rack and pinion versus belt?
Posted by goinreverse
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Re: rack and pinion versus belt? February 22, 2010 11:21AM |
Admin Registered: 17 years ago Posts: 1,915 |
Larry_Pfeffer Wrote:
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> Forrest,
>
> First off, please forgive me for not following
> your work on printable rack and pinion drive
> systems more closely. What software is needed to
> run your rack and gear scripts?
>
You need the open source, free Art of Illusion 3D modeling app. You dump the scripts in the...
C:\Program Files\ArtOfIllusion\Scripts\Tools
...folder and then access them through the scripts option on AoI.
> Have you made any measurement of the backlash, due
> to the rack/pinion themselves? (That is, the
> back/forth motion possible when the pinion is not
> permitted to rotate. I realize that this will
> also be a function of the slop in the linear
> slideways.) Backlash becomes very important for
> milling, something I think will become important
> for speeding up the building of large parts.
> (Extrude faster, using a larger extrusion orifice,
> and then mill off the blobs that ooze outside the
> desired profile, once per layer.)
>
Herringbone gears have very little backlash. The slight printing imperfections in the ones I've printed seem to indicate that there is zero backlash. I've not made formal measurements, mind. Because the gears are plastic, I would not recommend them for use if you are planning to do milling. CNC milling generates significant xy stresses which, I'd guess, makes printed plastic racks and gears problematic.
> My repStrap currently uses leadscrews, but your
> work really has me convinced that printable
> rack/pinion should replace bought threaded
> driverods for the machines I attempt to print. I
> also find it notably cool that the Herringbone
> gear pattern can be extruded, but would be quite
> difficult to make using a conventional mill -- or
> even a hobbing machine (at least the ones I've
> actually seen outside of books.)
yeah, additive printing can do things that are difficult or impossible with subtractive CNC milling. I have come to the conclusion that we've got to stop thinking of our printers as just a poor man's CNC machine and start finding design solutions that exploit their strengths.
-------------------------------------------------------
Hell, there are no rules here - we're trying to accomplish something.
Opportunity is missed by most people because it is dressed in overalls and looks like work.
Thomas A. Edison
-------------------------------------------------------
> Forrest,
>
> First off, please forgive me for not following
> your work on printable rack and pinion drive
> systems more closely. What software is needed to
> run your rack and gear scripts?
>
You need the open source, free Art of Illusion 3D modeling app. You dump the scripts in the...
C:\Program Files\ArtOfIllusion\Scripts\Tools
...folder and then access them through the scripts option on AoI.
> Have you made any measurement of the backlash, due
> to the rack/pinion themselves? (That is, the
> back/forth motion possible when the pinion is not
> permitted to rotate. I realize that this will
> also be a function of the slop in the linear
> slideways.) Backlash becomes very important for
> milling, something I think will become important
> for speeding up the building of large parts.
> (Extrude faster, using a larger extrusion orifice,
> and then mill off the blobs that ooze outside the
> desired profile, once per layer.)
>
Herringbone gears have very little backlash. The slight printing imperfections in the ones I've printed seem to indicate that there is zero backlash. I've not made formal measurements, mind. Because the gears are plastic, I would not recommend them for use if you are planning to do milling. CNC milling generates significant xy stresses which, I'd guess, makes printed plastic racks and gears problematic.
> My repStrap currently uses leadscrews, but your
> work really has me convinced that printable
> rack/pinion should replace bought threaded
> driverods for the machines I attempt to print. I
> also find it notably cool that the Herringbone
> gear pattern can be extruded, but would be quite
> difficult to make using a conventional mill -- or
> even a hobbing machine (at least the ones I've
> actually seen outside of books.)
yeah, additive printing can do things that are difficult or impossible with subtractive CNC milling. I have come to the conclusion that we've got to stop thinking of our printers as just a poor man's CNC machine and start finding design solutions that exploit their strengths.
-------------------------------------------------------
Hell, there are no rules here - we're trying to accomplish something.
Opportunity is missed by most people because it is dressed in overalls and looks like work.
Thomas A. Edison
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Re: rack and pinion versus belt? February 22, 2010 02:02PM |
Registered: 16 years ago Posts: 251 |
Forrest,
The low-backlash you report from your printable herringbone gears is great news!
Given that, it may be possible to use printable rack/pinion for milling.
Just as a thought experiment, assume that we could use either microstepping, or additional gear pairs to get small motions, even if the final drive gears had big teeth. (Big teeth presumed for the final "moving the table" stage for strength to resist milling forces without permanent deformations.) I think coarse herring-bone gears might work reasonably well for a mill -- and even if the gears had shorter lifetimes compared to steel or bronze, one could print out spare set(s) while the gears were still in pretty good shape.
Here's something a bit more blue sky, I'm also thinking about how to print (or otherwise make with home-buldable tools), linear bearing stages (like trapezoid ways) that can take the forces of light machining (e.g. Aluminum.) It may be that for those, one is better off milling a pattern into foam, and casting something into it, perhaps epoxy-concrete, with metal bearing surfaces, such as sintered (oil impreganated) bronze.
Larry Pfeffer,
My blog about building repstrap Cerberus:
[repstrap-cerberus.blogspot.com]
The low-backlash you report from your printable herringbone gears is great news!
Given that, it may be possible to use printable rack/pinion for milling.
Just as a thought experiment, assume that we could use either microstepping, or additional gear pairs to get small motions, even if the final drive gears had big teeth. (Big teeth presumed for the final "moving the table" stage for strength to resist milling forces without permanent deformations.) I think coarse herring-bone gears might work reasonably well for a mill -- and even if the gears had shorter lifetimes compared to steel or bronze, one could print out spare set(s) while the gears were still in pretty good shape.
Here's something a bit more blue sky, I'm also thinking about how to print (or otherwise make with home-buldable tools), linear bearing stages (like trapezoid ways) that can take the forces of light machining (e.g. Aluminum.) It may be that for those, one is better off milling a pattern into foam, and casting something into it, perhaps epoxy-concrete, with metal bearing surfaces, such as sintered (oil impreganated) bronze.
Larry Pfeffer,
My blog about building repstrap Cerberus:
[repstrap-cerberus.blogspot.com]
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Re: rack and pinion versus belt? February 22, 2010 02:25PM |
Registered: 16 years ago Posts: 184 |
Forrest: Given a RepStrap with Threaded rod drive. How long do you think that it would take to make 3 - 9" racks and 2 pinion gears. Also will the racks fit together to create 1 - 18" rack. If so this is a good upgrade for the basic RepStrap unit to get it to be able to generate Mendel parts.
Bob Teeter
"What Box?"
Bob Teeter
"What Box?"
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Re: rack and pinion versus belt? February 22, 2010 02:32PM |
Admin Registered: 17 years ago Posts: 1,915 |
I wouldn't be able to venture a guess. As far as I know Nophead and I are the only people who have ever been able to print anything successfully with a threaded rod repstrap. For me that's been so long ago and fraught with problems that I'd hesitate to guess. For Nophead, his system is quite special and he is a total genius at making such things work properly. Nophead could easily print such gears and racks as fast or faster than I can on my Rapman printer.
-------------------------------------------------------
Hell, there are no rules here - we're trying to accomplish something.
Opportunity is missed by most people because it is dressed in overalls and looks like work.
Thomas A. Edison
-------------------------------------------------------
Hell, there are no rules here - we're trying to accomplish something.
Opportunity is missed by most people because it is dressed in overalls and looks like work.
Thomas A. Edison
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