gcode resetting my surface zero to Z-0.200"

Re: gcode resetting my surface zero to Z-0.200"

Postby TReischl » Fri Apr 19, 2019 8:09 pm

GME wrote:
Good to know, but I doubt that I would ever use it in my practical world. Were I to make a clock face, or some odd shape, I would start with a square or rectangle and cut out the shape. I would use tabs to hold. I don't use a vacuum table, and double faced tape/tape with CA glue is more trouble than the maple clamping elements and t-tracks I use. So, an offset toolpath would always cut out in a square pattern for me.

I'm sure folks with vacuum tables, and others will find the information useful, though. Thanks for sharing.

Gary


Here is an example of using an offset method to finish carve:

20190410_174941_resized.jpg


The finish pass was limited to the outer boundary of the model, the rest of the areas that you see were pocketed out to create clearance for the collet and other junk hanging below the router. There would be no point in finishing a rectangular area, a huge waste of time since this piece is about 22 inches tall. The model itself is about 1.75 thick. Just because I start with a rectangular piece does not mean I have to finish using a raster method. So, doing a clock face would look just like this only much simpler. I also used tabs on the piece when I went to cut it free from the block. This one hangs on the front of my shop just for fun, it is painted.

20190419_150359_resized.jpg
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Re: gcode resetting my surface zero to Z-0.200"

Postby GME » Fri Apr 19, 2019 11:33 pm

TReischl wrote:
GME wrote:
Good to know, but I doubt that I would ever use it in my practical world. Were I to make a clock face, or some odd shape, I would start with a square or rectangle and cut out the shape. I would use tabs to hold. I don't use a vacuum table, and double faced tape/tape with CA glue is more trouble than the maple clamping elements and t-tracks I use. So, an offset toolpath would always cut out in a square pattern for me.

I'm sure folks with vacuum tables, and others will find the information useful, though. Thanks for sharing.

Gary


Here is an example of using an offset method to finish carve:

20190410_174941_resized.jpg


The finish pass was limited to the outer boundary of the model, the rest of the areas that you see were pocketed out to create clearance for the collet and other junk hanging below the router. There would be no point in finishing a rectangular area, a huge waste of time since this piece is about 22 inches tall. The model itself is about 1.75 thick. Just because I start with a rectangular piece does not mean I have to finish using a raster method. So, doing a clock face would look just like this only much simpler. I also used tabs on the piece when I went to cut it free from the block. This one hangs on the front of my shop just for fun, it is painted.

20190419_150359_resized.jpg



Nice model. Turned out well. I like the paint job. Did you create it from scratch, use and .stl, or start with a .bmp, .jpg, etc. and go from there. However you did it, good job!

I guess I'm not following your description completely, at least as it relates to my rosette. Referring back to my rosette, I started with a square block, and cut out the circular shape (bullseye) in the middle. Never touched the block, except in the center area. I zeroed to one corner of the block. When I simulated cutting with an offset, the cut went in a square. Had I cut out the bullseye in the center with a profile cut, it would have gone in a circle, but that would make no sense for door/window rosettes. So, when you mentioned no point finishing the rectangular area, I related to that. There was no point in finishing the square area around the bullseye.

Also, I didn't suggest that I had to finish with a raster cut. I could have used an offset, but decided to go with the raster. Actually, my choice was more or less arbitrary. I ran the simulation with raster, it looked okay, so I cut that way. Nothing more to it than that.

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Re: gcode resetting my surface zero to Z-0.200"

Postby TReischl » Sat Apr 20, 2019 12:49 am

A lot of this stuff is very arbitrary, sometimes too much so. Every now and then I start cutting and think WHY IN THE HECK AM I DOING IT THAT WAY!!!!!

If you put a circle around the actual rosette to be cut and then selected Offset you would not have had so much up and down movement. Also, generally speaking on parts like that, you will bet a better finish, well maybe not, if you remember to cut with the grain while you are going up and down over the hills and valleys. It is a toss up but one thing is for certain, by doing an Offset type of cut the job would run faster because the machine would not be limited by all those z moves. It would move down a bit and then cut full programmed speed around the rosette.

As for the pirate dude. He is a purchased model that I pretty much disassembled and reworked to get the effect I wanted from it. I have gotten real good at drawing vectors in Corel and fast. So quite often I will purchase a model that is one big honking stl file and then take it apart and adjust things or add/remove things from it. I only model something when nothing is available. One of my favorite tricks is to get rid of lettering I do not like and replace it with something I like better. No one ever talks much about editing existing models. It is a handy tool to have.
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Re: gcode resetting my surface zero to Z-0.200"

Postby Mr.Chips » Sat Apr 20, 2019 2:12 am

Thanks TR

I set those look ahead figures.

And yes my Z screw is a one start, my thinking was the stepper could transmit more torque than a five start. Using a 2 start acme on the X axis and a 5 pitch ball screw on the y axis.

You all have got me thinking about rack and pinion, looking around at different builds and how they handle backlash.

TR do you have pictures posted on your machine?

Put my Z stepper back on made some hold downs out of maple and V cut a couple of samples for the women’s lunch, no steps lost, funding fine, no hard to cut Chinese characters, just old fashioned English. But ran at my super conservative settings IE 40 IPM. And your recommended V&A settings.

Yes there off center this is just showing what the font and material look like.
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Re: gcode resetting my surface zero to Z-0.200"

Postby TReischl » Sat Apr 20, 2019 1:45 pm

Mr.Chips wrote:And yes my Z screw is a one start, my thinking was the stepper could transmit more torque than a five start. Using a 2 start acme on the X axis and a 5 pitch ball screw on the y axis.

You all have got me thinking about rack and pinion, looking around at different builds and how they handle backlash.

TR do you have pictures posted on your machine?

Put my Z stepper back on made some hold downs out of maple and V cut a couple of samples for the women’s lunch, no steps lost, funding fine, no hard to cut Chinese characters, just old fashioned English. But ran at my super conservative settings IE 40 IPM. And your recommended V&A settings.

Yes there off center this is just showing what the font and material look like.


You are correct that your one start screw will transmit more torque. However that torque comes at the price of increased rpm required to achieve a given lineal feed rate. That motor has to really fly to achieve higher feed rates. When you are plunging you really do not need a whole lot of torque because gravity is on your side.

OK, looks like you have it basically running. Now that you understand the gcode controls the feed rate you can start tuning the machine. That is why Mach3 calls it "motor tuning". You do not need to cut stuff while tuning until you feel you are close to the optimum settings. The place to start is with X/Y axis. First set the velocity much higher, on a screw machine like yours I would set maybe 250. Create a program that does stuff like profiling with the feed rate set to increasingly higher values until you either fail and start to lose steps or you reach the maximum velocity. If you reach maximum velocity then it is time to increase the accel and rerun. I would increase the accel by about 5 each time and when it fails back it off by about 2 until it runs correctly.

This was all done with air cutting so there was no side load on the spindle. Run your test cuts in wood. If the machine fails back off the accel until it does not. Eventually you will reach a point where the feed rate vs the accel is acceptable to you. There is no way for anyone to tell you what those settings will be because we do not know your machine.

Important: There is a feed rate that no matter what you have your accel set to the machine will fail because the motor does not have the power to run it at that feed rate. You would not want to run at that level anyway because the accel would cause your parts to look weird.

My machine is essentially an old style CNC Router Parts machine. I use the trucks from them and the motor side plate that spring loads the pinion into the rack. That is how backlash is handled, essentially there is none.

I am not crazy about linear bearings on these type of machines mostly because of the dust issues. On the industrial machines I designed we used expensive way covers to protect them but that is not practical for most of us home hobby type guys. I like the trucks that CNC Router Parts provides. Simple, effective and adjustable. They run on flat cold rolled steel.

Here is a link to a YouTube video I posted a few years back that shows the machine cutting at 800 IPM:

https://www.youtube.com/watch?v=Pt8n43_YRjI

It is a little blurry but you can pretty much see what is going one and how the machine is constructed.

Ok, I am going to say something a bit snarky. I take what I read over on the CNC Zone with a grain of salt. There are some folks over there who know what they are talking about, but there are also a whole bunch of wannabe engineers who enjoy postulating about theoretical issues and others who rely on what is "common knowledge". A really good way to see how to build a machine is to look at a manufacturer or supplier who has been successfully building machines and does not have all sorts of complaints about the machine they provide. In other words, I did not engineer this machine. I took what looked like a good design that worked and then figured out how to build it and save some money at the same time. But I used the key pieces they had already designed and proven to work.

Is my machine perfect? Far from it. But the basic design and construction are very good. As time goes by I make incremental improvements to it. My first machine was a pretty typical wood construction el cheapo machine. I was not sure how much I would actually use the machine in my day to day projects so did not want to put a bunch of money into something that would sit in the corner most of the time doing nothing. Well, it proved so useful building lots of other things like jigs, fixtures, tools, mortising, tenoning, etc that I decided to build a much better one.
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Re: gcode resetting my surface zero to Z-0.200"

Postby Mr.Chips » Sat Apr 20, 2019 3:17 pm

TR,
Thanks so much for taking the time and go through things I should have learned ten years ago, and explaining why you have taken a particular tack, and have been successful. I agree that there are sudo CNC engineers that have more opinions than experience, and it’s difficult for the beginner to sort through it.

Having the pinion spring loaded to the rack appealed to me rather than simply tightening it against the rack, because the rack will never be perfectly aligned or stay that way over time, and wear happens especially in the heavily used sections of the rack, and a spring loaded pinion stands a better chance to keep engaged over the worn and unworn sections.

On my machine In motor tuning I can’t set the X V any higher than 187, using keyboard input or the slider, but on the Y it can be set to a V of 591. Is there a maximum limit being set somewhere in Mach that I need to reset to get the X above 187?

So you would recommend a five start acme thread on the Z axis, just want to make sure before I start working on it.

Thanks
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Re: gcode resetting my surface zero to Z-0.200"

Postby TReischl » Sat Apr 20, 2019 9:41 pm

Mr.Chips wrote:On my machine In motor tuning I can’t set the X V any higher than 187, using keyboard input or the slider, but on the Y it can be set to a V of 591. Is there a maximum limit being set somewhere in Mach that I need to reset to get the X above 187?

So you would recommend a five start acme thread on the Z axis, just want to make sure before I start working on it.

Thanks
Hager


Hmmm, could it be that you have the acceleration set to a different value than what you have on Y axis? Mach is a bit nasty in that you have to confirm each axis setting otherwise what you type in does not take hold. Hit the Save Settings button every time you make changes for each axis. Other than that I do not have a clue. I am not near my machine right now or I would go take a look and see what is what.

Definitely would recommend a 5 start screw. If you look on the CNC Router Parts website you will see that is what they use and sell. Simply put that means it works. I do not work for CNC Router Parts. But if you browse through their site you will find all sorts of useful parts for building a machine. If you browse through the CNC Router Parts forum over on the CNC Zone you will be hard put to find anyone complaining about their machines, that says a lot.
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Re: gcode resetting my surface zero to Z-0.200"

Postby Mr.Chips » Sat Apr 20, 2019 10:16 pm

Yup, been hitting “save axis settings” after changes, that’s no biggie.

OK since I’m focusing on improving the Z axis, a switch over to a 1/2” RH 5 start acme thread and nut won’t be a big deal like it would if I were changing over to rack and pinion.

Although to get a rack mounted on the X axis extrusion all I would have to do would be to remake the horizontal spacers between the vertical Z assembly support. But that’s for another time.

Thanks
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Re: gcode resetting my surface zero to Z-0.200"

Postby TReischl » Sun Apr 21, 2019 12:35 am

IMHO rack and pinion on Z axis is nice to have but not all that much of a benefit to machine operation. When you think about it a bit Z plunges to position the bit to height which is never a very long move and then it goes up and down when doing 3d type work but those are also short moves. The most I have ever done on a straight move in Z axis is a little over 2 inches on a model that had straight up and down walls. So there is no real speed advantage to using R&P on a Z axis.

You sure as heck know more about your machine now than you did ten years ago I bet. :D
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Re: gcode resetting my surface zero to Z-0.200"

Postby wmgeorge » Sun Apr 21, 2019 1:28 am

I have never heard of a having rack and piñon on the Z? All my machines have had screw on the Z and 2 had ball screws on X & Y, this last one is rack & piñon X & Y, ball on Z of course. There are large commercial machines with ball screws on all, instead of R&P on X&Y but they are not your common hobbyist machines :D
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Re: gcode resetting my surface zero to Z-0.200"

Postby Mr.Chips » Sun Apr 21, 2019 1:33 am

NOT on the Z. On the extrusion that the Z is mounted on and moves the Z assembly X- to X+. Sorry for the confusion.
And I didn’t want to see if you were paying attention.
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Re: gcode resetting my surface zero to Z-0.200"

Postby Mr.Chips » Sun Apr 21, 2019 1:54 am

I took my Hitachi router out of the equation today, it was starting to be a little noisy so new top and bottom bearings and brushes. Should be good for a couple of more years.

Got my Z axis 5 start RH 1/2” acme thread and backlash nut ordered. And the rest of the parts already here for the Z axis rebuild.

At the bottom on my current Z acme thread I have a mount and bearing. I’ve looked at several machines and they don’t use a bearing on the bottom end, so I’m just going to let that 5 start be loose and free, but keep the npmount as the bottom Z axis stop. That makes things kinda self align.

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Re: gcode resetting my surface zero to Z-0.200"

Postby wmgeorge » Sun Apr 21, 2019 2:05 am

Mr.Chips wrote:I took my Hitachi router out of the equation today, it was starting to be a little noisy so new top and bottom bearings and brushes. Should be good for a couple of more years.

Got my Z axis 5 start RH 1/2” acme thread and backlash nut ordered. And the rest of the parts already here for the Z axis rebuild.

At the bottom on my current Z acme thread I have a mount and bearing. I’ve looked at several machines and they don’t use a bearing on the bottom end, so I’m just going to let that 5 start be loose and free, but keep the npmount as the bottom Z axis stop. That makes things kinda self align.

Hager


My Z ball screw has a bottom bearing.
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Re: gcode resetting my surface zero to Z-0.200"

Postby Mr.Chips » Sun Apr 21, 2019 2:09 am

What holds the Z assembly when you power off?
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Re: gcode resetting my surface zero to Z-0.200"

Postby GME » Sun Apr 21, 2019 7:47 am

Mr.Chips wrote:What holds the Z assembly when you power off?



The stepper, at least mine did when I used a 5 start screw.
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