twforeman's build

edwardrford
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Re: twforeman's build

Post by edwardrford » Mon Apr 01, 2013 1:27 am

Just wanted to drop in and say that I've been following your blog since you started writing about shapeoko, and I absolutely love it. I look forward to checking it every day to see what you've been up to.

Keep up the good work, and keep the posts coming!

-Edward
Shapeoko 1 #0 - a couple of upgrades.
Shapeoko 2 #0 - a couple of upgrades.
Shapeoko 3 #2 - Stock

twforeman
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Re: twforeman's build

Post by twforeman » Thu Apr 11, 2013 2:33 am

Thanks Edward.

I built a new dust shoe last night. It turned out great!

Teaser photo:
shoe3.jpg
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As usual full details on my blog.
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twforeman
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Re: twforeman's build

Post by twforeman » Tue Apr 23, 2013 12:05 am

More accuracy tweaking tonight. Found some issues and fixed them.

Teaser photo:
x-axis.jpg
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Full details on my blog.
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twforeman
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Re: twforeman's build

Post by twforeman » Wed Apr 24, 2013 12:43 pm

Had a little setback last night re: accuracy. More investigation is required.

More details on my blog.
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WillAdams
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Re: twforeman's build

Post by WillAdams » Wed Apr 24, 2013 2:25 pm

ISTR that the initial design of the ShapeOko included Finite Element Analysis modeling --- I'd really like to see a compleat model of it, (w/ upgrades as options which can be turned on and off) in an opensource program and then fed into GRBL as parameters to dynamically modify the path based on the expected stresses (this would be an extension of the current acceleration considerations).

Perhaps this sort of thing could be done externally and one would feed modified G-code to the machine?

(Or am I suffering from a bad case of Platonic-physics-idealism?)

Increasing the structure / rigidity of the machine to improve precision is kind of brute-force, no? But even so, I think analysis would improve our understanding of where / how to effectively improve the machine's structure.

For my part, I'm regretting not considering the balance of the gantry when I added the holes for doubling up my X-Axis Makerslide.
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets

twforeman
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Re: twforeman's build

Post by twforeman » Wed Apr 24, 2013 2:33 pm

An interesting idea, but I'm pretty sure GRBL doesn't have any code space left to implement such a thing.

Adding rigidity is never a bad thing, and I still have some flex in my Z assembly that I need to address.

That said, I don't think my positioning issues are related to flex or lack of rigidity.

For what it is, I think the ShapeOko design is a pretty good one, and properly tuned I expect to get an accuracy of +/- .010" out of it. I'd be really happy if I could get +/- .005"
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cvoinescu
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Re: twforeman's build

Post by cvoinescu » Wed Apr 24, 2013 3:26 pm

Will, I would meet you half way (or a tenth of the way, more likely). Let's calculate the mass of the moving parts (gantry as a whole, and the X carriage with Z axis and spindle on it), estimate friction, choose a minimum desired force at the tip of the tool, and use those together with the torque-vs-speed diagram from the datasheet of the stepper motor to work out a viable acceleration profile. Then modify GRBL or Marlin or TinyG to support an acceleration limit that depends on the current velocity, and use that for feed moves. Do the same calculation again but without the milling force, and use that for traverse moves.

That would help you drive the machine reasonably close to its maximum capabilities, and it shouldn't be computationally difficult for Marlin and certainly not for TinyG (may be a little tricky for GRBL, though). Some sort of feedback (a measure of the actual forces encountered while moving) would be lovely to have, but it would require a precise position encoder (resolution much finer than a full step) and a faster CPU (or additional hardware) to process it. Without feedback, stepper motors can only be used in this "make 'em big and drive 'em hard" mode, always enough power for the worst case load; the only thing we can do is be smarter about what we consider the worst case at any given moment.
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LTMNO
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Re: twforeman's build

Post by LTMNO » Thu Apr 25, 2013 1:13 am

Very nice build... inspiring...
Curious, I was looking at the Rigid Trim Router, how is is working out for you?
ShapeOko #1508, TinyG Controller, Dual Y, ACME Z-Axis, MeanWell(S-350-24v), NEMA 23's, 1m Squared t-slot table, OpenRail and the Original Z Makerslide and all Motor Plates...

twforeman
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Re: twforeman's build

Post by twforeman » Thu Apr 25, 2013 3:03 am

I have no complaints about the Rigid 2401 router. Though the only reason I'm using that particular router is because I already had it. :)

I also solved my accuracy problems tonight.
accuracy.jpeg
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As usual, full details on my blog.
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LTMNO
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Re: twforeman's build

Post by LTMNO » Thu Apr 25, 2013 1:23 pm

Hello Again, great blog, just subscribed...
Curious, if its not too much trouble could you take a picture of your 'Photointerrupters' and how you hooked them up.
Looks like a great cost effective way to have a limit switch.

Thanks
ShapeOko #1508, TinyG Controller, Dual Y, ACME Z-Axis, MeanWell(S-350-24v), NEMA 23's, 1m Squared t-slot table, OpenRail and the Original Z Makerslide and all Motor Plates...

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