro which tells the machine the procedure to use.
Hopefully you could have multiple macros, to home the machine in different places? I believe it's possible.
The main reason to put the home sensor in the middle of an axis is to reduce the amount of error (caused by things like thermal expansion of the leadscrew). If you are cutting small objects it is best to have the home sensor close to the middle of the small object.
I'll begin with my standard disclaimer of "I'm certainly no expert" but...
I'm not sure I understand why there would be any advantage to home to the center of an axis. If you home to a switch in the middle of an axis, you may not use that same switch as a limit switch because it will trip any time it comes near it - not advantageous.
I use hall switches on my machine and what I did was to put them on the moving part of each axis i.e. one each on the XY&Z axis. I then have magnets at each end as home/limit switches.
To get to different areas of the machine, I simply use offsets in my code. So, home once, rapid over to different areas of the machine. All of my work fixtures are indexed to a machine cut fence at X0Y0 that is very repeatable. When I take my table off for maintenance, I just need to scootch my fence "in" a little bit and re-run my cutting program to reproduce my X0Y0.
-Andy B.
http://www.birkonium.com CNC for Luthiers and Industry http://banduramaker.blogspot.com
You may not be an expert, but you're a lot smarter than me!!
I don't speak "offset" yet as my first machine only has cutting area of 19"x16". The ShopDroid has a cutting area of 7-feet by 4-feet, so its a different story [let me tell you the ways!!!].
I am not planning on limit switches so that is not a concern. [This was Gerry's suggestion and he is smarter than me too!]
Like you, I have fences of the X- and Y-axes, and when I replace the spoil board, the fences get replaced and cut again with a 1/4-inch bit, which is all I use on the smaller machine [aka Bub CNC] as the Dewalt DWP611 only has a 1/4 inch collet. DWP611 1.25 HP Max Torque Variable Speed Compact Router with LED's | DEWALT Tools
The reason I thought of having three sets of home switches is that I can calibrate to three different points as the Droid is being used in three distinctly different ways. Less distance from home switch for better tolerances. And in theory it should not make a difference how far from a home point the axes move, though please understand that I am more of a designer than a wood machinist, so I know me [all to well!] and the fewer assumptions I make about the physical world, the better off I am.
The reason I am building a large CNC is that I have an aversion to having my hands near metal things that are sharp and spinning at high speeds, hence there have been instances where I would spend a day making a jig to make two cuts that took 10-minutes. I view a CNC machine as the ultimate jig. All I have to do is design the part for the cutting capabilities of the CNC machine, and the jig is just part of the process. "Tabs" are my friends.
I do appreciate your questioning me [I am married so am use to it] and in the end your questioning and examples will make the Droid a better and more functional machine.
I wouldn't go that far!
So here's the thing. As I understand it, the errors in the drive mechanisms aren't really cumulative, they're cyclic. e.g. if you're using a .003/" tolerance ballscrew, you will be within .003" of where you think you are at any distance. e.g. at 1" you could be 1.002 and at 6" you could be at 6.002 but you should never be at 6.018 as that's not how the error works on these things.[snippity]
Like you, I have fences of the X- and Y-axes, and when I replace the spoil board, the fences get replaced and cut again
[snippity]
The reason I thought of having three sets of home switches is that I can calibrate to three different points as the Droid is being used in three distinctly different ways. Less distance from home switch for better tolerances.
So, if you're already using fences, you can simply make however many fences you like all over your machine and make offsets to each fence's 0,0.
If a fence is far from your home switch it really doesn't matter as the error from your drive system is probably repeatable. So long as you're not losing steps, it should be as accurate as having a home switch right there.
-Andy B.
http://www.birkonium.com CNC for Luthiers and Industry http://banduramaker.blogspot.com
Sure, for many people there would be little advantage to having the home switch in the centre.
It is an accuracy issue for thermal expansion. Steel leadscrews expand at about 12 microns per metre per 'C. So if your leadscrew is 4 feet long, and you home at one end, small parts cut near that end will be pretty good.
But parts cut near the other end (4 feet away) are subject to the tolerances of 1.3 metres of leadscrew. So a cold machine at 16'C, vs a hot machine where the screw might easily be warm to the touch (45'c) is about 30'C expansion which is 12um * 1.3 * 30 = 468um difference, which is 0.468mm. So those parts will be displaced 0.468mm which is a LOT if you want to make precise parts.
In woodwork it probably does not matter if your furniture has a 0.468mm error on one edge, but for some users that make small fiddly stuff (like me) that might matter a lot.
You made a very good point that a home switch in the middle of an axis will be useless as a limit switch! I only use soft limits so had not really considered that issue.
Zool- Yep you are correct if you put the home switch close to the job you will get the best accuracy and repeatability with homing (in regards to cutting that job).
The ShopDroid has rack-and-pinion drives, so not concerned about leadscrew expansion. Also there will be no limit switches, only soft limits.
My chief concern is time. If I am making small parts I need the router out of the way when the cut part gets taken out and the new stock to be cut gets placed on the table.
The ShopDroid has high sides because of the rack-and-pinion drive system, and as the keyboard/mouse and monitor are on the right side, it is best for me to have the secondary X/Y-axes fence closer to the right side. With the main home position, if you will, in the far left-hand corner, having a second home position closer to where I would be standing will save me time and steps. [More production = more money = happier wife! This may be the ultimate driving force.]
In addition, the ShopDroid will be set up to cut dovetails and box joints vertically, like these:
http://www.youtube.com/watch?v=4Aw4lElTecg]ShopBot Cutting Dovetails - YouTube
http://www.youtube.com/watch?v=ccS2W2O9CJY]Cutting Dovetails on a Joes Hybrid 4x4 1/2 - YouTube
http://www.youtube.com/watch?v=hQRTLXeBA58&feature=related]Box Joint on CNC 4x4 Hybrid Joes - First Try - YouTube
For these types of cuts, the router will be on the "near side" of the table just like in the videos. Having the router move inches instead of feet to a home position is the major consideration in this case. That ole money thing again. [Happy wife is a happy life!]
As for putting X-Y fences all over the table: I built the larger machine [4-feet by 7-feet] to cut larger parts or cut nested parts hence the table at some point will have to be clear.
In woodworking, as in metal working, its the set-ups that take all the time. If there is a means to shorten set-up time, anyone would go for it.
Further, I am more of a designer than a wood machinist, so for the portions of the process that are in the physical world, if I set something up that I do not always have to think about and do calculations [those details again] I am better off as I can produce faster and with assured accuracy. In a nutshell, I can double-check and not calculate. And someday I will be able to speak "offset", but one thing at a time.
Roman, I am quite happy with accuracy in my furniture to 0.015625-inch. And I still have a bridge for sale too.
Thank you both for your thoughts and input.
PS. My dear long suffering wife is not overpowering and money grubbing. She is a clinical psychologist and can be quite insistent about certain topics. What is most irritating about her is that more often than not she is correct in her assessment of a situation, and it is hard to argue with her. I hate to lose, so avoiding arguments is the best way not to lose!! I also divert her attention by keeping the house spotless, all the laundry clean, all her clothes ironed, and the refrigerator full. I have time-efficient procedures for all these tasks too. She sees 25 to 30 troubled souls a week, plus does all her own billing, so I am of the opinion that she does not need to be irritated when she walks though the door at night, so I constantly think about how to use my time to everyone's best advantage.
Last edited by zool; 11-14-2011 at 11:31 AM. Reason: clarification
I hadn't considered that but let me throw out a few more confounding factors -
1) As you use the machine, it will get warmer so you should probably re-home as time goes on.
2) As the screw expands, your home position on the screw will change so, any cyclic error will be different depending on temp so, your repeatability may be changing.
-Andy B.
http://www.birkonium.com CNC for Luthiers and Industry http://banduramaker.blogspot.com
I think that there must still be an issue with thermal expansion for R&P as well - they're still made of steel.
Having multiple home switches doesn't help you with this unless you have hard points on your table referenced to your multiple home switches.
As for putting X-Y fences all over the table: I built the larger machine [4-feet by 7-feet] to cut larger parts or cut nested parts hence the table at some point will have to be clear.
In woodworking, as in metal working, its the set-ups that take all the time. If there is a means to shorten set-up time, anyone would go for it.
I think that something you may want to investigate is some sort of removable referencing system. e.g. you could drill holes in your spoilboard for drill bushings. Make a rough fence with dowel pins in the bottom. Attach to the table and then cut the fence with the machine homed to that switch to create some sort of reference 0,0 coordinate on the table.
When working on big pieces using the whole table, remove the fence. When working on stuff at other points on the table, re-locate your fence in its home using the dowel pins.
-Andy B.
http://www.birkonium.com CNC for Luthiers and Industry http://banduramaker.blogspot.com
Yet another luthier plaguing my life!!
I can't tell whether you guys are a blessing or not! Until I develop a definitive opinion, I will listen closely. Actually, luthiers are at the top of the woodworkers. I really am in awe of your skills and art.
BanduraMaker stated: I think that something you may want to investigate is some sort of removable referencing system. e.g. you could drill holes in your spoilboard for drill bushings. Make a rough fence with dowel pins in the bottom. Attach to the table and then cut the fence with the machine homed to that switch to create some sort of reference 0,0 coordinate on the table.
You are correct and I have a plan. First stage, so production gets going, is to use the ShopDroid to machine holes in its spoilboard for 1/4-20 plastic oval head nylon bolts [they do not ruin bits]. For each new set-up for cutting smaller parts, install new fence [MDF] and machine that new fence so 0,0 is coincident with the "intermediate home position", which will be around the center of the table.
There will also be the "permanent home position," which is in the far-left corner and which will be used for cutting the larger pieces, using X-Y fences that run the length of the axes. There will also be the "cutting dovetails and finger joints home position", which is the near-left corner, which will also be permanent, and which will be oriented to the permanently attached fixture for machining dovetails and finger joints vertically. This is so they are "true" dovetails and finger joints. There are methods to cut these with the stock being horizontal, though these do not meet my requirements.
The second stage of the plan coincidences with the installation of the vacuum clamping system to hold stock while it is begin machined. In one of the many piles of "stuff" about my studio, are the larger parts [tanks, vacuum pump] for the vacuum system as shown here: Do-It-Yourself Vacuum Veneer Press.
As part of the second stage there will be "pop ups" for indexing like these: http://www.youtube.com/watch?v=X6hVL9bomh4&feature=related]Two Minute Setup! - YouTube
The idea behind the Shop Droid is to have a versatile machine because of what I want to make and how I want to make it. Roman's electronic home switches and his statement that more than one home position is possible with them, solved the last [if there ever is such a thing with DIY CNC!] large conceptual challenge.
I do acknowledge that there are more elegant and erudite methods, offsets being one of course. I am not that detail oriented and know my limitations especially in the physical world, and since a machine serves its master [that's the theory] I am going to have more than one home position as that is how I can best use the CNC machine's capabilities for the reification my designs.
Having three fixed home positions gives me constraints, else wise, my mind would wander all over finding marvelous ideas, and never an accomplishment.
By having these three home positions, that orients my thinking to the table, which leads back to axis orientation and movement capabilities which leads back to the stepper motor controller which leads back to the g-code which leads back to the CAM software which leads back to the CAD software conversion process which leads back to the CAD software which ultimately leads back to the rambling inside my head bone. As you can see, what is in my head bone is the BB in the tin can.
I save the modicum of detail orientation I have for my designs which are rigorously mathematical: Every design begins with its overall size based on the Golden Mean, and then the design progresses to functionality with the use of either the Fibonacci Sequence or The Orders.
After all, constraints are what makes for creativity.
Again, many thanks for your concerns, insights, and ideas.
I leave you with this: Satisficing.
Satisficing describes the situation where people settle with a solution to a problem that is "good enough".
People do not seek the best possible solutions to problems, but operate within "bounded rationality".
The term 'to satisfice' denotes the situation where people seek solutions or accept choices or judgments that are 'good enough' for their purposes, but could be optimized. In the tradition of rationalistic economic decision-making, it was conventionally assumed that individuals seek the optimal result. Instead it is often rational to seek to satisfice in that the process of looking for better solutions/results expends resources. A better solution would thus have to justify the extra costs carried in finding it.
I love it! As a "minimalist" designer of hardware and software I do this all the time. Good decision making is to take care of the things that matter and be willing to gloss over the things that don't. And being logical and unbiased enough to know the difference.
My CNC machine is quite "satisficed", it takes care of rigidity and precision quite well, but does not care about looks. So it works really well, but looks kinda "Junky".
Anyway, I'm very Satisficed with the result!
Herbert A. Simon PhD, would glow at that remark.
Dr. Simon is responsible for how western economic societies think about its thinking.
Herbert Simon - Wikipedia, the free encyclopedia
Seems like a smart guy.
After very many years of computer programming ie telling a computer exactly how to think, what steps to take, how to organise things etc I realised that I had "re-programmed" my own thought processes and improved them in a similar way.
I think the smartest people in the world are those that have worked on the process of logic, improving thinking itself. Programmers, lawyers and philosophers.
After providing litigation support to attorneys for 15-years, I am convinced that Shakespeare is the only one that had a clear idea of how to improve lawyers.Seems like a smart guy.
I think the smartest people in the world are those that have worked on the process of logic, improving thinking itself. Programmers, lawyers and philosophers.
One of them really smart ones - AFAIK, the only person toSeems like a smart guy.
win a Nobel and also a Turing.
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